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March 24

Mean tropical year

Is the "mean tropical year" the average of the four tropical years measured respectively starting at the vernal equinox, summer solstice, autumnal equinox and winter solstice, or is it based on a mathematical "continuous" averaging taken over all possible tropical years through the four seasons? I have seen it described in both ways -- does anyone have a definitive answer? 86.134.46.159 (talk) 01:02, 24 March 2008 (UTC) (BTW... I should mention that the Wikipedia article Tropical year contradicts itself in this respect. In one place it says one thing and in another place it says another.)

how do i become taller?

ow i'm over 20 and my height is 5'4" so i want to more tall than before so how can i do? besides go living in asia 141.149.55.113 (talk)

(moved from WT:RD) :D\=< (talk) 04:45, 24 March 2008 (UTC)

There's nothing you can do.. try wearing shoe inserts or buy shoes with thick soles. There is distraction osteogenesis, but it's stupid and, well, absolutely insane. :D\=< (talk) 04:49, 24 March 2008 (UTC)

Aren't you the same person who asked the same question back in January? Do reread the answers at that link. Also read the "Cosmetic lengthening of limbs" section in the distraction osteogenesis article Froth referenced. —Steve Summit (talk) 05:07, 24 March 2008 (UTC)

I'm over 20 and my height is 5'4" so what's the problem? Why would you want to be taller? I think that I'm the perfect height, don't you? Are you saying that I should want to be shorter or taller? Why the hell would I want to be what I'm not? I also don't write poetry - should I worry about that and want to be a poet? Look 141..., you're asking a question like "I am white and I want to be black" or some other such other bullshit. You can and should develop the things that you are good at and not concern yourself with those things over which you have no control. And, asking the likes of us to address the things over which you have no control is really stupid. --hydnjo talk 05:56, 24 March 2008 (UTC)

No use berating the guy for asking a question. Perhaps he thought there might be an easy way to increase his height. (Certainly several completely bogus 'herbal' products are advertised.) Perhaps he has some legitimate and practical reason for wanting to be taller. (Just because we can't think of one off the top of our heads, doesn't mean it can't be true.) Most of all perhaps the guy was just curious. There's nothing at all wrong with that. The point is that it's crazy to rant at someone based not on what they said, but based on your opinions of what you suppose their motives for saying it might be. 72.10.110.107 (talk) 13:50, 24 March 2008 (UTC)

You know, this question was once asked the Cecil Adams on The Straight Dope. He gave some good answers; I'd recommend reading it. Neal (talk) 16:26, 24 March 2008 (UTC).

There is no available drug therapy which can help you grow taller except for in paediatrics where growth hormone therapy can be used, but in adults this is useless. Other than using the |rack, I think you're stuck at 5'4". CycloneNimrod (talk) 17:55, 27 March 2008 (UTC)

Bamboo

I would like to know the kinds of bamboos. Please!

Is there somthing within the Bamboo article that you don't understand? --hydnjo talk 05:59, 24 March 2008 (UTC)

I mean kinds of bamboos! Names of them!I searched in Bamboo but I didn't see that! so....!

The bamboo article says bamboo's in the subfamily Bambusoideae, which has a list of a bunch of kinds of bamboos. It looks like it lists them all, but may be not(?) -Haikon 06:23, 24 March 2008 (UTC)

) thanks u so much! To u all!

How come so many invasive species come from Japan?

...to the United States and Europe? May be "so many" is an exaggeration. I can only think of two, those ladybugs and kudzu, but if you think of Japan as a group of Pacific islands, two is a lot. I mean you probably couldn't import an invasive species from New Zealand or Hawaii if you tried. And given some of the peculiar animals native to Japan, it would seem like that ecosystem would be more on the receiving end of pest invasion.

Anyway, I'm trying to find general rules or theories regarding invasive and non-native species to answer this question, and I'm not coming up with much. (Except a "Baker's rule", and I haven't even found that really, not stated by Baker him/herself anyway.) A lot of isolated ecosystems have been screwed up because of non-native species, and in each case it's understood pretty clearly how and why, but I can't find an explanation of how any why this would happen in general, not just in a given case. Anything at all like an answer or points in the right direction would be greatly appreciated. -Haikon 06:44, 24 March 2008 (UTC)

Your first statement appears to be slightly flawed. New Zealand plants are a problem in other countries, e.g. [1], [2]. It is of course true that exotic plants are more of a problem in NZ then NZ plants in other ecosystems, but then nothing you've said suggests that this is any different from Japan except that the Japanese invasive species are more widespread, but then again, the Japanese ecosystem was always a lot less isolated then NZ or Haiwaii (meaning it was a lot less different). BTW, from what I can tell it is inaccurate to call the Harmonia axyridis a Japanese invasive species. It may be native to Japan but from what I can tell it is also native to other countries. It appears even more clear cut with the kudzu. All these two examples really tell you is that the Japanese ecosystem was not that isolated. You could just as well say any species which is native to Bali or some other small island and invasive comes from a tiny island even if in reality it is native to a lot of places. To answer your second question, in general a species will become invasive if it is able to better fill a niche then any of the existing native species. Countries with highly isolated ecosystems such as New Zealand tend to have a lot of niches which can be more effectively filled by something from somewhere in the very wide world out there. Consider New Zealand for example where the lack of large ground based predators meant that most native animals particularly birds obviously were adapted to such a situation leaving it ripe for invasion by ground based predators. Obviously for very diverse, non-isolated ecosystems like Europe, Asia or whatever, it is unlikely that there will be many niches left unfulfilled or that there will be a whole lot of invasive species coming from the small number of isolated ecosystem which are able to better fill a niche. Nil Einne (talk) 09:16, 24 March 2008 (UTC)

Good answer, Nil. And of course we have an article on Invasive species, which is immensely improved from when I last saw it a couple of years ago. --Allen (talk) 17:04, 24 March 2008 (UTC)

Big bang expansion thing

Okay, space is expanding so from my head it appears my head is the center of expansion. Got it. But am I to understand that at the atomic level space is not expanding? Electrons are not getting further away from the nucleus and the space between atoms and molecules is the same density and the distance between them is the same but what about the distance between planetary orbits? Is that expanding as well? If so by how much in a billion years? 71.100.1.65 (talk) 10:11, 24 March 2008 (UTC)

Short answer is no, space is not expanding at the atomic level because the dominant force that determines the interactions betweens atoms is the electromagnetic force, not gravity. Space is not expanding at the scale of planetary orbits either because the simplifying assumptions on which the Friedmann equations are based are only physically correct on scales of millions of light years or more. For the long answer see this question and its answers on March 21 above, and our metric expansion of space article. Gandalf61 (talk) 13:07, 24 March 2008 (UTC)

Okay, so only gravitational space is expanding? 71.100.1.65 (talk) 20:26, 24 March 2008 (UTC)

Wow, we've got a lot of questions on this lately! --Captain Ref Desk (talk) 14:30, 24 March 2008 (UTC)

Going back to the dots on the balloon analogy in our previous attempt at this question. Draw dots on the balloon, lets call those dots galaxies. Now inflate the balloon - dots get further apart. Now draw some more dots, lets call these dots atoms. take some short pieces of wire and glue the ends to adjacent atoms. Lets call the pieces of wire atomic bonds or crystal lattice. Inflate the balloon again. Do the atoms get further apart? Now give the 5 year old their balloon back. SpinningSpark 23:12, 24 March 2008 (UTC)

Right. Space is expanding on subatomic levels, but nothing is getting farther apart as such things are, in one way or another, stuck together. But if space were expanding fast enough, you might get a big rip. Someguy1221 (talk) 23:33, 24 March 2008 (UTC)

Not sure that we do know that space (or, more precisely, the space-time metric) is expanding on subatomic levels. I see three problems with this:

1. The Friedmann equations, which are used to model the large scale expansion of space, are derived by assuming a homogeneous and isotropic distribution of matter and energy. This is only physically realistic (even as an approximation) on supra-galactic scales of millions of light years or more. The Friedmann equations certainly do not apply to anything smaller than a galactic cluster.
2. The large-scale expansion of space does not have to imply a homogeneous expansion at all places and scales. How do we know that the expansion is not confined to intra-galactic space, for example ? AFAIK, there is no evidence or conclusive argument that says the expansion of space has to be homogeneous.
3. To even begin to model the behaviour of the space-time metric at sub-atomic levels would require a theory of quantum gravity, which does not yet exist. Gandalf61 (talk) 09:51, 25 March 2008 (UTC)

Forgive me for asking a homework question, but how many different hormones are there in the human body?

Discovered at least -- I've searched this all over, and it seems a particularly pointless question to ask (given that we also have to detail every petty step in various signal transduction pathways), but alas, I can't seem to find a source that lists *every* single human hormone, or at least one that tells me that this is every single human hormone discovered so far (and numbers them). John Riemann Soong (talk) 14:33, 24 March 2008 (UTC)

There are hundreds, are you sure this isn't specific to a certain syllabus? --Mark PEA (talk) 16:13, 24 March 2008 (UTC)

Way too numerous to list - there are literally dozens and dozens of small hormones secreted along with the major ones where the physiological function is poorly under stood. However, the predominate hormones are the following (off the top of my head):

• Epinephrine
• Norepinephrine
• Dopamine
• TSH, T4, and T3, Calcitonin
• Parathyroid Hormone
• FSH, LH for reproduction
• The androgens for sexuality and reproduction
• Growth Hormone
• Prolactin
• Oxytocin
• Antidiruetic Hormone
• The hypothalamic tropic hormones (also known as releasing factors)
• Glucagon
• Insulin
• Somatostatin
• Secretin
• Gastrin
• Aldosterone
• Cortisol
• Corticosterone
• Vitamin D3

There are more, but I can't rack my brain any longer Wisdom89 _{(T / ^C)} 18:01, 24 March 2008 (UTC)

Well this is precisely my problem -- I don't want to list them all, I just want a nice (2-digit? 3-digit?) number. John Riemann Soong (talk) 18:16, 24 March 2008 (UTC)

Yeah, extremely difficult per my first comment. Physiologists and endocrinologists incessantly disagree about what substances (mostly small peptides) even constitute a hormone. If I had to give an educated guess (and it is educated) for the major hormones, it would be around 120. Wisdom89 _{(T / ^C)} 18:24, 24 March 2008 (UTC)

here is another list of the major ones, but as others note, some hormones, like the various melanocortins are cleavage products of a pro-hormone (in their case, Proopiomelanocortin). How many different hormones there are from each pro-hormone differs by which criteria you wish to use. Do you wish to count the pro-hormone as 1 or do you wish to count all the possible cleavage products? If you wish to use conservative criteria, there may be around 50, if you wish to include anything anyone has ever called a hormone, perhaps 100-150. Rockpocket 18:45, 24 March 2008 (UTC)

Movie science: what can or can't you tell about a torpedo from its sound?

In the movie The Hunt for Red October, there's a scene in which a sonar operator reports that an incoming torpedo "went active the moment it was launched" and that the torpedo has acquired its target. Is it real science, or is it just artistic license taken by the moviemakers, that a sonar operator is able to tell if a torpedo is armed and has a lock on its target just by listening to its sound? --71.162.242.38 (talk) 16:25, 24 March 2008 (UTC)

I asked myself the same question. A torpedo can be sent out running slow and quiet so that its target might not know it's there until it's too late. Subs maneuver slowly when they aren't going anywhere in a hurry, so the torpedo doesn't need to go very fast to get over near its target. A wire-guided torpedo will be steered by the attacking sub to get it near its target, at which point it will told to turn on its own sonar and home on that, what the movie called going "active", I guess. Faster torpedo propellor speed means higher pitch and louder. (If the torpedo hasn't hit anything after a certain amount of time has passed, and the wire isn't connected any more, it will conduct a search pattern automatically, at which time the attacking sub had better have gotten its butt out of the area.) I would guess that the search sonar and the final homing sonar would differ in some audible way, so that you'd be able to tell when it had "acquired" its target by merely listening. As for whether the torpedo is "armed", I think we're supposed to imagine that Jonsey knows a hell of a lot more about this whole business than we ever will and that some combination of indicators and knowledge of the workings of Russian torpedos clues him in, so just sit back and enjoy the show. --Milkbreath (talk) 16:48, 24 March 2008 (UTC)

As for "has a lock" -- yes, that's easily determined. If you have a bearing to a sound source (e.g. a torpedo) and that bearing doesn't change, the torpedo is on a collision course with you. If the bearing changes, it's heading somewhere else. As far as arming, I'll just go with Milkbreath's encouragement to enjoy the show -- active sonar corresponding with armed torpedo is a reasonable assumption, and I don't recall the dialog precisely enough to nitpick anyway. — Lomn 17:00, 24 March 2008 (UTC)

As said by MilkB, most torpedoes, eg Mark 37 torpedo don't turn on the active sonar until they are close, so when you hear that happen you want to try not to be where the torpedo is going. A sonar operator can tell the difference between a "search" and "tracking" pattern in the same way that an aircraft can tell the difference with radar. A search pattern sweeps the transmission through 360^o, or at least a wide angle. Tracking sweeps over a narrow angle, trying to keep the target illuminated constantly. The military consider tracking an aggressive act and cause for shooting back by the way. So basically, if the sonar operator can hear all the enemy pings or chirps hitting his vessel with no gaps (there would be gaps while the search sonar is pointing somewhere else if it was not tracking) then he can conclude his ship is being tracked. SpinningSpark 19:34, 24 March 2008 (UTC)

arsenic weight per gallon

I am desining an arsenic treatment plant for a small town in CO and I was crious to know how much a gallon of arsenic would weigh?

Thank You,

Michael miklroy04@yahoo.com

The article on Arsenic_contamination_of_groundwater might provide a good place to start. It looks as if most arsenic is in the form of dissolved arsenic salts, and therefore the weight of material to be removed may be dominated by the substance used to remove the arsenic, not by the arsenic itself. JohnAspinall (talk) 16:53, 24 March 2008 (UTC)

1 gallon (US) = 3.785411784 litres, Density of arsenic 5.727  g·cm−3, 1litre = 1000 cm3

So 1 gallon weighs 3.785411784 x 5.727 x  1000 =21679g = approx 21.7kg (that's about (under) 48 pounds)87.102.16.238 (talk) 16:56, 24 March 2008 (UTC)

collapsible longboard???

I heard that some yuppies use a longboard for transportation, which I might be interested in doing also, since I walk for 7 minutes to the metro dozens of times a day. Is this is a nutso idea? Why?

are there any collapsible longboards? THank you!

The positive is it might be slightly quicker, if the pavement is smooth and level. The negatives are that you are more likely to fall or trip other people, you have more weight to carry when not skateboarding, it may be illegal in certain areas, people may view you as childish or a menace, and you won't get as much exercise. I'd say the negatives win. StuRat (talk) 20:03, 24 March 2008 (UTC)

Are people still using folding aluminium micro-scooters in the city? Julia Rossi (talk) 02:15, 25 March 2008 (UTC)

A much easier idea is a moped. ~user:orngjce223 how am I typing? 16:38, 26 March 2008 (UTC)

Static zappage

I work in a library with very fuzzy carpeted floors and metal on the door handles. I am getting shocked almost every time I get up and touch things. It seems that most of the other employees don't get shocked. Are there people who have a higher potential for being shocked? Is there anything I can do to cut down on the number of times I get shocked? I'm starting to get nervous before I open the doors...

It also depends on the clothing you wear - that could be a disparity between you and the other employees. Wisdom89 _{(T / ^C)} 17:54, 24 March 2008 (UTC)

Try comparing the types of shoes you and the others wear, especially the soles. I'm betting that's the answer, as different types of soles pick up a charge more as you trot about. --Captain Ref Desk (talk) 18:09, 24 March 2008 (UTC)

I agree with the previous answers. Also, perhaps your job tends to keep you in one room and/or you walk around on the carpet more, so that a higher charge builds up before you touch the door handles. You might want to intentionally touch the door every few minutes to prevent static buildup. Then again, maybe you are the subject of a secret psychological experiment the other librarians are performing and that would invalidate the results. :-) StuRat (talk) 19:55, 24 March 2008 (UTC)

Leave your hand in contact with something grounded, like a metal lamp, when you get up out of your chair. Carry something metal with you to draw the arc with before you touch the doorknob, maybe a coin or paper clip. Much of the pain of such zaps is actually from the momentary heating of the skin where the arc occurs, and if the arc hits the paper clip first you won't feel that part of it. --Milkbreath (talk) 03:27, 25 March 2008 (UTC)

Why is violet reddish?

Why does violet look more red than green, even though green is closer in wavelength? My first thought was that the higher frequencies of violet are an octave of the lower frequencies of red. However, the shortest wavelength of violet is 380 nm and 740 nm as the longest for red, so the octave of violet is not visible. --196.209.178.23 (talk) 20:13, 24 March 2008 (UTC)

It is because the red receptor in the human eye has a slight response to second harmonic wavelength also. This happens to peak towards the high end of the blue spectrum which causes us to interpret light of this wavelength as violet. SpinningSpark 20:26, 24 March 2008 (UTC)

Oh sorry, I did not bother to read all your question. I have some plots of human eye response somewhere from BBC colour vision research which definitely show a second smaller peak in the red response. Of course, you can never find this stuff when you need to answer a question. I assume you got your figures from the color vision article which seems to fail to show this second peak. Possibly the other figures there are non too accurate. SpinningSpark 20:38, 24 March 2008 (UTC)

Human cone responses

Human cone responses

Take a look at this, you can just see the second peak, it is very small, the plot is relative level instead of dB as any sensible engineer would have done. But you are right that it is well off the second harmonic. SpinningSpark 21:16, 24 March 2008 (UTC)

Cladistic definition of crown groups

Let's imagine metatherians and prototherians become completely extinct in a few years, and eutherians are the only surviving mammals. Cladistics define the class Mammalia as:

"the last common ancestor of all living mammals and all of its descendants"

In this imaginary situation, this would mean "the last common ancestor of all eutherians and all of its descendants", thereby declaring marsupials and monotremes as non-mammals! Isn't this a little absurd? How do you solve this paradox? -- Leptictidium (mammal talk!) 20:14, 24 March 2008 (UTC)

After reading Tudge The Variety of Life I came to the conclusion that all of cladistics is absurd. Non-avian dinosaurs, "no such thing clade as fish" - really whatever next. SpinningSpark 21:21, 24 March 2008 (UTC)

I think the cladistic definition would simply be changed to "the last common ancestor of metatherians, prototherians, and eutherians". It might be stated that way in some technical definitions even now. Note that the ICZN does not currently regulate taxa above family level, so classes, etc. are in flux anyway.

Cladistics only makes sense if you accept that the goal of taxonomy is to reflect evolutionary relationships. As Spinningspark points out, fish are actually 3 or 4 separate clades [depending whether you put hagfish and lampreys together; I'm used to 3 clades, jawless fish, cartilaginous fish, bony fish]. Vultur (talk) 22:16, 25 March 2008 (UTC)

Balloons and teleportation

I'm writing a story in which one of the characters can teleport instantaneously from place to place. At first, I intended this to be silent, but my brother has pointed out to me that her sudden appearance would result in some pretty intense displacement of air, so the sound of her teleporting should be a lot like that of a very large balloon exploding.

I think this is kind of awesome, but I want to make sure it's right before I use it. What do you all think? --Masamage ♫ 21:07, 24 March 2008 (UTC)

I assume that when you say teleport instantaneously you mean not only that the travel time is zero but the rematerialization period is also zero. If the rematerialisation period was longer (i.e. star trek) there would be no massive displacement of air, ir would be gradual. Anyway, I doubt there would be a sound akin to an exploding balloon. The balloon sounds like that because it is a large amount of air being released from a small area having previously been under very high pressure. To suddenly materialise in air (assuming that all the air is deflected away from you from your centre, rather than being trapped between your particles as you materialise?) would produce something akin to a sudden rush of wind, as the amount of air in the space now occupied by your character has been pushed outwards. The speed of which would, in theory, only be enough to get it out of the way (maximum distance is the same as the dimensions of your character) and the air would probably not go very far before hitting other air molecules. Less of an exploding balloon, I'd say, and more of a sudden, thick but short gust of wind? That is again, of course, depending on the speed of your materialisation. SGGH ^speak! 21:26, 24 March 2008 (UTC)

Yes, you have it about right for how fast I was thinking she would materialize (although the idea of slow, Star Trek-style beaming is interesting, too). So then, if I understand you right: the displaced air isn't under enough pressure to make that loud and sharp of a noise, so in actuality all that would happen is a sort of fwoosh sound, and maybe nearby people's clothes wafting a little in the wind. And a similar thing would happen to fill the space where she left, right? --Masamage ♫ 21:36, 24 March 2008 (UTC)

(ec) It depends on the mechanism you've chosen for your particular fiction. If air is forced out of the volume to be occupied by the incoming traveller extremely rapidly (as with a near-instantaneous teleportation) then it will generate a shockwave as it moves—a small sonic boom. It will, indeed, be loud.

Now, your teleporting individual would be in a world of hurt if they don't materialize from their center out—that would trap air molecules within the body. Very messy. Slow materialization could be problematic, too—what happens if the character moves during teleportation? A bit of liver here, a bit of lung over there, blood flows down the left leg and back up the right, no problem....

Of course, you could always choose a mechanism where a 'swap' takes place. Simultaneously beam in your character, and beam out the air. If done correctly, it's quiet at both ends. TenOfAllTrades(talk) 21:43, 24 March 2008 (UTC)

Since the method of travel has some air of unfeasability or even ridicule to it, I'd personaly go for a more humoristic sound like a pop or plop or even a whizz or shebang. Anyways. Think too that you could make the business of teletransportation easier if instead of moving just the physical person, you define a volume (a la Terminator) of air emveloping that person. Since it teletransports indiscriminatly a volume of space it can even be used as a plot twist in a story. See you later. Shwabwabwabwabwaaawawawa ... piuut, pop. 200.127.59.151 (talk) 21:44, 24 March 2008 (UTC)

One more thought, depending on whether you're doing science fiction or fantasy. You could generate a 'force field' or something of that sort at the reception point to move the air out of the way slowly; by 'slowly' I mean the field boundary doesn't expand faster than the speed of sound. Your character (with air from his departure point around him) can just pop into the premade vacuum as quick as he likes. Again, nice and quiet. TenOfAllTrades(talk) 21:47, 24 March 2008 (UTC)

Rematerialization time cannot be zero, because the air molecules can't move faster than light to get out of the way. If you got them moving close to the speed of light, I think you'd have a pretty violent event, especially if the teleportee resembled John Goodman. Either the machine would have to force the air molecules aside before materializing the person where they had been, or the person would have to materialize from the center out, in which case they would be subjected to whatever force was needed to move the air. On the sending end, no such problem, and I'd expect a rather soft unidentifiable slap or pop sound. How about you take the air from where you're going and put it back where you came from; swap the person and the air? --Milkbreath (talk) 21:50, 24 March 2008 (UTC)

Hmm, okay. So one vote for a windy sound, one for a sonic boom, one for a patooie, and one for it not even being possible. Also, two votes for swapping the person with the air; my brother had suggested that, too. The weird thing about that, though, is that anything in the air gets popped over, too; dust, smells, poison gas, etc. Also, if the places had different barometric pressures, there still might be some wind. (And if she teleported into a wall, she'd leave a statue behind.) --Masamage ♫ 21:56, 24 March 2008 (UTC)

Note that apparently this was followed in the recent film Jumper, though I haven't seen it. I read an interview with the director in Entertainment Weekly where he talked about the whoosh you'd hear by suddenly creating a little vacuum where you once were. He was quite proud of himself for figuring that one out. --Captain Ref Desk (talk) 22:00, 24 March 2008 (UTC)

too bad he couldn't figure out how to make a good movie --LarryMac | Talk 15:39, 25 March 2008 (UTC)

Of course, you could always decide that the teleportation mechanism is a swap rather than a one-way jump. If the teleporter jumps from A to B, the volume of air that she displaces jumps simultaneously from B to A. Then it could be totally silent -- although of location A is far enough away that the barometric pressure is different there, then there might be a small sound at location A.

And, doing it this way, what if there is water or a solid object at location B? Then perhaps a person-sized hole would appear in that water or object, and a corresponding chunk of water or other material would be transported to B, where it would fall to the ground with an almighty crash or splash. And if that material was part of a living thing, it could get rather hideous.

Just a thought -- you are welcome to use it if you like it. --Anonymous, 23:11 UTC, March 24, 2008.

According to our lexicon (and also the Jargon File), the sound of teleportation is "bamf", and this comes from the Marvel Universe. Also, in Sam Hughes', "Fine Structure" stories, teleporting sounds like a thunderclap. – b_jonas 18:04, 25 March 2008 (UTC)

well, if you're going to be serious about it.... you've obviously got to deal with the air or whatever occupying your target zone, and displacing it causes a lot of problems, so swapping it makes the most sense.

but also, conservation of momentum; if you're getting teleported from Australia where you're whipping along with the surface of the earth, to the US where the surface happens to be heading in the opposite direction at equal speed, you're going to appear with a net relative velocity of like 1500 mph. this will cause a certain amount of noise, depending on what you smack into, including just the air. Gzuckier (talk) 18:42, 25 March 2008 (UTC)

The conservation of energy issue has come up in fiction before. I recall a murder-mystery-science-fiction story (probably by Asimov, as he liked that sort of thing) in which a key plot point dealt with teleporter travel between points at different altitudes. In the book's early-model teleporters, excess gravitational energy would show up as added heat in the teleported person or object. (My back-of-the-envelope calculations put the temperature change of a human body at about 2.5 degrees Celsius per kilometer of altitude, or about 1.3 degrees Fahrenheit per 1000 feet.) Round-the-world teleportation (and the associated problems of relative velocity) were not addressed. TenOfAllTrades(talk) 16:38, 26 March 2008 (UTC)

b_jonas, Sam Hughes used the swapping method, but the person was teleported into space (technically, they were teleported into a coal seam, which was then teleported into space), so it sounded like the one-way version. 67.182.186.132 (talk) 23:03, 25 March 2008 (UTC)

It certainly wouldn't be a really loud crack/pop, but it could be a bit of a whoosh. Quite unlike Ms. Rowling's Harry Potter. ~user:orngjce223 how am I typing? 16:42, 26 March 2008 (UTC)

More Teleportation

In Robert Heinlein's Stranger in a Strange Land Michael idly toys with the idea of destroying the solar system by teleporting a piece out of the centre of the sun. Although capable of doing this he does not actually go ahead so we never got to see how it would turn out. Would this work, and how big a piece would be necessary? SpinningSpark 23:47, 24 March 2008 (UTC)

I can't see it destroying the solar system unless enough was transported out to alter the gravitational system into essentially a binary star system. However, if a sizable chunk of the Sun's interior was transported onto Earth, it could probably destroy the planet. StuRat (talk) 03:26, 25 March 2008 (UTC)

Not sure, but I think the idea was that the consequent collapse into the now empty space would cause some kind of nova followed by crispy planets. Would it? SpinningSpark 07:47, 25 March 2008 (UTC)

Wouldn't taking out a significant chuck of the core of the Sun effect its fusion reactions as "the core is the only location in the Sun that produces an appreciable amount of heat via fusion: the rest of the star is heated by energy that is transferred outward from the core"? I guess that would be the destruction of the solar system, but certainly life on earth. -- MacAddct  1984 ^{(talk &#149; contribs)} 14:07, 25 March 2008 (UTC)

If you removed enough fuel from the core it would prematurely become a red giant. That would destroy the earth, not sure about planets at more distant orbits.

What about the effect on orbits? if any?Gzuckier (talk) 18:36, 25 March 2008 (UTC)

As the sun loses mass its gravitational force weakens, causing the planets to move to higher orbits. This paper discussed in the NY Times suggests that even despite the higher orbit, a red giant sun will still swallow the earth.66.152.245.18 (talk) 19:05, 25 March 2008 (UTC)

An abrupt change in the Sun's mass would convert each planet's orbit into one that was higher on average, but still passed through the point where it was at the time of the change. So if the planet happened to be near perihelion, its aphelion would get higher but its perihelion would stay about the same: it would be a more eccentric orbit. If it was near aphelion, the orbit could become less eccentric than before (depending on how eccentric it previously was, and on the amount of mass change). --Anonymous, 23:33 UTC, March 25, 2008.

This just reminded me of the Stargate episode, Exodus where a Stargate connected via a wormhole to another stargate that was orbiting a blackhole was shot into a star. Mass from the star was sucked through the wormhole by the black hole and the star went supernova.--Shniken1 (talk) 23:52, 25 March 2008 (UTC)

March 25

Red wine "breathing"

Does it really make a difference if you uncork a red wine bottle a couple hours before drinking it? There can't be more than a square inch exposed to the air. I can't really see how it could affect the rest of the wine. I know some people let it breath in a wide caraffe, but I know a number of wine people who will insist on just uncorking the bottle for an hour or so before serving.

Have there ever been any blind taste tests to see if people really could tell the difference between wine that has breathed or not?

James. 00:51, 25 March 2008 (UTC)

Hello James. You're right in that the small surface area from just uncorking the bottle does very little. It is somewhat of a silly practice. (Like sniffing the cork :p) However the process of decanting can have a pronounced influence on the tannins (at least the perception of them) and aroma development of the wine. The act of pouring the wine, with the motion and the splashing, will also contributes quite a bit to this aeration. While I'm not familiar with any published blind tasting test, there is an easy experiment that you can do at home. You don't need a decanter, just pour yourself a glass of wine and let it sit for half an hour. Even in that short period of time, the wine in your glass (with the larger surface area) will show some change in the aromas and flavors due to the aeration. Though do note that the extent of change will vary depending on the wine. Some wines (like Burgundies) will have more noticeable changes due to aerating than say a California Zinfandel. Agne^Cheese/^Wine 03:14, 25 March 2008 (UTC)

It's very easy to do double-blind. Take out two wine glasses. Tell your friend to stay in the living-room. Pour one glass. Go talk to him for half an hour. Tell him to come into the kitchen for a minute...meanwhile, pour the second glass. See if he can tell which was aerated.

Sorry, to make it DOUBLE-blind, tell him to come in and see which one is aerated before you yourself know :)

Get two bottles of decent Australian Shiraz (should be around US$10-US$20 at the moment). Open one 4 hours before dinner and decant (or pour), the other directly before dinner. Be sure to keep all the wine at room temperature. Even I can taste the difference, and I'm a barbarian.The undecanted wine typically is harsh and has a slightly bitter note, the decanted one is much more mellow and fruitier. --Stephan Schulz (talk) 09:55, 25 March 2008 (UTC)

Even better, to answer James' original question: If you have a Trader Joe's market near you, buy two bottles of "Two Buck Chuck". Both should be the same grape and vintage year. Open one bottle, but don't pour it! Just let it sit open on your kitchen counter for, say, 4 hours, with the other bottle next to it to ensure both stay the same temperature. Then have a friend or family member go alone into the kitchen, open the second bottle, and pour an equal volume of each into two identical glasses, and note secretly which glass is the aired-out one. Your assistant then leaves the kitchen. You go in and taste, and see if you can detect not just a difference, but whether one tastes better than the other.

The reason I suggest Two Buck Chuck is because I have noticed that among all the wines I have bought, Two Buck Chuck experiences the most profound change, almost becoming un-drinkable a day after you open the bottle. This test will determine whether that 1 square inch of surface area makes any difference after opening a bottle. ~Amatulić (talk) 17:24, 25 March 2008 (UTC)

Even better if you can get three samples going - the unopened, the opened, and a decanted one. And then, of course, you're going to have to do something with all that wine you've just opened - sounds like an interesting dinner party experiment to me (which also means you get results from multiple people). Confusing Manifestation(Say hi!) 23:12, 25 March 2008 (UTC)

There is a small pourer which induces air into the wine as it is poured so you don't have to wait (agonising!) before drinking. Use mine every day, Hic, pardon.--Artjo (talk) 08:41, 26 March 2008 (UTC)

Hormonal Cycles In Men

Hello there! I was wondering whether men have some type of hormonal cycle at all, whether it be during certain times of day, of the week, or of the month, and where a certain hormone is more prevalent or at its peak at one moment than at others. I'm not suggesting men would have a similar cycle as the menstrual cycle in women, but I was just wondering whether there are times when a certain hormone is more active or less active.

Men have diurnal hormone cycles for such things as cortisol, ACTH and growth hormone - among others. Wisdom89 _{(T / ^C)} 00:59, 25 March 2008 (UTC)

Melatonin is a good example. Rockpocket 06:51, 25 March 2008 (UTC)

Please read the article on Circadian rhythm. If you have any questions remaining, feel free to ask. Best wishes, --Dr Dima (talk) 12:28, 25 March 2008 (UTC)

Also, there is the GnRH --> LH --> T negative feedback loop. Basically, the hypothalamus (little gland in the brain) releases an hormone called GnRH that tells the pituitary gland (another little gland in the brain) to release a hormone called LH. The LH then proceeds to the testes and tells them to secrete testosterone (T), a steroid hormone with which we are all familiar. But then the testosterone, circulating through the blood, tells the hypothalamus to stop secreting GnRH, which in turn slows down LH production, which in turn slows T production, which permits GnRH secretion again... This is a classic negative feedback loop with a period of, if memory serves, roughly four hours, and again if memory serves this does result in periodic peaks and troughs of adrenaline, which can have both physiological and psychological effects. See [[3]], for example. It is analogous (or homologous) to the female GnRH --> FSH --> E/P cycle. It also bears mention that men have been reported (though the homology is subject to controversy) to undergo "andropause" after middle age. Vance.mcpherson (talk) 13:37, 25 March 2008 (UTC)

How do I become a stuntman?

I love Jackass and Dirty Sanchez. I like doing extreme, painful stunts to impress my friends (found something that I'm good at). How do I get to be on TV like those guys? I don't wanna be just another one of those guys who posts his stuff on YouTube and gets called a reckless idiot. I want to be a reckless idiot on TV.

You must have an exceptional pain threshold that can be put to good use. There's stuntschool.com in the USA here[4] and googling "stunt man training" gets you lots more stuff you might like – our articles stunt performer, stunt double and stunt coordinator look brief. Otherwise popping this whole thing onto the entertainment desk might get more details. Please sign your posts with four ~ and good luck, Julia Rossi (talk) 02:05, 25 March 2008 (UTC)

Hanging swamps

I'd like to start an article on hanging swamps but can only find a few things on google limited to the Blue Mountains outside of Sydney and on wikipedia, only to one in particular though there are more. Does anyone have references they could suggest? Are they found in other parts of the world as well? Thanks, Julia Rossi (talk) 02:08, 25 March 2008 (UTC)

SOunds like they would have another name - perhaps alpine meadow. In the ACT a sphagnum bog is the source for the Cotter River. Graeme Bartlett (talk) 03:52, 25 March 2008 (UTC)

Superficially they look like a combination of both. The trees only come to the edge of it, and it's on a slope rather than level ground, without many rocks. Julia Rossi (talk) 07:33, 25 March 2008 (UTC)

online versus offline wetlands

What is the definition of an online wetland? I expect it has something to do with being in a drainage line but where is the line drawn in terms of the hydrologic capacity of an online versuus offline wetland?

Yeah, I think has something to do with how it drains (online=draining, offline=not draining, most of the time). I don't know where I picked that up, though. But I believe it has nothing to do with the amount of WiFi access within the area tho :P ~user:orngjce223 how am I typing? 16:48, 26 March 2008 (UTC)

Atomic Force Microscopy

I've got an assignment on AFM and one of the questions relates to metal nanoparticles on a teflon coated magnetic stiring bead and how to image them. I'm a bit ^stuck with how one would go about imaging this as the surface needs to be quite flat. Would it simply be a matter of cutting a piece of the stirrer bead off and flattening it with a press of some kind? Any other ways in which the stirring bead can be flattened so that it can be imaged? How flat would it need to be? Thanks --Shniken1 (talk) 05:22, 25 March 2008 (UTC)

I wouldn't suggest flattening it as that could significantly change the structure. Instead, you need to cut a very narrow slice and put it on a slide. StuRat (talk) 06:31, 26 March 2008 (UTC)

What model Saab is this?

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I can't ID it from the Saab article, but am guessing it's one of the older models. BrokenSphere^{Msg me} 05:37, 25 March 2008 (UTC)

Hi Brokensphere, I found something like it here[5] of a 96V4 also butterscotch coloured, but doesn't give the year. Julia Rossi (talk) 07:08, 25 March 2008 (UTC)

Ps, if you scroll down further to the white one, they put it at 1970. Cheers, Julia Rossi (talk) 07:10, 25 March 2008 (UTC)

It looks like a Saab 96 - see especially the picture of the 1965 model near the bottom of the article. Are you sure this is a science question? 84.239.133.86 (talk) 07:56, 25 March 2008 (UTC)

Or maybe a Saab Sport given the chrome striping at the bottom (although strictly speaking it should be a double stripe, unless one's been lost - see here). I don't think the 96 had any chrome stripes, unless they added them later. --jjron (talk) 10:00, 25 March 2008 (UTC)

Stuck in fetal position?

When I was much younger... something like 12, I woke up one morning and couldn't get out of the fetal position. It hurt one of my hips (maybe a hip flexor muscle) so much when I tried to straighten that leg out that I had to straighten up slowly over the period of about half an hour it seemed. I'm not asking for advice, just a list of possible things that might have caused this, or any other insights... but no advice please. Sancho 06:23, 25 March 2008 (UTC)

Muscle cramp? Dismas|^(talk) 09:02, 25 March 2008 (UTC)

Stupidity? Weasly (talk) 12:21, 26 March 2008 (UTC)

Given the following two premises: (1) a large body of science fiction which creates a connection between pregnancy, fetuses, and alien abduction, and (2) the existence of sleep paralysis and its supposed explanation for alien abduction; is it possible you are or were a character in a science fiction novel? Nimur (talk) 14:42, 26 March 2008 (UTC)

Battery life meter

One of the more annoying "features" of my cell phone is that the battery life meter doesn't tell you how much life is left in the battery. It tells you how much is left if you continue doing whatever it is that you're doing with the phone until the battery is depleted. So if I just open the phone up, I could have 3/4 of a charge. If I start taking photos and sending them to my friends, the battery indicator goes down rather quickly and sometimes even causes the phone to warn me that the battery is running low. Although if I close the phone and re-open it, I again have 3/4 charge. Is there a term for this sort of battery meter other than annoying? Dismas|^(talk) 08:26, 25 March 2008 (UTC)

"Typical" :-). But I'm not sure what you want it to do. A battery life meter can't give you some sort of absolute measure of how much time it's got left, because that's dependant on the usage, especially for something like a mobile phone with a small battery and high fluctuations in demand. If you were doing something like playing a radio on batteries where the current draw was constant, an absolute measure would be more feasible. If anything this is a 'smart meter', because it's detecting your current usage and adjusting the available life shown on the meter accordingly. --jjron (talk) 09:44, 25 March 2008 (UTC)

This reminds me of the Rand McNally GPS unit I had. It would estimate my ETA based on my current speed, not on the average speed of the trip so far. The result was that when I stopped at a traffic light it said the trip would take an infinite amount of time to complete. StuRat (talk) 06:27, 26 March 2008 (UTC)

Did it actually use the infinity sign? If so then I must credit the programmers/engineers for having a sense of humor--droptone (talk) 11:35, 26 March 2008 (UTC)

No, it said something like 9999 minutes, the largest number it could display. StuRat (talk) 13:53, 26 March 2008 (UTC)

Hey, it could be worse. My cell phone won't tell me what time it is if it loses signal. I'm all for it checking it dynamically with the tower and updating as necessary, but totally being unable to tell time without a signal? Terrible design. --Captain Ref Desk (talk) 13:02, 26 March 2008 (UTC)

Axes of rotation, revolution, magnetic field, of the earth

Among the axes of rotation, revolution around the sun, and magnetic field, of the earth, which are parallel to each other, and which are not? Why are they parallel (or not)? --Masatran (talk) 09:44, 25 March 2008 (UTC)

See Earth's rotation for starters. The diagram Image:AxialTiltObliquity.png is quite simple to interpret for the relationship between rotation and revolution. For 'why', particularly see the section Origin of rotation and the pages that links to. See Earth's magnetic field for the magnetic field - it is close to the geographical rotational axis, but not the same. --jjron (talk) 10:18, 25 March 2008 (UTC)

As for why the magnetic poles don't match the North and South Poles, I believe that is because the Earth's composition is neither uniform nor static. Different materials conduct the magnetic field better than others, which deforms the field slightly. Interestingly, the magnetic poles aren't necessarily on the exact opposite sides of the Earth, vary over time, and even invert over long time periods, ty[pically after a long period of instability. StuRat (talk) 06:24, 26 March 2008 (UTC)

Effect of elliptical orbit of earth on climate

The distance of the earth from the sun changes over the year because the orbit is elliptical. What effect does this have on the climate of the earth? --Masatran (talk) 09:53, 25 March 2008 (UTC)

Some of the ice ages are thought to be one consequence. Check out Milankovitch cycles. 88.114.125.67 (talk) 10:24, 25 March 2008 (UTC)

The effect should have a time period of one year, right? It will be hotter when the earth is closer to the sun, and colder when the earth is further away from the sun. Is this effect present? And what is this effect called? --Masatran (talk) 10:31, 25 March 2008 (UTC)

Seasons? Dismas|^(talk) 10:35, 25 March 2008 (UTC)

When I was a kid, I thought likewise. But now I know that seasons are caused by the inclination of the north (or south) pole towards the sun. --Masatran (talk) 10:52, 25 March 2008 (UTC)

Masatran is right. There's a very easy way to see this. The effect of an elliptical orbit would be to make the whole earth warmer or cooler. The effect of an orbital tilt will be to make the northern hemisphere warmer while it makes the southern hemisphere cooler. (And vice versa six months later.) As the Season article points out, it's the latter we observe: "At any given time, regardless of season, the northern and southern hemispheres experience opposite seasons." JohnAspinall (talk) 13:52, 25 March 2008 (UTC)

The Earth is slightly hotter at perihelion than at aphelion, and this is a one-year period (give or take, I think there's some precession thrown in there as well) as you surmised. However, any effects are dwarfed by the changes resulting from the Earth's axial tilt (that is, seasons). If I recall correctly, aphelion corresponds roughly with northern summer and southern winter. — Lomn 13:06, 25 March 2008 (UTC)

That is correct. I've heard that this, along with the presence of the gigantic Antarctic ice cap, makes Southern Hemisphere winters colder than Northern Hemisphere ones at the same latitude.

I don't think it is true that northern winters are warmer than southern ones. A quick comparison of the latitudes of North American cities to southern Australian ones shows the opposite is true, c.f New York City with Melbourne or Hobart. I don't know how representative this is though.--Shniken1 (talk) 23:20, 26 March 2008 (UTC)

According to our article, "Climates in the southern hemisphere overall tend to be slightly milder than those in the northern hemisphere except in the Antarctic which is colder than the Arctic. This is because the southern hemisphere has significantly more ocean and less land. Water heats up and cools down more slowly than land." I guess I was thinking of the antarctic/subantarctic regions, which are definitely colder. Vultur (talk) 20:52, 29 March 2008 (UTC)

In terms of insolation, the difference between aphelion and perihelion is about 6%. At 40° latitude, there's a factor of about 2.1 in insolation comparing winter and summer solstices. Icek (talk) 14:45, 29 March 2008 (UTC)

Concentrating DNA samples

If I have DNA which I want to concentrate 2.5x, could there be a problem with, say storing the tubes open in a container with some of those sodium silicate dissicating crystals to lower humidity? They can't be run through a column because that's where they've been already and that process involves too much loss. --145.29.23.38 (talk) 11:22, 25 March 2008 (UTC)

Why not do a standard ethanol precipitation of the DNA and resuspend the dried pellet in a smaller volume? it won't take more than half an hour or so. -- Flyguy649 ^talk 15:43, 25 March 2008 (UTC)

Never done it before (I'm just a lousy intern) - I'll ask my supervisor if we can do that. Thanks very much :) --145.29.23.38 (talk) 17:00, 25 March 2008 (UTC)

Fairly simple. Just increase the volume of your DNA sample with Tris buffer (doesn't have to be much). Add 3-5 volumes of either cold isopropanol or ethanol and centrifuge for 30 minutes at 15,000 RPMs (JA-20 rotor) or 12,000 RPMs in a microfuge depending on the size your sample. When the pellet is present, simply redissolve it in 2.5x's less Tris buffer. Wisdom89 _{(T / ^C)} 18:48, 25 March 2008 (UTC)

Or you could check if there is a vacuum centrifuge in the building (no article yet, but is basically spins the DNA while evaporating the liquid. Rockpocket 07:19, 27 March 2008 (UTC)

Dutch tulip forecast

It has been snowing and cold in Holland all through the Easter weekend, and beyond. Can anyone refer me to a website with a forecast for the 'peak' of the 2008 tulip season. It must change...with the weather, I would think. Presumably as the weather stays cold, the peak moves further into April. Thanks if you can show me to a reference where I can get an estimate for the peak days/weeks.

The scientific method

This image summarizes the basic technique for study of the Earth's interior. Nimur (talk) 14:46, 26 March 2008 (UTC)

How do scientists find out about the updates and changes in the earth's crust? What are the technolgies needed to find out about the structure/different layers of the earth?

You'll probably want to start with the Composition and structure section of our article on the Earth and work out from the links there to get all the details. TenOfAllTrades(talk) 16:15, 25 March 2008 (UTC)

You can also look at the geology, Plate tectonics and stratum articles. Sandman30s (talk) 14:24, 26 March 2008 (UTC)

Don't forget to read about seismic waves. Seismometers are essential instruments (technology) and by comparing the readings at different locations, we can infer the structure of the earth. Nimur (talk) 14:45, 26 March 2008 (UTC)

Mobile Phone Noise

First of all, I live in the UK, which I guess may be relevant.

When I leave my mobile phone next to seemingly another peice of electrical equipment, there is a noise which prempts text messages and calls. My tv, computer, hi-fi, anything.

It's that strange "du duh-de-duh duh-de-duh" noise (which I put into Google, but alas...) What causes it and why does it show up on everything, even things that wouldn't be thought to be interferred with my a mobile's signal? A good example of that would be through my Ipod, and out of my earphones.

Thanks a lot. Fenton Bailey (talk) 16:04, 25 March 2008 (UTC)

Every time your telephone communications with a central cellular tower (when you have an incoming call or message, or periodically when the phone handshakes with the tower) it broadcasts a fairly strong radio signal. The wires of your headphones, speakers, stereo, or television act as (not-very-good) antennas which pick up some of that radio signal and overlay it on top of whatever else you're listening to. TenOfAllTrades(talk) 16:13, 25 March 2008 (UTC)

I have found the effect is more severe when the phone is near an amplifying device (powered speakers, for example); this suggests that the cell phone's RF transmissions may couple directly into the amplifier, rather than the feed wires as antennas. Surely it's some combination of the two. Nimur (talk) 14:48, 26 March 2008 (UTC)

That is correct. I use this little fact to tell my friends their phone is about to ring by paying attention to the car radio, they still haven't figured out how I do it. 206.252.74.48 (talk) 16:59, 25 March 2008 (UTC)

Heh, I do that too. They ask how do I do it, and I just say "nerd-sense". — Kieff | Talk 01:31, 26 March 2008 (UTC)

Electromagnetic interference.--Shantavira|^{feed me} 17:40, 26 March 2008 (UTC)

Why do deep footprints in snow look blue?

I was walking in the snow with my daughter today, and we had to cross some deep drifts, where our feet sunk over a foot into the snow. When we looked into the holes there was a distinct blue tinge, though the snow itself was white. My daughter asked me why this is, and I didn't know. Pools of melt-water were crystal clear, with maybe a slight greenish tint but that could have been because of the grass at the bottom, so it is not because of absorption by the water, unless it acts differently as ice. -- Q Chris (talk) 18:21, 25 March 2008 (UTC)

I don't know if this is the explanation, but water is a bit blue. See color of water. Ahh, here we go- one of the references used in that article is this which I think is pretty relevant. Friday (talk) 18:24, 25 March 2008 (UTC)

If the surface of the snow was in direct sunlight, the bottom of your footprint could look blue because it is shadowed by the wall of your footprint. Outdoor shadows look blue because they are illuminated by the blue sky, a phenomenon that photographers will be familiar with. I have found the color difference to be very noticeable on snowfall. -- Coneslayer (talk) 18:45, 25 March 2008 (UTC)

Indeed, red is scattered less than blue by the atmosphere, so a larger fraction of red (than of blue) comes straight along the direction from the sun, and smaller fraction of red (than of blue) comes from the other directions. If the hole walls block the direct sunlight, the bottom of the hole will be illuminated by the light which has a larger fraction of blue (compared to the fraction of blue in the white light, that is, the light you see on the snow that is illuminated from all directions). So the snow is not blue, it is white; rather, the light illuminating it is relatively rich in blue. On the other hand, water and transparent ice are genuinely blue, see blue ice (glacial). --Dr Dima (talk) 20:58, 25 March 2008 (UTC)

Quantum Number Sets

The quantum numbers article (http://en.wikipedia.org/wiki/Quantum_numbers) says that the magnetic quantum number should be between the negative and positive values of the azimuthal quantum number.

If I come across the notation 3d₄,+1/2 or 5f₅,-1/2, would those be considered wrong? Because d=2, so the magnetic quantum number should be between -2 and 2, so 4 doesn't make sense. Same with f being 3 so 5 doesn't fit between -3 and 3. -- Zealz (talk) 23:49, 25 March 2008 (UTC)

That's correct. Those symbols don't refer to any real states. —Keenan Pepper 02:41, 26 March 2008 (UTC)

March 26

Faster than light/Big Bang question

Whatever universe theory currently has scientific consensus (which I assume is based on the Big Bang model) seems to suggest that the universe is 13.73 billion years old and 93 billion light years in diameter. The Big Bang theory also states that the universe started from one point of infinite density. Therefore what seems to add up in my head is that the matter in this point which is now at the far reaches of the observable universe must have moved at least 46.5 billion light years in 13.73 billion years at most, which is faster than light. Is this the case, and if so how is moving FTL possible in this case? 212.49.210.38 (talk) 02:56, 26 March 2008 (UTC)

Take a read of this URL http://www.astro.ucla.edu/~wright/Dltt_is_Dumb.html which is the reference given to expalin the misconceptions in the time. The basic reason is that you cannot measure a distance between two point seperated so far in time. At great distances the relationship becomes non-linear. Graeme Bartlett (talk) 03:13, 26 March 2008 (UTC)

(ec) See Observable universe#Misconceptions. DMacks (talk) 03:14, 26 March 2008 (UTC)

Simplified explanation: the oldest photons that we can detect are the photons in the Cosmic microwave background radiation, which were emitted about 400,000 years after the Big Bang. It has taken those photons about 13.7 bn years to reach us. But in those 13.7 bn years the space between here and the places where those photons were emitted has expanded. It is possible for space itself to expand faster than light - the speed of light is only a limit for objects moving through space. So the places where these photons were emitted 13.7 bn years ago are now about 46 bn light years away from us, not because anything has moved, but because space itself has expanded. (Yes, yes, I know I haven't mentioned the cosmological constant, the changing value of the Hubble parameter, red-shift, the curvature of space, the difference between comoving co-ordinates and proper distance etc. etc. etc. - that's why I called it a simplified epxlanation) Gandalf61 (talk) 12:26, 26 March 2008 (UTC)

The explanation leaves the impression that if objects A and B are at points 1 and 2, 1 billion light years apart, then the "space" between them could "expand" to 4 billion light years in a period 1 billion years, somehow without objects A and B moving faster than the speed of light. Would this same process be applicable to 2 objects 1 light year apart, which could via "space expansion" become 4 light years apart in 1 year? Why couldn't Spaceman Biff use "space contraction" to travel between 2 planets 4 light years apart in 1 yea4 without travelling faster than the speed of light. If the distance between points can increase via expansion, why is the process irreversible? Sorry for the simplistic question, but the usual explanations lead to such conjecture. Edison (talk) 13:44, 26 March 2008 (UTC)

If the planets are 1 light year apart when Biff sets out from planet A and Biff travels at the speed of light and we assume that the planets are stationary with respect to each other but the space between them is rapidly expanding then it will take Biff longer than 1 year to reach planet B. On the other hand, if planet B is 4 light years from planet A when Biff reaches it, then his journey will have taken less than 4 years, because of the expansion of space. To see the hypotehtical effects of a rapidly contracting space-time metric, I guess you could run the movie in reverse. All these times are in the frame of reference of both planets - in Biff's frame of reference, travelling at the speed of light, the journey takes zero time and he covers zero distance. Gandalf61 (talk) 14:53, 26 March 2008 (UTC)

You may want to read the article on the Alcubierre drive. — DanielLC 20:30, 26 March 2008 (UTC)

The quick answer as to why we couldn't use contraction of space to travel FTL is that we haven't found a decent way yet - various models have been proposed to do just that, but almost invariably they require at least one of two things: (a) thousands of times more energy than is available in the known universe, and (b) some unknown type of exotic matter that could somehow generate "negative energy". The Alcubierre drive apparently doesn't require much exotic matter any more, but it still needs some, and as yet there's no proof that such a thing even exists. Confusing Manifestation(Say hi!) 23:18, 26 March 2008 (UTC)

I am no expert by any means but my understanding is that shortly after the big bang the universe was indeed expanding much faster than the speed of light.Em3ryguy (talk) 00:24, 28 March 2008 (UTC)

Red cross society in Taiwan?

Hi, maybe this can be a sensitive issue. Since (the current elections in republic of china), among protests on tibet, etc. But i want to focus on the question putting aside any political blur.

Okay, basically, i have been trying to look here Category:Red Cross national societies, but i didn't get any clue about this

Is there a Red cross society in Taiwan (R.O.C) and in China (P.R.C)?, are those countries represented in one of them? or splitted?.

I really need to get a clue about this. Thanks in advance. --HappyApple (talk) 06:59, 26 March 2008 (UTC)

Taiwan appears to have a Red Cross Society, see [6]. The graphic of the website identifies itself as "The Red Cross Society of the Republic of China".

Blood/urine tests

This is not a request for medical information, as you'll see. I had blood work/urine test last Saturday, and the doctor's office called today to tell me there's a "slight problem." They can't tell me what it is over the phone, and I'm not free for the next two days. I had already made an appointment to review the results this Saturday, so I'm worried that they called me now. Do doctors make these calls if it's just high cholesterol? Thanks. Imagine Reason (talk) 15:36, 26 March 2008 (UTC)

Quite possibly. If you have high cholesterol (the fact that a lot of people have high cholesterol doesn't lessen the problem) your doctor will want to advise you what you can do about it and possibly perform further tests.--Shantavira|^{feed me} 15:50, 26 March 2008 (UTC)

Why would they tell you the results over the phone for free when they can make money if you come in for an appointment? I wouldn't worry yet.

72.211.184.40 (talk) 15:51, 26 March 2008 (UTC)

If the tests indicated anything that might represent an urgent medical problem then your doctor would have advised you to present yourself at the local emergency ward or after-hours clinic. Beyond that, it would be entirely inappropriate – not to mention futile – for us to speculate as to what your test results might mean. TenOfAllTrades(talk) 15:53, 26 March 2008 (UTC)

That's not good. I'd rather it be cancer than AIDS! Imagine Reason (talk) 16:12, 26 March 2008 (UTC)

User:TenOfAllTrades/Why_not? - to further expand on TenOfAllTrades point! Good luck with your results. CycloneNimrod (talk) 17:44, 27 March 2008 (UTC)

I could be wrong, but I don't expect in most cases your doctor would have advised you to present yourself at the emergency ward or after-hours clinic for either AIDS or cancer (in other words, you shouldn't rule any of these out, although I'm not suggesting you expect them either). Urgent medical attention is something like 'you might be going to have a heart attack soon' or 'someone spiked your food with arsenic'. Nil Einne (talk) 18:29, 27 March 2008 (UTC)

" a slight problem" often means that the lab messed up the sample and needs another, so don't panic just yet.

Thank you, all. It turned out to be a "slight" liver function abnormality, although I'm immunized against Hep B and have not had a hep infection. Imagine Reason (talk) 02:07, 30 March 2008 (UTC)

Good to hear that it doesn't appear to have been anything major Nil Einne (talk) 17:34, 31 March 2008 (UTC)

Hail

Why does hail never seem to settle (unlike snow)? If and when it does settle, is there a name for it?--Shantavira|^{feed me} 15:46, 26 March 2008 (UTC)

Possibly because, per the article, hail comes from thunderclouds, which require reasonably warm surface temperatures to form. Algebraist 16:01, 26 March 2008 (UTC)

Hail is little balls of ice, so can't compact much. The best you could get is to force the air between the hail stones out to form a solid sheet of ice. This might happen if it's near freezing and you put a lot of weight on it, like by driving a car over it. StuRat (talk) 16:17, 26 March 2008 (UTC)

I may not understand the question, but what about this hail is not settled?

Hail is the closest thing to snow here in the tropics. I don't think it settles into a deposit as it melts away even during the thunderstorm.--Lenticel ^(talk) 23:34, 26 March 2008 (UTC)

I'm assuming that Shantavira is referring to the fact Given a little time, and maybe a little wind, A foot of light-fluffy snow can "settle" into half a foot of heavier snow. Hail, being rigid balls of ice, won't do that. Or maybe he means to say "accumulate" in which case the answer is "Because hail shows up with above-freezing temperatures, so usually it melts instantly. But sometimes it doesn't as in that photo. I don't know what you'd call that except 'hail, on the ground'." APL (talk) 06:49, 27 March 2008 (UTC)

There have been occasions of hail forming "drifts" due to floating along with runoff from the parent thunderstorm, even piling several feet high. -RunningOnBrains 23:34, 27 March 2008 (UTC)

Regenerating Limbs

Has anyone heard any recent updates on the possibility of human limb regeneration just like the starfish?

Also, when our skin heals say from a cut, why does it not "remember" what that particular section of skin was before the cut? I mean is, why does it leave a scar? --Jonasmanohar (talk) 17:50, 26 March 2008 (UTC)

I don't think human ability to regenerate limbs is changing much. You may be interested in the article scar. Friday (talk) 17:55, 26 March 2008 (UTC)

Depending on the severity of the wound, excessive deposition of collagen by fibroblasts at the expense of re-epithelialization (the epidermis) causes the scar. Wisdom89 _{(T / ^C)} 21:05, 26 March 2008 (UTC)

The current edition of Scientific American has an article on the subject. --Gerry Ashton (talk) 21:40, 26 March 2008 (UTC)

See Regeneration (biology) as well. There are some human sections there. --Lenticel ^(talk) 22:26, 26 March 2008 (UTC)

This was actually the featured article in Scientific American this month[7]. Check it out, this might be what you're looking for. Mac Davis (talk) 23:21, 27 March 2008 (UTC)

Here [8] is a news story about a man who managed to chop off a fingertip, and doctors regrew it. All it took was sprinkling on the wound a powder developed by Dr. Steven Badylak of the University of Pittsburgh's McGowan Institute of Regenerative Medicine. The powder was "a substance made from pig bladders called extracellular matrix." Edison (talk) 23:48, 27 March 2008 (UTC)

Intestinal Dysbiosis

Does anyone know where I can read valid information on Intestinal Dysbiosis? Is it anywhere in Wiki?

Our (inadequate) article is at dysbiosis. --Sean 18:41, 26 March 2008 (UTC)

global warming

what evidence that global warming is occuring, and what evidence is there that it isnt occuring?

See global warming and related articles. At this point there's little doubt that it's occurring- scientific disagreements are generally over the details these days. Friday (talk) 21:22, 26 March 2008 (UTC)

See in particular scientific opinion on climate change. It looks like it's now almost impossible to find scientists who deny that anthropogenic global warming is occuring and has been for some time. Algebraist 21:54, 26 March 2008 (UTC)

I'd like to cut in and mention that he wasn't asking for numbers of scientists, he was asking for evidence pro or con. Mac Davis (talk) 23:10, 27 March 2008 (UTC)

At this point most of the serious opposition has taken to arguing that it doesn't matter, or it isn't really caused by humans all that much, or that it can't be stopped, or that measures to stop it would be economically prohibitive, etc., with only the real fringe arguing that no change is happening at all. (At least, that's what I've noticed.) --Captain Ref Desk (talk) 21:58, 26 March 2008 (UTC)

The intersting data are those that indicate, not that global warming is happening (this is indisputable, but it could be a cyclic phenomenon), but that it's happening faster than it ever has before. Core samples of glacial ice at the poles, and analysis of fossilized pollen (thus indicating periodicity of tropical / temperate cycles over millions of years) indicate that the globe is warming more and faster than at any other point in at least a few million years since the Industrial Revolution. At the risk of climbing upon a soap-box, it is frustrating as a scientist and an educator to hear people talking about "opinions" regarding global warming. Everyone's entitled to their own opion. But no one is entitled to their own facts. Facts are facts. One can argue that the data are corrupted or inaccurate, one can dispute the rigor of the methodology in collecting the data, one can even produce a contradictory data set. But one cannot simply say that they don't believe in global warming, for example, without first accounting for the data that support it. This is not an even-handed debate. It really isn't a debate at all. Vance.mcpherson (talk) 16:29, 27 March 2008 (UTC)

No argument at all -- and I share your frustration about the "opinionization" of reasonable facts -- but for clarity, may I ask if you in fact meant "since the Industrial Revolution the globe is warming more and faster than at any other point in at least a few million years"? :-) —Steve Summit (talk) 02:47, 28 March 2008 (UTC)

Time on the moon

This maybe a strange (or even a rather dumb) question but I was wondering whether the moon has been divided in different timezones. For example: if you were to live on the moon on the place where Neil Armstrong made his famous small step, what time would it be when on earth it's 12:00 pm (GMT)?

No, it hasn't; there would be no reason. On the Apollo missions, I believe they simply used Houston local time, so 12:00 pm GMT would have been 7:00 am CDT during Apollo 10, 11, and 15; and 6:00 am CST during Apollo 8, 12, 13, 14, 16, and 17. --Anonymous, 6:22:22 pm EDT = 22:22:22 UTC, March 26, 2008.

Bear in mind that the length of a lunar day is a little bit more than 27 Earth days. (The Moon doesn't turn very quickly on its axis.) Time zones on Earth mean that the sun rises at about the same local time all around the world; people go to work, have lunch, return home, go to sleep, etc. at similar times by their local clocks.

On the moon, one would go through about two weeks of daily activities between local sunrise and sunset, and two more weeks of activity between that sunset and the next sunrise. You're not worrying about local sunlight as a cue to tell you (and your body) when to get up and when to go to sleep. If you called your buddy on the night side of the moon, you wouldn't have to worry about waking him up; he's not going to stay in bed for two solid weeks. It's much more convenient to not have time zones on the Moon—that way, you can do business with someone on the lunar farside and have everyone awake at the same time. Up until now, there's only ever been one small group of Americans on the Moon at any given time, so they've simply stayed on Houston time—the local time zone that they were talking to on Earth.

The question of what local time will be chosen for use by permanent settlers on the Moon is still open. Will Russians insist on Moscow time for their moonbase while Americans use Houston or Washington? TenOfAllTrades(talk) 23:03, 26 March 2008 (UTC)

Armstrong & co probably did use Houston time among themselves because they were in communication with Houston and that made sense in the context of the mission, which was only a few days duration. But they "came in peace for all mankind'', so we now generally use UTC time when referring to it; our article says that they "touched down on the moon at 20:17:39 UTC on 20 July 1969". As for future settlements, regardless of which country's citizens do the settling, why on Earth (no pun intended) would they use a time system that applies only to the Earth for a heavenly body that, well, isn't the Earth? That would seem to come from an attitude that the Moon is somehow part of the Earth, or at least owned by Earth. It would be like American colonists of some newly discovered island in the Mediterranean making it run on Los Angeles time - absurd. They'd have to establish a base meridian, probably the place where Armstrong & co touched down, and divide the Moon up into an appropriate number of zones, which wouldn't be 24, by the way. -- JackofOz (talk) 23:24, 26 March 2008 (UTC)

I object to the bit about "They came in peace for all mankind, so we use UTC." Wikipedia uses UTC because that's appropriately neutral Wikipedia style. But anyone who remembers the event is likely to describe it in terms of their own local time zone. --Anonymous, 04:09 UTC, March 27, 2008.

Objection noted. What you say is true for individual memories; but if asked, free of any other context, the exact date on which the first Moon landing occurred, a more accurate answer would be "It's arbitrary because calendars aren't defined on the Moon. Even if we align it to the Gregorian Calendar used on Earth, it would still depend on which place on Earth you chose as the reference point, because Earth uses many different time zones, and it happened on 19 July 1969 in some time zones and 20 July 1969 in others. As a compromise, scientists usually resort to UTC as a standard - but still arbitrary - way of expressing time, and work out the date accordingly. On this basis, it happened on 20 July 1969". -- JackofOz (talk) 07:08, 27 March 2008 (UTC)

Having a time system based on the Moon's local day/night cycle doesn't strike me as a practical approach. The only reason we need time zones on Earth is so that local clock time follows our diurnal rhythm wich follows local solar time. On the Moon, that just wouldn't happen—no one can stay away for two weeks and then sleep for two weeks. On what basis, and for what purpose, would one create time zones on the Moon?

What new clock system would you propose? You can't alter the length of the second without creating massive headaches for every scientist and engineer on the Moon. If you create a clock system or calendar based on the Earth second, you're stuck with having odd numbers of minutes in an hour or hours in a day to get the hour/day to line up with some natural cycle of the Moon's orbit or rotation. Further, if the Moon isn't tied to a terrestrial clock, then the difference between lunar time and Earth time will be constantly changing—is noon here going to be in the middle of the 'night' on the Moon next week? Three months from now?

Besides, the Moon is part of the Earth, as far as I'm concerned. It's stuck in our gravity well. Unless we do something really blindingly stupid, the population of the Moon is always going to be a tiny fraction of the Earth's. Why set up a time system that has no readily apparent benefit for the lunar colonists, and makes it more difficult for them to communicate and do business with the billions of people on Earth? TenOfAllTrades(talk) 00:27, 27 March 2008 (UTC)

That strikes me as more of an argument for fixing our own problems on Earth and not worry about ever colonising the Moon. We're obviously talking hypothetical here. But for the sake of argument, if there were a permanent colony on the Moon, and if they used an Earth-based time system, how would that work? It would have as much relevance as using the time system they use on Uranus. The Moon doesn't have the same relationship with the Sun as we do, so diurnal patterns are out the window for starters, and the 24-hour clock which is based on the rotation of the Earth would be utterly confusing, counter-intuitive and hopeless. I appreciate that our body clocks are more-or-less in line with the 24-hour clock, and they'd have to deal with the same problem that people from the tropics or the temperate zones experience when they go to the Arctic and have months of daylight and months of darkness. Yes, they'd have to stay in communication with their Earth-bound colleagues, but that presents no greater an intellectual problem than Russians in Vladivostok communicating with their cousins in Kalinigrad, 14 (?) time zones away. There would have to be a system for converting the "time" at any moment in time at any point on the Moon's surface to the the corresponding moment of time at any point on the Earth's surface, and vice-versa. If they can get to the Moon and back safely, that would be child's play. -- JackofOz (talk) 01:02, 27 March 2008 (UTC)

Up above, someone asked, "why on Earth would they use a time system that applies only to the Earth?" Because we're creatures of habit, that's why, and we really like our units. Units of time, for some reason, most of all: though systems of length and mass measurement have come and gone, the hour, minute, and particularly the second have been just about universal since they were invented (except for one short-lived experiment during the French revolution). My guess is that we'll be using hours, minutes, and seconds for quite a while after we have an Earth day to synchronize them to. (And once we stop caring about days, the leap year and leap second problems will go away!)

In the far-future civilization described by Vernor Vinge in his novel A Deepness in the Sky, the hour and minute have fallen out of use as well, but the second is still going strong, and properly decimalized. A kilosecond is about 15 minutes or a quarter of an hour (a perfectly useful amount of time); a megasecond is about 11 days, and also perfectly useful (not too far from our week); and so forth. It's not clear what they use for an absolute reference, but there's a delightful passage describing the origin they use for computer timekeeping:

Programming went back to the beginning of time. It was a little like the midden out back of his father's castle. Where the creek had worn that away, ten meters down, there were the crumpled hulks of machines -- flying machines, the peasants said -- from the great days of Canberra's original colonial era. But the castle midden was clean and fresh compared to what lay within [his own ship's] local net. There were programs here that had been written five thousand years ago, before Humankind ever left earth. The wonder of it -- the horror of it, Sura said -- was that unlike the useless wrecks of Canberra's past, these programs still worked! And via a million million circuitous threads of inheritance, many of the oldest programs still ran in the bowels of the Qeng Ho system. Take the Traders' method of timekeeping. The frame corrections were incredibly complex -- and down at the very bottom of it was a little program that ran a counter. Second by second, the Qeng Ho counted from the instant that a human had first set foot on Old Earth's moon. But if you looked at it still more closely... the starting instant was actually about fifteen million seconds later, the 0-second of one of Humankind's first computer operating systems.

—Vernor Vinge, A Deepness in the Sky, ch. 17

—Steve Summit (talk) 02:21, 27 March 2008 (UTC)

No, no, and no. They kept time on the Apollo missions using Mission Elapsed Time, which starts at zero at liftoff. 98.201.87.17 (talk) 05:15, 27 March 2008 (UTC)

The question has been asked "for what purpose would we propose a new time system for the Moon ?". Obviously it couldn't guide our sleep/wake cycle, since we can't make that 27.3 Earth days long. However, one purpose would be for adjusting solar panels which are aimed at the Sun. Many such system are likely automated, but for those which must manually be adjusted (say a portable unit used by an exploration team), a daily adjustment, or perhaps twice daily adjustment, might be appropriate. Knowing which lunar time zone you were in would help you determine how to aim it. You would also need to know how far north or south you are. Of course, you could just visually aim it at the Sun and ignore the math. Perhaps the more serious issue is knowing when the Sun will set, depending on your lunar time zone, so you can get back to base for the 14 Earth day lunar night, when solar power will be useless. Hopefully the base either has a sufficient capacity to store solar power over that period or uses nuclear power. StuRat (talk) 19:28, 27 March 2008 (UTC)

Medical equipment grounding

I have noticed that medical equipment seems to have a grounding terminal of some sort (the symbol is something like a circle within a triangle) which is separate from the normal earth ground. The ground (electricity) article doesn't mention anything about it, and I can't find it on commons:Category:Power supply symbols. What is that pin for? --cesarb (talk) 23:18, 26 March 2008 (UTC)

Is it a ground symbol within a circle? If so, this seems to indicate a connection to safety ground via the equipment. Usually, you will find that this terminal is connected to the metal casing of the instrument and therefore to the mains ground lead (and hence real ground). Such a terminal would allow the protective connections of transducers external to the equipment to be connected easily to safety (mains) ground. Say you had some gear that might tend to float to high or dangerous voltages, then connecting it to this terminal would prevent it. Simply, if you want a real ground connection, you have it here! —Preceding unsigned comment added by 79.76.201.53 (talk) 02:17, 27 March 2008 (UTC)

No, it's the opposite: the circle is within the symbol. --cesarb (talk) 03:43, 27 March 2008 (UTC)

Are you in Brazil? What is an example of one machine that has this so we can look for a picture? When you say "grounding terminal", is it a female banana jack or a screw or what? How do you know that it is separate from the normal earth ground, and what does the "normal earth ground" look like? --Milkbreath (talk) 15:28, 27 March 2008 (UTC)

Lots of medical equipment can run from an internal battery, right? I wonder if these terminals are there to "tie together" multiple pieces of equipment that aren't plugged in to the mains, to prevent sparking, ground-loops, etc. -- Coneslayer (talk) 15:35, 27 March 2008 (UTC)

(ec) Its not the symbol for signal ground shown in ground (electricity)#electronics? I don't know about medical equipment, but professional audio broadcast equipment commonly has a separate terminal for technical ground which is isolated from the safety ground connection. This is so the studio or whatever can provide a 'clean' signal ground to the equipment free of the 'dirty' noise going down the safety earth wire due to power supplies and the like. As I say, I don't really know much about medical instruments but I would guess they have a similar problem in that a small amount of noise on the ground connection can cause large errors in the readings. When a technical ground is not available the signal ground would normally be linked to safety ground since this is better than nothing. Most equipment I have come across have a terminal internally connected to safety ground immediately adjacent to the technical ground terminal in order to enable this linking to be conveniently easy and the manufacturer supplies the equipment with the link in place. It is therefore good to go out of the box and only an installer who has a technical ground facility needs to mess with it. You could also try [Symbols.com on-line encyclopedia of symbols] which allows you to search by graphic symbol type as well meaning although I could not find what you describe. SpinningSpark 15:45, 27 March 2008 (UTC)

Spinningspark is on the right track. There is a ground-loop connection on most of my medical equipment. It is used to ensure that the signals from the equipment have the same ground reference. This is important when using multiple machines to get a running history of data on more than one patient (primarily for studies). Some machines are very susceptible to this, such as EKG machines. It is not truly a ground because the wire I use to connect the machines couldn't handle the current if something were to spike. There is still a real ground going to the power outlet. -- kainaw™ 16:03, 27 March 2008 (UTC)

Almost it; it's the one shown for signal ground but with an extra circle within the triangle. --cesarb (talk) 03:38, 28 March 2008 (UTC)

I think cesarb is describing the equipotentiality symbol (IEC 417, No. 5021), as shown here [9]. It is a warning to the user that all terminals marked with the symbol are internally shorted together. For example, on an oscilloscope with BNC inputs, all the shields are usually shorted together. You might want to remind the user of this so that he doesn't try connecting the ground clips on his scope probes to different potentials. The symbol specifically does not mean that the point is grounded, although in practice it usually is. --Heron (talk) 10:58, 29 March 2008 (UTC)

March 27

Turtles

When a turtle pulls its head into its shell, does its spine buckle or contract? 70.162.25.53 (talk) 01:11, 27 March 2008 (UTC)

Have you been reading Cat's Cradle? Anyway, the article you linked has the answer: it depends on the turtle. Pleurodira fold their neck to the side, while Cryptodira pull their neck straight back. Algebraist 01:51, 27 March 2008 (UTC)

I disagree. The article does not seem to answer his question. Now that 70.162.25.53 has mentioned it, I'm sort of curious too. How is the spine in the neck constructed so that it can change length so dramatically? APL (talk) 06:37, 27 March 2008 (UTC)

The "spine" of a tortoise is more like part of its shell. See this cutaway section of a tortoise and the mechanics will be obvious.--Shantavira|^{feed me} 15:07, 27 March 2008 (UTC)

Neat! APL (talk) 13:38, 28 March 2008 (UTC)

Why a Horseshoe-shaped Gamut of Visible Colors?

The color space article describes visible colors in the RGB color model, the gamut, represented as a 2-D horseshoe shape. Are all 10 million visible colors found in this (idealized) 2-D image? Why a horseshoe shape? Is the shape a horseshoe on account of the underlying physiology of color reception in humans? Mark465 (talk) 14:52, 27 March 2008 (UTC)

The article on gamut wasn't wikilinked, see specifically Gamut#Representation_of_gamuts. It's really shaped more like a triangle with one rounded side and one rounded corner (the three corners being the three primary colors), than like a horseshoe. I too am interested in understanding the reasons why the range of possible chromaticities has a rounded blue-green side and straight blue-red side. ---Sluzzelin talk 15:11, 27 March 2008 (UTC)

See also CIE 1931 color space. ---Sluzzelin talk 15:17, 27 March 2008 (UTC)

There are three fixed points on these kinds of diagrams representing the three primary colours, which in turn are the wavelength of peak responses of the three kinds of cone detector in the human eye. These three points form the apexes of a triange. The straight line from the Red apex to the Green apex represents a fully saturated mix of the Red and Green wavelengths represented at the apexes. The colour along this line varies continuously from the red through orange and yellow to green. Similarly, the straight line between the Green and Blue apexes represents a fully saturated mix of green and blue light. However, not all light in nature is a mix of these particular three wavelengths, in fact most of it is not. Monachromatic yellow light, for instance, may appear as the same yellow as a mix of red and green light but it has a greater saturation. Since a mix of red and green light with no blue is considered to be 100% saturated, monochromatic yellow must be more than 100% saturated and is described as supersaturated. It must, therefore, lie outside the linear triangle thus accounting for the curves on the diagram. The Red-Blue axis is not curved because mixes of red and blue can only be achieved by mixing two wavelengths and so monochromatic supersaturation cannot occur and the line is therefore straight.

Anticipating the next question - why is monochromatic yellow supersaturated? The reason for this is that red/green mixed yellow obviously has wavelength component of green which is a shorter wavelength than the monochromatic yellow. At this wavelength there is some stimulation of the blue receptor also (mono yellow also stimulates the blue cone but to a much lesser degree). This stimulation of blue means that there is some component of red, green and blue in the eyes response. All three are interpreted as white, so the net result is yellow plus white or in other words desaturated yellow. Since this desaturated yellow has been predefined as 100% saturation, a more saturated yellow must consequently be supersaturated. Luckily for the television companies, supersaturated colours do not occur in nature much, so the fact that RGB television cannot reproduce them is of little consequence. SpinningSpark 16:13, 27 March 2008 (UTC)

It isn't that clear that there are three specified primaries which result from the maxima of cone receptors. The CIE color space isn't set up that way. How about magenta, cyan and yellow as alternative primaries? Edison (talk) 03:53, 28 March 2008 (UTC)

The CIE colour space uses three primaries (called the tristimulus in the article) which are arbitrarily chosen but close to the average human peak cone responses. The difficulty with humans is that they are all different so the human tristimulus is fuzzy, varying from person to person. My post above was really trying to describe the concept of supersaturation in general and was not particulary referring to the CIE colour space (although it does apply). Red-green-blue (RGB) colour spaces are used because light is detected in the human eye in terms of RGB. RGB is also most convenient where colours are being reproduced by an additive process of light such as in television or computer monitors. Where colours are reproduced by a subtractive process such as in printing then it becomes more convenient to use a cyan-magenta-yellow (CMY) colour space. In particular, printers favour the CMYK colour space. It is also worth noting that tristimulus based colour spaces only work for humans and other species with equally useless colour vision. Many species of birds, bees and moths have five colour receptors so RGB colour reproduction would not fool them for one minute. As for species like the pistol shrimp or mantis shrimp, their colour vision is so good that it would be necessary to reproduce a mix of wavelengths near identical to the original scene before they would be satisfied with television pictures. SpinningSpark 10:02, 28 March 2008 (UTC)

Alternative medicine

Is there any branch of conventional (western) medicine that would at one time in the past have been considered alternative medicine, or is that by definition impossible?--Shantavira|^{feed me} 14:58, 27 March 2008 (UTC)

I don't know how far back the term "alternative medicine" was used, but there are examples of things that are mainstream thinking now and were not in the past. A great example is the good old germ theory of disease- now accepted by all but the quackiest of quacks, yet it was seen as quite outlandish by the medical establishment when first introduced. "Tiny little bugs made you sick?? Ridiculous. Come on by and I'll fix your humors for you, and you'll be all better." Friday (talk) 15:06, 27 March 2008 (UTC)

Right. Good question. My answer was going to be "Yes, practically all of it", for the reasons Friday mentions. I was thinking of Ambroise Paré and the treatment of battlefield wounds by ligation and clean compress when the rule was cauterize for bleeding and pour hot oil in any holes. (Say what you will about the French, they have produced some bright boys.) --Milkbreath (talk) 15:20, 27 March 2008 (UTC)

Germ Theory is a good answer, but I'm not sure "Practically all of it" works. It seems like there is a lot of modern medicine that never passed through a phase where it was practiced regularly, but not by mainstream doctors. (Though it depends a lot on how narrow you're allowed to define a "branch...of medicine") However, The first paragraph Wikipedia's article on alternative medicine offers a surprisingly broad definition of the term that probably covers even techniques undergoing legitimate clinical trials by mainstream researchers. By that definition "All of it" would be the right answer. APL (talk) 16:14, 27 March 2008 (UTC)

"The Web That Has No Weaver" is a fantastic resource on Chinese Traditional Medicine that may help untangle the philosophical kinks. Western Medicine is evidence-based, and has been for some time, and is largely based upon the principle that different people, with similar medical conditions and similar bodily make-up, should be treated in roughly the same way. TCM is also evidence based, in the sense that it works, but is based upon the principle that every individual must be treated individually based upon their unique energy patterns and fluid movements. That makes it virtually impossible to compare TCM and Western medicine; it is impossible to do a double blind study on a TCM treatment because the practitioner must necessarily know what they are doing. It is also impossible to do a rigorous statistical analysis with statistical significance on TCM treatment for a given condition, because in TCM every patient will be treated differently, and consistency cannot be assured. Western forms of naturopathic medicine follow similar philosophies. So while the treatments themselves may share homology, the philosophies are too divergent for appropriate comparison. Vance.mcpherson (talk) 16:37, 27 March 2008 (UTC)

I'm sorry to derail, but I can't let that pass. Statistical comparisons are ideal for comparing situations with inconsistencies if you use a large enough sample. Are you honestly saying you couldn't do a study that says "Of Ten thousand people with illness X who were treated with western medicine Y% recovered, and of ten thousand other people with illness X who were treated with traditional Chinese medicine Z% recovered." because there's a chance that one of the TCM patients might have gotten lucky and gotten a better treatment? Granted, It may not tell you the scientific validity of TCM,(or western medicine for that matter.) but it would give you an idea which of the two approaches are more likely to work, which is far more useful. APL (talk) 18:00, 27 March 2008 (UTC)

Continuing the derailment... yes. TCM is not disease based, but rather patient based. It is the patient, not the disease, that is treated. Therefore, for example, two people with acute angina, of the same height, weight, race, and sex, may be treated with a completely different set of medications, acupuncture and other regimens, based upon factors like Qi flow, etc. Every patient is different. Further, TCM focusses upon prevention; by the time the disease sets in, it's argued, it's for the most part too late. One could say, for example, that X people with angina were treated with TCM and Z% recovered, as you say, but there would be implied thereby X different treatments. Contrast this to Western Medicine statistics, where one would never say y people were treated for angina in a bunch of different ways, and z% recovered. We'd be insisting on a highly controlled experiment. Sorry to be unclear. Vance.mcpherson (talk) 18:30, 27 March 2008 (UTC)

I'd still say a comparison could be done with a suite a treatments, so "X% recovered using Western treatment A while Y% recovered using TCM treatments B-Z". However, a more useful approach might be to have all patients evaluated for TCM and determine which TCM treatment would be recommended. You could then split each group into two, and conclude "X1% recovered using Western treatment A while Y1% recovered using TCM treatment B", and "X2% recovered using Western treatment A while Y2% recovered using TCM treatment C", etc. You might thus find that some TCM treatments are useless while others are quite effective. As for the preventative aspect of TCM, western medicine also has preventative meds, like those that keep cholesterol or high blood pressure in check. Those could be compared with TCM methods and we could study which prevents a heart attack or other negative health effect the longest. Again, we could break down the study groups based on recommended TCM treatment. Of course, as far as prevention goes, I'd say a healthy diet and lifestyle, exercise, not smoking, avoiding stress, etc., will win every time. Those should ideally be also included in any study, so we don't end up with large numbers of people eating double bacon cheeseburgers every meal and taking drugs to try to prevent the damage, when the far better option is to just eat better. StuRat (talk) 18:59, 27 March 2008 (UTC)

I'm no statistician, but it seems to me that a look at world life expectancies constitutes a very good study of the relative efficacy of the two philosophies, and others, to boot. This is especially true if we're talking about prevention, and the numbers include unweighted infant mortality, which they usually do, I believe. The map I've linked to indicates that Western is better than Chinese, which is better than Indian, and African might just be worse than nothing. --Milkbreath (talk) 19:31, 27 March 2008 (UTC)

I don't think that approach is very useful because there are so many factors which vary from place to place. For example, one of the single most important factors is probably basic sanitation. Do they dump raw sewage into the same rivers from which they drink untreated water ? If so, take 20 years off their life expectancy. So, using such figures to determine which specific medical treatment is best is unlikely to work. StuRat (talk) 20:29, 27 March 2008 (UTC)

The comparison being made is between two schools of thought, two incompatible conceptions of the mechanism of disease. Civilizations that fail to pay due heed to the role of pathogenic organisms in disease will not practice adequate sanitation. That's what I meant by "prevention". --Milkbreath (talk) 21:56, 27 March 2008 (UTC)

The reason they don't have sewage and water treatment plants isn't that they don't believe in germs, it's because they lack the resources to do so. That map seems to correspond very well with per capita income, not philosophy. Haiti, for example, is the one spot of red in the Western Hemisphere. Why ? Not because they have a radical different approach to disease treatment and prevention, but because they are dirt poor. StuRat (talk) 00:05, 28 March 2008 (UTC)

I don't feel qualified to debate world health issues, and this is not the place for that. But I would add that however poor people are, they can choose to reject a religion that makes them ritualistically drink and bathe in some of the most polluted water on earth with dead bodies in it and buffalo dreck, etc. And perhaps per capita income correlates pretty well with the realistic world view and rejection of mysticism that goes along with Western medicine. I'm outta here. --Milkbreath (talk) 00:22, 28 March 2008 (UTC)

I should back up a bit. I was very interested in researching the scientific and medical basis of TCM a few years back, and ultimately in investigating a possibility of the synthesis of TCM and Western medicine. I was told vehemently by some in the TCM community that this could never be done. It's counterintuitive because we're used to Western approaches to thinking about scientific method. Take StuRat's excellent example. "Some TCM treatments are useless while others are quite effective"... this would make sense to the Western scientist, but not in TCM. TCM is predicated upon the idea that the treatment will work if administered in the right context... and if it doesn't work, then there were other factors not considered. For example, if I have anxiety prior to a test, I might take a liver tonic because liver heat results in anxiety. But I couldn't only do this; if I have a weak spleen, for example, (which may predispose me for example to autoimmune disease, allergy, etc., but also governs liver, if memory serves), then it may be more advantageous to achieve spleen yin-yang balance. This may be achieved through a combination of herbs and acupuncture, or medicinal soups, or even a simple diet change. For example, my TCM doctor says that my spleen is cold and damp, which means I should avoid grains except rice and drink warm liquids. This is especially necessary to control insomnia. See, it's really a very different, quite incomparable system. I can't just say "take ginseng to increase your energy" in quite the same way as I can say "take this antibiotic to clear this disease". I highly recommend looking at "The Web That Has No Weaver", ([[10]]) by Ted Kaptchuk for an excellent review of this system. The title of the book is a good analogy -- the human body is "the web that has no weaver" -- there's no beginning or end, and there's not exactly a cause-effect relationship between a pathogen and a disease. Anger could be caused by liver heat or disrupted qi... and on and on like that. Vance.mcpherson (talk) 19:41, 27 March 2008 (UTC)

You're spleen is damp ? LOL. I'd be worried if it wasn't. But seriously, beware that those with a questionable treatment method often come up with some reason to claim it can't possibly be tested, so it can never be shown to be ineffective. A trick chiropractors like to use is to push down on your extended arm before and after a treatment and amaze you by how much better you are able to resist their push, which they swear is just as hard as before the treatment. Of course, this could logically be solved simply be substituting a fixed weight to apply the same force both times, but they aren't interested in doing it that way, for obvious reasons. Another favorite of charlatans is to say "your negative energy (skepticism) is what made the treatment ineffective". Back to the TCM discussion, I'd ignore TCM treatments for "damp spleen" and such. Those people who are concerned that their spleens are damp can go right to the nearest TCM practitioner, as western meds has nothing for this "serious problem". However, I believe TCM does indeed tackle a number of issues which western meds also tackle, such as headaches. And, as I've noted previously, there are ways to design a scientific study to compare the two treatment approaches for such conditions. StuRat (talk) 20:41, 27 March 2008 (UTC)

Actually my chiropractor used an electronic force measuring device. Totally objective measurement. My left arm showed a pronounced difference, right arm was unchanged. There is no need for charlatanry in your example. ~Amatulić (talk) 20:49, 27 March 2008 (UTC)

An "electronic force measuring device" sounds like something that could be tampered with, possibly using a remote control, while a fixed weight could not (unless they can pull a switch on you when your back is turned). A needlessly complex device should be another warning sign that something weird is going on. More generally, the scientific method demands that you not use subjective methods of evaluating effectiveness, which is what TCM will suggest, but instead use objective measures. If they feel people's skin and tell them their "qi" is flowing better, this is of no use in evaluating effectiveness. If, on the other hand, the patient's bad cholesterol level is down in multiple blood tests, this indicates the treatment is doing some good. StuRat (talk) 20:54, 27 March 2008 (UTC)

(Sigh). Some folks just can't let go of preconceived notions. You could do it with a spring scale (which another chiropractor did, with similar result). Using an electronic device doesn't make the chiropractor dishonest; in my case it simply allowed him to record the data more easily in his computer. There was no calibration or adjustment between tests, just comparison of forces each time. If your chiropractor doesn't perform the measurement objectively, that doesn't mean that others don't. ~Amatulić (talk) 21:04, 27 March 2008 (UTC)

You mean you failed to observe any calibration or adjustment between tests. This doesn't mean it didn't happen, just that you didn't see it. It could be as simple as a lever that's pressed or dial that's turned when the device is handled to as complex as a remote control or timer. The only way to be certain it was not changed is to use a device which can't be changed, such as a fixed weight. StuRat (talk) 21:49, 27 March 2008 (UTC)

...or a fixed spring scale, as I already mentioned. Pay attention. ~Amatulić (talk) 22:12, 27 March 2008 (UTC)

I did, and you didn't say "fixed". I have a spring scale at home that is adjustable. Did you examine the scale thoroughly to determine that it can't be adjusted ? StuRat (talk) 23:57, 27 March 2008 (UTC)

Ok, but NONE of that would stop you from treating "traditional Chinese techniques as administered by a well trained doctor" as a single unit and comparing that unit against western medicine in general. To say that the medical techniques are not "disease based" is fine, but presumably, if someone has a disease, their doctor will attempt to either cure it or relieve the symptoms, correct? We could find ten thousand people from each of the two categories that all have disease X, wait a few months, and compare the results. This would provide useful information even if each of the TCM patients received different treatments, so long as those treatments were expertly chosen by whatever rules and criteria TCM doctors normally use.

Statistics could be used even within TCM. You could do a study that says something like "Of the 10,000 TCM patients with disease X, 159 of them recieved treatment Q. Of those 159, a large percentage dropped dead instantly. Treatment Q's effectiveness is therefore in question." I'm exaggerating for comedic effect, but you get my drift. APL (talk) 21:12, 27 March 2008 (UTC)

(outdent)

Derailing further: some aspects of TCM do lend themselves to western-style clinical testing. Regular intake of the herb jiaogulan, for example, has been shown consistently to reduce cholesterol. It's one of the few examples I know of that has solid test results behind it. That's one example where one can use TCM to treat a specific condition rather than adapting a different treatmen to a patient.

Getting back on topic: To answer the OP's question, I'd say one example of conventional medicine that may have once been considered "alternative" is physical therapy. And most herbal treatments are considered "alternative" until some drug company comes along and figures out how to synthesize the active ingredient, as was the case with ephedra, from which pseudoephedrine was derived. ~Amatulić (talk) 20:50, 27 March 2008 (UTC)

...not to mention willow bark. -- Coneslayer (talk) 01:42, 28 March 2008 (UTC)

re: jiaogulan -- yes, but from a TCM perspective, it is warm and it enhances yin while supporting yang, so you wouldn't want to take it if you had excess yin or excess warmth!Vance.mcpherson (talk) 14:26, 28 March 2008 (UTC)

Moon falling into Earth

How close does the moon have to be to fall into Earth's gravity? --Jonasmanohar (talk) 17:38, 27 March 2008 (UTC)

It's already in earth's gravity. We do have an article on the orbit of the Moon. Someguy1221 (talk) 17:46, 27 March 2008 (UTC)

Ok, then I meant crash into earth... --Jonasmanohar (talk) 17:50, 27 March 2008 (UTC)

How close does it have to be to crash? Very close indeed. ;-) As the article linked to above explained, the Moon is (very slowly) getting further from the Earth. Friday (talk) 17:53, 27 March 2008 (UTC)

(Edit conflict) Just to be clear, the moon is already significantly affected by the Earth's gravity. Otherwise it wouldn't orbit the earth. What I presume you really want to know is how close does the moon have to be to the earth such that it will no longer be in a stable orbit around the earth and will eventually crash into the earth. Unfortunately I don't know the answer except that as I expected, the moon isn't actually a truly stable orbit around the earth, see [11]. Not remembering physics well enough, I can't calculate what sort of distance change is necessary. But to bear in mind it's not that the moon is going to suddenly start 'falling' into the earth at high speed. Rather, there will be a distance where the moon is in a truly stable orbit, beyond which the moon will get closer over time. However at first, the distance change will be minimal such that even though the moon will eventually theoretically crash into earth, it will take billions and billions of years for this to actually happen such that the sun will become a red giant before then so presuming the earth and moon even last that long, it will never actually have happened in any case. Of course, the closer the moon gets to the earth, the less time it will take for it to collide with the earth so that at a certain distance, it will possibly have happened were the moon really the close Nil Einne (talk) 17:56, 27 March 2008 (UTC)

You also have to decide at what velocity the moon is traveling in whatever reference frame. You could keep it where it is but just slow it down enough, and it will hit the Earth right quick. But I also forget how to calculate the velocity/distance necessary for crash for an elliptic orbit. Someguy1221 (talk) 18:03, 27 March 2008 (UTC)

(EC again) BTW, do bear in mind this isn't a simple calculation. Both the earth and the moon have a momentum.[12] This momentum was gained during their formation, it's not as if someone simply dumped a planet and a moon in the middle of space and let them start moving. If these momentums had been different, then things would be different. [13] In other words, what I'm trying to say is you can't simply visualise it as a simple system as I have a moon with mass M and a planet with mass E, what will happen when they are distance ME from each other? (Answer I think, many different things could happen including the moon could simply crash into the earth without ever actually orbiting presuming both were simply completely static from the beginning and there was actually no other mass at all [NB this is obviously an impossible system]) Nil Einne (talk) 18:09, 27 March 2008 (UTC)

Final comment: The note on the Orbit of the Moon article about how no one is actually sure what will happen to the earth-moon system after the orbit of the moon reaches 47 days sums up quite well the fact that when you actually start to think about them, these are quite complex systems Nil Einne (talk) 18:16, 27 March 2008 (UTC)

Since we're clearly talking about different things, let's make it clear, there is a distinction between placing the moon in an unstable orbit such that it eventually hits the Earth, and placing the moon in an orbit that actually comes with a moon radius of the Earth's surface (i.e., they will hit during a single orbit). The latter is what could be calculate with relative ease, not that I remember how. Someguy1221 (talk) 18:20, 27 March 2008 (UTC)

I think it's safe to say that if you could place the Moon into any orbit you liked, you would not want to place it close enough that it could hit our atmosphere, because that would cause its orbit to decay and it would almost certainly crash eventually. According to wikipedia The Exosphere ends at about 10,000km from the surface. (for reference, the moon currently does not get close than 363,104km) APL (talk) 18:26, 27 March 2008 (UTC)

OK, placing the moon in an orbit that actually comes with a moon radius of the Earth's surface (i.e., they will hit during a single orbit). --Jonasmanohar (talk) 18:24, 27 March 2008 (UTC)

Actually, the better answer is if the Moon is within the Earth's atmosphere, or closer than 10,000 km, as APL said above. The Moon's radius is only 1,737 km. StuRat (talk) 18:40, 27 March 2008 (UTC)

Correct my if I'm wrong, but in order to maintain a stable orbit, distance is inversely proportional to velocity. That is, a closer orbit will need to be faster in order to be stable. Now, the moon isn't exactly stable, but it's pretty close. If we were to slow it down substantially or pull it closer to earth without speeding it up, the orbit would begin to decay. How long will it take? Not sure. --uǝʌǝsʎʇɹoɟʇs(st47) 19:50, 27 March 2008 (UTC)

Actually I think if you go faster, you fly away. A closer orbit is slower, but gets round the Earth faster. However, once the Moon comes within the Roche limit, wouldn't it break into pieces anyway? Franamax (talk) 20:10, 27 March 2008 (UTC)

If you can just satisfy yourself that orbital energy for a circular orbit is one half the kinetic energy at escape velocity, it's pretty clear that the minimum velocity for orbit increases as the radius of the orbit decreases. It's thetotal travel time around the Earth that decreases. Someguy1221 (talk) 20:17, 27 March 2008 (UTC)

Huh? The converse of your statement is that as the radius of orbit increases, the minimum velocity decreases, right? I don't think that's correct. The faster you move, the more energy you have, the farther away you fly. Isn't that how the shuttle does it? Franamax (talk) 20:31, 27 March 2008 (UTC)

I take that back. Brain is smoking and making funny noises. Franamax (talk) 20:39, 27 March 2008 (UTC)

Roche Limit. Objects only break up inside the Roche limit if there is nothing other than gravity holding them together. This is sometimes stated as the pile-of-sand model. Crystalline rock, on the other hand, is held together by forces a lot stronger than gravity. There are many examples of objects in the solar system quite happily existing inside the parents Roche limit. SpinningSpark 22:58, 27 March 2008 (UTC)

Yes, some moon-sized objects can exist within the Roche limit, but not by much. At some point, the tidal forces will rip it apart, and I am almost completely certain that this would be well before the moon would impact the atmosphere. Of course, all of this is assuming the moon's orbit is coming closer to the earth; it is actually receding at a few millimeters a year. -RunningOnBrains 23:20, 27 March 2008 (UTC)

True, but even if the Moon did break up, that wouldn't mean that the parts would crash into Earth. They might just form a ring. However, the lack of rings around the terrestrial planets seems to imply that those rings don't last for long. StuRat (talk) 23:52, 27 March 2008 (UTC)

(unindent) The Moon's gravitation produces tides which raise the water level over a meter at numerous locations. Would not a closer Moon produce higher tides, ultimately inundating most of the land mass, even before the Earth was rendered uninhabitable by movement of its crust resulting in earthquakes and volcanoes as the Moon drew nearer, long before there was any contact? Edison (talk) 03:49, 28 March 2008 (UTC)

Yes, the tides would be higher and earthquakes would also be produced. Towards the end the atmosphere would be heated by contact with the Moon, too. StuRat (talk) 14:42, 28 March 2008 (UTC)

A detailed description of this process is to be found at [14]. Edison (talk) 15:49, 28 March 2008 (UTC)

E=MC^2

What is the whole proof to the equation E=MC^2? —Preceding unsigned comment added by 68.252.70.175 (talk) 23:37, 27 March 2008 (UTC)

Mass-energy equivalence might be useful. Algebraist 23:44, 27 March 2008 (UTC)

If you mean the derivation, the original form of it is here. It's a little opaque if you aren't used to the notation and math Einstein is using but if I recall it relates to the energy a photon imparts on the inside of a box in space or something along those lines. --Captain Ref Desk (talk) 23:53, 27 March 2008 (UTC)

One way of checking the equation for reasonableness is by dimensional analysis. The units of energy (on the left side) are kilograms times meters ² per second², by definition. The units of the right side are kilograms times C², which is equivalent to kilograms times meters ² per second², just like the left side. The only thing missing is a constant to allow for the choice of units. The equation would not balance in dimensions if it were E=MC, or E=M²C, or E=MC³, etc. Edison (talk) 03:38, 28 March 2008 (UTC)

Which is fine, but that just says that if there is some kind of mass-energy equivalence, then the constant of proportionality will have dimensions of Length ^ 2 / Time ^ 2. Just through dimensional analysis you will be unable to tell whether that constant was c^2, or something involving the Hubble constant and Planck length. Of course, if you formulated a theory where the constant had dimensions of Length ^ 3 * Time / Mass ^ 4, then yes you might suspect you'd done something wrong. Confusing Manifestation(Say hi!) 15:11, 29 March 2008 (UTC)

March 28

Shape of the Milky Way Galaxy

I remember when I was younger and more interested in astronomy reading that the Milky Way was a spiral galaxy, like the Andromeda galaxy, but while browsing various articles, I came upon the Milky Way article, which said that it was a barred spiral galaxy, which surprised me. When did astronomers figure out that it's a barred spiral galaxy instead of a spiral galaxy? Was there some discovery in the past decade that allowed them to see that it is in fact a barred spiral instead of a spiral galaxy? How do astronomers know what shape the Milky Way is and where the arms are? By judging the distance of tons of stars and laying out a map? How are astronomers able to guess at what lies on the other of the core? Thanks in advance. – Psyche825 _(talk) 04:28, 28 March 2008 (UTC)

Adaptive optics is certainly one breakthrough during the last ten years, that has helped astronomers to dramatically enhance the accuracy and resolution of star charts among other things. I cannot elaborate as I am by no means an expert in astronomical modelling. Sandman30s (talk) 09:36, 28 March 2008 (UTC)

Yes, this conclusion must have been reached by an analysis of the distribution of stars and interstellar gas and dust clouds using observations at various wavelengths. Radio astronomy, for example, allows us to see details of the Galactic Center that are hidden at visible wavelengths. Apparently the crucial evidence that clinched the case for a barred spiral structure were infrared observations made in 2005 using the Spitzer Space Telescope. Gandalf61 (talk) 11:13, 28 March 2008 (UTC)

Ah, thanks. A quick Google search about the Spitzer telescope turns up quite a few articles with more information. – Psyche825 _(talk) 06:09, 29 March 2008 (UTC)

Quantum: Measurement vs. Schrödinger Equation

1. Article Copenhagen interpretation: Each measurement causes a change in the state of the particle, known as wavefunction collapse.

2. Article Schrödinger equation: The Schrödinger equation is commonly written as an operator equation describing how the state vector evolves over time.

Although I don't fully understand quantum mechanics, the two items above seem to be related to each other.

When an observable of a quantum system is measured, the state $|\psi (t)\rangle$ of the system can be expressed as

$|\psi (t)\rangle =\sum _{i}\psi _{i}|i\rangle$ (1)

where $|i\rangle$ is the $i$th eigenfunction, which is associated to eigenvalue $i$, of the observable and

$\psi _{i}=\langle i|\psi (t)\rangle$ (2)

which will "suddenly" or "discretely" collapse from $|\psi \rangle$ to one of terms, say $\psi _{a}|a\rangle$, of the right-hand side of (1). The rest of the terms not associated to eigenvalue $a$ simply vanish after the measurement.

On the other hand, Schrödinger equation

${\hat {H}}(t)\left|\psi \left(t\right)\right\rangle =\mathrm {i} \hbar {\frac {d}{dt}}\left|\psi \left(t\right)\right\rangle$ (3)

where

${\hat {H}}(t)=-{\frac {\hbar ^{2}}{2m}}\nabla ^{2}+V\left(\mathbf {r} ,t\right)$ (4)

describing how the state vector $|\psi (t)\rangle$ evolves over time. When the state $|\psi (t)\rangle$ of the system is measured, the apparatus measuring the system will interact with the system and makes change to the potential field $V\left(\mathbf {r} ,t\right)$. Therefore, the state $|\psi (t)\rangle$ should evolve "smoothly" or "continuously" according to the varying potential $V\left(\mathbf {r} ,t\right)$ during the measurement. According to Schrödinger Equation (3) and (4) together with $V\left(\mathbf {r} ,t\right)$, we should be able to figure out the final state of the system after the measurement.

It seems that the measuring process can be explained by the two ways, wavefunction collapse & Schrödinger equation, above. Do they contradict? Is "wavefunction collapse" compatible with "Schrödinger Equation"? - Justin545 (talk) 08:12, 26 March 2008 (UTC)

Yes, they do contradict. There is no place for a collapse in Schrödinger's Equation, which is one reason why David Bohm concluded that there can be no collapse of a wave function, that it's a figment of the model. — kwami (talk) 08:34, 28 March 2008 (UTC)

Figment of the model? I'm amazed that they do contradict since the two items are considered to be postulate of quantum mechanics in some textbook of quatum mechanics IIRC. It should imply at least one of the two items is wrong. So has David Bohm or some one else solved the contradiction? And how about the experimental evidence? Experimental evidence supports which one? - Justin545 (talk) 08:55, 28 March 2008 (UTC)

The Copenhagen interpretation is just that, an interpretation. It has no empirical support (or at least it didn't some years ago) and is in no way an axiom of QM. I've heard people who use it make the excuse that none of the other interpretations have any empirical support either, even though some of them are less counter-intuitive than Copenhagen. Bohm attempted to create a deterministic hidden-variable QM, but was unable to solve some fundamental problems before he died. One of his students continued with his work, but I don't know if he ever got anywhere. — kwami (talk) 09:04, 28 March 2008 (UTC)

I think neither Schrödinger equation nor wavefunction collapse could be axiom of QM. Therefore, they are considered to be "postulates" of QM. Schrödinger equation seems to correctly predict the spectral lines of each atomic models. On the other hand, wavefunction collapse seems to correctly predict the phenomenon of quantum entanglement. And both of the predictions has been observed by many experiments. The experimental results seem to support both of the two items. But there may be some subtle differences are missing (enough precision? relativity?). When reading the article Copenhagen interpretation, we should also notice the sentence "The Copenhagen interpretation consists of attempts to explain the experiments and their mathematical formulations in ways that do not go beyond the evidence to suggest more (or less) than is actually there." - Justin545 (talk) 09:41, 28 March 2008 (UTC)

>> "There is no place for a collapse in Schrödinger's Equation"

Theoretically, is it possible to build a thought experiment in which the measuring process is simulated and use the Schrödinger equation to find out the result of the experiment? Had some one done this job before? - Justin545 (talk) 10:02, 28 March 2008 (UTC)

As above, it is an open problem. There are ongoing efforts to create "measurement" systems that can be fully modeled quantum mechanically via Schrodinger's equation for all parts of the system. Observationally it is certainly true that wavefunctions "collapse", by which one means that a single particle state interacting with a much larger collection of particles will usually be observed to reside in an eigenstate, however the mechanics of how this occurs is not well understood. The dynamical timescale is apparently quite short, and the systems that need to be modelled fairly large (e.g. 30 or 40 plus particles evolving simultaneously). Dragons flight (talk) 16:02, 28 March 2008 (UTC)

It is likely to get only numerical solution to Schrödinger's equation for so many particles. Finding the solution of exact expression for so many particles seems impossible.

After reviewed the article wavefunction collapse this morning, I noticed this:

By the time John von Neumann wrote his famous treatise Mathematische Grundlagen der Quantenmechanik in 1932, the phenomenon of "wave function collapse" was accommodated into the mathematical formulation of quantum mechanics by postulating that there were two processes of wave function change:

1. The probabilistic, non-unitary, non-local, discontinuous change brought about by observation and measurement, as outlined above.

2. The deterministic, unitary, continuous time evolution of an isolated system that obeys Schrödinger's equation (or nowadays some relativistic, local equivalent).

In general, quantum systems exist in superpositions of those basis states that most closely correspond to classical descriptions, and -- when not being measured or observed, evolve according to the time dependent Schrödinger equation, relativistic quantum field theory or some form of quantum gravity or string theory, which is process (2) mentioned above. However, when the wave function collapses -- process (1) -- from an observer's perspective the state seems to "leap" or "jump" to just one of the basis states and uniquely acquire the value of the property being measured, $e_{i}$, that is associated with that particular basis state. After the collapse, the system begins to evolve again according to the Schrödinger equation or some equivalent wave equation.

It seems that we should treat wave function change as an if-then-else statement in programming. If the change is discrete then use wavefunction collapse method else if the change is continuous then use Schrödinger's method. Not quite a an elegant way in science. - Justin545 (talk) 02:30, 29 March 2008 (UTC)

Any mathematical model that involves "alakazaam!" is obviously fundamentally flawed. However, QM is also the most precisely confirmed theory in human history. As a result, you get the null "Shut up and calculate!" interpretation, which seems to be what most people actually abide by. — kwami (talk) 18:19, 28 March 2008 (UTC)

It sounds like you (kwami) are really sick of quantum theories and those people who are learning it. Unfortunately, I am not here trying to pick a fight with someone over my post. I mean maybe you want to ignore this post and take a rest for a while. - Justin545 (talk) 00:41, 29 March 2008 (UTC)

Nuclear fission

What is the formula for the typ eof Nuclear fission used in power plants? The article has no formulae at all. —Preceding unsigned comment added by Anthrcer (talk • contribs) 09:36, 28 March 2008 (UTC)

The reaction in the top picture is ²³⁵U + n → ²³⁶U → ⁹²Kr + ¹⁴¹Ba + n + n + n. I think that would be fairly typical for anything other than a breeder reactor. The daughter nuclei aren't always the same though. There are a range of possibilities, but the first two steps stay the same. AlmostReadytoFly (talk) 09:48, 28 March 2008 (UTC)

In the case of fission, formulae don't tell you much, as there is a fairly even chance as to what the end-products (the fission products) will be. Pick two arbitrary fission products and you can figure out how many neutrons will be released, and by doing the binding energy calculations, how much energy will be released (in one of a few forms). Power plants don't use a different type of nuclear fission than anything else; where they differ is in the arrangements used to facilitate the fission reactions in different concentrations of uranium, etc. --Captain Ref Desk (talk) 11:18, 28 March 2008 (UTC)

Our article on fission product yield tabulates the most common products of uranium-235 fission, though it doesn't give specific formulae for the fission reaction. In general, the products will be as AlmostReadytoFly says—pick a couple of nuclei from the table that account for all your protons, any 'leftover' neutrons are free neutrons released by the fission. TenOfAllTrades(talk) 13:48, 28 March 2008 (UTC)

STS-123

Why was the hydrazine exhaust more pronounced in this flight than others? Nick (talk) 12:47, 28 March 2008 (UTC)nicholassayshi

I don't know, but here's our article: STS-123. One factor that can make exhaust more visible is humidity in the atmosphere. While on a dry day water vapor will instantly become invisible, on a humid day it can remain indefinitely as an exhaust trail. Under ideal conditions any exhaust particles can also serve as nucleation sites to cause cloud formation. Shock waves can have the same effect. Light conditions will also make the exhaust more or less visible. If it is lit up against a dark sky, that's when it will show up best. This lighting condition is most common before dawn or right after sunset, so the 2:30 AM launch doesn't seem likely to be illuminated by the Sun, but could still be illuminated by the rocket combustion. That seems to be the case in this pic: [15]. StuRat (talk) 16:22, 28 March 2008 (UTC)

doctors whose expertise is diabetics

How do you call a doctor whose expertise is Diabetics ? 'Diabetician' is probably wrong. BentzyCo (talk) 15:55, 28 March 2008 (UTC)

I would think that it's a sub-specialty of endocrinology. -- Coneslayer (talk) 15:56, 28 March 2008 (UTC)

(Which means that the physician's business card may describe him as an endocrinologist.) Individuals interested in a career in endocrinology will first finish a regular medical degree (MD). To become an endocrinologist usually requires at least a two- or three-year fellowship on top of their general training. Many endocrinologists specialize on a specific area within the field (diabetic medicine, reproductive medicine, etc.). TenOfAllTrades(talk) 16:07, 28 March 2008 (UTC)

There are also nutritionists/clinical dieticians who will advise you on a new diet for diabetics. I'm not sure if any handle diabetes alone or if they all handle multiple special diet planning. Also, many may not hold doctorate degrees. StuRat (talk) 16:20, 28 March 2008 (UTC)

It would be a metabolic sub-specialty of endocrinology. Wisdom89 _{(T / ^C)} 18:47, 28 March 2008 (UTC)

I looked up on the internet a doctor (in the US) who is an expert in treating diabetes. The website describes him as "Specialties: Diabetes, Endocrinology & Metabolism, Internal Medicine" and he is Board certified in Internal Medicine and Endocrinology. In the UK I found one who described himself as "Consultant Diabetician and Endocrinologist." So the terminology may vary regionally. Even in the UK "diabetician" seems to be more of an informal usage by patients rather than a professional certification. Edison (talk) 00:15, 29 March 2008 (UTC)

"Diabetologist" has some currency in the U.S. - enough to merit an entry in Merriam-Webster's Dictionary that dates the first use of the term as 1970. - Nunh-huh 01:41, 29 March 2008 (UTC)

That could also refer to a scientist who studies or specializes in or researches diabetes as well - probably why you might find mentions of the term floating around in literature. Wisdom89 _{(T / ^C)} 02:54, 29 March 2008 (UTC)

Well, I suppose it could, but in actual use, it generally doesn't. - Nunh-huh 00:15, 30 March 2008 (UTC)

We call them "Diabetes Specialists." There are CME courses for diabetes specialists and national testing to be officially titled as a diabetes specialist. Right now, I'm beginning a study on how much treatment of diabetes is improved in clinics that employ diabetes specialists. None of them call themselved diabeticians or diabetologists or anything of the sort. -- kainaw™ 03:00, 29 March 2008 (UTC)

Climate change

Given the clearly disturbing events that have just happened a few days ago regarding a 160 km piece of an ice shelf buckling, just how concerned should the world be. Also if the ice shelf does collapse, which areas will most likely be affected, the northern or southern hemisphere? I think we can all agree that we need to start looking for a new planet --77.100.6.191 (talk) 18:37, 28 March 2008 (UTC)

Take it easy. An ice shelf buckling is not going to destroy all life on Earth. Ice floating on water doesn't even increase sea levels when it melts. Ice on land does, but likely only a fraction of an inch worldwide. If all of the ice on Antarctica and Greenland melted, then you would have a significant sea level rise of tens of feet. That would be trouble for some low-lying coastal areas, especially those below sea level. However, as long as this happens slowly enough, we will be able to compensate by moving inland or constructing sea walls. Human life will survive. Now, would it be wise to take some of the resources we would otherwise put into evacuating coastal areas and spend that on slowing global warming, instead ? Sure, that would be a more efficient use of those resources. StuRat (talk) 18:51, 28 March 2008 (UTC)

Okay, this is an excuse to advertise my own work on an interactive tool for seeing regions vulnerable to sea level rise: http://www.globalwarmingart.com/sealevel A complete melt-down would be 65 m (210 feet) and have a dramatic effect, but that is very unlikely and would require a very long time even if it did happen. More likely is somewhere between 0.3 and 2 m (1-6 feet) during the next hundred years, which is important only to isolated regions, like New Orleans and the Netherlands, that are already very close to sea level. Speaking of efficient use of resources, another good one would be to stop building so many beach front properties. Property losses due to hurricanes in the US have increased 10-fold in recent decades, but that is mostly because so much more construction is being built in vulnerable areas. Dragons flight (talk) 21:05, 28 March 2008 (UTC)

Hi. Wow, that looks like a really useful tool, and perhaps just as useful as Flood Maps. The Wilkins Ice Shelf, even if it melts completely, should not be a global catastrophe. However, if Pine Island Bay melts, well, uh, that's another story. Hope this helps. Thanks. ~AH1^(TCU) 21:35, 28 March 2008 (UTC)

Hi. Woah, a mere 25-metre sea level rise would flood large areas around the Caspian sea, acording to that link. Thanks. ~AH1^(TCU) 23:00, 28 March 2008 (UTC)

One problem with these kind of maps is that they usually take into account only elevation, thus showing things like a greatly enlarged Caspian Sea, or a water-filled Death Valley, etc. This one seems a bit better in that its legend is labeled "Elevation Relative to Sea Level" -- which does not necessarily mean "filled with water". Pfly (talk) 18:55, 29 March 2008 (UTC)

Wilkins Ice Shelf

The spectacular series of pictures of a large piece breaking off from the Wilkins Ice Shelf clearly show the broken piece turn from white to blue as the crack progresses through Feb and March. Why is that? Surely it would not have got noticeably thinner in that short space of time. SpinningSpark 18:43, 28 March 2008 (UTC)

I think there was a subtle change in the angle that caused it to reflect light differently (it appears to be higher up on land and lower by the water). In Antarctica the sunlight is coming in at such a shallow angle that any change in the surface angle can put the entire surface in shadow. Shadows on snow and ice often appear blue. StuRat (talk) 18:58, 28 March 2008 (UTC)

Hi. How is it impossible for ice to melt in the space of a month? If it never melted, then it would refreze the next winter, and events like Larsen B would be impossible. Could it be that as the ice became detached from the main shelf, it started to crack, and the colder water, interspersed with large chunks of ice, created a "gel-like" structure overall and became a combination of ice and fresh water? Or, is it really impossible for it to melt that quickly in the space of a month? Didin't Larsen B turn blue when it was melting? How could Arctic ice, similar albeit less thick, melt so quickly if the ice cannot change in thickness? Will the Wilkins Ice shelf, the part that broke off at least, refreze around May and June? Thanks. ~AH1^(TCU) 21:43, 28 March 2008 (UTC)

Earth Hour - feasable or not?

As far as I know about power stations and electricity, it costs more power to halt a power station for an hour and restart it afterwards, than to keep it running. So, what if the Earth Hour succeeds in an impressive way, and everyone turns off everything for an hour. What could possibly happen? Where goes all the generated power? Wouldn't it be dangerous if suddenly everyone turns everything off? Wouldn't all the power stations blow off? with a 10% drop as last year, certainly not, but what about a 95% drop? --V. Szabolcs (talk) 20:04, 28 March 2008 (UTC)

Power networks have pumped-storage hydroelectricity facilities which consume excess electrical power during periods of low demand, using it to pump water from a low reservoir into a high reservoir. The water is then released during periods of high demand, when it generates electricity by driving turbines. In effect, these facilities act as huge rechargeable batteries. This allows the energy company to even out fluctuations in demand on the grid and to run their base load power plants at or near a constant peak efficiency. Gandalf61 (talk) 20:25, 28 March 2008 (UTC)

Thanks for the quick answer. I knew about the water pumping at the hydroelectric stations, but aren't those fluctuations statistical, so they usually never change very much too quick? If everybody at the same time turns everything on or off, wouldn't it cause strange effects? --V. Szabolcs (talk) 21:07, 28 March 2008 (UTC)

(ec) Well that's one solution. Other, not so widespread, options include undergound compressed air storage and NaS batteries (molten sodium batteries have ridiculous capacities, but only operate at high temperatures). For the large part though, much of the power infrastructure is still managed by taking plants on and off-line and allowing voltages to drift by several percent as you do so. Most electronics are tolerant of minor changes in the voltage which gives power suppliers room to adjust the amount of energy they are delivering without having to always react instantly to changes in demand. Dragons flight (talk) 21:16, 28 March 2008 (UTC)

Different types of power plants can be shut down and restarted on different time scales. Base load power plants (conventional coal or nuclear facilities) take hours or days to start up. Peaking power plants (oil-fired and especially gas turbines) can be started or shut down in minutes. The output of most hydroelectric plants can be regulated easily (often in seconds) by adjusting the flow of water through their turbines. Extremely rapid changes in demand (on time scales shorter than a few seconds) will result in brief increases or decreases in the grid's voltage. How easily the power grid can respond to rapid shifts in demand depends on how fast those changes occur, the size of the change, and the makeup of the grid's generating capacity.

The condition you're describing – where a power plant running at full output faces a sudden sharp drop in demand – is called load rejection. Power plants are designed to shut down safely when this occurs (as can happen during a major transmission line failure, for example—see Northeast Blackout of 2003), though restarting tripped plants can take hours or days. TenOfAllTrades(talk) 21:25, 28 March 2008 (UTC)

Hi. Should someone add Earth Hour to the on this day for the main page March 29, as well as edit the article on March 29 to mention Earth Hour, or should I do that myself? Thanks. ~AH1^(TCU) 21:46, 28 March 2008 (UTC)

I've mentioned Earth Hour in the March 29 artcle. --Bowlhover (talk) 04:37, 29 March 2008 (UTC)

Sounds like an interesting experiment, and I plan to do my part. An imbalance between generation and load due to everyone turning off lights at the same instant would cause the power frequency in the affected region to increase a bit above the normal 60 Hz until the steam valves could react by decreasing the input power to the generators. Most people will not alter their usage during the appointed hour. Other load which will not be affected includes electricity used to operate in full or in part the heating plants, refrigeration systems,stores, electricity used in industry, that used to operate electric trains,for operating elevators, restaurants, streetlights, sewage plants, hospitals, broadcasting operations, and many other portions of the load. The baseload plants will be dispatched according to the expected load. Baseload plants could be tripped offline if the load dropped too abruptly, and they would takw a while to restart. Peakers are smaller units designed to start rapidly and to change their output rapidly to follow loadswings. If folks in each timezone turned off their lights frop 8 to 9 pm local, there would be interesting swings in the powerflow on the tielines between utilities on either side of the time zone boundary. The US is connected a grid,(or rather grids) with large areas interconnected to allow one area to back up the next when load is added or when generation drops. It sounds like a field day for burglars, if residential security lights are turned off. Edison (talk) 22:28, 28 March 2008 (UTC)

I suspect it's a truism in control theory (and if someone can confirm this, I'd be grateful) that the best regulation can be achieved only with anticipation of future events. Machines aren't good at predicting unpredictable events in the future, but people can be. I suspect that, as the publicity surrounding Earth Hour has increased, the word has gone out to all the power plant operators everywhere (via whatever bulletin-board or chat system they use) that they'd be well-advised to have their finger closely on the throttle at 8:00 tonight.

I wonder, too, how far this observation goes in explaining what I hear has recently been discovered to be the inherent instability of large-scale electric power generation and transmission networks. We'd like to think that those networks, and all their regulation and protection mechanisms, are fully automated, removing us unreliable people from the loop. But if the systems are operating close enough to the edge (of capacity or stability or any other factor) that the best possible regulation is absolutely required, and if the best possible regulation requires more anticipation than "dumb" machines can possibly handle, then humans may be unavoidably part of the system, meaning that the possibility of human error (with arbitrarily catastrophic results) can't ever be entirely eliminated. —Steve Summit (talk) 18:50, 29 March 2008 (UTC)

"People can be good at predicting unpredictable events"?!?!? Would you, ah, care to rephrase that? --Anon, 21:45 UTC, March 29, 2008.

Well, okay, if you want to be pedantic about it, would you settle for "People can be good at reading the newspaper and anticipating events that couldn't have been predicted when the power grid management system was designed N years ago"? :-) —Steve Summit (talk) 22:52, 29 March 2008 (UTC)

How about Earth Away From Home? I now have my breaker box wired with contactor relays for each and every circuit and the contactor relays setup for remote control so that instead of shutting everything down for just an hour I can shut everything down including such electric appliances as the electric water heater when I leave for work. Except for the security system my house is dead until I return. That's everything off for at least eight hours a day. 71.100.15.236 (talk) 00:06, 29 March 2008 (UTC)

Well, I killed the main breaker in my home at 8 and restored power at 9. I did not see much of a blackout at neighbors' homes. During the hour I had a battery radio on, a fire in the fireplace, and a few battery lights, candles and kerosene lamps burning. It was a pleasant interlude, for what it's worth. It will be interesting to see if the experiment caused a measurable change in power demand. Edison (talk) 02:19, 30 March 2008 (UTC)

what causes water drops to join up?

I'm not talking about condensation, or the formation of water drops. I'm asking what is the name (if one exists) of the phenomenon of water drops clumping up to join a larger mass.

There are two scenarios in which i've seen this: first, when it's raining outside, and water drops slide down my car window, as they travel, they absorb more drops, gaining in mass and velocity. Second, if given enough time, and the frequency is right, free falling water drops will seem to clump up and form larger clumps.

I heard this refered to as the 'Moydo (Moydow?) Effect' but can't find any reference to it. Does anyone have a clue if this phenomenon has a name (other than water clumping, of course)204.154.43.244 (talk) 21:53, 28 March 2008 (UTC)

It's largely a function of surface tension. The most volume enclosed by a given surface area (or the least surface area required to enclose a given volume) is a sphere, and water tends to sit as spherically as possible given the constraints of gravity, intervening surfaces, and so forth. — Lomn 21:57, 28 March 2008 (UTC)

Do you mean the Marangoni effect ? SpinningSpark 22:16, 28 March 2008 (UTC)

More generally, perhaps coalescence? Sadly we don't seem to have much info on that, although it can be fascinating. 81.157.46.230 (talk) 01:44, 29 March 2008 (UTC)

Also, capillary action might be at work here, although this is related to/involves surface tension effects, in addition to intermolecular forces. Wisdom89 _{(T / ^C)} 03:03, 29 March 2008 (UTC)

Thermal ballast

Is it more energy efficient to keep a freezer and a refrigerator as empty as possible or to keep them loaded to the max.? —Preceding unsigned comment added by 71.100.15.236 (talk) 23:35, 28 March 2008 (UTC)

Personally, I believe it makes little difference, although having it fuller will probably make it slightly more efficient. And my hero agrees with me. —Steve Summit (talk) 00:49, 29 March 2008 (UTC)

I would define efficiency in terms of how much food is kept cold per dollar. In that case, an empty freezer is running at 0% efficiency. StuRat (talk) 04:02, 29 March 2008 (UTC)

If you have the type of freezer with a front-opening door and shelves, then every time you open the door the cold air flows out and it replaced by warm air from the room, which then has to be cooled again. In that situation it's more efficient to keep it full, since frozen food doesn't convect! I did see a suggestion somewhere though that you could reduce that problem by filling excess freezer space with empty cereal boxes to hold the cold air in place. Freezers with drawers also solve the problem. Eve (talk) 13:26, 29 March 2008 (UTC)

However, when you do put food in, you would then need to remove a cereal box full of cold air, and that won't help efficiency. StuRat (talk) 14:21, 29 March 2008 (UTC)

If it was a cereal-box-sized piece of food you put in, it would have displaced the equivalent volume of cold air anyway. —Steve Summit (talk) 14:54, 29 March 2008 (UTC)

Talking Budgerigars - sex difference

Why is it (usually) easier to teach a male Budgerigar to talk than a female? Why do male birds usually develop a larger overall vocabulary than females? --90.242.159.224 (talk) 23:45, 28 March 2008 (UTC)

Probably to impress the females. Male birds usually have many distinguishing features, like more colorful feathers, for the same purpose. --V. Szabolcs (talk) 08:28, 29 March 2008 (UTC)

Puck of the most words made the Guiness Book of Records in 1995[16] – he was a bloke, too. Julia Rossi (talk) 08:49, 29 March 2008 (UTC)

See sexual selection. --Captain Ref Desk (talk) 20:04, 29 March 2008 (UTC)

March 29

Canned tuna

Is canned tuna cooked? 71.100.15.236 (talk) 01:02, 29 March 2008 (UTC)

In short: yes. There's some information about it at Tuna#Canned tuna. --Masamage ♫ 01:14, 29 March 2008 (UTC)

Okay, cooked but a couple of other questions... it looks like there is no minimum amount of tuna per can to call it tuna. 90% water or oil and 10% tuna and its tuna. No one would probably buy it again but what about 10% tuna, 41% catfish and 49% water? 71.100.15.236 (talk) 02:31, 29 March 2008 (UTC)

The cans have to contain a certain weight of tuna after the liquid in the can is drained. See here for the FDA regulations on canned tuna, specifically part c. Someguy1221 (talk) 11:07, 29 March 2008 (UTC)

cd recycling

Can cd's be recycled? If so, do you put them in with normal municipal recycling? I know the procedure might vary from place to place, so fyi, in my city of Perth, my local council (Claremont) uses mixed recycling, ie. without source separation. thanx in advance, 130.95.106.128 (talk) 07:10, 29 March 2008 (UTC)

I recycle mine as coffee cup coasters. Seriously, they can be recycled. Try this [17] google search string. You will also see that there are a lot of charities that will take them to make interesting products. SpinningSpark 13:12, 29 March 2008 (UTC)

Sodium Bicarbonate Vs Constipation?

Why does Sodium Bicarbonate help in going to the toilet? I know it is an has a much higher ph than the stomach but why does this result in the need to visit the toiler 5 mins after drinking it mixed with warm water? Is it bad for the stomach to use on a regular basis?

Lopex —Preceding unsigned comment added by 86.4.182.208 (talk) 08:42, 29 March 2008 (UTC)

When you mix Sodium bicarbonate with stomach juice it foams up making carbon dioxide gas, which build up pressure in the digestive tract, that pushes the contents out. Too much will give you pH imbalance, and also too much sodium. Graeme Bartlett (talk) 22:18, 29 March 2008 (UTC)

I am not convinced that a pressure build up in the stomach will have a direct pressure-based effect on the lower bowel. They are separated by several metres of soft small bowel which would absorb the pressure and apart from that, if there is that much pressure build up (again, questionable) surely it would escape upwards through the gullet, giving a vomiting effect. Bowel movements are associated with psychological stimuli in some people and the thought that something will effect the bowels does just that. An alternative explanation may be related to the gastrocolic reflex, even so five minutes seems a bit quick. Richard Avery (talk) 07:19, 31 March 2008 (UTC)

As for regular basis, once things are back to normal, probably no need. Julia Rossi (talk) 07:53, 31 March 2008 (UTC)

I would think the more likely explanation of any laxative effect of sodium bicarbonate is induction of hyperosmotic diarrhea. On the other hand (or on the other end), sodium bicarbonate's "fizzy" effect is used in suppositories, and acts by inducing a feeling of rectal "fullness", with the expected reflex action. Bicarbonate isn't really a popular laxative - it's used more as an antacid - and of course, it's considered bad form to use any laxative regularly without consulting a physician to see if there is an underlying problem that need to be addressed.- Nunh-huh 09:53, 31 March 2008 (UTC)

What is the difference between a UPS and a inverter ?

Media:Example.ogg —Preceding unsigned comment added by 124.124.1.131 (talk) 12:17, 29 March 2008 (UTC)

An inverter is a device for converting dc power to ac power. An Uninterruptable power supply (UPS) stores energy it obtains form its input (often in a battery, but it could be something else, eg a flywheel) which it applies to its output if the primary source fails. A UPS will often contain an inverter because its output may be ac while it has stored power as dc. However, in principle, a UPS might not have an inverter if its output was required to be dc. SpinningSpark 12:29, 29 March 2008 (UTC)

SpinningSpark is right. Also, sometimes people may say "inverter" when they mean UPS. I knew someone who had a home-built UPS system, basically a inverter, a charger, and a big battery. They called it an inverter even though that was just one part of the system. -- 71.91.127.85 (talk) 16:25, 30 March 2008 (UTC)

If you remove the DC input to an inverter, the AC output will immediately go to 0VAC. If you remove the (usually AC) input to a UPS, the AC output will not change (much). A UPS includes an inverter, a battery, and a battery charging system. -Arch dude (talk) 23:41, 30 March 2008 (UTC)

blackout --- caused by global warming?

I would like to know if I got it right that global warming also has something to do in any way with having power/electrical loss or blackout. Thank you in advance for the reply. —Preceding unsigned comment added by 119.93.229.75 (talk) 12:30, 29 March 2008 (UTC)

In general no, but the drought in Australia, which could have been global warming related, nearly lead to blackouts becuase of lack of water to hydro-electric plants [18] -- Q Chris (talk) 13:11, 29 March 2008 (UTC)

Indirectly, I suppose you could say that global warming leads to more use of air conditioning leads to higher electricity usage leads to more risk of brown- or blackouts. (Contrariwise, of course, more electrical usage for air conditioning leads to more global warming...) —Steve Summit (talk) 13:43, 29 March 2008 (UTC)

Hi. I just thought of something, could the 2003 European heat wave somehow been related to the 2003 Italy blackout, even if indirectly? Thanks. ~AH1^(TCU) 13:56, 29 March 2008 (UTC)

The electric company here in our city has announced a citywide blackout and giving "global warming" as a reason. —Preceding unsigned comment added by 119.93.229.75 (talk) 14:35, 29 March 2008 (UTC)

Wild guess - is this perhaps something to do with Earth Hour ? Although I thought that was supposed to be a voluntary initiative, so I don't see why a power company would announce a blackout. Anyway, there is a list of participating cities in our Earth Hour article. Gandalf61 (talk) 15:01, 29 March 2008 (UTC)

Rules for making Baryons

I'm trying to understand what are the rules for making baryons. I know baryons are made from 3 quarks (screw pentaquarks for now), any quarks. Since there are 6 different quarks, then we have 6^3 combinations of 3 quarks. However, from the Δ⁺ and the proton, each with quark composition u/u/d, it looks like the spin orientation has to be taken into account. Since each quark can be in +1/2 or -1/2 spin state, then we have 12 different quarks/quarkstates possible for each of the three quarks, which gives us 12^3 different combinations of three quarks. If we remove the degeneracies (such as ssd (3/2),sds(3/2),dss(3/2)), then we have 364 (12+11+10...+11+10+9...+10+9+8+...3+2+1+2+1+1) distinct combination of quarks/quarkstates.

Now I'm not sure of this, but I think that it is the modulus of the spin that is important, so particles with spin -3/2 and -1/2 really are the same than the particles with spin 3/2 and spin 1/2. Removing these degeneracies leaves us with half the particles, and thus we have 182 distinct baryons that can be made from three quarks.

Also, there seems to be some states that are forbidden - the Δ⁺⁺ cannot be in spin 1/2 configuration, and there are some duplicate combinations &Lamba;⁰ is uds (1/2) and so is Σ⁰. Headbomb (talk) 16:18, 29 March 2008 (UTC)

The top quark does not form baryons, according to our article, because its lifetime is too short. Apart from that, I think any combination of three quarks gives a baryon (and the corresponding three anti-quarks gives the baryon's anti-particle). If the three quarks all have the same flavour then their spins must align (because of the symmetry of the state) and you get a spin 3/2 baryon. If the quarks do not all have the same flavour then their spins may align to give a spin 3/2 baryon, or their spins may not align, which gives a spin 1/2 baryon. Quarks can also exist in excited states within a baryon - so the spin 1/2 Σ⁰ is an excited state of the Λ⁰. See list of baryons and particle zoo. Gandalf61 (talk) 13:12, 30 March 2008 (UTC)

Top Ten Chemicals Produced

I need to find the top ten chemicals produced in any given year from 1973 to the present. I have done some online searches but have found very little data. Please help.Jdbauman283 (talk) 19:06, 29 March 2008 (UTC)

Do you mean chemicals deliberately produced by humans on the earth in a manufacturing chimcal industry process? (ass opposed to naturally produced, in space, a waste product, or grown or quarried). Graeme Bartlett (talk) 22:21, 29 March 2008 (UTC)

Obviously they meant man-made. Is that obvious? that's what I'm answering anyway - see below

Sulphuric acid is always a big one. Also see Chemical industry . " Polymers and plastics, especially polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polystyrene and polycarbonate comprise about 80% of the industry’s output worldwide."

Also ammonia, fertilzers.

plus liquid nitrogen/oxygen

Here's a very out of date list http://pubs.acs.org/hotartcl/cenear/960624/prod.html 87.102.16.238 (talk) 11:14, 30 March 2008 (UTC)

I recall from the sulfuric acid article once, that sulfuric acid was actually the number one highest purposefully produced industrial chemical in terms of mass. Mac Davis (talk) 17:52, 30 March 2008 (UTC)

Do residential security lights reduce burglary?

In the Earth Night thread above I saw this comment: sounds like a field day for burglars, if residential security lights are turned off. And wondered whether such lights actually deter burglary. My understanding was that it is usually easier to see a person in the dark outside without lights than it is to see a person lurking behind a bright light. In other words, a smart burglar would use security lights to advantage. Am I misinformed? Pfly (talk) 19:12, 29 March 2008 (UTC)

I'd suspect you're mis-reasoning. If it is non-lighted at night it can be hard to see anything, something we forget in our current constantly-lit existence. Yes, standing behind a bright light can make it hard to be seen, but that requires 1. being able to get "behind" the light in the first place, and 2. knowing exactly whom you are hiding "behind" the light from (hence the quotation marks around "behind"—to someone on the other side of you, you're in front of the light!). I don't honestly see how even a smart burglar, much less the normal variety (which any public defender can tell you are not usually the best and the brightest), would use basic security lights to their advantage in a practical way. In any case, it's also a psychological case: someone under spotlights is probably more likely to feel like they are being seen, or at least could be seen, that someone without them, regardless of whether anyone is looking at them or whether they might also be able to be seen at night. --Captain Ref Desk (talk) 19:56, 29 March 2008 (UTC)

According to the article on light pollution, the International Dark-Sky Association (which is honestly a biased source) says that there's apparently no current scientific research supporting (or opposing) the idea that lighting increases security. And there's plenty of anecdotal evidence out there. I personally think most people overdo it. (The light pollution haze from the city actually does a better, more uniform job lighting my place than having proper security lights would). -- Consumed Crustacean (talk) 22:06, 29 March 2008 (UTC)

Hi. Security lights are so annoying because their glare prevents good observation of the night sky. Besides with all these street lights around it would already be bright enough. A good security system shoul only activate when the burgler is detected trying to enter the house and not up all night (most burgleries happen during the day). Thanks. ~AH1^(TCU) 23:50, 29 March 2008 (UTC)

Ah ha, I believe I did hear this idea from someone from the International Dark-Sky Association on the radio. Biased, of course. And certainly it is easy to think up examples (and places) that are obviously one way or the other. I can imagine it would be difficult to do a good scientific study of the matter. Then again, I know certain towns and suburban areas have had "dark sky" programs for years. I'd think there would be studies of those kind of places and crime rates over time. Not that it would show causality, and would be limited to the kind of neighborhoods that would actually implement such programs. Still, I wonder.. Pfly (talk) 01:28, 30 March 2008 (UTC)

When Los Angeles had a big earthquake about a decade or two ago, the power went out and the milky way was visible. People rushed outside during the earthquake, and most have never seen the real milky way before. The reason? The Los Angeles city lights have been washing out the stars for all this time. In the past 50 years or so, stereotypes have developed about what the night sky really looks like, because most urbanites have never seen the real night sky. So, a lot of people called to ask the observatory if a sudden brightening of the milky way had caused the earthquake. The observatory workers tried to explain that this is how the night sky is supposed to look. The L.A. residents didn't believe them. Pfft. ~AH1^(TCU) 21:12, 30 March 2008 (UTC)

efficiency question .

what portion of energy is wasted as a result of friction of an automobile ? how efficient will maglev train be compare to conventional vehicle ? —Preceding unsigned comment added by Shamiul (talk • contribs) 20:37, 29 March 2008 (UTC)

Pretty much all of the inefficiency in an electric car is a result of some type of friction. There is friction in the engine and transmission, rolling friction in the wheels, air resistance is a type of friction, and brakes use friction. If all friction could be eliminated, say by traveling in a vacuum, using regenerative braking, etc., then the only energy used would be in raising the elevation of the car, providing heat and A/C, running the lights, and maybe the radio. Internal combustion engines also suffer major inefficiencies due to incomplete combustion and heat bled off to the environment from the radiator. Electric cars also suffer inefficiency due to battery leakage. StuRat (talk) 21:42, 29 March 2008 (UTC)

Have you seen our engine article?. And does this answer your question? 81.93.102.185 (talk) 21:50, 29 March 2008 (UTC)

What do you see?

Do the eyes of all mammals see the same spectrum of what we call "visible light"? Seems like they do.. any particular reason? Seems like a predator who developed eyes that could react to infrared radiation would quickly dominate their environment. :D\=< (talk) 20:38, 29 March 2008 (UTC)

A very similar question was asked last December and got a lot of responses. (Just putting that out there, not trying to discourage more answers, thoughts.) --Captain Ref Desk (talk) 21:10, 29 March 2008 (UTC)

See our article on the eye and retina. It has to do with the physiology of the cells in the latter. rods and cones. Wisdom89 _{(T / ^C)} 21:55, 29 March 2008 (UTC)

Let me quote Richard Dawkins in the ancestor's tale page 147. "All eyes on our planet are set up in such a way as to exploit the wavelengths of electromagnetic radiation in which our local star shines ... For an eye that has commited itself to biochemical techniques suitable for this loosely bounded range of wavelengths, the laws of physics impose sharper bounds to the portion of the electro-magnetic spectrum that can be seen using those techniques. No animal can see far into the infrared. Those that come closest are pit vipers, who have pits in the head which, while in no sense focusing a proper image with infrared rays, allow these snakes to achieve some directional sensitivity to the heat generated by their prey. And no animal can see far into the ultraviolet although some, bees for instance, can see a bit further than we can. But, on the other hand, bees can't see our red: for them it is infrared. All animals agree that 'light' is a narrow band of electormagnetic wavelengths lying somewhere between ultraviolet at the short end and infrared at the long end. Bees, people and snakes differ only slightly in where they draw the lines at each end of 'light'" emphasis and typos added by me. -- 71.91.127.85 (talk) 19:21, 30 March 2008 (UTC)

I assume its because water is only transparent within a narrow range of frequencies.Em3ryguy (talk) 21:13, 30 March 2008 (UTC)

March 30

Tongue rolling genes

From Mendel's list I've looked at that section in the Tongue article and it mentions curling the tongue lengthwise. I know someone who can flex the tongue muscle in three different ways: curling lengthwise, turn it over and fold the tip back flat on itself like folding a piece of paper – all without help from fingers. How common is this – is it genetic and how is it passed along? His parents don't seem to have the knack, but his grandfather could touch the tip of his own nose. Julia Rossi (talk) 02:13, 30 March 2008 (UTC)

I don't know much about genes, but I know from Wikipedia that as soon as people discovered genes, they said that genes were responsible for just about every single behavior of the body that was unexplainable. I would personally not believe that being able to move your tongue in certain ways does not come from your genes, but rather something else. Mac Davis (talk) 17:47, 30 March 2008 (UTC)

While it is right to criticise a naive view of absoulte genetic determinism, building bodies is an area where genes obviously play a huge role. I probably wouldn't be able to fold my tongue back as described no matter how much I tried, just like I cant change my eye color, my genes just built my body not to be able to do those things. -- 71.91.127.85 (talk) 19:33, 30 March 2008 (UTC)

I believe that certain tongue-rolling abilities are genetic. Edison (talk) 20:23, 30 March 2008 (UTC)

gas molecule unpredictability

If you set up a barometer in a controlled environment with perfectly stable 1 atm air pressure, would you ever see any sort of noticable fluctuation? Would the heat death of the universe occur before you even had a billionth of a percent chance of seeing a 1-second millimeter rise/drop in the mercury, or is it actually quite likely? I'm just looking for very round answers here :D\=< (talk) 02:59, 30 March 2008 (UTC)

I just realized how absurd that question is.. the part about the perfectly stable air pressure pretty much makes no sense! Let's say the number of gas molecules in the chamber is stable, there's no external influences like heat causing convection, and the average air pressure is 1 atmosphere. :D\=< (talk) 03:03, 30 March 2008 (UTC)

Wind or pressure/temp changes would cause fluctuations. If there is no wind or pressure/temp change, I wouldn't expect any fluctuations until the mercury evaporation has a noticeable effect. StuRat (talk) 03:07, 30 March 2008 (UTC)

Well I just mean from gas molecules not hitting the surface. Like how if every air molecule happened to be bouncing exactly away from your mouth, then your lungs would collapse from lack of air pressure.. except with the surface of the mercury :D\=< (talk) 06:49, 30 March 2008 (UTC)

Consider a simple approximation: If each particle is approximately independent, then we can pretend that the direction it is moving (e.g. up-down, left-right, etc.) is random. Pressure is created by particles bouncing off a surface. Under normal conditions ~50% of the particles in any given volume will have a downward component to their motion. Let's consider, what is the probability that only 45% or less of particles have a downward motion. This would correspond to a 10% reduction in the downward flux and hence the instanteous pressure.

If the motion is random, then the number moving down is governed by combinatorics. Specifically, the probability of $N_{down}<=\alpha *N$ is

${1 \over 2^{N}}{\sum _{i=1}^{\alpha N}{N \choose i}}$

$={1 \over 2^{N}}{\sum _{i=1}^{\alpha N}{N! \over {i!(N-i)!}}}$

$\approx {1 \over 2^{N}}{\sum _{i=1}^{\alpha N}{N^{N} \over {i^{i}(N-i)^{N-i}}}}$

$\approx {1 \over 2^{N}}{N^{N} \over {{(\alpha N)}^{\alpha N}{((1-\alpha )N)}^{(1-\alpha )N}}}$

$={1 \over 2^{N}}{1 \over {{\alpha }^{\alpha N}{(1-\alpha )}^{(1-\alpha )N}}}$

$=({0.5 \over {\alpha }^{\alpha }{(1-\alpha )}^{1-\alpha }})^{N}$

Where I have used approximations appropriate for large N. If α = 0.45, then this reduces to $0.995^{N}$. So with a hundred particles, a 10% fluctuation occurs ≈0.995¹⁰⁰ = 60% of the time. For 2000 particles this reduces to 4 in 10⁵. For macroscopic ensembles, e.g. 10²³ particles, the odds of 10% fluctuation at random is essentially 0 for all practical timescales. Dragons flight (talk) 08:27, 30 March 2008 (UTC)

Simplify your gedankenexperiment by using a J-shaped tube with a vacuum at the tall end and a gas (at one ATM0 at the other. Replace the "mercury" with a perfect theoretical fluid that cannot react with or absorb gas. Now do the math again. -Arch dude (talk) 23:29, 30 March 2008 (UTC)

"japanese algae" keychain

My friend has this keychain, which is a sealed plastic container filled with a liquid and two green spherical puffs which she says are marimo. The liquid looks like green-colored water with oil floating in a layer on top. Could marimo actually survive in this kind of environment, or are they probably just green pom-poms? --Anakata (talk) 03:24, 30 March 2008 (UTC)

Another possibility is that it's real, but not alive. It could be preserved in some liquid like formaldehyde. StuRat (talk) 13:45, 30 March 2008 (UTC)

Sure its possible, with the right mix of microorganisms, but I am very skeptical. I'd imagine that the smaller the ecosystem, the harder it is to balance and keep healthy. I was poking around for info about ecospheres and people say that they are highly sensitive to changes in light and temperature. Being repeatedly stuffed into a warm dark pocket does not sound conducive to a stable ecosystem. -- 71.91.127.85 (talk) 19:39, 30 March 2008 (UTC)

Wow. Marimo sound cool - thanks to WP, I've learned something else new. Are there any legitimate sports-based applications for these green balls? --Kurt Shaped Box (talk) 19:50, 30 March 2008 (UTC)

Hawaii up from Alaska...?

If you look at Google maps you can see a line of submarine mountains that runs South from Achayvayam, Russia off a jetty, past the West side of Attu Island to a point about 1,800 miles East of Tokyo and then runs South East about 500 miles to Midway Island and then another 1,500 miles or so where it terminates at Hawaii. Does this mean that the hot spot that is still creating Hawaii actually originated in Russia and if so how long ago? —Preceding unsigned comment added by 71.100.0.187 (talk) 05:30, 30 March 2008 (UTC)

It looks that way (well, the hotspot stays fixed and the tectonic plates move over it, but same difference). About 80 million years. See Hawaii hotspot and Hawaiian-Emperor seamount chain.

Hi. Well, The plate that Hawai'i is situated over is constantly moving northeast, so the islands eventually move, then a new island is remade in its place. The old islands eventually erode and sink underwater. This creates a chain, and it is eventually eaten by the North American place at the destructive boundary. I think I've heard from various places that the Hawai'i chain was nonexistant during the Cretaceous. A new volcano is being created off the coast of the Big Island, and will soon replace it, but it's still got many kilometres and hundreds of thousands of years to go. Hope this helps. Thanks. ~AH1^(TCU) 21:19, 30 March 2008 (UTC)

Reversing the effect of Sun tanning on skin colour.

Is it possible to reverse the effect of sun tanning on skin colour ? Does sun tanning permanently change skin colour ? —Preceding unsigned comment added by Shamiul (talk • contribs) 08:33, 30 March 2008 (UTC)

Yes, if you stay out of the sun, your skin will eventually return to its original paler colour. However, you may tan more quickly next time you are in the sun. Also note that persistent overexposure to the sun can permanently damage your skin in a number of ways. See the article Sun tanning. SpinningSpark 12:30, 30 March 2008 (UTC)

Hi. I the summertime, I often get a "sandal tan" from wearing sandals. This usually lasts for several months, then fades away around wintertime. It usually redevelopes around late spring. I think it takes about a week to develop, and a few months to fade, although a remnant can still be seen that persists until next summer. Since it becomes darker than usual the next summer, it is often easier to get it again. Hope this helps. Thanks. ~AH1^(TCU) 21:23, 30 March 2008 (UTC)

MA and VR Can Opener

How do you calculate how much effort you put on a can opener?

Bzinc (talk) 12:40, 30 March 2008 (UTC)

Would that be Mechanical advantage and Velocity Ratio you would be after? And would this be a homework question? The Lever article might help you. SpinningSpark 12:54, 30 March 2008 (UTC)

What do t hese mean?

I love science, and a lot of the articles have images like on them. I was wondering if anyone would tel me what they mean, because someone (we're brothers) doesn't like me. Thanks! Yamakiri ^T_C § 03-30-2008 • 14:32:00

Ribbon diagram. TenOfAllTrades(talk) 14:59, 30 March 2008 (UTC)

Ahhh! My attention span! It's average! Nooooooooo! Yamakiri ^T_C § 03-30-2008 • 17:14:05

add milk now or later?

I'm about to take a shower and so made an extra-hot coffee to drink when I'm done. I'm going to put some room-temperature milk in it, but should I do so now or when I'm back?

If I do it "now" then the very hot coffee will not have a chance to retain its heat while I shower, since it will be brought a bit right away.

If I do it "later" then the very hot coffee can hold onto its heat a bit, although of course losing some while I shower, only to be brought down a bit later.

It seems the two choices should be identical, but in fact, does heat follow a curve, where the farther from room temperature something is, the faster it loses heat? In this case, I'd better add the milk now, since it will save 15 minutes of heat loss. —Preceding unsigned comment added by 79.122.31.17 (talk) 15:39, 30 March 2008 (UTC)

That's correct. Heat flow is proportional to the temperature difference between the two reservoirs (in this case your cup of coffee and the surrounding air). So if your coffee is hotter, it will loose more heat. Of course, other things may come into play - putting milk into very hot coffee may scald the milk, putting the taste off. --Stephan Schulz (talk) 15:51, 30 March 2008 (UTC)

Thank you. —Preceding unsigned comment added by 79.122.31.17 (talk) 15:54, 30 March 2008 (UTC)

I dispute Stephan Schulz's explanation: If the initial temperature difference (coffee - ambient/milk) is X, and you want to have a fraction p of coffee and a fraction 1-p of milk in what you're going to drink, then you could mix the two now: The temperature difference drops to X*p, and if the heat flow is proportional to the temperature difference, then it will decrease exponentially with some factor a: δT = X*p*exp(-a*t)

where t is the time. If you do it the other way around, it will fall off exponentially to X*exp(-a*t), and then you add the milk, and the outcome is again X*p*exp(-a*t).

However, heat transfer by thermal radiation increases with the difference of the fourth powers of the temperatures, and this will make adding the milk "now" superior. Icek (talk) 17:10, 30 March 2008 (UTC)

That's strange. You have me completely baffled. Sticking just with Newtons law of cooling for the moment and ignoring the Stefan-Boltzmann radiation law to keep it simple. The black coffee at every moment up to when the milk was put in is losing heat at a faster rate than the white cup. After the milk is put in, the two cups are identical composition. How can the (ex) black cup be at the same temperture when it has lsot more heat. SpinningSpark 18:27, 30 March 2008 (UTC)

Icek is computing with both milk and environment at 0K, I think. --Stephan Schulz (talk) 18:28, 30 March 2008 (UTC)

I don't think so, he has used ΔT throughout. SpinningSpark 18:48, 30 March 2008 (UTC)

Don't forget that coffee with milk has a lower heat transfer coefficient than black coffee. --Allen (talk) 20:12, 30 March 2008 (UTC)

Well that was exactly my point. The white cup is losing heat more slowly so it should end up at a higher temperature. Anyway, after a monumental struggle with the maths (for me anyway), I've worked out what the difficulty is. There is a hidden assumption in the Icek analysis that each gram of coffee is losing heat at the same rate (per ^oC of course). Since the white cup has more grams of liquid it is losing heat at a faster rate than the black cup at the same temperature. This precisely cancels the faster rate of heat loss of the black cup. Happily for the laws of thermodynamics, conservation of energy has been restored and we can all rest easy again. In a real world cup, the heat loss is not proportional to the mass of coffee, but rather to the surface area of the cup since the internal masses are insulated from the surface. So I would still go with the white cup, entirely based on Newtons law of cooling, without having to invoke black-body radiation or crackpot ice cream manufactures (and yes, I do know it does work despite sounding crackpot). SpinningSpark 21:04, 30 March 2008 (UTC)

See Mpemba effect. Gandalf61 (talk) 20:14, 30 March 2008 (UTC)

Isaac Asimov wrote that adding the milk early is the best choice if you want the coffee to be hotter later. Edison (talk) 20:21, 30 March 2008 (UTC)

North American bird ID, complex song, PBS "life of birds"

I was just out in my back yard (North Texas, suburban) and noticed some birds presumably doing courtship behavior. The males were dark/black colored, slighlty irridescent and the females more drab and lighter brown. They were approximately the size of a mocking bird. The reason they caught my attention was the complex but short song the males (presumably) would sing. It is a song I remembered from The Life of Birds TV series. It was extremely short, maybe .5 to 1 seconds long but it contained many notes. If I recall, the TV series showed a sonagram of the song and maybe said that it was the fastest (in notes per time unit) song in the bird world. The male would sit next to the female, when she was looking at him he would puff up his feathers and start the song, as he sang he would bow his head down, finishing the song with his head far down. I'm just curious to get an ID of the bird so I can do some more research about it. I have read through the PBS website on the series and tried to do some flowchart-style identification I found on the web but have been unsuccesful. Thanks. -- 71.91.127.85 (talk) 16:44, 30 March 2008 (UTC)

I'm looking at the Rusty Blackbird. The song can be heard here at Cornell's excellent site. --Milkbreath (talk) 17:15, 30 March 2008 (UTC)

Yeah thats the one, and thanks for the link. -- 71.91.127.85 (talk) 19:03, 30 March 2008 (UTC)

Calculating Mechanical Advantage

How do I know how much force I put on a can opener? and how much force is then put on the can? Bzinc (talk) 16:58, 30 March 2008 (UTC)

MA = Output

  Input

but IDK how to find out the can opener thing. Yamakiri ^T_C § 03-30-2008 • 17:18:07

The fulcrum of the lever is where the can-opener rests on the edge of the tin. Measure the distance from the fulcrum to the pointy end of the can-opener where the force is applied to the tin. Measure the distance from the fulcrum to the end of the handle where you apply the force. You now have enough data to calculate mechanical advantage. Work out for yourself how to calculate the MA - I am not going to do ALL your homework for you. The force applied depends on how much force your arm provides and the mechanical advantage - again, work out for yourself how that would be calculated. SpinningSpark 18:45, 30 March 2008 (UTC)

a can opener is a type of lever. But both the force you apply and the force the can applies to the blade, are on the same side of the "fulcrum" (the hinge). On my can opener, the blade is about one inch from the hinge, and my hand grip applies force at about five inches from the hinge. You must measure your own can opener, and then apply the correct math. If you cannot figure it out, then please come back and ask another question: we will not do your homework, but we will certainly help you with your homework. Here is a bonus question: How is force actually applied to the top of the can, and what is the correct unit of measurement? You know that you cannot push your thumb through the can top, so why does a can opener work? -Arch dude (talk) 23:11, 30 March 2008 (UTC)

Friction

if you wanted to reduce the friction between two objects what would you do —Preceding unsigned comment added by Caseywirth (talk • contribs) 17:58, 30 March 2008 (UTC)

Add a lubricant like grease, cooking fats, or graphite etc. Yamakiri ^T_C § 03-30-2008 • 18:18:11

Invent something round which rotates in between the two objects. Let´s call it a wheel? --Cookatoo.ergo.ZooM (talk) 22:43, 30 March 2008 (UTC)

Or possibly a ball bearing. Algebraist 23:07, 30 March 2008 (UTC)

Or maybe reduce the force holding them together, such as a partial lift on the upper object, loostening screws, expanding a screw top through heat. For example when openeing a jam jar lid, it is easier if you don't force it down as you turn. Graeme Bartlett (talk) 02:37, 31 March 2008 (UTC)

And don't forget sonic lubrication. StuRat (talk) 02:58, 31 March 2008 (UTC)

Would a radio work under 1 foot of water?

Would a radio work under 1 foot of water? Obviously we're assuming its in a waterproof container or something, but would the radio waves penetrate the water? —Preceding unsigned comment added by 79.75.132.81 (talk) 19:06, 30 March 2008 (UTC)

Short answer is no. It might be possible to design something that works in only one foot of water but I doubt it. If it were possible the military would have it already. Submarines need to surface to use their radio. Submerged, they use acoustic systems usually. They can use VLF up to 20 metres in depth but you need something large like a submarine to contain the equipment. ELF can be used even deeper, but only for reception. The transmitter would be impractically large for any existing vessel. There are other problems as well, see Communications with submarines.

Devices fitted to animals for scientific tracking only work while the animal is on the surface, or else they are designed to float on the end of a tether - see this picture of a manatee being tracked. SpinningSpark 19:32, 30 March 2008 (UTC)

I would expect a radio to be able to receive signals under one foot of water. The dropoff of signal strength with depth would depend on the frequency. Why not put an expendable cheap am/fm radio in a well sealed widemouth gallon jug and push it under the surface of the water for a test, at the beach or in a swimming pool? If your head is under water you can listen for the strength of the sound from the radio. Having headphone leads or a speaker or microphone cord stick up out of the water would invalidate the test. Edison (talk) 20:19, 30 March 2008 (UTC)

The attenuation is very severe because of the conductivity of the water. Where ground-penetrating radar is used in geophysics, they can only manage a couple of inches if the soil is wet. And that is with the antennae right above the surface being surveyed. If you want to put the remote station some distance away you haven't got a hope of getting it to work at all. Yes, it does depend on frequency - penetration improves with decreasing frequency (or increasing wavelength). That is why submarines use VLF. The wavelength of this band is 10 to 100 km. You need a big antenna - not suitable for the swimming pool. With ELF the situation is astronomically worse, a geophysical feature (such as the Rocky Mountains) needs to be used for the antenna. Even the connection "leads" are around 30 km long. SpinningSpark 22:14, 30 March 2008 (UTC)

Radios work much better in fresh water than in salt water because the salt water is a lot more conductive. This is why remote control submarines always come with warnings not to use them in salt water. Anecdotally, I've read that R/C model submarines that can go four or five (or more) feet down in lakes, lose their signal under only a foot of ocean water. I have no idea how accurate those numbers are, I've never tried it myself. APL (talk) 13:27, 31 March 2008 (UTC)

The article on Evanescent_waves gives the basics. Although its examples are oriented towards optical waves (light), the basic physics is the same for radio waves. The article points out that the rate of exponential decay (as a function of distance from the surface) depends on wavelength; that is part of the explanation of why ELF can be used by submarines. JohnAspinall (talk) 13:31, 31 March 2008 (UTC)

Drinking water

Some time in the late '70's or early '80's my grandfather showed me a magazine article (I think it was in national geographic but not sure) that refrenced a study concerning drinking water quality. In it, the author stated that "Polar, Wisconsin has the worlds best drinking water." I am doing some research and am having trouble locating this article. I have had other peop[le tell me they remember seeing this article, but no-one can tell me what magazine or exactly when it was published. I would greatly appreciate any help in locating this information. I have tried researching National Geographic archives, Guiness book of records, our local library, and internet searches all with no results, It may be that it is old enough that it isn't cataloged anymore, but someone, somewhere must know where I can find this. Please help! steveg-1960 —Preceding unsigned comment added by Steveg-1960 (talk • contribs) 19:34, 30 March 2008 (UTC)

Slowpitched softball

If I slowpitch a softball with good backspin, does that encourage a ground ball or a fly ball, and why? What are the physics (for dummies) involved? Thanks if you can explain.

It's because of Coriolis effect. Basically if you spin a ball a layer of air on the surface of the ball will also spin with it. Say the ball spins clockwise and is traveling to the left. The top of the ball will be going at the same direction as the airflow, while the bottom goes in the opposite direction. When it goes in the same direction, it has very little drag, because the speed difference between the ball's surface and the surrounding air is small, whereas if it goes in the opposite direction it has lots of drag, because the speed difference is much higher. When one side has very little drag while another has lots of drag, it will start to change its trajectory (like when you walk into a pole, if you hit it with your left shoulder you will turn left after you hit the pole, because there's lots of drag on your left side). --antilived^{T | C | G} 05:08, 31 March 2008 (UTC)

It's the Magnus effect, not the Coriolis effect, and the direction of the resulting force for a ball with backspin is upwards. Gandalf61 (talk) 12:18, 31 March 2008 (UTC)

I would expect that the main effect of strong backspin, at the speed of a softball, would not be anything to do with coreolis but simply the friction when the spinning ball contacts the bat. Which would tend to make the ball fly downwards off the bat. DJ Clayworth (talk) 14:34, 31 March 2008 (UTC)

Where are all the physicists? Anyone who has ever played ping-pong knows that a backspin volley makes your opponent hit it off the end of the table, and a topspin volley makes him hit it into the net. This is the way the ball will come off his paddle due to your spin. The mechanics of this are counter-intuitive, them being the same as the motion of the ball in the air. A topspin pitch makes for grounders, and a backspin pitch makes for fly balls, if you only count the movement of the ball off a bat swung along the ball's predicted pitched path in the air and striking the ball in the center when perpendicular to its path. --Milkbreath (talk) 15:00, 31 March 2008 (UTC)

Global warming

In the last few years, global warming has become an often-discussed issue not only in scientific circles, but also in everyday life. We are warned against it, we have been told about the terrible consequences it could potentially have, and there are groups dedicated to fight climate change. So, I wonder, why is global warming actually so bad?

We are told that mankind is altering Earth's natural state, but our knowledge of the geological history tells us that in fact ice caps are a rare event in our planet's history, happening only in a handful of ice ages. Not only was the Earth devoid of ice caps during most of its history, but also the temperatures in the geologic past were almost always higher. During periods such as the Carboniferous, the Mesozoic and the Eocene, global temperatures were much higher than they currently are, and all of these times were periods in which life thrived and many species radiated – amphibians, dinosaurs and mammals, most notably. On the other hand, since the Azolla event and the break-up of Antarctica and Australia started cooling the planet, the climate has steadily deteriorated and with it, biodiversity has steadily become smaller, especially since the Miocene.

People also seem to equate a hotter climate with a drier climate. Yet the tropical rainforests show that is not (necessarily) true. A huge part of the Earth's species live in the Amazon rainforest, and African and south Asian rainforests are also blooming with life despite their tropical latitudes. The Eocene, with its PETM, was a period in which the Earth was covered in rainforests and other vegetation, showing that there is no necessary correlation between a warmer climate and a drier climate. Rather, the rise of grasses since the Miocene seems to indicate that cooler periods are drier periods.

Let's move to another oft-cited problem of climate change: freak climate episodes become less rare. Hurricanes become more common and heat waves become a greater problem. The sea level rises. Well, IPCC estimates that the current trend of ice melting in the Greenland ice sheet can cause a rise in sea levels of one metre during the next millenium. 1.000 years is more than enough for human civilisation to adapt, and even taking into account other ice sheets around the world, the sea level rise is still far from not being manageable. Adaptations can be made to protect coastal cities, and even paying for developing countries to get those adaptations ready would be costlier than the economic cost of fighting global warming. The fact that heat waves may become more common is compensated for by the fact that cold waves will become rarer: scores of people died in Uzbekistan last winter when temperatures dropped below -40º C, and many people – and animals – have a harsh time in winter.

On the other hand, the benefits would be many: the Northwestern passage open to ships all year long and ice-free; availability of mineral resources currently buried under tons of snow in the poles; an increase in biodiversity... Believing that, without human intervention, the Earth's climate will remain stable is a naive phantasy. We're currently in an interglacial period, so things should be colder in the future – how will we feel when polar caps cover Stockholm, Moscow, Montréal or London? How will we feel when hundreds of tropical species become extinct because cold destroyed their ecosystems? Fighting global warming is like leaping out of the frying pan into the fire: we have a choic between an icehouse world or a greenhouse world, and we are much more suited to the latter.

If the so-called ecological dangers of global warming aren't really dangers (biodiversity thrives in the heat!), and the economic cost of fighting it is higher than what it would cost to adapt, why is there so much insistence on global warming being bad? Aren't we against it because we're told it's bad, without even knowing what it means? Aren't we just afraid of changes, even though we're now in a "freak" period of Earth's history and warming would just bring everything back to normal?

So, wouldn't humanity – and life on Earth as a whole – be better off if all the money which is invested in fighting global warming were invested in more urgent and real problems such as desertisation, pollution of water, deforestation, protection of endangered species, etc.?

88.1.139.15 (talk) 22:10, 30 March 2008 (UTC)

This very much looks like WP:SOAP, not a question. Anyways, there is quite a number of unjustified assumptions in your "question", the major one being that not the absolute temperature is a problem, but the change in temperature. The climate has been quite stable for the last few 1000 years, and human populations and ecosystems are adapted to this stable state. Oak forests will not move North at kilometers per decade (even if there are no humans in the way). For a farmer in Mali whose fields dry up it's little use to know that the season for growing rye has increased by two days in Siberia. Indeed, in the long term the climate will change anyways. But humans live in the short term. The best assessment of the effects of global warming we have is the IPCC Working Group II report.[19]. From the Summary for Policy Makers: "Impacts of climate change will vary regionally but, aggregated and discounted to the present, they are very likely to impose net annual costs which will increase over time as global temperatures increase." --Stephan Schulz (talk) 22:32, 30 March 2008 (UTC)

Also, if I'm not mistaken, isn't the main problem with CO_2 not the warming that it has already caused, but the potential future warming. Complex systems take a while to reach a steady state; I have read that if humans stopped emitting all greenhouse gases today, the global temperature would continue to rise (by a few degrees a century) for a few hundred years, to well beyond what has occurred in the past few million years. Life thrived in periods of warmth because these earth warmed over many many millenia, allowing natural selection to take its course. Evolution cannot occur fast enough to adapt to the current warming properly. -RunningOnBrains 22:47, 30 March 2008 (UTC)

(ec) Please re-read the instructions at the top of this page. The reference desk is here to respond to questions of fact. It is not here to "start debates or to post diatribes." In my opinion, the only further responses to this post will be suggestions of where (other than here) this issue should be discussed. -Arch dude (talk) 22:38, 30 March 2008 (UTC)

Agreed, unless the poster has an actual question for the Reference Desk in amongst that rant, in which case could he/she please delete the rant from around the question so we can read it. SpinningSpark 22:49, 30 March 2008 (UTC)

(edit conflict)Hi. Well, it's a very complicated issue. True, the climate is rarely stable for very long periods. However, most of us, if we found out that we are living on this borrowed time, would like to prolong this time as much as possible. Now, with sea level rise, the only way I can think of to protect cities all around the world, is to build a massive seawall, along every single coastline around the world, leaving no gaps, and stretching 50 metres high and 100 metres deep. Why? Well, let's say that you build a wall around a coastal megacity. However, if this wall is breached by a major storm or earthquake, or if sea levels rise, say, 5 metres and the highest part of the base of the seawall is 5 metres, the water would flood from the other side.

Global warming would also produce environmental disasters that could destroy cities. How would you feel, if your city became too dry, or under water, and forced to evacuate? We would have to make domed cities, live underground, or in space. Why is hot associated with dry? Well, it's not really. Global warming could make coastal reigons flood, and coastal deserts flood too. However, inland, even in rainforests, places could turn to desert. According to a book I'm reading, "With Speed and Violence: Why scientists fear tipping points in climate change", tropical rainforests, like massive ice sheets, are usually stable but can suddenly collapse. Fires can destroy rainforests, allow billions of tons of methane to be released (like Borneo in that huge El Nino a decade ago), and our deforestation of rainforests is not helping.

Also, global warming will not prevent another ice age. In fact, it can trigger one. Remember the Younger Dryas era? The ice age was in full melt, when suddenly, freshwater was released into the ocean, and boom, ice age for another 1,300 years. Also, although not as quickly as depicted in The Day After Tomorrow, melting water can trigger a disruption in the ocean currents. I suggest you read that book I'm reading. It's up-to-date, too. Some say this could cause a mass extinction worse than the K-T one. Would we want that? I think not. Also, the Greenland ice sheet, as well as the West Antarctic Ice sheet, and perhaps even the East Antarctic ice sheet, are unstable, and can be lubricated from the bottom. Pine Island Bay, for example.

Also, nature prefers slow changes. Also, the statement about "biodiversity thrives in the heat" is not nessicarily true. In the ocean, most plakton, as well as coral, thrive in current temperatures. Turn it up a few degrees, and they die. During El Nino, it becomes overheated off the coast of Peru, plankton die, and so do fish. When you change the sea pressure, temperature, salinity, etc, by a miniscule amount, many species of jellyfish suddenly bloom by the billions, killing off other lifeforms in the ocean and inhabit dead zones (especially the Nomura's jellyfish). Also, some periods, like the late Permian, were hot as well as dry.

Also, have you read about global dimming? This isn't really fighting against climate change, but masking its effects. For 3 days after 9/11, air traffic was grounded. Suddenly, the US experienced unusually sunny and warm conditions. Also, as the Himalayan glaciers melt, and this could happen by midcentury, there will no longer be a constant supply of water, threatening water supplies for 500 million people. The monsoon? It has become erratic and unpredictable over the years. Already, lakes in Nepal and Bhutan are filling with water. Hence: without water, we'd all drown. Also, more flooded areas means hurricanes can travel farther inland. At this rate, even with the melting arctic, oil will likely run out in a few decades and peak immediately. If sea levels rise, Tuvalu will likely be history by midcentury. Also, many species, as well as people, thrive in the arctic.

Global warming is not nessecarily good news for food production. Many species of plants, such as rice, fail to produce good results if you turn up the temperature 1 or 2 degrees. Forests could even go form a carbon sink to a carbon source, with the sun being blocked more often, more trees being pushed into unsuitable territory, and more fires. Also, the forest pine bark beetle is eating many trees in Canada and the United States. If this continues, over half of the pine trees could be damaged or destroyed by midcentury. Also, the dangerous and urgent global warming is already here. Already, towns are drowning below sea level. Have you read a list of possible doomsday scenarios? True, we all choose to deny the truth and live on with our lives, going business-as usual and hoping the worst will never happen in our lifetimes. Yet, it already has, for millions worldwide. So why do we choose to do something? Well, because we can at least do something to delay the parts of climate change caused by our own actions, and hopefully our children will not suffer. That's the reason for many people to help fight climate change, think of the children.

In fact, at this rate the truly poor countries will never be developed. Yet, fighting climate change would only push us back a mere 2 years by 2100, if we start now, that is. Why don't we help more urgent issues? This is an urgent issue, and its long-term implications will be even worse. Also, global warming has been listed as the #2 urgent threat to humanity, second only to a nuclear war, but this is far more likely. Also, global warming might trigger wars as economic instability is pushed to the brink. If we did nothing, civilization would collapse, simple as that. However, although it would probably collapse anyway, don't we at least want a future, for civilization to exist as long as possible, and to help ourselves continue to exist for the time being? Nobody can predict what will happen 1000 or a million years from now. However, this issue is happening right now, and yes we can make a differnece, and it'll be a difference for the better because civilization, the economy, and the environment all prefer stability, even if we can just prolong that stability a little bit.

I already know that climate change will be a reality we will have to face, but if we do something now, then we won't have to face as many horrors later. Also, have you noticed a lot of these urgent issues are somewhat related to global warming? Even disease is spreading, killing off many humans as well as animals, partly owing to global warming. So, it's a very complicated issue, but yes, action on it does help somewhat. Hope this helps. Thanks. ~AH1^(TCU) 23:10, 30 March 2008 (UTC)

<my2cents> Over geological time scales Human induced global warming could be seen as insignificant as life will adapt to it. Over the period of a human generation the effects of gloabl warming could be seen as nothing short of apocaliptic. </my2cents>

--Shniken1 (talk) 00:41, 31 March 2008 (UTC)

If as you claim, pumping out carbon dioxide to produce global warming may be necessary to avert an 'icehouse world' there is a simple solution, start doing that when we need it. As it stands, there is no evidence we need it at the current time, all the evidence suggests it's harmful and will result in an increase in temperatures, not a stabilisation. Sure once the earth starts to cool, we can consider it. It's not as if it's hard to do. The problem is that the reverse, removing the carbon dioxide that we've already put there, is a lot harder to do therefore it's exceptionally dumb to do it when we don't need it for the sole purpose of preventing a long time in the future 'icehouse world' or ice age Nil Einne (talk) 17:32, 31 March 2008 (UTC)

Mirror, Mirror

If I have room with four walls, floor and ceiling, all made out mirrors--and one wall is a two-way mirror, the material that's a mirror on one side, but see through glass on the other--what would I see if I looked into the room?

I guess my question is--what does a mirror reflect if there is nothing in the room to reflect?NetLace (talk) 22:17, 30 March 2008 (UTC)

Assuming that the mirrors aside from the two-way allow no transmission of light, I would think that such an apparatus would act as a blackbody. Unless the room were a few hundred degrees Celsius, you would see nothing. -RunningOnBrains 22:28, 30 March 2008 (UTC)

Well, there's no person or thing in it, but that doesn't mean there's nothing at all. Assuming there's a light source, the mirrors would reflect each other as they reflect the corners and joins in the mirror room until you've got that labyrinth or hall of mirrors thing happening. Without a light source there'd be no reflection to track anyway. You could try it on a small scale model to test it. Julia Rossi (talk) 22:33, 30 March 2008 (UTC)

Hi. Well, if I understood your question correctly, and there is a light source, it will appear like an endless tunnel. If you have a webcam, for example, and turn on a program that displays what the webcam sees, and the image is inside a rectangular box, then try pointin gthe webcam at that box. What happens is, the box appears like an endless tunnel, and if you shake the webcam, the tunnel shakes. Also, if you could stand between two mirrors, held facing each other, and looked at one of them face-on, yet you are small enough not to be blocking anything yet large enough to see the whole mirror, you'd see an endless tunnel, and maybe endless images of yourself inside it. The tunnel doesn't really appear endless, however, because as you look farther inwards, the deeper frames are not bright enough to be shown. Hence, if you take two mirrors, and put them at an angle to each other, and shrink the angle, you get more images. Thus, if you turn them towards each other, there should (theoreticly) be an infinity of images. However, many factors prevent us from actually seeing into infinity. Hope this helps. Thanks. ~AH1^(TCU) 23:23, 30 March 2008 (UTC)

That's right, you'll see an endless tunnel of mirrors, one copy of the room after the next, and getting darker as they are farther away. Just one point needs to be added and that's that the conditions described in the original posting require a light source to be in the room. A two-way mirror, also called a one-way mirror, is simply a partially silvered mirror that you look through from a darker room into a lighter one. You can see through it into the light room because there's enough light in there for you to be able to see by even when only a fraction of it gets through the mirror. In the setup described, you will see a copy of the lamp in each copy of the room. But because the two-way mirror is partially silvered, the more times the light reflects, the less there is of it, and so the "farther" copies of the room look dark. --Anonymous, 09:50 UTC, March 31, 2008.

The semi-silvered mirror is symmetric, except that one side is subject to higher ambient light, so it's harder to see through from that side. Tangential question- do anisotropic "two-way mirrors" exist? Specifically, do materials exist with higher reflectivity coefficient in one direction than the other? (Surely there are materials with variable reflectivity based on the incident angle, but are any known with directionality? Nimur (talk) 19:24, 31 March 2008 (UTC)

March 31

Something semi-interesting about Cockatiels...

Anyone here have experience with keeping large numbers of Cockatiels? I was told today by someone who does that in aviary conditions, the birds form a loose social hierarchy based upon how 'natural' their plumage appears. In other words, the birds with wild-type plumage tend to dominate birds of alternate colour mutations when it comes to feeding, mate selection, choice of nest box, etc.. Apparently, the more grey feathers and the closer its resemblance to a wild 'tiel, the more 'respect' the bird gets from its flockmates. Pieds/whitefaces/pearls are somewhere in the middle and the lutinos and albinos are at the very bottom of the pile.

I'd never heard of this before (I've never noticed anything similar with the various shades of budgie I own) but it sounds absolutely fascinating (to me, at least - maybe not to you). Does this sound familiar to anyone? Any link to writings on the subject? Thanks. --Kurt Shaped Box (talk) 00:41, 31 March 2008 (UTC)

Sharing genes with bacteria

What percentage of our genes, approximately, do we share with bacteria? And what other species do we have such information for? Is there a table I could see somewhere? Thanks!

James 01:12, 31 March 2008 (UTC)

For the second part of your question, the chimp is the best example for genetic similarity - about 95%. See here. Wisdom89 _{(T / ^C)} 01:26, 31 March 2008 (UTC)

The human genome consists of about 30,000 human genes; about 1,000 of these are nearly identical to analogous genes in bacteria. I don't know of a table; as far as I know you'd have to look at each organism's genome individually. - Nunh-huh 01:34, 31 March 2008 (UTC)

Be mindful though, that there isn't really a true consensus on the actual number of human genes (protein encoding). I've seen estimates range from 25,000 to 80,000. This is a good link [20]. Wisdom89 _{(T / ^C)} 01:45, 31 March 2008 (UTC)

Thanks for the interesting replies. I'm surprised by Nunh-huh's reply that we share about 1/30th of our genes with bacteria. After writing this question, I was able to come up with a little more research, and found that we have about 3 billion base pairs, while many bacteria have only a few million base pairs, which would put the upper-bounds of our similarity at under 1%, but I guess there is probably large variation in the size of bacteria DNA. — James 13:18, 31 March 2008 (UTC) —Preceding unsigned comment added by 63.138.152.238 (talk)

There's a difference between the number of base pairs and the amount of genes that are expressed (or at least, are currently known to be expressed). Bacterial DNA tends to have a lot less non-coding DNA in it than humans. The important point here is that a while humans differ a lot from, say, yeast, we both need to be able to convert sugar to energy and perform other metabolic functions, and those genes are highly conserved. -- JSBillings 15:24, 31 March 2008 (UTC)

There used to be such a table in WP. After a bit of guesswork and searching through page histories I found it in this old version of Genomics. It was deleted on 10th October 2006. --Heron (talk) 20:52, 31 March 2008 (UTC)

DIY Lab hood

I am trying to make a DIY laminar flow hood. I have already built the the hood and have used a plenum coupled with a furnace blower and HEPA filter to create the laminar flow stream. I would like to add a UV light for sterilization. I want to just buy a UV bulb and put it in a standard fixture (Like so: Fixture and Light but none of these lights appear long enough! Am I going about this improperly? Is there a special fixture I need to use a UV light?

Thank you!

Ebenbayer (talk) 02:08, 31 March 2008 (UTC)

I'm fairly certainly that any UV fixture you purchase does not have to extend the entire length of the laminar cabinet. My experience with such hoods is 1.) The UV light isn't really that effective at sterilization when the hood is not in use and 2.) A small fixture is enough to illuminate everything behind the UV protective shield. You might want to try contacting NuAire, which is where my laboratory purchased their flow hood. I'm sure they sell accessories for them. Wisdom89 _{(T / ^C)} 02:19, 31 March 2008 (UTC)

Thank you for the response, the problem I am having is that the light bulb length appears to short for the fixture, not that the fixture is to short for the hood (sorry to not be more clear). I just seem unable to find a site that sells a fixture that would interface with the germicidal bulbs I referenced. —Preceding unsigned comment added by 128.113.36.116 (talk) 12:57, 31 March 2008 (UTC)

You can get away without one if the hood is used a lot. I have two commercial ones in my lab and neither have a UV light fixture. Just clean everything regularly with >70% ethanol. —Preceding unsigned comment added by 82.36.27.228 (talk) 17:38, 31 March 2008 (UTC)

Dosage of medication

What's the term for giving someone a larger dose of a medication when starting them on the drug and then cutting it back to a smaller dose once they've ramped up the dosage in their body? I'd like to read the article on it so that I can understand why this needs to be done with some meds but I don't know the term. Thanks, Dismas|^(talk) 02:58, 31 March 2008 (UTC)

Loading dose. The article needs expansion and probably won't be of much help. - Nunh-huh 09:42, 31 March 2008 (UTC)

Yeah, thanks. That took me less than a minute to read and I'm still not any closer to knowing why a loading dose is necessary. At least now I have a term for it though. Thanks! Dismas|^(talk) 09:53, 31 March 2008 (UTC)

It depends on the pharmacokinetics of the drug in question. Some drugs are cleared from the body relatively slowly. In order to maintain a constant concentration of these drugs within the body, only small doses need to be taken—but if one only administers small doses, it can take a long time for the drug to reach a useful concentration in the body after starting therapy.

Consider the hypothetical drug foosporin. Suppose it has a long lifetime in the body, and only ten percent of it is cleared from the blood each day by the liver and kidneys. Suppose also that the drug works best when the total amount in the body is exactly one gram. So, your maintenance dose of foosporin is 100 milligrams (100 mg) per day—just enough to offset the amount cleared.

Suppose you just started taking 100 mg of foosporin every day. On the first day you'd have 100 mg in your system; your body would clear 10, leaving 90 mg. On the second day you'd have 190 mg in total; your body would clear 19 mg, leaving 171 mg. On the third day, you'd be up to 271 mg total; your body would clear 27 mg, leaving 244 mg. As you can see, it will take many days for the total amount of drug within the body to come close to 1 gram (1000 mg) and achieve its full therapeutic effect.

For a drug such as this, a doctor might prescribe a loading dose of one gram to be taken on the first day. That immediately gets the drug's concentration in the body up to the therapeutically-useful level. First day: 1000 mg; the body clears 100 mg, leaving 900 mg. On the second day, the patient takes 100 mg, bringing the level back to 1000 mg; the body clears 100 mg overnight, still leaving 900 mg...and so forth. TenOfAllTrades(talk) 19:00, 31 March 2008 (UTC)

Nanoparticles

Size (nm)	Number of atoms	Fraction on surface (%)
0.5	1	-
1	8	100
2	64	99
5	1000	50
10	8,000	25
20	64,000	12
40	512,000	6
80	4,000,000	3

Is the above table (approximately) accurate? I extrapolated (and rounded) the last few entries. It is for spherical particles isn't it? (I may insert this into nanoparticles) Cheers, Shniken1 (talk) 04:01, 31 March 2008 (UTC)

The percentage on the surface doesn't appear to be quite correct. Using a cubic structure, you could use the formula 100-[100(N^1/3-2)³/N] to find the percentage given N atoms. This gives me the following results:

Number of atoms...	Fraction on surface (%)
8	100
64	88
1000	49
8,000	27
64,000	14
512,000	7
4,096,000	4

StuRat (talk) 05:04, 31 March 2008 (UTC)

hair loss

hi, it is said that it is normal to lose 50-100 hairs a day, but how come we don't go bald as i am quite convinced that the rate of hair growth is much slower than the rate of loss. thanks :) —Preceding unsigned comment added by 218.250.158.232 (talk) 10:39, 31 March 2008 (UTC)

If the rate of hair growth were much slower than the rate of loss, we would all go bald. Perhaps you are going bald, if this is the case for you? For those of us who are not going bald, the rate of hair growth cannot be much slower than the rate of loss and you shall just have to unconvince yourself :) Skittle (talk) 11:51, 31 March 2008 (UTC)

Another way to look at it: On average, people have about 100,000 hairs on their head.[21] Each hair grows at a rate of about 1/2 inch per month. So your total hair growth is 50,000 inches per month, or 1643 inches per day. As long as your total hair loss (including haircuts) is less than 1643 inches (or 136 feet) per day on average, you should be holding steady against balding. jeffjon (talk) 12:47, 31 March 2008 (UTC)

Buffer solutions

Hello. Do you think you could offer a brief explanation of how buffer solutions work? I (think) I get what they are, as in what they're overall effect is, but how they work has never made sense to me. For example, if you add HCl to water, the water molecule splits into H+ and OH- (or really into H3O+ and OH-, if I recall?) and the OH- accepts the H+ from the HCl, neutralising it. But surely just as many protons are donated by the water as are accepted, so why would this have a neutralising effect? What have I misunderstood? Skittle (talk) 12:00, 31 March 2008 (UTC)

Water isn't a buffer solution, so yes, if you add HCl to water you get an acid. Algebraist 13:36, 31 March 2008 (UTC)

Really? It was always used as an example of a buffer solution that could buffer both acids and alkalis, at A level. Skittle (talk) 16:05, 31 March 2008 (UTC)

Water can act as an acid or a base, as it is amphoteric. It's a relatively poor buffer. Wisdom89 _{(T / ^C)} 17:48, 31 March 2008 (UTC)

For water alone, there exists an equilibrium between three species:

2H₂O ←→ H₃O⁺ + OH^-, often written in simplified form as

H₂O ←→ H⁺ + OH^-

This dissociation is spontaneous, but tends to sit well to the left—at room temperature only about 1 of every ten million water molecules is dissociated into charged species. When hydrogen chloride gas dissolves in water, it dissociates as well:

HCl ←→ H⁺ + Cl^-

This reaction proceeds essentially to completion, elevating the concentration of hydrogen ions (H⁺) in solution. By Le Chatelier's principle, this pushes the equilibrium from the first two equations back to the left—some of the excess hydrogen ion in solution reacts with hydroxide (OH^-) to re-form water. This still leaves a surplus of hydrogen ions, rendering the final solution acidic. TenOfAllTrades(talk) 18:19, 31 March 2008 (UTC)

Pain of death

Do people dying of congenital heart desease experience unbearable pain and if so what is the cause of the pain? 71.100.4.126 (talk) 13:05, 31 March 2008 (UTC)

Have you read Congenital heart disease? I'm not quite sure if you have the right disease. Are you sure you don't mean Coronary heart disease or Congestive heart failure? Nil Einne (talk) 17:23, 31 March 2008 (UTC)

Commercial aviation \ Airports: Penalty box

ORD airport layout.

What is it for? It is provided at O'Hare International Airport nearby A 5 (around 87° 55' W 51° 59' N). Thanks, --Scriberius (talk) 17:46, 31 March 2008 (UTC)

The 'penalty box' is just a (somewhat whimsical) name given to an area in which aircraft can be temporarily parked, usually either while waiting for a gate to open up, or after boarding to free up a gate for another aircraft. (Notes: [22], [23].) TenOfAllTrades(talk) 18:25, 31 March 2008 (UTC)

Thermoregulation

A mother complains that her 3year old child's head is hot while the extremeties are cold. What are the physiological mechanisms responsible for this symptoms--82.128.29.40 (talk) 20:55, 31 March 2008 (UTC)Oyinmart