The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
I would like to open a discussion about a thunderstorm and tornado hypothesis I have developed. Where in Wiki would be the best place to present the theory and data I have compiled as it is to long to be placed here?
Thanks
Original research doesn't belong anywhere on Wikipedia. There are lots of places where you can start a blog; that's what you need. Looie496 (talk) 05:53, 13 July 2009 (UTC)[reply]
I'm thinking that [1] looks like an OK forum and on [2] there's even a discussion on tornadoes. These are good places to discuss your hypothesis. As other stated, wikipedia would have been the wrong place :-) EverGreg (talk) 09:30, 13 July 2009 (UTC)[reply]
Once your hypothesis is published in reputable, peer-reviewed journals (Nature (Journal) or The Journal of the American Meteorological Society - for example) - and has perhaps been received favorably at some prestigious meteorological conferences - then Wikipedia should probably have an article about it. But until then, it's just some idea some guy had...and if we had articles about every idea any random person had - we wouldn't be an encyclopedia anymore! Our job is to collect facts - and your hypothesis isn't yet a fact - other than "It is a fact that you thought about it"...and that's not a particularly notable fact. Good luck with turning your hypothesis into a theory!
Remember: A good hypothesis explains phenomena for which we currently have no good explanation - and it makes predictions that can be tested experimentally. SteveBaker (talk) 11:42, 13 July 2009 (UTC)[reply]
This site says it's an aufwuchs eater: "Feeding off the bottom of the aquarium, it gets most of its nutrition from left over food and algae. If there is no algae or left over food present, supplement with high quality flake food, sinking carnivore pellets, freeze-dried bloodworms, and tubifex". --Sean15:54, 13 July 2009 (UTC)[reply]
Wood - ie Bogwood or driftwood is a very good idea - for juveniles it can be essential - not only does the wood provide roughage - but aufwuchs can grow and colonise the driftwood far better than glass/other things in the aquarium.
They might like soft leaved plants like cabomba (they will totally eat it if they do)
Also in the aquarium catfish wafers (ie plec wafers are good)
Image 11 - Aufwuchs - if you are wondering what aufwuchs are - they are the tiny things that live on slimy rocks that you find in a river - image 11 is of slimy rocks - they eat the slime, the things that live in the slime, and the green algae that is part of the slime.
In fact they are alot like sheep or cows - that eat grass - constantly grazing (obviously they are smaller)
Last image - very long stomach.
Also in the wild they will eat dead stuff - eg dead fish, or dead animals that have fallen in the water - ie carrion. But most of the time they just graze - they're not fussy eaters.83.100.250.79 (talk) 17:58, 13 July 2009 (UTC)[reply]
Note that aufuchs/periphyton contains a lot of small insects and larvae - so there is 'meat' in it - a bit like meat and vegetable stew.83.100.250.79 (talk) 18:00, 13 July 2009 (UTC)[reply]
Alcohol and Exertion
Not medical advise.
I get exceptionally winded when working out hard for more than 20 minutes. After that, it feels like I can't go on and my lungs are gonna burst. However, one day I went to a bar before hand and had a vodka shot with a friend. 15 minutes later, I went to work out and for some odd reason, I was able to work out beyond 20 minutes and not feel like my lungs were gonna burst. I was sweating, my heartright was up and I did the same exact thing I did everytime I went to the gym.
So to test this again, I repeated this the next week. Monday, no vodka shot, same situation, winded after 20 mins. Tuesday, one vodka shot, was not winded.
What medically could be happening? I am not looking for medical advise. I am asking those medically inclined how the alcohol could somehow affect the lungs in such a way that it allows for more oxygen, I dunno. --Reticuli88 (talk) 15:17, 13 July 2009 (UTC)[reply]
(Wild speculation) could it be that the alcohol relaxes your muscles a little? I'm just guessing, but without my inhaler any amount of sport is liable to make me gasping for a deep breath, yet with my inhaler (a wonder of modern medicine I might add) I can compete with almost all my friends in terms of longevity of energy. Perhaps the alcohol is having a similar impact as my inhaler does (which I think is that it relaxes the ventricles/something in my lungs to make breathing easier). ny156uk (talk) 15:43, 13 July 2009 (UTC)[reply]
Alcohol is known to dilate blood vessels (see here and here), increasing blood flow. I'm unaware of any information on the effects of alcohol on the lungs. Disclaimers notwithstanding, you should direct any serious inquiries to a medical professional. — Lomn15:52, 13 July 2009 (UTC)[reply]
While you might be correct, there may be some bias built into your experiment. The scientific controls would seem to be lacking, the exact amount of time you spend lifting vs resting, the quality of how you do the exercises, other things you've done that day, what classifies as "winded" and so on. Just the belief you have formed that alcohol has improved your performance may affect your results. Perhaps while you're trying things, however, you might have a go with caffeine - I've heard it's one of the most effective legal performance enhancing drugs and that many competitive athletes use it before events (I read specifically on runners). TastyCakes (talk) 16:33, 13 July 2009 (UTC)[reply]
I agree with this. Scientific studies say that alcohol reduces the ability of muscle cells to use glycogen, their primary fuel. Since alcohol also impairs judgement, it is likely that you're not really working as hard after the drink as without it. I have to say that for me personally, the sedative effect of alcohol is so strong that I would never think of taking a shot before working out, it would make me too lethargic. Looie496 (talk) 17:05, 13 July 2009 (UTC)[reply]
Einstein equations for scalar field plus gravitation
My question is: Is it true that static solutions to the Einstein equations for a real scalar field
coupled to gravity always have a singularity? I found this statement in several research papers, but
without any reference to a paper or book where this is proved (I know that there exist some explicit
examples of such solutions with singularities, but I am interested in a more general statement).XYZsquared (talk) 16:19, 13 July 2009 (UTC)[reply]
Amount of life on Earth
Is this quantity fairly constant? I guess you can interpret this question in terms of the number of living cells. Whenever any living organism dies it provides food and nutrients to some other organism which then can reproduce. So, barring a global catastrophe, is the amount of life on Earth constant? —Preceding unsigned comment added by 75.52.253.33 (talk) 16:47, 13 July 2009 (UTC)[reply]
Probably not. Atmospheric carbon dioxide and oxygen levels have varied quite substantially for the last billion years, and amount of sunlight available for photosynthesis was not exactly constant, either. Besides, different species comprised the bulk of the biomass at different times. So I do not see any solid basis for your hypothesis. Sorry. --Dr Dima (talk) 17:05, 13 July 2009 (UTC)[reply]
I'm not aware of any rigorous data on this, but I would say it's surely not constant across all time scales. On a yearly time scale, the amount of land life is quite a bit higher during the northern hemisphere summer than during the northern hemisphere winter. On geological time scales, the total amount of life seems very likely to decrease during heavily glaciated periods, and also following catastrophes that lead to mass extinctions. Looie496 (talk) 17:11, 13 July 2009 (UTC)[reply]
Organic matter doesn't always get consumed by another organism. It sometimes gets turned into oil, for example. Limestone contains large amounts of animal produced calcite. There are various other examples of ways organisms get removed from the cycle. --Tango (talk) 17:40, 13 July 2009 (UTC)[reply]
The number of living cells on Earth may be constant over a decade, a century or a millennium. That is possible. I don't think there is any reason to believe that the number of living cells in one decade in time is likely to be any different from the number of cells alive in an adjoining decade. The questioner should specify what time frame is intended to be considered. Bus stop (talk) 17:53, 13 July 2009 (UTC)[reply]
white paint to fight golabal warming plan?
I read on CNN today the the US secretary of Energy wants to fight global warming by painting roads and the roofs of buildings white. My question is, will the amount of global warming fighting from the reflected sunlight be more then the penalty of producing millions of gallons of white paint? Googlemeister (talk) 18:25, 13 July 2009 (UTC)[reply]
I'm not going to calculate this. Where is that sunlight going to be reflected to? the heat will just be hanging around 4 feet above the roadways instead of 4 inches above. Overall I can't see it making any difference. The making of the paint and the labour to apply it would involve substantial costs, not to mention additional accidents from driving on glary and slippery roads. A white roof may reduce INTERNAL temperatures slightly in a building (but not as much as good insulation would). But the air above the roof is much hotter than over a dark roof which absorbs more heat (tho' this will radiate back more heat once the sun is off it). This is fine for keeping the interior of a building cool. Otherwise, this type of scheme just rearranges the deck chairs by a few feet; it won't reduce the total heat in the atmosphere....which is where global warming is happening, not under our wheels. - KoolerStill (talk) 19:01, 13 July 2009 (UTC)[reply]
Not quite true. White reflects a lot in the optical wavelengths. The atmosphere is quite transparent in the optical - that's how most of the heat came down from the sun in the first place. So a lot of the reflected light goes back into space. On a global scale this is a very small contribution. However, it reduces heat in cities and buildings, and hence reduces the need for air conditioning - which a) uses energy and hence (with the currently prevalent technology) causes CO2 production and b) adds to the urban heat island effect (there ain't no free lunch from the second law of thermodynamics...), causing cities to heat up, requiring more air conditioning... I don't know how quickly this pays of, but (some) roofs need regular painting anyways, so painting them in a highly reflective color the next time seems like a no-brainer. --Stephan Schulz (talk) 19:12, 13 July 2009 (UTC)[reply]
Painting roads a reflective white sounds like a horrible idea for a sunny day. Not to mention it would make it difficult to stay on them or anticipate curves when they are covered in snow. Livewireo (talk) 20:52, 13 July 2009 (UTC)[reply]
It sounds like another bullshit solution for a real problem; instead of addressing the problem head on, lets propose an ultimately worthless and probably even harmful solution (see Ethanol fuel, especially Corn ethanol ). The better solution is to instead work on accelerating non-combustion technologies (like solar and wind) or to get the hydrogen economy up and running. The problem with those solutions is not that they are substantially harder to implement, its that there are monied interests on maintaining the old infrastructure, or in coming up with solutions like ethanol fuel which was merely an excuse to make Archer Daniels Midland a shitload of cash. These are all distractions from the real solutions, and the sooner we get on implementing the final solutions, the better we all will be. --Jayron32.talk.say no to drama21:17, 13 July 2009 (UTC)[reply]
Does anyone know whether their "back of the napkin" calculations included the green-house gases emitted in producing that much paint? Also what type of paint were they talking? Whitewash won't stay put, so they'd have to consider something polymer like. They'd have to apply a pretty thick layer because otherwise it's just going to rub off in a hurry. With a thick layer your road will get as slippery as ice or you'll have to add grit. (OR around the corner from where I used to live in Germany a company managed to coat a bike-path in bright red polymer. They had to redo it after the first couple of cyclist's accidents.) Adding grit in turn will erode the rubber of tires like shoe-marks on no-wax floor, again leading to dark tracks. Unless they come up with a formula for white asphalt this sounds like a half-baked idea. Passing a law to have homeowners use white shingles when redoing their roof won't look pretty, will take a while to take effect (average roof life=10-15 years) but is doable. 71.236.26.74 (talk) 22:16, 13 July 2009 (UTC)[reply]
Putting the paint on roofs is not a silly idea - there are paints that aren't too harmful to the atmosphere - and it really doesn't matter if the stuff cracks and breaks up because 90% of the surface will probably still be reflective decades later. However, this isn't the thing that's going to save the planet - if it made a 1% improvement - I'd be very surprised indeed. Picking lighter materials for the roof makes more sense - pale grey roof-tile rather than dark brown or black. Waterproofed concrete roofs rather than tar-covered roofs - light-colored stone chips embedded in tar roofs where they can be retro-fitted. Rooftop gardens are probably a yet better idea. But there are two effects going on here. One is that the total albedo of the planet is improved - but that's likely to be a tiny effect. The other is that the interior of the building will be kept cooler - which in hot climates has the potential to dramatically reduce the amount of air-conditioning required. I think that's actually the main reason for doing it - and you don't have to go so far as to have a totally white painted roof to do that. Simply choosing lighter colored materials gets you most of the benefits. Painting roads does seems like a bad idea - but building concrete roads instead of tarmac is probably a reasonable alternative. The only snag is that concrete production uses a hell of a lot of energy and produces a TON of CO2. Of course when we finally realise that we have to stop oil production, there won't be any tarmac around anyway - it's basically just a waste-product of oil refining...so no more oil refining means no more tar. Currently, concrete is the only alternative...which is not so great. SteveBaker (talk) 23:06, 13 July 2009 (UTC)[reply]
Our so-called ecological footprint is largely a result of the technology we use and the energyconsumption - a person can do about 100 W of work, yet your average person's energy consumption is around 3000 W (on average, not just working hours). That's our real impact. However, our literal footprint (the amount of surface we occupy on the planet) is not all that great. And most of that is agricultural land. The actual built-up area is just a fraction of the Earth's surface. I can't find any figures, but let's assume that's on average 20 m² per person (eg 200 m² for someone living in a 10 storey building). Let's take a world population of 5 billion. That makes for a total of 100 billion m², which is 100.000 km². Earth's surface is 500 million km². So our houses occupy about 0.2 % of Earth's surface. That's a tiny amount, and even that would require a major effort. There are much better ways to invest our time and money, to put it extremely mildly.
Also, not all roofs are fit for this. In Europe, most roofs have tiles. Not that that would not be doable, but it would be butt-ugly. Especially since white buildings have a tendency not to stay white, so you'd have to do a lot of cleaning. And, as anon points out, this is especially true for roads, where you get the extra disadvantage of drivers being blinded by the light, increasing the already catastrophic deathtoll on roads (about 30 million dead and counting).
Now I don't mind if people think of alternative solutions - that's a good thing. The problem is that silly solutions like these, that can be debunked with a bit of secondary school knowledge, draw attention away from the real solutions like the development of solar cells, because it reduces them to 'just another one of the solutions'. If some politician without a clue has a silly plan that's good. At least he's thinking. What's bad is that he doesn't consult (or ignores) people who do have the brains to implement secondary school knowledge. That a news agency reports this idea makes perfect sense. But they also should have someone with some intelligence on their staff who can at the least ask the right questions, thus effectively debunking the idea.
Now I hope I haven't made any mistakes in my reasoning or calculation, because else I'll get this little rant flying back in my face. :)
Btw, Jayron is right about biofuels. Solar cells are at present already 10 times more efficient than plants can ever be (20% vs 2%). And you can put them wherever you like - on rooftops or in deserts, where they don't compete with food-production. And you don't have to harvest of process anything (which costs energy) - just install them and sit back (well, almost, but certainly in comparison). That said, it might make sense to use the parts of food-crops that are not the food-bit. That won't have a very high energy content, but if you already produce this 'waste', you might as well throw it in the oven of an power plant. The gain may be small, but the same goes for the required effort if you just use what you already have more efficiently. At least, that's just a thought of mine - please debunk where needed. DirkvdM (talk) 11:22, 14 July 2009 (UTC)[reply]
Have you ever considered that solutions being offered by a Nobel Laurette and the US government might not actually be debunked by secondary school knowledge? Either because you don't really understand the proposal, or because the implications are different than you imagine? Dragons flight (talk) 11:47, 14 July 2009 (UTC)[reply]
A Nobel Laurette perhaps, but you appear to have far more faith in the US government in scientific areas then I do. After all, the lawyers are the ones who are in charge, not the scientists, and the job of a senator is 1 part helping the country and 6 parts looking good to the voters. Googlemeister (talk) 19:08, 14 July 2009 (UTC)[reply]
The problem is that DirkvdM is only seeing one side of the benefits here. Whilst he's 100% correct that the amount of light we'd reflect back out into space would be negligable - he's neglecting the important part. A dark-roofed building is going to be hotter inside than a light-roofed one. If it's a LOT hotter - and in a place with a warm climate - that means that you're going to need airconditioning...and the amount of energy consumed by air conditioners is FAR from negligable! Worse still, the airconditioner puts out yet more heat into the outside environment - causing something of a feedback effect. Painting the roof white cuts out a significant chunk of heat - which saves on the airconditioning - which cuts yet out more heat and CO2. So the simplistic 'percentage of the earth's surface' calculation - while true and interesting - doesn't explain why the US government thinks it's a good idea. The true calculation would have to estimate the amount of additional energy expended by airconditioners in black-roofed buildings - and compare that to the total energy consumption of humanity. As I said - I doubt it's as much as 1% - but since it's a fairly cheap fix (and every little helps), new buildings really OUGHT to have lighter colored roofs (not bright white paint...but maybe lighter tiles and white gravel pressed into black tarmac roofs) - and I'd like to see the government moving towards mandating that by law. SteveBaker (talk) 20:35, 14 July 2009 (UTC)[reply]
You don't need to mandate any particular building material. Just tax energy enough while subsidizing remedies. Dirk, you seem to believe in the silver bullet. I don't. It will be extremely hard to find one technique that will cut carbon emissions by 50%. But we only need to find 50 that each reduce it by 1% (of the original, otherwise around 70, says the mathematician in me) to have the same gain. --Stephan Schulz (talk) 21:13, 14 July 2009 (UTC)[reply]
Dragon's Flight, read the question. I can't comment on the original proposal, because there is no link. But the question is about "painting roads and the roofs of buildings white". If that was in the orignal proposal, then obviously they weren't thinking about airconditioning, because else they would have left the roads out. (A bit of a late reaction, sorry.) DirkvdM (talk) 17:55, 19 July 2009 (UTC)[reply]
Steven Chu is not an idiot, so such notions arise from a misinterpretation of what he's proposing. He's an expert in cooling atoms with laser light, so I'm pretty sure he understands the physics of heating and cooling. His colleagues think so.
Anyone who's paid any attention knows that a white T-shirt is cooler in the afternoon sun than a black T-shirt. This fact applies to buildings that are air-conditioned: using white siding, or white exterior paint, or light-colored shingles will reduce the amount of heat that's absorbed by the building.
The questioner doesn't need a bunch of half-baked opinions: s/he needs references to Chu's proposal and expert reactions to it. Chu was not talking about 'painting roads white', he was talking about using lighter-colored materials to make roads. (Compare the heating of asphalt to that of concrete.) He's not talking about applying millions of gallons of white paint to existing surfaces; he's talking about changing the color of materials that are going to be produced anyways so that they reflect light back into space (as the clouds and the ice at the poles do.) If you really want to understand energy use and options well enough to understand what's being said, I highly recommend this book (it's a free download). Those who prefer to engage in pointless and non-productive bickering won't be interested. Twang (talk) 22:24, 19 July 2009 (UTC)[reply]
1) Are the images of moon, planets and nebulae impressive?
2) Is imaging the sun impressive?
3) Are we talking laptops and software for best effects?
I suppose the most important question....
4) Even if I get a good telescope and laptop [and a few years of observations] are we really still talking about "fuzzy dots" rather than good solid images? —Preceding unsigned comment added by 89.242.135.49 (talk) 22:21, 13 July 2009 (UTC)[reply]
4) you can get best images in the world, selling them for $$$$$ and giving names to new comets in case you got good telescope and patience to do the observations. Vitall (talk) 22:40, 13 July 2009 (UTC)[reply]
WARNING!!! EXTREME DANGER!!! Do not EVER look at the sun through your telescope. You will quite literally burn out your retina before your eyelid has time to close. There are ways to use a telescope to project an image of the sun - but even then, you have to be really careful because you are not only concentrating the light - but also the heat. If you accidentally leave your telescope with the main lens cap off - and it happens to be pointing to a place where the sun will be in a few hours time - you could come home to a burned out house! You have to be super-careful when using a telescope in daylight.
That said:
The moon looks very impressive - it seems somehow more "real" than the naked eye view. Planets - less so. You'll be able to see the rings of Saturn - but it's not going to be a huge, sharp image. Most of the other planets are relatively featureless. Nebulae are soft smudges...this isn't the Hubble we're dealing with!
The sun...well, WARNING!!! EXTREME DANGER!!!...remember?! Let's not go there! You can safely get a good image of the sun with a home-made pinhole camera (a sheet of cardboard with a pinhole in it taped across a window works well) to produce a magnification of say 2x to maybe 8x in a darkened room. That lets you see prominances and sunspots - it costs $1 to make and it's SAFE. So just forget all about using an actual telescope to observe the sun...bad, bad, BAD idea! There are ways to do it - but you have to be really careful and do it exactly right...not the sort of thing I'd advise an amateur to attempt when the pinhole camera approach works so amazingly well.
The single greatest thing about computer-driven telescopes (those with TWO axis motorized mounts) is that when they are properly set up - you can tell the thing "Find me Jupiter" and it'll obediently take you there. That's a lot easier than messing around with star charts and ephemerus to find the darned thing - and as a beginner, one fuzzy off-white blob looks much like another - if you're trying to get the thing focussed in on Jupiter and you're actually pointing at a star five degrees away...you're in for a frustrating experience. The other thing a motorized mount does for you is to automatically counteract the slow rotation of the earth - which can be really annoying when you're trying to set things up because the star or planet you're looking at keeps moving! The computer can fix that for you - which is especially nice if you want to take long-exposure photographs.
A lot of what you see will indeed be dots...or (in the case of most of the planets) slightly enlarged dots. The moon and Saturn are very cool - but if that's all you're going to use it for, you're better off borrowing one for a few nights. When there is a comet just below naked eye visibility, the telescope will bring it into amazing clarity...probably the best thing I ever saw in my 8" reflector was comets. You can also pick up things like the space station...but without a fairly fast computerized mount, it's hard to keep it in view!
One other HUGE thing to think about is how good the "seeing" is where you live. If there is a significant city anywhere within the range of the horizon - or a small town somewhere within a mile or two - or even a street lamp 100 yards from the end of your back yard - then you may have a hard time seeing ANYTHING other than the moon and the brighter comets clearly. This cannot be over-emphasised. If you don't have REALLY dark nights - forget it - don't buy a telescope. I have an 8" reflector - which isn't a great telescope - but it was good enough when I lived out in the wilds of nowhere with a gigantic hill between me and the nearest main road. When we moved to the USA and bought a house just 20 miles from Dallas - there was simply nothing in the sky worth seeing other than the moon. Everywhere else, you just see a dim glow of the city lights reflecting off of the sky...no astronomy is possible under those circumstances.
Another consideration is the weather. You obviously need a lot of clear-sky nights (People from Seattle need not apply!) - but remember that you can't do astronomy indoors. You'll be outside - late at night - for hours (potentially). In cold climates - this is no fun! Serious amateur astronomers soon realise that they need a mini-dome system so they can be at least sheltered from the worst of the weather.
Uh, Steve? There are safe full-aperture solar filters for telescopes that are made from materials that block enough of the Sun's light to make it safe for direct observing. That being said, an 8" telescope, even with a filter, might deliver an image bright enough to hurt while looking at it. Large-aperture telescopes are generally not good for observing the moon, either, one reason being that the light will be very bright, and another is that the magnification required to resonably work with such an aperture might make the moon appear too large. How much an 8" telescope costs depends on the type: expect to pay roughly $450 US for a Dobsonian of that size, $1300 for a Newtonian reflector, and $2500 for a Schmidt-Cassegrain. That's without any special equipment such as CCD cameras and the like. An 8" telescope may also be good for imaging deep sky objects. ~AH1(TCU)00:27, 14 July 2009 (UTC)[reply]
Yes, it IS possible to observe the sun - with care - with the RIGHT equipment and knowledge (and I said that) - but it's really dangerous - and we really shouldn't be recommending it...especially when a pinhole camera and a darkened room works every bit as well. I've heard of people who assumed that the "moon filter" that comes with many larger aperture scopes was a "sun filter" - and lost an eye in the process. On an 8" telescope - even the moon is bright enough to hurt your eyes (that's why most scopes come with a "moon filter"). Most scopes that come with a sun filter are much less than 8" aperture. Remember - the sun filter that works for a cheap 4" scope is letting through four times too much light if mounted on an 8" scope! This is totally not a thing for a novice telescope user to be messing with...losing an eye is just FAR too serious. SteveBaker (talk) 01:30, 14 July 2009 (UTC)[reply]
Extra warning: I had a telescope that came with a filter for solar observation at the ocular end (eyepiece). Someone at my astronomy club told me that that is also dangerous because, as Steven pointed out, you are not only concentrating the light, but also the heat. That heat still reaches the ocular, which may burst, as a result of which splinters may come off. If you've got your eye at the ocular, those splinters may end up in your eye. Sun#Observation_and_eye_damage also mentions this. The way to obsserve the Sun is by projection, as Steven mentioned. I believe that's how Galilei also did it - he held a piece of paper behind the telescope, on which he then copied the image. A modern alternative to Galilei's method is to mount a digital camera behind the telescope, connect that to a computer and view the image on your computer screen. And of course take photos. I'm not sure if this will work with a standard camera, but there are setups for this. Of course you still need a filter to avoid damaging the ocular or the camera's ccd (its retina, so to say). But even if that goes wrong, you'll still have your eyesight intact.
To get an idea of how beautiful the images are, you might contact an astronomy club to meet up with them on an observation night. They'll probably let you have a look through their equipment. And then you'll be able to compare and decide what kind of equipment you like best.
Btw, the most beautiful thing I ever saw was the Moon - with the naked eye. That was a few days after new moon, just after sunset, with just a narrow strip lit up by the Sun (waxing crescent). The rest of the Moon was quite visible, and suddenly I saw the Moon for what it is - a huge rock at a huge distance. Until then, I knew that, but that was the first time I saw it. Then it sunk in that that strip of light was a mere reflection of the Sun, which gave me a feel for the immense amount of light it emits. And that's just our little corner of our galaxy, which is just one of billions of galaxies. I never felt so tiny. Mind you, this was not so much what I actually saw, but the realisation of what it was that I saw. The same holds true for the zoomed in versions of whatever you see in the sky with your telescope. For example, Hubble images can be very beautiful in an abstract sense, but when you realise what they really are, they're mindboggling. A lot of beauty comes from knowing what it is that you're seeing. DirkvdM (talk) 09:11, 14 July 2009 (UTC)[reply]
The first time I had the opportunity to look at Jupiter through a relatively small refractor (perhaps 3 inches) it was literally breathtaking to see the moons of that planet standing out in clear detail. Years later, with my own similar telescope, and some care, it was possible to see the weather bands around Jupiter as well as its moons, and to see the rings of Saturn. A larger telescope such as the OP discusses, especially with a computer controlled drive, would make it much easier to find and observe planets. A CCD camera should make it possible to create some amazing photos. Edison (talk) 14:23, 14 July 2009 (UTC)[reply]
A spring in space
If you had a setup so a ball was put onto a spring and tied back with some force to compress the spring (as in space the ball would be weightless, no?), and then the ball was released would it oscillate forever? What would cause damped motion--no air in space, no friction due to it oscillating up and down without touching anything.
xxx(ball) (compressed)
xxxxxxxx(ball)
xxxxxx (ball)|[plate|
2) If the setup involved placing a plate a distance x from the compressed spring so that x was less then the amplitude of the springs oscillation would it strike the plate and come back (3rd law force of plate on ball), compress the spring and then repeat infintly? I think energy would be transferred to the plate though no?
3) Finally what happens if the plate in question to is replaced with a piezoelectric crystal. Could that serve as a battery? (obviously this is just a hypothetical question)
If we're talking about a physical spring, there will be some friction inside the spring itself, so it will lose energy over time. With an ideal spring, or eg. a gravitational field working as one, it's possible for your ball to oscillate forever, at least in an isloated system. For example, a planet orbiting a star can actually be seen as oscillating along two perpeticular axes.
Regarding 2) and 3), as you've already said, when you make the ball strike the plate you transfer the energy, so you'll at best be able to recover the energy you already put in the system by compressing the spring, most of it however would be lost heating the ball and the plate. You're right that this could be used for energy storage, but the efficiency would probably not be very impressive.
It won't work forever. As I already said, energy will be lost in the form of gravitational waves. This will be unimaginably slow, but it will happen. 67.182.169.172 (talk) 00:17, 15 July 2009 (UTC)[reply]
Sky colors on remoter stars
So If the star is white, then what will be the color of planet's sky, if Terra-like. Would white sun make white or purple sky? I know a blue star make a golden sky, what about a blue-white star will make deep yellow or pale yellow sky. A orange star is said on one site to make turquoise sky while pink star gives green sky.--69.226.33.240 (talk) 23:47, 13 July 2009 (UTC)[reply]
I believe the Sun is white. It just looks yellow because the blue light is scattered by the sky, hence the sky looking blue. — DanielLC00:02, 14 July 2009 (UTC)[reply]
Our sun IS white - but when the light enters the atmosphere, the blue light is scattered (that's why the sky is blue). Because our eyes basically see only mixtures of red, green and blue light - when you subtract some blue, you have more red and green than blue. Red and green makes yellow - so from down here at the bottom of the atmosphere, the sun looks a little yellowish.
Sorry, but this is not entirely accurate: white stars are classified as A-class on the spectral scale, while the Sun is G-class (i.e. a yellow star).
76.22.37.87, I don't think you see the true science world. I've been told, human eyes do a terrible perception shift. Language scientifically, ur sun looks yellow in cmputer screen, white when seen in our blue sky, who knows what you'll see in space. 76 IP, you don't see strange human shifts on earth, when you go to Mars or Moon, then all your color vision cell will go hay tangle.--69.231.5.71 (talk) 21:24, 14 July 2009 (UTC)[reply]
Sorry i need to fix 76 IP's answers. He just don't know enough. For a gentle reminder, is just to clarify the rules the goal of desk is the answers to be "done right". If answers is not answer right then this destroys purpose of desk. Questioners won't want to go back and try to see what the answers is wrong. Questioners usually wants answers answer right at the "first time". And also we people won't want to bite newcomers. Since 76 IP answer is too simple and to general, it's good ot just fix comments and leave it ther.--69.231.5.71 (talk) 21:42, 14 July 2009 (UTC)[reply]
The color of the sky is determined by the nature of raleigh scattering - and the color it scatters depends on the size of the particles in the atmosphere - not the color of the star. So if the earth was orbiting a different star, then there are two possibilities:
If there is a reasonable amount of blue light being emitted by the star - then the sky will be blue.
If there is little or no blue light from the star - then the sky will be black and you'll be able to see stars in the daytime sky.
Just to clarify: You can only ever see stars in the daytime if you shield your eyes from the sun or anything lit by the sun. This applies on the hypothetical planet Steve describes in the same way it does on the Moon. --Tango (talk) 02:11, 14 July 2009 (UTC)[reply]
I believe the Sun is considered yellow because that is the area of the spectrum where it radiates the most intensely. However, it could easily be considered white, as it emits strongly throughout the visible spectrum. -RunningOnBrains(talk page)21:53, 14 July 2009 (UTC)[reply]
Is just plot of spectrum Sun counts as yellow. When you actually go in space, you look as a totally different things. Your human eyes is very sensitive. Same situation as Mars. you won't even notice the coral color at all if you actually going to it personally. That's enough.--69.231.5.71 (talk) 22:01, 14 July 2009 (UTC)[reply]
July 14
Electonic ab belts/abdominators/whatever they're called...
(I'm sure that WP has an article on these - but I'll be damned if I can find it) So, those battery-powered ab belts that supposedly use electricity to rhythmically contract the muscles of the abdomen (or the muscles of whichever body part you've attached it to) and promote muscle growth without actually having to exercise and turn flabby guy --> ripped guy - quackery or effective way? I suspect that I already know the answer to this (I bought one on a whim years ago and it didn't really do much except make my abs twitch mildly for the couple of hours that the battery lasted - and the couple of hours that the next battery lasted). Is there any real science behind these devices? --Kurt Shaped Box (talk) 01:05, 14 July 2009 (UTC)[reply]
I think this is absolute BS, they're just trying to steal your money. You want strong abs, do lots of crunches (and it won't cost you a penny).
76.21.37.87 (talk) 01:30, 14 July 2009 (UTC)[reply]
Does anything help unjoin PVC?
I have a custom shaped PVC part for electrolysis. A part inside needs fixing, the only way I can get tools close enough is to remove the PVC pipe that is bonded to it. Does anyone know of anything that helps unbond PVC pipes. It looks like the bonding material is clear light yellow substance. I don't know if it is PVC cement or something else, but it looks bonded. My current method is to slowly cut slits into the PVC pipe and chisel it out.--155.144.40.31 (talk) 01:16, 14 July 2009 (UTC)[reply]
Thanks I heated it up and basically peeled it off.
The stuff I use (which is for plumbers - and is a bright purple color) melts the PVC - the glue itself hardly matters because once it's done it's stuff, the two pieces of PVC have become one piece - and nothing will get it apart. Personally - I'd look for longer/thinner tools to try to fix the problem without too much destruction...but without a lot more information, it's hard to suggest what tools might help. SteveBaker (talk) 01:42, 14 July 2009 (UTC)[reply]
The glue does matter, as it fills in the spots where the melted PVC didn't touch. Interesting fact: the primer is not inherently purple, but colored that way so that building inspectors can verify that it was used. --Sean13:27, 14 July 2009 (UTC)[reply]
It seems unlikely, because problems of this sort are generally due to "miswiring" that develops over time, and any treatment requires time and experience to correct the miswiring. It seems entirely possible, though, that a drug that increases the plasticity of neural circuits could make physical therapies more effective. Looie496 (talk) 03:35, 14 July 2009 (UTC)[reply]
This is precisely what the wavelength is. So the answer depends on the wavelength of the light. For visible light, the answer is between about 400 and 700 nanometers. But it could be anything. Some radio waves, for example, are several meters long. —Dominus (talk) 02:51, 14 July 2009 (UTC)[reply]
The answer above must be correct, eventhough the question isn't since light doesn't have an alternation between a magnetic phase and a electrostatic phase (For one thing, the word static means "no change" so it wouldn't fit here). Both the electric and the magnetic fields oscillate simultaneously in phase (that is, they reach their maximum amplitude simultaneously). Dauto (talk) 11:50, 14 July 2009 (UTC)[reply]
Gaviotas sleeve pump
There is a kind of manual water pump, invented at the "appropriate technology" Columbian town of Gaviotas which they call a "sleeve pump" (Bomba de Camisa). Most of the descriptions of it I can find are taken from Alan Weisman's book Gaviotas, which includes a diagram. A reasonable excerpt describing it, with the diagram can be found here (although a higher resolution version of the diagram can be found at this Google Books version). Also, there is an installation manual (in Spanish, scanned into PowerPoint) here.
I have not been able to make out how the thing works. The diagram shows an outer sleeve being moved, but nothing else. No description of what air or water chamber is pressurized, exhausted, or lifted; just water magically flowing up in the right illustration. Can anyone explain what's supposedly going on? Thanks. -R. S. Shaw (talk) 02:45, 14 July 2009 (UTC)[reply]
From what I've read in the text on the preceding few pages, it appears to me that the sleeve is rigidly attached to the perforated casing it encloses, which therefore moves up and down with the sleeve in relation to the immovable piston inside the casing, thus creating the pressure that pumps the water. Looks to me like the diagram is wrong. FWIW
76.21.37.87 (talk) 08:44, 14 July 2009 (UTC)[reply]
What is this plant?
This weed grows all over Philadelphia. The leaves vary greatly in size, and sometimes span 30 cm or more. It is usually a low shrub. In the summer, it bears hard spherical fruits about 2cm in diameter. What is it?
I don't think it's a fig. I believe what you have there is Paper Mulberry. Our article doesn't seem to picture the lobate leaf forms of the immature plants, but compare the images here (particularly the bottom one, just above the map). Deor (talk) 16:13, 14 July 2009 (UTC)[reply]
Thanks. So far, I like the paper mulberry theory much better than the fig theory. This plant does indeed have a variety of leaf forms, with only the larger leaves being lobate. I will try to open up one of the fruits and see if it looks like a fig. —Dominus (talk) 17:22, 14 July 2009 (UTC)[reply]
Now that I've done some more reading and seen some more pictures, I am sure that this is correct. Thank you very much. 17:27, 14 July 2009 (UTC)
but I'm unsure whether it is already covered somewhere else in Wikipedia or if it should be a section in the Health article or Wellness (alternative medicine)? Is the term "wellness" used in this context a separate definition apart from alternative medicine? Is this a notable enough topic to write about? From what I know of the Wellness Wheel concept is that it's used in many drug and alcohol rehab centers as a harm reduction alternative to the 12-step program (see google books) yet I see mention of this nowhere. So I'm unsure if I should start the article going of those web refs or just update Health or Harm reduction or to include this ?new? concept. Better yet, if someone more educated in the field than I could take the lead and start me off with a short stub that would be great. -- Ϫ03:04, 14 July 2009 (UTC)[reply]
When is it too cold for Mosquitos?
My friend and I disagree about whether I'll cause us to have mosquito bites if I leave the window open with lights on inside tonight. Thing is it's quite chilly outside at the moment! My understanding is that under such conditions mosquitos would not be a nuissqnce. So who's right? Do mosquitos not roam on very cold nights? (even if they do yesterday and tomorrow, when it isn't really chilly)? Thanks! —Preceding unsigned comment added by 82.234.207.120 (talk) 03:44, 14 July 2009 (UTC)[reply]
minimum temp for mosquito growth is 8-10°C [4] so it needs to be that cold for the mosquitoes to stop developing. Also the insects survive the winter via hibernation or as eggs[5] so they won't bother you in the winter or anywhere where it is less than 8 C.--Lenticel(talk)04:02, 14 July 2009 (UTC)[reply]
ah, but I was talking about an exceptionally cold night in otherwise mosquito plagued season... So my question is not about breeding, but whether they will bite me on a cold night (where the previous or next night is a definite yes)... —Preceding unsigned comment added by 82.234.207.120 (talk) 04:23, 14 July 2009 (UTC)[reply]
As I said earlier, you have to be at winter temperatures (subzero) for the adults to to hibernate or die after laying their eggs. --Lenticel(talk)04:42, 14 July 2009 (UTC)[reply]
I've read somewhere that the temperature below which mosquito activity declines dramatically is around 13°C. ~AH1(TCU)09:07, 14 July 2009 (UTC)[reply]
researching Huauzontle and trying to ascertain different varieties..
on website "seeds of change" the picture is red and on gourmet sleuth the picture is green so I sent emails to relevant websites questioning this and got following replies..
from seeds of change .. "We have a great picture of it in our catalog on page 50 and it is most definitely red. It is also called Red Aztec Spinach. Chenopodium berlandieri is the species we sell. Maybe there is another one that is not red?" ..
from Gourmet Sleuth I got " I can’t speak for what product Seedsofchange.com is referring to but huazontles are long stemmed greens with tiny flower buds (which we can confuse you further because technically the buds are fruit..) The plant grows long stalks, has serrated leaves and the stalks get tipped with seed bundles. The seed bundles are prepared and eaten like a vegetable. The only huazontles I’ve ever seen are green in color so if they are selling something red.. not sure what that would be. That being said this plant does grow in the U.S. (treated like a weed) but was eaten by Native Americans. Our reference is Diana Kennedy, well known writer and considered one of the best authorities on Mexican food and culinary culture. We have more description in our dictionary (this link is to our new site which is still under development but feel free to check out the info)http://dev1.gourmetsleuth.com/Dictionary/H/Huauzontle-6125.aspx
THEN researched Chenopodium berlandieri and found pictures at Google Image Search which show most green but a couple red however no explanation as to why red or green or if 2 different varieties ... similarly on Wikipedia .. different varieties but no red .... can you please help me ... thanx 124.179.215.251 (talk) 05:21, 14 July 2009 (UTC)[reply]
Red leaves in plants are usually caused by the [anthocyanin] content. Some varieties will naturally contain more (cf red cabbage, near-black bell peppers). —Preceding unsigned comment added by KoolerStill (talk • contribs) 10:14, 14 July 2009 (UTC)[reply]
I have no idea if this is relevant, but in my garden I have both Red Orache and Fat Hen, both members of the Chenopodium family. If you look at our article on Atriplex you will see that there are plenty of members of this family which are edible. I don't know if this is what you were looking for but it might help.--TammyMoet (talk) 18:50, 14 July 2009 (UTC)[reply]
Mercury
How do humans eliminate mercury and it's compounds? It says that fish store mercury faster than they eliminate from their bodies. How does this compare with humans? Are that "natural" chelating agents that can be found in the (human) diet?174.3.103.39 (talk) 08:40, 14 July 2009 (UTC)[reply]
As far as I'm aware, humans also store mercury in adipose tissue, and eliminate it very, very slowly (over a period of years). Even worse, there are currently no known natural chelating agents, either in the human diet or anywhere else (not even the "miraculous" Acai berry). There are some synthetic chelators available (such as British Anti-Lewisite) to help the body get rid of mercury; however, they should only be used in case of severe mercury poisoning and then only with a doctor's prescription, because they are themselves somewhat toxic (like many other strong medicines). FWIW
76.21.37.87 (talk) 09:04, 14 July 2009 (UTC)[reply]
Judging from the mercury poisoning article, there's no particular elimination of mercury by the human body :-( quoting [6]: Methylmercury is believed to cause toxicity by binding the sulfhydryl groups at the active centers of critical enzymes and structural proteins. This is just my guess but i'm thinking from this, that mercury is expelled when enzymes and protein in the body are destroyed, as they frequently are. The rate of metabolism would seem to be the crucial factor then, but this is just my layman thoughts on it. Brain cells are not renewed the same way that say skin cells are, so mercury in the brain probably stays there :-(( EverGreg (talk) 09:15, 14 July 2009 (UTC)[reply]
Lack of hunger
I seem to remember reading something about a lack of hunger, even though a person hasn't eaten for several hours, as a sign of something wrong with them. Does this ring any bells with anyone? Dismas|(talk)09:08, 14 July 2009 (UTC)[reply]
I'm afraid that lack of hunger is a symptom of a very wide rang of diseases, though I can't recall one that has it as its only symptom. EverGreg (talk) 09:17, 14 July 2009 (UTC)[reply]
And, of course, if there was, we wouldn't be allowed to talk about it. --Anon, 11:10 UTC, July 14, 2009.
That is completely incorrect. We can discuss medical information all we like. We cannot attempt to diagnose a person through the Reference Desk if the person claims to have a lack of hunger. -- kainaw™11:21, 14 July 2009 (UTC)[reply]
Anorexia (deriving from the Greek "α(ν)-" (a(n)-, a prefix that denotes absence) + "όρεξη (orexe) = appetite) is the decreased sensation of appetite. While the term in non-scientific publications is often used interchangeably with anorexia nervosa, many possible causes exist for a decreased appetite, some of which may be harmless, while others indicate a serious clinical condition, or pose a significant risk.
Hmm, thanks for the link to the symptom of anorexia. And to those who didn't get their "we don't give medical advice" jackboots on, thank you! Dismas|(talk)16:43, 14 July 2009 (UTC)[reply]
I didn't decline to participate in helping you, I declined to participate in an experimental test of the hypothesis. I agree that you're asking a different question now. Before you asked whether the idea could be ruled out in principle, and I said I thought not. Now you're asking whether there is evidence, and the answer is that I don't know. It would surprise me if anybody had studied this, but I don't know for sure. Snopes has a lot of information about this, and classifies it as an urban legend. Looie496 (talk) 19:45, 14 July 2009 (UTC)[reply]
I think Snopes classifies it as a legend that "Jenkem" is popular in the USA. They don't seem to have any references on whether or not it's possible. APL (talk) 18:48, 15 July 2009 (UTC)[reply]
Remove your own posts if you want, but don't touch others'. If you don't like the replies given you for free by volunteers, feel free to ask your questions elsewhere. 87.114.25.180 (talk) 21:14, 14 July 2009 (UTC)[reply]
Oh joy the "it's free so don't complain" line. Sure is an easy excuse for not trying. I've removed MY OWN posts and left everyone elses, as you suggested. Onesevensix 77 (talk) 23:06, 14 July 2009 (UTC)[reply]
Someone has tried to help you. You just don't like the answers, for whatever reason (since you haven't bothered to explain why that person who has tried isn't answering your question) Nil Einne (talk) 01:08, 15 July 2009 (UTC)[reply]
That's funny... You think you should be entitled to "complain" about a free service and people not "trying", and you don't even have the decency to explain why you are complaining or you think people are "not trying" after waiting less then a day. I was reasonably polite before, but I don't care anymore. It seems to me Looie496 has answered both your questions quite well. You just don't like the answers, because the answers are that 1) No you can't say it's impossible or rule it out in principle because a lot of weird things can be produced under fermentation 2) It's unlikely anyone has studied whether you can get high off the fermentation products of shit, because no one gives enough of a shit about a silly hoax to waste their time on such a thing and so there's likely no definite evidence either way; and it appears to me you want to be able to say the jenkem thing is impossible but you can't. I'm sorry to have to tell you, but life is like that. There isn't always definitive evidence for something and sometimes you have to accept that, or if you really want definitive evidence, do the experiments yourself. Nil Einne (talk) 13:01, 15 July 2009 (UTC)[reply]
If the replies had bothered to explain that there was no evidence to cite then I might agree with you. As it was Looie496 reply just stated the obvious and implied I had asked him to sniff his shit. Of course I did not expect anyone to actually attempt this themselves to answer my question, I was expecting someone to just provide a few links to articles and web pages (of which do exist, despite your claims that no one gives enough of a shit to research into it). Then when I politely removed my original question and rephrased it to get better replies (note that I was entirely civil and did not even comment on Looie496s reply, I simply wanted to ask my question again in a better way) I was berated with "you've already asked this" responses and resistance to helping me. Onesevensix 77 (talk) 06:14, 16 July 2009 (UTC)[reply]
faster then the speed of light?
I understand that light will travel through a vacuum at something like 3*10^8 m/s, but are the individual photons actually traveling faster since they are not going straight, but are instead traveling as a sine wave? What is the actual speed of the particles then? Googlemeister (talk) 14:42, 14 July 2009 (UTC)[reply]
When an electromagnetic wave is depicted as a sine wave, the sine wave represents the magnitude (and possibly the orientation) of the wave's electric field. It does not represent a displacement in space of the photons or anything else. -- Coneslayer (talk) 14:57, 14 July 2009 (UTC)[reply]
boy is that the wrong answer. The real answer is that WHATEVER LIGHT DOES WHEN YOU SEE IT AS A SINE WAVE (even if it did move up and down, or in and out, or back and forth, or whatever else) is something ENTIRELY DIFFERENT FROM WHAT IT DOES WHEN YOU SEE IT AS A PARTICLE. Read wave/particle duality. You simply can't apply particle physics to the waveform of light, and vice versa. Beyond that, what a sine wave WOULD represent to a particle, is irrelevant. 82.234.207.120 (talk) 14:59, 14 July 2009 (UTC)[reply]
You can imagine light to be an EM wave. The electric and magnetic field vectors are sinusoids perpendicular to each other and the direction of propogation. This wave travels at the speed of light. Or, you can imagine light to be a photon, that is, a particle, moving at the speed of light. Hence, it has properties of both waves and particles. What property it will exhibit depends on the experiment. For example, you can imagine an experiment of Diffraction. Assume the source is such that it emits a single photon. The diffraction pattern is still seen. This means light is released as a particle and diffracts as a wave. However, by the complimentarity principle, it can neber exhibit both particles simultaneously. So, its your choice how you imagine light, but it still travels at the constant speed of light. Rkr1991 (talk) 16:29, 14 July 2009 (UTC)[reply]
Obviously the light itself travels at the speed of light, there is no question on that. But the photons that make up the light are going faster or not? They have to exist, if it behaves as both right? Googlemeister (talk) 16:48, 14 July 2009 (UTC)[reply]
To make it easier to understand... You are imagining that there are little particles called photons. Your imaginary particles are travelling at whatever speed you like. Realistically, there are no particles. The thing you are calling a particle is a thing that, at times, exhibits behaviour similar to a particle. At other times, it does not. You can consider the fact that it should travel faster than light if it was actually a particle an instance of when it is not behaving like a particle if you like. -- kainaw™16:54, 14 July 2009 (UTC)[reply]
From my understanding of light, it behaves either as a particle, or as a wave, only based on if it is being observed or not. Thus when it is not being observed, it is both. Thus particles would have to be able to travel faster then the speed of light. Is the logic incorrect, or is my understanding of the quantum nature of light off? Googlemeister (talk) 18:09, 14 July 2009 (UTC)[reply]
Photons travel in straight lines, not in sine curves. They travel in straight lines at exactly the velocity of light. Nothing about light travels in a sine curve. When people depict the electric and magnetic fields as being shaped like sine waves, it is a metaphor for a certain mathematical abstraction, which you are taking too literally. People also talk about alternating electric currents as being sinusoidal, but that does not mean the electricity travels through the wires along a sinusoidal path, or that there is anything else taking a wiggly path through space. —Dominus (talk) 18:25, 14 July 2009 (UTC)[reply]
BTW what you said about it behaving as a wave or particle based on wether or not it was being observed: I thought it always did so regardless. Theres something that doesn't happen when you observe it but it is still wave/particle. Isn't the photoelectric affect proof of light as a particle, and that affect is valid when you look or don't, as is the double slit correct?66.133.202.209 (talk) 04:39, 15 July 2009 (UTC)[reply]
Wow... This discussion has gotten way off. Light is not a particle or a wave. It is merely light. Depending on how we set up our experiment, we can show particle-like properties or wave-like properties. However, that is not because light "changes" between the two (as though it knows what experiment we are doing???) nor does it mean that light is "both" a particle and a wave; as though it were simultaneously two things at once. It is just one thing; light, and its behaving the same way all the time. Our models which require us to assign it into a binary system of either "particle" or "wave" is what is the problem... --Jayron32.talk.say no to drama06:10, 15 July 2009 (UTC)[reply]
Periodicity of ionization energies?
I've been set an exercise which consists of putting in order a series of chemical elements according to their first ionization energy, knowing only their atomic numbers. My textbook says that the first ionization energy increases within each period of the table, but Al has a lower IE than Mg, and S has a lower IE than P, for example. How am I supposed to do the exercise then? Can someone give me a nudge in the right direction? Thank you! --83.34.232.200 (talk) 15:02, 14 July 2009 (UTC)[reply]
There are rules-of-thumb as you see, but sometimes there's no way to be sure without looking up the actual values. Our ionization energy article is quite detailed and surprisingly complex--tells you that the actual specifics of IE are well beyond the general picture. There's a nice graph at ionization too, and you can see both the periodic nature and also the exceptions that don't follow the general trends. DMacks (talk) 15:40, 14 July 2009 (UTC)[reply]
Yes - read the article and look at the graph(s), as a possible hint - try comparing ionsiation energies diagonally if you want to avoid exceptions, also for all but the most dedicated (anally pedantic) of scientists the difference between Al/Mg is really just a blip (though it is real - not a measurement error)
Can anyone please indicate a good web-site with lots of (scientifically based) artists' impressions of views from the surfaces of planets in our Solar System - thanks. --AlexSuricata (talk) 18:51, 14 July 2009 (UTC)[reply]
If you're interested in some very fanciful paintings from before we had close-ups of the actual cratered, uninhabited planet surfaces, Time-Life published a book in the 1960s or even 1970s that imagined planetscapes for all of them — there were forests on Venus with flying alien gasbag creatures. Beautiful. I am pretty sure it's Planets in the Life Science Library, written by Carl Sagan (looks like his first book). Tempshill (talk) 23:18, 17 July 2009 (UTC)[reply]
Big Bang, how did it happen?
I really have no reason to disbelieve the big bang theory, and cosmic background radiation seems to outright prove it in my eyes. But I don't know how it could have actually happened.
The beginning of the universe, as Steven Hawking seems to explain, was a singluarity, similar in type but not scale to black holes. If there was infinite gravitational pull because it was a huge amount of mass in an infitesimal area, how could it possibly blow up?
I don't see it as likely that black holes, no matter how large they are, would explode, and they have some forces tugging outwards on their centers (the gravity of other black holes for example). The singularity at the beginning of the universe would have have gravity, obviously, holding it together, and that would simply overpower every other force that could exist.
I know an explosion happened, but black holes don't explode, and explosions need something to cause them right? Bah, just reading a discover article about steven hawking and this came back into my mind. Please help me understand. Thanks! —Preceding unsigned comment added by 192.234.122.9 (talk) 19:54, 14 July 2009 (UTC)[reply]
All of physics breaks down as you go back towards the original singularity. Therefore, notions of gravity that we understand now did not apply when the big bang occurred. -- kainaw™19:58, 14 July 2009 (UTC)[reply]
Well, Newton's law of universal gravitation is a "law" - but it's modified by things like General relativity - which is a "theory". All that we know about gravity is a mixture of laws and theories. But I hope you are aware that scientists don't use the words "Law" and "Theory" in the sense of "that which must be obeyed" and "theoretical". In science, those words mean something quite different. SteveBaker (talk) 20:17, 14 July 2009 (UTC)[reply]
I wouldn't go so far as to say that Newton's laws are completely wrong. They were based on empirical data, and are now considered to be an excellent approximation for most practical applications where a model of gravity is necessary. They break down in the extreme cases where the theory of relativity must be utilized. AniRaptor2001 (talk) 07:00, 21 July 2009 (UTC)[reply]
The fact is that we don't know why. We know for sure that it happened - but there is a real problem here. Just as with black holes, when distance goes to zero - many other numbers become infinite. Density is infinite, gravity is infinite, but any distance-related repulsive forces (such as the forces that keep the atoms nicely spread apart - or perhaps any repulsive forces due to dark matter and dark energy) also become infinite. Weirder still - all of space was ALSO compressed into that infinitesimal dot. Worse still, the fundamental particles we know about today probably didn't exist back then. Fundamental laws like the Pauli exclusion principle and the Heisenberg uncertainty principle are violated. So the physics of that first gazillionth of a second are really tough to figure out. We have a pretty good idea of the way things were a few milliseconds after the big bang started...but we don't (yet) have a good handle on the absolute zeroth instant. The physics of the interior of a black hole where some of those weirdnesses ought to be playing out - might (in theory) give us a useful starting point to study that - but the event horizon of black holes forever prevents us from studying them in any useful manner. SteveBaker (talk) 20:17, 14 July 2009 (UTC)[reply]
We don't know that it happened, if "it" means "the beginning of time". When you extrapolate the original big bang model backwards you get a singularity about 14 billion years ago, but people stopped taking that seriously when inflationary cosmology caught on, because inflationary models don't have an analogous singularity at a well-defined time in the past. Physicists still talk about the "beginning of the universe" being 14 billion years ago, but they don't really mean it (see Age of the universe#Explanation). In chaotic inflationary models the expansion that we see started as literally a kind of explosion in a pre-existing universe triggered by a certain kind of quantum fluctuation. The background universe in which that happened could have existed forever for all we know. Hawking has a pet idea about the origin of the universe called the no-boundary proposal which he talked about in A Brief History of Time, possibly misleading readers into thinking that it's part of the standard cosmological model. It's not, it's actually pretty fringe. Other physicists take Hawking seriously but they don't necessarily agree with his ideas about cosmology and quantum gravity (and they certainly don't see him as a genius the way the general public seems to). -- BenRG (talk) 22:09, 14 July 2009 (UTC)[reply]
And it's worth pointing out that Brief History of Time is, by the standards of cutting-edge theory, getting a bit long in the tooth. --98.217.14.211 (talk) 22:47, 14 July 2009 (UTC)[reply]
The general public (I include myself here) considers anybody who can understand this mindbending stuff in anything more than a superficial way to be a genius, for some definition of "genius". --Sean22:54, 14 July 2009 (UTC)[reply]
What is it. in laypersons terms? What does it look like? I read in a book that it is elastic - seems very odd for a ceramic. Is it partly metal, partly silicon, since ceramics are made from clay, and clay I think is mostly silicon? Is it a recent invention? 78.147.131.187 (talk) 20:19, 14 July 2009 (UTC)[reply]
They make sharpening stones (whetstone) out of it, amongst other things - it's usually light grey (or white when pure) in colour, and just like unglazed ceramic - except maybe a bit harder than the average. There's no silicon in it.83.100.250.79 (talk) 20:57, 14 July 2009 (UTC)[reply]
This image is almost certainly an alumina whetstone - if not it looks identical to one Alumina ceramic looks like this
After reading a news story about how a girl survived with two hearts I started to wonder if humans could conceivably live with a backup heart their whole lives. Would it be possible to have a circulatory system with two pumps where if one fails the system remains viable? TheFutureAwaits (talk) 20:22, 14 July 2009 (UTC)[reply]
In principle, sure. The biological concept is accomplished by the lungs, kidneys, and eyes, among other organs. — Lomn20:26, 14 July 2009 (UTC)[reply]
It seems a bit iffy to me. If the two hearts didn't beat in PERFECT synchronism - and with approximately the same pressures - then high pressure blood from one heart would flow against the tricuspid valve of the other - and those things are only held shut by the pressure - so they'd blow back open...right? I could imagine all manner of Very Bad Things happening. But we probably need a biologist to tell us more about that. Obviously, other heart designs would be possible that could overcome this...but the Mark I human heart doesn't sound like the right machine for the job. SteveBaker (talk) 20:51, 14 July 2009 (UTC)[reply]
Thanks Steve, this is exactly what I'm getting at. Say you could redesign the human circulatory system. Would it be possible to design a system which could function despite one or many pumps failing? What would such a system look like? TheFutureAwaits (talk) 21:09, 14 July 2009 (UTC)[reply]
We're trying to answer a question with woefully incomplete information. Were there were actually two functioning hearts linked to the same circulation? Was it actually a birth defect in which instead of a four-chamber heart there were two two-chamber hearts serving the two sides of the circulation (pulmonary circulation and systemic circulation)? The "news" is notorious for hyping up some oddity yet not providing real information about what was going on. Can the OP at least link to the news story? --- Medical geneticist (talk) 21:21, 14 July 2009 (UTC)[reply]
Here's the story if you're really interested [9]. Please note I'm not really interested in learning more about this case, it was just the inspiration for the question. What I'm really interested in knowing is as follows: TheFutureAwaits (talk) 21:30, 14 July 2009 (UTC)[reply]
Say you could redesign the human circulatory system. Would it be possible to design a system which could function despite one or many pumps failing? What would such a system look like? TheFutureAwaits (talk) 21:30, 14 July 2009 (UTC)[reply]
It would look like a guy with two or more hearts, each capable of pumping hard enough to support life. They would be connected in parallel and share the same nervous impulse. In the event of failure there would have to be some sort of sphincter or valve preventing back flow round the failed organ. —Preceding unsigned comment added by 83.100.250.79 (talk) 22:43, 14 July 2009 (UTC)[reply]
I don't see how they could be in parallel. If the second heart fails then the first one can only pump into the opening of the second, after which everything gets clogged. I suppose there could be some side artery between the first and second heart where blood could go around the second and back into the main artery. Not sure if this could actually work though. TheFutureAwaits (talk) 23:46, 14 July 2009 (UTC)[reply]
I just ate a bag of peanut M&M's...yes, I know...an entire bag is kinda piggy. Anyway - I tore the end off of the bag and dumped out the usual 30 or so randomly colored M&M's into a shallow dish on my desk. I'm working - concentrating on a tough programming problem (rendering shadows cast from a non-uniform point source - if you must know) - and I swear that I am paying zero attention to picking up M&M's...until there are only seven left - when I happen to notice that they are ALL blue. This seems like a rather improbable thing...there are maybe 5 colours - so the odds are something like eighty-thousand to one against this happening by chance. So I'm wondering whether my subconscious doesn't really like blue M&M's and hasn't been telling the conscious "me" all this time? I should probably repeat the experiment a few times...right? SteveBaker (talk) 20:46, 14 July 2009 (UTC)[reply]
There could have been an error at the packaging plant and some bags did not get the proper mix of colors. I also recall a couple of contests from years ago where the winning bag was all 1 color. You could have just eaten a $1,000,000 bag of M&Ms. Googlemeister (talk) 20:51, 14 July 2009 (UTC)[reply]
No - I'd have noticed immediately when I dumped them out if they were all blue. I was obviously concentrating on the bag when I opened it
Maybe blue ones are heavier? but tell us more about you're non uniform point source - that sounds more interesting - though not that difficult on the surface - a point source always produces sharp shadows no matter what the intensity of the light - sounds like you just need more bits in the shadow map to express the non-shadowed intensity - it's always easier to say rather than do isn't it.83.100.250.79 (talk) 20:53, 14 July 2009 (UTC)[reply]
Yes - but it's omnidirectional so I can't do the usual "planar rendering from the point of view of the light source" trick - I've got to mess around with rendering to a cube-map. Anyway - I don't need help with that - I need to know about my brain's hitherto unsuspected aversion to blue food! SteveBaker (talk) 20:56, 14 July 2009 (UTC)[reply]
Coincidences do happen. Also, while the odds may be one in 80,000, how many packets of M&M's have you eaten in your life? Enough, I imagine, for the odds of the last seven M&M's in one of those packets being all the same colour being significantly higher. Also, it isn't 80,000:1, it is more like 16,000:1 - you don't want the odds of the last 7 being blue, you want the odds of them all being the same colour. You would have been just as surprised had they been all red. --Tango (talk) 21:24, 14 July 2009 (UTC)[reply]
Excuse *ME*! 80,000 bags of M&M's?! If I'd consumed M&M's every day since 1954 (when Peanut M&M's were first introduced) that would make 4 bags a DAY! Every single day! Now THAT would be "piggy"! SteveBaker (talk) 05:06, 15 July 2009 (UTC)[reply]
You don't need to have had 80,000 bags. Say you've had 1,000 bags, at odds of 80,000:1 (which are wrong anyway, but I'll go with that number), the chance of one of those bags having the last 7 blue would be , that's over 1%. Plenty of 1 in 100 chances happen and you wouldn't think twice about it. --Tango (talk) 16:55, 15 July 2009 (UTC)[reply]
It's a very, very common elementary school science "experiment" to see whether the color distributions in M&Ms and other candies are identical. They are often not, probably due to poor mixing. There is no a prior reason to suspect that the packet actually has even distribution to begin with, which obvious affects the odds-making quite a bit. --98.217.14.211 (talk) 22:29, 14 July 2009 (UTC)[reply]
(edit conflict) Yes that's right, I work in a M&M's factory (peanut division), and the blue ones always go in first. Somedays, when the boss isn't looking we don't bother to shake them to mixed the different colours, sometimes people just forget - "did you shake that one", "think so"... (lie)83.100.250.79 (talk) 22:47, 14 July 2009 (UTC)[reply]
That might actually be close to the truth. Presumably, the open bags are moved beneath a series of hoppers that each spew forth a set amount of M+Ms of a particular colour... --Kurt Shaped Box (talk) 00:29, 15 July 2009 (UTC)[reply]
But they'd have gotten shaken up when loaded into the vending machine, shaken more when dropped three feet into the output hopper - and completely mixed up when I dumped them into the bowl. It's hard to imagine that there would be much correlation between the order they were dumped into the bag and the order they were in the bowl. SteveBaker (talk) 05:10, 15 July 2009 (UTC)[reply]
Color distribution on M&Ms is not even. In the mid-70s Cecil Adams claimed that they were 90% brown and yellow. If the color distribution is still close to that (And I can't say I've noticed.) then your coincidence is even more surprising. APL (talk) 22:46, 14 July 2009 (UTC)[reply]
Of course it's dangerous to interpret any given event, but there's quite a bit of experimental work in the psychophysics literature showing that people are generally averse to blue-colored food. In fact there is even evidence that coloring a food blue influences the way people perceive its flavor, for example this paper. Looie496 (talk) 22:48, 14 July 2009 (UTC)[reply]
Before concluding that anything miraculous has occurred I want to know more about how one pays zero attention to picking up M&M's but picks them up anyway. Some brain activity must be involved in reaching out to a particular M&M. Were the M&M's in the field of view? What colour was the dish? Were more than one M&M touched at a time? Can the subject taste the difference between any M&M colours while blindfolded (a follow-on experiment) ? Which colour(s) of M&M eaten to excess would cause the subject to feel the most shame about being piggy? A point source cannot be non-uniform. It sounds like you have a ray tracing exercise. Cuddlyable3 (talk) 23:00, 14 July 2009 (UTC)[reply]
Well - my conscious mind was not carefully picking the non-blue ones first. One can grab a random candy from a dish without actually consciously thinking about it. I wasn't CONSCIOUSLY choosing to eat the non-blue ones...which is what makes me wonder whether this decision had been made by some lower level brain function. The M&M's were in a chromed plastic dish - it would have been visible in my field of view - but I wasn't conscious of looking at the dish - my gaze was mostly fixed on my computer screen. I don't know what you mean by "were more than one M&M touched at a time". I'm pretty sure I can't tell the difference in the flavor. Piggyness comes about from not PLANNING to eat more than a couple of M&M's but then belatedly noticing that there were only seven left. It's computer graphics - not physics - the point source does whatever the heck I tell it to do. If I say it's a non-uniform point source...then that's what it is! In this case, imagine a very small lightbulb with a lampshade over it (idealised as a point source because it makes the math easier) such that the light from it is not evenly distributed. This is for computer games - performance is at a premium and ray tracing is WAY out of the realms of the possible! SteveBaker (talk) 05:01, 15 July 2009 (UTC)[reply]
I would imagine a "non-uniform point source" would be a source which emits different light in different directions, but all from one point. --Tango (talk) 00:06, 15 July 2009 (UTC)[reply]
Explaining Were more than one M&M touched at a time?: this question investigates the process by which each M&M was selected unconsciously. The subject might A) have aimed to pick a particular M&M and operated arm, wrist and fingers appropriately, or B) grabbed a bunch of M&Ms and then used the sense of touch in the fingers to drop all except one M&M to eat, or C) none of the above. Supplementary question: how many M&Ms does the subject typically have in the mouth at the same time? I'll repeat the question Which colour(s) of M&M eaten to excess would cause the subject to feel the most shame about being piggy?.Thank you for explaining your non-uniform point source. Perhaps you use a this or this shading of objects. Look towards the light source and apply the same model. Multiply the modelled illumination with the modelled reflection and then you can play. Cuddlyable3 (talk) 12:59, 15 July 2009 (UTC)[reply]
Yeah - I've been doing computer graphics for 25 years...I know about shading algorithms (which is what Gouraud and Phong are...well, almost, they are actually surface normal interpolation strategies). My problem is to do with casting shadows - not those kinds of "self-shadowing" things. I was certainly eating them one at a time...I wasn't paying attention to how I was picking them up - but I'd have to say it was almost certainly one at a time. The subject's conscious brain doesn't give a damn about the colors - piggyness is an approximately linear function of number of M&M's consumed divided by elapsed time between first and last M&M - the value of the function is explicitly defined to be zero when the number of M&M's consumed is less than 2. The subject's unconscious brain doesn't seem to comment on piggyness - since it's shovelling them in at a high rate. However, the issue of color is the question at hand. SteveBaker (talk) 19:26, 15 July 2009 (UTC)[reply]
If you told us the number of M&Ms in the bag, and the total number of blue ones, then the probability could be calculated. Its an example of the classic beads in an urn (no replacement) combinatorial problem. I'm trying to remember the formula. But, assuming that the probability is the same as the first 7 m&ms being blue, then the probability would I think be B/M x (B-1)/(M-1) x (B-2)/(M-2) ..... x (B-7)/(M-7). Note that the other n million people who have eaten a bag of M&Ms and whose last seven items were not blue, have not reported it to Wikipedia. 92.27.155.47 (talk) 23:18, 14 July 2009 (UTC)[reply]
Assuming he didn't count them in advance you have to assume they are independent with equal chance of each colour (you could assume each bag has equal numbers of each colour, but that doesn't seem to be the case), so it is just 56 (there are 6 M&M's which need to be the same colour as the first one, you don't care what colour the first one it). --Tango (talk) 23:39, 14 July 2009 (UTC)[reply]
Please explain how you caculated " 56 "? I am not familiar with M&Ms, but if you are supposing that there are five different colours and that they are in equal proportions, then your estimate for all-blue would be (1/5)7 which is one in 78125, or (1/5)6 which is one in 15625 for seven in a row being the same colour. Actually, that is correct only for bags of infinate size or for where the M&Ms are put back in the bag: when a blue M&M is removed, it changes the proportions of the remaining colours in the bag, so the B/M x (B-1)/(M-1) x (B-2)/(M-2) ..... x (B-7)/(M-7) calculation is more correct. 78.145.23.157 (talk) 20:26, 16 July 2009 (UTC)[reply]
You might care about the color of the first one. If his final seven M&Ms had all been brown, the most common color, would he have considered it notable? APL (talk) 00:33, 15 July 2009 (UTC)[reply]
You can actually order M&M's in 60 pound bags of single colors of your choice from the M&M web site, including colors that you don't find in the normal retail packs, like black and white. 70.90.174.101 (talk) 04:02, 15 July 2009 (UTC)[reply]
The whole point here is that, while it is unusual, such event occuring truly randomly is not impossible. It isn't that YOU at 80,000 bags of M'n'Ms. It's likely that 80,000 bags are consumed pretty regularly (I'd even hazard DAILY), so such an event happens to someone every day. That it was your turn today is rare, but not impossible. Look, I have a buddy that lost a poker hand (7-card stud, no wilds) where he had a straight flush and lost to a higher straight flush. You can play poker your whole life and probably never even play in a hand where a straight flush occurs; and yet he was in one with two. It is weird, but any event based on random chance DOES happen. --Jayron32.talk.say no to drama06:03, 15 July 2009 (UTC)[reply]
The current page at mms.com doesn't have percentage information but this archived page does: 12% brown and red, 15% yellow and green, 23% blue and orange. I wonder how much they paid the consulting firm that came up with those percentages. Anyway, the chance of n randomly selected Peanut M&Ms being all the same color (with replacement) is 2·(12n+15n+23n)/100n. For n=7 that's about one in 14,000. Without replacement it would be somewhat more unlikely, but I'd need to know the total M&M count per pack for that. -- BenRG (talk) 09:45, 15 July 2009 (UTC)[reply]
Alien hand syndrome shows that the hemisphere which doesn't have access to the speech center can indeed have its own opinions about things. I guess we can assume your two hemispheres aren't in serious disagreement over whether you like blue M&Ms, but I'm just saying that the psychological explanation is feasible, and perhaps a more likely explanation than the 1 in 80,000 chance. It seems likely to me that it takes some small but significant degree of conscious effort for you to recognise bright blue things as food, and so you're less likely to put those ones in your mouth automatically. 213.122.68.146 (talk) 06:41, 15 July 2009 (UTC)[reply]
If they were in your peripheral vision you may have subconsciously been picking the ones that stood out more/had higher contrast against the bowl/other M&M's given the ambient lighting. Zunaid11:50, 15 July 2009 (UTC)[reply]
My guess is: you actually prefer the blue ones and therefore subconsciously saved the best ones for last! Sort of like the old Smarties commercial: "Do you eat the red ones last?" I found myself saving the red ones to the end without even realizing that I was doing so! Now, I consciously eat my M&Ms from my least favorite color (they all taste the same!) to my most favorite (blue and red). —Preceding unsigned comment added by 216.154.20.38 (talk) 14:52, 15 July 2009 (UTC)[reply]
I just ate a whole bag of peanut M and M's and didn't pay attention to any of the colors. after reading this post, I will in the future! cheers, 10draftsdeep (talk) 18:13, 15 July 2009 (UTC)[reply]
"M&Ms are Tasty! They melt in your mouth, not in your hand. Melting before being consumed was a problem with chocolate, which was otherwise highly useful as an emergency ration for soldiers. In World War 1, the U.S. Army issued chocolate bars to soldiers to be eaten for energy needs when normal food could not be brought to the at front line positions. Knowing that any normal guy would eat a tasty chocolate bar long before the hypothetical emergency, the Army adulterated the chocolate bars with sawdust and kerosene. Edison (talk) 01:50, 16 July 2009 (UTC)[reply]
Hello. If ionic compounds are polar and like dissolves like, why are some salts water-insoluble at SATP? Thanks in advance. --Mayfare (talk) 21:51, 14 July 2009 (UTC)[reply]
"like dissolves like" is a general observation of a certain trend, not a fact (and definitely only a result not a physical law or the cause of anything). If "whatever holds molecules together and to each other" is stronger than "whatever interactions happen between solute and solvent", the chemical is not very soluble. See solubility for a detailed discussion. DMacks (talk) 22:11, 14 July 2009 (UTC)[reply]
In the case of ionic salts, that would be the relative strength of the ions' electrostatic attraction to each other vs. water molecules. If the ions are more attracted to each other than to water, then the salt will not dissolve. Generally, salts where one or both ions are monovalent (with the exception of some fluorides) are water-soluble, whereas those where both ions have a valence of 2 or more are water-insoluble because their electrostatic attraction is much stronger. Note also that for the purpose of determining solubility, fluoride ions behave as though they have a valence of 2 or more, even though they really are monovalent.
When they say "fluoride ions behave like they have a valance of 2" I think what is meant that fluoride ions (F-) show similar solubility characteristics as 2- ions eg sulphate - this is because of F- ions small size ... small size or high charge makes the ion more strongly interact with electrophiles. It's not the electronegativity.
Also if a compund is only partially ionic the solubility is affected (eg CuI is insoluble, but KI is soluble) - there are a lot of factors, but it's simpler when both the anion and cation are good at forming ions eg Cl- , K+ , Mg2+ , NO3- etc...83.100.250.79 (talk) 22:25, 15 July 2009 (UTC)[reply]
I understand that there is a limit to the degree of cold (absolute zero), but is there a limit to how hot things can get? Obviuosly in the moments after the big bang, the temprature would of been huge, but can there be a higher temprature, either naturally (in supernovas etc) or synthetically (in collisions and heating [I read that scientists have heated a substance to 510 million degrees!]). Andy (talk) 23:57, 14 July 2009 (UTC)[reply]
There is no theoretical limit to the best of my knowledge. There is a practical limit imposed by the total amount of energy in the observable universe, of course. You may be interested in the concept of negative temperature, which is, in a sense, temperature hotter than infinitely hot. --Tango (talk) 00:04, 15 July 2009 (UTC)[reply]
Good stuff, very interesting, just out of curiousity, what is the hottest temprature ever created, both in a lab or naturally? Cheers. Andy (talk) 00:41, 15 July 2009 (UTC)[reply]
That's not quite analogous to absolute zero. Absolute hot isn't the highest temperature achievable, it's the highest temperature that our theories are capable of describing meaningfully. --Tango (talk) 03:13, 15 July 2009 (UTC)[reply]
As Tango states, defining a limit is difficult, because what is "hot" can be counter-intuitive. Your scale goes in a loop from kind of +0K (cold) to -0K (hot). Hotter than 10^32 K is of little physical relevance (or at least doesn't make sense until we figure out quantum gravity), though, as Ranemanoj said. —Anonymous DissidentTalk16:33, 15 July 2009 (UTC)[reply]
Indeed, as AD states, we need to figure out quantum gravity before knowing what happens around Planck temperature. It might well be that there is a limit, but it won't be necessarily the current definition of Planck temp. (also because the choice of using G instead of 8πG in that def. is quite arbitrary, and one which I'd disagree with). There might well be no limit at all. We just don't know it yet. --A. di M. (talk) 16:55, 15 July 2009 (UTC)[reply]
Show me a system in a container which you claim is at the highest possible temperature, and I claim I could heat it up a bit. There is no "highest possible temperature" unlike absolute zero. Edison (talk) 01:45, 16 July 2009 (UTC)[reply]
This does not prove that there is no highest possible temperature --- it just proves that it cannot be reached. See Achilles and the Tortoise (same holds with speed of light and acceleration). (Might be there is none but your argument isn't a proof for it.)95.112.156.108 (talk) 20:31, 16 July 2009 (UTC)[reply]
July 15
Beetle factoid
Something I heard on the radio the other day.
"If you were to randomly arrange all the macroscopic animal life on earth in one long line - then every fifth creature would be a beetle."
I see what they were getting at but if you were to arrange them in a truly random nature, then there is no telling just where in the line the beetles would fall. I know, I'm picking nits... Dismas|(talk)00:28, 15 July 2009 (UTC)[reply]
They are claiming that 1/5th (20%) of all macroscopic life is beetles. See beetle. The percentage is closer to 25%. So, every 4th creature would be a beetle. -- kainaw™01:59, 15 July 2009 (UTC)[reply]
Indeed, the source has "Beetles comprise 25% of all described animals and plants, single-handedly making them the primary contributor to earth's biodiversity. The 350,000 descrubed beetle species are members of largest order of life on Earth. Coleoptera." Algebraist02:03, 15 July 2009 (UTC)[reply]
The term "macroscopic" is kinda vague - I'm sure you could make the answer come out anyway you wanted by picking a more exacting standard for what size of creature you're talking about. Haggling over whether the number is 20% or 25% is kinda silly in the face of that. SteveBaker (talk) 04:40, 15 July 2009 (UTC)[reply]
I suspect that what he meant was that the Beatles were never publicly crucified, which is not what one usually a great sign of popularity. Googlemeister (talk) 13:51, 17 July 2009 (UTC)[reply]
Ultimate Revenge/Punishment - Paralysis with no possibility of communication
Is it theoretically possible to perform an operation on someone/dose them with something that would render them completely and permanently paralyzed with no way to communicate (no blinking, no twitching etc) but still leave them completely aware of themselves and their surroundings (without killing them of course)?
They could then live out a full lifespan knowing that someone did this to them but never being able to tell anyone who - the ultimate revenge/punishment? Exxolon (talk) 00:39, 15 July 2009 (UTC)[reply]
Disregarding the fact that I now hope I never meet you in real life (☺), yes, it is certainly possible, although they would have to be on life support, and future advances in medicine may be able to tap directly into people's brains, allowing them to communicate despite any neurological damage.[citation needed] -RunningOnBrains(talk page)00:43, 15 July 2009 (UTC)[reply]
I think that if you sever the spinal cord just below the medulla oblongata, you can paralyze the subject from the neck down. FWiW
76.21.37.87 (talk) 00:51, 15 July 2009 (UTC)[reply]
It would probably be simpler with present technology to simply (in addition to the above) put out the eyes, puncture the eardrums and use chlorine gas to destroy the senses of taste and smell for a similar effect. The victim's conscious mind would probably vanish into a black hole after a few weeks/months. --Kurt Shaped Box (talk) 01:24, 15 July 2009 (UTC)[reply]
The OP says "still leave them fully aware of their surroundings". So personally, I'd go with severing the spinal cord, and pull out the tongue so the subject can't say anything to anyone (not that I'd do that to anyone, of course, except to a terrorist or to a child molester).
This is not the ultimate revenge or punishment. As covered many times in literature for thousands of years, loss of hope is the ultimate punishment. To lose hope, you must first have hope. Classic example: Imprison a person for, say, 30 days. On the last day, punish the person for something that happened over the imprisonment and extend the punishment another 30 days. On the last day, punish the person again with another extension. Repeat this until all hope is lost. -- kainaw™02:03, 15 July 2009 (UTC)[reply]
I deem your portrayal of hope to be a good thing as somewhat facile. It's only when we lose hope that we begin to gain some beginnings of a true, sustainable, authentic self. To hope is to dislike your present reality. Vranak (talk) 18:28, 16 July 2009 (UTC)[reply]
It's certainly possible. All you would have to do is take somebody with locked-in syndrome and paralyze the eyes. People with end-stage Parkinson's disease may be in a state something like this. In principle it would still be possible to communicate with such a person by directly reading brain activity, but if you ignore that approach, it is definitely possible. Looie496 (talk) 02:12, 15 July 2009 (UTC)[reply]
As Looie496 pointed out, even with complete loss of motor control, communication is still theoretically possible. I recall recently seeing a news report or documentary on experiments where subjects were able to control a mouse cursor using brainwave activity picked up by a sensor filled skull cap. I wasn't able to find a wikipedia article, but did find this similar story on the web. Such technology could allow your paralyzed victim to pick letters off the screen, form words, and eventually tell the police who dunnit. -- Tcncv (talk) 02:19, 15 July 2009 (UTC)[reply]
Actually, this is the state we are all in, all the time. We think we can communicate with people. But that is actually an illusion. We are just a brain in formaldehyde. The formaldehyde has wikipedia molecules added to it. Bus stop (talk) 02:21, 15 July 2009 (UTC)[reply]
Nonsense. There is no 'we'. My consciousness is the entirety of existence. Everything else I may perceive is merely a delusion constructed unconsciously in order to maintain my sanity. --Kurt Shaped Box (talk) 02:42, 15 July 2009 (UTC)[reply]
I believe I could send Morse code (slowly) by turning the Alpha waves on and off, even if all sensory nerves and motor nerves were out of commission. These are easily monitored by scalp electrodes. Regardless of whether they were in fact monitored, I would amuse myself by cursing my captor. The role model for this is Malcolm, the black guy in 2001 Maniacs who is about to be crushed by a large press controlled by an antebellum racist zombie, Mayor Buckman. Mayor Buckman says "Do you have any last wish?" Malcolm says,"Yeah. Kiss my black ass!" and spits in the zombie's one functioning eye. Zombie says to assistant, "Next year remind me to omit the'"Last wish' part." Edison (talk) 04:19, 15 July 2009 (UTC)[reply]
I have actually suffered from this a couple of times on waking up. It only lasts about 10 seconds though and a huge hypnic jerk knocks me out of it.
This is actually known as sleep paralysis, caused by a persistence of REMatonia after waking. I used to get it regularly when I was younger, definitely the scariest thing I ever experienced, until I understood what was going on and could just relax until I woke up properly.Mikenorton (talk) 15:24, 15 July 2009 (UTC)[reply]
The trick is to hold ones breath. Under sleep paralysis I have found that I still have control over my breathing. Asphyxiation wakes up whatever part of me that is still sleeping. EverGreg (talk) 21:30, 15 July 2009 (UTC)[reply]
(EC) I would question both the efficiency and the costs of any such measure. Punishment has three major functions: deterring other individuals from committing the same type of crime, motivating the individual who committed a crime to change his/her behavior in future to conform to legally/socially accepted behaviors and preventing the individual who committed the crime from doing it again. The effectiveness of [{capital punishment]] in general is debated. Your method would exacerbate the costs and further reduce any impact. Since your prisoners would be unable to communicate, there would be no reports from them on the horrors of their situation. So you'd have to bank on prospective perpetrators finding the mental image of locked-in syndrome and pictures of individuals in prison hospital beds connected to a barrage of tubes and monitors more objectionable than life in prison or a death sentence. IMHO not very likely. More likely would be that this type of punishment would add to the suffering of the victims and their families. Even if they feel entitled to retribution at first they may feel remorse later because this punishment doesn't provide sufficient closure. Depending on their moral and ethics views they may feel diminished by the harshness of the punishment. (They are also much more likely to consider the punishment harsh than someone who has stepped so far out of society as to consider committing a crime.) Most societies have a hard time these days covering the cost of caring for critically ill individuals. Your version would artificially increase the numbers in the category requiring the most intensive care and that on a long term basis. (Most patients requiring intensive care are either so ill that they die after a while or they recover sufficiently to classify for less intensive care options or even release from hospital.) I couldn't think of any way to justify that. At least in the US, there's criticism that a large portion of the prison population is suffering from some mental illness. Providing adequate care for those and improving living conditions in high crimeareas would be a better use of funds to reduce the rate of violent crimes than the method you are considering.71.236.26.74 (talk) 17:20, 15 July 2009 (UTC)[reply]
You have a good point here -- why go to all that trouble paralyzing a terrorist or child molester and then keeping him alive for many years, when it would be more effective to just shoot him and be done with it?76.21.37.87 (talk) 01:14, 16 July 2009 (UTC)[reply]
Note: the movie cuddlyable mentions is a work of fiction and not a documentary. Effects scientific studies report for isolation tanks are usually positive [11]. 71.236.26.74 (talk) 08:24, 16 July 2009 (UTC)[reply]
Sorry I came to it via a more direct link p227/278 have something. Probably not the best reference, but there are quite a few studies out there. It's used in therapy. Will try to post better stuff if I can find the time. 71.236.26.74 (talk) 01:36, 17 July 2009 (UTC)[reply]
Sensory deprivation used in therapy?! With all due respect, I really have trouble believing that. I know that it was one of the tests used for astronaut training, and most astronaut interviews state that even a few hours of sensory deprivation is extremely distressing. Also, there are (unconfirmed) reports that the Soviets used sensory-deprivation-like techniques for prisoner interrogation / punishment, and almost all of the prisoners either spilled the beans within a few days (couple of weeks at most), or lost their mind. I don't see how sensory deprivation can be used in therapy.
I am going to say, considering the excellent points presented above, it is impossible to do so whilst leaving the person as a conscious, sapient mind. The mind is just something the brain is doing, and far from being the mysterious black box of puzzles it once was, we now have the capacity to look in and watch the brain doing that. That mouse cursor brain thing shows the key point. No matter how much you detach the person's mind from any natural, "everyday" output channel (speech, hand gestures, eyebrow waggling, whatever), there is still an output channel you can't possibly disconnect (that is, the brain activity that makes up the mind itself) without killing the mind. Maelin (Talk | Contribs) 12:52, 16 July 2009 (UTC)[reply]
I haven't looked at that article, but the basic reason is because when you're moving, you can compensate for an error by turning the wheel a little bit to the side you're falling toward, but that doesn't work when you're at a standstill -- you can only compensate then by shifting your weight, which involves a much longer time delay. Looie496 (talk) 02:55, 15 July 2009 (UTC)[reply]
The first answer is correct. Angular momentum plays very little role on a bicycle. it is more important for the understanding of the motorcycle dynamics. Dauto (talk) 05:29, 15 July 2009 (UTC)[reply]
Our Article says Angular momentum conservation plays more of a role on lighter vehicles like bicycles. Angular momentum conservation through counter leaning un addition to balancing with the handlebars is the complete answer, as given in our article. Rkr1991 (talk) 05:52, 15 July 2009 (UTC)[reply]
Nuh-uh, Looie's answer is correct. There have been experiments with bicycles with locked steering. I suppose I ought to be able to cite that, and I can't, and anyway I probably read it on the reference desk in the first place ... but I believe it's true. Bike wheels do make nice gyroscopes but aren't significant in that capacity in stopping you falling off. 213.122.68.146 (talk) 06:58, 15 July 2009 (UTC)[reply]
The idea here is that because the contact-patch of the wheel is BEHIND the axis it pivots on, when you lean it automatically tends to steer into the lean. Exactly what you would want it to do to keep you upright. This built-in feedback makes it very easy to stay balanced because the bike is constantly "trying" to steer itself under your center of gravity. APL (talk) 13:06, 15 July 2009 (UTC)[reply]
In other words, the angular momentum does help by providing a force which completes a (mechanical) negative feedback loop; the actual balance is accomplished with the steering corrections. As Dauto has pointed out, the net effect of the angular momentum is small; but the bicycle attempts to self-right because of the fork mounting of the front tire. (Consider the front tire fork mounting as a mechanical "amplifier" which senses deviations in angular momentum, and magnifies them via the kinetic energy sourced from the forward motion of the bicycle). The human can hold the handlebars and assist in the steering. Perturbations from balance upset the angular momentum, and push the tire back towards the upright steering. This is why minutely different designs of front wheel mounting dramatically change the steerability and stability of the bike. Nimur (talk) 22:04, 15 July 2009 (UTC)[reply]
Nimur, the fork feedback works even if the bike is not moving at all (try it) and therefore has nothing to do with angular momentum. A bike's wheel doesn't spin fast enough to have any important effect. A motorcycle is a different matter. Ask anybody that knows how to drive a motorcycle if steering it is any different than steering a bike. Ask them if they have to pull right in order to turn left Dauto (talk) 04:56, 16 July 2009 (UTC)[reply]
I strongly recommend that everyone who is even considering replying to this thread carefully re-read our Bicycle and motorcycle dynamics article before replying. IMHO, it's one of the finest science articles in the whole of Wikipedia (why isn't it an FA?†) - and it's correct, well written, approachable, beautifully illustrated - and properly referenced - as opposed to about half of the replies here so far that are complete twaddle! SteveBaker (talk) 07:21, 16 July 2009 (UTC)[reply]
The simple answer is that the wheels of a bike can be easily moved back under the center of mass, in response to an undesired lean, when moving forward, by steering the front wheel in the direction of the lean. The faster the bike is moving, the more quickly the contact patches move for the same steering input. When stationary, there is some ability to move the front wheel contact patch from side to side because of the front wheel steering geometry, specifically the feature called trail, but it is limited and slow compared to when moving forward.
The geometry and mass distribution of many bikes is such that the torque necessary to turn the front wheel appropriately can be generated by the bike itself, if moving forward at the right speed. The factors that influence this self-stability include the "trail" mentioned above, mass distribution of the entire bike and of just the front end, and inertia of the wheels, especially the front wheel.
While the gyroscopic effects of the spinning wheels is often cited, David Jones proved by experimentation that they are not necessary for a bike to be "easily ridden" in his famous 1970 Physics Today article. A spinning wheel provides no direct resistance to tipping. Instead, when the spinning front wheel is subject to a tipping torque, it reacts be precessing about a third axis, perpendicular to both its spinning axis and the axis of the applied tipping torque. This is approximately the steering axis. Thus, this precessing can contribute to the bike's ability to steering in the direction of a lean automatically. -AndrewDressel (talk) 12:16, 16 July 2009 (UTC)[reply]
Article here (doi:10.1038/nphoton.2009.116), poorly formatted draft at arXiv:0903.5117. They seem to be talking about a nonlinear interaction in a medium which (they say) is already predicted by Maxwell's equations, so it's theoretically very old. It isn't literally a force between electromagnetic waves, but between charged particles in the medium. The reason for the newspaper reports is not that the paper is important, it's that Yale issued a press release, and most science reporters don't know how to do anything but parrot press releases. Why they issued the press release I don't know, but inevitably they're going to inflate the importance of the work because the point is to get free advertising for Yale. I would ignore it. The paper is science as usual, the reporting is horrible science reporting as usual. -- BenRG (talk) 10:08, 15 July 2009 (UTC)[reply]
There are plenty of studies on facial tics, or microexpressions related to lying, but I'm curious if anyone knows of a source of videos or other resources on the specific issue. What I'm ultimately interested in are source videos that compare people lying to those that aren't, and in high enough format that they're useful. Bonus points if they involve law enforcement. I realize this is a tall order, but if there are any good studies (even without video) outside of what I can find on pubmed/jstor I'd be interested. Thanks. Shadowjams (talk) 05:27, 15 July 2009 (UTC)[reply]
I want to show that the torque caused by gravity is equal to the torque that would be produced by an point particle of mass M at the centre of mass. I've been trying to evaluate the sum Σ (m_i*g*r_i*sin(θ)_i), but I haven't been able to reduce this to MRg*sinθ (where R denotes the position of the centre of mass). Is there a way to do this, or does it suffice to show that the total force due to gravity is equal to the force produced by a point particle of mass M at R, and then multiply this by R to get the torque? (I wouldn't think so). —Preceding unsigned comment added by 70.52.44.188 (talk) 05:44, 15 July 2009 (UTC)[reply]
I don't understand. About which point are you taking Torque ? If it is the centre of mass, as conventionally taken, wouldn't the torque that would be produced by an point particle of mass M at the centre of mass be zero ? Rkr1991 (talk) 05:58, 15 July 2009 (UTC)[reply]
Oh, well maybe this is a clearer explanation of what I'm asking (sorry if I can't explain myself properly!): Supposed an object is fixed in such a way that it will pivot about a certain axis. Assuming that the gravitational field is constant, what is the torque produced by gravity? I know that the answer should be MRxg, where R is the position vector of the centre of mass, but I don't know how to derive it. My normal approach would be to sum all the torques τ_i acting on each particle of the object, which by Newton's Third Law should equal the total external torque (ie the total torque produced by gravity, should that be the only external torque acting). On the other side of the equation, I get Σ (m_i*g*r_i*sin(θ)_i), which I'm having trouble evaluating. PS I know that the total force due to gravity can be treated as if the entire mass were concentrated on the centre of mass, but can we extrapolate from this that the total torque due to gravity is equal to MRxg? —Preceding unsigned comment added by 70.52.44.188 (talk) 06:29, 15 July 2009 (UTC)[reply]
The Nephrite variety of Jade consists of amphiboles in the solid solution series tremolite-actinolite-ferroactinolite. Jade is either iron-rich tremolite or actinolite, the former being lighter green and the latter darker. The maximum iron content for tremolite is 10% Fe of the total Fe+Mg, from 10-50% it's an actinolite, any higher then it's a ferroactinolite. Synthetic tremolite and actinolite certainly exist, but I doubt it would be cost effective to try to produce large quantities. Mikenorton (talk) 09:30, 15 July 2009 (UTC)[reply]
Water Wheel Power
Would it be possible to power a household which uses 1000 kWh per month using a water wheel? How big would it have to be and could I possibly build several smaller ones or is one big one the way to go? TheFutureAwaits (talk) 12:24, 15 July 2009 (UTC)[reply]
A household usually has peak energy demands around 10kW though, so if you are only generating 2kW, probably can not run the refrigerator, the oven the AC and the clothes dryer at the same time. Googlemeister (talk) 14:29, 15 July 2009 (UTC)[reply]
The short version: yes. "Power via water wheel" is a useful approximation of hydroelectric power. Examining industrial applications, it's clear that multiple smaller systems are a useful way to scale requirements. As for "how big", a more useful question is what sort of water flow you need. This thermodynamics book includes a sample problem for ideal power generation at the Hoover Dam. Note that both water flow rate and elevation change are relevant to the power that can be supplied. — Lomn14:45, 15 July 2009 (UTC)[reply]
Water power is far more reliable and continuous than solar or wind (unless the creek goes dry or the pipe freezes or the intake gets clogged with twigs). Your water wheel or Pelton wheel microgenerator should be sized to supply your peak load.This will be several times your average load. If you cogenerate, then the utility absorbs the excess and supplies the deficiency, reducing the required size and cost. For a Pelton wheel, high pressure water from a point quite elevated is desirable. The flow of water is the limiting factor for how many kilowatt hours you can produce before the water level drops. An old water wheel like mills of the 19th century is not the ideal way to run a generator, but is has been done. Years ago on TV they showed a former textile mill where a man had hooked up the old water wheel to an alternator,. It produced 30 kilowatts continuously. This would be 518,000 kilowatt hours each month, worth perhaps $20,000 when sold to the utility. It was probably extremely inefficient. The typical microhydro has a 100 foot drop from water intake to Pelton wheel and the flow is a few gallons per minute. As for number, for such a small load it would be practical and economical to buy one turbine/generator. If you set up to sell the surplus to the utility, then you should be able to use the utility as a backup, eliminating any advantage of multiple units. Keep things simple. See Micro hydro or Google the term. Some of the vendors can advise you on components suitable for your situation. Edison (talk) 16:20, 15 July 2009 (UTC)[reply]
Before you go ordering parts online and calculate a setup, check local EPA regulations and county water resource/use rules. Depending on your location you may have to provide alternative habitats for local wildlife, have to pay a fee for operating your water-wheel or it may be outright prohibited. Try to find an official in charge at your county government who can help you finding out what laws and regulations apply. Work your way up from there. (If you take this as legal advice, I'd have to instruct you to contact a lawyer instead.) 71.236.26.74 (talk) 17:41, 15 July 2009 (UTC)[reply]
This water wheel would give DC right? And most houses I know are wired to use AC, so there might need to be other modifications as well. Googlemeister (talk) 18:45, 15 July 2009 (UTC)[reply]
Probably - yes. But you're probably going to need to store the power for when you need it and to smooth out variation in your day/night demand cycle - so most likely, you'd have a basement full of car batteries that you'd charge from the water wheel - and then use an Inverter (electrical) to convert the output of the batteries to AC. SteveBaker (talk) 19:07, 15 July 2009 (UTC)[reply]
It might be more efficient to build a dam and only let through the amount of water you need at any given time. During off-peak times the water level behind the dam will build and then go down again during peak times. You might annoy being further downstream, though! --Tango (talk) 19:38, 15 July 2009 (UTC)[reply]
If you build a dam, the level of permitting needed may be quite high, since a dam which holds back a large volume of water can cause considerable damage if it fails. Microhydro often uses an intake which is not really a dam, above the falls of a stream, rather than having a dam sufficient to produce the required head. Microhydro often produces say 24 volt DC which is stored in batteries and converted to AC through an inverter. An inverter which ties to the utility may eliminate the need for batteries, as you cogenerate. Utility permission should be sought. They have brochures on how elaborate the interface and protective relaying has to be. It gets more complex as the generator gets larger. For a few kilowatts it should be minimal. Edison (talk) 21:58, 15 July 2009 (UTC)[reply]
Thanks for all the great info! So if I were to use a Pelton wheel to generate 1000 kwh per month is there a reasonable estimation of what the radius of the wheel would need to be? The water flows at about 5 mph and drops about 10 feet in the area I want to build the wheel although I suppose I could use tubes to divert the flow and create a steeper, higher pressure drop. TheFutureAwaits (talk) 21:03, 16 July 2009 (UTC)[reply]
Well, I'm not an expert on water-wheel design - but I'd guess that you want the weight of the water to be pushing down on the wheel for as much of the drop as possible because any water that falls through any distance without being attached to the wheel is wasting energy. However, to do that - you'd have to have a 20' wheel with the hub of the wheel level with the surface of the water - and having it drag through the water would cause a lot of energy loss...hence, I presume the basic design for a classic over-shot wheel (like in the photo to the right) where the water is fed in at the top of the wheel - roughly level with the inlet height - falls with the wheel for as close to half a rotation as you can manage - then empties out at the bottom - roughly level with the outflow height. That would require (in your case) a 10' diameter wheel. That would capture as much of the energy as possible. However, knowing the speed of the water doesn't help unless you also know the volume (ie the flow rate. After all - I could probably get a 5mph, 10' drop water flow from a super-soaker...but that's not going to turn a 10' diameter water wheel! You would need to vary the width of the wheel and/or the size of the 'buckets' or 'scoops' in order for it to store all of that volume of water as it falls - without any spilling over and going to waste. The knowing the volume of water that the wheel is holding would allow you to calculate the torque that the wheel could exert - and with appropriate adjustments for frictional losses, you could use that to estimate the energy output.
If you knew the flow rate (cubic feet per second or whatever) - we could make an estimate of the energy you might be able to extract...but without that information, we have no clue. SteveBaker (talk) 23:59, 16 July 2009 (UTC)[reply]
You may need a water turbine instead of a water wheel. (I would have thought they are synonyms, but there seems to be only a partial overlap.) This page says there are several options depending on the specifics of your site. [12]71.236.26.74 (talk) 02:19, 17 July 2009 (UTC)[reply]
I've just read the article Water turbine -- from what I gather, a 10' drop ain't enough for a Pelton wheel (it needs at least 15' for best efficiency), but a Kaplan turbine would be right at home with a 10' drop (in case you don't know, a Kaplan turbine is the kind of turbine that looks like a ship's propeller). So, TheFutureAwaits would be better off putting in a Kaplan turbine instead of a Pelton wheel. Also, SteveBaker, a Pelton wheel ain't like your regular water wheel cause it don't use the weight of the water but its velocity for propulsion -- so you don't have to install it level with the inflow, and in fact it's better to place it as low as possible so's you get the most velocity from the drop.
Good idea, 71 IP -- a Banki turbine's a better choice for a small / variable flow rate, while a Kaplan turbine's better for a fairly big, more-or-less constant flow rate. It really depends. 76.21.37.87 (talk) 05:59, 17 July 2009 (UTC)[reply]
There's also the maintenance issue. It says Bankis are easier to maintain. I remember the first private wind turbines often overtaxed their builders' time, energy and abilities that way. 71.236.26.74 (talk) 06:14, 17 July 2009 (UTC)[reply]
I should get a job at Nasa :-). The chart's in meters. OP only has a 3 m drop. Kaplan it is. (I should buy myself a trout and whack myself.) 71.236.26.74 (talk) 18:17, 17 July 2009 (UTC)[reply]
As an aside, if the flow rate is more-or-less constant, the OP should consider a Kaplan turbine with fixed-pitch blades instead of variable-pitch, it should save him / her a whole bunch of maintenance. If the flow rate is very variable, though, then variable-pitch blades are the only option.
The English wiktionary defines "pavement cell" as Brachycystidia in the gills of some species of Coprinus. But pavement cells also exist in plants. So what exactly is a pavement cell? --Leptictidium (mt) 13:28, 15 July 2009 (UTC)[reply]
I'm not familiar with pavement cells of any sort, but I can tell you that it is quite common in microbiology for names like that to be given to multiple things that have no meaningful relationship to each other. In the brain, for example, there are "granule cells" all over the place, and the only thing they have in common is that they are all small. Most likely "pavement cells" are just cells that look sort of like they are paving a surface, under a microscope. Looie496 (talk) 14:26, 15 July 2009 (UTC)[reply]
In fish, pavement cells are also known as 'respiratory cells' and in saltwater fish they are very flat, so Looie is likely to be right in suggesting that they have been named for their shape, rather than any biological similarity to plant epidermal cells. Mikenorton (talk) 14:59, 15 July 2009 (UTC)[reply]
Cleaning oil stain from thermal plastic elastomer
How would one clean oil off of the surface of a thermal plastic elastomer (mixture of PVC and silicone)? I've tried soap and water. Also alcohol, but no luck. --68.102.170.184 (talk) 13:43, 15 July 2009 (UTC)[reply]
How likely do you think it is that a small computer which makes a computer case made of water-proofed sisal woven over a frame, will be adopted by major computer companies like Dell and HP? N.B. sisal would save energy by allowing heat to escape. (Cross-posted to computing board) --Patar knight - chat/contributions17:43, 15 July 2009 (UTC)[reply]
People who run their computers with the case off not uncommonly fry some part because the airflow generated by the fans no longer reaches that part. Manufacturers'd have to start over with testing for airflow/heat management. Other than the flow in an enclosed case, the leakage through your "open" case would be hard to quantify and would likely vary wildly. Dust entering the case and sisal fibers disintegrating from the weave would be other factors to consider. You could coat the fiber to prevent that, but that would somehow run counter to the whole "natural" idea. Admitting that most computers would be obsolete and replaced before the case got too grimy would also not in the manufacturers' best interest. There might possibly be a small market in the ecologically conscious home computer market, but for most business applications it's rather unlikely to become a widespread option IMHO. 71.236.26.74 (talk) 18:01, 15 July 2009 (UTC)[reply]
I thought of that at first, but quite a few plastic materials used for cases start out as "Class A" and just reach higher grade by having Flame retardants added. If it works on cotton it should work on sisal, too. (See the article why that would make the case a lot less "green") 71.236.26.74 (talk) 18:46, 15 July 2009 (UTC)[reply]
I think you could extract fibres from the sisal and make some sort of a paper mache-like substance that would make a reasonable case - it could easily be treated to make it fire-resistant. The problem would certainly be heat though - a metal case acts like a huge heat-sink - a case made of pretty much any kind of plant material would probably make a good insulator - and that's a disaster.
However, this is all really unnecessary. Computer cases are commonly made of aluminium[citation needed] - and that's a VERY recyclable metal. It would be simple to dump computer case panels into the same recycling stream as old coke cans. The difficulty with recycling computers isn't the case - it's the circuit boards, hard drives, keyboards and (especially) displays. These are very 'mixed' materials which are almost impossible to separate out into useful recycling streams. A typical circuit board has fibreglass and resin for the board itself - with layers of valuable copper buried inside it and bonded very firmly to it's surface - with lead/tin alloy solder firmly affixed to it, plastic and ceramic chip casings, all manner of little plastic and brass parts. Steel connectors often with gold plating. Then inside the chips you've got silicon, more gold, who-knows-what nasty stuff inside resistors, capacitors and any little batteries and such - all kinds of exotic metals inside things like LED's. Glass and LCD-panel monitors are an even bigger nightmare - lead and phosphors in the CRT, weird liquid crystal chemicals in the LCD's. Power supplies often have toxic chemicals in the windings of the transformer coils. It's really a mess to sort this out in a cost-effective way.
So fixing the problem of recycling the cases of old computers is solving a non-problem and creating a bunch of new problems (as alluded to above) in the process. What's needed (and it's hard to see how it'll happen) is to figure out how to recycle everything OTHER than the case.
If for some reason we were really passionate about case recycling, the solution (since cases never break or wear out) would be to require the circuitry of all new computers to fit into a standard sized case (deskside computers pretty much do that already). The manufacturers could then offer to sell you a new set of electronics that slotted right in to your existing case. This isn't difficult for an individual person to deal with. I haven't bought a new computer for 16 years! I just keep swapping out parts (and occasionally cases) from one generation of machine to the next.
Computer cases=steel not Al, Transformer windings = not toxic at all really - just glue. (Large industrial transformers from the 1960s ~10kW+ = toxic yes). 83.100.250.79 (talk) 22:31, 15 July 2009 (UTC)[reply]
(83.100.250.79: Please don't interpose your replies in the middle of someone else's comments - it rapidly gets very confusing. I've moved your reply to the proper place). Anyway - the cases of all three of my home PC's are aluminium - including all of the internal rails and bracings...there may be the odd steel one - but it doesn't change the conclusions. Steel (like most other pure metals) is also childishly easy to recycle. It's not the problem here. Consider recycling CRT's, hard drives and motherboards...it's tough. I'll take your word for the nature of the goop in the transformer windings - but again, the precise details don't matter - the issue is that there are a LOT of weird and wonderful materials (many of them toxic) inside a typical computer - and sorting them out at any reasonable price is FAR beyond our current ability. SteveBaker (talk) 07:14, 16 July 2009 (UTC)[reply]
sorry that was an accident
Actually I don't totally agree on the toxicity of computer parts - in a landfill there's no much issue, BUT if they are incinerated then yes there is a toxicity issue.
One part that is trivially recyclable is the solder. It's also possible to extract the copper by shredding and density separation - I'm not sure if this is economically viable. As part of the desoldering recycling operation there should be all the surface mount components separated - as for re-using these - I doubt intel et al would be very keen on losing out on the obsolescence/replace product lifestyle. The chips, capacitors, and resitors I wouldn't know what to do with - possibly the caps could be density separated and recycled. That leaves the ICs mostly - as far as I know they are totally unrecyclable in terms of materials/energy - especiallly in an economic sense. (Though they do have a store of energy as order - so if you can make a "order converts to entropy=electricity" machine you might be onto a winner. One product of the recycling process I've left out is the shredder glass fibre/epoxy board - any suggestions as to what to do with this.
Recycling of electronic parts can be done, and is done - though not total recycling. And only a fraction of the waste goods actually gets recycled as far as I know.83.100.250.79 (talk) 14:59, 16 July 2009 (UTC)83.100.250.79 (talk) 14:19, 16 July 2009 (UTC)[reply]
Desktop and deskside computer cases are easy to re-use if you really want to. If you don't want to re-use the case, they are also trivially easy to recycle, since they have effectively the same mix of materials as an automobile body. On average there are thousands of times more material in car bodies than in computer cases, so the computer cases have effectively zero additional impact on recycling if done correctly (i.e., throw the old case in the back of a car on the way to the car recycling center, or if your municipal garbage system uses magnets to separate out the steel, the cases will be treated like "tin" cans.) For servers and other large installations, the industry is trying to find more elegant solutions such as blade computers that have relatively less case material per computer. As Steve said above, the stuff inside the case a a much bigger problem. If you have a computer at home, you should worry about the energy it uses, not about recyclinghte case. You can also worry about all tjhe plastic in a laptop case, but these are more similar to other small appliances.
Computers are becomming a whole lot more effecient by every purely technical measure: cost per instruction executes, power per instruction exececuted, weight (material to recycle per instruction executed.) A modern Mac mini or plug computer is massivley more capable than a ten-year-old desktop, but uses less tha a tenth of the energy or material. Unfortunately, we all just keep upgrading to better conputers and then don't actually use the extra capability. This appears to be changiong somwhat with the advent of the netbook. -Arch dude (talk) 22:05, 15 July 2009 (UTC)[reply]
Arising from the above, are computer cases made out of aluminium rather than steel
I'm still amazed that computer cases are made of Al, the ones I'm aware of have all had a skin of steel or plastic.(Not counting mac books etc) However I accept SteveBakers comments about the rails (ie the internal frame and attachment points) being made made out of Al - there is one really good reason for this - and that's that alumimium is a lot easier to machine than steel - specifically putting screw holes in steel is a lot harder. Al is not cheaper. I doubt the reason is lightness (excluding laptops were this matters)83.100.250.79 (talk) 14:04, 16 July 2009 (UTC)[reply]
I'm skeptical about the aluminium case too. All the aluminium cases I've seen are premium cases like Lian-Li cases, whereas most normal cases are made from SECC (most, if not all, of these and these are made from steel). I'm putting a [citation needed] tag on Steve's claim. --antilivedT | C | G01:39, 17 July 2009 (UTC)[reply]
I don't think it's likely that Dell or HP would ever make a sisal computer case, but it sounds like a typical thing that the case mod community might do, especially with lower powered motherboards. mini-itx.org has a lot of photos that you might like. Look down the list of projects on the lower right hand edge of their main page. 67.117.147.249 (talk) 08:32, 21 July 2009 (UTC)[reply]
decarboxylation
I assume carbon dioxide a good leaving group? What's the mechanism of heat-driven decarboxylation usually, e.g. like in THC? I can't imagine protons being good nucleophiles, however... does the CO2 usually take the electrons with it? Does the bond cleave homolytically?
I suspect the CO2 LG takes the bonding electrons with it, such that you get a carbocation (or a carbocation-like transition state?) -- would that explain why longer-chain COOH's are easier to decarboxylate? Is a tert-COOH group the easiest to decarboxylate? John Riemann Soong (talk) 18:24, 15 July 2009 (UTC)[reply]
Someone uploaded an image displaying the mechanism for the decarboxylation of a ketoacid. I haven't been able to find the mechanism of decarboxylation of something like acetic acid.
"does the CO2 usually take the electrons with it" sounds like you will have a redox problem, unless you plan on losing H– (hydride) later:
RCOOH → R+ + –COOH
And homolytic cleavage of C-C bonds is also unlikely unless you have some radical initiator. Is there a reason you need to look further than
RCOOH → RCOO– + H+
RCOO– → R– + CO2
? The two examples given, salicylic acid (which looks like the relevant substructure in THC) and β-ketoacid, in essence each just help accelerate one or both of those steps. A Lewis base intramolecular deprotonation (step #1) via 6-membered transition-state looks even better than "just" an acid doing its acidic business, and making it a 6-e– pericyclic reaction with no formal charges in product is easier than two steps with charged alkyl structures. DMacks (talk) 05:13, 16 July 2009 (UTC)[reply]
Several reasons come to mind. One would be that the temperature of the water you are drenching your head with is usually cooler then the ambient air temperature and almost certainly cooler then your body surface temperature. Added to that, when the water evaporates, it takes away heat similar to how an ice cube works to cool your drink. Finally, sometimes your sense of touch has a difficult time telling the difference between damp and cool. Googlemeister (talk) 19:18, 15 July 2009 (UTC)[reply]
Our article on the common cold notes that current science finds no causal link between cold weather and the cold. While behavior favored in cold weather increases your likelihood of getting sick, and while exposure to cold weather can cause cold-like symptoms, standing in the rain does not increase your chances of getting the cold. — Lomn19:45, 15 July 2009 (UTC)[reply]
That's actually a back-formed explanation for the old-wives tale that having a wet head causes the common cold. While having a chronicly low body temperature (like hypothermia levels) may weaken the immune system, at that point you have other things to worry about than the sniffle you may get. When studies have been done, there is no causal link between ANY non-infectious external stressors and getting a cold. You get a cold because you have been in contact with someone else with a cold. And that's about it. --Jayron32.talk.say no to drama01:15, 16 July 2009 (UTC)[reply]
According to these British researchers the final word isn't out yet on cold weather and colds [13]. However OP seems to have the top and bottom confused according to this link [14] also featured in our article it's cold feet, rather than a cold head that contributes to catching a cold. 71.236.26.74 (talk) 05:22, 16 July 2009 (UTC)[reply]
It's very simple really. Water, in it's native state, is cold. Our heads are very warm. So, cold things make hot things colder. Vranak (talk) 18:44, 16 July 2009 (UTC)[reply]
And exposure to cold temperatures can cause vasoconstriction, which keeps white cells from getting where they're needed -- so it could make it easier to catch a bug (although it doesn't by itself cause the common cold). FWIW
76.21.37.87 (talk) 05:37, 17 July 2009 (UTC)[reply]
question about ticks
I was reading our article about ticks and came across this
"Some species stalk the host from ground level, emerging from cracks or crevices located in the woods or even inside a home or kennel, where infestations of "seed ticks" (the six-legged stage of newborn ticks) can attack in numbers up to 3,000 at a time[citation needed]. Weak or elderly dogs and puppies are particularly endangered and can die from anemia from a sudden influx of seed ticks[citation needed]. Seed ticks also attack horses, cattle, moose, lions and other mammals, causing anemia, various diseases, paralysis and even death."
This sounds rather unlikely, but I do not know enough about ticks to know if this is vandalism, or what. Does anyone know about these seed ticks? Googlemeister (talk) 19:05, 15 July 2009 (UTC)[reply]
wikipedia seems broken, google keywords from your text and you'll find the pages it's from. Could't save edit with links - getting "out of captcha". 71.236.26.74 (talk) 20:04, 15 July 2009 (UTC)[reply]
I poked around in Google Book search, and although I didn't find any mentions of seed ticks specifically causing anemia, I did find many references to ticks causing anemia, and to seed tick infestation of livestock. So it doesn't seem too improbable to me, based on the minimal amount of research I did. —Dominus (talk) 20:49, 15 July 2009 (UTC)[reply]
I know original research is frowned upon but I witnessed in southern Spain, several years ago, many hundreds of tiny ticks ascending the wall of an enclosed yard where two dogs had previously been kept. It was an unnerving experience. Richard Avery (talk) 21:41, 15 July 2009 (UTC)[reply]
How the heck does Spock calculate the odds on things? He is always doing this in Star Trek. Are the odds quoted in the dialogue accurate or are they just technobabble? —Preceding unsigned comment added by 216.154.20.38 (talk) 19:32, 15 July 2009 (UTC)[reply]
Star Trek is fiction. The circumstances it portrays are fiction. Any odds related to those circumstances are fiction. We could make in-universe guesses about "how Spock does it" (my guess is that computers are good at math), but at the end of the day, the writers pick a number backed up by an uncertain degree of educated guesswork. — Lomn19:40, 15 July 2009 (UTC)[reply]
It's probably just technobabble. If you give a specific example we can try and see if we can work out how the odds would be calculated. --Tango (talk) 19:44, 15 July 2009 (UTC)[reply]
No - that's really the whole problem. Jim will say "Call the guards - I'll pretend to have a mild tummy ache and when they rush in you just do the old Vulcan neck pinch - then we'll grab their guns and fight our way out through that army of guys with oddly wrinkled foreheads." - then Spock will say "But the odd of that working are only 2.34574950596%" - and then they go do it anyway and it works. There is simply no way to put "odds" on that because the 'unknowns' are easily enough to push the error bars on the estimate out to 100% such that any decision based on that estimate would be no better than flipping a coin. The problem with writing a script for a supremely logical being is that scripts are written by script writers - who are without doubt NOT supremely logical people! SteveBaker (talk) 22:00, 15 July 2009 (UTC)[reply]
Who, in turn asked Twiki <shudder> - who asked B-9 (who is 97.43% likely to continue have no Wikipedia article written about him by about the middle of next week) SteveBaker (talk) 21:53, 15 July 2009 (UTC)[reply]
B-9 is the robot from the original "Lost in Space" TV series who says "DANGER, Will Robinson, DANGER!"...whilst waving his arms around crazily (I'd like to meet the programmer who thought THAT was a useful engineering feature!) and being completely unable to tell anyone what the danger actually is! He also gave probability estimates with crazy over-precision for unfathomable events. (You can just imagine the scene at NASA's robotics division: "Hey boss - I'm coding the emergency response subroutine for the new B-9 'bot. I'm thinking that it should say "DANGER!" in a loud, assertive voice, flash it's front-panel lights and then carefully explain the reason for the emergency?"..."Well, that's alright but could you maybe make it also mention the names of any nearby crew members whom it happens to like? Oh - and how do you feel about making it wave it's arms around in a wild and panicky way? But do we really need to bother explaining what the danger is? I think we could save some money and not bother implementing that part.") SteveBaker (talk) 09:02, 16 July 2009 (UTC)[reply]
The worst thing about Spock's estimates is that they are ALWAYS wrong. SPOCK: "Well Captain, we've only got a 1.234% chance of getting away with your crazy plan." - KIRK: "That's good enough for me!"...and Kirk is always right (or at least extremely and consistently lucky). You're left just itching to hear: SPOCK: "Your plan has a 99.99% chance of working!"...but we just know that Kirk would then think of an even sillier plan. SteveBaker (talk) 21:53, 15 July 2009 (UTC)[reply]
Ironically, the law of large numbers should start to kick in (well, 72 episodes or something). If Spock consistently suggests the odds of success are 10%, doesn't that mean that by the end of 10 shows, there should have been 9 catastrophic failures? There are only so many times you can "beat the odds" before you must conclude that the odds were not properly calculated. Nimur (talk) 22:15, 15 July 2009 (UTC)[reply]
And that's really the horrible part of it: Spock is supposed to be amazingly logical - yet he seemingly ignores his own utter failure at estimating realistic odds. Worse still, he always gives a ridiculous amount of precision to his estimates - which is really not the sign of a logical mind. The script writers couldn't resist doing the same thing with "Data" in STTNG - but at least the remainder of the crew are given the opportunity to mock him for doing it. They made an entire plot-line out of Data's inability to speak 'contractions' (do not - rather than don't, etc) - where his "brother" is able to do so easily. Data continually strives to be more human no matter the cost - and is able to reprogram himself and teach himself singing, painting, playing a musical instrument and (with rather less success), dancing...yet he is quite unable to add the following five lines of code to the input of his speech unit:
if ( situation == casual && word [ n ] == "do" && word [ n+1 ] == "not" )
{
word [ n ] = "don't" ;
word [n+1] = "" ;
}
...but this is why it's fiction...other than that the scriptwriters needed this in order to 'sell' the character - there is no reason for it. Why did Suung fail to use a more realistic color of plastic on Data's skin when almost every other aspect of his master-work is so stunningly human? And for chrissakes why doesn't the Enterprise raise it's shields automatically when an unrecognised craft comes within 10,000km rather than waiting for some dithery old captain to tell the weapons officer guy to do it?!? SteveBaker (talk) 23:07, 15 July 2009 (UTC)[reply]
Two points here : 1) Even if I knew that it was standard operating procedure for the computer to raise shields automatically on a "Red Alert", I might still give the order to double-check. Especially with the number of automation problems Enterprise seems to have. (It would also give me a few extra seconds to think before my crew expected some brilliantly unorthodox solution to the crisis.) 2) There are probably lots of times where Spock estimates some mundane thing and is right. If Spock says "I estimate a 97.25% chance we will survive this with no difficulty." and then he turns out to be right, it wouldn't wind up on TV. We have to assume that there are 'ordinary' missions between the exciting ones that make it on the show. Otherwise the entire crew would be insane by the end of the first season. APL (talk) 05:36, 16 July 2009 (UTC)[reply]
"Red Alert" is supposed to raise them automatically, according to an episode of ENT. So why the captain needs to say so is unfathomable. If you calculate it, the chances of a 10% plan working 10 times in a row are small - but not impossible. If you were enacting daring plans that were fairly likely to succeed - who'd want to watch something that boring? Vimescarrot (talk) 23:14, 15 July 2009 (UTC)[reply]
In their defence, his problem may have been with working when they should and shouldn't be used - it isn't as simple as casual vs formal. It depends on the emphasis, intonation and even cadence of the sentence. --Tango (talk) 00:23, 16 July 2009 (UTC)[reply]
The new film made similar mistakes. In the early sequence, everybody on the bridge of whatever ship it was is being blinded by some time travel anomaly thing, which is looming huge and ridiculously bright out the viewscreen. Finally the captain arrives on the bridge and says, "Computer: polarise viewscreen" which causes a sunglasses-style darkening to slowly wipe down over the viewscreen. I almost choked at the idiocy of this and the way it heralded further potential idiocies almost ruined the film for me. Why didn't the viewscreen do that automatically? I wondered. Why does nobody else on the bridge have the authority to order that? Star Trek - especially the original series - is written to be cinematic and entertaining to the seething masses who aren't likely to think too much about it, not to be realistic or sensible. Maelin (Talk | Contribs) 01:18, 16 July 2009 (UTC)[reply]
Even the captain's order doesn't make sense. The viewscreen isn't some kind of periscope where the same light as is emitted by the object you are looking at gets to your eye - it's a camera and a screen. Polarised lenses block light, that isn't needed when there is a computer inbetween the object and the image. --Tango (talk) 04:42, 16 July 2009 (UTC)[reply]
Yes, but I don't think that's what was intended. I haven't actually seen the film yet, but it sounds like it was just meant to darken the image in the same way sunglasses work. --Tango (talk) 12:44, 16 July 2009 (UTC)[reply]
It's not as bad as Total Recall, though. They have a big red button that has to be pressed to close the shutters and prevent the air being sucked out and taking the people with it. --Tango (talk) 12:44, 16 July 2009 (UTC)[reply]
Um, why is this at the Science desk anyways. Let's see, for those of you that take this shit WAY to seriously, Dramatic tension and Plot device and Macguffin are good places to start. The whole point is that Spock makes the situation look worse because he decides there's no way Kirk can work his way out of it. When Kirk does it's even more amazing. There's not anything more complicated than that. Of course, since it is a work of fiction, 100% of the time the ending is predetermined. --Jayron32.talk.say no to drama01:11, 16 July 2009 (UTC)[reply]
Spock could be making some rough assumptions, and then estimating the odds out to way too many decimal places. (Perhaps to show off his innate Vulcan ability for mental math?) It's like he's doing a Fermi problem and giving the answer to the nearest hundredth of a piano tuner. APL (talk) 05:30, 16 July 2009 (UTC)[reply]
What is the danger of using 3-ohm speakers with 4-ohm receiver?
(Cross-posted from Entertainment desk on advice of someone there) My A/V receiver says the minimum speaker impedance it supports is 4 ohms. You have to set it to a special setting for 4-ohm speakers which I have done. But my front left and right speakers say that their impedance is 3 ohms. What is the danger in this? Is the danger to my speakers (which would be okay), or to my receiver (which would not be okay)? Thanks, Mike R (talk) 19:58, 15 July 2009 (UTC)[reply]
There isn’t that big of a difference between 3 and 4 ohms in this situation. You’re unlikely to cause damage to either your receiver or your speakers. The power that your speakers would need to handle if the volume was cranked all the way up will be a little more than if they were 4 ohm speakers, but that’s unlikely to be a problem as long as the volume is kept at a reasonable level. Because of the lower speaker impedance, the damping factor is going to be a little lower than the designers intended when they were planning the receiver’s impedance bridging, so the audio quality may be slightly lower than if the speakers were 4 ohms. But most people wouldn’t hear a noticable difference. Red Act (talk) 21:20, 15 July 2009 (UTC)[reply]
It would be difficult to say whether the speakers or the output stage transistors would fail first if you connected 3 ohm speakers to an amp rated at 4 ohms minimum and cranked up the volume, but as a testing engineer, I wish I could be there when the smoke test was performed. Edison (talk) 01:40, 16 July 2009 (UTC)[reply]
Would you by any chance know the power rating (wattage rating) of your amp, and of your speakers? That would be helpful to help judge which of your amp or your speakers would get smoked first if the volume got cranked too high.
Edison’s EE-fu is much stronger than mine (I have a minor in EE and a little professional experience with electronics, but Edison's a fully qualified, experienced pro), but it seems like your amp probably ought to be safe as long as it wasn’t turned up more than about ¾ of the way. If I were in your shoes, though, I would probably limit it to turning it up to no more than half way, though, just to provide an extra margin of safety. Depending on the power rating of your speakers, it’s possible that they wouldn’t be able to handle the volume turned up even half way (or they might possibly be able to handle the volume turned all the way up), but it sounds like you aren’t as concerned about potential damage to your speakers as to your amp.
When I said that you were unlikely to cause any damage to your amp or speakers, I guess I was making the assumption that you like listening to your music at a peaceful, calm level like I do. I never come anywhere close to pushing the limits of my amp or my speakers. However, rereading your post, there’s actually nothing in your post that precludes the possibility that you’re someone who’s wanting to crank your system as high as you can possibly take it. Were you hoping to blast some AC/DC at full volume, or were you just wanting to peacefully mellow out to a little Bach? (The type of music isn’t actually important, of course, just the volume.) Red Act (talk) 05:01, 16 July 2009 (UTC)[reply]
Fry's no longer is as well stocked in small parts as they used to be, but it should be no problem to find a small case, a 1 ohm resistor and a couple of connectors (plug/socket) online. Heck, if you don't trust yourself with a soldering iron you can probably even find the wire-wrap no-solder type somewhere. Tinker, tinker plug-in, problem solved. 71.236.26.74 (talk) 08:48, 16 July 2009 (UTC)[reply]
Actual loudspeaker impedance is more complicated than just the quoted nominal impedance. The output power of audio amplifiers is usually specified for a simple resistor load even though that is not typical of a loudspeaker. The shape of the curve in the above link suggests that changing from a 4 ohm to a 3 ohm speaker would only cause a slight loss of damping at a few hundred Hz which might give some barely perceptible ringing. (Putting a 1 ohm resistor in series makes this worse not better.) Cuddlyable3 (talk) 11:21, 16 July 2009 (UTC)[reply]
Besides damping factor, there is the actual power dissipation to consider. Voice coils on loudspeaker can overheat and burn out. If the amp were putting out an average power of 40 watts per channel the 1 ohm resistor would have to dissipate 10 watts when in series with a 3 ohm speaker (ignoring resistance of the resistor versus impedance of the speaker). A 1 watt resistor would burn out after a while. Avoid injury or property damage which might result from smoking the resistor. Speaker cones can also tear, which the OP did not indicate was a big worry. Edison (talk) 19:12, 16 July 2009 (UTC)[reply]
July 16
The Cancer Genome Atlas
Did they name it that just so the abbreviation would be composed of letters that represent the bases of DNA? or is it just a coinkydink? —Preceding unsigned comment added by 129.64.55.234 (talk) 13:35, 16 July 2009 (UTC)[reply]
While I don't see a specific "what's the name mean?" on their site, "TCGA" strikes me as too topical to be a coincidence. I would guess that there's a degree of backronyming at work. — Lomn13:45, 16 July 2009 (UTC)[reply]
I mean, "Atlas" is an interesting word to use. They could have easily named it The Cancer Genome Project. Maybe they got bored of the word "Project" 129.64.55.234 (talk) 14:02, 16 July 2009 (UTC)[reply]
I recently watched a Ted Lecture [18] by Kamal Meattle in which he outlines how to create an oxygen neutral building by using 3 varieties of plants that:
-Remove Toxins from the air (Money Plants)
-Provide oxygen during the day (Areca Palms)
-Provide oxygen during the night (Mother-in-law's Tongues)
The specific plants he names might not work for me because of sunlight/space/decor/availablity reasons in my home. Where can I find a list of common household plants in order of oxygen production? Or by Toxin removing ability (I know that can be ambiguous)? How much do these attributes vary from plant to plant (Does it even matter what plants I get?)
I had been under the assumption that oxygen production was based off sun facing surface area of the plant and how much of that sunlight it processes, since the oxygen is a byproduct of photosynthesis, but then it seem strange that plants would produce any oxygen at night, like the Mother-in-law's Tongue, so I am now comptelely lost as to what determines the above attributes.
I suspect that guy is a crank and should be ignored. His biography (linked to from that page) doesn't suggest any scientific training and his technique makes no sense. As you say, oxygen is produced by photosynthesis, it can't be produced at night (unless you leave your office lights on over night, I guess). As for removing toxins, as far as I am aware the only "toxin" plants remove from the air is carbon dioxide, also by photosynthesis, and you don't need to worry about that as long as you have reasonable ventilation. --Tango (talk) 21:04, 16 July 2009 (UTC)[reply]
People who give talks at TED (conference) are not usually cranks - and should almost certainly not be ignored. As it happens, it looks like all of his claims have at least some truth to them. Our article on Sansevieria trifasciata (Mother-in-law's tongue) says (with a pretty decent reference) that they remove "certain" toxins from the air and can flourish in low light levels. That may well mean that they can continue to do photosynthesis under artificial lighting - which may be why Meattle thinks they emit oxygen at night...but in complete darkness, that seems impossible. There are three completely different plants called Money plants - but I suspect he means Epipremnum aureum which (according to our article) is good at sucking up all sorts of pollutants. Areca is a family of about 50 different kinds of palm tree - we only have articles on a few of them - and most of those are slim on details - but Areca catechu is claimed to be a popular indoor plant so that's probably what this guy is talking about...however, pretty much all green plants will produce oxygen during the day...so that's an easy choice. SteveBaker (talk) 23:34, 16 July 2009 (UTC)[reply]
Your "decent reference" is a broken link... Given that any half decent ventilation will get plenty of oxygen into a building, I'm still voting crank. Even TED can get fooled. --Tango (talk) 00:19, 17 July 2009 (UTC)[reply]
You are entirely wrong. The reference is to a scientific paper - the link to a copy of the paper on the NASA site is broken - but simply typing the title into Google and accepting the first hit gives you the paper. Did you watch the TED lecture? Ventilating a building is not "oxygen neutral" and it wastes heating/airconditioning energy. The goal of making a building oxygen-neutral has value. SteveBaker (talk) 02:49, 17 July 2009 (UTC)[reply]
Nasa has a couple of pages, this one works [19] and discusses TCE, Benzene and Formaldehyde reduced in a chamber of plants. They don't single out Sansevieria. A place called Stennis Space Center seems to have studied plants for cleaning air and waste water. BTW: Pollutant would probably be a better term than Toxin here. Maybe that's what is causing the confusion. 71.236.26.74 (talk) 00:36, 17 July 2009 (UTC)[reply]
Actually, that's a good ref. The reason why words like "toxin" and "polutant" and things like that are often dismissed is because of their non-specific nature which makes claims which use those terms largely unfalsifiable. If you want to believe a claim, find one that lists specific compounds which are filtered by the plants. Which it looks like you have done. But in general, that's why words like "toxin" are clear bullshit markers. Nothing filters "toxins". Things may filter or remove specific compounds or classes of compounds, but if so then those compounds can be identified, and any serious scientificly-based report on such methods WILL list those compounds. If it doesn't, it's bullshit. --Jayron32.talk.say no to drama01:48, 17 July 2009 (UTC)[reply]
If anyone could find an explanation of the mechanism somewhere could you post a link? I've found a couple of studies for quantative analyses, but nothing explaining the mechanism so far. 71.236.26.74 (talk) 02:43, 17 July 2009 (UTC)[reply]
Is someone here planning to build a spaceship / nuclear submarine? Cause these are the only two applications I know of where being "oxygen-neutral" would matter at all.76.21.37.87 (talk) 04:42, 17 July 2009 (UTC)[reply]
Thanks guys for all your help. I'm not sure I know much about which ones produce more oxygen than others, but the NASA link was very helpful for toxin. Apparently the NASA stuff was already on Wikipedia and I wasn't looking hard enough: List_of_air-filtering_soil_and_plants. While you do have a point 76.21, by putting enough plants in my house to cancel out my oxygen use in addition to it already be ventilated I am actually creating an oxygen rich environment, so perhaps I shouldn't be expressing my desire as specifically archiving an "oxygen-neutral" environment. Plus, I think ANY submarine would probably want to be oxygen neutral, not just nuclear ones. The scientific names were actually in the video now that I look back at it:
Chrysalidocarpus lutescens, Epipremnum aureum, and Sansevieria trifasciata
Which are actually all from the NASA list, credited for removing xylene and toluene for the first one in the above list and formaldehyde for the second two.
Where can I find a list of parasympatholytic drugs? (Need not be drugs prescribed by medics, just chemicals that act as parasympatholytica no matter of strength or side effects.)
Second question: if the parasympathic nervous system was malfunctioning (to any degree) what would be the effects on the body?
How much gravity on another planet would be necessary to have an atmosphere where people could thrive (assume other factors such as average temp, composition, are similar to earth although I'm interested in what other factors would have an influence). Also, how much gravity could people comfortably live with? TheFutureAwaits (talk) 20:57, 16 July 2009 (UTC)[reply]
We really don't know what gravity humans can live in. Pretty much no research has been done on gravity greater than Earth's, and pretty much the only research on lower gravity is zero gravity and humans can't survive in that for long without taking some precautions (lots of exercise, mainly, I think). I'm not sure about gravity and atmospheres. I know temperature is a big factor - it is easier to "hold on to" cold air than hot air. That's why Titan has a thick atmosphere (about 50% greater pressure than Earth) despite being much smaller than Earth. The composition also matters - humans can survive (at least temporarily) with about a fifth of Earth's atmospheric pressure if it is pure oxygen or with pressure of about 10 times Earth's if you replace most of the air with something inert like Helium (see Heliox). I think composition also affects pressure and density - Venus has about the same gravity as Earth and is really hot, so you would expect it to have a thinner atmosphere, but it is actually about 100 times thicker. I'm guessing that's because it is mainly CO2 which is a little under twice as heavy as air (per mole). --Tango (talk) 21:28, 16 July 2009 (UTC)[reply]
(after ec without rereading the new contribution) Sorry that I don't have sources to cite but from what I have heard, the size of our earth is on the verge of being too light and loosing hydrogen (THE key element for live as we know it) and being too heavy and attracting excessive hydrogen and finally becoming a gas giant. I'm hoping for answers that are less based on private memory and hearsay. 95.112.156.108 (talk) 21:30, 16 July 2009 (UTC)[reply]
We have lost all our (free) hydrogen. The only hydrogen that remains is that in compounds with heavier elements (particularly oxygen in water). Any hydrogen that gets released into the atmosphere escapes sooner or later. Free hydrogen isn't important for life. --Tango (talk) 21:36, 16 July 2009 (UTC)[reply]
As far as I understand, on a geological time scale any hydrogen, temporarily bound or not, will escape a lighter planet with a temperature comparable to earth. Look at venus, look at mars. 95.112.156.108 (talk) 21:50, 16 July 2009 (UTC)[reply]
The hydrogen on Earth is pretty permanently bound. It undergoes various chemical reactions but that just changes what it is bound to. There aren't many naturally occurring reactions that produce free hydrogen. I've certainly never heard of any risk of running out of water before the sun heats up and boils it all off. --Tango (talk) 23:03, 16 July 2009 (UTC)[reply]
The temperature on Mars CAN get up to Earthlike values - they've recorded 70 degF on a few occasions. However, mostly it's way colder - and Venus is crazily hotter. SteveBaker (talk) 14:12, 17 July 2009 (UTC)[reply]
The question is how much gravity is necessary for a planet to have an atmosphere where humans could thrive. The answer is just enough gravity to hold water vapor for a large amount of time. A Mars sized planet is likely close to the right answer. Dauto (talk) 05:51, 17 July 2009 (UTC)[reply]
No one knows at the moment (No one even knows how much water is gone and how much is just "hidden", e.g. subsurface). There are some hypothesis were the water went and why and when, but the history of mars is not really known to any degree of certainty. And btw, also for venus we do not understand at the moment what "planetary development" has led to its present state. So science cannot answer these questions at present, because we do not have any additional samples beside earth for a habitable planet. --TheMaster17 (talk) 09:57, 17 July 2009 (UTC)[reply]
We know from studies of craters and erosion that water has been on the Martian surface 'recently in geological terms'. The gravitational force of Mars hasn't changed measurably for a billion years - so how come the water would have stayed around for all that time if a lack of gravity was the cause of it 'going away'. That means that it wasn't a lack of gravity that caused the water to "go away" - or all of the evidence of flowing water would long ago have been eradicated by meteor impact and wind erosion. SteveBaker (talk) 14:12, 17 July 2009 (UTC)[reply]
There is water on Mars. May be your question should have been 'how come there ain't no ocean on Mars anymore' The answer is related to surface temperature and pressure. The question was about surface gravity. Some of Mars water has likely been lost due to low gravity over a period of hundreds of millions of years. That's more than enough time for humans to thrive which was the citerion stablished by the question. Dauto (talk) 16:20, 17 July 2009 (UTC)[reply]
Yes, if the atmospheric pressure is too low it can be bad for people. But that's a separate question because surface pressure is not determined by surface gravity alone. You also must take into consideration the atmospheric total mass. Dauto (talk) 04:03, 18 July 2009 (UTC)[reply]
Pluto's diameter and why gas giant's moon number keep growing
Is Pluto 1400 miles or 1500 miles (0.18 or 0.19 x Earth). [20] say Pluto is x0.18 Earth, NASA say is 0.19 x Earth. Which one is accurate. I thought Microsoft Windows, any kids website is not a valid source. Is Saturn up to 61 moons right now? Anyways, how we know gas giant's moon keep growing. First when last Voyager 2 went to Uranus and Neptune, they had 15 and 8 moons, then in 2000 Uranus had 22 moons then finally Uranus have 27 moons, and finally Neptune have 13 moons. When last Voyagers visit Jupiter, it had 16 moons, then few in 2000 Jupiter's moon jump to 20s, then 30s in 2003 Jupiter's moon skyrocket to 61 moons then finally it's 63. Saturn's moon start with 18 moons, then 30s, then 56 in 2006, then finally 61. Did they use HST or what tools to find new and new moons. Is this possible numbers of Uranus and neptune will continue skyrocketing? Could somday Uranus have up to 40 moons and Neptune have over 19 moons? adn jupter and Saturn over 100 moons?--69.228.145.50 (talk) 21:00, 16 July 2009 (UTC)[reply]
I don't think we know the diameter of Pluto very accurately. It depends on its albedo - how bright its surface is. If it is quite dark then it must be quite big in order to reflect the amount of sunlight it does, if it is brighter then it must be quite small. As for the moons, we just keep discovering more (they've all been there the whole time, we just hadn't noticed them). A lot of them are very small and there is no reason to believe we've found them all or will do any time soon. You also have to remember that there isn't really any difference between the tiny dust particles in the rings and the smallest moons (other than size, obviously), so you could argue that we already know of millions of moons around each gas planet - it depends where you draw the line. --Tango (talk) 21:34, 16 July 2009 (UTC)[reply]
O, this explains why scientific plotting always fails. Even surface temperatures can't be pin right. By the way nothing is space is exactly pin right, always universally error bars. People can literally say Venus is >1000 F, this is why we have book say Venus is 600 C. I would say Jupiter and Saturn have 100s of moons if 100% is found, for Uranus and Neptune, this is impossible to be over 50 moons if 100% of them if found.--69.228.145.50 (talk) 22:18, 16 July 2009 (UTC)[reply]
There are always error bars, you are right, but for some things they are pretty small. We've sent probes for Venus, so we have a pretty good idea of its temperature. The error bars on our measurements will be much smaller than the variation in the temperature. --Tango (talk) 23:05, 16 July 2009 (UTC)[reply]
Glycerin free personal lubricants
I notice many new "personal" (sexual) lubricants proclaim they are glycerin and paraben free. What about those ingredients are bad during sex? --70.167.58.6 (talk) 21:51, 16 July 2009 (UTC)[reply]
True, but not applicable to the substances the OP listed. Only water-based lubricants (i.e. not Vaseline) should be used with condoms, for the reason you state. Glycerine is a common allergen, and parabens are both allergens and potential carcinogens; these are the reasons for wanting lubricants without those ingredients. jeffjon (talk) 12:50, 17 July 2009 (UTC)[reply]
I wonder the valid source of this site. Most showing I see is African plate moving north, the slide show African plate moving east only, eventually it suppose to collide with European plate closing Arabian and Black Sea. Isn't North and South Amercan plates moving west only no north. I don't expect over 15 lattitude north shifting in about another 100 million years. I expect at least the Northern Africa would be up to Artic Circle in 100 million years. Australia is just quickly moving north, and will collide and form a huge nountain in East Asia.--69.228.145.50 (talk) 22:23, 16 July 2009 (UTC)[reply]
Have anybody else besides those 3 people in July 1969 Buzz what's his name, Neil Armstrong and anyther guy all 79 right now have been on Moon. Have anybody been on dayside of Moon, or only night side. Do we have 1000s of people been on Moon or it's only those 3 peoples in 1969. Space travel is not a vacation spot. It is not just few days to get to Moon, I expect two weeks from Earth to Moon. Plus to survive in space, people have to bring gravity to hold things together, and lots of foods and fuels and liquids, and place to sleep and shower on.--69.228.145.50 (talk) 23:49, 16 July 2009 (UTC)[reply]
As a matter of interest, have Aldrin and Collins ever expressed any resentment towards Neil Armstrong? I know that there's been plenty of comedy sketches about 'nth men on the moon' being bitter about their lack of historical recognition over the years... --Kurt Shaped Box (talk) 02:16, 19 July 2009 (UTC)[reply]
If it’s seeming like that tiny Lunar Module is too small to hold everything needed for a trip to the moon, you are right. Although the most exciting photos and videos of the moon landing only show the lunar module, the lunar module was only one piece of the Apollo spacecraft, which did hold enough stuff. Not much fuel is needed to get back from the moon, since it’s relatively easy to escape from the moon’s gravity, due to there being a lot less gravity on the moon than on the earth. Escaping the earth’s gravity, however, does require a lot more fuel, which is why the Apollo spacecraft started out on the tip of a huge launch vehicle.
A bed to sleep in and the ability to take showers are luxuries of modern living, that aren’t really requirements when you’re on a monumental adventure.
Gravity isn’t required to hold things together. The main thing that holds thing together are chemical bonds.
I could go into the details of how the energy content of the fuel used on the Apollo missions was enough to get the Apollo spacecraft traveling fast enough so that it could get to the moon in only a few days. However, no offense if I’m wrong, but I’m guessing that you’re fairly young, and haven’t yet taken the elementary physics classes that would be required for you to understand the explanation. However, the idea of it being impossible to reach a speed fast enough to get to the moon in three days isn’t even something that we have listed as being one of the objections of the moon landing hoax conspiracy theorists. Red Act (talk) 01:24, 17 July 2009 (UTC)[reply]
As to the question about which side of the Moon, all of the Apollo missions landed on the near side of the Moon (the side facing the Earth), so they could communicate with the Earth by radio; and they all landed when it was daytime at the landing site, and left when it was still daytime, so they didn't have to deal with the day/night temperature change and so they had full sunlight to work by. (Remember, daytime on the moon lasts for almost two weeks. Apollo 17 stayed longest on the lunar surface, about 75 hours.) --Anonymous, 04:46 UTC, July 17, 2009.
ec. the sides of moon they been on is nighttime with most photos we have with no suns, yes the image always fails when trying to make things look true when try to pin a green dot to show you what it will look like when you actually on moon. Different gravity and lighting conditions on moon, beleive it or not; the images we take is 99.99% hopelessly wrong, then our orange, blue, green light go haywire. Dummies think it is so easy to say Moon is gray, that's just balonies! We had this discussion many times in past, that's over!--69.228.145.50 (talk) 21:21, 17 July 2009 (UTC)[reply]
They landed during lunar morning for idea temperature, and on the side facing earth for best radio contact. We will soon be celebrating the 40th anniversary on earth, but I would like to point out that the moon's phase will not be correct (because Earth's revolution around the sun is not closely linked to Moon's revolution and orientation around Earth). Flimsy human calendars fail to capture useful astronomical information! LCROSS arrived around lunar morning a few weeks ago; it's probably a better "anniversary" than July 16 or July 20, from the point of view of the Moon. Nimur (talk) 14:30, 17 July 2009 (UTC)[reply]
At the risk of stating the obvious : The Moon has its own gravity. It does not have as much gravity as Earth, but it still has a useful amount. The astronauts don't need to bring any with them. This is a good thing because there is no known way to make gravity "portable". (When NASA needs to "hold stuff down", they usually glue Velcro to everything Velcro.) APL (talk) 14:52, 17 July 2009 (UTC)[reply]
Gravity is portable, you just need a really huge engine. If you built a spaceship of the same dimensions and weight as earth, and you could move it around, then you would in effect have portable gravity. You would have to ask if the endeavor would be worth the resources though. Googlemeister (talk) 18:30, 17 July 2009 (UTC)[reply]
The OP should remember the name Buzz Aldrin. He is not to be confused with Buzz what's his name the inventor of the rubber suction cups used to hold things together in space. Cuddlyable3 (talk) 01:45, 19 July 2009 (UTC)[reply]
Good point, Cuddlyable. Unfortunately, few people bother to learn the names of true American heroes like Lewis and Clark, Davy Crockett, Charles Lindbergh, Amelia Earhart, John Glenn, and Buzz Aldrin anymore; instead, they learn all the names of the latest trashy, slutty celebrities like Britney Spears, Christina Aguilera, George Michael, Snoop Dogg, Alec Baldwin, George Clooney -- you name it. In fact, this generation's (MY generation's!) knowledge (or lack thereof) of American history is perfectly shocking. Maybe that's the reason why God told me to write historical ballads. I wouldn't be surprised if most people my age thought that the Alamo was only a car-rental company... :-)
76.21.37.87 (talk) 02:12, 19 July 2009 (UTC)[reply]
Just for fun, and as an example of what I mean, here's an actual student's answer to an actual teacher's in-class question (I got this from the website www.stupidest.com): Teacher: "Who was the first man to walk on the Moon"? Student: "Louis Armstrong". :-)
76.21.37.87 (talk) 02:17, 19 July 2009 (UTC)[reply]
July 17
Some people smell bad. Why?
I've found over the years that some people smell very bad to me. I'm not talking about people who're dirty or flatulent or unwashed or have bad breath or have body odor typically associated with heavy exertion and/or sweating; rather, it seems more that some people's body chemistry creates an odor I find extremely unpleasant. It's difficult to characterize or describe; it smells of nothing but "smelly person". I have also noticed that others often seem not to detect any such an offputting smell from the same people I find smelly, at the same time I find them smelly. What's at work here? Is it akin to the ability (or lack thereof) to taste PTC? 00:04, 17 July 2009 (UTC)
It's mostly to do with what you've been eating, what they've been eating and what you're used to. The compounds in many aromatic substances survive just fine in the body and then get exuded with the various bodily fluids, including the sweat we make almost constantly. Curry, for example, has a very distinctive odour and people that eat a lot of it will tend to exude that smell from their breath and bodies. If you're not used to that because you and your family don't eat lots of curry, then you'll be very aware of the change in odour. It works the other way as well: you may be smelling very strongly of milk, or pepper, or any one of a number of things, but you'd be unaware of it because it's part of your background smell. Matt Deres (talk) 13:16, 17 July 2009 (UTC)[reply]
Let's not overlook the smeller's own nose. If you've got too much X in your system, certain odors will repel you more than the usual person. Vranak (talk) 14:35, 17 July 2009 (UTC)[reply]
Putting fiber in my fiber
Is there any downside to adding Benefiber to Metamucil? Are two types of fiber compatible (one is a guar gum and the other is psyllium husks) --70.167.58.6 (talk) 00:08, 17 July 2009 (UTC)[reply]
I'm afraid we can't give medical advice, but I will point out that, baring very unusual circumstances, you can get plenty of fibre in your diet by just eating plenty of vegetables. --Tango (talk) 00:15, 17 July 2009 (UTC)[reply]
I'm not asking about medical advice. I'm asking if mixing compound A and compound B have a chemical reaction or produce any harmful substances. It's a science question, not a health question. --70.167.58.6 (talk) 12:37, 17 July 2009 (UTC)[reply]
Not offering any advice here, but consumption of very high levels of fiber (along with inadequate water, I think) has been known to cause intestinal blockages. ike9898 (talk) 17:35, 17 July 2009 (UTC)[reply]
"I'm asking if mixing compound A and compound B have a chemical reaction or produce any harmful substances." -- It shouldn't, cause neither compound is reactive under normal conditions (they're both mostly cellulose anyway, i.e. sawdust). FWiW
76.21.37.87 (talk) 01:51, 18 July 2009 (UTC)[reply]
is there a simple passive filter that would "round off" the lower-frequency square waves (i.e. low-passing the fundamental of the square waves so they would approximate sine waves) without attenuating the higher frequencies?
the nominal human hearing cut-off of 20kHz would suggest that any periodic wave above 10kHz would sound the same since higher harmonics can't be heard (very well). Is this actually the case? If so, are distortion specs on tweeters above 10kHz worth much?
To the first question, yes — a suitable low-pass filter will attenuate the higher frequencies, leaving the fundamental (and lower harmonics, depending on the filter) essentially intact. Here's a YouTube video demonstrating the principle with square and sawtooth waveforms: [21]. The simple RC circuit shown in our article would serve. TenOfAllTrades(talk) 02:47, 17 July 2009 (UTC)[reply]
I’m not sure if I’m understanding your first question correctly, but if I’m correctly rephrasing it, it sounds like maybe you’re wanting the amplitude of the fundamental frequency on the filter’s output to be higher than the amplitude of the fundamental frequency on the input, due to the presence of the higher frequencies on the input? Like by having the filter somehow phase-shift the higher frequencies such that they’ll contribute to the fundamental frequency on output, rather than just being attenuated? That isn’t possible with a linear passive filter, e.g., any filter consisting of just resistors, capacitors and inductors, but it would be possible to do something like that with a nonlinear passive filter.
It isn’t true that any periodic wave above 10kHz will sound the same. For example, an 11kHz sine wave sounds quite different from a 19kHz sine wave. So if a tweeter attenuates those two frequencies differently, that’s going to make an audible difference. Red Act (talk) 03:35, 17 July 2009 (UTC)[reply]
Sorry. English is a dangerous language in unskilled hands.
The toy can produce a wide tonal range but the (555) oscillator produces square waves. I was wondering if the lower frequencies can be (simply) "sine-ufied" without attenuating the higher ones. I'm guessing not.
What I meant was, since a 15kHz square wave is made up of 15kHz, 30kHz, 45kHz, 60kHz, ... sinusoids and nothing above (nominally) 20kHz can be perceived, that any 15kHz waveform would sound the same as a 15kHz sinusoid. Sounds (haha) too easy.
“Not with a linear passive filter” would be an answer to your first question.
That’s true, a 15kHz sine wave would sound the same as any 15kHz waveform, as long as the 15kHz component of the waveform had the same amplitude and phase as the sine wave. However, your original question number 2 asked if distortion specs were worth much above 10kHz. If a frequency response distortion causes the tweeter to disproportionately attenuate the 15kHz component of a sound, that’s going to be audible. Was the 10kHz a typo, and you meant to say 20kHz? If you meant to say 20kHz, then the answer would be yes.
I’m afraid some audiophile is going to come along and point out that some people can actually detect distortion above 20kHz, and I’m sure that’s true, particularly with younger people. But this discussion is a theoretical one based on the assumption that people can’t hear anything above 20kHz. Red Act (talk) 06:56, 17 July 2009 (UTC)[reply]
To provide a mostly-useless answer to the first question: yes. A Fourier series decomposition of a 15kHz square wave shows that the 15kHz component is already a sine wave. The higher frequencies that you desire not to attenuate are what turn your 15kHz sine wave into a square wave (see the animation in square wave). So, if you really seek to turn a 15kHz square wave into a 15kHz sine wave with all the higher frequencies unattenuated, your passive filter of choice would be … a wire. – 7408:33, 17 July 2009 (UTC)[reply]
The OP is incorrect in supposing that a 15kHz square wave is made up of 15, 30, 45, 60... kHz sinusoids. A square wave has only odd-multiple harmonics i.e. a 15kHz square wave is made up of 15, 45, 75... kHz sinusoids. (Even multiple harmonics exist only if the wave is rectangular.)
I think the OP questions whether distortion of tones above 10KHz matter, i.e. is easily audible, and the answer is no. (A tweeter could produce harmonics starting at 30kHz due to symmetrical distortion or starting at 20kHz due to asymmetrical distortion. Neither is easy to hear.) A different question is whether the tweeter has level frequency response over its audible range because that affects the reproduction of possible harmonic content of all tones below 10kHz, which includes most music.Cuddlyable3 (talk) 01:29, 19 July 2009 (UTC)[reply]
Here in China the voltage is 220V. I've recently bought a Game Boy Micro which comes with a power cord (not an adaptor) to charge the battery saying it should only be used with 110V.
I'm currently using a stepdown converter, but am wondering if this is really necessary.
Why? Because I see kids all over the place playing JPN Game Boy Advanceds and Game Boy Micros and charging them willy-nilly.
Too high a charge voltage could make the batteries blow up, and also fry the dioderectifier that changes the AC from your socket to the DC needed to charge batteries. Stick to using your stepdown converter at all times.
76.21.37.87 (talk) 04:57, 17 July 2009 (UTC)[reply]
Theory vs. law
I have some homework which states:
Discuss how theories such as those above [Newton's/Galileo's theories about gravity] develop into laws with time & experimental testing.
Now, this is implying that laws are somehow better or more solid than theories. My understanding is that a law is simply a description of what happens, while a theory is an explanation for observations. How would I answer the homework question? (This is going to be marked, and I have NO way of talking to my teacher about the question at any point before the work is due.) --wj32t/c04:16, 17 July 2009 (UTC)[reply]
It looks to me like your understanding of the difference between a physical law and a theory is more accurate than your teacher’s! Unfortunately, the “theories develop into laws” idea that they teach at some schools does not mesh well with how those terms are actually used by scientists. My impression is that the “theories develop into laws” idea is just something they teach in like junior high or high school, and isn’t something you’d be likely to encounter in college. I don’t know the best way to explain to your teacher that this wasn’t a very good homework question. Red Act (talk) 04:52, 17 July 2009 (UTC)[reply]
Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misevaluation, but it is our policy here to not 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 how to solve such problems. Please attempt to solve the problem 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. Thank you. —ScheinwerfermannT·C05:00, 17 July 2009 (UTC)[reply]
Thank you for using HumanBrain(r). HumanBrain(r) is one of the most advanced WetWare(tm) systems available. Please note that the new HumanBrain(r) LanguagePack II(tm) (European Languages/English) is now available. LanguagePack II(tm) adds the ability for semantic analysis beyond simple keyword scanning. LanguagePack II(tm) is a free download for your HumanBrain(r). Installation can take between 5 minutes and 10 years depending on existing programming and specific HumanBrain(r) model employed. --Stephan Schulz (talk) 09:27, 17 July 2009 (UTC)[reply]
Judging from the idea that the development occurs after time and testing, your teacher may be confusing the difference between theories and laws with the difference between hypotheses and theories. Maelin (Talk | Contribs) 05:02, 17 July 2009 (UTC)[reply]
As far as marks are concerned, just give what the teacher expects. Assume a Law to mean something like indesputably proved beyond doubt fact of life, and explain how a theory matures into a "Law" over time through tests by experiments and observation. However, afetr you are marked, do have a discussion with the teacher about this. Rkr1991 (talk) 05:31, 17 July 2009 (UTC)[reply]
It’s kind of intellectually repulsive to intentionally give an incorrect answer, but I think that probably really is the best advice. There’s no point in getting marked down just to prove a point, and actually knowing the right answer is what’s really important, anyway, not whether the teacher acknowledges you for knowing the right answer. It’s also probably best to point the teacher’s mistake out to him quietly, after class, rather than pointing it out to him during class. I pointed out a couple of my high school math teacher’s errors in class right after he made them, and it really made him kind of not like me a little. In my experience, college profs are much less flustered by being corrected in class than high school teachers; in fact, they’ll often thank you for correcting their mistake. Red Act (talk) 11:16, 17 July 2009 (UTC)[reply]
Your should tell your teacher (in a tactful way) that their hypothesis that "theories develop into laws with time & experimental testing" is not supported by the way that these terms are used in the scientific community. As evidence, show your teacher these pages - [22], [23], [24]. Clear consensus is that there is no hierarchy of proof or reliability between theories and laws - the only difference in usage (and it is a very marginal one) is that the term "law" is usually applied to a short and concise statement or principle whereas a "theory" is a larger and more complex body of interrelated concepts with a wider, more general scope.
Maybe I am being cycnical here, but it seems to me that the erroneous idea that "theories develop into laws with time & experimental testing" could be used to set the stage for the bogus "evolution is just a theory" argument. Gandalf61 (talk) 11:28, 17 July 2009 (UTC)[reply]
Well, I think you can do this right and still get good marks - and since you CLEARLY have a better grasp of this than your teacher, I'm strongly of the opinion that you should stick to the truth no matter what. The trick here is to write the truth - and yet still answer what the question is really seeking for you to explain - which is how a "hypothesis" turns into either a theory or a law with time and experimental testing. This is more work for you - but that's what happens when you stand up for a principle.
I think you need to write two sections:
Firstly, you need to deflect the question into one that you CAN answer. You must explain how the standard dictionary definition of the words "theory" and "law" differ sharply from common scientific usage - look the words up in a dictionary - and quote what it says. I found this, for example. Explain that you are assuming that the word "theory" in the question is being used in the non-scientific sense of the word (As Merriam-Webster puts it "6 a: a hypothesis assumed for the sake of argument or investigation b: an unproved assumption". However, you can't make it sound like this is just your opinion because essays like this aren't about opinion. You also can't make it sound like this is something you heard from a bunch of random guys on the Wikipedia reference desk (which it's not because you already knew it). You are going to have to find some solid references that you can point to that say this - preferably more than one. You need to be able to say that "so-and-so (a highly respected scientist/organisation) said such-and-such (which supports your claim) in such-and-such document (hopefully something your teacher can easily find and read - but at least something respectable...but not Wikipedia - which many teachers hate)". For example, you could quote the American Association for the Advancement of Science here - in the section "Is evolution "just a theory"?" - they say "In detective novels, a "theory" is little more than an educated guess, often based on a few circumstantial facts. In science, the word "theory" means much more. A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment. Such fact-supported theories are not "guesses" but reliable accounts of the real world. The theory of biological evolution is more than "just a theory." It is as factual an explanation of the universe as the atomic theory of matter or the germ theory of disease. Our understanding of gravity is still a work in progress. But the phenomenon of gravity, like evolution, is an accepted fact.". This clearly says that a theory is a RESULT of time and experimental testing - not the STARTING POINT for such work. That done and clarified, you can proceed to do the assignment you were given - because you can't use this little misunderstanding to duck out of doing the work!
Now, having established (eg from Merriam-Webster) that the word "hypothesis" would be a better choice, you must proceed to explain how a scientific hypothesis can develop into either a scientific theory OR a law with time and experimental testing...because that's what the homework assignment is all about - and if you don't do it, you won't get a good grade. You've actually increased your workload in the process - because now you need to describe how a THEORY gets made as well as how a LAW comes into being. But it's worth the effort.
I'm 99% certain that your efforts will be rewarded with a decent grade IF you do it like that - subtly and with style and integrity - and not whining at the teacher's incompetence!! On the off-chance that you have an utterly bone-headed teacher (I sure hope not!) - you might ask your teacher to "help you understand" by providing an example of a "theory" that turned into a "law" - we know that there aren't any - so you're on solid ground here - you may have to say "but that wasn't a theory - that was just a hypothesis". If all else fails, you may need to get your parents to appeal the grade to a student councillor or the head of the science department - or the principle...whatever it takes. I had to fight for my son's (correct) answers to bogus questions on many occasions...and every time, we won and he got a good grade in the end. But if you do it right - and back up your assertions with solid references - I'm sure you'll be OK without any fuss whatever.
You're in good company by the way - my personal hero (Richard Feynman) was particularly displeased with these kinds of errors in assignments and school books and took on a personal crusade to try to eradicate them that wound up with him having to write three of the best Physics books in existance - "Feynman's Lectures on Physics". The fight over the teaching of evolution in US schools lies entirely in the misunderstanding (intentional or not) of the word "theory". I applaud your knowledge and your desire to stand by your principles. No matter what, you'll always know that "You were right" - and that's worth more than a grade.
Thinking about this a little, my guess is that the OP’s textbook is correct, which is where the OP got his correct information from, and it’s just the teacher that’s made a mistake. If the textbook matched the teacher, the OP wouldn’t have gotten confused and asked us for a clarification. So pointing the teacher’s mistake out to the teacher might be as simple of a matter as pointing out the pertinent page(s) in the textbook. Red Act (talk) 14:52, 17 July 2009 (UTC)[reply]
Also intriguing is Galileo's report, based on experiment, that balls of unequal weight do not only fall at different rates, but that the lighter one initially pulls ahead of the heavier one until the heavier catches up. In the early 1980s the science historian Thomas Settle tried to repeat Galileo's falling-body experiments and, astonishingly, noted the same thing. He suggested that fatigue induced in the hand holding the heavier object tends to cause this hand to let go more slowly, even when the dropper believes the objects are released simultaneously.
I'm a bit confused. Is this actually true, or is the article just saying that Galileo observed it but it's wrong? Why would this (the lighter one being faster at first) happen? --wj32t/c06:20, 17 July 2009 (UTC)[reply]
If the two objects are mechanically released at precisely the same time in a vacuum chamber, the two objects will fall at exactly the same rate, even initially. The effect of the lighter one falling faster initially only applies to the sloppier situation in which the objects are dropped in air, by hand.
The fatigue hypothesis seems reasonable to me. Another hypothesis that seems reasonable to me is that it isn’t due to fatigue, per se, but that it takes longer for a tightly clenched hand to unclench than a lightly clenched hand, simply due to it involving a greater change in physiological state. Another hypothesis that seems reasonable to me is that when one’s fingers move rapidly out from under something really light, something like the Bernoulli effect will basically cause the feather to get sucked downward slightly. But the latter two hypotheses are purely original research. Red Act (talk) 07:22, 17 July 2009 (UTC)[reply]
Galileo's result is only approximate because he couldn't test it in a vacuum - and air resistance has an effect. But done 'properly' with some kind of mechanical release system in a vacuum, there would be no such effect as our OP describes. SteveBaker (talk) 13:12, 17 July 2009 (UTC)[reply]
Didn't Galileo roll same sized but different weight spheres down an incline, rather than merely dropping things? The effort of holding on an ioncline would not be great. A mechanical release would be an obvious control. Ref checking is indicated. Edison (talk) 14:41, 17 July 2009 (UTC)[reply]
kindly help....for spectrophotometer
1) how to calibrate and standardise visible spectrophotometer using aquous solutions?
2) which aquous solutions should be used for it? and what should be their concentrations? —Preceding unsigned comment added by Ddrcpan (talk • contribs) 06:56, 17 July 2009 (UTC)[reply]
I believe you calibrate by putting a test tube with distilled water, which will reflect, refract and absorb the minimal amount of light of any liquid, into the machine and taring it so that that whatever is reflected, refracted or absorbed is blanked. DRosenbach(Talk | Contribs)17:19, 17 July 2009 (UTC)[reply]
Documenting 2009 solar eclipse
Someone else may have asked something similar already, sorry if this is a repost!
I'm going to be observing the solar eclipse next week and I hope to take some footage/pictures, and I'm just wondering how careful I should be. I've got a recent Canon Ixy (Powershot) just so that I can have some sort of video record, and I will be photographing using my Nikon D60 and a 200mm lens. I've never photographed an eclipse before so I'm not really expecting anything spectacular (besides it won't be complete where I live) but I'm mainly concerned for the safety of my cameras! Basically every website I look at warns me that the eclipse could harm the lens/sensors of my digicam, and I guess I need a solar lens? of some sort to protect them, but what exactly am I looking at purchasing here, how much will it set me back, and where can I get one? Also, is it possible to make my own? If anybody knows a site with some easy instructions to make a home-made eclipse glasses, please let me know! And lastly, is it really necessary to use a solar lens for a digicam, or is that just a precaution for when you're getting in really close? Thanks! 210.254.117.186 (talk) 08:31, 17 July 2009 (UTC)[reply]
What do you mean by "getting in really close"? The distance to the sun won't change. I can assure you that taking pictures with a normal digicam without any filter will destroy the sensor of the cam. When there was a total solar eclipse here in germany, where I live, two friends of mine destroyed their cams in this way. NEVER look at the eclipse with your naked eyes, use an appropriate filter! In germany there were special glasses on sale weeks before the eclipse, which were certified to protect human eyes. Normal sunglasses won't do! It might seem that the sun is "dark" enough, but in reality it isn't. You will damage unprepared optical equipment, including your eye, if you point it to the eclipse. There are cases in the literature where people went partially blind from staring into an eclipse, so I'm begging you not to take the risk of loosing your sight. --TheMaster17 (talk) 10:10, 17 July 2009 (UTC)[reply]
I don't know about damaging the sensor - I think that quickly pointing the camera, taking the photo and then pointing it away again should be OK...but perhaps it's not worth the risk. But in any case, the problem is that in a non-total eclipse, the amount of light coming from the sun will overwhelm the sensors and you won't get a decent picture. Digital cameras can only handle so much light before they have hit the maximum number that the sensor can output and everything goes completely white. So I think you could benefit from having a filter of some kind to cut the amount of light down to something reasonable. You could test this by trying to take photos of the un-eclipsed sun...which will be only maybe twice as bright as a half-eclipsed sun. Obviously (I hope!) you understand that staring at the eclipse with unprotected eyes is very dangerous - and looking at it through your camera's optical viewfinder is possibly even more dangerous...especially if you have an optical zoom. By all means line up the shot using the LCD viewfinder if your camera has one...that's entirely safe. I've been saying this a lot recently - but I'll say it one more time. Observing the sun (and even photographing it) can be done very effectively by projecting an image of it through a pinhole into a darkened room. If you have a window facing where the sun will be during the eclipse - you can tape some thin (preferably black) cardboard to the windows to make the room completely dark - and poke a small pinhole into the cardboard to let in some sunlight (this is effectively just a 'pinhole camera'). This will project an image of the sun onto any flat, white surface held up in front of the pinhole - which you can move closer to make a smaller but brighter image or further away for larger and dimmer. You can also make the image brighter - but fuzzier - by slightly enlarging the pinhole - dimmer but sharper by using a finer pinhole. It's easy to experiment. You won't hurt your eyes or your camera by looking at this image. It's very cool (especially now that the sunspots are coming back) and everyone should do this at least once - eclipse or no eclipse! Using a conventional camera with flash turned off and a 'macro' or 'closeup' lens setting if your camera has one - lets you take photos of the projected image that will look really great. Best of all, you can get everything set up and take practice photos of the uneclipsed sun any time to be sure you have everything right for the big day. That's a good idea - because you only have a few minutes to get what you need - and you don't want to be fiddling around getting the camera settings right. Just be sure to do the setup at the same time of day as the maximum amount of totality that's predicted so you'll have the best-facing window for the event. SteveBaker (talk) 12:51, 17 July 2009 (UTC)[reply]
I forgot a piece of pinhole camera advice. To get a really SHARP image - cut a square hole a couple of inches across in your cardboard and tape some aluminium kitchen foil across it. Then punch your pinhole in the foil. It makes a much smaller and more accurate hole for the ultimate in sharpness. SteveBaker (talk) 13:09, 17 July 2009 (UTC)[reply]
Total solar eclipse during totality, March 29, 2006, Sallum, Egypt, Playing with double shadows during an eclipse You can use an ordinary camera to take pictures during a solar eclipse. Be sure to SECURELY mount a piece of #14 welder's glass in front of the camera (Not the side with the display the other side i.e. before the light hits the camera.) I tried a mylar filter last time and was unhappy with the results. (It was expensive but buckled and got me reflections on the images.) Friends used the welder's glass and got awesome pictures. Since your eclipse is not total you don't have to worry about removing/putting on the filter arrangement during the event. That usually makes for more difficult constructions. Build yourself a solid frame or box. Sticky tape or Duck tape are not suitable for this task. Make sure absolutely no light can enter the setup except through the welder's glass. There are many things to observe apart from the sun turning into pac man. See if you can spot double shadows as in my pic. (No the guy was not Aquaman or an alien with extra knuckles between his fingers:-). Have fun, but be safe. --Lisa4edit (talk) 15:40, 17 July 2009 (UTC)[reply]
is there a true difference between regular cables (hdmi, USB, internet) and those made by "boutique cable" manufactures that include gold plated connectors?
puzzles me is that the cable is still copper so would any benefits from the gold connectors be negated by the copper wire?
im looking for scientific reasons (from a metallurgy, engineering perspective) for a difference or lack thereof. Im not looking for an audiophiles perspective, they tend to buy anything if its expensive. seems as though they are victim to the the placebo effect.
EDIT
so it seems that gold plating prevent corrosion, makes sense, but is there any true sound difference between monster cable(and similar cables) and normal priced audio cable.
one of the claims ive heard is that with monster cable you hear "more of the nuances of the music"
Well, for digital signaling, there is no difference. All decent cables that follow the standards are plenty good enough to carry the digital signal. Boutique cables for digital signals are a scam. For analogue transmission, cable quality can make a difference. But even there, gold plating is not going to have a significant difference. If you can hear the difference between decent and overpriced cables, James Randy has ONE MILLION DOLLARS for you.[26] --Stephan Schulz (talk) 11:39, 17 July 2009 (UTC)[reply]
The gold plating isn't actually that expensive - you can get fairly cheap gold plated cables if you want.
The gold plating ensures that the connector will not corrode or rust, but a rust free alloy would do just as well.
There's and additional complication that a junctions between different metals have properties (eg think thermocouple) - which potential could actually degrade the signal - in practice there is not a difference.83.100.250.79 (talk) 11:49, 17 July 2009 (UTC)[reply]
The theory to gold plated connectors is that gold resists corrosion better than copper, so gold plated connectors can wind up having a lower contact resistance than copper ones, particularly in a damp environment. I have had a 50-year-old copper phone connector corrode to the point that it made for a staticky phone connection, and perhaps that problem wouldn't have occurred had the connector been gold-plated. Of course, digital devices become obsolete way before they’re that old. Red Act (talk) 12:20, 17 July 2009 (UTC)[reply]
Gold plating is most useful on cables you will need to plug and unplug often. Gold is soft and will somewhat lubricate the connection as it slides in and out. For connectors that stay in place for most of their life - that are maybe unplugged when you move house or something...meh - any old cable of the appropriate standard will do. The most ridiculous thing is when audiophiles claim to be able to hear the difference between gold plated cables and the regular kind. Audiophiles have a problem. They are like most of us geeks who love to debate the merits of Linux versus Windows or MINI Cooper's versus Mustangs - to endlessly tweak the object of their joy to get another 1% of performance out of it...except that their field of interest is 'solved'. We can't buy the perfect car or the perfect computer - but we can all have essentially unlimited quantities of perfect (in the sense of 'better than human perception') audio at any time we want from a sub-$100 box that you can buy at any Walmart. There is nothing left to be geeky about...no conceivable reason to rush out and buy this years sexiest $10,000 stereo system beyond the shape of the knobs and the color of the LED's. Sadly, these people retreat into a world of their own where they claim they can tell the difference between two ethernet cables used to connect their PC to their media center (yes, really!) when it's a completely lossless digital connection with error recovery built in at the software level. These people will happily pay $1000 for a set of cables just so they can "one-up" their audiophile buddies. Check out these [27] nut-jobs who sell cables with silver conductors instead of copper at hundreds of dollars for what would normally be a $1 cable. Their advert reads: "These cables allow deeper insight into the textures of the critical mid-range, leading to improved intelligibility of vocals, greater resolution of acoustic spaces around the instruments, more real-sounding instrumental timbres, etc. It’s not only beneficial on acoustic instruments – it also gives greater insight into studio techniques, the timbres of synthesisers and guitars etc. Nuance and emotion in vocal and instrumental performances come to the fore."...completely ridiculous of course. It's actually rather sad. SteveBaker (talk) 12:30, 17 July 2009 (UTC)[reply]
The bullshit related to cables is legendary, but I'd say that nothing can top the $485 wooden volume control knobs they were pushing a few years back: [28]. Alas, these knobs are no longer being sold by the original manufacturer. TenOfAllTrades(talk) 14:16, 17 July 2009 (UTC)[reply]
I have restored telephones and telegraph equipment over 100 years old. Soldered connections still conduct. Tinned connections screwed together generally still conduct. Bare brass or copper may develop surface oxidation which insulates, even though no gross corrosion is seen. A goldplated connection should still work fine after that interval. Ordinary audio connectors, with copper inside and some silvery looking outer conductor (tin?) or the connection of vacuum tube pins in their sockets can become oxidized and noisy after ten years or more. Gold plating would likely help maintain continuity. Edison (talk) 14:39, 17 July 2009 (UTC)[reply]
In general there are some bad cables - in my experience once problem is that caused by metal connector shields (the plugs) - on analogue video I've found these to sometimes give noticeable (really noticable) noise.
Only buy ones with a insulating plastic plug - these are often the cheapest.
I have found that it makes a difference, probably because of oxidation resistance leading to less static etc, plus more expensive cables tending to generally be better-made than the cheapest ones. Cables with gold plated connectors cost a few bucks extra if you shop around and I think it is worth it to do so. I wouldn't get the scammy ones where they charge several times more for a lot of marketing crap. They're basically the same cables. 67.117.147.249 (talk) 00:50, 19 July 2009 (UTC)[reply]
There’s no need to report a UFO sighting, as governmental and scientific organizations will just assume that it’s just yet another natural event that people have gotten overly excited about because they can’t immediately identify it. However, some of these UFO organizations will probably be happy to hear about the “sighting”. The Unidentified flying object article lists some phenomena that might help you make a guess as to what the thing actually was. Red Act (talk) 11:27, 17 July 2009 (UTC)[reply]
If you have a video or at least a picture of the thing, someone here might be able to help you identify it as being ball lightning or a meteor or whatever. Or was it all over too quickly to take a video or picture of it? Red Act (talk) 11:35, 17 July 2009 (UTC)[reply]
A UFO (in the original sense of "any flying object that you can't immediately identify") is a singularly irrelevant event. A UFO (in the more modern sense of "a flying saucer") is essentially certain to be a case of you failing to correctly identify a UFO (in the old sense of the initialism)! In either case is it no more than a passing curiosity. The curious thing about the modern use of "UFO" is that people almost always use in the sense of "A flying object that I've already identified as a flying saucer"...hardly 'Unidentified'! Unidentifiable flying objects might be more interesting! Anyway - as Red Act says - the old 1960's idea that these things had to be reported to the air force or something is long gone. Tell your friends - find a bunch of flying saucer nut-jobs and tell them - but nobody else gives a damn. SteveBaker (talk) 12:02, 17 July 2009 (UTC)[reply]
As my old father used to say (ex-RAF) any FO that is not I is a UFO (or any Flying Object that is not Identified is an Unidentified Flying Object) and it remains a UFO until it becomes I. --TammyMoet (talk) 19:23, 17 July 2009 (UTC)[reply]
I've seen two "flying saucers" recently, and both turned out to be USAF aircraft (one was a Blackhawk chopper, the other one a C-17 Globemaster). 76.21.37.87 (talk) 02:02, 18 July 2009 (UTC)[reply]
I saw a UFO once about 10 years ago, while I was out walking the dogs with my girlfriend one night after dark. A reddish-orange object made a rapid, curved arc through the sky. The UFO remained unidentified for about 5 or 10 seconds – until I got close enough to see that there was a house in that direction, and I saw the person sitting in the second-story window of that house, who I realized had just flicked a still-lit cigarette butt out the window. Red Act (talk) 02:30, 18 July 2009 (UTC)[reply]
A thermometer broke in a hot tub
I'm working at a hotel and a thermometer in the hot tub broke, leaking some blue, oily substance into the tub. It didn't look anything like mercury but I don't know enough about mercury to know whether it's possible to make it look blue and.. oily. I've heard they often use semiconductors in thermometers although I won't vouch for that.
What do you suppose the liquid substance is? What should I do? Should I clean the tub with water, soap.. should I close it indefinitely? --88.149.11.100 (talk) 12:17, 17 July 2009 (UTC)[reply]
It is an oil, nothing special. Mercury is silver and doesn't in any way behave like an oil. It rolls and, if spilled into a tub, will quickly roll down the drain. Use a cleaner for oils (most kitchen cleaners work well). -- kainaw™12:42, 17 July 2009 (UTC)[reply]
Are you sure it's an oil? I didn't know they could be used in thermometers. If you're sure then this should be all right but I would like to get a confirmation just to be sure, nothing personal Kainaw :) --88.149.11.100 (talk) 13:00, 17 July 2009 (UTC)[reply]
There are two common types of thermometers used in this sort of application. The cheap ones use a bimetal strip. Those are usually obvious because they have a dial display. The more expensive ones use an oil. They tend to have a digital display. Even if it is a bimetal strip, an internal lubricant oil is used to keep the strip from sticking to itself. Neither design uses mercury. In fact, it is rare to find mercury in thermometers. If you go look at them in the store, most are digital, many have a red oil, and a couple might have mercury (if you are lucky - I haven't actually seen a mercury one in a long time). Also, if it were mercury, it would behave like mercury. Mercury is very heavy. It quickly goes to the lowest point on any surface. By quickly, I mean that it appears like it has intelligence and is racing towards a destination. In a tub, the lowest point is the drain, so it would quickly roll straight down the drain. -- kainaw™13:09, 17 July 2009 (UTC)[reply]
I've run into mercury thermometers every now and then in labs; but they're generally only used in certain applications where the temperatures get into hundreds of degrees celsius - it's generally not used for more mundane applications because of its now-recognized toxicity. I also agree with Kainaw that if it was mercury, you'd know it - mercury behaves very differently to the other liquids you encounter in everyday life. It was almost certainly some kind of dyed oil or alcohol that may be slightly poisonous but will do nobody any harm if diluted in a tub of water. ~ mazcatalk13:33, 17 July 2009 (UTC)[reply]
My dad used to show me the mercury from mercury thermometers when I was younger, but it sounds like they're not as common any more. When I think about it it would probably sink if it were mercury but my first thought was to ask- I didn't really want to take any chance with this. Thanks for your helpful answers though :) I cleaned the tub and everything seems to be all right now, I'm more knowledgeable about thermometers now which is never a bad thing ;) User:BiT --88.149.11.100 (talk) 15:39, 17 July 2009 (UTC)[reply]
This is probably just marketing hype. Xylitol (q.v.) is merely an artificial sweetener. Chewing practically anything (apart from dry foods that absorb water) will stimulate saliva production.--Shantavira|feed me15:09, 17 July 2009 (UTC)[reply]
(Not entirely hype - see below.)
The sweetness is designed to make you salivate. Xylitol is used because it is sweet, and less likely to have the problems associated with using normal sugar:
One possibility for this is that bacteria that can metabolise are rarer (or don't exist) compared to bacteria which can metabolised sucrose or glucose - reason being that xylitol is a 'new' sugar...83.100.250.79 (talk) 15:33, 17 July 2009 (UTC)[reply]
Xylitol is a sugar alcohol. The cooling effect described in the article may provide added relief. Since Xerostomia includes tooth decay as one of the symptoms. chewing gum with sugar is probably not a good idea. I don't know if the existing bugs have trouble with the "alcohol" portion of the sugar alcohols. Hand sanitizers are made from alcohol gel, but the "sugar" part may counterbalance any antibacterial effect. Lisa4edit (talk) 16:09, 17 July 2009 (UTC)[reply]
Sugar alcohols are not anything like hand sanitizer alcohol. It's not really the sugar alcohol acting like a poison. Cavities are caused by acid producing bacteria. These bacteria can't process Xylitol because it's not food so there isn't "alcohol's antibacterial effect is canceled by the sugar feeding effect".129.64.55.234 (talk) 16:39, 17 July 2009 (UTC)[reply]
Thanks. Do you know how they differ? I had thought the "alcohol" group at the end interferes with some part in the bacteria's membrane. Could you clarify the process and explain why it doesn't do what it does for sugar alcohols? Lisa4edit (talk) 17:50, 17 July 2009 (UTC)[reply]
Think you're just wrong. sugar, cellulose etc all have lots of alcohol groups, and they don't interfere with bacteria as far as I know. You should present some evidence that what you thought is actually true, rather than expecting people to provide responses based something that you haven't provided any evidence to be true.83.100.250.79 (talk) 18:22, 17 July 2009 (UTC)[reply]
looking for information on a type of water-powered hammer
I saw a type of water-powered hammer used for striking coins. It was water-powered, but not a trip hammer. It consisted of a big beam with a heavy weight on one end (the hammer) and a bucket on the other end. Water poured into the bucket, and when it would get full, it would sink down, lifting up the weight. Then, when it would get to the bottom, the water would pour out of the bucket and the hammer would drop. I thought it might be a trip hammer, but that's based on a cam and a rotating shaft, which this didn't have.
I wouldn't refer to that as a water-powered hammer. I would refer to it as a gravity-powered hammer. It doesn't matter what raises the hammer (water, rocks, a mule...), it is gravity forcing the hammer down to produce the desired result. Unfortunately, Googling for "gravity hammer" will not return any useful results. -- kainaw™16:39, 17 July 2009 (UTC)[reply]
When did it become common knowledge among reasonably well-educated people that mercury is highly toxic? When I was a child, a broken thermometer meant *FUN*, since my mother would let my brother and me play with the mercury that came out. Its behavior was so alien (the little spheres coalescing into larger spheres, etc.), that it provided hours of entertainment. Now when I hear of a mercury leak at a school they shut the whole thing down and send in the guys in hazmat suits. Should my mother have known better in the late 1970s? If it matters, she was Rhodesian/Zimbabwean, a nurse, and we lived in Brazil. Thanks. --Sean23:11, 17 July 2009 (UTC)[reply]
It was already a big deal when a thermometer broke in our house in the late 50s early 60s. People have varying attitudes toward risks. Risk assessment is not just done in the documented orderly way described in out article, but happens in our heads pretty much constantly. Different people and cultures come to different results. We happily take our kids on trips in cars, but cringe or cry child abuse when we see someone hand a machete to a toddler in a stroller. The comparatively delayed and remote risk of mercury poisoning may have paled when compared to more immediate severe risks your mom encountered every day. You may still have fared better than some who made a big fuss, because one method of removal was vacuuming up the mercury, which of course made the problem a whole lot worse. Out of sight and out of mind wasn't out of the air. Lisa4edit (talk) 16:37, 17 July 2009 (UTC)[reply]
Years ago it was common for high school chemistry students to play with mercury, rolling it around in the hand. If a thermometer broke, kids played with the glob of mercury rolling it around on the floor until it disappeared into a crack. If it broke in a kids mouth, they just spat out the mercury and glass fragments. It was claimed (by a family doctor years ago) that the elemental mercury in the thermometer was not in a form easily absorbed by the body. On the Mr. Wizard TV show in the 1950's the kids learning about science were commonly exposed to mercury, as in the electromagnetic "jumping spring" where it was used for electrical contact. The splashing and sparking could have put a fair amount into the air. Many electrical experiments/demonstrations work vastly better with mercury than with brine or just metal to metal contact. It is hard to replicate some of the early electrical work of Michael Faraday without mercury for a friction-free highly conductive electrical connection. Probably in the 1970's some of these science demos became things the kids read about instead of things they saw or did. Likewise mercury manometers were previously used in high school physics and chem labs to measure pressure or to demonstrate barometer function. Perhaps dial or electronic pressure transducers replaced them. It was well known in the 1800's that chronic mercury exposure caused brain damage ("Mad as a hatter") but it was probably assumed that brief exposure did not have lasting effects. Mercury/silver amalgam fillings are still in millions of mouths. When did they stop putting mercury in tooth fillings? Edison (talk) 19:13, 17 July 2009 (UTC)[reply]
When I took high school chemistry in the early 1970s it was still the way Edison describes it. So mercury is toxic; big deal, you won't get enough exposure to matter. Today the attitude is to err much more on the side of caution. --Anon, 19:21 UTC, July 17, 2009.
I found an article from December 1963 about the U.S. Public Health Service banning a toy which contained drops of mercury. It says "If the toy should break and scatter mercury beads in hidden areas the fumes from the element could cause brain damage." A 1960 article behind paywall also cites a toy pulled from the market by authorities because it contained mercury.So I'd say it was "common knowledge among well informed persons " by then. But pretty much ignored by most for years after, like the dangers of smoking or the need to wear seat belts when driving. By 1970 there were numerous stories about the danger of trace amounts of mercury in fish and mercury vapor from spills. In the 1960's the U.S. used more mercury in pesticides than other countries, which were banning it after health problems were noted. Edison (talk) 19:31, 17 July 2009 (UTC)[reply]
In 24 BI (before internet), facts did not spread so easily. Whereas today we can google information on mercury, or other things to find information, back then it was much more difficult. Googlemeister (talk) 19:54, 17 July 2009 (UTC)[reply]
Which date exactly are you using as the start of the internet epoch? As far as I can tell, Unix epoch is the closest thing - the "internet" has no clean event which marks its beginning (first router? first TCP packet? first domain name lookup? first www server? first html render?) Any of these types of events can be counted as the start of the internet. Nimur (talk) 22:18, 17 July 2009 (UTC)[reply]
Your mention of car seats gave me a chuckle, since my mom also put us kids in "car seats" similar to old-skool drive-in trays, where we were just kind of hooked loosely onto the back of the driver's bench seat for reasons not of safety, but of getting a better view out the windshield. :) --Sean23:11, 17 July 2009 (UTC)[reply]
I played with lawn darts! (Hint: when the other guy throws, it's good to be paying attention.) And had a chemistry set with dozens of poisonous substances. And rode a bicycle hundreds of times and never had a helmet or padded knees and elbows. And speaking of bench seats, remember when as a kid in the back seat you could roll down your window more than an inch and a half? Everybody's afraid of everything now. 69.245.227.37 (talk) 07:25, 18 July 2009 (UTC)[reply]
I also played with a chemistry set that had a whole bunch of poisonous substances, like NaOH pellets, 3M HCl, two different ferrocyanates, and copper sulfate (I remember wondering what copper sulfate tastes like, but my dad told me that it's poison, so I didn't try it). Also, I played with mercury when I was little (and I'm none the worse for it, I must say). And I actually raced my bike, downhill on a busy street, without any helmet (and then braked it with my sneakers, it had a really unreliable coaster brake that didn't always work). And once I rode on a train's rear buffers with a 50-pound pack on my back. And another time I flew over the mountains of Alaska in a tiny little single-engine plane (didn't do any piloting, though). And occasionally I've handled (dilute) HF with my bare hands -- no gloves, no goggles, no nothing! Must I add that I'm into martial arts? Reckless?! No, just taking calculated risks. 76.21.37.87 (talk) 07:58, 18 July 2009 (UTC)[reply]
As far as I know, organic compounds of mercury are highly toxic and accumulate in the brain. Metallic mercury or its ions are still toxic but much less and is a hazard mainly for the kidneys, as good or bad as most heavy metals. Many people living today have mercury in there teeth. Compact fluorescent lamps contain mercury, too. I guess the released amount from a shattered one is in about the order as the vapours from a shattered mercury thermometer. So I wouldn't panic when a thermometer breaks. The other thing is the mercury drop going down the sewer and finally distribute itself to the environment. 93.132.138.254 (talk) 08:22, 18 July 2009 (UTC)[reply]
I agree with you 100% that the hazards of metallic mercury are overrated and that it's not such a big deal if a thermometer or a light tube breaks. But I must warn you that dumping mercury down the sewer is a bad idea cause it'll go into the water and any fishes that swallow some will turn it into methylmercury and get poisoned (maybe even die) and also become poisonous for us people to eat. If I had a mercury thermometer (light tube, Ignitron, whatever) and it broke, I'd just gather up the mercury into a jar and turn it in for toxic waste disposal.
Is the pH of vinegar too high to attempt Fischer esterification with ethanol and vinegar over a hot frying pan? The yield prolly wouldn't be too good, but since what I'm aiming for is flavor detection, an equilibrium product of 0.1% (at room temperature) would do very well.
There is this story on some wikipedia page about a mother warning her kid about lots of things not to do while she's away including not to put jelly beans up his nose. He had never done that so he immediately had to try. So, I won't link the page and I hope you don't want to know this for any unhealthy reasons that came to my mind. Lisa4edit (talk) 16:22, 17 July 2009 (UTC)[reply]
I don't think pH has as much to do with it as Ka which measures the strength of the acid. The acid catalysts listed in Fischer esterification have very low Kas. Maybe you should try it. The reaction takes a long time in aging wines but if there's heat applied, the reaction might speed up and produce just enough for your needs. —Preceding unsigned comment added by Coolotter88 (talk • contribs) 16:57, 17 July 2009 (UTC)[reply]
You actually need to know the equilibrium constant for
Acetic acid + ethanol <> ethyl acetate + water
Acetic acid will promote this reaction - even Ammonium Acetate can promote this type of reaction - however the speed of the reaction may be slow - I recommend a pressure cooker - doing this you will get an equilibrium amount of ethyl acetate - whatever that is - the trick is to have as little water in as possible.83.100.250.79 (talk) 19:25, 17 July 2009 (UTC)[reply]
Is Ka that important? See I thought it was H+ concentration that catalysed the reaction but possibly I guess acid strength would be important to help prevent a reverse reaction even in favourable pH. Also, it's ethanol and vinegar -- common edible solvents -- and I expect the majority of my yield would be my starting reactants (discounting evaporation) -- why would it be dangerous? I mean, I add vinegar to all sorts of ingredients with active essential oils and flavors all the time. If I added something that was pseudohygroscopic -- flour or some kind of starch -- I guess that would help absorb the water? (It would also fry, but hey.) John Riemann Soong (talk) 23:13, 17 July 2009 (UTC)[reply]
Acidic bitterness
How can lidocaine have been identified as the source of a bitter taste, when it comes in a solution of HCl, which is acid? I thought acid is sour and bitterness is associated with alkaline? DRosenbach(Talk | Contribs)17:15, 17 July 2009 (UTC)[reply]
One way: the taste occurs when lidocaine is injected intravenously or subcutaneously. There need be no direct involvement of taste sensory neurons, as there might be if topically applied, and there is no change in pH when injected, as the HCl is quickly dissociated and buffered. - Nunh-huh21:48, 17 July 2009 (UTC) (Addendum: pH of Lidocaine HCl injectable without epinephrine is about 5.0-7.0 in the bottle).[reply]
colour of the moon
Hi there!!
I would like to know what material on the moon's surface makes it white. Or is it just the strong light of the sun that makes it so? Please help me out.--Lightfreak (talk) 17:55, 17 July 2009 (UTC)[reply]
The moon is not white; it's black, or more precisely very dark gray. It only reflects about 10% of the light that hits it -- an object you would call white would reflect something more like 90%. If you visit the National Air and Space Museum, they have a slice of moon rock you can touch, and you can see the color.
However, human color perception is relative. An object is judged to be light or dark in comparison to the things around it. This means that when an object is seen against a much darker background, like a light in the sky, it is impossible to see it as having a "dark" color like brown or navy blue or dark gray. You see red or yellow or blue or, in this case, white.
(XX) The image caption "showing how bright the bright parts are" is misleading. All large areas of the Moon are black to dark gray, it's just that some parts are even darker than others. The photo was made with an exposure sufficient to show detail on the surface -- the same sort of compensation that our brain does automatically, so it reproduces the way the Moon appears to the eye. If there was a true white object in the photo, large enough to see, it would look grossly overexposed. If the exposure was made correct for the white object, then the image would show how dark the Moon really is. --Anon, 22:48 UTC, July 17, 2009.
And by the way - you are very weird - a picture of a whitish moon is no good, but a picture of someone touching a triangle is. Fucking wierdo.83.100.250.79 (talk) 00:26, 18 July 2009 (UTC)[reply]
Our chlorophyll article has some info about the optical properties. The nature of any molecule is to absorb only certain wavelengths (colors) of light (affected by structure, pi bonds, non-bonded electrons, and metal atoms, among others). The nature of chlorophyll is to absorb several "non-green" colors, so what's left is green. DMacks (talk) 19:38, 17 July 2009 (UTC)[reply]
That still leaves the question of why chlorophyll absorbs those non-green colors and not green. (Why hasn't evolution "tuned" chlorophyll to absorb green light.) Turns out that short wavelength light (the blues and violets) contain a lot of energy, so it makes sense to absorb those. On the other hand, as a blackbody radiator, the sun puts out most of its radiation (number of photons) in the lower wavelength region (the reds, oranges, and yellows), so you'd want to capture that as well. What's left is the stuff in the middle (green), which isn't particularly energetic, nor particularly prevalent. While it would be best to capture those wavelengths too (making plants black), they don't give enough of a benefit to drive evolution to that point. This analysis changes with different the different emission profiles of different stars. I vaguely recall news reports about research which hypothesized what colors plants on extra-solar planets would be, given the above considerations. -- 128.104.112.87 (talk) 19:57, 17 July 2009 (UTC)[reply]
Actually I believe it's because of the constraint of the photoreceptors, and because chlorophyll evolved in the ocean (and established enzymes are hard to modify), and the ocean provides a color filter of its own. I believe there's an explanation that states that green light in sunlight was actually too intensive in the ocean for it to be useful -- in the sense that it would be overly damaging to the pigment itself, so chlorophyll evolved in a way *not* to absorb too much of it. If you look at http://en.wikipedia.org/wiki/File:Solar_Spectrum.png you can see that sunlight actually has a lot of green light relative to the other wavelengths. John Riemann Soong (talk) 23:08, 17 July 2009 (UTC)[reply]
Cigarettes against tear gas?
Per a news story[31], antigovernment protestors in Tehran were "lighting cigarettes and putting them in front of one another's faces to ward off the effects of the tear gas." Is there any merit to this belief? I was told that tear gas effects are worse if you rub the facial skin and especially the eyes, so swim goggles are useful to keep it out of the eyes, and that since it is a powder and not a gas, an N95 respirator mask provides some protection to the lungs, better than a bandanna over the mouth and nose but clearly not as good as a gas mask. I was also told that water to flush the eyes was useful. But what possible protective effect would come from cigarette smoke around the face? Edison (talk) 18:40, 17 July 2009 (UTC)[reply]
Vaseline on the skin is also an old recommendation from demonstration organizers, but about as many sources say it makes the teargas worse, sine the material gets dissolved in the petroleum jelly. Other demonstration organizers in the past recommended vinegar or baking soda[32]. Any reliable sources? Not much useful and referenced info in the Tear gas article. Edison (talk) 18:57, 17 July 2009 (UTC)[reply]
I don't know - but I know that heavy smokers can have a reduced response to some stimulants/allergens (tear gas stimulates a response rather than actually being harfull I think) - eg smoking can stop allergies such as pollen hay fever.. However I think you need to actually smoke some cigarettes for this to work.. Just a guess.83.100.250.79 (talk) 19:21, 17 July 2009 (UTC)[reply]
Conversely, smoking (or smokers...not sure if it's an effect of the smoking at the time or of the result of some long-term response to smoking) reportedly makes one more able to detect cyanide. Not that cyanide is being used on the protesters (I hope!). DMacks (talk) 19:41, 17 July 2009 (UTC)[reply]
WARNING, ANECDOTAL EVIDENCE FOLLOWS I used to be in the United States Air Force. Airborne Battle Management to be exact. Since we were flying around, directly above the battlefield they had us go through the same training the Combat Controllers (the USAF's version of Navy Seals, Army Rangers, etc). This training included frequent trips to the gas chambers. I believe the gas in the chambers was CS gas, but they also used tear gas on us occasionally. I am, and have been for a long time, a heavy smoker. Before I went in, I smoked a cigarette. When I came out, I smoked a ciggarette. My eyes watered. My friends were dripping with mucous.
It could be that either (a) the cigarette smoke desensitizes the mucous membranes, making them less susceptible to the effects of the tear gas; or (b) the nicotine actually has a toxic effect that is opposite to that of the tear gas, and so acts as an antidote. I'm not really sure about that last part, I got to look it up. BTW, CS gas is tear gas.
Just looked it up -- nicotine does stimulate the sympathetic nervous system, which would tend to suppress tear secretion -- so you could say that it acts like an antidote. FWIW
If you carry a sine in a riot they hit you on the head, besides throwing tear gas. I saw a cop do this, and he was obviously outdoors a lot because he was a tan gent. Edison (talk) 20:02, 18 July 2009 (UTC)[reply]
"I saw a cop do this, and he was obviously outdoors a lot because he was a tan gent." -- Oh, I get it now (didn't at first)! HAHAHAHAHA! ROFLMAO! 76.21.37.87 (talk) 00:56, 19 July 2009 (UTC)[reply]
...its retention for nautical and aviation use is important for navigational reasons, since the length of a nautical mile is almost identical to a minute of latitude. As a result, distance in nautical miles on a navigational chart can easily be measured by using dividers and the latitude indicators on the side of the chart.
In an era of cheap calculators and flight control radar, what is the benefit of something being "almost identical to a minute of latitude?" Does that "almost" keep you from smacking into a mountain in the clouds, or "almost" get you to a landing strip on some speck of land in the Pacific before you run out of fuel? It's hard to see why such approximate navigation would be very useful today. Edison (talk) 21:41, 17 July 2009 (UTC)[reply]
Useful? It's useful because it is a functional and standardized measurement of airspeed. Unless you are asking, "why doesn't the worldwide aviation system shift from knots to kph as a measurement of airspeed," which is a different question. Tempshill (talk) 22:15, 17 July 2009 (UTC)[reply]
It's basically just history - the seafaring roots of the nomenclature and the (then) convenience when using maps for long distance travel. Nowadays, it's just something that's way too embedded in expensive physical objects (planes, control towers, etc) and in the brains of their operators to change. Aircraft often remain in service for 30 years - and their pilots are around for a similar amount of time - any change-over period would take decades to achieve. Worse still, it would require approval internationally since aircraft spend a lot of time going from one country to another. They also measure altitude in feet rather than meters. It's hard to imagine what benefit there would be from such a costly and difficult change. SteveBaker (talk) 00:03, 18 July 2009 (UTC)[reply]
Stomach aches and depression
I recall reading something years ago about how because of the way your brain is wired, physical pain in the stomach can lead to emotional depression. sounds kinda fishy, but i remembered reading it because i'm profoundly hungover and also a bit bummed out. thanks
70.122.109.186 (talk) 19:55, 17 July 2009 (UTC)[reply]
Any continual pain or illness or disability can lead to depression potentially - but I'm not aware of anything specific about the stomach, and doubt it very much.83.100.250.79 (talk) 20:22, 17 July 2009 (UTC)[reply]
While we can't diagnose your specific condition, you are also asking if this link might be true. I doubt it. The problem (and one reason why we can't give such advice) is that depression can be caused by physical (brain chemicals) or psychological (ill family member, etc.) causes. The latter, of course, being more about the fear of loss, the empty part of your life if that person dies, etc.; yes, there is a "feeling in your gut" that can be related to concern over that family member, but it would be a symptom, not a cause, of depression.
Also, see our article on Memory - what you read might be coming to you in a different form than you read it. Maybe that's why it seems fishy; you're not recalling it the way it was.
Nietzsche wrote something to the effect of 'the Holy Spirit resides in the entrails'. I couldn't agree more. Though when you're suffering from indigestion and depression you probably aren't too interested in philosophy. I recommend cutting back on your meat intake until you feel better. It's not trivial to digest, and there are a lot of unscrupulous men out there who will raise profoundly unhealthy animals to be fed to undiscriminating people. It's an evil business sometimes but it's been the way of things for so long that nobody bats an eye. Vranak (talk) 23:58, 18 July 2009 (UTC)[reply]
July 18
Car incident types
Quotation: "Lane change accidents are noted as one of commercial vehicle fleet's top 3 accident types." Anyone know(or at least can guess) what the two others accident types? Vitall (talk) 04:39, 18 July 2009 (UTC)[reply]
Rear-enders are the most common kind of car crashes, I'm sure of that. WP:OR: I've myself been rear-ended twice within a year or so, once by an 18-wheeler (OUCH!!!) and the second time by a jeep. FWIW
76.21.37.87 (talk) 05:02, 18 July 2009 (UTC)[reply]
There would of course be more than one way to define "accident type". However, from page 31 of this document, it looks like rear ending is indeed the most common accident type, and the second most common is hitting a fixed object. The referenced document lists the third most common accident type as “side swipe (opposite or same direction)”, which does seem like it would include a typical lane change accident. Red Act (talk) 08:52, 18 July 2009 (UTC)[reply]
First, I am a regular user, but for obvious reasons I am not logging in to post this question. Second, I am not asking for medical advice, but for artices (WP or other) relating to the question.
A few years ago I was with a girl who was a frequent liar. The first time she claimed to be pregnant I was 16, and believed her. About a month later she claimed to have had a miscarriage. I believed her. The second time, I was probably 17. I wasn't so sure about it this time. Soon after she claimed to have had another miscarriage. This happened a few times more, and by the time I left her I didn't believe that she had ever been pregnant.
Now, my current girlfriend is going through a miscarriage. At about 4 weeks into the pregnancy.
Now I'm wondering if my first girlfriend may have been telling the truth, and the miscarriages are somehow related to me. Is there any connection between males and miscarriages?75.93.119.255 (talk) 05:45, 18 July 2009 (UTC)[reply]
I'm not an obstetrician, so please don't take this as medical advice, but the only way a male could present a risk factor for miscarriage is if he's a heavy smoker (if he smokes more than 2 packs a day, then his wife / girlfriend could be up to 3 times more likely to have a miscarriage). However, if you're not a heavy smoker, then there's no conceivable link between you and your current girlfriend's miscarriage. In this latter case, the current miscarriage is not your fault (or hers, for that matter), and your first (ex)-girlfriend is a damned rotten liar. FWiW
76.21.37.87 (talk) 06:47, 18 July 2009 (UTC)[reply]
From personal experience here: having had at least 5 misses myself, and talking to doctors about why, it seems that about 50% of all pregnancies end in miscarriage: sometimes the period is just a few days late but there is still a pregnancy which has ended. So don't blame yourself for this. It's a natural feature of being a woman. Oh - and you may wish to consider using contraception to prevent pregnancy and therefore miscarriage occurring in future. --TammyMoet (talk) 08:32, 18 July 2009 (UTC)[reply]
I'm also not an obstetrician but I would have to disagree with 76. There's no reason why a male can't be a factor in miscarriages. If the miscarriages are caused by genetic defects (e.g. chromosomal abnormalities), then that could be either the male or the female. E.g. [33][34][35][36]. Also there's no way we can know that 'your first (ex)-girlfriend is a damned rotten liar' as 76 suggested. Even if you aren't a factor, it easily possible your ex-girlfriend had a fertility problem of her own. I woulld also emphasise TammyMoet's point. Miscarriages are hardly uncommon and probably more common at such a young age as your first relationship (although 4+ is fairly unlikely without some sort of problem, that could still go away naturally). And if you don't want to have a baby, you need to look at more efficient contraception since it sounds like whatever you've been doing hasn't been working. And finally, if you are concerned about your fertility, you should see a specialist. Nil Einne (talk) 10:14, 18 July 2009 (UTC)[reply]
OK, I take back the "damned rotten liar" part. However, if there are 5 miscarriages in a row, it's highly unlikely that genetic defects are a factor in all of them. No, 75 IP's genes can almost definitely be ruled out as a factor, so assuming that 75 IP is not a heavy smoker (which would be a factor) and that his first ex-girlfriend was telling the truth (which she might or might not have), then it would mean that she had an infertility problem of her own (as Tammy pointed out) and that the current miscarriage was simply a random misfortune. So, to recap: if 75 IP is a heavy smoker, he should quit smoking or at least cut back to less than a pack a day; if not, then he is not a factor in his girlfriend's miscarriage.
Well, just to be a smartass, it doesn't appear that I need any contraceptives. But everything else makes sense. And it was 4 in 2 years. 6, if you count both sets of twins she claimed... Now you understand why I didn't believe her. Still don't, but I'm wondering if maybe one of them was real...75.93.119.255 (talk) 10:54, 18 July 2009 (UTC)[reply]
Carriers of a Balanced translocation can be at high risk to have a fetus with an unbalanced chromosome content thus leading either to frequent miscarriages or children with disability. If the information you were given by your partners is correct then I would follow Nil Einne's recommendation to see a specialist. --- Medical geneticist (talk) 11:53, 18 July 2009 (UTC)[reply]
I know you're being a smartass but believe me, miscarriages are not trivial, and indeed carry risks to the health of the mother. If you do have something wrong with you which causes your progeny to spontaneously abort, the least you could do is prevent the pregnancy occurring in the first place. And you'll not find out if there is something wrong until you see a specialist. Have some common decency man! --TammyMoet (talk) 12:35, 18 July 2009 (UTC)[reply]
This is 75.93.119.255. Just for the record, my second girlfriend already had a baby when we started dating. And I worked my ass off to provide for them both. Please remove the personal attack, it was highly uncalled for.DrewSmithWhat I've done22:18, 18 July 2009 (UTC)[reply]
Twins are usually diagnosed by ultrasound, somewhere between 14 and 20 weeks. A miscarriage at that stage is serious, often requires hospitalisation, and would be hard to miss by anyone seeing the patient on a nearly daily basis. Girls whose periods are not totally regular may imagine themselves to be pregnant for a few days' lateness, then imagine a miscarriage when the period does start. An amount of wishful thinking may also involved. together with testing out the reactions of boyfriends and family.
Also, bears might not hibernate. The Book of Animal Ignorance says it's "torpor"; our article on that says torpor is hibernation, but there's still some debate as to whether black bears do it. Though you're right, they do layer up fat before they do it. </trivia> Vimescarrot (talk) 11:57, 18 July 2009 (UTC)[reply]
Fish etc don't become obese as mammals do. (Actually some sites say fish can become obese - but I'm not sure - they can develope poor morphology due to lack of exercise - but I'm not sure about 'obese' )83.100.250.79 (talk) 12:15, 18 July 2009 (UTC)[reply]
Hmm... seeing how much fat ants can actually store would make an interesting research project for some entomology graduate student. I can see the paper now: "subjects were fed Snickers (Mars Incorporated, Hackettstown, NJ) three times daily..." – ClockworkSoul15:19, 18 July 2009 (UTC)[reply]
Even the humble Amoeba can slow the signs of obesity
If specimens of Amoeba proteus are fed exclusively on colpidia, they become very large and extremely fat and sluggish ..[38]
They can store energy as glycogen or fat:
Fat and glycogen are two distinct types of storage material present in Amoeba proteus[39]
There are some fish whose flesh contains hardly any fat at all -- haddock and cod, for example, are less than 1% fat. So, although I don't know for sure, I doubt that those animals would be able to store fat to any significant degree. Looie496 (talk) 05:36, 19 July 2009 (UTC)[reply]
I cannot find anything about that. I can think of two reasons for this: either it's utterly complicated and not well understood or it can be so easily reduced to the question of irreducibility of polynomials of a single variable that no one cares to tell. What is it? 93.132.138.254 (talk) 09:35, 18 July 2009 (UTC)[reply]
It's a math problem, yes. But on the IT desk and on the math desk are the people who are posing questions --- here on the science desk are the people who read questions: for fun, to broader their horizon, and, in regard of the previous, as kind of a nearly effortless side effect, help with ideas and answers. That's the difference I can't ignore. But when there is no more of an answer than "go and learn some math" then I see there's no place to put those kind of questions and it's only a waste of time. And I won't ask about what is meant be "leading term" in the article of Gröbner basis, not here nor there. 93.132.138.254 (talk) 17:29, 18 July 2009 (UTC)[reply]
Yes, multivariate factoring is complicated.
Yes, the math desk is the right place to ask.
Wikipedia's coverage of symbolic algebra is actually not all that good (compared with other math subjects), but a google search for "multivariate factoring" may help you get started. 67.117.147.249 (talk) 00:59, 19 July 2009 (UTC)[reply]
Gravity
Did Newton have a theory for gravity, or did he just create a law for it? If Newton didn't, does that make Einstein the only one with a theory for gravity? --wj32t/c09:47, 18 July 2009 (UTC)[reply]
There isn't any difference between what you are saying. There isn't any difference between a 'law' and a 'theory' in science, there are only mathematical relationships that can be used to accurately predict outcomes. —Preceding unsigned comment added by 58.111.132.76 (talk) 09:55, 18 July 2009 (UTC)[reply]
No, a law is a statement whereas a theory is an explanation. If those aren't the definitions, then that's what I'm asking anyway. --wj32t/c11:03, 18 July 2009 (UTC)[reply]
If you think of a law as a mathematical framework to compute things, say F=Gm, and of a theory as a deeper (whatever that is) framework that helps to understand (whatever that is) how an effect comes to exist (say, you describe chemical bonds using the laws for the electrical field), then neither Newton nor Einstein did have a theory. The first puts in the mass, not understanding what this really is, the other puts in curvature of space-time, not explaining where this comes from. But the distinction is rather artificial and subjective. 93.132.138.254 (talk) 10:22, 18 July 2009 (UTC)[reply]
I get what you're saying, but then is there any possible way for gravity to have a "theory" behind it, since it's a fundamental force? --wj32t/c11:06, 18 July 2009 (UTC)[reply]
The distinction between a scientific law and a theory has rather vague, subjective boundaries, and part of the difference is just that the term “law” was more popular historically, and “theory” is more popular now. However, Einstein’s general theory of relativity is arguably more of a theory than Newton's law of gravity, in that there’s more of explanation given as to what is going on. Newton’s law of gravity, to modern eyes at least, is not much more than one equation, with a definition of what each of the terms in the equation is. General relativity consists of not only Einstein’s field equations, but the explanation that those field equations are describing how the stress-energy tensor causes a curvature in spacetime. But part of that difference is just a subjective matter of perspective. The fact that spacetime is curved is very unobvious, so Einstein’s explanation seems quite important. However, in Newton’s day, the explanation that every two point masses might attract each other was also a very unobvious observation. So they are arguably both theories. Red Act (talk) 11:23, 18 July 2009 (UTC)[reply]
All that people mean when they call gravity fundamental is that we don't currently explain it as a consequence of something else, not that we won't ever do so. Newton famously refused to speculate about the mechanism of the gravitational interaction (hypotheses non fingo), but I think he believed there was some mechanism because he didn't believe in direct action at a distance. In a way general relativity provided that mechanism by explaining Newton's action-at-a-distance law as a consequence of a (rather different looking) local law. It's not clear we should use the name "gravitation" for both. Newton's law of gravity wasn't the first either. The first law of gravity was the observation that things fall to the ground of their own accord, which must predate recorded history and probably even H. sapiens. Newton's discovery was universal gravitation, which is the fact that the same force that makes things fall to the ground is also responsible for the motion of the planets. In a sense by carrying the name "gravity" from one phenomenon to another we've decided by fiat that there will always be something fundamental called "gravity". -- BenRG (talk) 11:34, 18 July 2009 (UTC)[reply]
Principia: "I have not yet been able to discover the cause of these properties of gravity from phenomena and I feign no hypotheses... It is enough that gravity does really exist and acts according to the laws I have explained, and that it abundantly serves to account for all the motions of celestial bodies
The same section also metions that he did "..invented two mechanical hypothesis in 1675 and 1717" - though it seems he wasn't happy with them - so he had guesses at theoretical origins of gravity, but nothing he was satisfied with.83.100.250.79 (talk) 11:47, 18 July 2009 (UTC)[reply]
It's obvious to me that the questioner is asking if newton had a hypothesis for the origin of the gravitational force (and by extension the form of the force/distance equation) - as such "Newton's aether-stream hypothesis" seems to be one of them - it doesn't seem (though I may be wrong) that he accepted gravity as a fundamental force, and would have wished to explain it in terms of some motion (ie an explanation via the laws of motion )at least that's what I think is the case83.100.250.79 (talk) 11:52, 18 July 2009 (UTC)[reply]
Newton's theory of gravity was that there was an force called Gravity. He had no explanation of what caused it on a physical level. He postulated that there was a thing called Gravity, it existed, and it could be understood with his equations. He was roundly criticized in his time for postulating an "occult" force, something that wasn't based in other known natural properties. Over the years of course people assimilated the force of gravity into their understanding of the natural properties of the universe, which is why we find it so unproblematic today, even though the Einsteinian explanation gets rid of the force altogether and makes it all a question of the path of least resistance in spacetime. --98.217.14.211 (talk) 14:15, 18 July 2009 (UTC)[reply]
How far can the average human shout? I've checked the Vociferation article and it says the maximum audio levels but I'm not sure how to work out the distance that people could hear them, nor how loud the average person is. 92.233.244.115 (talk) 12:21, 18 July 2009 (UTC)[reply]
I can't find anything about it online but in one of my From Our Own Correspondent it talks of people in (I think) Spain that had a language that they'd shout across mountains to each other. It has be to a number of miles, but the environment will be the biggest factor - plus it depends on whether you count using 'nature' to amplify you or not? After all in some building in London (St Pauls Cathedral? You can whisper along the edge of the wall and it will move round the build and the person on the other side will hear you. ny156uk (talk) 17:00, 18 July 2009 (UTC)[reply]
From [41] you can see Australia's loudest shout (Done by a crowd) can do 115.8 decibels. When you double the distance you reduce the intensity by 1/4, but since decibels is logorithmic, this works out to be ~6 decibel reduction for each time the distance is doubled. 0 Decibels is considered the threashold of hearing, so the distance can be doubled 115.8/6.02=~19.234. This gives us a distance, in perfect conditions, of 2^19.234=~616,595 meters (since I'd assume the originally measured amount of decibels is at a length of 1 meter, but I couldn't verify this). So we get 616 km or 383 miles. Obviously this could never occur in the real world since you can't hear something of 0 decibels over even the faintest noises of wind. 100 miles may be more reasonable for a real world max. I've seen reports of people shouting across lake Michigan (can't find source now) which is 60 miles across in most areas, but I'm not sure the distance where the guy shouted was. Anythingapplied (talk) 17:48, 18 July 2009 (UTC)[reply]
My somewhat dated (1990) copy of the Guinness Book of World Records, on page 33, says
"The normal intelligible outdoor range of the male human voice in still air is 200 yards. The silbo, the whistled language of the Spanish-speaking Canary Island of La Gomera, is intelligible across the valleys, under ideal conditions, at 5 miles. There is a recorded case, under freak acoustic conditions, of the human voice being detectable at a distance of 10 ½ miles across still water at night. It was said that Mills Darden (see Heaviest Men) could be heard 6 miles away when he bellowed at the top of his voice."
As far as shouting across Lake Michigan, I think you’re thinking of being able to see across Lake Michigan under unusual circumstances, as in the article quoted in this post[42]. (I never thought I’d use the Flat Earth Society as a reliable source, but they’re copying a now-unavailable Holland Sentinel article verbatim.) Red Act (talk) 21:37, 18 July 2009 (UTC)[reply]
There were people whose duty it was to wake up those who were on duty in the Temple in Jerusalem [Mishnah: Shekalim 5:1]. The noise that they made was so loud that King Agrippas said it could be heard as far away as 32 kilometres [Jerusalem Talmud: Shekalim 5:1] or according to another version 12 kilometres away [Babylonian Talmud: Yoma 20b]. Simonschaim (talk) 11:42, 19 July 2009 (UTC)[reply]
The article gravitation of the Moon states that the acceleration due to gravity near the surface of the moon is about 1.63 m/s^2. When was this determined? Specifically, before the moon landing, had the moon's gravitation been correctly predicted? --bdesham★19:07, 18 July 2009 (UTC)[reply]
Interestingly, you don't need to know much to calculate an approximation: Newton's law of universal gravitation says gravity near a massive object only depends on its mass and the distance from it.
If you know the earth's gravity and diameter, you can calculate its mass.
If you know the mass of the earth and the orbit of the moon, you can calculate the moon's mass: Planetary_motion is also governed by the same gravitational laws.
If you know the moon's mass and diameter, you can calculate the approximate gravity at its surface.
Now this all assumes the moon is approximately homogeneous, which we know is only sorta-approximately true (the article you linked talks about variations and their causes, and the very first sentence talks about mapping from orbit...did we send orbital probes before landing missions?), but if we're talking just a decimal-place or two and "average" "near the surface", seems a reasonable guesstimate. DMacks (talk) 19:34, 18 July 2009 (UTC)[reply]
Please help me out here. You state "If you know the mass of the earth and the orbit of the moon, you can calculate the moon's mass." OK, consider a satellite in a circular orbit 10000 miles above the Earth. What is its mass? Is there more info in "orbit of the moon" than I am seeing? Edison (talk) 19:53, 18 July 2009 (UTC)[reply]
I meant to ask "What is the satellite's mass?" There can be a satellite in orbit at the same height as the International Space Station with 1/1000 of its mass. The orbital height of the satellite tells you nothing about its mass, does it? Edison (talk) 01:28, 19 July 2009 (UTC)[reply]
Knowing the earth's gravity and diameter doesn't get you the earth's mass, it gets you the earth's mass times the universal gravitational constant (which is itself hard to measure). And how does the orbit of the moon allow you to calculate the moon's mass? You can use it to get GMearth, but that's all I can see. Algebraist20:12, 18 July 2009 (UTC)[reply]
The distinction between the case of an artificial satellite and the moon is one of mass. While for very nearly all intents and purposes an artificial satellite has an utterly negligible mass when compared to the Earth, the moon masses a little bit more than 1% of the mass of Earth. For a circular orbit, the orbital period (T) is related to the orbital radius (r), the gravitational constant (G), and the two bodies' masses (M and m) by the relation
T2 = 4π2r3 / G (M + m)
(See also Standard gravitational parameter.) For artificial satellites, M >>> m, so we usually just drop the mass of the satellite and assume a constant orbital velocity at a given altitude. For the moon, the apparent orbital period will be just a trace shorter than it 'ought' to be under that assumption; the discrepancy can be accounted for by the moon's mass. TenOfAllTrades(talk) 20:26, 18 July 2009 (UTC)[reply]
Of course, I'd forgotten that trick. That gives you the moon's mass in terms of the earth's mass, and you can calibrate the earth's mass with earthbound measurements of G. Algebraist20:53, 18 July 2009 (UTC)[reply]
Indeed (@Algebraist), "Knowing the earth's gravity and diameter[...]gets you the earth's mass times the universal gravitational constant", which if we assume is a constant we just look up in some well-refereed publication that is reputed as being usable for the types of calculations at hand. If we use the same constant in all calculations, seems like we'll be good for comparison to earth's gravity (the original question) even if the absolute intermediate values (e.g., "mass of earth")aren't as correct. DMacks (talk) 20:42, 18 July 2009 (UTC)[reply]
Actually, I'm fairly sure all of the steps above can be done knowing only the products GM and Gm. For the question being asked I don't think it is necessary to know G or M by itself. One of the reasons G is so hard to measure is that you can only get at it when comparing gravitational forces to non-gravitational ones. Dragons flight (talk) 05:00, 19 July 2009 (UTC)[reply]
Okay, so we can determine GMEarth from surface gravity on Earth and radius of the Earth, both of of which are known very accurately. And in principal we can determine G(MEarth + MMoon) from the period and semi-major axis a of the Moon's orbit. Then we subtract GMEarth fromG(MEarth + MMoon) to find GMMoon. Problem in practice is that GMMoon is only about 1% of GMEarth, so to find GMMoon to an accuracy of, say, 1% you need to know G(MEarth + MMoon) to an accuracy of 0.01%, and so you need to know the semi-major axis a of the Moon's orbit to an accuracy of about 0.003% (because G(MEarth + MMoon) is proportional to a3). In other words you need to know the semi-major axis of the Moon's orbit to within about 10 km. In a pre-spaceflight era, that seems like a big challenge. Gandalf61 (talk) 09:14, 19 July 2009 (UTC)[reply]
Yep, that's a tough measurement, and I can't think of a clever way to get it. (I can't guarantee that they didn't have one, but it seems unlikely.) I did a bit of poking around, and found that Michelson (of Michelson-Morley) and Gale did some experiments around World War I that aimed to directly measure the tidal force of the Moon from the Earth's surface. Morley did some painstaking measurements with some cast-iron pipes and microscopes, and was able to derive an estimate of the Moon's mass: [43][44][45]. The number he came up with was about 30% low, but it was a remarkable achievement given the magnitude of the effect he was measuring.
Another approach would be to try to locate the barycenter (center of mass) of the Earth-Moon system. The ratio of the Earth-barycenter and moon-barycenter distances tells you the ratio of the two bodies' masses. Unfortunately, the wobble that puts into the Earth's orbit is only about 3000 miles/5000 km to each side, and the Earth orbits the barycenter at only about 10 meters per second. I'm not sure if there's any clever way to make those sorts of measurements with pre-spaceflight technology.
Per Dragons flight below, there were of course several missions that orbited or flew by the moon years before there were actual landings; highly precise measures of the moon's mass would have been easily derived from those flights. TenOfAllTrades(talk) 13:58, 19 July 2009 (UTC)[reply]
With Newton's insights into the nature of gravity, the rough radius of the moon, and an assumption that the moon is made of rock, an 18th century scientist could get the right answer within 20% or so. More directly there were several lunar orbital missions before the lander missions, so the gravity would have been well known before any human set foot on the moon. Dragons flight (talk) 13:35, 19 July 2009 (UTC)[reply]
Yes, most likely a head of a predator. It doesn't really matter whether it looks more like a snake, a tree-frog, or a lizard; it reduces a chance of being attacked and eaten all the same. Big eyes + big mouth = danger = do not approach. --Dr Dima (talk) 00:48, 19 July 2009 (UTC)[reply]
Some research was performed on the larval markings of this species, and it was determined that the false eyes deter predators because, no matter what angle they are viewed at, like the eyes of the Mona Lisa, they appear to follow you.CalamusFortis03:08, 19 July 2009 (UTC)[reply]
Strange question, I know - but this came up (no pun intended) during a discussion of the mechanics sex in space with some cow-workers today.
Presumably, the guys on long-term space station missions have jerked off in space (probably though boredom as much as anything else) - but is it on record as to who the first guy to 'boldly cum where no man has cummed before' actually was? I'd be very surprised if NASA or the Russians hadn't asked one of their spacemen to try having a wank during a mission to see if it worked up there.
This is slightly off-topic, but why would ejaculation in weightlessness be any different than on Earth? I mean, the "internal ballistics" should be entirely the same - the neurons fire, the muscle contracts, the cosmonaut comes. There is no "gravity assist" involved :) . As for, erm, who came first - I really don't know. Sorry about that. --Dr Dima (talk) 03:02, 19 July 2009 (UTC)[reply]
Is it too much to ask for a little decorum here? Phrases like 'boldly cum' chafe my sense of decency, and I don't mind telling you. Vranak (talk) 04:41, 19 July 2009 (UTC)[reply]
Mostly likely, anyone who has masturbated in space (and I admit it's not unlikely) did so in a private, unmonitored location and does not discuss it. That said, considering that zero gravity has been simulated for films by using a jet in free fall, it is possible that someone has or could produce public pornography in a zero-gravity environment - but this would be extremely expensive. Dcoetzee08:16, 19 July 2009 (UTC)[reply]
Huh? According to our article, at least, phytic acid is found in the hulls of nuts, seeds and grains. And all of the listed sources of phytic acid are grains, legumes, or seeds. And this source referenced by the phytic acid article gives lettuce and spinach as examples of foods that are devoid of phytic acid. The question was about milk vs. leafy greens, and neither one of those contains phytic acid. Red Act (talk) 08:21, 19 July 2009 (UTC)[reply]
This article says “even when it comes to calcium, the complexes [(salts)] found in leafy green vegetables such as bok choy are absorbed more readily than those in dairy foods.” This yogurt manufacturer, not surprisingly, has a contradictory point of view. This looks like it may be one of those questions where it can be difficult to get a clear-cut, unbiased answer. To get a good answer, it will probably be necessary to stick purely to research articles, and even then check to see who’s funding the research, as it apparently is a contentious issue. Red Act (talk) 09:14, 19 July 2009 (UTC)[reply]
I don’t want to pay to see the articles I find from Google Scholar, so I’m basing a lot of this post on the little snippets I can see in the search results. But it looks like calcium absorption from most leafy greens (e.g. kale, collards, bok choy, turnip greens, mustard greens, basically anything from the brassica family) is considerably better (40-59%) than calcium absorption from milk (32%). Spinach and watercress, however, are exceptions, since most of the calcium in those is bound up as calcium oxalate. The yogurt manufacturer above, not surprisingly, only lists calcium absorption rates from spinach and watercress, and completely ignores calcium absorption from all those non-oxalate leafy greens. Red Act (talk) 10:01, 19 July 2009 (UTC)[reply]
Bizarrely, our calcium in biology article doesn’t list the calcium content of a single leafy green, even though calcium absorption from most leafy greens is better than from milk, and the article lists lots of foods with far less calcium per serving than leafy greens, according to the reference the article cites. E.g., according to the reference, a cup of cooked collards has more calcium than a cup of skim milk (357g vs. 306g)! I guess that article’s editors have an anti-leafy-green bias. Red Act (talk) 11:34, 19 July 2009 (UTC)[reply]
Reflecting light vs color
I'm shining a green laser onto flat surfaces. I know from experience that the light that reflects back into the eye is a lot dimmer on a black or dark surface. What color would reflect the green laser the best? White seems like a likely answer but what about a green surface of the same hue of the laser? -- penubag (talk) 04:50, 19 July 2009 (UTC)[reply]
If you want a very non-quantitative, crude, rule-of-thumb answer, then white would be your best bet. White reflects all or most of the visible spectrum quite well, so you have little (however, still nonzero) chance to hit an absorption spectral line with your laser wavelength. You are right assuming that green surface reflects green light better than red or blue surface; but "better" does not mean "well", and green is not a single wavelength. So I'd choose white over green if I were you. Quantitatively, on the other hand, your question is unanswerable as posed. The problem is, we only have three types of color receptors (cones) in our eye, but infinitely many distinct wavelengths in the visible part of EM spectrum. Thus, infinitely many different combination of wavelengths produce the exact same color percept in a normal healthy human. In other words, many different surfaces with different absorption spectra will look the same shade of green under the same light source. And this tells you very little about the reflection coefficient at the precise wavelengths that your laser emits. Hope this helps. --Dr Dima (talk) 05:17, 19 July 2009 (UTC)[reply]
IMPORTANT: please NEVER experiment with reflecting a laser into your eye. A reflected laser light can still damage the retina very efficiently and permanently, and some of the damage does not become apparent until much later. Just don't do it. --Dr Dima (talk) 05:23, 19 July 2009 (UTC)[reply]
Thank you very much for that answer, you explained it very thoroughly.
Is reflected light from a laser onto sheet of paper dangerous? My particular laser is a Class 3B. From the Laser_safety article, it says, "A Class 3B laser is hazardous if the eye is exposed directly, but diffuse reflections such as from paper or other matte surfaces are not harmful." My friend's laser is 10x more powerful and can pop balloons and burn skin under exposure but I never thought anything of it. -- penubag (talk) 05:48, 19 July 2009 (UTC)[reply]
You are welcome. And, regarding laser safety, Class 3B can definitely cause permanent eye damage. Reflection from a surface is not necessarily much less dangerous than the direct exposure, for two reasons. First, even when the surface looks matte, it is hard to judge by eye how much light is reflected into any direction; a significant portion of the beam may still undergo specular reflection, depending on the local surface conditions. Second, it is impossible to control all reflections; not even in the lab, and definitely not at home. In any home there always are reflective surfaces around (mirrors, windows, cups, jars, polished metal handles, your wrist-watch, etc.) and, inevitably, laser will be reflected off those surfaces and into your eyes every once in a while. So doing this kind of home experiments with a Class 3B laser is not recommended to say the least. However, it may be a very good idea for a science project, provided (1) a proper eye protection is used whenever required, (2) laser beam travels in a horizontal plane that is substantially lower than the eye-level of the shortest of the participants, and (3) no-one EVER lowers his head to the level of that plane when the power is or may be on. The reflected light level can - and should - be measured with a photodiode or a similar device, and NEVER with an eye! By the way, using a photodiode you can perform the measurements with and without an Integrating sphere to measure total reflection and specular reflection, respectively. --Dr Dima (talk) 07:18, 19 July 2009 (UTC)[reply]
firefly
Recently while walking by a graveyard a friend noted that the fireflys looked like souls rising from the graves. It did look like they moved in a generally upwards direction. Tonight I observed the flight paths of fireflys around dusk at a cook out in northern Virginia. As I watched I noticed that in general they would light up as they moved upward at least nine out of ten times. It seemed that their flight paths would involve an intentional drop in elevation so that they could rise from a near standard elevation at each lighting. To be more exact they would hover fly laterally to a point in space dip at an angle, hover, than light as they moved up ending well above their flash point and sometimes hovering before moving laterally to a new location. I don't remember fireflys doing this when I was a child in Maine; in fact I remember many fireflys lighting up as they moved in lateral directions looking like zig zags. But that was a few years back and my memory may be bad. I was wondering if anyone knew anything about firefly behavior and could explain the correlation between moving up and lighting up?--OMCV (talk) 04:57, 19 July 2009 (UTC)[reply]
