::You're speaking in terms of gravitational ''force'', not gravitational potential. Gravitational potential strictly increases as one moves out from the center of the Earth. [[User:Someguy1221|Someguy1221]] ([[User talk:Someguy1221|talk]]) 23:06, 10 April 2008 (UTC)
::You're speaking in terms of gravitational ''force'', not gravitational potential. Gravitational potential strictly increases as one moves out from the center of the Earth. [[User:Someguy1221|Someguy1221]] ([[User talk:Someguy1221|talk]]) 23:06, 10 April 2008 (UTC)
== How does this collet work? ==
Hi all,
I just got a second-hand Black & Decker rotary tool, like a [[Dremel]], which is supposed to have a "universal collet system". I'm pretty sure it has all the parts. However, I'm confused about how the [[collet]] works. On the assumption that it's the small metal sleeve with a wide head, then it looks almost exactly like the one at the bottom of the image [[:Image:MachineColletExamples.jpg|here]]. However, ''it does not have any slits in it''. It's a tube and the sides are completely solid. How is it supposed to tighten with no slits in it? I've tried putting in the "nut" part of the tool and tightening the nut, and I can still easily slip the bits that came with the tool.
Am I missing something? What is the point of a collet without slits in it?
Thanks! — Sam 23:52, 10 April 2008 (UTC)
Revision as of 23:52, 10 April 2008
Welcome to the science section of the Wikipedia reference desk.
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.
soil is conductor to electricity. and as we know as the volume of conductor increases it's resistance decreases. the earth is huge in size and contain lot of soil(which is conductor). so theoriticaly the electrical resistance of the earth should be near to zero. is the earth a super conductor ? —Preceding unsigned comment added by Shamiul (talk • contribs) 06:30, 4 April 2008 (UTC)[reply]
No. It would have to be one continuous conductor for that logic to apply. There are many insulating materials, such as air pockets, in the soil, each of which will increase the resistance. StuRat (talk) 07:13, 4 April 2008 (UTC)[reply]
No, the Earth is a poor conductor. The law that "as the volume [actually cross-sectional area] of conductor increases it's resistance decreases" is only approximately correct for long, thin wires. If the length of the wire is short in comparison with its thickness, the law stops working. The Earth is practically a sphere, not a wire at all, so the law is meaningless when applied to the Earth. If I drive two big metal spikes into the ground, one here and the other a mile away, the resistance between them will be very high. If one of the spikes is halfway around the world, there will be no measurable signal at all (at least for DC; maybe for ELF waves you could see something, but it would be quite difficult). —Keenan Pepper13:58, 4 April 2008 (UTC)[reply]
If the Earth wasn't a good conducter of electricity, it wouldn't work as a ground. Although the Earth isn't a wire, the size of it makes resistance largely based on the size of the electrodes, rather than the distance between them. — DanielLC15:44, 4 April 2008 (UTC)[reply]
DanielLC is right. The local conditions dominate the resistance between two buried electrodes. The earth resistance can be modelled as a set of concentric shells around each electrode. The inner shells have a small surface area, so they need to have a low resistivity in order to produce a low total resistance. This is why it matters where you bury the electrode. Beyond a certain distance, called the 'sphere of influence' of the electrode, the shells have such a huge surface area that even poorly conducting soil has a low resistance when summed over the shells' area. That means that if you planted two electrodes on opposite sides of the Earth, you would get pretty much the same resistance, for a given soil type, as if you planted them a hundred yards apart. The Earth is indeed used as a return conductor in some power transmission applications, but it's risky because you can set up unwanted voltage differences in the ground.
Anyway, returning to the question, it doesn't matter how big the Earth is or how big the electrodes are, the planet isn't a superconductor because it isn't made of superconducting materials. Superconductors conduct electricity in a qualitatively different way from normal conductors. You can make the resistance of a conductor arbitrarily small by enlarging the conductor, but you can't make the resistance exactly zero: only superconductors have that property. --Heron (talk) 18:54, 4 April 2008 (UTC)[reply]
As far as not being made of superconducting materials, I have to disagree. All we've got to do is cool the place down to a few Kelvin and apply a few MBar of pressure and there's enough in the crust that it just might work. Shame we wont be around to see that Furmanj (talk) 10:00, 5 April 2008 (UTC)[reply]
Good answer, Heron. It does depend mainly on the quality of the electrodes. I take back part of my answer, which was misleading if not wrong. —Keenan Pepper05:14, 5 April 2008 (UTC)[reply]
"The earth resistance to the current, compared with that of a long line, is next to nothing," [1] per Chambers's Encyclopedia,(1883) p438. The resistance is basically that of the grounding electrodes, so that a large and deep electrode, or multiple long ground rods in parallel, or one consisting of the water mains of the town lowers the resistance between the ends of the circuit far lower than any practical metallic conductor connecting two distant points. The earth is not a superconductor, but with its numerous parallel conduction paths it can be a very good conductor for the earth return used with long metallic single conductor circuits. Edison (talk) 00:47, 5 April 2008 (UTC)[reply]
rube goldberg machine
I'm going to be building a Rube Goldberg machine. The chain will be initiated by a falling domino and the 'objective' of the machine is to have a marble hit a domino at the end of the whole process. Can anyone give me some ideas on what to build? --hello, i'm a member | talk to me!06:34, 4 April 2008 (UTC)[reply]
The simplest design might be to have a row of dominoes hit a marble hanging on a string which then strikes the last domino. Add complexity from there. StuRat (talk) 07:19, 4 April 2008 (UTC)[reply]
At one stage you could whisk aside a curtain to reveal a picture of Hillary Clinton taking the oath of office, which scares a Tasmanian devil so badly that it runs down a plexiglass pipe to the other end of a seesaw. --Milkbreath (talk) 10:23, 4 April 2008 (UTC)[reply]
My suggestion is to look at the sorts of things that other people have built, and take inspiration from there. I believe that there are a number of Rube Goldberg competitions, some of which get very "creative". You can also alway find examples on video sharing sites (YouTube, Google Video, etc.) -- 128.104.112.85 (talk) 15:48, 4 April 2008 (UTC)[reply]
In the very crude movie "Waiting", in the restaurant that they work in is a really neat Rube Goldberg contraption on their wall. Every now and then in the film they show parts of it, but at the very end after the credits, they show it work. An empty glass is put on a plate that starts the contraption going. In the end, a bottle of beer is poured into the glass. You might consider renting that movie and look at some of the events. But, I will warn you again, the movie is very crude.--Wonderley (talk) 08:05, 7 April 2008 (UTC)[reply]
Papadums
When I cook commercially made papadums in the microwave, it takes 30 seconds for three, 40 seconds for four. But if I put one in, it needs 15 seconds. What's the reason? Julia Rossi (talk) 07:39, 4 April 2008 (UTC)[reply]
Perhaps something else (the glass plate or whatever container is in the microwave) is heating up as well. Or it could be rounding error. – b_jonas09:05, 4 April 2008 (UTC)[reply]
The magnetron that is the heart of the microwave oven is a vacuum tube and like most vacuum tubes, it includes a heater that must heat up before thermionic emission of electrons can begin inside that vacuum tube. This takes several seconds. So during those first few seconds while the heater itself is warming up, electrons aren't flowing in the magnetron tube so no microwaves are being generated so the oven isn't doing any cooking. If you listen carefully as the microwave oven starts operating, you'll often be able to hear its sound change as the heater reaches operating temperature. Because it is only at this point that the microwave oven starts drawing a lot of power from the power line (mains), you may hear:
The hum of the oven increase
The cooling fan, stirring fan, or turntable motor slow down a little
The famous "incinerate a CD" experiment will provide a very-dramatic exhibition of this effect.
Proventil is a Beta2 adrenergic agonist. It is not a class of drugs considered to be resistance-building in the human body. However, there are concerns with long-term use in asthmatics, a fear that they may make asthma uncontrolled. A quick Google search on Beta 2-adrenergic agonists "long-term use" will surely turn up a few studies on the subject. -- kainaw™15:28, 4 April 2008 (UTC)[reply]
Humans surviving in space
Can humans survive in an area of space where we se massive amounts of dust forming new suns?
As long as they're not too close to one of the stars and in a space-suit or ship, then I'd expect so. I think gamma ray and x-ray bursts occur when stars die, not when they form, so that should be OK. You wouldn't want to be moving too fast relative to the dust, or that could damage the space-suit or ship, which would be needed to provide air, water, food, and regulate the temperature. Although, for temp, you could probably find an ideal location where light from the star(s) would provide just the proper amount of heat, but you'd still need to distribute the heat from the part facing the star(s). StuRat (talk) 14:13, 4 April 2008 (UTC)[reply]
Google Scholar offers a list of citations. For this article, check [4]. Unfortunately, no citation is listed so far. This is not too surprising for a 2007 article, though. --Stephan Schulz (talk) 15:45, 4 April 2008 (UTC)[reply]
After reading the article about heavy water, I was intrigued and would like to do a photography shoot of heavy ice cubes that sink, not float, in water. But where can I get heavy water? Is it available for sale somewhere? JIP | Talk15:27, 4 April 2008 (UTC)[reply]
It should be available from most places which sell isotopic materials to scientific researchers. For example Sigma Aldrich sells it (as deuterium oxide) for about $1/mL (Enough water to get a couple of ice cubes should cost you under a hundred bucks). Be advised, however, that due to it's potential use for nuclear purposes, there may be (I can't say for certain) extra regulatory hurdles to jump through before they will sell it to an average person off the street. -- 128.104.112.85 (talk) 15:37, 4 April 2008 (UTC)[reply]
You'd need tons of the stuff to use it for real nuclear purposes. Not to mention a few other things as well. I'm pretty sure that in the amounts he is talking about there are not even export restrictions. --Captain Ref Desk (talk) 14:44, 6 April 2008 (UTC)[reply]
(ec) You can order it from just about any large chemical supply house. Sigma-Aldrich sells 99% pure deuterium oxide for about one U.S. dollar per gram (plus shipping). I don't know if it's possible to have chemicals – even harmless ones like heavy water – delivered to a residential address; you may need to have it delivered to your workplace, or even have a friend in a chemistry or biology lab buy it for you. For what it's worth, you don't need to worry about any nuclear safety regulations; it's non-radioactive and not regulated in any special way. TenOfAllTrades(talk) 15:43, 4 April 2008 (UTC)[reply]
$1/mL seems like a high price to pay for 99% pure deuterium oxide. United Nuclear offers 20 mL of Ultrex grade, 99.999% pure heavy water for $17. There's nothing to indicate that they don't ship to individuals, so the same should be true for other chemical dealers. Obviously try to find a local store to avoid paying shipping and handling costs, but the price should be less than $1/mL for 99% pure heavy water. --Bowlhover (talk) 00:36, 5 April 2008 (UTC)[reply]
Sorry, I misremembered the page and thought it used mL. Since the Sigma-Aldrich price was cited in dollars per gram, however, the conclusion of my post is still true. --Bowlhover (talk) 02:40, 5 April 2008 (UTC)[reply]
And don't forget to do the opposite too: a chunk of normal ice or some other almost-as-dense-as-water object floating in normal water, and then the same object floating in heavy water. --Anonymous, 22:07 UTC [Insert joke here about daylight saving being "heavy time"], April 4, 2008.
United Nuclear doesn't sell outside Merka. I'll try my chances at Sigma Alrdich though, as they already seem to have sales offices in Finland. For $100, I could get apparently get a whole decilitre of heavy water, which would make for many heavy ice cubes. I'm already starting to design pictures of cocktails with the ice at the bottom of the glass, not at the top. JIP | Talk18:41, 6 April 2008 (UTC)[reply]
The Finnish Wikipedia referred me to Onemed Group. I asked them, and the reply was that they don't sell to private persons. I could try that Sigma-Aldrich place but I'm beginning to think I won't have much luck there either. Damn, this stuff is difficult to get hand of. I'd understand it if I were trying to buy tritiated (super-heavy) water, which I understand is extremely dangerous, but normal heavy water shouldn't be. JIP | Talk17:42, 10 April 2008 (UTC)[reply]
The first image is an example of backlighting: two colored lights behind a set of test tubes filled with water. The second image (the computer keyboard) is probably lit by two diffuse light sources (umbrella reflectors or similar): a blue light above the object, and a yellow light to the left. --Carnildo (talk) 20:38, 4 April 2008 (UTC)[reply]
I'm in the UK and while watching a recent documentary regarding Steven Hawking and the latest 'string theories' my partner asked me a simple question and I was stumped. My partner is in no way a scientist and questioned, 'So is this fact or just what people think?'. Can any model of the universe be proven as factual or is it just mathematical modelling? This question may seem silly to the scientists out there but I regret I am not one of them. I teach six year olds! Thank you for your wisdom! Kirk UK —Preceding unsigned comment added by 88.144.9.132 (talk) 00:09, 5 April 2008 (UTC)[reply]
It's a theory. Mind you, that doesn't mean it should be dismissed easily. Theories have been tested and found to accurately model what we know of the universe, and Hawking's theories are no exception. String theory on the other hand is mostly just a mathematical model. The term "theory" is more of a cultural attachment than a scientific appellation, because string theory requires some rather wonky things to be true for it to work. And we don't have the capacity to test those things right now, so it's more of a "string hypothesis." It's mathematically sound, but not necessarily accurate. -- Kesh (talk) 01:33, 5 April 2008 (UTC)[reply]
The easiest way to think of the difference between facts and theories is that facts are simple bits of data about the natural world, whereas theories are explanations about the natural world. An example: it is easily observable that a ball dropped from your hand on Earth will fall towards the ground. This is a fact. The reason for this is the theory. Isaac Newton would have said that the mass of the Earth itself exerted a force on the ball, pulling it to the ground. Albert Einstein, by contrast, said that the mass of the Earth deformed spacetime in such a way that towards its center was the path of least resistance for the ball. Two very different explanations of the same phenomena; two very different theories.
Any model of the universe will be a theory by definition. It is a model. It is not the sort of thing that is a "fact", a small piece of data. This is not a problem. Facts are not "proven" theories, facts and theories are two totally different categories of information.
Einstein's Special and General Relativity are both theories. Newton's theory of gravitation is, as the name implies, a theory. Darwin's idea of natural selection as the engine of evolution is a theory.
Is String Theory a theory? Well, it wants to be a theory. Is it really one? Scientists and philosophers disagree. Some don't even think it is a theory because there isn't any way it can currently be proven incorrect. If an explanation about the natural world cannot be tested—proven right or wrong—then it is not a scientific theory. For example, instead of Newton or Einstein's theories I could just as easily say that my theory of why the ball falls is because there are invisible, intangible fairies who carry the ball to the ground. It's a theory that perfectly accounts for any phenomena that one might see. But that's the problem: you can't do anything to test it, you can't possibly prove it wrong. As such, you cannot distinguish between my theory and Newton's theories when it comes to which is more correct. So this is not science. You can distinguish between Einstein's and Newton's theories—they give different experimental and observations predictions in some cases, and indeed it turns out that Einstein's theories perform better than Newton's.
So anyway, back to String Theory. It's very dubious whether it can be truly tested at the moment. At the moment we have no way of distinguishing between a universe run by String Theory and a universe run by the Standard Model of physics. Someday fairly soon we will be able to test some aspects of some variations of String Theory, but even if those tests come back negative they won't really distinguish between String Theory itself and anything other than String Theory. There are some highly imaginative experiments with tools we do not have and may never have that could test String Theory, but given that they are not real options it's not clear that they count towards the philosophical question. Anyway, it's an active question.
Sorry to lecture; your question seemed to me to have two questions in it (what is the difference between fact and theory, and is String Theory a theory). I tried to be clear but not condescending, maybe I have been successful, maybe not... --Captain Ref Desk (talk) 01:58, 5 April 2008 (UTC)[reply]
Hello all.
I am looking for a site which has detailed descriptions of new(est) technology in the field of recycling the water used by train washing machines. I have looked, but been unable to find anything useful.
Thanks in advance for any help.
Are you sure that trains actually have washing machines ? I would think that the expense of hauling around the washing machines, dryers, and water would be prohibitive. For things like towels and bedding on sleeper trains, they could instead drop off dirty laundry and pick up clean laundry at each station. That's how I'd do it if I ran a passenger railroad. StuRat (talk) 13:52, 5 April 2008 (UTC)[reply]
In the railway business they refer to them as 'Carriage Wash' machines, you might try some heavy duty railway company like GEC.
Gauge to track relative movement
Does anyone know a name for the type of gauge shown in this image? Do we have an article on it?
The device is intended to track the relative movement of two objects (in this cases, two parts of a wall that has split apart). I think most of us who live in earthquake zones have seen a few of these; I imagine that they must also be used for buildings that are settling unevenly in other contexts as well.
Feel more than free to edit the description on Commons and add any appropriate categories: this is one of those cases where having snapped the photo does not mean I know a lot about the topic at hand. - Jmabel | Talk05:08, 5 April 2008 (UTC)[reply]
They are all over downtown Charleston. The engineers and insurance companies properly call them strain gauges. -- kainaw™17:59, 5 April 2008 (UTC)[reply]
Admittedly I only know what I can find on the web, but everybody seems to call them crack gauges, tell-tales or something similar: [7][8][9][10][11][12]. There is exactly one example of the name "mechanical strain gauge" being applied to the thing we are talking about, and that's on Wikipedia. Everywhere else, the latter term seems to mean either a linear displacement gauge with a dial or a penis-measuring device. --Heron (talk) 10:28, 6 April 2008 (UTC)[reply]
I would object to calling it a "strain gauge" as 1) that's a well-defined term for an electrical sensor and 2) the gadget in the picture isn't measuring strain; once the object under test cracks, there's no strain left, just a variable displacement.
They measure strain on a foundation as a crack widens. I have always assumed that is why the insurance paperwork refers to it as a strain gauge. It could simply be that they don't want to use common terminology because legal paperwork is specifically designed to be unreadable for those who aren't "in the know." -- kainaw™23:59, 6 April 2008 (UTC)[reply]
Like I said, once the object under test fails (in this case, the foundation cracks), the strain is no longer defined.
Calling it a strain gauge is at least a little confusing because there is another device that is more well known as a strain gauge (an electro-mechanical device that measures strain). Any articles on these two different things should make it clear that there is another thing that might go by the same name. ike9898 (talk) 13:38, 8 April 2008 (UTC)[reply]
Sifting flour
A British recipe for pancake (thin compared to the American variety) calls for me to sift the flour to "air" it. Later, it has me stirring in eggs, milk and water. Is there going to be any of the original air left after all that whisking? Will the air-content of the batter be any different depending on whether or not the flour is sifted? Wont the liquid displace any pockets of air between the flour grains? ----SeansPotato Business15:41, 5 April 2008 (UTC)[reply]
Sifting of flour is superfluous with modern, high-quality flour stored properly. Originally, sifting was used to get out all kinds of undesirable stuff, and to break up clumps sticking together due to humidity. Just use flour out of the package, unless you like the ritual (it makes a nice, even mound of flour ;-). Be aware that most European flour is plain, i.e. not self-raising. Self-raising flour will make very different pancakes (though they can be nice as well, of course). --Stephan Schulz (talk) 16:43, 5 April 2008 (UTC)[reply]
Sifted flour will be slightly less dense, which matters in the U.S. where people measure out so many "cups" (8 fluid ounces) of flour. It would make little difference in the rest of the world where people measure so many grams of flour. Edison (talk) 19:34, 5 April 2008 (UTC)[reply]
Yes, this is important. See Hausner ratio. If the recipe was written for measuring without sifting and you want to follow the recipe closely, you'll probably match it better by not sifting. Measuring is more important in baking than it is in some other types of cooking, for a variety of reasons. ike9898 (talk) 19:40, 7 April 2008 (UTC)[reply]
Most American flour is also non-self-rising. I think self-rising flour is only common in the South, where it is used for biscuits. -- Coneslayer (talk) 19:36, 5 April 2008 (UTC)[reply]
Also, just because flour starts out lump-free at the factory doesn't mean it always stays that way. It could get a few drops of water in it that form lumps (say if the scoop used to get the flour was just washed). Or, even worse, it could have bugs in it (living or dead). I'd rather find this out when sifting than when I bite into one. StuRat (talk) 01:50, 6 April 2008 (UTC)[reply]
A useful pancake tip: If you want light, fluffy pancakes and the recipe calls for water, use seltzer instead. The carbon dioxide in the seltzer will come out of solution and make for lots of tiny gas bubbles in your batter.
When making British pancakes, light and fluffy isn't really relevant. In fact, adding more air bubbles is just risking holes that will drip lemon juice :) English pancakes are sort of halfway between crepes and American pancakes, which are closer to scotch pancakes or dropscones. 130.88.140.121 (talk) 13:01, 8 April 2008 (UTC)[reply]
Blood vessel cells
Not a homework question; do the cells of the blood vessels obtain oxygen and nutrients from the blood the vessels are carrying or do the veins and arteries have their own circulatory system as the heart does?--TrogWoolley (talk) 21:34, 5 April 2008 (UTC)[reply]
I am in a play "The Farmer's Daughter." In the show, a girl makes a drink called Glug. Before giving it to me she pulls a fireplace poker out of the fireplace, and puts it in the drink.
In the movie, the drink flames and goes out. That would be a pretty neat trick. Does anyone know how we could pull this off? Keep in mind there is no fire in the stage fireplace and I have to be able to drink this beverage.
For the drink, water with a little bit of pure (or 80%) ethyl alcohol very carefully poured on top might do it. If the alcohol is warmer, it might lie on top of the water for a while before mixing. To get the fire, hide an electric sparker in the tip of the poker and a trigger in the handle of the poker. Have a stagehand with fire extinguisher ready and waiting if you try this live or in rehearsal and make sure your costume isn't flammable. Franamax (talk) 02:09, 6 April 2008 (UTC)[reply]
Flaming liquids sound rather dangerous to me, both to the actors and the audience if it starts a general fire. Perhaps some type of lighter, set on high, hidden on the far side of the glass, could create enough of a flame without being so risky. StuRat (talk) 02:23, 6 April 2008 (UTC)[reply]
Whatever you do, the key word here is safety, safety, safety. Applause happens once, burn scars are forever, fire deaths last longer. From the video clip (which we all assume you obtained copyright release for): watch the actress hand, her grip is curious; she dips deliberately into the cup as if to contact something, then pulls back a little, then removes the poker; the cup is opaque; the scene ends, as all movie scenes do. No way to tell what happened there, I'd guess a pilot light in the cup, she pushed a trigger to open the main gas line, then the key grip guy shut the gas off. Did the drinker actually drink anything? Did the cup get subbed in for the next take? There could be a whole lot missing where the entire set went up in flames. Safety, safety, safety. Franamax (talk) 07:26, 6 April 2008 (UTC)[reply]
Any "high-proof" liquor will burn (because of the included ethanol). The problem is that the alcohol fire is practically invisible under the stage lights. You might find that doping the drink with table salt (sodium chloride) will produce visible flames. That's basically what I did once when a production needed two flaming brazier-style lights (although nobody was going to drink from the braziers so I used straight alcohol, probably (poisonous!) methanol). Today, though, I'd probably fake it with streamers, fans, and lights (for reasons of safety). Heck, if it only has to flame for a few seconds, you could probably design that same streamers/lights/fan mechanism into a cup and power it with NiCd batteries; LEDs can be very bright with very little power and a brushless DC computer fan draws almost no power either.
It should be clear by now that this was not an appropriate question for the
Reference Desk: if you're going to have a fire on the stage, you'll need a
professional stage effects person, and not advice from random people at
Wikipedia. --Anonymous, 20:56 UTC, April 6, 2008.
Anonymous, if I got bad advice, I wouldn't use it. Flaming drinks and food are not uncommon. I was just getting ideas that maybe I had not thought of for the drink and the ignition source. Suggestions like adding table salt to make the flame more visible makes the stunt safer. Not drinking beverages with a skull on the bottle's a pretty good idea too. ;-) So, it seems pretty appropriate to me. But thanks for your concern.
Franamax, I didn't exactly obtain a copyright release, but the trailer on the TCM web site has a "Embed this video on your site" button, so I assumed it was OK.--Wonderley (talk) 23:33, 6 April 2008 (UTC)[reply]
As far as I'm aware, 'embed this video on your site' usually refers to code which allows you to embed the hosted video on your website. It should not be taken as allowing you to redistribute the content by hosting it on your own website. You may very well be allowed to redistribute the trailer but the information at hand isn't enough to say you are Nil Einne (talk) 15:46, 7 April 2008 (UTC)[reply]
Yeah, Einne. "Embed this video on your site" usually refers to code which allows you to embed the hosted video on your website. And, that's what I did. I don't know why you might even think otherwise.--Wonderley (talk) 18:58, 7 April 2008 (UTC)[reply]
I didn't actually check out your site, but was going from what I read by you and Franamax which made it sound like you thought it was okay to host video on your site because there was an 'embed this video' link on the original site. I apologise for any confusion Nil Einne (talk) 12:43, 8 April 2008 (UTC)[reply]
I don't know, but it seems to me that for the East African sp. it is some kind of communication. They do it with each other, and they do it when not on their home territory. kwami (talk) 04:43, 6 April 2008 (UTC)[reply]
Thank you Kwami, it makes sense - just that it's seems unusual for a bird to flutter and wag constantly, though it is low-key. And strange that the article doesn't comment on it's namesake feature. Julia Rossi (talk) 08:56, 6 April 2008 (UTC)[reply]
The reasons for the behaviour are actually slightly unclear although a recent study suggests that it signals vigilance to potential predators. I have updated the article and linked to the study. As for the article not having it before, well, there are lots of birds and I assure you WP:BIRD is flat out trying to improve them! Sabine's Sunbirdtalk02:38, 10 April 2008 (UTC)[reply]
mental capacity
Is there a test which rates mental capacity on the basis of reducing to minimum form a logical equation having a certain number variables and states? 71.100.173.69 (talk) 06:54, 6 April 2008 (UTC)[reply]
No. Tests for mental capacity are designed so that they can filter out something like "innate capabilities" from "learned abilities". In your example, a genius who has never taken algebra would probably rate as a dullard based on lack of experience with the formalities alone. --Captain Ref Desk (talk) 14:30, 6 April 2008 (UTC)[reply]
The cream (fat) is actually more valuable than milk. Cream normally comes in smaller containers, but you might find some overlap, like a 1 quart container, so you can compare prices in the store. You'll also notice that skim milk is often a bit cheaper than whole milk. StuRat (talk) 02:41, 7 April 2008 (UTC)[reply]
Ice cream! Many processed foods include some sort of fat; you don't see butterfat too often, partly because it is relatively expensive. The expense suggests to me that there is no great surplus of butterfat. ike9898 (talk) 19:29, 7 April 2008 (UTC)[reply]
Future costs of photoelectric cells?
Will photoelectric cells become cheap enough to cover the walls and roof of my house with, or will the price always be high because they contain some rare element? 80.0.106.237 (talk) 19:44, 6 April 2008 (UTC)[reply]
They don't contain any 'rare' elements, per se... the silicon that is used in the majority of terrestrial solar panels can be found in sand. However, there are huge energy and cost barriers needed for processing pure silicon and making solar panels. The energy cost takes about twelve years of average use to recoup. As for cost, I estimated that it would take me ~30 years to recover the costs of installing solar panels on the roof of my house. This may be different depending on where you live (I'm from Rhode Island... sun can be limited in the winter). I know that in California they are topping a lot of department stores with panels to combat peak energy-use times (such as the summer). I also think the technology is improving every day, so solar panel housing may not be far off! --138.29.50.28 (talk) 23:25, 6 April 2008 (UTC)[reply]
Energy returned on energy invested (EROEI) is poor only for monocrystalline and polycrystalline silicon solar cells. For amorphous silicon or thin film solar cells EROEI looks much more promising. Keep a eye open - they are going to hit the mass market in the next few years. Cambrasa18:40, 11 April 2008 (UTC)[reply]
Current solar cells also suffer from the problem that they only use a small portion of sunlight's frequencies. We need solar cells that convert the entire optical range (and infrared and ultraviolet light) into electricity. This will hopefully allow the energy used to produce them to be more quickly recouped. StuRat (talk) 02:45, 7 April 2008 (UTC)[reply]
A search using "production doubles price photovoltaic" gives opinions that when the production of solar cells doubles, cost drops 18-30%. The source I listen to uses 20-30%.Polypipe Wrangler (talk) 10:21, 7 April 2008 (UTC)[reply]
When I did a research project on silicon solar cells, I remember reading somewhere that they have followed Moore's Law just like CPUs for the last 30 years, except that the time it takes to halve the price per unit of power generation is much longer - namely 8 years instead of 18 months. I think yes, solar cells will probably one day be cheap enough to compete with electricity generated from power plants. But it might take another couple of decades.
The rare element issue isn't always the bottleneck - exotic elements used as dopants and transparent conductors are only needed in tiny quantities. And even non-silicon cells such as CdTe cells can be easily recycled. Cambrasa18:46, 11 April 2008 (UTC)[reply]
How small can computers get in the future?
I've decided to ask this here rather on the Computing Desk as it is more about physics than software. Soon, I hope, computers will be able to use human speech as their input and output, doing away with keyboards and screens for some applications. Will it then ever be possible to have computers, with the equivalent power of a laptop, that are small enough to fit on a keyring? And how small could the talking thinking computers of SF films be in actuality in the future? I'm thinking about the limits to the smallness of microchips, and would quantum computing be smaller? Thanks 80.0.106.237 (talk) 20:02, 6 April 2008 (UTC)[reply]
We can already make a computer that is as capable as a laptop but that will fit on a keyring. (cell phone)
We have had competent speech recognition on home computers for fifteen years
We have had speech output for longer that that
The theoretical limit on information storage is the Bekenstein bound. We are many orders of magnitude away from it
The "practical limit" of achievable size reduction and speed increase is ten years in the future, or appoximately a 32-fold improvement from our existing capability. This has been true since 1950. In 1950, the limit was to be reached in 1960. In 2008 the limit is to be reached in 2018.... See technological singularity.
I have to disagree on us having had competent speech recognition for 15 years. I would define "competent" as being as good as the average human. I don't know of any speech recognition software that can understand a 100,000 word vocabulary, in a nosiy room, without first being trained to an indivual's voice. When they can do that, I'll call them competent. StuRat (talk) 02:36, 7 April 2008 (UTC)[reply]
I think I'll stay with the keyboard regardless. It's a faster way to input (when you know how to type) than speech, and nobody has to know what I'm doing. And it's bad enough that people blab on and on to their cell phones in coffee shops—imagine if they were all blabbing to their computers (and their computers blabbed back)!
In any case, note that you don't necessarily need to miniaturize everything. If you came up with fast, secure, and cheap wireless interfaces, you could have a tiny thing in your ear that just interfaced with the central computer. It becomes a communications issue, not a processing one. This is featured in many SF movies and books, too (the second book of the Ender's Game series comes to mind). --Captain Ref Desk (talk) 23:53, 6 April 2008 (UTC)[reply]
Computers will get smaller, faster, and more capable as they become more refined to specific purposes. Similar to object-oriented software design, computers will begin to take on specific tasks while communicating with one another. Why have a clock in your cell phone when your watch does that job just as well? Why have a camera lens in your phone when it can be in your glasses, already pointed at what you want to photograph? Why have a phone in your pocket and a earbud on your ear when the earbud can handle all the call-placing tasks itself? In the future, we'll wear a network of mini-computers without thinking of them as anything more than helpful gadgets. The idea of a computer that does a million different tasks will be abandoned for the average person. In fact, many people don't like them already. -- kainaw™01:45, 7 April 2008 (UTC)[reply]
Have you read our article on Moore's Law, and its section on the limits? You're right to think about limits in the size of semiconductor microchips. At a lecture I attended on quantum computing, it was suggested that technology is approaching the size where quantum tunnelling of electrons will become an issue. As for quantum computers, it's hard to say as no-one has come up with a way to do everything a computer needs to do. The first steps which are being taken are pretty big though, as they often need lots of vacuum and/or optical equipment. AlmostReadytoFly (talk) 08:54, 7 April 2008 (UTC)[reply]
I am doing a science project about whether a helium filled football or an air filled football can be thrown further. Do you know how or where I can go to get helium inside of a football?70.18.162.125 (talk) 20:22, 6 April 2008 (UTC)CD[reply]
I'd start with party-supplies places. If they can inflate a balloon with helium, they may be willing and able to inflate a football. I say "may be able" because I don't know if there will be problems connecting a football to the tank.
Some issues:
The gas used in party supplies may not be pure helium. It only has to be light enough to make a balloon rise, and diluting it with a heavier gas light nitrogen may make it cheaper.
Helium leaks out of things faster than air does, because the atoms are so small. So you'll want to take the football directly from the place where you get it filled to the place where you want to throw it.
I would expect the difference will be too small to be meaningful. (Even if so, that doesn't mean the project is a bad idea! If you prove there's no significant difference, you've still proved something.) A well-designed experiment would involve plenty of throws with each ball, and statistical analysis such as a chi-squared test to determine whether the differences are significant.
If the same person is throwing the ball several times, they will get tired, or they will first get more warmed up, and then get tired. So you don't want to do something like 5 throws with air followed by 5 with helium. Use an alternating pattern or something like ((air, helium, helium, air), repeat as many times as desired).
For the same sort of reasons, if different people are throwing the ball, have half of them do air first and half do helium first.
Have fun. --Anonymous, breathing air, 21:11 UTC, April 6, 2008.
I agree with the above comments, but also suggest that you not tell the person throwing the football which version he has, as that may affect his throw. StuRat (talk) 02:29, 7 April 2008 (UTC)[reply]
Are there any documented cases of people regenerating limbs (or digits) that they've lost? I know that this is generally impossible, but my impression (IANAD) is that medically impossible things do happen sometimes, and our species certainly has a long history with amputation. 71.239.209.220 (talk) 20:36, 6 April 2008 (UTC)[reply]
Our article on Regeneration (biology) has some (imperfect) sections on regeration of human organs and fingertips, the only extremeties observed to regrow. It says what is basically true, that there is evidence children have the capacity to regrow lost fingertips, although there is more or less anecdotal evidence this can occur in adults as well [14]. Someguy1221 (talk) 22:36, 6 April 2008 (UTC)[reply]
Homemade Water Filtration?
How can I filter blue food colouring out of water using a homemade filter? I do not have access to activiated charcoal. Are there other materials that are as effective at cleansing water? Thanks, Perfect ProposalSpeak Out!21:22, 6 April 2008 (UTC)[reply]
Can you make charcoal by burning wood or toast. If so you can make activated charcoal. Another way to do it is by fading. Intense focussed sunlight will bleach your blue colour. I am assuming that your blue will not be easy to chemically alter to a clear substance. Indigo can be reduced to white. Some you can bleach with chlorine bleach. Graeme Bartlett (talk) 21:29, 6 April 2008 (UTC)[reply]
You might end up with a big pile of soggy blue paper and no liquid! Graeme Bartlett (talk). In the natural world water is purified by bacteria, and other living things consuming the organic matter. Distillation will do a pretty good job too. 05:42, 7 April 2008 (UTC)[reply]
Some manner of solar still might be the easiest solution. It is a bit slow, however, so may be impractical if you've got large amount of blue water you need to process. There are ideas on that and a few other homemade filters in the Steampunks' Guide to the Apocalypse, I don't have a huge amount of faith in that source, but if you're just looking for ideas, it's worth a look. APL (talk) 14:13, 7 April 2008 (UTC)[reply]
In case you didn't know, it is really easy these days to get activated charcoal. Most pet stores will carry it in the fish section (used for treating aquarium tank water) - although I wouldn't recommend using it for food use. Alternatively, you can probably find some in camping/outdoor supply stores. However the easiest method is to just buy a Brita style water filtration cartridge from your local grocery store. Most of the drinking water filters use activated charcoal to remove impurities. -- 128.104.112.85 (talk) 20:24, 8 April 2008 (UTC)[reply]
If the challenge is to do it without activated charcoal, one strategy we use in the lab to soak up stains doing gel electrophoresis is to use a wadded-up tissue placed in the corner of a soaking tray. The tray is slowly rocked back and forth, and in an hour or so the tissue soaks up a considerable amount of the blue dye. Jeff Dahl (Talk • contribs) 23:24, 8 April 2008 (UTC)[reply]
A uniform surface charge density of 20nC/m2 is present on the spherical
surface r=0.6 cm in free space.
a) Find the absolute potential at P(r=1cm, θ=25°, φ=50°).
b) Find VA-B (potential difference between point A and point B) given points
A(r=2cm, θ=30°, φ=60°) and B(r=3cm, θ=45°, φ=90°). —Preceding unsigned comment added by Yabadapado (talk • contribs) 22:21, 6 April 2008 (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. Someguy1221 (talk) 22:30, 6 April 2008 (UTC)[reply]
One way to approach this is to work out capacitance of the sphere and then calculate the voltage on the surface for the chargd. There would be other more direct ways to work it out however. Graeme Bartlett (talk) 05:50, 7 April 2008 (UTC)[reply]
Are there any indoor plants that do well in inner spaces without much light ? (like halls that are a bit dark and gloomy with no window). Thanks for any info. --AlexSuricata (talk) 22:42, 6 April 2008 (UTC)[reply]
Ferns are probably not a good idea, because they need more humidity than is usually found in homes. Other good low-light house plants include philodendron (many types, trailing and bushy), spathiphyllum (peace lilies), aglaonema (Chinese evergreens), dracaena (many types), sansevieria (snake plant), polyscias, Kentia palm (Howea forsteriana), parlor palm (Chamaedorea elegans). I agree, however, that if there are no windows at all, you can't grow anything. I suggest that you buy at least two plants of the same type and then rotate them from dark to semi-dark locations. I would switch them around at least once a week, preferably every few days. That way you can have lush plants everywhere in your house. This is something I have done successfully for years.--Eriastrum (talk) 20:19, 8 April 2008 (UTC)[reply]
My neighbor has a very annoying dog. Specially when the dog is alone it is very loud. I thought I could buy a dog whistle to 'train' the dog so it can let me alone. As it starts to bark I could blow the whistle as loud as I can. Does this training method will work? 217.168.3.246 (talk) 00:08, 7 April 2008 (UTC)[reply]
It would have to be loud enough to bother the dog. I suspect that dogs have far more tolerance for loud noises and vocal strain than we do. Therefore, you would get tired of blowing the whistle long before the dog would shut up. Perhaps some type of automated system similar to an air horn could work, where you just press a button and it sends out a deafening sound at dog-ear frequencies until he gets the idea and shuts up. Of course, other dogs in the neighborhood will also be affected, and may actually start barking as a result. You'd need to aim the horn right at the target dog to try to limit this side-effect. I'm assuming the dog is left outside, I can't imagine this having the desired effect on a dog inside a house.
At this point I should probably point out that these While E. Coyote schemes are less likely to work than just informing your neighbor politely of the problem. Perhaps then he would leave the dog inside the house where it can hopefully bark until it's throat bleeds without bothering you. StuRat (talk) 03:06, 7 April 2008 (UTC)[reply]
Dog whistles seems to be both capable of attracting dogs and inflicting pain. On the contrary, a dog's hearing is more sensitive than a human's. That is why they get scared easily by fireworks as they would sound like grenades to them. My dog almost hanged herself in her leash during the New Year celebration. Anyways, I think inflicting pain to the animal to make it get the point is a bad idea. As StuRat said, it is better to inform your neighbor about the problem--Lenticel(talk)09:36, 7 April 2008 (UTC)[reply]
To actually get the dog to behave (versus just locking it in a sound-proof room), you probably would need to use pain, or at least discomfort, in some form. The use of a choke collar is one technique used in obedience schools, for example. This may seem cruel, but if the alternative is to put down a dog that just won't behave properly, isn't a brief period of pain a better choice ? StuRat (talk) 14:01, 7 April 2008 (UTC)[reply]
Choke collars don't actually choke the dog—a dog's esophagus is in the middle of their neck, and is well insulated from such a collar (unlike a human's neck). They just add a lot more control to the collar. Pain and discomfort play a minor role in training; usually it is based around rewards. And there are usually more alternatives than putting down the dog because it doesn't behave "properly" in minor ways. In any case, you should not try to inflict pain and discomfort on someone else's dog—it's a bad idea, and it's possibly illegal. --Captain Ref Desk (talk) 15:21, 7 April 2008 (UTC)[reply]
I can't think of a way to train dogs not to bark by giving them a reward. If they are silent and you reward them, how would they know they are being rewarded for their silence ? On the other hand, if they experience pain or discomfort each time they bark, they could likely figure that link out. StuRat (talk) 01:44, 8 April 2008 (UTC)[reply]
Dogs, like most animals hate getting soaked. A sudden downpour or even the threat of a good soaking can sometimes divert the attention of a dog away from whatever is making it bark. A perimeter can be established using agricultural, landscape or golf sprinkler heads, which typically have ranges of 30 to 50 feet or more. Neighbors will usually complain that your water is crossing the property line and landing on their property. When the neighbor complains simply ask if the rule of not letting water cross the property line applies to sound as well. If the answer is "yes" then an agreement may be possible to eliminate the cause to the water crossing the property line. If the answer is "no" then complaint should be ignored until the answer changes to yes. (Disclaimer: This is not legal advice.) Mimus polyglottos (talk) 13:11, 7 April 2008 (UTC)[reply]
Most cities have rules about dogs barking too much. Bark collars are effective and not cruel as far as I know. They're certainly less cruel than sending a dog to the pound for annoying the neighbors too often. I use one for one of my beloved dogs who loves a good yap. I would definitely avoid any solution where you're molesting the dog in any way, as that could lead to a conflict where you're in the wrong. --Sean13:59, 7 April 2008 (UTC)[reply]
I think that's why he wanted to use a "silent whistle", so he can molest the dog privately, without triggering the wrath of the owner. There is some president for using such sounds on humans for this effect, such as the Mosquito, an annoying high-pitched sound that only kids and teenagers can hear, which keeps them from congregating in businesses' parking lots and scaring off customers. StuRat (talk) 14:06, 7 April 2008 (UTC)[reply]
The difference there is that the teenagers can easily leave the (presemuably private if the sound is coming from a private device) area. However the dog is basically locked up and can't leave the place and would probably have no idea why someone is blowing a whistle at it Nil Einne (talk) 16:03, 7 April 2008 (UTC)[reply]
Sean is right—talk to the owner, suggest a spray bark collar. I have seen them used very effectively on dogs with barking issues. They are humane and cheap. They just release a little bit of citrus when the dog barks (dogs hate citrus), and quickly the dog learns that when the collar is on, they shouldn't bark. They don't always make this a universal rule (probably depends on how smart the dog is—I knew a very smart dog that knew that the second the citrus ran out he could bark again), but it's a workable solution for a barking dog. If your neighbor objects, tell him that it is his responsibility to make sure his dog is not a nuisance when he leaves the house; not only is this part of being a pet owner, it's likely a requirement of local code.
Any of the other approaches are very bad ideas. You don't have any experience training dogs (obviously). You shouldn't be trying to train your neighbor's dog without their knowledge and permission. You could find yourself in legal hot water for harassment of their dog. But from a simply ethical point of view, you wouldn't want them doing something like that to a pet of yours, would you? You'd probably rather they talked to you about it in a civilized way and you could come up with an acceptable solution, wouldn't you? --Captain Ref Desk (talk) 15:21, 7 April 2008 (UTC)[reply]
If for whatever reason you are really unable to talk to the person about this, you could send a polite computer printed anonymous note informing the person of the problem through the mail. Presuming you have other neighbours, your neighbour likely won't know who sent it. Provided you ensure your note is polite and not in any way threatening, I'm doubtful you'd get in legal trouble in most jurisdictions (but this is not legal advice and I could easily be wrong). However I would strongly recommend you approach the person directly. If they refuse to do anything about it, you may be able to get your local animal control or council to do something about it depending on where you live (e.g. http://www.ccc.govt.nz/Animals/DogBarking.asp & http://www.waitakere.govt.nz/cnlser/aw/dogs.asp). Nil Einne (talk) 15:34, 7 April 2008 (UTC)[reply]
According to the Madrid City Council website [16] and Babelfish, dog owners have an obligation "To adopt the measures that are precise to avoid that the animals can instill fear, to suppose danger or threaten, or to cause annoyances to the people." It sounds to me like persistant barking would be counted as "cause annoyances to the people" so it's easily possible the Madrid council will do something about it if the owner doesn't/refuses. If you indeed live in Madrid and understand Spanish, you could probably find out more by looking through the website. If you live in Viladecáns or somewhere else, look for the appropriate website. In any case, as I mentioned earlier, it is vital you inform the owner first since the council is far less likely to take action if the owner isn't aware of the problem (at best, they will inform the owner which will likely mean he or she will just be more annoyed that whoever it was didn't tell them directly) Nil Einne (talk) 15:53, 7 April 2008 (UTC)[reply]
It would be great if it were that simple in all cases. Consider a Jewish store keeper from NYC who moved into a suburban area in the the Deep South. His neighbor is outraged by the presence of a Yankee Jew living next door. According to the neighbor the only thing the Jew had going for him is that he is not Black. The neighbor has dogs. Fortunately they are not big dogs. Unfortunately their bark is louder than big dogs. The neighbor also has chickens, being originally from a rural area. The suburb being a block from a river is frequented by raccoons and possums looking for a meal. Chickens are a favorite item along with left out dog food. The neighbor leaves his dogs outside all night to guard the chickens. The shop keeper's mother is dying of cancer in the back bedroom, 8 feet from the fence that separates the properties and 16 feet from the chicken coop. She is awakened by the ruckus every night. After 20 or 30 minutes it tapers off. Finally it stops. Just as she is falling asleep, same thing. This pattern repeats itself over and over again until daybreak. The shop keeper complains to animal services with audio/video evidence. Animal services says it can't help him without his first obtaining signatures from families living close but at separate addresses. The test case for the soundness of the law was a mother who worked for the county and her daughter who lived in a rear apartment of the same house. Since their addresses were not the same they qualified for help from animal services to issue citations under the law. They attested to the soundness of the law. The shop keeper's case was not addressed, however, because there were no other families in the neighborhood willing to go against his neighbor. The shop owner was finally forced to find another residence for his mother. The rear bedroom was not usable and had to be shut off. The other bedrooms and living spaces had to be sound proofed. 71.100.160.37 (talk) 16:14, 7 April 2008 (UTC)[reply]
Don't talk to your neighbor. If he doesnt't cave in and you have to go on with plan B (silent whistle) or execute plan C (killing it), he will know who it was. —Preceding unsigned comment added by 80.58.205.37 (talk) 16:52, 7 April 2008 (UTC)[reply]
He'll find out that his neighbor's house has a lot of stray dogs. The silent whistle will attract hordes of stray dogs and they will camp near it.--Lenticel(talk)03:32, 8 April 2008 (UTC)[reply]
Hi. Well, the farthest galaxies that are visible with any type of telescope are about 13 - 17 billion light-years away. They're in the Hubble Deep Field or maybe the Hubble Ultra Deep Field, if I'm not mistaken. However, the universe is believed to only be about 12 - 15 billion years old, and beyond that boundary, the galaxies' light did not have time to reach us and you're looking at them before they existed. I think some of their distances might be calculated by redshift. Remember there might be galaxies an infinite distance away from us, they're just too far to be in the observable universe from our location. Hope this helps. Thanks. ~AH1(TCU)00:48, 7 April 2008 (UTC)[reply]
"that we know of" limits this to an answerable question. In 2004, galaxy Abell 1835 IR1916 was discovered to be 13,230 million light-years away. I haven't read about any further ones in the last few years. -- kainaw™01:39, 7 April 2008 (UTC)[reply]
The universe is now believed to be 13.7 billion years (discovered February 2003). So you can't have galaxies > 13.7 billion light-years. Textbooks before February 2003 would reflect the 12-15 billion year universe age. This was discovered by NASA with 1% error. Check the almanacs out for the sources. Neal (talk) 16:53, 7 April 2008 (UTC).[reply]
It depends on the distance measure used. Comoving distances, for example, can exceed 13.7 Gly without implying an object age older than the universe. See Distance measures (cosmology) referenced by Icek below, along with Observable universe#Misconceptions and Dltt is Dumb. Really, you should all be comparing redshifts, because that is the directly measurable quantity, and has no dependence on cosmological parameters or choice of distance measure (comoving, light-travel-time, etc.). If you insist on comparing distances, make sure you're talking about the same distance measure (e.g. comoving) and that the distances were obtained using the same assumed cosmological parameters. -- Coneslayer (talk) 18:11, 7 April 2008 (UTC)[reply]
Long skis go faster than short skis. Long skateboards go faster than short skateboards (I think). What is the reason (physics) for this phenomena.~ davidwinkelaar —Preceding unsigned comment added by Davidwinkelaar (talk • contribs) 03:16, 7 April 2008 (UTC)[reply]
The long ski can spread the load and displace less snow. I don't know about the long skateboard though, it may be you can stoop lower to reduce wind resistance. Graeme Bartlett (talk) 05:47, 7 April 2008 (UTC)[reply]
The length of high-speed skateboards is primarily a result of laying down on them. It is not specifically because the long boards inherently go faster. -- kainaw™18:22, 7 April 2008 (UTC)[reply]
I would assume that all cosmetic products will eventually decay/emulsify, rendering them unusable. In the case of sunblock, I would expect the titanium dioxide to stay unchanged, so it may have sunscreen properties. You probably wouldn't want to use it, though.18.96.7.121 (talk) 04:55, 7 April 2008 (UTC)[reply]
It's possible that it may do more harm than good if it gives people a false sense of protection, and end up spending lots of time in the sun. - Akamad (talk) 11:49, 7 April 2008 (UTC)[reply]
Hi. Yes, sunscreen can be harmful, if you put it that way. Let's say that you put on sunscreen and inscect repellent at the same time, which I recomend you do not do. Sunscreen goes under the skin, while insect repellent, which contains poisonous deet, should stay on top of the skin. So, if you apply both at the same time, the two can mix, and the sunscreen can bring some of the deet into the bloodstream. Sunblock, however, should be fine, as the chemicals stay on top of the skin. Remember that sunscreen contains a lot of chemicals that we might not be used to. Also, remember that even "water-resistant" sunscreen only stays for about 40 minutes, and "waterproof" sunscreen only stays about 80 minutes while underwater. Also, remember that the eyelids, lips, ears, and the neck are most sensitive to sun exposure. Hope this helps. Thanks. ~AH1(TCU)21:14, 7 April 2008 (UTC)[reply]
Video card adhesive
What sort of adhesive is typically used when glueing something onto a video card? A part fell off, and I know exactly where it goes, but I'm not sure what glue to use. --AtTheAbyss (talk) 12:41, 7 April 2008 (UTC)[reply]
If it is the heat sink, you need a thermal interface material. If it is something else, you would have to connect all the small wires which have been broken, without getting a larger resistance than the original one, and without getting a larger capacitance between the wires (a larger capacitance could be caused by conducting parts being closer to each other than they were before). Icek (talk) 14:15, 7 April 2008 (UTC)[reply]
I'm not really sure what it is. It's a small silver-colored piece of metal with a textured grid surface. It's about an inch long I think; I'm not sure how wide. There are no wire involved. It was just glued to the surface. I have an ATI Radeon 9800XT. --AtTheAbyss (talk) 14:33, 7 April 2008 (UTC)[reply]
Looking at pictures of that card, it looks like it may very well be a capacitor. They are surface mounted - silver on both ends and have a textured wrap covering the middle. You need to solder them back on if they come off. -- kainaw™18:24, 7 April 2008 (UTC)[reply]
This should go without saying, but if you have capacitors dropping off your video card, you probably have bigger problems than just getting them stuck back on. That said, I'd strongly suspect the part in question is indeed a heat sink. If it isn't, or if you're not sure of your skill at applying thermal adhesive, I'd recommend taking the card (and the loose part) back to the store you got it from. If it's fixable, they'll fix it — if not, they can sell you a new card. If it indeed "just fell off", it may even be covered by the warranty. —Ilmari Karonen (talk) 22:04, 7 April 2008 (UTC)[reply]
Actually, there's a good chance the card is not covered by warranty any longer. THe 9800XT is quite an old card and it's easily possible the editor bought it more then 2 maybe even 3 years ago. Nil Einne (talk) 12:27, 8 April 2008 (UTC)[reply]
I'm not sure it's the heatsink. THe piece is less than half an inch thick, if that. I appreciate all the help so far guys and gals.--AtTheAbyss (talk) 12:07, 9 April 2008 (UTC)[reply]
Cog Railway System
how is the energry transfer from engine to wheels to enable it to climb such steep gradient( going up and coming down)? it must be facing a lot of friction, how does it overcome that? what are the advantages and disadvantages of this system compared to a normal railway track? Nathelly wee (talk) 14:11, 7 April 2008 (UTC)[reply]
Your question looks a lot like it might be a physics homework problem—perhaps you could start by sharing your thoughts on the question, and we might be able to help you over the rough spots? TenOfAllTrades(talk) 14:16, 7 April 2008 (UTC)[reply]
Here's a hint: In a cog railway system, there may not be any significant energy transferred to the wheels.
Just for information, could you tell me wich telescope is the brighter (for visual observation of galaxies, nebulae, clusters, ...) : a Newton 200mm/1000mm (focal ratio=5) or a Schmidt-Cassegrain 305mm/3048mm (focal ratio=10) ?
The 305mm telescope is brighter. Since it has a larger aperture, it can collect more light, and the amount of light collected is the apparent brightness of the object being viewed. The focal length is simply how quickly the light converges; it has no effect on brightness.
The reason photographs taken at higher focal ratios are dimmer is because cameras shrink the aperture to increase the focal ratio. The only other way to increase the ratio, increasing the focal length, would zoom in the camera. --Bowlhover (talk) 20:41, 7 April 2008 (UTC)[reply]
Hi. Also, remember that larger telescopes are harder to store, heavier and harder to carry around, and more difficult to set up. The focal ratio is more important to the magnification rather than the light collection, and too much magnification will spread out the light from deep-sky objects. With the 200 mm telescope, using a 20 mm eyepiece, for example, will give 50x, while using the 305 mm telescope will produce 152x. However, sometimes a higher magnification can be a good thing. Remember however, that a higher magnification will produce a smaller field of view. So if the 20mm eyepiece had an FOV of 50 degrees, using it on the 200mm will produce a 60-arcminute FOV, which is good for observing the Orion nebula, most large galaxies, and large globular clusters, while using it on the 305 mm will give a 20-arcminute FOV, which is 9x smaller in area and better for smaller globulars, galaxies, and nebulae. Remember, however, that you can often get many different eyepieces for different magnifications, often ranging from about 5mm to about 40 mm for 1.25-inch barrels, and up to about 50 or 60 mm for 2-inch barrels (especially common on Schmidt-Cassegrains), and you can also also use barlow lenses to double or triple the magnification, which both these telescopes should be able to handle. Remember that the effects of aperture and magnification are squared, so a 305mm telescope should have about 2.3x more light-gathering capability, or about 130% better, ignoring the size of the secondary mirro. Try comparing these parameters on a telescope simulator or calculator. Hope this helps. Thanks. ~AH1(TCU)21:29, 7 April 2008 (UTC)[reply]
It's probably a one-shot technique that they're using. The cells (or an aliquot of cells) are taken at a single timepoint and fixed. 7-AAD will easily penetrate what's left of a cell's plasma membrane after fixation in cold ethanol, methanol, or acetone. TenOfAllTrades(talk) 20:12, 7 April 2008 (UTC)[reply]
Dog skeleton curiosity
My adult pointer/whippet mix has a strange feature at the very tips of her last (or near to last) floating ribs: the end 1/2" or so of rib seems to be jointed, such that I can flip it back and forth like the tip of my index finger. This feature is the same on both her left and right, and twiddling it causes her no discomfort. What is this? Are the ends of dog ribs made of cartilage? I've looked for dog skeletons online, but not found anything useful. Note that this is a general question about dog anatomy, and not a request for veterinary advice as there is no problem. --Sean16:49, 7 April 2008 (UTC)[reply]
It's definitely not a bone joint. Ribs do have a lot of flexibility to them, to accomodate breathing, etc., both in human and dogs, but I wouldn't go so far as to call them cartilage. Perhaps your dog's ribs are even more flexible than most. StuRat (talk) 19:27, 7 April 2008 (UTC)[reply]
This is not uncommon in young dogs. The ventral part of the dog's rib is made of cartilage. This is true in other animals, including humans, I think. The darker part of the rib is cartilage The cartilaginous part of the rib meets the bone part in a costochondral junction known as the knee or genu. Only the last rib (the 13th) (or no rib at all) in the dog is a floating rib. In young dogs, the cartilage in the ribs is flexible. It calcifies and stiffens with age. That flexibility is what saves a lot of young dogs' lives when they are hit by cars.
With this condition, the flexibility of the cartilage in a floating rib allows it to flip back and forth. I'm not sure if this happens at the junction or further down. --Joelmills (talk) 15:20, 8 April 2008 (UTC)[reply]
organic chemistry(Catenation)
Carbon and silicon both have the same electronic configuration yet only carbon shows the property of catenation Why??Diya 16 (talk) 17:37, 7 April 2008 (UTC)Diya[reply]
Or at least now that I added some information that silicon can form bonds to other silicon atoms. Not sure your question is completely correct in its premises:) DMacks (talk) 18:10, 7 April 2008 (UTC)[reply]
Solid magnesium nitrate is apparently somewhat hazardous because it is an oxidizing agent. I am wondering if it would be any more or less hazardous when it is dissolved in water (saturated solution). I am mainly interested in the context of workers or consumers that might come into contact with such a solution in a hypothetical situation. ike9898 (talk) 19:22, 7 April 2008 (UTC)[reply]
Dissolving in water will reduce fire hazard, but increases the risk that a breakage or spill will result in your substance going somewhere you don't want it. Graeme Bartlett (talk) 21:19, 7 April 2008 (UTC)[reply]
What about skin contact? Is skin contact with a saturated solution any more of less dangerous than skin contact with the solid? ike9898 (talk) 13:32, 8 April 2008 (UTC)[reply]
Origin of Universe - nothing has to be somewhere- doesnt it?
If the universe suddenly came into being from nothing (a zero dimension, zero time nothingness), (as some theories say), where and how did this nothingness exist? I mean even nothing has to be somewhere dosent it? —Preceding unsigned comment added by 79.76.170.42 (talk) 00:18, 8 April 2008 (UTC)[reply]
It didn't exist. By virtue of being nothing it was not a thing and therefore never had a spatio-temporal location, as it preceded spacetime. Hope someone tells me I'm wrong though 81.96.161.104 (talk) 00:24, 8 April 2008 (UTC)[reply]
The accepted theories of physics simply don't cover what happened before the Big Bang; they generally posit that time literally began existing in that event, and so there is no meaning to "before the Big Bang." This may not be literally true however, and it is merely part of the model; indeed, the model (based on the standard model and general relativity) actually breaks down at the moment of the Big Bang, since it can't handle the singularity. Once again, the singularity, the infinite density of energy, at the moment of the Big Bang is also part of the model, and may not be literally true. Big_Bang#Speculative_physics_beyond_the_Big_Bang contains links to some popular alternative models. Someguy1221 (talk) 00:28, 8 April 2008 (UTC)[reply]
Does what Stephen Hawking once said--Whatever happened before the Big Bang could not affect the Universe after--still stand? If so, it may be a partial answer to the OP--there's simply no connection between what may have happened beforehand, even if that can be defined, and what happened in the Big Bang, so to talk of "nothing into something" is misleading. Imagine Reason (talk) 02:55, 8 April 2008 (UTC)[reply]
If the universe came into being from a zero dimensional point, then it makes as much sense to say it happened everywhere as nowhere, seems to me. Or to play on the thread title here, nothing is everywhere? Pfly (talk) 02:22, 9 April 2008 (UTC)[reply]
Super powers
Assuming medicine continues to develop at the same rate it is now, as do robotics and science in general, what's the closest we could come to super-powered human beings in the next 20-50 years? The powers can be temporary but robo-suits don't count. What sort of super-powers is it feasibly even vaguely plausible that we could develop? 81.96.161.104 (talk) 00:24, 8 April 2008 (UTC)[reply]
Work is underway artificial retinas.[18] Right now they're extremely primitive, so I don't know if they'll qualify as "super powers" in your 20-50year time frame, but you could imagine them being made to work on ultraviolet or infrared. That'd be a neat super power. APL (talk) 00:39, 8 April 2008 (UTC)[reply]
Most "super powers" in comic strips involved violating conservation of energy one way or another (e.g. the beams just come out of nowhere). So if we're discounting everything like that, we're probably talking just about enhancement of existing abilities. It wouldn't be too hard to imagine better hearing, for example—we've already got hearing aides that are pretty small. But I don't know why you're discounting robo-suits—humans have always done better when they've learned to use technology along with their own natural abilities, rather than trying to just improve their natural abilities. It also makes more economic sense to have one set of tools that anybody can use than to try and modify each individual themselves. But anyway, these are practical considerations, and not much fodder for fun speculation... --Captain Ref Desk (talk) 00:50, 8 April 2008 (UTC)[reply]
I'm fine with robotic enhancement, but the suits could not be small enough to be manouvereable in that little time. Robotic legs that can jump 50feet counts as a super-power, to me, but a huge clunking suit that can run at 10mph and has guns for arms doesn't. And what about genetic modification? Could we have ant-strength? Or poisonous saliva? The ability to change your hair length/colour? Maybe skin colour? There must be some great traits out there to steal.
I'd go for a direct brain-internet type link, lets you research anything by thinking hard about it somehow. Any other brain enhancement, extra memory, some type of processing demultiplication? 200.127.59.151 (talk) 02:21, 8 April 2008 (UTC)[reply]
From a biological perspective:
Healing factor - if we could figure out how to incorporate the regenerative qualities of other animals like starfishes (using gene theraphy) then we are all set.
hi, I like a drink occasionally and have noticed (as i approach 40) that ale really settles the stomach. I had for the past few years had a rather mild IBS type thing going on.
Is there a chemical present in ale that is perhaps sorting this all out nicely?
?? For your number 2 and number 3, I assume you're talking about clouds? Or what we see in general? This seems pretty.. either point lacking, or it's a quiz. *shrug* Neal (talk) 02:09, 8 April 2008 (UTC).[reply]
Click on the pictures to see descriptions on the image page of what is in the pictures. For 2 and 3, I'm looking for confirmation that my Google Mapping of what I saw out of the aeroplane window isn't totally off-beam. I initially thought 3 was the main part of the Thames Estuary, but then I realised nothing on the map was matching what I saw on the picture, so I looked around a bit on the map, and spotted the distinctive shape of Mersea Island. But ideally I'd like someone else to say "yes, that looks like you've identified it correctly". One day, of course, all cameras will automatically have GPS geocoding built into their picture metadata. But until that day arrives, we have to scribble notes on bits of paper, or, in my case, rely on memory and detective work afterwards. Unfortunately I have a nice picture of hills in Eastern Europe that is pretty much unusable as I don't remember where in the country the picture was taken... Picture 2 is also a case where my Google Mapping needs double-checking. As for the clouds in picture 1, see commons:Cloud - an amazing resource for different cloud types. But I need an expert to identify the clouds here. I would also like an expert to confirm my identification of what I now think is a gannet in picture 4. So yes, a quiz of sorts, but also me looking for some corroboration and confirmation. Carcharoth (talk) 02:18, 8 April 2008 (UTC)[reply]
Yes, I must remember not to sit near the engines and the wings if I want to engage in amateur aerial photography! :-) But seriously, does no-one else here use Google Maps to check things like this. It is great fun! Carcharoth (talk) 02:25, 8 April 2008 (UTC)[reply]
On topic spur, to get that blue tinge off the iamges you can use a photo editor like Microsoft Photo Editor, to reduce the blue brightness and increase its contrast by the same amount, perhaps to 75%, it gives a more natural looking colour for things viewed a long way through air. Graeme Bartlett (talk) 05:33, 8 April 2008 (UTC)[reply]
The dead bird in image 4 is certainly a northern gannet, given that it was taken in England. The markings on the bill are distinctive and you can see the pointed, black-tipped wings. It certainly is not a gull. I'm not an expert, but I been a birder for many years.--Eriastrum (talk) 20:00, 8 April 2008 (UTC)[reply]
Thanks. I've asked at WikiProject Birds just to be sure (I'm sure you will see the question there as well). I've asked about a picture of some swans over there as well. Carcharoth (talk) 21:18, 8 April 2008 (UTC)[reply]
Herbivores with horns
Do herbivores like antelopes and buffalos ever defend against predators consistently? As a child my father would tell me that certain animals would form circles around their young and defend against lions and such, but I've never been able to confirm any instance of the behavior. Thanks in advance. Imagine Reason (talk) 02:57, 8 April 2008 (UTC)[reply]
Herbivores don't need horns to defend the young. I believe elephants will do so, for example. Surprisingly, though, many large species which travel in herds and would seem to be capable of defending the young opt not to. I chalk it up to predation actually being good for the species in the long run, by only allowing those with the strongest genes to pass them on. StuRat (talk) 03:14, 8 April 2008 (UTC)[reply]
Yeah, um, I was actually looking for an example also partly to refute group selection, including species selection. The best explanation I've come across to explain this odd behavior is Richard Dawkins's gene selection, which is sometimes reflected in apparent individual selection--an antelope that goes against the lion might win, but the benefit is shared by everyone else in the herd, including everyone who's disappeared from the battle, while the cost is very real and probably fatal to the brave individual. Thus any individual that carries such a "brave" gene will mostly likely die out from any species. I suspect that species that can communicate effectively, including dolphins, will exhibit more cooperation. Imagine Reason (talk) 03:32, 8 April 2008 (UTC)[reply]
Musk oxen are the exception that proves the rule. Any species using this tactic that was co-extensive with primitive humans is now extinct. Musk oxen were the only species that used this tactic and whose range had at least a few spots with no humans up until the time (about 1880) that humans became squeemish about driving (mammal) apecies to extinction. I seem to recall written descriptions from the midd-1800's of hunting parties finding a herd of musk oxen and calmly shooting them all one by one, as they stood in a circle. There are earlier accounts of Inuit hunters doing the same thing, more slowly and more carefully, with spears. -Arch dude (talk) 01:10, 9 April 2008 (UTC)[reply]
If a force of gravity is an effect of space-time distortion by gravitational field, how can it be explained, that the force is much, much stronger, than one might expect from such a tiny distortion? E.g. on Earth's surface, acceleration due to gravity is 9.81 m/s2, but Earth's gravitational field curves space-time very miserably and cannot cause such huge acceleration. Maybe, I'm missing some important points. Abdullais4u (talk) 10:54, 8 April 2008 (UTC)[reply]
There's no reason to think that the earth has a small effect on space-time, because it's all relative. You said that "Earth's gravitational field curves space-time very miserably", but compared to a 1 kg mass, the earth has a huge effect on space-time. - Akamad (talk) 11:11, 8 April 2008 (UTC)[reply]
Well, Earth's effect on space-time still not big enough, even when you're comparing Earth's mass to a kilogram. Light beam, flying-by Earth, bends only to some millionth parts of a degree. Abdullais4u (talk) 11:53, 8 April 2008 (UTC)[reply]
Keep in mind that gravity follows the Inverse-square law, so the distortion you describe drops off very quickly. Also, light is only barely affected by gravity, having zero rest mass, so it takes an immensely massive object to produce observable gravitational lensing. -- JSBillings12:30, 8 April 2008 (UTC)[reply]
If light bends only a millionth of a degree, then so would a rock traveling along the same path at highly relativistic speed. That's the essence of the equivalence principle. We think of light as being only slightly effected by gravity, but that's only because it usually moves so fast. In an optical cavity in which light can reflect back and forth between two mirrors for one second before dissipating (and such things are not unheard of), the light would fall 4.9 meters if the mirrors were exactly vertical, the same distance a rock would fall. So light falls in a gravitational field, just like anything else. (In fact, the mirrors of an optical cavity are almost always curved and tilted at some tiny angle to prevent the light from falling, but that doesn't invalidate my argument. Light will fall like a rock if you give it a chance.) —Keenan Pepper12:44, 8 April 2008 (UTC)[reply]
KP, I knew your general point about light falling like a stone was true, but doubted your assertion that it was a practical concern with current technology (I thought it would dissipate too soon to be an issue), so did the math for letting light fall for a second at one of the LIGO facilities that uses a 10 watt laser across a 4 kilometer long range and assuming 99.99% reflective mirrors: , which is certainly detectable, at about the strength of a CD drive's laser. Thanks for disabusing me of some false knowledge! --Sean15:22, 8 April 2008 (UTC)[reply]
Why does a match (or any fire) smoke the most the moment the flame goes out? And while we're here, what exactly are we seeing when we look at a flame. The best I could think of was ionizing O2, which doesn't really explain it.
Our candle article provides a fair description of what's happening within a flame, but most of the light comes from incandescent carbon particles. Fire and Flame have more information.
Visible smoke is usually the result of incomplete combustion. You get the formation of small carbon particulates which are of a large enough size to substantially perturb light. If you have more complete combustion, these carbon particles oxidize fully to carbon dioxide - a clear, colorless gas. So you get the most visible smoke when combustion is weak/failing - like when the material is wet, or the fire is smoldering, or when it is just extinguished. -- 128.104.112.85 (talk) 20:06, 8 April 2008 (UTC)[reply]
Sorry. I mean the milk of infected cows does not contain prions, or at the very least that researches have tested for the presence of prions in infected cows' milk and found none. Someguy1221 (talk) 23:10, 8 April 2008 (UTC)[reply]
This demonstrates why it's always a good idea to ask questions that can be answered, unambigously, with yes or no. In this case "Is the prion present in dairy products made with milk from BSE-infected cows ?". People could still answer "We don't know", if this is the case. StuRat (talk) 16:58, 9 April 2008 (UTC)[reply]
Related to this question is that of whether prions can be transmitted via milk. The latest research [19] says the answer is "Yes." Scrapie is a disease in sheep spread by prions, and it was transmitted via sheep milk to the ewe. The report denied any evidence of transmission of prions to humans via milk. Seems strange only lambs would be infected. Edison (talk) 17:33, 9 April 2008 (UTC)[reply]
I have found threefour ootheca of the Chinese mantis (Tenodera aridifolia sinensis) in my neighborhood. How can I tell when they are going to hatch, so that I can hope to take pictures of the hatching process for Commons? I know precision is impossible, but the general seasonality, necessary precedent weather conditions, or other natural processes that preceed the hatching would be helpful. GRBerry14:14, 8 April 2008 (UTC)[reply]
Hatching usually takes between 3 and 6 months. The young may hatch all at once or in batches over a period of several weeks.[20] Another suggests hatching occurs spring/summer of the following year. Julia Rossi (talk) 07:30, 10 April 2008 (UTC)[reply]
Precision flash – what would it be like to use a stethoscope to track the nymphs becoming active? The hardened ooth is just packaging for them. Borrow or make one and bobsyerunkl... Julia Rossi (talk) 10:25, 10 April 2008 (UTC)[reply]
The stethoscope is a good idea, and we already have one. I'll try it; hopefully the highway a couple roads away won't render it useless. Hopefully with four now found I can also be alerted by the hatching of one to photograph the others. GRBerry13:52, 10 April 2008 (UTC)[reply]
It's a cool project. Maybe adapting industrial ear muffs, a biker helmet or wooly hat with turnup would give you a noise break. Awaiting the pics, Julia Rossi (talk) 23:17, 10 April 2008 (UTC)[reply]
Food intended as whose primary function is food
Just for the sake of my own personal edification (and morbid curiosity), I'm trying to come up with a list of foods humans eat whose primary biological function is to be food. The two obvious ones I can think of are milk and honey. Excluded from the list would be meat (whose primary biological purpose is to be the muscles and organs of the animal it comes from) and leafy vegetables (whose primary biological function is to enable photosynthesis). But I'm having trouble deciding on things like fruits, nuts, seeds, and eggs. On the one hand, you could say their primary biological function is reproduction, but all of them (I think) also contain material intended to supply energy (i.e. be food) for the growing seedling/embryo. So would these go on the list or not? And a lot of plants rely on birds to eat their fruit so that the seeds will be dispersed in the birds' excrement; so maybe one could say the primary function of (at least some) fruits is to be food for the birds that will be dispersing the seeds. And what about root vegetables like potatoes and carrots? Isn't the function of roots to store energy for the plant to use? And if so, doesn't that mean their function is basically to provide food for the plant? What do the rest of you think? —AngrIf you've written a quality article...14:22, 8 April 2008 (UTC)[reply]
Hmm, the minute you start saying that nature has an intent, it's murky. One could say that deer muscle is meant as food.. for lions. The whole ecosystem evolved together, by necessity. There are connections and dependencies everywhere. Friday(talk)14:25, 8 April 2008 (UTC)[reply]
They are not intended to be eaten. They are intended to provide a good growing environment for the seeds inside the fruit. If we eat all of the fruit and never allow any to turn into new trees, then the old trees would eventually die and the fruit would no longer be available. -- kainaw™14:37, 8 April 2008 (UTC)[reply]
Oh really? My whole mindset of the purpose of fruit has been wrong all along! I was once told that it's so animals eat the fruit and spread the seeds around. -- MacAddct 1984(talk • contribs)14:40, 8 April 2008 (UTC)[reply]
Hmm, the fruit article states: "The sweet flesh of many fruits is "deliberately" appealing to animals, so that the seeds held within are eaten and "unwittingly" carried away and deposited at a distance from the parent." -- MacAddct 1984(talk • contribs)14:42, 8 April 2008 (UTC)[reply]
Most fruit has indeed evolved in such a way as to facilitate the dispersion of seeds. Take for example, the strawberry (technically an false berry, not a berry) - the red part is in fact not a seed, the seeds are the white/yellow little hard bits on the outside. The part that we like to eat turns sweet and red when the seeds are ripe, causing the whole to be eaten, and the seeds defecated away from the parent plant. Thus, to the extent that purpose is meaningful, all accessory fruits clearly have a sole function of being eaten by something, and most fruits humans eat have a, but not sole, function of enticing something to eat the fruit and disperse the seeds contained within, while the seeds contain their own energy stores. Nuts, seeds, and eggs, on the other hand are generally intended to be the energy store for the embryo within - but oaks, for example, depend on acorn dispersal agents to move their seeds away from the parent, and thus must make acorns that are palatable to such animals as food in return for a few getting lost and becoming plants. (Yes, acorns are also a human food.) Modern corn has clearly evolved under human selection for edible seeds (compare Teosinte) ... as have most other human eaten crops. So in that sense, most seed foods are also evolved to be eaten. I'm not as sure of the balance among nuts, but suspect acorns may be representative here. I'm not aware of any eggs that need dispersion by dispersion agents. GRBerry14:50, 8 April 2008 (UTC)[reply]
I can see that argument. It assumes that the seeds will still be viable when pooped out. It also assumes the plants purposely evolved into a relationship where they cannot multiply on their own. They require animals to eat the fruit. Both are rather big assumptions. In my opinion, the simpler explanation is better. The plants provide a rich growing environment for their seeds - which animals have evolved to enjoy eating. -- kainaw™14:53, 8 April 2008 (UTC)[reply]
When you look at ecosystems from a low-level biological perspective, the amount of cross-dependency is really quite astounding. So these may be big assumptions, but you find examples of this everywhere. Forget reproduction- you and I could not even digest the food we eat, without the help of our gut fauna. Friday(talk)15:01, 8 April 2008 (UTC)[reply]
That's not necessarily true - there are studies with rats and mice which are kept free of microorganisms and are about as healthy as normal rats and mice. If you are isolated from microorganisms you would probably do well as long as you get all vitamins in sufficient quantity (I think vitamin K and biotin are synthesized by some common human gut bacteria). Note that cellulose is not degraded in normal human intestines - so it would probably not be a problem if a few additional polysaccharides are also not degraded (the degradation by bacteria happens primarily in the colon, so the human can hardly use any resulting monosaccharides; starch, on the other hand, is degraded by human enzymes). Icek (talk) 17:57, 8 April 2008 (UTC)[reply]
Seed predation, biological dispersal and seed survival rates are topics of scientific study. Here are a couple of papers with a decent online presence (to someone not subscribed to any journal or JSTOR or ....) that include all the terms "rainforest seed survival rate insect". What happens to only partially eaten seedsEffect on mangrovesA particular species. I've seen elsewhere estimates that for rainforest seeds that end up under the parent, 0% of seed s survive insect predation, but that was probably a species specific study. Similarly, insects living under an oak can kill more than 95% of those seeds that hit the ground under the tree and escape mammalian and avian predation. On the other hand, an adult oak can live for centuries and produce hundreds of thousands of acorns, only a few of which need to live to become trees in order to keep the species going - in fact, on average, one tree needs to produce one child tree... so the needed surival rate is barely more than 0%, and might be hard to measure in a scientific study. All plants are essentially high r, low K strategists, though some are higher r than others like the nut bearing trees. GRBerry15:18, 8 April 2008 (UTC)[reply]
Friday, I tried (not entirely successfully, I see) to avoid the words intend and intent and speak of the "primary function" instead. I think it's safe to speak of things in nature as having functions. Now it really does seem that many plants have evolved in such a way that their fruits are palatable to animals, in order that the seeds may be dispersed more efficiently and effectively. But that doesn't necessarily make it the case that the primary biological function of fruit is to be food for animals. On the other hand, it may well be the case that the primary biological function of fruit is to supply energy to the growing seed, which is the same thing as being "food" for the growing seed. —AngrIf you've written a quality article...16:27, 8 April 2008 (UTC)[reply]
According to GRBerry's comment, my understanding that the fruit provides a fertile growing area for the seed is incorrect. It actually causes insects to quickly devour the fruit (and seed). If that is accepted, then the fruit is only viable as a method of getting seeds mixed into another fertilizer (animal feces) and dropped onto the ground. But, claiming that this benefit is "indented" is what bothered me. I do not see any form of evolution as the result of intent by a plant. Also, if we accept that the function of the fruit being nice to eat is an intended function from the plant, then it is easy to argue that the reason animals taste nice is because they are intended to be eaten to kill off the weak animals, leaving the strong ones to reproduce. -- kainaw™16:34, 8 April 2008 (UTC)[reply]
With evolution, a particular function can't be considered to have evolved intentionally for to fill that role -- it was a process of selection that produced that phenotype. For example, many of the aforementioned fruits evolved from ancient plants that might have dispersed their seeds in another way, or a different animal. As for tasty animals -- I doubt that a prey animal would have much selective pressure to be more tasty, since being preyed upon effectively ends the gene's ability to propagate. The 'tastiness' is most likely the result of the evolution of the predator's sense of taste and preferences. Taste is a way to determine the content and quality of food, so something tasty would provide the predator with much-needed nutrition. -- JSBillings16:59, 8 April 2008 (UTC)[reply]
I agree that my use of the word "intended" in the title and question is something of a pathetic fallacy, so let's stick to "function". Now even that can be hard to define; things can have more than one function, and deciding which of them is the primary function is probably highly subjective. Maybe my question is unanswerable. I only asked because it recently occurred to me that milk is unique in being the only food "intended" (whatever that means) to be food. But then it immediately occurred to me that honey is also "intended" as food, so milk isn't unique after all. And then the more I thought about, the more I realized that an argument could be made for many other foods being "intended" as foods, and that's when it occurred to me that speaking of "intent" was complicating things and so maybe I should reformulate the question in terms of primary biological function. So I did, and I still think it's an interesting question, but I don't think there's ever going to be a definitive list of foods whose primary biological function is to be food such that everyone can agree that for any given foodstuff, that foodstuff unambiguously either does or does not belong on the list. —AngrIf you've written a quality article...17:01, 8 April 2008 (UTC)[reply]
Honey is a manufactured product (albeit by bees), so I think it could be cataloged as a food right along side of twinkies. Also, a lot of organisms that either are, or produce substances that are food have evolved, and their ecological niche is not static. For example, mammary glands in mammals are believed to be adapted sweat glands. You're going to have to specify your definition of 'food'. -- JSBillings17:34, 8 April 2008 (UTC)[reply]
Selective pressures should favor undelicious meat but this would lead to problems in overpopulation and the restoration of energy into the system. I would venture to hypothesize that there might be a sort of meta-darwinian selection that disfavors unbalanced ecosystems. For instance, the fundamental niche of a species is limited in an ecosystem to its realized niche. Our articles on niches attribute this to competition but that doesn't explain why species are, to my knowledge, not found outside their realized niche at all when competition would only restrict their appearance in niche overlap. I might be espousing an aspect of the Gaia hypothesis. — Ƶ§œš¹[aɪm ˈfɻɛ̃ⁿdˡi]19:02, 8 April 2008 (UTC)[reply]
Since our own bones and muscles store nutrients which may be used during famine, rather like tubers, and many animals recycle their skin, let's stick to foods whose function is to be eaten by another creature, excluding internal or attached symbionts: Definitely most fruits; some plants can hardly reproduce unless their seeds pass through an animals gut. Milk. Nectar (function is to attract pollinators). Aphid & scale honeydew. Hemolymph (many mother spiders let their young suck them dry—there are also other non-mammals that feed their young from their bodies after birth, though none come to mind at the moment). Beltian bodies. I'm sure there are lots more. kwami (talk) 21:52, 8 April 2008 (UTC)[reply]
Oops! Forgot that you were looking for human food. Nectar still counts, though it's extremely minor. I wouldn't count honey, since its function is to be food for bees, not us. Nuts neither—in most cases, at least, the primary function of a nut is as a seed, which is why so many are toxic (including almonds, before we domesticated them). kwami (talk) 22:24, 8 April 2008 (UTC)[reply]
Given that the function of genes is to make more copies of themselves, and given the wide prevalence of cattle on the planet, one could argue that the function of all parts of the cow, especially the tasty bits, is to further the species by being human food. The cow has responded to selection pressure and become docile and nutritious, thereby expanding its numbers far beyond what could be achieved by being nasty and stringy. So tenderloin counts as "primary biological function is to be eaten by humans" and the cows have done rather well at it, their burps are threatening the planetary envionment. Franamax (talk) 23:23, 8 April 2008 (UTC)[reply]
I'm starting to regret asking the question. Kwami, yes, honey definitely counts since (1) humans eat it and (2) its primary function is to be food for an organism different from the one producing it. And as far as I'm concerned cows don't count regardless of how much they've been genetically engineered to be tasty and nutritious. Nuts and seeds are out, since their primary function is to grow into new plants. Fruits are sort of a borderline case - their primary function from the plant's point of view is to serve as seed distribution mechanisms. To return to the convenient pathetic fallacy, the plant doesn't care about nourishing the animals eating the fruit, the plant cares about getting its seeds distributed, and takes advantage of animals' appetites to accomplish that goal. Eggs are also a borderline case - eggs can be considered the animal equivalent of a nut or seed, so their primary function is to grow into baby chicks (or whatever), but of course the contents of an egg are "intended" as food for the embryo. An unfertilized egg, while being tasty and nutritious for humans and weasels, is of no use whatever to the chicken, so from the chicken's POV it has no function at all. —Angr05:51, 9 April 2008 (UTC)[reply]
I think you're right about potatoes and carrots and the like, they store energy (food) for the plant to use. But they are only part of the plant, so by the same logic one could consider animal fat to be perform the same function (it does keep the animal warm too though).--Shniken1 (talk) 07:03, 9 April 2008 (UTC)[reply]
Mirror
Maybe a silly question but... is the light reflected in a mirror the same light that fell on the mirror? To clarify, if a photon strikes a reflective surface, does it bounce off, or is it absorbed and a "new" photon emitted in it's place? Astronaut (talk) 14:41, 8 April 2008 (UTC)[reply]
I saw part of a documentary the other day about Stephen Hawking (maybe it was the same one as mentioned previously). In the part I saw, the documentary explained that throughout the universe particle/anti-particle pairs are spontaneously created and then anihilate a small fraction of a second later - presumably they are created from the conversion of dark energy - but near a black hole one particle can fall into the black hole and the other particle escapes. The thing that bothered me was the assumption that it is always the anti-particle that gets dragged into the black hole, giving the appearance of particles escaping from the black hole. Surely particles and anti-particles would be equally likely to escape the black hole, and then encounter each other and anihilate. So, do particles appear to escape from black holes (and I just missed the bit of the documantary which explained it fully), or do black holes absorb dark energy with no outward effect on the rest of the universe? Astronaut (talk) 15:19, 8 April 2008 (UTC)[reply]
There is no assumption that only particles (not anti-particles) survive. If the produced particles are photons, there is no issue, because the photon is its own antiparticle. If other particles are produced, as you say, it could be the particle or its antiparticle, leading to annihilations. These annihilations produce... photons. Either way, the Hawking radiation is in the form of photons. -- Coneslayer (talk) 15:51, 8 April 2008 (UTC)[reply]
Pre Genus Species
Before science discovered flies were not the spawn of rotting meat, before they'd even classified the creatures with proper names, what did people identify flies as? Did they just call them "flies"?
Beekone (talk) 17:38, 8 April 2008 (UTC)[reply]
Well, not "flies" per se -- that experiment in spontaneous generation was conducted in Italy, not in an English-speaking area. However, people did call flies by their common name in whatever the relevant language was, and have for thousands of years -- probably since language originated. I'm not sure what other alternative there could be. To take the housefly specifically, though, the scientific name -- musca domestica -- is the Latin for house (domestica) fly (musca). — Lomn17:47, 8 April 2008 (UTC)[reply]
Cool, that's exactly what I was wondering about. Between all the differences in modern and old English maybe there was a term that had gotten lost, but if they just called them house flies or we can logically assume that they did that's exactly what I need. Thank you! Beekone (talk) 20:29, 8 April 2008 (UTC)[reply]
DNA
please tell me what is the best proffesional text book about DNA
I doubt there is a 'best' If you are studying as part of a course, doesn't the course list a recommended text book or books? If it really doesn't try asking your course coordinator/professor for advice Nil Einne (talk) 07:43, 9 April 2008 (UTC)[reply]
gold from rock
What are the steps to get the gold out of the rocks. my friend gave me a rock from a mine and i want to learn to brake it up and get the gold --added by Cameron from WP:HD on behalf of 24.121.165.249.
We have an article on Gold extraction, but it should be noted that several of the listed methods are EXTREMELY dangerous and should not be tried at home. Just to stress that a little more -- enjoy the piece of ore you were given, don't try to extract the gold, it is way too risky. --LarryMac | Talk18:14, 8 April 2008 (UTC)[reply]
The traditional method used by the ancient Egyptians is to grind up the rock into fine powder (good luck!) and then wash or pan it in the traditional way. The gold particles sink while the rock dust washes away. No chemicals needed and should be 100% safe (just don't breathe the dust); have fun with this project! Jeff Dahl (Talk • contribs) 23:12, 8 April 2008 (UTC)[reply]
Also note that you may very well spend more money to extract the gold than the tiny amount of gold is actually worth. StuRat (talk) 16:14, 9 April 2008 (UTC)[reply]
Domesticated animals often overeat, while wild animals rarely do because they have to work for each meal. They burn energy hunting or foraging for food, and do not have the luxury of an unlimited supply. Have a look at the obesity article, which covers humans as well as other mammals. As for if they would "pop", I don't know, but this picture seems to indicate they wouldn't. D0762 (talk) 19:32, 8 April 2008 (UTC)[reply]
There are some old people where I live and they are always complaining about the local yobs congregating around the library car park and being generally anti-social. Eventually our local council told them that a new system had been fitted called "mosquito" which wards off teenagers by emitting a high pitched sound, like a cat scarer does. I find it hard to believe that you can target teenagers specifically with such as device. Is the council lying to them?
Of course, you can't precisely target teenagers this way. Not all teenagers will hear the sound, and some non-teenagers will hear it. As for whether there's a Mosquito installed at your library, I'd ask a teenager. --Allen (talk) 20:33, 8 April 2008 (UTC)[reply]
And most children with their parents will hear it too. From what I recall, the device doesn't really achieve the desired result as well as, for example, playing loud classical music seems to. Entertainingly, you can get 'the Mosquito' as a ringtone, the theory being that the students can hear their phone ring without the teacher being alerted. In practice, many teachers and teaching assistants can hear it, as can many other students who get annoyed by this whining sound. 130.88.140.121 (talk) 11:47, 9 April 2008 (UTC)[reply]
They don't target teen's in particular. Its just an annoying sound that is played. If you are walking past you hadly notice, its only if you want to hang around and stand there that it gets on your nerves, this is the point, just like playing classical music. Teens don't hear any frequencies that adults and children don't.--155.144.40.31 (talk) 03:43, 10 April 2008 (UTC)[reply]
Not true. The mosquito is specifically a higher frequency. As people age, they are less able to hear higher frequencies. On average, a teenager can hear higher frequencies than an adult. This is the point. Of course, younger children can also hear those frequencies, often more clearly than teenagers, but younger children don't get a say in stopping 'youths' hanging out. 130.88.140.121 (talk) 09:12, 10 April 2008 (UTC)[reply]
Terminology question
As a humanities student poorly versed in anything resembling science, I'm having some difficulty interpreting the following sentence: "They express identical epizootiological patterns characterised by devastating dieback epizootics and panzootics when they infect susceptible unchallenged host populations."
I did some Googling and found the book you're reading. It looks like it this section may have been written in a hurry. I can't even parse the grammar of the next sentence after the one you quote. "Dieback" usually refers to plants or sessile animals, not mammals. I guess it's being used here to mean "fatal". "Unchallenged" does seem to have some meaning in the context of populations, based on Googling, but I don't know exactly what it means. I would guess it means populations that haven't been exposed to a given disease before. --Allen (talk) 20:48, 8 April 2008 (UTC)[reply]
True, the book could have done with some very serious copy-editing, but people writing about dead cows are few and far between, so I guess I'm stuck with it. :) Thanks for your help, that seems to make sense... Random Nonsense (talk) 21:17, 8 April 2008 (UTC)[reply]
Yes, the syntax is hopeless, but we can at least pick those two words from the mire. "Dieback" is a term from ecology: it referes to a population, not an individual. a plague can cause a dieback, meaning a population reduction. "Unchallenged host population" is a term from epidemiology. A population that has never been exposed to a pathogen is "unchallenged." Classic examples are The black plague in europe, syphilis in Europe, and measles among native Americans. In the sentence you quote, "suceptible" is redundant. A related term is "greenfield epidemic." -Arch dude (talk) 00:38, 9 April 2008 (UTC)[reply]
I don't agree that "unchallenged" and "susceptible" mean the same thing. Human populations which have never been exposed to smallpox but have been exposed to cowpox, and thus developed a smallpox immunity, would be one example. They are "unchallenged" but not "susceptible", to smallpox. For the reverse case, look at mad cow disease. A population exposed to this may not develop an immunity, in which case they are not "unchallenged" but are "suceptible". StuRat (talk) 16:09, 9 April 2008 (UTC)[reply]
Gull behaviour
Today, whilst having a bite to eat in the town square, I observed a new (for me) piece of gull behaviour. As I sat on a bench eating my burger, I watched the local urban avifauna going about their business - the pigeons and starlings pecking around on the cobbles for scraps, a few gulls bathing, swimming and sleepily hanging around in the fountain. A pretty normal afternoon scene, as it goes - until one of the pigeons walked a little too close to the edge of the fountain pool and then turned its back, as though to walk back in the direction it came.
Quick as a flash, one particular Herring Gull snapped wide awake - and pounced. I've never seen a gull move like that before - it lowered its head, flattened its body to the water and elongated itself, then skimmed across the surface incredibly quickly (and presumably silently), covering the distance between itself and the pigeon in a couple of seconds. I don't think that the pigeon expected it either - the gull's beak closed around its neck from behind before it even had the chance to look around. The gull rolled a full 360, flipping the pigeon into the water without letting go of it and somehow ending up on top. Then it pushed its (the pigeon's) head underwater and held it there, driving with its wings as though to apply more force. The pigeon was struggling wildly but the gull's strength was far superior.
If some kids hadn't intervened at that moment and scared the gull away, I fully expect that it would've waited for the pigeon to drown before chowing down on the carcass. The sodden pigeon had a nasty-looking throat wound and struggled to fly after they'd pulled it from the water - so maybe the gull tracked it down later to finish the job?
So, has anyone ever seen a gull hunt like this before? The actions of this bird today reminded me of those crocodile vs. antelope encounters from wildlife documentaries on the Discovery Channel. There was definitely something crocadillian there about the way the gull submerged its head to eye level. --Kurt Shaped Box (talk) 21:10, 8 April 2008 (UTC)[reply]
These are dinosaurs with feathers, mind. If I am to speculate wildly (to entertain us both)) what you saw might have been a strange trace of ultra-carnivorous behaviour (and I kid you not, avian dinosaur has been made redirect to bird, I laughed like mad). 81.93.102.185 (talk) 21:35, 8 April 2008 (UTC)[reply]
I find it quite interesting that a gull understands the concept of 'death by drowning' - bearing in mind that gulls float like corks and that drowning a gull would be only slightly less difficult than drowning a fish. I definitely see the reptile in there when I watch magpies interacting with each other on the ground. They remind me of those quick little lizards that live in the desert (I think the long tail helps). --Kurt Shaped Box (talk) 21:48, 8 April 2008 (UTC)[reply]
Reminds me of the youtube video of the pelican snapping up a pigeon in the park. Gulls are carnivores, not just piscivores, but I thought the mostly raided nests for fledglings and pups. Maybe hunting is a bigger part of their life than we give them credit for. kwami (talk) 22:00, 8 April 2008 (UTC)[reply]
I just found this on YouTube (searched for 'gull hunting'). The bird in the video (towards the end) displays similar behaviour to the one I saw today, though 'my' gull was much lower in the water. I've seen large gulls killing rats and mice on occasion - by shaking them and bashing their heads against the ground. --Kurt Shaped Box (talk) 22:12, 8 April 2008 (UTC)[reply]
Aye - perhaps they deliberately try to knock them out of the air and into the drink? You ever see a gull's 'air crash' attack against a corvid or a bird of prey? --Kurt Shaped Box (talk) 00:40, 9 April 2008 (UTC)[reply]
The Coot is lucky that the gull is probably only after the bread
Aye, they'll happily scrounge off humans and scavenge our organic refuse - but one look at the shape of the beak should tell you what they were built to be capable of. This (right) is a wonderful image. For a first-hand demonstration of the ferocity of these birds, try approaching a female gull of the largest species you can find in your area when she's sitting on her eggs, maintaining unblinking eye contact at all time. If you're lucky, the rest of the gulls in the area might take a keen interest in you showing you what they've got too... :) --Kurt Shaped Box (talk) 23:15, 10 April 2008 (UTC)[reply]
Anyone know if there's any truth to the legend that they fed vodka-soaked bread to the gulls in the final scene of The Birds in order to make them docile? There's quite a few semi-humourous stories about the making of that film - my favourite probably being the one about Hitchcock neglecting to tell Tippi Hedren that she was about to get a real, angry gull to the face as soon as the cameras started rolling - so that her reaction would appear 'authentic' on film... ;) --Kurt Shaped Box (talk) 23:24, 10 April 2008 (UTC)[reply]
That innocent cruisy impression they give needs rounding out in the article, maybe with a section on the dark side of gulls. That coot pic would do it, Julia Rossi (talk) 23:30, 10 April 2008 (UTC)[reply]
Sex is healthy, but sex with multiple partners carries a high risk of disease, so I'd think monogamy or near monogamy would be healthy. kwami (talk) 22:19, 8 April 2008 (UTC)[reply]
Well, if you're going to go there, then in a society which does not allow divorce, but does allow remarriage after the death of a spouse, you could get some very unhealthy results. kwami (talk) 07:32, 9 April 2008 (UTC)[reply]
How exactly do cosmologists determine how far away a star/galaxy etc is? It seems that if they're infering based on chemical composition, energy levels and brightness then they coulkd easily be wrong as stars could actually much brighter but further away or something similar. How accurate are the distances given between the Earth and stars? Are they debated within the field? 81.96.161.104 (talk) 22:44, 8 April 2008 (UTC)[reply]
See the article cosmic distance ladder for an explanation of methods used to measure stellar distances.
You might also want to look at the main sequence article. Stars fall into families with known compositions and luminosities. If you know the spectral properties of a star, you know where it falls on the main sequence, so you know how much light it's putting out, and you can compare that with how bright it appears in our sky and from that get an idea of the distance.
Certain stars such as cepheid variable stars oscillate in brightness, and these have fairly well tight correlation between luminosity and periodicity. Thesehese stars, when found in other galaxies, can be used as a "brightness standard" to judge the distance to galaxies.
But it should be noted that redshift tells us nothing about distance, only our relative speeds. Its up to other methods to determine expansion of the universe which combine to figure out the distance.--155.144.40.31 (talk) 03:36, 10 April 2008 (UTC)[reply]
Good question. There are fifteen to twenty interlocking methods, each applicable to a particular range of distances, and all underpinned by some heavy duty models of stellar evolution, cosmology and statistics. Here is a specific example showing how 8 different methods are used to estimate the distance to the Virgo cluster. There are uncertainties in these measurements, but notice that some of those uncertainty ranges are less than 10%, which is quite remarkable. Gandalf61 (talk) 15:00, 9 April 2008 (UTC)[reply]
Intelligence as something attractive
Disclaimer: This is not a personal question but personal advice will be appreciated.
Okay here it goes. There's a girl which I am attracted to. She's not that pretty but she extremely intelligent (she graduated suma cum laude) and is a very impressive public speaker. My question is, do males get attracted to intelligence as well or should we "ahem" get interested in the female anatomy only. Note that I'm a biologist first and a hopeless romantic later.
It's also about picking the best mate for the continuation of the species, so if you see intelligence as positive thing to pass on to your children then maybe that could make you attracted to her. 81.96.161.104 (talk) 00:30, 9 April 2008 (UTC)[reply]
I subscribe to the view that no one reproduces for the good of the species. Insofar as their behavior improves the survival of the species, they are only demonstrating an evolutionarily stable strategy. The result here, of course, is the same--intelligence improves the chances a child will survive--but we must remember that others' children may be affected adversely as a result. At the very least, they are deprived for at least a while of the availability of the mother's good genes. Imagine Reason (talk) 01:10, 9 April 2008 (UTC)[reply]
Trying to use a reductionist approach to make sense of individual preferences is pretty hopeless. There's no good evolutionary explanation for, say, furries. It's easier to use psychological explanations. There are more things involved than simple natural selection when we are talking about human societies. On some level, James Joyce was, like all males in a species, just trying to procreate. But that fact doesn't illuminate his work at all, and doesn't distinguish between him and any other male in the species. --Captain Ref Desk (talk) 00:34, 9 April 2008 (UTC)[reply]
I disagree. I think it's the Stickleback fish that will mistake a red bottomed toy for a receptive female. Human fetishes may be a misfiring of our arousal mechanisms in the face of modern creations that remind us of something in prehistoric past. As for artistic ventures, the brain is obviously using some of its communications abilities. Imagine Reason (talk) 01:10, 9 April 2008 (UTC)[reply]
"Do males get attracted to intelligence"? Of course, some do. Some don't. It's hard to generalize human mating preferences. In practice I've found that most males cannot fathom a long term relationship with a female mate smarter than themselves, at least in the US.
Two things, on the one hand, maybe it's about selection and evolution: you're attracted to mental proficiency = success potential to enhance and promote the survival of your own genetic material. On the other, you value a powerful, confident mind. Lucky for you it's a girl as well. My observation is males like to be the smarter/stonger in a pairing – that could be an ego thing and/or an instinct to protect the family group. Julia Rossi (talk) 01:58, 9 April 2008 (UTC)[reply]
I think the problem is a two way street. It's probably true that the majority of males indeed have problems accepting a partner who is smarter then them but I would say it's equally true many females have problems accepting a (long term) partner who is not as smart as them. While I'm sure there's at least some biological component to this, I wouldn't over-emphasise it. Even in the modern world, there is still a strong culturally ingrained view that the male partner should be the smarter (and stronger) one. Nil Einne (talk) 07:57, 9 April 2008 (UTC)[reply]
Agreed. There's a big component of environment and cultural conditioning. The nice thing is when someone finds they're attracted, and it's mutual esteem, everything else (including judging) just fa-ades away. Julia Rossi (talk) 10:12, 9 April 2008 (UTC)[reply]
The problem I see here is trying to explain being attracted to intelligence from a evolutionary point of view. The main stumbling block is that the visual markers for intelligence aren't as pronounced as say a formidable bosom or a symmetrical face. I would tend to think that intelligence isn't something that one would be able to specifically select for in pre-historic times. Intelligence by itself though would enhance the ability for an individual of a species to thrive whereas others of the same species with a lesser intellect would not (as much). The result of this of course is an individual who is bigger/stronger and all around more healthy looking than other members of the species. However I would tend to believe that being attracted to an intelligent girl is more a result of the culture you grow up in and not so much any inborn genetic preference. PvT (talk) 10:52, 9 April 2008 (UTC)[reply]
Don't forget things don't have to have a direct effect to be selected for. For example, if the more intelligent human is able to find a better cave, build a better tool, find better food, decorate themselves better, win a fight against a stronger competitor or even simply be smarter in working out to to convince a potential mate to choose them, these may very well have a significant effect on mate choice Nil Einne (talk) 11:30, 9 April 2008 (UTC)[reply]
Or if intelligence is correlated with an ability to tell jokes, use wit, make music, etc so that the male can get the woman to have sex with him. Further reading on this approach can be found in Geoffrey Miller's The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature.--droptone (talk) 11:53, 9 April 2008 (UTC)[reply]
Curious how, despite the actual situation in the question, you manage to fall straight back into evolution being about man evolving to get women to to have sex with him. Oh that mighty hunter! Cultural programming is strong. 130.88.140.107 (talk) 18:26, 9 April 2008 (UTC)[reply]
My post was meant mainly as a response to the idea proposed by previous posters that questioned whether intelligence could be selected for in the realm of sexual attraction. Another issue is that I am not really interested in answering the original question which asked if males are attracted to intelligence in females (which has to be the case some of the time given the OP claimed that he was) and the next question about whether men should be attracted to intelligent females or merely to females' anatomy (which mixes normative questions with biological ones to which I (a) do not feel comfortable answering giving the complexity of those sorts of questions and (b) was unsure exactly what the OP meant in his normative use of "should").--droptone (talk) 11:59, 10 April 2008 (UTC)[reply]
That intelligence brings pleasure in this case is obviously a physiological event, which in turn was programmed for at least partially by genes alone. If beauty (aka symmetry) represents health while intelligence improves survivability, then there may be a stable trade-off between the two, and in a section of the population intelligence may be selected over physical attributes so long as the gain from a good brain overcomes the decline in health. Imagine Reason (talk) 18:05, 9 April 2008 (UTC)[reply]
Thanks to all for their explanations. At least I know now that there's a biological side in my preference for intelligence. Now I'm planning on how could I impress her with my intelligence. Well, I think that's beyond the scope of the reference desk.--Lenticel(talk)21:55, 9 April 2008 (UTC)[reply]
Breaking away to all the evolutionary psychology here, I believe I am attracted to intelligence simply because I couldn't bear to be with somebody I couldn't relate to. Mac Davis (talk) 23:11, 9 April 2008 (UTC)[reply]
Will someone please explain to me why bands occur in nanocrystals containing only a few hundred to a few thousand atoms? The article says the number of atoms must be on the order of so why does this occur with so few? Zrs 12 (talk) 00:49, 9 April 2008 (UTC)[reply]
That article suggests that 'bands' are simply a term used to describe the electronic energy levels of a solid when lots of atomic orbitals (with similar but slightly different energy levels) come together. One atom will still have a conduction 'band' but rather than a band of different energy levels it will be one discrete electronic transistion (an electron jumping from ground to excited state). When lots of the discrete energy levels come together they produce bands of slightly different energies. Hope that makes sense.--Shniken1 (talk) 04:13, 9 April 2008 (UTC)[reply]
I know, but why are there bands (continuums of electron orbitals) when there is such a small congregation of atoms? Zrs 12 (talk) 18:53, 9 April 2008 (UTC)[reply]
The article appears very clear about this: sharing of electrons between multiple atoms "produces a number of [...] orbitals proportional to the number of atoms. When a large number of atoms (of order 1020 or more) are brought together to form a solid, the number of orbitals becomes exceedingly large, and the difference in energy between them becomes very small, so the levels may be considered to form continuous bands of energy." Thus a "band" is never a true continuum, it is always a collection of individual levels, with the number of levels similar to the number of atoms. If there are "many" atoms, and thus "many" levels, it will be convenient to ignore the discrete nature, and think of the band as a continuum, but there is no general definition of what constitutes "many" in this sense. Only in the context of a particular experiment will there exist a definition of "many", given by how small an energy difference between successive levels can be and still affect the outcome of that experiment. The number 1020 in the article is meant as an indication of the vast number of atoms in a "typical chunk of solid", not as a definition of "many". If the number of atoms is small enough that it makes sense to think of the individual energy levels within it, as may be the case in some nanocrystals, people may still choose to refer to this collection of levels as a "band". --mglg(talk)17:40, 10 April 2008 (UTC)[reply]
Current electricity
In current electricity questions, we frequently come across questions in which it is given that say a positive charge is moving from left to right or a positive charge is moved in an electric field, etc..
i want to know that how can a positive charge be moved?? because positive charge is present on protons and the protons are bounded inside the nucleus so how can we move the protons inside a conductor or elsewhere when they have been bounded by the nucleus. also as i have been taught that current is caused by flow of free electrons, do we have free protons of this type too, which can be moved?? —Preceding unsigned comment added by GK ROCKS (talk • contribs) 03:55, 9 April 2008 (UTC)[reply]
The direction of an electrical current is defined as the direction a positive charge would flow. This was defined before the electron and proton were discovered and now that we know that it is the negative electon that carries the current it has become quite confusing. It is however possible to move a positive charge, if you put electrodes in a salt solution the cations (+) will move to the negative electrode. There are also carbon nanotube wires that may be able to carry protons as a current, or in particle accelerators.--Shniken1 (talk) 04:20, 9 April 2008 (UTC)[reply]
If you knock an electron off an atom, say in a semiconductor, it will leave behind a positive charge, sometimes described metaphorically as an electron "hole". If a nearby electron then "fills" that hole (takes the place of the first electron), then it will leave behind a positive charge. So no, the positive charge itself doesn't move, but the result is the same as if it did. It's like a sliding puzzle, where it is the plastic numbers you slide around, but from a distance it looks as though the hole is moving around. Also, in an acid battery, both positive and negative ions are traveling in opposite directions. The details of whether electrons are traveling in metal or ions are moving through a solution are not relevant to describing the circuit. kwami (talk) 07:26, 9 April 2008 (UTC)[reply]
You might find the article on ion very helpful. In most cases around the home, current is the flow of electrons through a metal conductor (wire). The reason these charges move is because they are subject to a force due to an electric field - this the easiest way to cause a charge to move. In many chemical batteries, current also includes ions in solution undergoing an electrochemical reaction. In some more obscure cases, such as Earth's Van Allen belts, current can be a complicated interaction of ions, electrons, and time-varying electromagnetic fields. In this case, yes, we have free protons caused by ionized hydrogen; there are many other types of positive ions. Nimur (talk) 15:06, 9 April 2008 (UTC)[reply]
Note that in Electrophoresis (and other situations where you have current passing through a salt solution) in addition to the negative ions moving one way, you'll have positive ions moving the other way as well. In a solution of common salt, for example, it is not free electrons which travel to make the current, but the Cl- and Na+ ions which move back and forth. -- 128.104.112.85 (talk) 17:23, 9 April 2008 (UTC)[reply]
For an analogy, consider warm and cold air. If you leave the wooden front door of your house open, but the glass storm door is still closed, the house will cool down more quickly. Some people might call this "letting the cold in", although technically it's "letting the heat out", since heat is the vibration of atoms and cold is the lack of this vibration. However, you can think about it either way, it doesn't really matter on a practical level. Similarly, you can think of protons flowing from one location to another, even though they really don't do that, if you like. One exception would be ionized normal hydrogen, where you do indeed have flowing electrons and protons. StuRat (talk) 15:46, 9 April 2008 (UTC)[reply]
StuRat, I have a long-standing complaint against the anecdote of "letting the cold in/letting the heat out." The flaw in the analogy is that it fails to consider convection, or bulk motion of air mass. In the purely thermodynamic sense, it is true that heat always flows from hot to cold reservoirs; but in the unique case of fluid motion, cold air can move due to a pressure gradient, viscous dragging, and a wide range of complicated interactions. So, in fact, opening a door is neither letting heat in or out; it is letting air in or out; and that air carries a certain amount of heat with it convectively. Nimur (talk) 16:04, 9 April 2008 (UTC)[reply]
That would be why I included the glass storm door in the example, to prevent any air from entering or leaving the house. Thus, only heat transfer occurs. StuRat (talk) 17:03, 9 April 2008 (UTC)[reply]
If you rub a glass rod with a piece of silk the glass will acquire a positive charge. (while the silk acquires a negative charge). If you move the glass rod from left to right, you are moving a positive charge. What is complicated about this? Edison (talk) 18:03, 9 April 2008 (UTC)[reply]
The fact that a proton isn't flowing from one atom to the next maybe. But anyway as someone said it current was said to flow positive to negetive by convention. Once we discovered protons and electrons we realised they got it wrong. Electrons flow from negetive to positive in a circuit while the protons just sit there. Or a 'hole' (a proton with no matching electron) moves from one atom to the next flowing positive to negetive--155.144.40.31 (talk) 03:30, 10 April 2008 (UTC)[reply]
I have a real problem with the notion of protons jumping from atom to atom. That would constitute transmutation. Add a proton to an atom and it becomes a differnet element. Add or subtract an electron and it stays the same element. The change in binding energy would be large if protons jumped from atom to atom to effect a flow of current. That is not what hole current is. Edison (talk) 04:19, 10 April 2008 (UTC)[reply]
I know that some microorganisms can get their nitrogen requirements met with inorganic substances such as nitrate salts or urea. Others need organic nitrogen sources such as peptones or amino acids. I am looking for some rules of thumb along these lines, e.g. "most fungi can be cultured with nitrates" or "gram-positive bacteria usually require amino acids". Any little bit of information you can offer could help; maybe we can come up with a rule of thumb if none exists. ike9898 (talk) 14:57, 9 April 2008 (UTC)[reply]
There's some information in our article on nitrogen fixation; that doesn't fully answer your question, though. Nitrogen fixation refers to conversion of near-inert atmospheric nitrogen into bioavailable forms. I gather that you're looking for the broader set of organisms that can use any bioavailable inorganic nitrogen to generate all the amino acids de novo. Unfortunately, our article on amino acid synthesis doesn't list the organisms with these capabilities, though the navboxes at the bottom of that page cover all the important biochemical pathways involved. TenOfAllTrades(talk) 15:45, 9 April 2008 (UTC)[reply]
Orbit
If an object on a satellite is propelled radially toward the mass being orbited what will be its path? Will it orbit at a more eccentric orbit, or will it return to the same orbit as the satellite from which it was thrown?
Cslloyd (talk) 15:17, 9 April 2008 (UTC)[reply]
To make sure I'm understanding the suggestion, we're talking about a guy on the space station throwing a baseball at the Earth (more or less), right? In that case, and neglecting out air resistance and such, the baseball will orbit with a slightly different eccentricity (though not necessarily more, depending on the orbit of the space station) while still crossing the orbit of the space station. Fully raising or lowering an orbit is generally accomplished by complimentary thrusts at opposing points in the orbit, not with a single thrust. — Lomn15:43, 9 April 2008 (UTC)[reply]
If the baseball is thrown with sufficient speed towards earth, it will enter an eccentric orbit with a collision to the planet's surface. This is almost intuitive; throwing a ball down does make it go down; the trick is that it is thrown from a moving "platform" and already has a (very significant) angular velocity / angular momentum. You can compute the trajectory if you know its initial orbit and the velocity it is thrown at. It is also worth noting that large transfer of momentum to the baseball will also result in equal and opposite reaction on the astronaut, to conserve momentum for the complete system. Nimur (talk) 15:52, 9 April 2008 (UTC)[reply]
(Addendum) As Lomn pointed out above, it is also possible that the baseball's new orbit does NOT collide with the planet (neglecting air resistance and only considering "hard impacts"). In that case, the new orbit will be more eccentric, as mentioned by Lomn, but will intersect the original point where it was thrown from. Nimur (talk) 16:00, 9 April 2008 (UTC)[reply]
If an object were projected from a satellite in low earth orbit in a retrograde direction with about 1% of the satellite's orbital velocity, it would reenter the earth's atmosphere and burn up or land depending on its aerodynamics. A velocity of "throwing" of 170 mph or thereabouts should suffice. This would be at a right angle from the direction posited by the questioner. Edison (talk) 17:56, 9 April 2008 (UTC)[reply]
...but the golf ball that was hit from the ISS in Nov 2006 is still in orbit nearly 30 18 months later - see this tracker. Apparently NASA predicted it would stay in orbit for only 3 days ... Gandalf61 (talk) 19:58, 9 April 2008 (UTC)[reply]
Our article Hertz has a table conveniently telling us all the forms of "hertz" combined with all the SI prefixes. The familiar ones like kilohertz, megahertz, and gigahertz are there, but so are units smaller than the hertz, from the decihertz (0.1 Hz, i.e. once every 10 seconds) all the way down to the yoktohertz (10–24 Hz, i.e. once approximately every 3 x 1017 years (about 23 million times longer than the age of the universe). My question is, are these units of frequency smaller than the hertz ever actually used in real-life applications? I don't just mean the really implausible ones like the yoktohertz, I mean even things like the millihertz (once every 16'20"), microhertz (once approximately every 11.5 days), and nanohertz (once approximately every 31.7 years). Is there anything in real life whose frequency is actually measured in those units? —Angr16:53, 9 April 2008 (UTC)[reply]
A quick google search (ignoring the definition pages) yields the following scientific topics (primarily journal article titles):
Millihertz Quasi-Periodic Oscillations from Marginally Stable Nuclear Burning on an Accreting Neutron Star
Isolation transformer passes millihertz signals.
Millihertz Oscillation Frequency Drift Predicts the Occurrence of Type I X-ray Bursts
The Last Few Microhertz: Eliminating Remaining Discrepancies Between Observed and Calculated Solar Oscillation Frequencies
Golf: Solar Signal for Frequencies Below 5 microHertz
T violation and microhertz resolution in a ring laser
Pulsar Timing Array -- A Nanohertz Gravitational Wave Telescope
Probing the Nanohertz Gravitational Wave Background
That makes sense, thanks! And to judge from one of the titles listed above, pulsars' radiation emissions can also be measured in Hz. That article says pulsars' periods range from 1.5 ms to 8.5 s, but presumably it could also be stated in terms of frequency ranging from 120 mHz to 670 Hz. Next question: in my original post I wrote that 1 nHz corresponds to a frequency of approximately 31.7 years; am I right in thinking that 12:00 midnight on New Year's Day also occurs at a frequency of approximately 31.7 nHz? Or have I screwed up my math somewhere (all too possible)? —Angr18:06, 9 April 2008 (UTC)[reply]
What I was mostly interested in is knowing whether I got it right that when 1 nHz corresponds to a frequency of x years, then years occur at a frequency of x hertz. I wasn't expecting that apparent coincidence. —Angr21:06, 9 April 2008 (UTC)[reply]
The examples you give all differ from the unit of hertz by only a SI prefix. I have most commonly seen scientific notation used to express smaller frequencies in plain hertz like (e.g. 2.3×10−3 Hz), but the metric prefixes are systematic and (many of them) common enough that it seems either (e.g. 2.3 mHz) should be clear to the reader, which is what is really important. You may also find that for applications where very low frequencies are common that the measurements used are instead that of periodicity or wavelength rather than frequency. I'm sure you could easily do Google searches for variations of herz ("millihertz", "milli hertz", "mHz", "centihertz", "centi hertz", "cHz", etc.) to see if you come up with anything. What is the purpose of the question? Is it idle curiosity, or are you trying to determine whether it would be proper to use a value in a particular context, or what? --Prestidigitator (talk) 18:04, 9 April 2008 (UTC)[reply]
It's mostly idle curiosity, perhaps with an eye to adding a discussion of these units at Hertz#Applications, which at the moment only discusses things measured in hertz and the units larger than the hertz (kHz, MHz, GHz, etc.). —Angr18:12, 9 April 2008 (UTC)[reply]
Heavy water question
Because of the laws of thermodynamics, just having heavy water lying around in a non-sealed container will cause it to react with the light water vapour in the air, gradually causing a situation where I have plain old light water lying in the container and an extremely thin concentration of heavy water vapour in the air around me. Of course given little enough heavy water in the first place, this is perfectly safe, but it will lead to loss of valuable heavy water. So my question is, how quickly will this happen, and what can be done to slow it down? JIP | Talk17:43, 9 April 2008 (UTC)[reply]
This is a very difficult question to answer quantitatively. This page goes into a bit of a discussion about half of the problem—how fast does liquid water move to the gas phase in an evaporative process? (At constant humidity, you have a dynamic equilibrium between evaporation and condensation, such that water is entering and leaving the liquid phase at constant, equal rates.) The rate of exchange of heavy water into the gas phase is going to depend greatly on the surface area of the container, the depth of the container, the amount of mixing and circulation of the liquid in the container and the air above it, the temperature, any agitation of the liquid-air interface, etc..
If you use a broad, shallow pan of warm heavy water and put it into a room with a fan blowing over the surface (or even better, with a bubbler circulating room air through the liquid in the pan) the equilibration between light and heavy water will occur many orders of magnitude more quickly than if you have the liquid in cool bottle with a narrow mouth sitting in still air. TenOfAllTrades(talk) 18:47, 9 April 2008 (UTC)[reply]
Just to complicate things still further, once you have a mixture of H2O and D2O in the liquid phase, you'll get some HDO (half-heavy water? :-) due to hydrogen ion exchange. That gives you three molecular species to keep track of. JohnAspinall (talk) 20:39, 9 April 2008 (UTC)[reply]
I don't actually have any heavy water yet. I'm trying to purchase some, in order to conduct experiments on heavy ice in normal water. As I have not done anything like this before, I want to make sure of the necessary precautions in advance. JIP | Talk20:59, 10 April 2008 (UTC)[reply]
In most cases the controlling quantity is average air velocity. In a matter of seconds after being exposed to air, a microlayer of air saturated in heavy water vapor will form above the heavy water liquid. In most environments the rate at which this is transported away from the liquid surface is governed by the average air speed (only in very, very still air is diffusion more important than local turbulence). Because of things like leaky doors and air conditioning, empty indoor environments typically have ambient air speeds of 0.1 - 10 mm/s. To order of magnitude, you might expect to lose heavy water at a rate that is of order the area of your exposed surface times the ambient air velocity times the saturation vapor density. Which suggests a number like 10-70 mg lost per cm^2 of surface area exposed per hour in an empty room. If you are doing silly things like admiring your heavy water and breathing over it, one could easily increase this by one or more orders of magnitude. Obviously the best solution is to keep your heavy water in a sealed container whenever possible. Dragons flight (talk) 06:52, 10 April 2008 (UTC)[reply]
What histone modifications exist at <<DNA sequence>>?
Does anyone know a method by which one could ascertain the histone modifications that exist in a population of cells at a particular DNA sequence? I know the reverse is possible (finding out what sequences enjoy the comfort of particular histone modifications). ----SeansPotato Business17:45, 9 April 2008 (UTC)[reply]
Anergy
An article I read from 1993 describes a process of anergy where the immune system's response to a specific antigen can be inhibited (at least temporarily) while the rest of the immune system is left unaffected. This exists naturally to prevent our bodies from destroying themselves, and seems to show promise in tissue grafting and the treatment of autoimmune diseases but our article on anergy is just a stub. I'm assuming that 15 years would allow enough research to substantiate some of its potentials. Is this something that the scientific community hasn't done much research on or have Wikipedians failed to document major studies on it since 1993? — Ƶ§œš¹[aɪm ˈfɻɛ̃ⁿdˡi]19:27, 9 April 2008 (UTC)[reply]
Disadvantage to bilingualism in evolutionary point of view
It's been shown that babies can distinguish all the phonemes available, and that as they get older they find it more difficult to distinguish phonemes that are not important in their native language. If exposed to two languages, they retain the ability to distinguish the phonemes important to both languages. I understand in a general sense that pruning brain connections is an important thing, but in this case there's no evidence that bilingual (or multilingual) children learn their first language any worse than monolingual kids, or have any other disadvantages. So why do we lose this ability? What are we gaining from that? moink (talk) 21:04, 9 April 2008 (UTC)[reply]
I don't think it would be wise to assume that we gain anything from losing the ability to distinguish foreign phonemes. It could simply be a side-effect of the way our brains learn language. (A spandrel (biology).) --Allen (talk) 21:28, 9 April 2008 (UTC)[reply]
In fact, according the article I just linked to, Noam Chomsky believes language may itself be a spandrel, which would render the entire question moot. --Allen (talk) 21:30, 9 April 2008 (UTC)[reply]
Not only that but higher life expectancey is a relatively mordern thing that may have never had a part to play evolutionarily because we were never able to age to beyond the point. You don't have to go back to far for life expectancy is the low 20's.--155.144.40.31 (talk) 03:23, 10 April 2008 (UTC)[reply]
My understanding is that the ability to learn language (not just phoneme distinction, but all aspects of grammar) is directly related to brain plasticity so that, once your brain becomes less plastic, your ability to acquire language diminishes. Diminished plasticity, I'm sure, has a number of evolutionary benefits. — Ƶ§œš¹[aɪm ˈfɻɛ̃ⁿdˡi]04:14, 10 April 2008 (UTC)[reply]
The angle of the phasor is inverse tan of (Vl - Vc) / (Vr), (or inverse tan of (Xl - Xc)/ R). Obviously Vr (or R) is the magnitude in real direction and Vl-Vc (or Xl-Xc) is the magnitude in the perpendicular. So you just need to know the capacitor impedance and the resistance--155.144.40.31 (talk) 03:18, 10 April 2008 (UTC)[reply]
Scientists say that galaxies are moving away from each other, so the Universe is expanding. If the Universe was expanding, and we are integral parts of it, wouldn't that mean that we were expanding too? If so, wouldn't this mean that there would be no noticeable difference in distance over time? If this is the case, then galaxies must be moving away from each other for a different reason.--ChokinBako (talk) 22:57, 9 April 2008 (UTC)[reply]
We would be expanding, but there are forces holding us together - on the small scale, mostly electromagnetic force, and on the larger scale more often gravitational force. Imagine you and a friend are standing, along with lots of other people, on the surface of a giant balloon, and you're holding your friends hand. When the balloon gets inflated, everyone moves away from each other, but you and your friend stay together because you're still connected. Confusing Manifestation(Say hi!) 23:04, 9 April 2008 (UTC)[reply]
Hi. When I went to a nearby plaza recently, I saw some huge sandbanks, the remnants of giant snowbanks that have melted and left their sand, dust, and other material in a huge heap. I mean, even with a huge snowbank, you would have thought that it would have eventually melted and left behind maybe a few deposits of dust, right? Well, no. It appears that due to this winter's amazing snowfall amounts, the snow contained extra amounts of sand, and created a heap. Now, I know that what usually happens is, snow from the streets gets shovelled onto the lawns, the snow contains dirt, as the snow melts, the dirt is left behind, the melting water forms mini-rivers flowing over silt, and as the water from the dirt evaporates, it turns into sand, and spring wind blows the sand across the street, forming mini-sandstorms, and the cycle repeats again.
However, at this plaza, from which probably about 20,000 square metres of snow was shovelled into one place, a huge snowbank, and later a resulting heap developed. Well, this heap is huge, and I think it must weigh 1000 tonnes. It's still wet, but I think as the water evaporates this heap will remain. First of all, where does all the dirt come from? Yes, I know that as the snow is shovelled, it must contain massive amounts of sand from eroded ashphalt, tar from the cars and roads, remnants of road salt, dirt carried from grass by water to the roads, sand carried from elsewhere from dust blown from previously melted snowbanks, silt from nearby places, dirt carried by walking people, grains of metal from the machinery of the snowploughs, dust from industry, manufacturing, and heavy machinery, atmospheric dust, as well as dust, pollen, and pollutants carried down by snowflakes, but why such a massive amount?
Also, why does a snowier year tend to bring larger heaps, is it because more snow requires more shovelling and picking up the dust from the roads, or because of more dust in the snowflakes deposited? Also, what will happen to the heap? Will it stay until next winter and keep building up, will it be manually shovelled away by heavy machinery, or will it be blown away by the wind and eroded by water? Either way, wouldn't that create massive sandstorms in the area as it dries up and is carried to nearby areas? If a sudden windstorm blows on the dust, would it bring sand to areas kilometres away? If it rains (heavy rains are in the forecast within the next few days), will the rain cause it to stick to itself, or erode it away?
Or will some people just use it as a bike ramp? Will it affect local wind patterns? Thanks. ~AH1(TCU)00:46, 10 April 2008 (UTC)[reply]
Apologies for a banal answer to such a cosmic question, but are you sure it couldn't have been the remnants of the sand (sometimes mixed with salt) which is typically spread on snowy/icy roads to increase traction? The snowier the winter, the more of that they have to spread, and it all ends up somewhere. —Steve Summit (talk) 02:40, 10 April 2008 (UTC)[reply]
As to what will happen, I suggest phoning the organization that arranged for the snow to be piled up there and asking them. That would either be the plaza management if the snow was all from the parking lot itself, or else your local city hall (or county government or whatever) if they arranged for snow from elsewhere to be dumped in the parking lot. --Anonymous, 03:26 UTC, April 10, 2008.
decision sequences
Is there a publication which shows decision/results sequences in which subjects had a choice of doing one thing or another, for instance to stay inside and stay warm or go outside without adequate clothing and become cold, with each decision sequence ending in a result, for instance the number of persons that developed a cold as the result of following one sequence of another? 71.100.160.37 (talk) 02:33, 10 April 2008 (UTC)[reply]
Lots of publications (both fiction and non-fiction) feature decision/results sequences. Can you be more specific? Also, from our common cold article: "Although common colds are seasonal, with more occurring during winter, experiments so far have failed to produce evidence that short-term exposure to cold weather or direct chilling increases susceptibility to infection, implying that the seasonal variation is instead due to a change in behaviors such as increased time spent indoors at close proximity to others."--Shantavira|feed me09:03, 10 April 2008 (UTC)[reply]
Colds are a good example but I am really looking for longer sequences with many more decision points such as someone ending up as a CEO versus a security guard position. BTW - One of the motives for having a statistically based sequence is that I completely disagree with the conclusion set forth above, which is based on experiments and not everyones actual experience. 71.100.160.37 (talk) 21:45, 10 April 2008 (UTC)[reply]
They both have the same etymology (echidnas are not named after the mythological monster). Echidna the mammal comes from Latin echinus, from Greek εχίνος (ekhinos, meaning hedgehog), from εχίς (ekhis, meaning snake). As you can see in Echidna (mythology), they both come from the root εχίς. 70.162.25.53 (talk) 03:35, 10 April 2008 (UTC)[reply]
To confuse things a bit, the animal kingdom also has a genus named Echidna which fits the mythological description glancing eyes and huge snake, great and awful, with speckled skin, eating raw flesh beneath the secret parts of the holy earth (Don't know about the "fair cheeks"). According to the article on Homonym (biology) the name was first proposed for the aquatic genus and thus the eel has priority. The spiny genus was renamed Tachyglossus. ---Sluzzelintalk11:30, 10 April 2008 (UTC)[reply]
"When one gets older, the skin looses elasticity" sounds like half of a skin-care ad! Can you tell me what the other half would be, in an NPOV way? (ie what is the solution? I've always wondered what the science is behind it once you remove the marketing). Thank you! —Preceding unsigned comment added by 217.116.40.195 (talk) 15:49, 10 April 2008 (UTC)[reply]
Haha, well I don't think there is any 'solution' for it, it's just a fact of life; however, I'm sure many skin product companies assure their customers that their products will guarantee them wrinkle free skin. Maybe botox injections? -- MacAddct 1984(talk • contribs)16:01, 10 April 2008 (UTC)[reply]
why can't humans focus on two objects simultaneously like the chameleon? please also include the answer to my email - *redacted* thank you.
Daniel Dennett has speculated that human consciousness may be a virtualization of a parallel processing machine as a serial processing unit (computing is moving in the opposite direction). The stream of consciousness that results would be hampered if our vision were divided into two exclusive fields. Imagine Reason (talk) 18:37, 10 April 2008 (UTC)[reply]
Apparently they've done the exact experiment on people with brain injuries whose two sides of the brain can't communicate. They are shown different pictures for each eye, and they end up making up stories that reconcile the differences without any conscious effort. Imagine Reason (talk) 19:33, 10 April 2008 (UTC)[reply]
I've watched a few computer simulations of black holes and can't help but wonder if they're slightly misleading
As far as I know a black hole is supposed to have a gravitational pull so strong that not even light can escape so in theory if you were to actually be in the vicintiy of one you would never know it existed because all the light that is usually reflected off surfaces in order for you to see them would actually be 'sucked' into the black hole.
This makes me think that the only way you could actually tell visually that a black hole was 'nearby' would be that there would be an unusual absence of light in a particular direction.
I guess my question is are these simulations purely to allow people to learn about the path of anything approaching a black hole or is there some scientific truth to the multitude of colours displayed in these simulations? —Preceding unsigned comment added by 82.44.178.36 (talk) 20:39, 10 April 2008 (UTC)[reply]
If I recall correctly, a black hole heats up nearby gases until they emit X-rays along the 'poles' of the singularity. Plus, if you see a space in the night sky where there's no light, that suggests the presence of a black hole. Correct me if I'm wrong, anyone, it's been a while since I took much interest in astronomy. Vranak (talk) 22:56, 10 April 2008 (UTC)[reply]
It's not that the black hole heats up gases; it's that if there is lots of matter around it will start to rub against other matter as it is pulled down into the black hole. Outside of the event horizon, what you see is the result of this friction. It's a lot of energy. See quasar. I think it's pretty neat—that something as apparently simple as friction is probably responsible for the most powerful energy sources in the universe. --Captain Ref Desk (talk) 23:20, 10 April 2008 (UTC)[reply]
(e/c) Outside the event horizon, the gravitational field around a black hole is just like that of any other large body of mass, like a planet or a star. Gravitational fields bend the path of light, so if there is a star on the other side of the hole to you, you will see a gravitational lensing effect. Confusing Manifestation(Say hi!) 23:04, 10 April 2008 (UTC)[reply]
it is only mass that is beyond the event horizon that is 'invisible' because the light it gives off gets sucked in. However before the event horizon matter can orbit the black hole just like a satellite orbitting a planet. And due to the strength of the block hole it would not be surprising to find large amounts of matter orbitting. I would guess the colours are meant to just be clouds of gas that are slowly orbiting and eventually going to fall through the event horizon.--Dacium (talk) 23:07, 10 April 2008 (UTC)[reply]
Clock of observer at center of the earth
Please follow my reasoning for a moment:
Suppose that there was a hollow cave at the center of the earth that allowed an observer A to "float" freely. The observer would, then, not experience any acceleration due to gravity, since an equal force would act on him from all directions (shell theorem).
However, here's the question. Suppose there was another observer B positioned a considerable distance away from the earth. Relative to observer B, would he perceive A's clock to run slower than his? My intuition tells me A's clock would run slower, since even though A does not feel any force acting on him, he's still surrounded by nearby regions of intense gravity. Is my interpretation correct?
Dmitry Brant (talk) 20:42, 10 April 2008 (UTC)[reply]
I don't see why. A's clock, unlike another that's floating in space orbiting Earth, isn't accelerating. If you consider the equivalence principle, there's no experiment, so long as A stays within the shell, for him or her to determine if the location is within the shell or very far away from Earth.Imagine Reason (talk) 20:58, 10 April 2008 (UTC)[reply]
Hmm. That's what I was thinking. Although the local field might have zero strength, the gravitational potential is definitely lower at A. It seems pretty obvious that a photon emitted from A will have lost energy and thus been redshifted if it reaches B. --Prestidigitator (talk) 22:28, 10 April 2008 (UTC)[reply]
Gravitational time dilation reaches its maximum at the surface of the planet (were gravity is the strongest) and falls away to zero at the center. At the centre of the earth there is no gravitational potential and time runs normally. For the guy way out in space there will be a very small gravitational potential, so his clock will run slower. If you assume he is so far away that the gravitational potential is also effectively zero, both clocks are the same and there is no dilation.--Dacium (talk) 23:00, 10 April 2008 (UTC)[reply]
You're speaking in terms of gravitational force, not gravitational potential. Gravitational potential strictly increases as one moves out from the center of the Earth. Someguy1221 (talk) 23:06, 10 April 2008 (UTC)[reply]
How does this collet work?
Hi all,
I just got a second-hand Black & Decker rotary tool, like a Dremel, which is supposed to have a "universal collet system". I'm pretty sure it has all the parts. However, I'm confused about how the collet works. On the assumption that it's the small metal sleeve with a wide head, then it looks almost exactly like the one at the bottom of the image here. However, it does not have any slits in it. It's a tube and the sides are completely solid. How is it supposed to tighten with no slits in it? I've tried putting in the "nut" part of the tool and tightening the nut, and I can still easily slip the bits that came with the tool.
Am I missing something? What is the point of a collet without slits in it?
1 - unidentified clouds
2 - aerial view (Spain)
3 - aerial view (UK)
4 - dead bird
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