The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
Does anyone know of the best free dicom viewer out there? I want one with all of the features of Osirix, but that runs on windows. Specifically I want the following features:
-A GUI interface.
-Installed from an .exe file, or other autoinstaller file.
-not web based (although if you find a web based one and you can help me set it up then that's fine)
-Viewer supports:
-Regular tools: cine, zoom, magnifier, pan, windowing
-Measuring
-ability to compare two or more images
-ability to colour enhance the images
- 3D mpr and post processing like OSIRIX.
It doesn't have to be open source. It just has to be free of charge. I do not need a pacs server, just a full featured radiology workstation. Please help me. I've searched google for months and come up with nothing except osirix. If there is a windows version of that i'll take it!!!!!
WTF are you screaming at us? I can't help but someone who can help out may decide not to by your ALL CAPS approach. Feel free to edit your question. -hydnjo (talk) 00:57, 17 April 2009 (UTC)[reply]
Is there another explanation for Black Holes besides being dense matter from which light cannot escape?
Has anyone considered the possibility that a black hole is simply a phenomenon produced by 2 bodies, such as galaxies, moving away from each other at a combined speed that is greater than the speed of light. For instance, our galaxy may "appear" to be a black hole to inhabitants of a neibouring galaxy which is moving in the opposite direction. Acknowledging that nothing can travel faster than the speed of light it is still possible for 2 bodies to be moving away from each other at a almost twice the speed of light. The light from either body would never reach the other thereby making them invisible to each other. Would this not produce a black hole effect?
Actually, even if two galaxies (on different sides of us) are moving away from us at near the speed of light, an observer in either one would still be able to see the other and would not see the other galaxy as moving faster than the speed of light (see this section on relativistic addition of velocities). Additionally, even if there were a galaxy we couldn't see, it wouldn't explain black holes or look like a black hole at all. It would just be something you couldn't see. It wouldn't explain any of the Black hole related phenomena that have been observed. Someguy1221 (talk) 03:56, 17 April 2009 (UTC)[reply]
We do not "see" distant galaxies because the light is red shifted. But the fact that far off galaxies are moving away from us is observed phenomenon, not just theoretical. We can observe galaxies moving away faster than light provided that they are no so far off that their light has not reached us yet. Galaxies which are too far off are beyond our observable universe. But yes, regardless of speed of our and far off galaxy, the speed of light coming from the distant galaxy will be the same. Black Hole is region of space that is within our range of observation and we cannot see light from it because light cannot escape from Black Hole due to very high gravity. It is nothing to do with speed of observer or that of Black Hole. If light not reaching us is criteria for Black Hole, then we can say we are in enclosed inside of a black hole ( which region of non observable universe) manya (talk) 05:03, 17 April 2009 (UTC)[reply]
From special relativity we know that the speed of light is the same in all frames. Starting with two planets moving away from some central point at near light speed in opposite directions, we can change to a frame where one of the planets is stationary. In this frame, any light emitted towards an observer on the stationary planet from the moving planet will still approach the observer at 'c'. So it's still going to get there, you can't out-run light. (Also, as mentioned by Someguy, the moving planet in this frame would not exceed the speed of light itself.) 129.67.117.21 (talk) 12:27, 17 April 2009 (UTC)[reply]
It is not the case that there were many observations of black holes and a theory needed to be developed to explain them. Actually, it is entirely the other way round. Black holes were predicted to exist (or at least the possibility) from the theory of gravity, and then astronomers went out looking for them. Thus there is no question of there being any alternative explanations. Although many candidate black holes have now been identified (Cygnus X-1 being the first) it would be a very rash astrophysicist who would make the claim that their existence is established beyond all doubt. SpinningSpark13:04, 17 April 2009 (UTC)[reply]
You don't need to change reference frames to understand why your reasoning is flawed. Say you're going to the "right" at 3/4 c and an object to your "left", that's going left at 3/4 c, emits some light toward you. The light goes to the right at c, which is faster than you're going, so it will eventually reach you. In cosmology, though, what you describe is possible, and the effect is something like a black hole turned inside outāthe event horizon is still a sphere, but instead of the inside being invisible from the outside, it's the outside that's invisible from the inside (and we're inside). That's still not the same as a black hole, thoughāthere's no way to confuse the two. -- BenRG (talk) 15:00, 17 April 2009 (UTC)[reply]
In order for an object to be moving away from us quickly enough to be receding faster than the speed of light, it would be beyond the boundary of the observable universe. So we would never *detect* them in the first place (to do so would be to observe them as they were before they were created). ~AH1(TCU)01:16, 21 April 2009 (UTC)[reply]
Coriolis effect and sniping
In the game Call of Duty 4, there is a part where we have to snipe a guy 896 meters away. Our captain says that we should take 3 things into consideration:
1 Variable Humidity
2 Wind speed
3 The Coriolis effect
My question is how does variable humidity and the Coriolis effect effect the bullet? You can read it here http://en.wikiquote.org/wiki/COD4#Cpt._MacMillan under Capt. MacMillan. āPreceding unsigned comment added by 116.71.49.171 (talk) 05:32, 17 April 2009 (UTC)[reply]
Wind is obious - it exerts a force on the bullet pushing it away. The coriolis effect is when the earth spins as the bullet is travelling, so by the time it hits the target, the bullet is now offline, even though it travelled perfectly straight, because the earth rotated relative to the bullet. Humidity reduces the density of the air, which will effect the total force of the wind and humidity.--155.144.40.31 (talk) 05:53, 17 April 2009 (UTC)[reply]
I haven't played the game, but I have had military training in long-distance shooting. Everyone has to do up to 500 meters and in special schools we go beyond that. Wind and humidity play a factor. The coriolis effect is brought up, but doesn't matter. The sights are set for distance to the target, taking the actual arc of the bullet into consideration. So, as you "click click click" the distance to the target, you are adjusting for the actual arc of the bullet. The main thing you do is adjust for windage (left and right) and then distance (up and down). If it is extremely humid, you add distance. Then, breath, relax, aim, steady, squeeze. In Call of Duty, do you have to adjust your sight left/right and up/down or do they have you just winging it by aiming a little up and a little off to the side? -- kainawā¢06:33, 17 April 2009 (UTC)[reply]
You don't adjust the sights in CoD4, you just aim a little off to the side. (Also, they don't really simulate the coriolis effect there at all, that's just patter. Ditto for the humidity. What matters is the wind (which is indicated by a flag nearby, so you can tell what direction it's blowing in, and how hard); the rest of it is just there to bring atmosphere to the scene. It does the trick, too.) -- Captain Disdain (talk) 10:23, 17 April 2009 (UTC)[reply]
Setting the distance isn't enough to account for the coriolis effect - you need to know what direction you are firing in as well. The maximum acceleration due to coriolis effect is velocity*angular momentum (but rotated 90 degrees). If we take a muzzle velocity of 1000m/s (and assume it doesn't slow down during travel, which isn't realistic, but nevermind) and the mean angular velocity of the Earth (from Earth's rotation) of 7.2921150 Ć 10ā5 radians per second, we get a coriolis acceleration of about 0.07m/s2. If the target was 1000m away, the bullet would take 1s to get there, resulting in a deflection of 35mm. That's a noticeable amount (although it's an overestimate in most cases), but probably far less significant than the wind. --Tango (talk) 11:15, 17 April 2009 (UTC)[reply]
The Coriolis effect does not exist when firing due east or due west. It has maximum effect when firing due north or due south. It has intermediate effect when firing at directions in between. ā GlowWorm.
GlowWorm, that's not right. To eliminate the coriolis effect you would have to shoot paralel to the earth's axis. That would be firing along the north-south direction with an upward (or downward) inclination identical to the local latitude. If you forget about the vertical component of the coriolis force (which gets masked by gravity anyways), the coriolis effect is identical in all horizontal directions. Dauto (talk) 19:02, 17 April 2009 (UTC)[reply]
I don't see that, Dauto. If a gun is north of the equator and fires due north at a target due north of it, the gun and the target are both on the same line of longitude. During the flight of the shell the target moves to the east. So does the line of longitude. So the shell will land west of the target. This is tricky to think about. Am I wrong? ā GlowWorm. āPreceding unsigned comment added by 98.16.66.104 (talk) 01:23, 18 April 2009 (UTC)[reply]
Yes, you are wrong. In the nothern hemisphere the coriolis force will deflect the bullet towards its right. If you shoot towards the north the deflection will be eastward. That happens because as it moves towards the north it is actually approachingthe earth's axis. from the equation for the speed of an object in circular motion we see that the bullet is actually moving eastward faster than the target (larger ) and that's why it appears to be deflected eastward. Dauto (talk) 05:11, 18 April 2009 (UTC)[reply]
Wouldn't it also have an effect on an east-west shot? Not because it's going off target to one side or the other but because the bullet is traveling slower or faster relative to the target. So if you're shooting eastward, the target is coming at the bullet as the bullet is moving towards the target. Therefore, you don't need to aim as high. Right? Dismas|(talk)05:19, 18 April 2009 (UTC)[reply]
Yes, there's a second effect but your description of it is also incorrect. Due to the earth's rotation, in a referential attached to the earth's surface there is a centrifugal force. We don't notice that force because it gets included into our perception of the gravitational force as the earth itself deforms under the influence of that force becoming a little flat (Yes a small fraction of what we perceive as gravity is actually centrifugal force). If you now shoot a bullet eastward, that bullet will be rotating around the earth's axis faster than objects attached to the earth's surface, creating an extra centrifugal force. That extra centrifugal force is not included in the local gravity force and must be perceived as a new force pushing the bullet away from the earth's axis. This force has both a vertical component upwards (that is an effect in the opposite direction to the one you incorrectly described) as well as a horizontal component southward. If you shoot the bullet westwards, you get the opposite effect and end up having an extra force with components downward and northward. This effect I describe now together with the one I described earlier are included under one umbrella as the coriolis effect. If you ignore the vertical component of the coriolis effect, you will see that between the two effects there is always a force towards the right of the direction of the movement of the bullet (in the nothern hemisphere). Moreover, this horizontal component of the coriolis force turn out to have the same magnitude independently of which direction you shoot the bullet. Neat uh? Dauto (talk) 06:40, 18 April 2009 (UTC)[reply]
So all in all the answer to the original question is its just patter for the Game(wind is the main issue)....and after 1000m a 35mm move of the rnd should not make a diffrence as you aim center of mass. 896m shot would produce less say a 27mm move of the rnd from the center mass of a human with a >50 CAL weapon(most suited for the distance and the job) wont make the slightest diffrence to the out come of the shot the guy would be dead(see u-tube exploding people from afghanistan when hit with .50 rnds) Only James bond kills somebody from 100 miles with a head shot. 1000m is center of mass if your trying to kill/assassinate there for Coriolis effect does not really apply, unless dealing with long range artillary.
In real life, ask the instructor. Wind... of course, humidity, yes, it changes the density of the air, so the bullet will slow down, and the coriolis effect will indeed make you hit another target's head at 900m or more if they are too close. Also, is true, the best way to snipe is to do it west-east or east-west, and from a top position so you dont have to correct the vertical angle, and btw, you dont need to be a math expert to take the shot, the experience and a plastic board with some parameters/data used to adjust the scope will help on the task. Elgatoduro (talk)
How can dumb electrons be so clever?
The behavious of things like for example electrons are described by complicated maths formulas, that require a high intelligence and a good education to understand. So how come a little electron knows how to behave? They cannot have computers hidden away inside them. 78.146.249.32 (talk) 11:12, 17 April 2009 (UTC)[reply]
They don't have to think how to behave. Their behavior is guided automatically according to the laws of physics, which we are still trying to decipher. It is like we have to calculate with what velocity and initial angle an object has to be launched to reach a certain distance according to the laws of physics, but when the object is actually launched, it (the object itself) doesn't calculate in the beginning of launch how far it has to go. It has no other choice but to reach that distance because it has no control over itself, it cannot think and react. It has to obey the laws of physics. For the projectile motion, those laws are simple. For describing electrons, they become complicated and require sophisticated mathematics and high intelligence. But the analogy still holds and electron having no other choice and no control over itself has to behave the way the laws of nature demand it to. - DSachan (talk) 11:22, 17 April 2009 (UTC)[reply]
And what's the problem with saying that? Your question is like asking 'when I let go of a stone, how does it know it's supposed to fall?' It just do. Dauto (talk) 14:05, 17 April 2009 (UTC)[reply]
Yes, that's exactly what he meant. You've got two alternative explanations here. 1) They just do 2) They were designed that way by someone or something that created them. But whichever it is, electrons don't need to be intelligent to do this, any more than a rock needs to be intelligent to know that it should roll downhill. DJ Clayworth (talk) 14:01, 17 April 2009 (UTC)[reply]
Actually, the behavior of an individual electron is not all that complicated, the problem with the calculation of their movement comes in when you have many subatomic particles acting together and influencing each other in a non-linear fashion. Truthforitsownsake (talk) 14:08, 17 April 2009 (UTC)[reply]
Some very complex-appearing behavior can arise from very simple rules. For example, Conway's Game of Life consists solely of rules simple enough that an 8-year-old can follow them. Yet from these rules you can get crazily complex behavior which would be difficult for people to explain. That's not unique to the GoL. Other simple rulesets show similarly complicated results (see Cellular automaton). Now, I'm not claiming that the behavior of electrons is the result of emergent behavior: what I'm saying is that electrons are following what are to them very simple rules (e.g. "move to a lower energy state"), but because of how these rules are constructed and how they interact with the environment, the overall behavior of the electrons appears very complex to us and requires complex math to represent because we don't "see" the world the same way an electron does. -- 128.104.112.117 (talk) 23:47, 17 April 2009 (UTC)[reply]
Also, the electron doesn't "know" how to behave. The OP is putting the cart before the horse here. We invent mathematical equations to model the behavior of electrons. But the equations don't tell the electron how to behave, they tell US how the electron will behave. The electron would continue to do what it did even if we didn't try to figure it out... --Jayron32.talk.contribs02:19, 18 April 2009 (UTC)[reply]
78.146, how do you behave at any given moment? You have a set of forces pulling you through life and at each instant you respond to those forces. Sometimes certain forces are stronger than others. Sometimes you do dumb things (so there goes your argument of having intelligence) - but you do those dumb things because local forces caused you to act that way. Other times you do smart things - but only because other forces drew you that way.
You are an electron, and an electron is you. You both respond to a complex set of inputs and neither of you have a "computer" (well, you have a brain, but it uses electrons to act). On a semi-related topic, see The Tao of Physics. Franamax (talk) 23:46, 18 April 2009 (UTC)[reply]
bodybuilding
hi everybody and thanks for reading this .. my question isĀ :
what are the negative results I can get from bodybuildingĀ ?
Does it have any negative effects on hormones and spermsĀ ? āPreceding unsigned comment added by Sha9law0 (talk ā¢ contribs) 11:43, 17 April 2009 (UTC)[reply]
You should talk to an expert about that, rather than random people on the internet. If you are a member of a gym, they will probably have personal trainers that can advise you. We have an article, Overtraining, which might answer some of your questions, but don't rely on us when your health is at risk. --Tango (talk) 12:01, 17 April 2009 (UTC)[reply]
A normal and healthy human can do heavy exercise -- including bodybuilding work -- with no adverse effect on hormones or sperms. Unfortunately, many professional-level bodybuilders have cheated with anabolic steroids, which can have serious negative effects on both hormones and sperms. --Sean14:22, 17 April 2009 (UTC)[reply]
I'd like to see some sources if you're going to make such claims. I don't deny of course that anabolic steroids seriously screw up your body and are one of the reasons many body builders suffer serious adverse effects. However while the human body is very good at compensating, it seems a fairly extreme claim to me that there will definitely no adverse effects on hormones or sperm from body building. Presuming we're talking about quite hefty body building, the exercise and diet can itself have some fairly major effects and it seems unlikely to me that these will have no effect (positive or negative) on your hormones or sperm (or for that matter other bodily functions). This doesn't mean I believe your going to go infertile from body building, simply that there's a difference between saying it will have no adverse effects and saying that it's unlikely to have extremely detrimental effects Nil Einne (talk) 22:23, 17 April 2009 (UTC)[reply]
I agree that I should have qualified what I said. I was thinking of a sensible amount of bodybuilding, but I agree that an absurd amount of bodybuilding could very well affect the sperms, for some definitions of "sensible" and "absurd". --Sean22:47, 18 April 2009 (UTC)[reply]
If you take steroids, obviously there are tremendous negative effects. If you don't, the major negative effects probably come from the huge amounts of food you have to eat to do top-level bodybuilding, and the heavy weighting of the food toward protein. There's also a problem in that bodybuilders are sometimes so musclebound that they have difficulty doing ordinary activities. Looie496 (talk) 18:19, 17 April 2009 (UTC)[reply]
You should also consider what else you would be doing with all your time that you would be spending in the gym. Will it stop you working or ruin your social life, or stop you having time to edit Wikipedia? There are also injuries resulting from improper use of equipment. Graeme Bartlett (talk) 22:01, 17 April 2009 (UTC)[reply]
Questions on cell size and multicellularity
What limits the size of a living cell? Why don't we see (for e.g.) cells the size of a dog?
Do prokaryotic cells show multicellularity? I know they form colonies, but do individual cells show division of labor/specialization? If not, why not? āPreceding unsigned comment added by 121.241.167.100 (talk) 12:56, 17 April 2009 (UTC)[reply]
One thing that limits cell size is the way that cells function. Cells require a large surface area to volume ratio. Now while technically, you could still have very massive cells with the same surface area to volume ratio, the structure would be such that the cell would pull itself apart from gravity. 65.121.141.34 (talk) 13:25, 17 April 2009 (UTC)[reply]
Ā”Grande!
Cells can get bigger than a dog! A Hypselosaurusegg (which, assuming it's like modern eggs, is a single cell) could reach a foot in length, larger than the dog at right. You could probably find an ostrich egg bigger than some dogs. And even the biggest dog has a nerve cell that runs from the tip of its tail to its brain, which is pretty long, if not "big". Also, see the discussion regarding division of labor here. --Sean14:38, 17 April 2009 (UTC)[reply]
I do not believe that large eggs are just one cell. I think thats a myth. For one thing, they would have terrible problems with the celluar equivalent of respiration, as their volume to surface area ratio would be very much different from a normal cell. 78.149.194.28 (talk) 18:26, 17 April 2009 (UTC)[reply]
To clarify the common misconception. Ova, that is the female gamete colloquially known as "eggs" are a single cell. Actual eggs, certainly are NOT. No ova I know of are larger than microscopic for any species. The largest cells are still likely nerve cells, as mentioned, there have been some documented to be several feet long; even given their thinness, that still makes them quite sizable. --Jayron32.talk.contribs19:34, 17 April 2009 (UTC)[reply]
Also, from our Egg (biology) article, "The 1.5 kg ostrich egg contains the largest existing single cell currently known...". Seems we really have a contradiction here. --Scray (talk) 20:44, 17 April 2009 (UTC)[reply]
Yeah, OK, so the human ova is a bit larger than microscopic. But really, only a bit. And the canard that an egg is a single cell misrepresnts what a cell is. It doesn't have organelles, it doesn't contain a cell nucleus or anything like that. Its basically a big sac of amniotic fluid and surrounding a smaller sac of nutrients to provide fuel for the growing embryo. Our article is actually probably wrong here. It calls avian and reptilian eggs "zygotes" That makes no sense. If the zygote develops into the embryo, then why is the egg still here?!? So yes, I will buy that the ovum is the largest cell in the body. But a chicken egg is still not a "cell", unless you redefine what a cell is to mean "everything that a cell is, and eggs too". --Jayron32.talk.contribs02:15, 18 April 2009 (UTC)[reply]
I just re-read your comment, and realize that you're specifically referring to the avian/reptilian yolk and albumin as lacking a nucleus and organelles. All right, I'll agree with that as a generalization. BTW, "ova" is plural, "ovum" is singular. --Scray (talk) 03:57, 18 April 2009 (UTC)[reply]
One more note: the Squid giant axon (not specific to giant squid - it's just a giant axon) can be 1 mm in diameter - a diameter easily visible to the naked eye; with a length that can be measured in meters, this is a huge cell. --Scray (talk) 16:40, 18 April 2009 (UTC)[reply]
The article correctly states not that an egg is a single cell, but instead it states that the ostrich egg contains the largest known single cell. So, tell me Jayron, If the yolk of the egg is not that cell, where's the cell? Dauto (talk) 04:55, 18 April 2009 (UTC)[reply]
As to division of labour, there is the awesome dictyostelium - but it's a eukaryote.Ā :( As far as the "why not" bit goes, I'm not sure that lack of a nuclear membrane is the defining factor in how cell specialization works, it comes down in the end to appropriate communication. Perhaps prokaryotes don't adopt this strategy because they've never had to? There are many paths to evolutionary success. I can't think of any definitive (published) reason why a prokaryote couldn't do the same thing. Interesting question though - there's my whole afternoon shot now!Ā :) Franamax (talk) 20:38, 17 April 2009 (UTC)[reply]
Suppose I shoot a bullet into a block of wood, knowing the velocity and mass of that bullet. How could I estimate the final resting position of the bullet? What other information would I need to know? 58.6.129.205 (talk) 13:42, 17 April 2009 (UTC)[reply]
I don't know the exact answer to your question, I'll leave that to our resident physicists, but I think you'd need to know the distance of the wood from the initial position of the bullet (in the gun), and the strength of the wood involved. Both these factors would have a large role to play in how far the bullet can penetrate the wood. Regards, --āCyclonenim |Ā ChatĀ 13:54, 17 April 2009 (UTC)[reply]
(ec)Our article on Penetration (weapons) sadly doesn't provide any information. This webpage [1] gives an equation by the 19th century French engineer Jean-Victor Poncelet, and a calculator to plug your own numbers into, which may be of use (Note that one of the users of the page spotted an error in the Java script for the calculator, hard to tell if it's been fixed). I presume that the various constants quoted would vary depending on the type of wood, orientation of the grain etc. Mikenorton (talk) 14:05, 17 April 2009 (UTC)[reply]
One questionably-useful data point from personal experience. A plain old lead round-nose .22LR round will penetrate a 2x4 of plain old lumber (I think probably pine, but I'm not sure.) However a 2x4 of weather treated wood will stop the same bullet. Clearly, the density and strength of the wood is a factor. Also consider bullet shape and cross-section. A smaller, more pointed bullet will penetrate most materials better than a bigger, blunter bullet. This sounds like one for Mythbusters- I imagine trying to estimate this is more complicated than simply performing some tests. Friday(talk)14:09, 17 April 2009 (UTC)[reply]
PS. (I mean penetrate the short way, not the long way. I don't remember trying it the other direction.) And the poster above brings up a good point about grain orientation- if a bullet can slip in between things, this is going to take less energy out of it than having to blast through things. Friday(talk)14:11, 17 April 2009 (UTC)[reply]
My dad said (WP:OR) that a 22 long would go an inch and a half into the end of a 2x4, farther than I would have supposed. I know that a 22 LR will penetrate seasoned 1x lumber (something over 3/4 inch thick: very old boards) and richochet around inside the building a couple of times, from shooting at an unoccupied farm outbuilding I owned, so it did not have the velocity to penetrate the 1x board on the far side of the building. Milage may vary depending on muzzle velocity, distance to target, mass and jacketing of bullet, and type of wood, grain orientation,angle of impact, and seasoning of the wood. Snipers, assassins, CSIs and police must have some empirical data. Edison (talk) 16:06, 17 April 2009 (UTC)[reply]
One of my friends asked me this, and i just can't figure it out. Somebody please help me!!
Proof that unicorns exist For me to prove that unicorns exist, it is enough if i prove that there exists at least a single existing unicorn(possibly a more stronger statement). so there are 2 cases
I don't think there's a paradox so much as a silly phrase. What is the distinction between "unicorn" and "existing unicorn"? If you strip that word, then the choices of "at least one unicorn exists" and "no unicorns exist" is quite clear. In this specific case, it looks like "existing" is used to mean living. Again, though, swap the word and there's no contradiction. ā Lomn15:25, 17 April 2009 (UTC)[reply]
You almost convinced me! Nice. Isn't the joke based on a shift from "there exists no existing unicorn" to "there exists a non-existing unicorn", that is not exaclty the same statement. pma (talk) 15:42, 17 April 2009 (UTC)[reply]
Listen here (for your friend). A contradictory object does not exist, but also, any object that does not exist may well have a contradictory property: this can be harmlessly assumed, for it does not exist. A contradictory property for a non-existent object is, of course, existence. Therefore a non-existent object enjoys the property of existence, so it exists pma (talk) 16:23, 17 April 2009 (UTC)[reply]
Assuming you don't just have a fetish for horses with strange frontal growths, you chose to discuss unicorns because they are objects which by definition do not exist. Any proposition in which they exist is wrong before it leaves the unicorn paddock. --Sean16:42, 17 April 2009 (UTC)[reply]
A silly play with words does not a paradox make. Said that, who is to say that unicorns do not exist? Any animal with one horn fits the bill. Dauto (talk) 17:19, 17 April 2009 (UTC)[reply]
It's pretty nonsensical. "Existing" is just an adjective - it's like "Blue" or "Pointy" - if I put the phrase "existing unicorn" in quotes then either there is an "existing unicorn" or there is no "existing unicorn" - which is clearly a true statement - just like either there is a "blue unicorn" or there is no "blue unicorn". But in any case - even with your interpretation - the two sentences are only "obviously true" when you interpret "existing" like you'd say "blue". Otherwise I can make paradoxes all day long by saying things like:
Either:
There are pink unicorns ...or...
There are green dragons
That's not a paradox - it's a set of statements that are simply false. So if you insist on this rather crazy interpretation of "existing unicorn" then you simply invalidated the entire statement by turning it into "Either unicorns exist or unicorns exist"...which is false. SteveBaker (talk) 17:41, 17 April 2009 (UTC)[reply]
This sounds a little like a play on the Black Swan Problem? Though I could be wrong as i don't fully understand why their statement is supposed to be a paradox. I could sort of read it similar to the Rumsfeld statement about there being known knowns and known unknowns, and unknown unknowns? (http://www.brainyquote.com/quotes/quotes/d/donaldrums148142.html). But at least Rumfeld's made a bit of sense. 17:55, 17 April 2009 (UTC)
I would say this is clearly a play on the ontological argument for the existence of God. It runs: Define God as a being that is best in every way. Clearly it is better for God to exist than not to exist. Therefore God exists. Vast tracts of philosophy have been written to argue about the validity of this argument. Looie496 (talk) 18:14, 17 April 2009 (UTC)[reply]
Me too, I thought to the logic-ontologic trick, but in fact it's not exactly the same... It seems to me that this one is more linguistic than logic.--pma (talk) 20:02, 17 April 2009 (UTC) As to Rumsfeld I thi(self censored).[reply]
Rumsfeld was a monst(self censored) but I think he made an very perceptive point and got screwed over for it. There really are known-unkowns and unknown-unknowns! Now, the context of his pontification, that was incredibly (self censored) and dismissive of (self-censored) and repugnant to every (self-censored). I do appreciate that contribution to world thought though, flawed as its presentation may have been. Franamax (talk) 20:55, 17 April 2009 (UTC)[reply]
This is discussed in one of the Smullyan books but I'm too lazy to look up which one even though I have them at home. Sorry. ā b_jonas18:30, 18 April 2009 (UTC)[reply]
I think this is a case of Equivocation. A classic example:
Nothing is better than eternal happiness.
A ham sandwich is better than nothing.
Therefore, a ham sandwich is better than eternal happiness.
The problem is that two different meanings of "nothing" are equated. I think the same thing is happening in your example, where two related but separate meanings of "existing" are being equated. The first "exists" in context means "the concept which follows has veracity", whereas the second "existing" means "is present in a tangible form". Stated slightly differently, the "There exists" in "There exists no existing unicorn" is an idiomatic phrase meaning "There is such a thing as a ...", with the "no" modifying the verb: The sentence "There exists no happy clown" means "There is no such thing as a happy clown". If we use that rephrasing, the "paradox" becomes:
In an electrostatic field, a positron will not move in the same way as either an electron or a proton. It will feel the same force as a proton, but because it's a lot lighter than a proton, it will move along a different path. Looie496 (talk) 18:59, 17 April 2009 (UTC)[reply]
File:SmartseLeg hair.jpgA close up shot of the hair in question with normal hairs for comparison
I have one 10cm long leg hair (not quite a world record, see here) why has this one hair grown so long? It's a lot thinner and whiter than my other leg hairs. Any ideas? Smartse (talk) 19:26, 17 April 2009 (UTC)[reply]
I've got a very fine, long, white hair on the side of my forehead, which I doubt was ingrown at any time. It grows back after plucking. --Kjoonlee17:13, 18 April 2009 (UTC)[reply]
Redox reactions and Lewis Acids & Bases
If an oxidizing agent gains electrons, does that make it a Lewis Acid? Similarly, if a Lewis Base donates an electrons, is it also a reducing agent?130.127.99.54 (talk) 20:16, 17 April 2009 (UTC)[reply]
Not really. A Lewis Acid-Base reaction is a covalent bond formation reaction. And its a specific kind of covalent bond formation reaction. Remember that a chemical bond consists of two electrons. Under most reactions, one usually thinks of each atom on either side of the bond donating one electron to make a two-electron bond. Kind like this:
Xā¢ + ā¢Y ā XāY
However, in a Lewis Acid-Base reaction, in the formation of the new bond, BOTH electrons come from one of the reactants. Thus, a Lewis Acid-Base reaction always looks like this:
A + :B ā AāB
In this case, the A is the "acid" and the B is the "base". A Bronsted-Lowery acid-base reaction is thus a special case of the Lewis reaction, where A is ALWAYS the H+ ion. But the more general Lewis Acid-Base reaction encompases a whole lot of other scenarios, such as the following reaction:
F3B + :NCl3 ā F3BāNCl3
In this case, the boron compound is "electron deficient", that is it has an empty orbital, or if you prefer, less than a full octet, which makes it an ideal "lewis acid". The nitrogen compound has a spare, unbonded pair of electrons, which makes it an ideal "lewis base". The thing about this is, unlike other acid-base theories, Lewis theory doesn't even deal with "H+" ions at all.
Now, redox reactions involve the transfer of electrons from one element to another, without necessarily forming any new bonds. For example, if you add say a piece of magnesium metal to a solution containing Copper (II) ions, you will get the following redox reaction to occur spontaneously, forming magnesium ions and copper metal:
Mg(s) + Cu2+(aq) ā Mg2+(aq) + Cu(s)
No new covalent bonds have formed. What happened here is that two electrons were transfered from the magnesium to the copper. So you see, though both types of reactions involve the rearangement of electrons in some way, they are very different sorts of reactions. Actually, EVERY chemical reaction involves the rearrangement of electrons in some way, so these two types of reactions are not all that unique in that regard. I hope this makes a little more sense. You may want to read Lewis acids and bases and Redox for more on these processes in general. --Jayron32.talk.contribs02:07, 18 April 2009 (UTC)[reply]
And a poorly done one too. Look at where the light is falling on the skull - only the front part is bright, the top and sides are in shadow. Now look at the shadow of the guy right next to it - the sun is falling on his back - so the skull should be brightly lit from it's right side...and it's not. SteveBaker (talk) 20:04, 19 April 2009 (UTC)[reply]
April 18
Coriolis force on a river in the northern hemisphere
"A straight river ļ¬ows with speed v in a direction Ī± degrees East of North. Show that the effect of the Coriolis force is to undermine the right bank. Does the magnitude of the effect depend on Ī±?"
My brain has shut off, I don't even know where to start! Thanks for any help,
This seem's to be a homework. Is that the case? I hope it isn't because the statement "the effect of the Coriolis force is to undermine the right bank." is actually incorrect. Dauto (talk) 01:01, 18 April 2009 (UTC)[reply]
Oh dear, it is part of my set work, yes! Perhaps that explains why I've spent so long trying to understand why and getting nowhere - what does happen then? I've read through the wiki article on the effect but I'm still not completely certain, gah! Mathmos6 (talk) 01:41, 18 April 2009 (UTC)[reply]
I think it should be true in the northern hemisphere. The rotation of the earth about its axis gives the water angular momentum. As the water moves north, it gets closer to the axis, so conservation of angular momentum means it tries to rotate more rapidly about the axis, like an ice skater drawing in her arms to spin -- this pushes it against the right bank. Looie496 (talk) 01:51, 18 April 2009 (UTC)[reply]
Okay, so assuming this is talking about the northern hemisphere, does the angle east of north affect the magnitude? Or equivalently, I suppose, will you have a different effect if the magnitude of Ī± is 0/90 degrees? You should have no effect along the hemisphere and 100% of the effect northwards, right? Mathmos6 (talk) 01:58, 18 April 2009 (UTC)[reply]
The effect doesn't depend on the angle . The coriolis force will indeed push the water rightward. The problem with the statement is that this rightward push will very lightly raise the water level on the rightside but that does not undermine the riverbank. To undermine the riverbank you would need an effect that speeds up the flow of the river on its right side. Coriolis effect doesn't do that. Dauto (talk) 02:10, 18 April 2009 (UTC)[reply]
Actually, a flowing river, being a fluid, would also be deflected rightwards as it flows. I am not certain the effect would be great enough to cause undermining of the river bank, but it may do things in the large scale like cause subtle differences in the overall way rivers flow across open plains and the like... --Jayron32.talk.contribs21:31, 18 April 2009 (UTC)[reply]
I'll try a qualitative answer here: steel is more efficient to recycle overall. I base this statement on the fact that steel is more widely recycled.
One factor in this is that it's more easy to collect and sort the steel. Crushing a car is easier than sorting six million pieces of plastic, and a bridge or a ship can pretty much be just thrown into a mini-mill. Plastics come in a wide variety of types (look at the number inside the recycling symbol on plastics, it goes up to at least nine) and are difficult to segregate since they need humans or spectroscopic/laser methods to sort. Steels by contrast can be sorted by weight and magnetic properties.
Another factor is that steel is much more dense than plastic. This comes into play when considering the cost of transporting the material back to the recycling facility, since steel "weighs out" before it "cubes out". This means that the trucks/trains/ships are carrying their maximum load, which is usually more fuel-efficient. Put another way, you probably need fewer trucks to ship the equivalent amounts of steel and plastic for their strength-weight-volume ratios.
And steel has the big advantage in thermodynamics that you just have to remelt it, you don't have to reform the molecular structure. With steel, you just make a melt, check its properties, then throw in a little more of what you need to get the exact metal alloy you're trying to produce. With plastics, you have to deal with thermal dissociation of the plastic molecules and more severe negative properties of the contaminants. Steelmaking is a metallurgical process, plastic is a chemical process.
As I said, those are qualitative impressions. If you had a million steel computer cases sitting beside a million plastic cases just outside your recycling facility, I'm not sure which one would win. I'd put my money on the steel though. The economics of recycling are very complex. But since people will come over to your house and tow your old car away for free, whereas they won't come over to get your plastic bags for free - again I'm betting on steel. Franamax (talk) 23:16, 18 April 2009 (UTC)[reply]
Recycling economics is complex; the deciding factor however in determining if it is economically feasible to recycle a material is in having uses FOR the recycled material. Take rubber tires as an example. They are a complete nuisance as a waste product (take up a lot of space, never degrade, etc. etc.) and so should be an ideal candidate for recycling them. However, they are completely worthless in that regard, as there are so few uses for recycled tire rubber. There are a few weird esoteric uses, such as paving running tracks and things like that, but really you can't even use it to make new tires out of, its a worthless material, so there is really no good reason to recycle it. The chemistry of plastics is similar. With steel cans, you melt down the steel cans and make more steel cans. Its simple and easy and means that you will always have enough demand to make steel recycling economically feasible. With plastics, it just doesn't work that way. You can't melt down plastic milk jugs and make more plastic milk jugs; the chemistry just does not support that sort of application. Sometimes, you can use the recycled plastics for alternate applications, but like with the rubber tires example, the demand created by these alternate applications is just not enough to make it as econimical as metal recycling. --Jayron32.talk.contribs04:56, 19 April 2009 (UTC)[reply]
I thought they fed milk jugs back to the cows who made them! And I'm pretty sure we ship all our old tires to Springfield, that fire's been burning for 20 years now.Ā :) Franamax (talk) 20:13, 19 April 2009 (UTC)[reply]
Power production from sea water by electrolysis process.
Would it be efficient to seperate hydrogen from sea-water by electrolysis process and then to produce electrocity by using the hydrogen in a gas turbine? āPreceding unsigned comment added by Shamiul (talk ā¢ contribs) 07:59, 18 April 2009 (UTC)[reply]
No. See First law of thermodynamics for why you cannot win, and Second law of thermodynamics for why you cannot break even. Splitting a water molecule requires exactly the same amount of energy that is returned when you recombine it. But none of the processes are 100% efficient - i.e. you lose energy. As a rough ballpark figure, in you configuration I would expect the loss to be around 60%. --Stephan Schulz (talk) 08:46, 18 April 2009 (UTC)[reply]
Certainly that isn't going to work in terms of getting free energy (but then there is no possible way to get free energy - period - because of the laws of thermodynamics). But there may be reasons to do it anyway. For example - it's proving very difficult to design batteries to make electric cars a particularly viable option - so using the electricity to make hydrogen and putting the hydrogen into the car makes some sort of sense. Also, if you were to supply power from wind turbines or nuclear power exclusively - then there would be times of day when you'd be producing more electricity than you need - and turning that energy into hydrogen, which you'd store and burn later when the need for electricity is higher. So there are reasons to do it - but none of them relate to getting energy for free - which is completely impossible by any means. I think Stephan's estimate of a 60% loss is an under-estimate. There aren't many gas turbines that are more than 60% efficient - and electrolysis is at best only about 80% - there are bound to be other losses. I'd be surprised if you got back 40% of what you put in. Probably, a gas turbine would be a bad way to get electricity from hydrogen - hydrogen fuel cells seem like a better bet. SteveBaker (talk) 20:02, 19 April 2009 (UTC)[reply]
Sleep
Last night, I had approximately five hours of sleep and not suprisingly, I am unable to think about mathematics today. Similarly, with regards to learning vocabulary (from another language), my short term memory did not seem to be up to its uaual standard. I also seem to be consistently thinking about sleep the whole day, unable to do much. I have thoroughly read the article on sleep but could not find the answer to this question - thinking in which areas of mathematics is affected most by a lack of sleep (and which areas are affected the least) and which aspects of thinking in general, are affected by a lack of sleep? I think this reference desk is the best place to post but hopefully I will get answers from the Wikipedians at the other reference desks. Also forgive any errors in my writing.Ā :) --PST10:55, 18 April 2009 (UTC)[reply]
Have you read Sleep deprivation? I wouldn't expect getting only 5 hours sleep for one night to have a significant effect, though. Plenty of people sleep that little routinely (studies vary in their conclusions about whether that is a good idea or not). I expect your problem is not that you are too tired, but rather that you are too sleepy. You need to do something to wake yourself up - I find sugar and light exercise to be the best way to do that. Once you've woken up and got going, you should be fine. --Tango (talk) 12:49, 18 April 2009 (UTC)[reply]
Thanks for your advice and comments. The other question I have is about sleeping too much. If I were to sleep in, although having slept for 10-12 hours, I feel sleepy 2 hours after having woken up. Describing it as sleepy might be inaccurate - rather it is a temporary drowsy sensation. Is it better for thinking, to sleep for around 10-12 hours or more, or a moderate amount? For me, it is usually around 8-10 hours of sleep that is the best for logical thinking. --PST14:27, 18 April 2009 (UTC)[reply]
I know what you mean - I find sleeping too long leaves me kind of fuzzy. Again, exercise seems to help (just 10 minutes brisk walk in the fresh air is often enough). I think a typical amount of time to sleep is 6-8 hours, although opinions vary on what is best (I remember a study that showed people that sleep an average of 6 hours a night live longer than those than sleep 8, which is the opposite of conventional wisdom). --Tango (talk) 14:59, 18 April 2009 (UTC)[reply]
Having a short (20 minute) midday nap can help immensely if you aren't sleeping enough at night. Our article Sleep is full of useful advice and data. SteveBaker (talk) 19:52, 19 April 2009 (UTC)[reply]
I agree - it's amazing how much better I feel after a short nap when I haven't been sleeping properly. However, it seems from the OP's question that the lack of sleep was a one-off, so hopefully they slept properly the next night and all is well now. --Tango (talk) 21:58, 19 April 2009 (UTC)[reply]
These seem like the symptoms of caffeine addiction to me. Give up tea and coffee and you will feel alert all the time, and go to sleep quickly and wake up alert and refreshed. The few days or weeks after giving up caffeine will not be so good. 78.147.2.142 (talk) 11:29, 22 April 2009 (UTC)[reply]
hiv transmission
can hiv be transmitted through kissing?
and
which is more likey a way of hiv transmission, swallowing cum or bareback sex?
I believe HIV can be transmitted through kissing, but it is quite unlikely. Cuts, sores, bleeding gums, etc. can increase the risk, though. Unprotected vaginal or anal sex is almost certainly a greater risk than oral sex, although cuts, sores and bleeding gums do, again, increase the risk. I remember an excellent table being linked to in a previous ref desk question showing the risks of various sexually transmitted infections being transmitted is different ways. I'll try and find it. --Tango (talk) 15:04, 18 April 2009 (UTC)[reply]
The only was HIV could be transmitted through kissing if the receiver has some form of cut in their digestive tract before the stomach. If not, the virus will be broken down in the stomach. It's pretty rare to catch HIV this way.
As for your second question, the former could only result in transmission if the above provision still applies. The latter, however, is much more likely as anal sex is, quite frankly, done in an area not designed for such activities and can result in more cuts within the anal canal. If semen enters a cut, it can transmit the virus to the other person. Regards, --āCyclonenim |Ā ChatĀ 16:06, 18 April 2009 (UTC)[reply]
There have not been any documented cases of HIV transmission by French kissing. This paper discusses reasons for the low HIV content in saliva. Despite this, the CDC cautions against French kissing with HIV positive people due to theoretical risk of transmission. AxlĀ¤[Talk]16:56, 18 April 2009 (UTC)[reply]
Hello Science Deskers!
(a) If I know the right acension and declination of any star, how do I do the calculation to figure out when that star has its heliacal rising? (I'm hoping there is a way to do some math and get an answer such as "19 days after the summer solstice", that kind of thing.)
(b) Once I figure out the answer, how would I adjust it to figure out when that star would have had its helical rising for any year in the past (such as 5 or 10 or 15 thousand years ago)?
Thank you, WikiJedits (talk) 16:00, 18 April 2009 (UTC)[reply]
What you need is a planisphere. Make sure you get one that is for the latitude where you live. You can also get free ones off the internet you can print yourself or software you can run, just try googling for it. If you want to do the trigonometry yourself, you will need a book, this one iss very old (1834) but because it is out of copyright you can view it online or print it out. I don't think trigonometry has changed much since then. SpinningSpark17:12, 18 April 2009 (UTC)[reply]
Thank you SpinningSpark. I have found a planisphere but can't figure out how to read a heliacal rising from it. For example, I put Spica over where it says Eastern Horizon, but the earliest time it gives is 5 am and the month over there is November. I know sunrise is way after 5 am in November. Is there a way to work it out by doing a calculation instead? I have looked at the book but it is way beyond me. Is there a method a beginner could use? (Also, do you or anyone else know the answer to my question b?) Thanks again, WikiJedits (talk) 01:52, 19 April 2009 (UTC)[reply]
My Planisphere is the Philips' one like the picture in the article so if you look at that you will understand what I am talking about. You are right that the first step is to put Spica on the Eastern horizon. The moving part of the planisphere has a time scale, and the fixed part has a calendar. At any particular date, this will tell you the time Spica will rise. If you look for 19th April, you will find that Spica is rising at about 7pm in the Northern hemisphere. This depends on your latitude which is why it is important to get a planisphere for your own location. Ok, so 7pm tells you that Spica is rising in the night sky (or before) at the moment and is nowhere near its heliacal rising. Next you look around the scale till you find a date at which the timescale is showing the time of sunrise for that date (again dependant on your location). 6am is at 30th October on the planisphere, so if sunrise is at 6am on that date, then that is the also the heliacal rising of Spica.
If you cannot deal with the trigonometry in that book, then you are not going to be able to do the calcualtion by hand. I suggest you get some software to do it for you, or else go and learn the maths first.
For 5 or 10 years in the past, there is virtually no difference to the date of the heliacal rising. For thousands of years in the past, you must take into account the precession of the earth. To do this you must first locate the position of the North Celestial Pole in the epoch which you are interested in. You can get that from this diagram. Next, you must move the pivot point of your planisphere to the location of the ancient North Celestial Pole (don't destroy your good one, print a throwaway one off the internet). Then you just proceed as before.
Thank you, I really appreciate the time you've taken. Think I get it now - I need a table of sunrise times and to compare it to the times and dates shown on the planisphere. Got one off timeanddate.com and doing that for Spica again (at 30N) gives me a best match with October 17, 5:58 am. Additional question 1 - the heliacal rising isn't exactly at sunrise, is it? Do I need to allow extra time? Would it be better to pick July 3 when sunrise is at 4:58 am? Cos that's quite a difference.
Additional question 2 - About the past calculation, I must be doing something wrong? I drew the north celestial pole circle on the rotating part of the planisphere and put the pin in a different place along the circle. But this didn't seem to make much difference (other than the planisphere not fitting together so well). For example, I tried it for halfway around the circle, or about 10,000 years ago, and putting Spica on the eastern horizon still has the fall months aligning with the morning times, when I would expect it to be the spring months. Do you know what I'm missing? Much thanks for all your help, WikiJedits (talk) 19:42, 19 April 2009 (UTC)[reply]
Turning radius of a vehicle
The turning radii of all four or more wheels of a vehicle are always different.What does the mean turning radius given in their specification mean? āPreceding unsigned comment added by 202.70.64.16 (talk) 17:10, 18 April 2009 (UTC)[reply]
Mean turning radius is the radius through which the centre-line of the vehicle turns. It is usually defined at the front wheels, the mean radius is different along the length of the vehicle in general. SpinningSpark17:38, 18 April 2009 (UTC)[reply]
Car manufacturers sometimes talk about the "turning circle" which is the smallest circle within which the car can do a complete 360 turn...that's a more useful measure - and refers not to the wheels but to the parts of the vehicle that stick out the most. For a car that has lots of "stuff" sticking out behind the rear wheels (like a US-style school bus), that can be a significantly larger number than the radii of the circles made by the wheels. For my car, the number in the handbook specifically excludes the door mirrors! SteveBaker (talk) 19:46, 19 April 2009 (UTC)[reply]
You probably won't be surprised to hear there are several different definitions. One useful one is the kerb to kerb diameter, ie effectively the narrowest road you can turn round in. The wall wall diameter is often used in Germany, I think it is a DIN standard. The Japanese use something else again. Greglocock (talk) 10:22, 22 April 2009 (UTC)[reply]
Sedimentary rock, evaporites: How does gypsum end forming a stratum .50m thick?
Where can I learn about the processes by which gypsum -probably originally sedimented in the form of thin little crystals- end up forming strata half a meter thick and spanning kms?
This question applies (in my curiosity) to all kind of evaporites.
In the articles about evaporites and sedimentary rocks, and in the books I've read, I don't see anything explaining the processes that undergo the evaporites once sedimented.
Jorgemelis (talk) 17:17, 18 April 2009 (UTC)[reply]
See also Sabkha (a supratidal salt flat), which is an environment in which thick gypsum deposits are often formed, sometimes in the form of desert roses. Evaporation at the land surface causes the rise of brines by capillary action and as these evaporate they deposit salt at the surface and gypsum and aragonite in the subsurface. In deeper water areas gypsum layers may be formed by crystallization at the air-water interface followed by sinking of the crystals to the bottom. Mikenorton (talk) 19:31, 18 April 2009 (UTC)[reply]
Lazy smokers
Which of these would improve the overall health of an inactive (no exercise) smoker with a typically bad, high-fat diet more?
I doubt there is an answer that applies in all cases. People have lived to be over 100 while smoking 20 a day, so stopping smoking won't necessary improve anything at all (although it most likely will). Exercise and diet are complicated things, there aren't simply "good diet" and "bad diet", "exercise" and "no exercise", so more information would be required. Also, it's necessary to know in what way the person is unhealthy - if they are suffering from Emphysema, stopping smoking will almost certainly improve their health more than the other two, for example. --Tango (talk) 20:26, 18 April 2009 (UTC)[reply]
I wondered if I might get that. Since I'm just curious in general, not looking at anyone or any particular set of circumstances in particular, I probably can't get a real answer as such - though anyone is welcome to come in with more input and opinions. Vimescarrot (talk) 20:37, 18 April 2009 (UTC)[reply]
Of course, health is highly individualized. One can speak in general terms for what works in averages, but you will always find anecdotes of 110 year old men who sit on their ass all day chain smoking unfiltered Camels and eating 5 pounds of bacon a day and washing it all down with Thunderbird wine. And you can not smoke, not drink, run 10 miles a day, and live by eating nothing but tofu, broccoli, and wicker and die of a heart attack at 45. Behavioral effects on health are measurable across large populations, and you should probably do whatever you can to improve your own health, but you can do nothing at all to guarantee that you will live longer only because you do everything you are "supposed" to do. --Jayron32.talk.contribs21:27, 18 April 2009 (UTC)[reply]
Yes - but it's a matter of probability. One person in a thousand who does all of those terrible things to their body will survive - but the other 999 will die an early death. Sure, there are anecdotes of individuals who smoked their entire lives and through sheer, blind luck survived. On the other hand, you have people like my father who tragically died in his early 50's from smoking just 10 cigarettes a day - or like my mother who suffered from most of the bllod pressure and heart disease symptoms of a 10-a-day smoker despite never having smoked in her life because of the second-hand smoke. That my father died so young is probably the only thing that saved my mother from doing the same. Picking the one person in a thousand who survived and hoping that you'll also be that lucky one person in a thousand and not one of the 999 more typical cases is exactly like saying "I'm going to give up working and assume that I'll win the lottery" - nobody in their right mind does that yet it's the exact same ridiculous thinking pattern. SteveBaker (talk) 19:29, 19 April 2009 (UTC)[reply]
It kind of depends on your exit-strategy. Do you want to live with maximal indulgence and go out with a bang? Suffer through lingering health problems? Exercise will improve your cardiac state, help your lung capacity to a certain extent and improve your feeling of general wellbeing - but there's all that dicomfort and sweating. Improved diet will lessen your risk of atherosclerosis, stroke and metabolic syndrome/diabetes - but there's the factor of being hungry all the time. Quitting smoking improves almost every risk factor there is (not diabetes) - but that could just mean you spend a long life wishing every minute of the day that you could have another smoke.
If quitting the evil weed is off the table, then a little of both of the other two. A half-hour brisk walk every day is a good start and eatcher veggies. But really, anything other than continuing to sit in a chair smoking and eating pork rinds is probably going to be an improvement. In the end though, everyone chooses their own way out the door.
Maybe you need to engage with your mother more - offer to cook some neat recipes and ask her to go out on regular walks with you. That way you get an equal benefit. Franamax (talk) 22:24, 18 April 2009 (UTC)[reply]
Exercise should be enjoyable if done correctly (endorphins and all that), and a healthy diet shouldn't leave you feeling hungry unless you are trying to lose weight (which should only by a short term issue). --Tango (talk) 01:02, 19 April 2009 (UTC)[reply]
For a heavy smoker, the answer is very likely stopping smoking. The other things make a difference, but unless the person is an inert obese blob, not as huge a difference as smoking. Looie496 (talk) 02:22, 19 April 2009 (UTC)[reply]
A mixture of OR, unsourced and read from sources but not cited:
@Tango, granted on the endorphin reward, but they take time to develop hence the initial discomfort. There's also the social factor, which is overall important. I tried working out at a gym once and didn't return. OTOH I will go for multihour walks with my friends or family anywhere and always. And despite the obvious handicap of being a smoker, I love playing squash, just because I'm competing against myself as much as the other player. Plus it's among the most exertive of sports, so you get the good stuff that much faster I suppose.Ā :)
And the unsourced part is to feeling hunger pangs. Perhaps I should call them cravings. Long-term exposure to high-sugar and/or high-fat diets set up feedback rhythyms which can result in habitual behaviour. Our reward systems are treated independently in our wiki articles - since I'm in the "unsourced/OR" bit here, I'll point out the large number of neurons comprising the "gut brain" concerned exclusively with feeding.
@Looie - oh yes, undoubtedly quitting smoking is much more than the "likely" answer. The way the OP posed it as a simple choice, it wins hands down. I'm pretty sure the various physiologists who attend this page will agree with me on the risk factors. Trouble is that life is a little more complicated than that. You have to address the risk factors that are easiest to change (IMO) first. To use your terminology, the OP was in a way describing an "inert obese blob" they are very concerned about. They wish to modify someone else's lifestyle and outlook. There's a lot of factors there beyond just presenting "what the people on Wikipedia said". But yes of course, quit smoking! Easier said than done.Ā :( Franamax (talk) 03:24, 19 April 2009 (UTC)[reply]
These activities complement each other nicely. When a heavy-smoking friend of mine started exercising, he found his desire for cigarettes decreasing. Conversely, if one stops smoking, then one breathes better, and might feel more like getting up and exercising! -GTBacchus(talk)02:44, 19 April 2009 (UTC)[reply]
The classic studies are MRFIT (Multiple Risk Factor Intervention Trial) and the Framingham Heart Study, although I don't have access to those studies at the moment. This study included 84,129 women. Relative risks of coronary events:-
Relative risk of coronary events over 14 years in the Nurses' Health Study
Risk factor
Increase in relative risk
Poor diet (quintile 1) vs. good diet (quintile 5)
1.90
Smoking ā„ 15 cigarettes per day vs. ex-smoker
3.5
Exercise < 1 hour per week vs. > 5.5 hours per week
Give up smoking - by a very large margin. Our article Smoking cessation gives a TON of useful information - what techniques for giving up work best, etc. I'll quote this for you because I think it's inspirational for the person doing the quitting:
The immediate effects of smoking cessation include:
Within 20 minutes blood pressure returns to its normal level
After 8 hours oxygen levels return to normal
After 24 hours carbon monoxide levels in the lungs return to those of a non-smoker and the mucus begins to clear
After 48 hours nicotine leaves the body and tastebuds are improved
After 72 hours breathing becomes easier
After 2ā12 weeks, circulation improves
After 5 years, the risk of heart attack falls to about half that of a smoker
After 10 years, the chance of lung cancer is almost the same as a non-smoker.
If the person doing the quitting can understand on a day by day basis what's getting better - they'll be more inclined to stick with it.
I don't think you'll get such immediate or profound benefits from either diet or exercise. However, it's very hard to be specific without a lot more information - and in any case, we're not allowed to give that kind of specific medical advice. Probably the very best advice we can give is "Go see a doctor" - they can weigh the pro's and con's with full knowledge of the state of the person involved. SteveBaker (talk) 19:19, 19 April 2009 (UTC)[reply]
Having quit once for 8 years, I can testify that the effects are immediate and profound. Not all of them beneficial, like searching the ashtrays in the basement to find stale old butts and light them up for two more drags, right down to the cellulose acetate in the filter. Overall, yes of course it's good to quit smoking (although I didn't have one-half a heart attack in those years, so I can't confirm your statisticĀ ;). But the little trap in my brain circuitry was still poised, it never went away - 8 years later when a friend offered me a $200 Cohiba at a wedding (I just had to destroy that value, c'mon), the trap was sprung.
My point is that all risk factors exist, but some can be mitigated more easily than others. It's not a trinary choice, it's a matter of what can most easily be achieved in the circumstances. GTB puts it well, an overall approach yields synergy. That's not what the OP asked originally, but they later revealed their overall concern - so I suggest an overall approach. It's what I do with my own mum, she's made her own decision to keep smoking - but she smokes nothing when we go hiking.Ā :) PS: I understand that this is not a scientific response Franamax (talk) 19:50, 19 April 2009 (UTC)[reply]
Actually, my overall concern is not with my mother. I was genuinely just curious. If I try any sort of logical approach with my mother, depending on her mood, she'll either look at me like I'm a joke, look at me like I'm stupid, or look at me like she's never seen me before. Oh - and thank you, everyone, for your epic input. Uhm...I apologise if you were only doing it because you thought it would be in some way functional.Ā :( Vimescarrot (talk) 23:11, 19 April 2009 (UTC)[reply]
O yes, I've googled it first. But many of the links are selling products. I found this one [3].What I want to know is how common it is? And its affect to health. roscoe_x (talk) 08:10, 19 April 2009 (UTC)[reply]
It depends. It will affect your health in two and only two ways. First, it will consume as much of your available income as you are willing to give the peddlers. If you otherwise spend this on Hamburgers and cigarettes, it will improve your health. If the alternative is to pay for and go to a gym, it will usually be detrimental. For the second way it may affect you, see Placebo effect. In other words, it's complete bunk, but should be fairly harmless by itself. --Stephan Schulz (talk) 09:15, 19 April 2009 (UTC)[reply]
There are a bunch of different type of electric field therapy and little evidence for effectiveness for any of them. It's not scientifically implausible that something like this could work, but there's hardly any actual positive evidence at this time. Looie496 (talk) 16:52, 19 April 2009 (UTC)[reply]
(I've got to stop looking at the websites for these things...it only makes me angry). [5] claims to explain how this works. Aside from the fact that this page is one large image - so you can't cut and paste the text (grrrr) and it's riddled with typo's - the actual "science" there is just a bunch of random jargon stringed end-to-end to look impressive. In the section "How the Electric Field Therapy works", we have:
"EFT is a simple, non-invasive technique that uses static electricity...". OK - fact #1 - it uses static electricity.
"The theory is that when an electric filed with high voltage AC is applied on a human body..." - well, firstly it's a "FIELD", not a "FILED" - but fact #1 said they use STATIC electricity. You can't have AC static electricity! Plus, if you apply high voltage AC to the human body (eg by sticking your fingers into an electrical outlet, it tends to DIE - not get better!
"...cells metabolism is stimulated by supplementing ions and the Acid-Base Balance of Electrolyte in the blood results adjusted." ...that's not even a grammatically correct sentence. But what makes you think the pH of your blood is likely to be wrong? There is no science saying that any of the conditions it claims to fix is caused by an error in the pH of your blood - and even if it were - passing AC current at high voltages isn't going to change the pH. Do you really want to take a machine made by people who can't put together a single coherent sentence and have it try to electrocute you? I really don't think you do.
"The H+ flow of ions in the organism can optimally be directed."...er what? Positively charged hydrogen atoms...like in water..."can optimally be directed"...Where? Why? What happens to all of the OH- ions that would be left behind? If you try to adjust the pH by moving the H+'s in one direction than you'll be adjusting the pH wherever the OH-'s would be in the opposite direction. But this is crazy! This is doing electrolysis on your blood! If it actually did this, it would kill you amazingly quickly!
"This is important because beside others, the co-ordinates of enzyme, the Ca++ household, the proteins of transportation in the blood and the general acid-base-homeostasis depend on these flows of protons and ions." - OK - the only way to write a sentence with so little meaning is to open a dictionary of scientific terms and write them down at random. There is no way to even try to analyse what this sentence means!
It gets worse, the company claims to have "ISO9001" certification. I've actually been through the certification processes for those standards and they are pretty hard to get - they relate to how products are designed and documented and represent the result of frequent inspections of your processes, etc. However, when you click on the image of the "certificate" - it's not an ISO document - but something awarded by some unheard-of Chinese organization. It's certainly not a proper ISO-9001 certificate.
This is so very bad...it's beyond ridiculous. PLEASE - don't pay them a cent of your money.
Thanks for all the information. My mom tried this. The one that made her belief there is something in this device is it made her feel electrical shock when the person touch her hand. roscoe_x (talk) 05:53, 20 April 2009 (UTC)[reply]
They probably connect you up to a Van de Graaff generator or something. That would make it feel like something is happening (because it is, you are becoming electrically charged, but that has no health benefits). --Tango (talk) 13:38, 20 April 2009 (UTC)[reply]
Do you mean by the body or in a laboratory? In the body it would be some kind of white blood cell which would then present a viral protein to another type of white blood cell which would then produce antibodies against it.
Thanks. The question is about how viral detection/identification can be performed in a lab context. What if the virus is unknown, or new? Would a clinical lab, say one at a hospital, be equipped to detect and confirm a new form of viral infection? Or is that only possible at a very well-equipped research lab? 173.49.18.189 (talk) 14:52, 19 April 2009 (UTC)[reply]
Hospital labs are equipped to detect known pathogens. Novel viruses would not routinely be screened for. The detection of novel viruses is a huge topic - there is no simple way to do it. Some viruses have been detected by looking for cytopathic effect in tissue culture. The hepatitis C virus was known to exist (as "non A, non B viral hepatitis") for more than a decade before Michael Houghton's group at Chiron discovered it by screening over a million cDNA clones in a phage library using serum from infected people to detect viral proteins. Today, techniques like random-primed PCR (with random-primed reverse transcription to detect RNA viruses) are available, but far from perfect. Of course once you've detected a virus, showing that it causes a specific disease is another challenge - we'll all loaded with viruses. --Scray (talk) 18:39, 19 April 2009 (UTC)[reply]
Photovoltaics and thermodynamics; ie, efficiency vs 'wasted' energy
Some considerable pondering hasn't cleared this up, and neither have I been able to find reasonable info in any of the articles I looked into, nor any of the archived reference desk questions some searches turned up.
Imagine a photo cell exposed to monochromatic photons are at the precise energy (ie, wavelength) which exactly matches the optimum energy for absorption in the cell; this is, I understand the band gap energy in traditional photo cells (eg, silicon). We will thus, be generating no phonons carrying 'excess' energy from the absorbed photons, there being an exact 'fit'. Phonon generation (energy therein will be wasted w/regard to electricity output) will be at least minimized. As nearly as I can make out, absorption and emission of photons being quantum mechanical events, there is no energy "leak" which eventually ends up in increased temperature of the photocell or attached structure.
It seems to me to be an exception to the usual energy conversion stricture which inherently includes some losses to the energy uber despot, entropy.
One thing that you've missed is recombination. You might absorb every incident photon with no losses, but the resulting charge carrier pair might not make it to the external circuit. See Quantum efficiency of a solar cell. I don't know if this is the main method by which entropy gets its revenge, but it's certainly one of them. There is also the fact that "no real source of electromagnetic radiation is purely monochromatic" (according to Monochrome). --Heron (talk) 11:30, 19 April 2009 (UTC)[reply]
(ec) I am not sure that the second law of thermodynamics prevents 100% conversion of energy from one form to another. What it does do is prevent 100% conversion to useful work. This will certainly come into play once you start trying to extract current from your cell; if through nothing else the joule heating of the circuit. In any case 100% conversion of photons is not practically possible. Some of them will hit the crystal lattice and become phonons, some will be re-emitted before the electron can be made to do anything useful, all real crystals have flaws which will lose some of the photons etc etc. SpinningSpark11:41, 19 April 2009 (UTC)[reply]
It does not violate thermodynamics because a pure plane wave of zero frequency width has zero radiation entropy, thus, there is no maximum possible conversion efficiency below 100%. The opposite extreme would be blackbody radiation at the same temperature as the cell itself, having maximum radiation entropy, none of the energy could be used to create work. Radiation obeys the laws of thermodynamics just as matter does. 129.2.43.42 (talk) 16:06, 19 April 2009 (UTC)Nightvid[reply]
My thanks all. It may be that the blinders of ignorance have loosened their hold slightly. My thought experiment was deliberately constructed to evade most practical issues and focus (ahemm..) on what seemed to be the key question. So the objection that there can't be a monochrome source is skew to the hypo; and likewise inefficiencies (ohmic and otherwise) during use of the electricity generated to something helpful (like running my automated beer fetching and opening robot, say). I was attempting to exclude such issues, mostly because they're as obiter dicta and so obscurantist. Recombination does indeed seem be something I'd not considered. Easy to miss, not being one at home in the labyrinthine complications of doped and dopey micro lattice structures, so I don't feel as terminally thick as I probably should. The anon contribution by 129.2... may be the very answer I was seeking, but alas I fell off the wagon as it made the turn into pure plane wave territory... In English this historian type can cope with, please...? ww (talk) 18:06, 19 April 2009 (UTC)[reply]
I don't know how helpful the analogy is, but in a volume of zero the mass of any continuous substance is zero, and if we have some mass in a zero volume the density is infinite. Similar considerations apply to the "spectral density" of light; if we have light with a continuous spectrum (that would give a continuous "rainbow"), the amount of light at exactly one frequency is zero. A finite amount of light at exactly one frequency (or in exactly one direction for that matter) has an infinite spectral density. This light can be thought of as coming from something "infinitely hot". Thermodynamics tells us that if the "hot part" of a heat engine is infinitely hot we can, in principle at least, convert heat to work with 100% efficiency. This of course is setting aside practical issues like reflection off the surface of the solar cell or carrier recombination. 69.140.12.180 (talk) 04:43, 21 April 2009 (UTC)Nightvid[reply]
It would be great if they really were "energy saving" but I think that would contradict the second law of thermodynamics. They are compact fluorescent lamps - I think this should help. Incidentally DYK that it's best to leave them on if you leave the room for less than 15 minutes because switching them on/off wears them out and could end up making them less efficient that incandescent light bulbs. Smartse (talk) 11:04, 19 April 2009 (UTC)[reply]
They are energy saving as you get the equivalent of 60w worth of light from an incandescent bulb for only 11w. The packaging of the 11w (230-240v) bulb I have says it gives 600 lumen, and is supposed to last 10000 hours. 89.242.147.172 (talk) 11:23, 19 April 2009 (UTC)[reply]
I don't believe CFLs are likely to be less efficient then incandescent bulbs if turned off in less 15 minutes. They do wear out a lot that way however and so in overall energy consumption and pollution terms as well as cost to the consumer terms, leaving them on is sometimes better then turning them off. See [6] for example Nil Einne (talk) 13:22, 19 April 2009 (UTC)[reply]
It's important to be clear on this: CFL's have a MUCH longer lifespan than incandescents when used in "normal" ways. They are vastly more efficient because they generate much less heat - so the laws of thermodynamics are not violated! They are more expensive - but pay for themselves in a very short amount of time because of the energy savings and the increased lifespan. The only significant drawback is the mercury they contain - which is a nasty pollutant. However, they use a lot less mercury than old-fashioned 'striplight' flourescents - and right now, properly recycling the darned things - or cleaning up mercury pollution afterwards are a LOT easier than dealing with global warming caused by the wasted energy from incandescent lights. SteveBaker (talk) 18:24, 19 April 2009 (UTC)[reply]
Steve, we must disagree on what "normal" use is. To me, it's switch it on when you need it, then switch the damn thing off when you don't. I put a CFL in my bathroom and it was toast within about four months. The incandescent in the fixture beside it is still working two years later. It operates maybe 30 minutes a day, but gets cycled regularly (I work at home and drink a lot of water). Do the math on that and consider that it takes 9 cubic metres of landfill soil to neutralize the mercury emitted if you throw the bulb in the trash (which I don't, but many people do). Furthermore, during heating season, six months of the year, I save NO energy by having a more efficient light. All that happens is that the other energy source comes on. If that happens to be fuel oil in a furnace vs. hydroelectricity, I'm net-subtracting from combatting global warming. (Mercury emitted from new dam reservoirs is a wash vs. CFL bulbs).
If your definition of "normal" is leaving a light on all day in an air-conditioned house, unquestionably a CFL is better. Whereas I call that aberrant behaviour!Ā :) Franamax (talk) 20:46, 19 April 2009 (UTC)[reply]
No matter ho much water you drink, that CFL should have been ok. You cannot generalize from a single fluke. Mine are warranted for 3 years minimum, and I have so far (3.5 years since I switched) had one dud after 3 weeks - and that was replaced without any discussion. As most electronics, CFL failure will tend to follow a bathtub curve, so a few early failures are to be expected. --Stephan Schulz (talk) 21:06, 19 April 2009 (UTC)[reply]
In contrast to the CFL sitting beside my couch, which has operated reliably for long durations for the last two years? I don't think it was a dud, although it's certainly possible that when you open a two-pack of bulbs one will fall into the bathtubĀ :) I disagree, current switching is a known factor which shortens the life of CFLs compared to incandescents. My habit, ingrained in childhood, is to switch off a light when you don't need it. I find the suggestion that I should leave the light on, consuming energy, in order to save energy - paradoxical.
You're right in a way, I should have kept my receipt, gone back to the store, complained. They would have replaced the bulb and thrown the old one into their garbage. I've researched this a lot - switching and enclosed fixtures are failure modes for CFLs, or at least were. The various commentary available covers several generations of bulb, so I'm not sure. What I do know is that I use CFLs everywhere I find them appropriate. In the bathroom, where they are switched 10-15 times a day - no, I don't see the math that tells me I should spend more for no net energy/CO2 saving and use mercury in the process. The one in the living room, definitely. The bathroom, nope! Franamax (talk) 21:33, 19 April 2009 (UTC)[reply]
Well, our article claims (with sources) that a 5 minute on/off cycle reduces CFL lifetime to about that of an incandescent lamp, or alternatively, that one on/off cycle is equivalent to about 6 minutes of lifetime. With a rated lifetime of 6000h (the lower limit) they should be good for 60000 cycles, or about 10 years - half that if you also actually leave them burning 6 minutes (which also factors into their lifetime, of course). Even if the numbers are somewhat optimistic, it looks very much as if you hit the front side of the bath tub.... --Stephan Schulz (talk) 22:20, 19 April 2009 (UTC)[reply]
Not sure how to phrase this.Ā :) Umm - we either need the bathroom light on for much less than five minutes or much more. Myself in particular.Ā ;) If I need to operate the lamp for more than four times what I need the actual light for just for the privilege of paying way more to get the same lifetime as an incandescent, it is costing me and the entire planet. As I say, the living-room lamps are fine, they're on for hours at a time. No way I'm going to put the bathroom light on all day and night though. I can spend less money and emit less CO2 using incandescent lamps. So that's what I'll do. But yeah, I'll put another CFL in, track the lifetime and do the math. See you in four months!Ā :) Franamax (talk) 23:43, 19 April 2009 (UTC)[reply]
But isn't that precisely the point? The lifetime will obviously be negatively affected by the times you turn it on briefly (but the energy savings won't be by much), however since it doesn't have a continous 5 minute cycle the lifetime will almost definitely be better then a incandescent and as already mentioned, the every savings remains there and costwise they could easily work out better. Also as I already mentioned elsewhere the idea you should leave the lights on is bull, few people who actually know what they're talking about recommend, I'm someone who nearly always switches off my lights even if leaving my room for only several minutes and the lifecycle on my CFLs have been fine. Indeed those that do seem to have had short lifecycles have been ones that are usually left on for a long while! Indeed my biggest problem has been incandescent lightbulbs breaking when I turn off a light then realise I still needed it or whatever, turn it back on and 'poof' there goes the filament. Really the best thing to do is to stop worrying about 'keeping the light on' and just use the light like normal Nil Einne (talk) 01:39, 20 April 2009 (UTC)[reply]
Just to avoid a possible misunderstanding: Lifetime (for CFCs and incandescents) is usually giving in burning hours ("on time"), not in calendar time. --Stephan Schulz (talk) 11:44, 20 April 2009 (UTC)[reply]
I've yet to see any reliable data indicating that oft made heat claim has any merit and simple basic physics suggests it's probably bull so I'm going to call it that. Heat travels upwards. We all know that (or should if we're going to be making claims about using lightbulbs for heating). That's one of the reasons why we usually install heaters on the ground. If you've ever touched a incandescent you know they get very hot (so do flourescents of course but I digress) and so those the air around them (even more so if your bulb is in a fairly or completely fixture) and probably even the ceiling etc. So guess what? A (probably substanial) portion of the heat you generate with your lightbulbs is very likely not aiding you in heating your home in a useful way at all. You obviously do gain something, from the infrared and from the heat that does radiate or convect but it's very likely only small proportion of what you're generating and whatever the case is definitely not all the wasted energy even if you happen to have a fan installed on your lightbulbs to try and cycle all that heat arpimd (so your claim that you save no energy is surely wrong). It gets even worse if you're using something more efficient like a heatpump or a gas heater or whatever. The simple fact is if you want to generate heat, the best thing to do is to use something designed to generate heat (we call them heaters), not try and use something who's sole purpose is to generate light (which surprise, surprise, is what lightbulbs are for). Also do you really heat your home for 6 months of the year? P.S. If you really don't believe me that it's not simply generating the heat but actually having the heat radiate in a meaningful way, then there's this anecdotal story. I bought an oil column heater, these are common in NZ. This was a real cheapie. Several other people have similar oil column heaters of the same power (1000W). I've found the oil column heater is actually fairly useless at heating my room despite having the same power (well this is rated, I've never tested it to see if it is really what it claims) as these better brand oil column heaters. Clearly the better ones are much better at radiating heat. Obviously these would use more power overall in general since my heater is likely to get hot and switch off whereas the other heaters won't switch off as much but I still feel confident enough to say that these more expensive heater make more efficient use of the power they do use in most circumstances. P.P.S. If you have data indicating that using CFLs during heating season doesn't save energy (hopefully taking in to account any potential confounding factors) then I'm perfectly willing to eat my hat but I doubt it. Nil Einne (talk) 01:39, 20 April 2009 (UTC)[reply]
I have the feeling that they do flicker, even if I can only detect it subconciously. Although I use them they do not seem as nice as incandescent bulbs, but do feel like flourescent lighting which I do not like. I'd like it if someone could provide the evidence to prove me wrong. 89.242.147.172 (talk) 11:48, 19 April 2009 (UTC)[reply]
There are many different kinds of CFCs, with widely varying properties and prices. I use the Phillips Softtone, which after warming up looks much like an incandescent to me. It did cost me around EUR 6 or 7 per bulb, IIRC. Cheaper bulbs will quite possibly have worse performance, both in light colour and in flickering. --Stephan Schulz (talk) 12:39, 19 April 2009 (UTC)[reply]
Note it is important to consider what you mean by 'worse performance'. For example, everything else being equal, cool coloured fluorescents (cool daylight for example) generally have better colour rendition (see colour rendition index) then warm ones. (The phosphors uses makes a big difference however whatever the colour temperatures). However in Western cultures, warm coloured lights which are closer to incandescent lights are generally preferred particularly for living spaces and are sometimes considered more natural (even though cooler lights are far closer to the epitome of natural light, the sun and bright daylight). From sources I've read and anecdotal evidence these preferences don't hold for Asian cultures however where preferences are more varied and often tend to the cooler end of the spectrum. If you can only detect something 'subconsciously' it could easily be simply that you want flourescents to be bad so they are. Nil Einne (talk) 13:42, 19 April 2009 (UTC)[reply]
That's all very true - but since you can buy CFL's that match either incandescent light's color or natural daylight color - there is no way that 'color' is a good excuse for not buying them. The fact that you get the choice is a huge plus. SteveBaker (talk) 18:24, 19 April 2009 (UTC)[reply]
I agree and apologise if my response distracted from the main point. It's simply a pet peeve of mine that people commonly suggest warm lighting is better or more natural since it seems to be a cultural thing and the more 'natural' concept is IMHO flawed (as with most claims that something is more natural). An interesting thing of course is that flourescents (not necessarily CFLs) have already taken significant hold in a number of Asian countries, whether this is because of the difference in colour temperature preferences (since I believe most early flourescents had a fairly high colour temperature) or is partly the cause of the different preference of a combination of both I don't know. Nil Einne (talk) 01:08, 20 April 2009 (UTC)[reply]
I seem to get a peculiar feeling on my skin when in a room illuminated by flourescent light - as if it were something to do with static electricity perhaps. Perhaps its just my imagination. 89.242.147.172 (talk) 14:06, 19 April 2009 (UTC)[reply]
Well if you get a peculiar feeling on your skin, then that's easy to test in a double blind fashion. You leave the room and someone throws a coin, or uses a better random method to decide whether to put an incandescent or CFL in the room. The person then leaves the room. 5 minutes later (well a preset interval so there is no need for contact between the two of you), you come in to the room well blindfolded so you can't possible see what light is present. Repeat multiple times (I would say at least 20.) If you are able to detect reliably whether CFLs or incandescents are present, then we know you are somehow detecting CFLs, perhaps because of a peculiar feeling on your skin. Nil Einne (talk) 14:11, 19 April 2009 (UTC)[reply]
The trouble is that it may be the color rather than flicker or (the extremely unlikely) skin tingle that would clue the person in to which is which. CFL's exist that are a pretty good match for incandescent color - but they aren't 100% perfect. Controlling for color in your experiment is much harder. SteveBaker (talk) 18:24, 19 April 2009 (UTC)[reply]
Well 89 said that he/she believed there was a skin tingle. IMHO it would be useful for 89 to test this if it continues to influence his/her thinking. I agree it's rather difficult to control for CFLs vs incandescents if you can actually see the light whether that's because of colour or flicker or simply because you believe CFLs are bad (and you can easily tell by the colour and other factors) hence the reason I didn't suggest any double blind tests until the OP mentioned a skin tingle Nil Einne (talk) 01:08, 20 April 2009 (UTC)[reply]
One last comment here - I regard CFL's as an emergency measure. Incandescents are such a huge problem for global warming that we simply MUST get rid of them as quickly as we can. In many places around the world, laws are being passed to outlaw these ridiculously inefficient devices...and incandescent light bulb factories are gradually switching production to CFL's. They simply have to go - whether you like it or not. However, LED lighting is the true way of the future. LED lights have an amazingly long lifetime - they are yet more efficient than CFL's - you can dim them nicely (tricky with CFL's) and you can even get them where you can adjust the color they produce to whatever your heart desires (I have one of these). Because they last so long, whatever pollution they create when they eventualy DO die is relatively unimportant because we won't be throwing them away so often. The only limitation on them right now is that the really bright ones are pretty expensive. We're seeing them appear in things like car tail-lights and traffic signals where the consequences of failure and the cost of replacement are high. This year, I think there were more LED Xmas tree lights on sale than incandescents in local stores here in Texas. I have a really fancy tri-color LED "bulb" in my home-office area (you can actually turn it on and off and set the color remotely from your computer using X10 protocol over the power lines!) - it was really just a hideously expensive gimmick - but it does work. It's plenty bright enough - and you can adjust it to produce "warm" lighting or "cold" lighting depending on your mood (you can also make it flash in various colors in time with music on your PC if you're into 1970's disco lights!) But as soon as they get cheap enough (and they undoubtedly will), I plan on switching over my home to slightly saner LED lights completely. SteveBaker (talk) 18:24, 19 April 2009 (UTC)[reply]
I've noticed (at least here in NZ) halogen bulbs that are compatible with ordinary sockets are now available. I believe these are being promoted because they are considered sufficiently energy saving that they will generally be allowed in places where incandescents will be banned. (Unfortunately this isn't going to be NZ since the new government abandoned that policy although given that nearly everyone else including China and our closest neighbour Australia are banning them I expect it's just a 'feel good' reversal since they'll probably still largely disappear.) They don't have the lifespan or anywhere near the energy savings of CFLs but if you absolutely refuse to use CFLs then IMHO you should use them. They are also dimmable although if used in dimmers they may not last as long (since they don't as hot as they should) nor save so much energy although it's my understanding they will always last at least as long as ordinary incandescents and will never use more energy. You're right about LEDs of course. They're also starting to get quite common in torches and other battery powered lights where the power savings (and longevity) is important and flourescents aren't possible. Nil Einne (talk) 01:08, 20 April 2009 (UTC)[reply]
I look forward to getting something similar to sunlight rather than the yellow gloom we are used to - although on the other hand it does signal the evening and hence probably helps you prepare to sleep. 78.146.75.232 (talk) 19:54, 19 April 2009 (UTC)[reply]
You may be interested in [7]. Also do note that cool daylight CFLs (and flourescents) with colour temparatures of around 6500K (lower are available if that's too high for you) are already vastly (IMHO and also based on colour temperatures) more similar to bright daylight then the yellow gloom and are available now (and in fact were the earliest flourescents I believe) Nil Einne (talk) 01:08, 20 April 2009 (UTC)[reply]
The great flaw of CFLs is that it costs about $1 (U.S) to recycle a CFL. An incandescent bulb can be purchased for less than 50 cents (US). A CFL can be purchased for about $3 or less with occasional rebates. Most consumers will not pay $1 to recycle a CFL, so they go into landfills and the mercury pollutes the environment. This is a neglected externality of the "bulb of the future." Edison (talk) 21:23, 19 April 2009 (UTC)[reply]
You're repeating some common, misleading arguments. There are organizations in many areas that recycle CFLs free of charge, including The Home Depot. You can also get mercury-free ones if that's for some reason not an option. If you get your power from a coal plant, the reduced power requirement saves more mercury from entering the environment than is actually contained in the light. Decent CFLs last longer than incandescents and obviously take less power, so your point on price is weak. -- Consumed Crustacean (talk) 21:30, 19 April 2009 (UTC)[reply]
Yes - that's true. I'd also argue against the "bulb of the future" moniker. CFL's are the bulb of today - they've been around for many years now. LED's (or perhaps, OLED's) are the bulb of the future. But at 10x to 30x the price of a CFL and 200x the price of an incandescent - it's hard to convince people to buy them until the price drops. But LED lights are good for 50,000 hours and use even less power than CFL's - so even at $50 to $100 a pop - they'll still pay for themselves over the very long term. 50,000 hours is a lot - if you put LED lights into a new house - the odds are good that most of them will still be in the house and working fine on the day it's demolished. So the issues of what toxic effects they might have in landfills is rather academic. You can flip them on and off as much as you want - they aren't as fragile as incandescents and CFL's so they work well in places like refrigerators and ceiling fan fittings and you can have them in any color you like - or even have RGB LED lights where you can adjust the color to fit your mood on any given day. Economies of scale will push the price of LED lamps down to more acceptable levels in not too many more years...so CFL's should be regarded as a stop-gap solution. SteveBaker (talk) 03:13, 20 April 2009 (UTC)[reply]
I have wondered the same thing. If incandescent bulbs become impossible to find we're going to have to come up with some sort of heating element/LED combo device to retrofit all of our lava lamps. (Also EZ Bake ovens if you're into that.) APL (talk) 03:54, 20 April 2009 (UTC)[reply]
I question your claim that "mercury-free" compact flourescent bulbs are available. Please provide a reliable source or a retraction. As for a merchant accepting old CFLs, the merchant still has to pay about $1 per bulb to get a recycler to accept them. It may be a public service on the part of the merchant, or a promotional method to increase traffic to the store, but it is still a neglected externality. If you Google 'recycle CFL you find that recyclers charge about 82 to accept 90 CFLs. A site that promotes use of CFLs says a consumer can buy a 30 bulb recycling container for $120, a higher cost per bulb than the initial purchase price. Is there presently a government audit system to verify that recyclers actually capture the mercury rather than charging a high price and then just putting them in landfill? Given the history of crooks in waste disposal in the U.S., it is just a matter of time until such a con is exposed. The bulbs still cost far more to recycle than incandescent bulbs cost to purchase, but the theoretical energy savings for the CFL would pay for the recycling. Has anyone determined how many CFLs get expensively recycled, compared to the number sold? I expect that the vast majority presently go into landfill and release mercury. Asking a merchant to provide "free" recycling will not work in the long run, because the recycling charge per CFL is about equal to the merchant's profit on the bulb. Edison (talk) 16:43, 21 April 2009 (UTC)[reply]
Okay, good thing you questioned me on that, as I'm no longer sure where I read that. As far as I can tell, they're still in the R&D phase. You've still ignored my point on coal plants and net mercury savings. On the rest of it: according to the compact fluorescent lamp article, price of CFLs at, say, The Home Depot, includes the price of recycling. This I can't verify due to the lack of source, but I haven't exactly expended much effort attempting to do so. Your entire point initially was that a consumer would not pay the extra dollar to recycle the bulb, which you've still failed to support; there was nothing to do with the costs and/or crookedness of the recycling process (which, uh, sources would be appreciated for). -- Consumed Crustacean (talk) 00:13, 22 April 2009 (UTC)[reply]
If CFLs are the same as flourescent lights, then why do CFLs take time to reach their peak brightness, but floursecent lamps get there more or less instantly? 89.240.60.225 (talk) 11:56, 20 April 2009 (UTC)[reply]
And then there are dimmers...
(Adding a subhead so as not to hijack the main thread.)
About 40% of the primary lighting in my house is on dimmers. I'm more than a little concerned about the "let's ban all the incandescents" argument, because I'm seeing no replacement for that capability. I tried a dimmable bulb last summer, and I tried another one that was supposedly some 'Next Generation dimmable' -- NEITHER OF WHICH LASTED THREE MINUTES.
So, what would the energy zealots have me do? I'm not about to replace all my switches with non-dimmable ones -- or is that what they would demand of me?
Dimmers reduce the current to the incandescent lamp filament, causing it to emit less light (and heat). The CFLs need the rated current to keep the (usually mercury) gasses in motion, to create the light. Slower motion is not enough to create visible light.
I agree the the future is with LED lights...these all run at very specific voltages and amps, but are so small that they must be installed in banks. This makes if feasible to switch out some banks, to reduce the total light given. Of course your dimmer rheostats are not going to selectively switch out banks, so you will need to replace them anyway. If the power to the LEDs is wired to bypass the dimmer, then the dimmer could control a set of relays which switch various banks of the LEDs in or out, depending on the current through the dimmer. This conversion would probably cost a lot more than buying new switches. KoolerStill (talk) 07:56, 21 April 2009 (UTC)[reply]
The problem with most dimmers is that they are work as a simple potentiometer by reducing the voltage - and for incandescents, that's fine because brightness is somehow proportional to voltage. However, with CFL's there is a certain minimum voltage, below which they can't produce light at all - so they are generally not dimmable. Ditto with LED's. What's needed in that case is an alternative kind of dimmer. In the case of LED's, the solution is to switch them on and off hundreds of times per second with the ratio of on-time to off-time varying depending on how bright you want them to appear - that's called pulse width modulation or "PWM" for short. Some dimmers actually do work that way - the ones with a fancy electronic 'touch plate' design seem to do that. With some LED light fittings, the electronics inside (which are already converting 110v or 240v into the 5v or so that the LED's need) can detect changes in the supply voltage due to dimmer switches and 'translate' that into PWM automatically. I don't think that works with all LED fittings and I'm unsure about CFL's. Anyway - for DaHorsesMouth, I'd point out that humanity is in a state of crisis right now. If we don't take really drastic action to resolve this impending global warming catastrophy then an awful lot of people are going to die - many species of plants and animals are going to go extinct. Many more people will starve, lose their homes or find their cities going the way of New Orleans. You, personally, will be considerably more inconvenienced than by merely having no dimmers on your light fittings. So suck it up - get with the program and help to save the planet - nobody said it was going to be painless. SteveBaker (talk) 14:07, 21 April 2009 (UTC)[reply]
See Dimmer. I have seen theatrical lighting dimmers from the 1920's which were giant rheostats which introduced resistance in series with the light to dim it, and I have seen large Variacs (variable autotransformers) from the 1950's which dimmed lights by reducing the voltage more efficiently, but modern light dimmers (for the last 25 years at least) use electronic switching to vary the portion of the AC cycle during which the current goes to the bulb. A rheostat type dimmer for controlling several hundred watts of lighting would dissipate a huge amount of heat and could not be contained in a plastic casing in a light switch, as is common. CFLs are readily available which work well with these dimmers. I have had some in use for a couple of years with no problem. They get gradually dimmer, but the color temperature stays about the same, while incandescent bulbs get gradually redder as the dim. Then at a minimum very low level of brightness, they go out altogether, while incandescent bulbs just keep getting redder and dimmer down to just perceptible. Dimmable CFLs cost 2 or 3 times as much as non-dimmable ones. Non-dimmable CFLs fail when operated with a dimmer. Edison (talk) 16:27, 21 April 2009 (UTC)[reply]
Rheostats are still an effective switching for DC voltages, which is what I had in the back of my mind when writing the above. The biggest advantage of LEDs, from the power saving point of view, is that they run on extremely low voltages, 3 to 5 volts, and run well on DC. This makes them very suitable to run from local installations of batteries, or from solar panels. They can give quality lighting on home-generated power, in other words, and on very small amounts of it at that. As solar panels produce DC, this also saves inverter costs, and the total needed is much less than running any conventional 110 or 240 lighting systems.KoolerStill (talk) 16:39, 21 April 2009 (UTC)[reply]
Editors skilled in electronics have reminded me in previous similar questions that LEDs are commonly controlled by electronic circuits which can regulate the current, or which can operate them on a duty cycle, and not directly from a battery. The brightness could be adjusted by reducing the portion of the cycle they were turned on. That is more efficient than introducing a series resistance which would waste energy in I2R losses. Switching is higher efficiency than a rheostat. Edison (talk) 22:58, 21 April 2009 (UTC)[reply]
How long do American electric kettles take to boil?
I'm used to 220volts, but in the US you only have 110volts. Does that mean that American electric kettles take an extremely long time to boil water? And are electric room heaters unknown in the US? I was reading the BS 1363 article and its discussion. Edit: I've just tried boiling one litre of tap water in a 240v electric kettle, and it took 2m 45s to boil, and exactly three minutes before it turned itself off automatically. 89.242.147.172 (talk) 11:30, 19 April 2009 (UTC)[reply]
In principle, you can get the same amount of energy independent of the voltage - you just draw a higher current. I would expect US equipment to be made to the relevant specifications. In other words, a simple heating device designed for 230 volts will work in the US, but will be much less effective. A device designed for 110 volts will likely fail, possibly in spectacular and dangerous ways, if connected to 230 volts. More complex devices will run into trouble either way, although many modern electronic devices are built to accept 100-240 volts, 50-60 Hertz, to be usable off nearly any mains supply in the world. --Stephan Schulz (talk) 11:58, 19 April 2009 (UTC)[reply]
American plugs are rated at 15 amps so the maximum power that can be extracted is 1650 watts. Poking around on US eBay their kettles seem to be generally in the 1000 to 1500 watt range, although I did find one that claimed 1750 watts and can boil seven cups in 5 minutes. By contrast, British plugs are rated at 13 amp and kettles are usually in the 2000 to 3000 watt range which is considerably more. Before anyone points it out, I know that 220 volts x 13 amps is less than 3kW but the British supply is not really 220 volts. It used ot be 240 volts, when we signed up to European harmonization at 230 volts (edited) the only thing that changed was the specified allowed variation in voltage! Don't believe everything you read on labels. So in summary, American kettles will boil slower, but not extremely slower as you state. SpinningSpark12:16, 19 April 2009 (UTC)[reply]
In NZ, the maximum current allowed by our normal plugs is 10 amps. Looking at my kettle which is the cordfree kind, it's rated at 2200-2300W. Nil Einne (talk) 13:18, 19 April 2009 (UTC)[reply]
I'd also point out that electric kettles are relatively rare in the US. When we wanted to buy one, we had quite a hard time of it. They aren't things that are ubiquitous in every household...and indeed the one we have has a low capacity and is incredibly slow compared to the ones we've owned in the UK. Most of the time, if we want boiling water, we use either the microwave or a pan on the stove - the former is faster for small quantities - the latter is faster for large quantities because the kettle is so small. There are similar issues with many other appliances. Mains-electric lawnmowers, for example, are relatively pathetic affairs compared to the ones we had in the UK - so relatively few people have them. Whether 110v or 240v was the better choice is a tough one. 110v is undoubtedly much safer around the home than 240v - but the hassle of having to have special multi-phase 220v outlets for running things like washing machines and hot-tubs is a real pain. I've recently been looking to buy an air compressor for running pneumatic tools in my garage - the 110v ones are crap but having to wire a special 220v outlet just to run the darned things is a real pain. I suspect that when electric cars and plug-in hybrids become common - the UK will use three-phase 480v charging outlets - and here in the US, we'll be stuck with 220v...which is going to be painfully slow. SteveBaker (talk) 18:01, 19 April 2009 (UTC)[reply]
That explains (partly) why they dont drink tea in the US - they cannot boil the water. They must just have coffee percolators. Makes me wonder how they "invented" instant coffee. Using an electric stove for cooking must be difficult too. 78.146.75.232 (talk) 19:47, 19 April 2009 (UTC)[reply]
I doubt that 100V is much safer than 240V (or 230V these days, +/- enough that it makes no difference). It's probably a bit safer, but is it really "much safer"? Especially since UK appliances will generally draw less current than their US equivalents (most appliances don't use anywhere near the maximum power available, so the UK and US ones will presumably use the same power) - current can be just as important as voltage when determining risk from electrocution. As for electric cars - UK charge points in public car parks, etc., might use 3-phase, but ones in private garages at people's homes won't - individual houses aren't generally connected to a 3-phase supply. It would probably be easier to increase the current than the voltage - the 13A limit is determined by the wiring inside the house, a separate high-current connection to the mains supply could be made (I don't know what the maximum current that can be drawn by an entire house is, but it is clearly much greater than 13A, although perhaps less than 13A times the number of sockets in the house). --Tango (talk) 19:05, 19 April 2009 (UTC)[reply]
Certainly 120 (or 100) volts is much safer than 240 (or 230). About half the current will flow, reducing the likelihood that the shock victim will be unable to let go of a bare wire, and lessening the chances of stopping the heart action.See page 160 of Electric wiring, residential by Mullin:[8]. Twice the current could make all the difference. The painfulness of an electric shock also increases with higher voltage at a higher than linear rate. Edison (talk) 19:51, 20 April 2009 (UTC)[reply]
First, the correct nominal North American voltage is 120, not 110 or 100. As to safety, 110-120Ā V is slightly better than 220-240Ā V in terms of shock hazard but slightly greater in terms of fire hazard since higher currents are required. However, a factor of about 2 is only going to matter if a shock or overheating incident is right on the boundary between serious and not-serious.
To match the original poster's original research, I just measured a liter of water into a Canadian 120 V electric kettle and boiled it. This kettle is old enough that it doesn't have an automatic shutoff and if it ever had a wattage rating displayed it's illegible now.
But it took between 5 and 6 minutes to reach a full boil, and I think you'll find that'd be typical today. Although the circuits are rated for 15 A, nobody makes appliances that draw a full 15 A because one other thing on the circuit would trip the breaker. The tap water going in would have been between 5Ā° and 10Ā°C, so, taking the mid-range of those numbers, the current draw would be 92.5/(120Ć5.5) kilocalories/volt-minute = just about 10Ā A. I'd be surprised if you can get a significantly more powerful one in North America.
--Anonymous, 19:40 UTC, edited 19:45, April 19, 2009.
Electric space heaters in the U.S. designed to operate on 120 volts only draw about 12.5 amps. so they only put out about 1500 watts of heat, enough for a small room. 240 volt heaters are also available, which can heat a larger room. 120 volt electric kettles in the U.S are sadly underpowered and do an inadequate job of boiling water compared to those running on 220 or 240 volts in the rest of the world. The inadequacy of 120 volts is the result of being the pioneer country in having central station electricity for heating, lighting and power. Poor insulation on the available wiring in the 1880's and a concern for safety from electrocution resulted in a distribution voltage lower than desirable in the light of 2020 hindsight. Edison (talk) 21:18, 19 April 2009 (UTC)[reply]
Here in Canada, (where many of us call electric utility poles "hydro poles") I can roughly confirm Anonymous experience with an electric kettle. I can boil 8 ounces of Canadian water and make a cup of coffee in roughly one Canadian TV commercial break (that's two minutes), so the power output is just fine for me.
The difference between a 120V vs. 240V shock is about three feet farther across the room in my experience.Ā :) Don't try this at home kids. Luckily there was lots of space around the water heater.
And in Canada at least, getting the higher voltage is pretty straightforward. The bulk of the streel-level distribution system runs at 240V, but the step-down transformer has a centre-tap, so it's a three-wire system. In your circuit-breaker box, you tap one or other of the 120V legs for most uses. For the big stuff, you just tie two breakers together by hooking up a different coloured wire to one of them. Voila, double the voltage, no problem at all! Of course, you need to use properly rated wire when you do it. Really big stuff like industrial machinery is a whole different story. Franamax (talk) 00:27, 20 April 2009 (UTC)[reply]
Unless your appliance is the kind that's always on when it's plugged in (as my kettle is), it also needs to be double-insulated if you're going to power it that way. Most devices in both Britain and North America are designed so the power switch is on the "hot" wire and the rest of the internal wiring is connected to the "cold", but when you take 240Ā V from a 240/120 circuit, both sides are "hot". (This is a safety issue, not a function issue.) --Anonymous, 00:45 UTC, April 20/09.
@SteveBaker: Here in the greater Toronto area, house current (117v @ 60Hz) electric lawnmowers are the norm; gasoline-powered ones are the conspicuous exception. And practically everyone has an electric teakettle in the kitchen. That situation is opposite to my experience growing up in the States, where electric lawnmowers were scarce and electric teakettles practically unknown. Many of the teakettles are garbage, and I have serious qualms about boiling water in a plastic vessel imported from a country well known for falsifying statements of compliance with material specifications and counterfeiting safety approval and certification labels. I therefore tend to boil water in a pot on the stove, or in glass in the Āµwave oven. But yes, 117v electric teakettles tend to be significantly slower by subjective perception than the 220-240v items with which I've had experience outside North America. āScheinwerfermannTĀ·C00:54, 20 April 2009 (UTC)[reply]
There aren't many plastics that melt below 100C and I'm pretty sure that they'd have thought of that when selecting which plastic to use! Most - if not all - electric kettles in the UK are plastic 'jug-style'. After all, you don't want a material that's a good conductor of heat OR electricity when you're designing an electric kettle. The ones you find in the UK are pretty highly refined gadgets - they are fast, even when there is a lot of water in there. They have auto-shutoff and a fill level indicator. They also have cords that are curled up like a telephone handset cord so they don't dangle off the edge of the countertop where kids or pets might grab them and pull a quart of boiling water onto themselves. By comparison, the ones I've found in the US date back to the stone age. SteveBaker (talk) 02:56, 20 April 2009 (UTC)[reply]
Re Americans not drinking tea. We do, just not hot and in liters. We make about a gallon of ice tea in one batch. which is then put in the fridge for later. So there's no rush as to how long it takes to brew it. For professionals there's stuff like this [9] 16.3 gallons / hour doesn't sound that slow. 76.97.245.5 (talk) 10:07, 20 April 2009 (UTC)[reply]
I thought the reason people didn't buy electric lawnmowers was because they didn't like being tethered? It seems like every one I've ever seen has had the cord repaired in at least one place. APL (talk) 12:47, 20 April 2009 (UTC)[reply]
This thread is turning into a forum discussion of transatlantic life styles. Ahem. Electric kettles work by Joule heating for which the governing equation is P = IĀ²R = VĀ² / R where P = heating power in watts, I = current in amps, R = resistance in ohms and V = voltage. Therefore if V is doubled then P increases 4 times. That is why a US kettle for 120 V would work spectacularly (and dangerously, so don't do it) in Europe on 240 V. Conversely a European kettle would take 4x as long to boil in the US, other things being equal. In practice similar powered kettles are made with resistive heating elements of 4x higher resistance in Europe than those in US.
The quoted voltages (which can vary by 10% or more) are actually the r.m.s values of alternating supplies, as are the I values in the equations above. As the the article explains, the r.m.s. value gives the average heating power.
A couple of trivial consequences of the differing supply voltages not involving kettles are
machinery outdoors, such as lawnmowers, on long extension cables may perform weakly due to voltage loss in the cable resistance in the US while this is rarely experienced in Europe
Just as a side note, not all kettles are electric. There exist the metal kettles you can but on the stove, which boils over 10L of water in about 15 minutes or so, but that's just an estimate (120V). ~AH1(TCU)00:38, 21 April 2009 (UTC)[reply]
Since you say 120 V, I assume you are talking about an electric stove. In that case, that estimated time sounds awfully low. Even if we assume a starting temperature of 25Ā°C, the current draw at 120Ā V would be 750/(120Ć15) kilocalories/volt-minute, which is 29Ā A. Stoves do have heavier wiring than normal outlets, but no way would a single stovetop element have that much power. My stove is on a 120/240Ā V circuit and is breakered at 40Ā A on each hot, and that has to supply the oven as well as the four elements ("burners"). I remember that on a previous stove where I had occasion to look at the wiring, each burner was on a 15Ā A fuse and got 120Ā V.
I just tried pouring a liter of water into a saucepan and bringing it to the boil. It took 7 minutes -- longer than the electric kettle. The heating element is probably comparable to the one in the kettle, but the saucepan does not fully cover it. I also put half a liter of water in a smaller saucepan. It had so much less contact area with the element that it took longer to boil, about 8 minutes. --Anonymous, 08:34 UTC, April 21, 2009.
HIV
I found out recently that in many countries, men who have sex with men are nto allowed to donate blood because they are in a higher risk group for HIV. But I don't see what the problem is; surely as long as you're tested and you're negative then you're fine to donate blood. What else is there to it? Thanks 92.7.20.157 (talk) 11:50, 19 April 2009 (UTC)[reply]
The problem is simply that the tests aren't 100% reliable (especially in the early stages of infection). There is a risk with any donor, but the risk with men that have had sex with men is greater and someone has determined that the former risk is acceptable and the latter isn't (probably because you can exclude men that have had sex with men without significantly reducing blood stocks, so there is very little cost and a significant benefit). --Tango (talk) 13:23, 19 April 2009 (UTC)[reply]
We have an article MSM blood donor controversy. As has been mentioned no test is 100% effective. In particular many of the older tests had large windows where a HIV would not be detected, however the new tests common in developed countries are better and have a shorter window. The bans vary from country to country but as our article notes, for a number of reasons the bans are sometimes controversal, particularly when it's a lifetime ban even more so when other high risk groups such as sex workers and intravenous drug users don't receive a similar ban. There are also questions raised about whether all MSM should be considered in the high risk group or whether some may be lower risk then people who are currently allowed to donate. [10][11][12]Nil Einne (talk) 14:06, 19 April 2009 (UTC)[reply]
The posters above are certainly right about higher-risk groups being excluded for medical and test-accuracy reasons. Another factor to consider is the experience of blood "suppliers" in the last few decades. The onset of HIV was not well handled (to say the least) and resulted in many infections among blood recipients and criminal charges for officials in at least Japan and France. A similar occurence happened with hepatitis C in Canada. If you were the director of a blood-donor clinic and knew you could go to jail if you did the wrong thing, would you go the safe route and bar entire classes of people, or would you say "nah, it'll probably be OK"? In Canada, last time I checked, you are asked if you spent any significant time in the UK in a certain time period and barred if you did, there is some risk that you might be carrying a TSE. You can generally still donate blood for research purposes in any case - but it will not be used in humans. Franamax (talk) 00:52, 20 April 2009 (UTC)[reply]
Ah, but it's nowhere near that simple, for this assumes male potential donors will answer honestly when asked the screening questions. There are those who feel a ban on gay male blood donors is not justified and/or not justifiable, and so will lie. This is not just a public health issue that can be resolved with a simple risk/benefit calculation; it has significant sociopolitical aspects and implications as well. āScheinwerfermannTĀ·C00:59, 20 April 2009 (UTC)[reply]
Clearly, there are at least these two goals: (i) make the blood supply safe, and (ii) legal protection for those collecting blood. As Franamax so aptly pointed out, the latter is a major driving force, and is served by asking the question of every donor. Lying on the part of the donors does not significantly increase the legal exposure for those who run the blood collection. I don't deny what you're saying about this being a complex web of issues, but the (somewhat simple-minded) thinking behind the screening questions is pretty clear. --Scray (talk) 02:19, 20 April 2009 (UTC)[reply]
Am I likely to have any of the water molecules from this iceberg in me now? How many? In the same way that my next breath is said to contain molecules breathed by Julius Caeser, the dinosaurs, and so on. I've been wondering what volume six billion water molecules woould have, if everyone in the world has one molecule from the iceberg in them. I wantched a tv programme last night (Channel 4, UK) that said the iceberg was ten times the size of the Titanic. Incidently, some of the details given in the programme were different from those given in the Wikipedia articles. 89.242.147.172 (talk) 13:55, 19 April 2009 (UTC)[reply]
If one assumes that the Titanic iceberg was only 10 metres on a side (and it was certainly larger than this), it contains 103 metric tonnes of water whereas the total water in the oceans is 1.3 x 1018 tonnes. Assuming this is all now thoroughly mixed we can expect this proportion of Titanic iceberg water to be in an average (say 100kg) human. Dividing by the molecular weight of water (34 u) gets about 1012 (one trillion) molecules per person. SpinningSpark14:59, 19 April 2009 (UTC)[reply]
Actually, there are even more than that, Stephan Schulz has pointed out that the molecular weight of water is 18, not 34, but was kind enough not to write my mistake on the page. SpinningSpark17:21, 19 April 2009 (UTC)[reply]
Ok, I did misinterpret you. I thought the 1012 was the number of water molecules in a typical person, rather than the number of water molecules from the iceberg in a typical person. (Had I thought about it, I would have realised that was far too small a number...) --Tango (talk) 16:39, 19 April 2009 (UTC)[reply]
(ec)Well, 1 g of hydrogen has 6E23 atoms, or 6E14 (600000000000000) per person. For H2O, or water, 18g holds as many molecules. Titanic displaced about 50000 tons. Depending on what "10 times means", the iceberg should have between 500000 tons and 50000000 tons. You do the mathĀ ;-). The other way round, 6 billion (US reading, i.e. 6E9 ) water molecules is about 1E-17 mol, or 0.000000000000000018 g (give or take a few zeros if I miscounted). --Stephan Schulz (talk) 15:03, 19 April 2009 (UTC)[reply]
I'm not sure this is a meaningful question - in a body of liquid water the molecules of H2O and constantly dissociating into H+ and OH- ions and recombining (but not necessarily in the same order), so the same molecules don't exist for long. I'm not sure how long a typical water molecule lasts for, but it's probably much less than the time since the Titanic was hit - although actually, you need to measure it from when the iceberg melted, which could have been at least a few years later. --Tango (talk) 15:12, 19 April 2009 (UTC)[reply]
Yes, you could, but that is a different question and could have a different answer. It's also a harder one to answer - I'm not sure how to determine how much oxygen or hydrogen there is in circulation - lots of it is locked up in the crust, mantle and core of the Earth, but the upper layers of the crust are involved in the mixing going on, so it becomes very difficult to work out where to draw the line. --Tango (talk) 16:39, 19 April 2009 (UTC)[reply]
Well, actually, the answer is easy, it's "yes". The difficult question to answer is "how many", that there is at least 1 is easy enough to show by taking extreme estimates. --Tango (talk) 16:52, 19 April 2009 (UTC)[reply]
The really difficult question here (aside from all of the annoying nit-picking) is whether sufficient time has elapsed for the atoms from the iceberg to have mixed sufficiently with those in the rest of the planet to make it reasonable that one or more would have made it into your body. The more recent the event, the less likely that is. So when you pick the more common choices like water that Julius Caesar peed - then the odds are much higher than for someone who was around in the 1990's. The Titanic iceberg only melted something like 100 years ago - so I doubt that it has been completely mixed into the rest of the water on the planet to the degree that Julius Caesars excretions have. But the efficiency of that mixing is undoubtedly the key here - and I'm not aware of any way to measure or even estimate the degree of that. If all the water in the world were not being swirled around by tides and such - I suppose you could use the MaxwellāBoltzmann distribution and the Random walk math to make some kind of measure of the rate at which the molecules would propagate outwards...but that would neglect other water transport mechanisms like tides and clouds being pushed around by the wind...it's a tough thing to attack convincingly. SteveBaker (talk) 17:45, 19 April 2009 (UTC)[reply]
Well, we can make a rough guess. [13] lists the self-diffusion constant of water as 2.2x10-9 m2/s. Using Fick's_law#Example_solution_in_one_dimension:_diffusion_length, with the concentration at position x=0 of 55.5 mol/L (the concentration of pure water), we find that at a range of 20,000 km (half the circumference of the earth) and at 97 years the concentration would be 55.5 mol/L * erfc(3853500). Now erfc(10) is about 2x10-45 (by [14]), and a larger parameter only makes the value less. (Note that extending the time to 2 thousand or 65 million years doesn't appreciably change things. Even at the age of the universe at 14 billion years we're still only at erfc(320).) Working in the other direction, in 97 years diffusion results in a concentration of 1 molecule/L at a distance of 38.9 meters (65 million years is 32 km). - I'd say that diffusion would play only a minor role, and other transport mechanism are much more important. -- 128.104.112.117 (talk) 23:28, 19 April 2009 (UTC)[reply]
Darn! I was hoping that the distance due to this kind of diffusion would be so big that we could neglect other sources. Oh well - so it's basically down to figuring out how much the waves, tides, winds, etc stir things up...that's really tough to figure out. SteveBaker (talk) 02:16, 20 April 2009 (UTC)[reply]
Since a rough calculation shows that the evaporation from the ocean over 100 years couldn't amount to more than 100 meters total, and the average ocean depth is several kilometers, there's a reduction factor of somewhere between 10 and 100 right there. Also, a lot depends on whether the ocean water in the region where the iceberg melted stayed on the surface or sank into the abyss, where it would have stayed for many years.
But in another sense all this is sort of irrelevant. The principles of quantum mechanics say that when water molecules are packed tightly enough so that their wave functions overlap, they do not have individual identities. There is actually no such thing as "the specific water molecules that made up the iceberg." Looie496 (talk) 02:53, 20 April 2009 (UTC)[reply]
Is there a cartographic projection such that if you cut it in half along the equator, rotated one half 180 degrees, and overlaid it on the other half, all points would be overlaying those directly opposite them on the globe? I've got a kid here who wants to dig holes through the earth and would appreciate this sort of visual reference. Ā ;-)
I am no expert on this subject but I very much doubt that there is a named projection for this. I certainly cannot find anything even remotely like that in my textbook (Steers) on map projections, nor does our article map projection. Of course, such a projection is possible, just about any surface is possible to project, it just hasn't been done. Can I suggest you download Google Earth which may help your youngster to visualise this by manipulating the globe? SpinningSpark15:39, 19 April 2009 (UTC)[reply]
No, certainly not without some bizarre discontinuity or pathology. This is forbidden on account of parity within the surface. A pure rotation keeps left turns left turns and right turns right turns. Yet if you travel on the surface of the Earth and turn right, a person remaining opposite you will make a left turn. 129.2.43.42 (talk) 15:58, 19 April 2009 (UTC)Nightvid[reply]
Ah, just beaten to it! I don't think there's a specific projection name for a map that shows antipodes. It's not really a projection per se, but a way of overlaying other projections. --98.217.14.211 (talk) 17:07, 19 April 2009 (UTC)[reply]
After looking on the article about antipodes, I found it amusing that there is almost no overlap of land on land in those superposed maps. Dauto (talk) 22:19, 19 April 2009 (UTC)[reply]
In that case, you'd probably be amused by the Land hemisphere (unless you already clicked through to it). Incidentally, the first external link in the Antipodes article is an entertaining mindscrew to get your head aroundĀ :) 80.41.73.141 (talk) 23:44, 19 April 2009 (UTC)[reply]
Hi, what are the equations used to calculate how much of each substance there will be at a certain point in time in a decay chain? Thanks, 96.255.93.227 (talk) 19:49, 19 April 2009 (UTC)[reply]
Why does the universe seem to be older than it is?
If I look in one direction using a powerful telescope I can see objects that are 13 billion years old. Now if I look in the opposite direction, I can also see 13 billion years old objects, which means that these objects are separated by 26 billion light years. However the age of the universe is only 13.7 billion years old, so how come the distance between these objects appears to be bigger than the universe itself? Laurent (talk) 21:54, 19 April 2009 (UTC)[reply]
If an explosion travels at lightspeed, its radius will be (lightspeed x time). Its diameter (which is what you're measuring) will be twice that. Vimescarrot (talk) 21:56, 19 April 2009 (UTC)[reply]
That doesn't answer your question. Never mind. It's something to do with relativity and the different perceptions of time and...and...and someone else will come along and correct my mistakes and explain it better, so I'd be better off not trying. Vimescarrot (talk) 21:57, 19 April 2009 (UTC)[reply]
The real reason is the metric expansion of space. Things cannot move faster than the (always constant) vacuum speed of light through space. But it's space itself that is expanding. Consider, as an example, a rubber balloon that doubles in diameter every second. Even if ants living on it are constrained to 5 cm/second, the distance between two given points on the surface will eventually increase much faster, and two ants at these points will move apart with the same speed even if they don't move with respect to the surface at all. For concrete numbers, assume the balloon has a diameter of 10 cm, and the ants are 1 cm (measured along the surface) apart. After 1 second, the balloon will have a diameter of 20 cm and the ants will be 2 cm apart. After 3 seconds, the balloon will have 80 cm, and the ants will be 8 cm apart. After 4 seconds, the balloon will have 160 cm, and the ants will be 16 cm apart - oops! The distance between the ants now has increased 8 cm in one second (and even weirder, they think they have not moved at all).--Stephan Schulz (talk) 22:34, 19 April 2009 (UTC)[reply]
As the last poster has pointed out the distance between objacts in the universe is expanding almost exponentially, so that distant galaxy that emitted some light 13.7 billion years ago that you can see now has been moving away from us all that time at ever increasing rates and is much further away now than 13.7 lightyears. (more like 40 lightyears if memory serves), and twice that distance if you compare galaxies in oposite sides of the sky. Dauto (talk) 22:42, 19 April 2009 (UTC)[reply]
Thanks for your answers. I still don't quite get it but I'm going to go through the articles you've suggested and post back here. Laurent (talk) 11:35, 20 April 2009 (UTC)[reply]
The universe isn't expanding exponentially yet. For most of the time since the big bang the expansion has been slowing down (roughly following a t2/3 curve), then a few billion years ago it flattened out and now it seems to be speeding up slightly. The simplest model that fits the current data is ĪCDM, which predicts exponential expansion (eHt) in the future, but it's too early to be confident that it's right. It's possible that the universe might end in a Big Crunch or Big Rip in as little as ~10 billion years. It depends on the nature of the dark energy. -- BenRG (talk) 12:20, 20 April 2009 (UTC)[reply]
Naively, a Hubble constant of 70.1 Ā± 1.3 (km/s)/Mpc does automatically result in an exponential growth. The growth is proportional to the size, which essentially is the definition of an exponential process, unless I'm very wrong (which is not impossibleĀ ;-). Of course, constants aren't and I think this one is particularly not... --Stephan Schulz (talk) 13:01, 20 April 2009 (UTC)[reply]
You are correct... the Hubble constant, H0, is the value of the Hubble parameter H(t) at the present day (t0). If we practice cosmology long enough, we may have to denote H0 with an epoch, as we do with stellar coordinates. -- Coneslayer (talk) 12:54, 21 April 2009 (UTC)[reply]
And you're correct that it's constant when the expansion is exponential. In ĪCDM it approaches a final value of about 60 km/s/Mpc. That's the H in the eHt from my last post. It was much larger in the past. At the decoupling time (when the cosmic microwave background was emitted) the Hubble parameter was around 106 km/s/Mpc. During inflation it was... oh I don't know, but something very large. A random forum discussion I googled says 1052 km/s/Mpc, which seems believable enough. -- BenRG (talk) 18:48, 21 April 2009 (UTC)[reply]
Given the context, I assume you mean the "standard" one most commonly found in proteins? You can look at our Proteinogenic amino acid table and check the melting-point of each. In the more general sense, our amino acid article talks about their structure, and in particular the idea of a zwitterionic form and its physical properties. Is there a "rule of thumb" regarding being an ionic structure and having either generally high or generally low melting point? DMacks (talk) 01:52, 20 April 2009 (UTC)[reply]
Well, they decompose before they melt. But any covalent molecule is going to become a gas at sufficiently low pressure, isn't it? Looie496 (talk) 02:43, 20 April 2009 (UTC)[reply]
True 'nuf. I guess I was thinking "solid at room temp" and ignoring what actual other state or physical change occurs when they the solid falls apart:) A real question is whether they really behave as "covalent molecules" (implying neutral, not covalent ions) or as ions. For example, Glycine is fairly low molecular weight, but it listed as a decomposition (rather than melting) temperature of 233Ā Ā°C: there are clearly important ionic interactions and intermolecular stabilization. DMacks (talk) 04:24, 20 April 2009 (UTC)[reply]
Could we say that in (terrestrial) biological contexts, amino acids are always solids and almost always dissolved in water? ike9898 (talk) 20:00, 20 April 2009 (UTC)[reply]
The Zwitterion form makes amino acids more behaving like NH3+ caboxylates. Like most acid and amine salts they have higher melting points as the amine and carboxylic acid they consist of. So most of the amino acids I know are solids. --Stone (talk) 20:52, 20 April 2009 (UTC)[reply]
Solubility is interesting. Standard guide is "ionic stuff is water-soluble", but our amino acid article in the "Zwitterion" section notes: "Zwitterions have minimal solubility at their isolectric point and amino acids are often isolated by precipitation from water after adjusting the pH to their isolectric point." DMacks (talk) 21:01, 20 April 2009 (UTC)[reply]
Are there any (real) animals that can spit/spray corrosive substances as a defence mechanism?
Question as topic. When I say 'corrosive', I mean 'literally corrosive' (as in substances of the type mentioned in the linked article), not your run-of-the-mill toxic/foul-smelling compounds. I'm pretty sure that I once read about a species of spray beetle that has two specialized glands, producing two chemicals which are harmless alone but which when mixed together and concentrated into a high-pressure jet at the point of exit, form an incredibly nasty, highly-caustic substance (though I might be wrong). Thanks. --Kurt Shaped Box (talk) 01:45, 20 April 2009 (UTC)[reply]
I'm guessing it depends what you mean by 'literally corrosive' and 'defence mechanism'. The formic acid a number of ants use for defense (and offense) is I presume somewhat corrosive as with most acids although I expect it may not be the only (or even primary) compound in some cases. Fire ants use an alkaloid venom Solenopsin which has "cytotoxic, hemolytic, necrotic" properties. I'm not sure what the pH is but I'm guessing it's high enough that the substance could be considered literally corrosive even if that isn't a key part of the stings action. It seems the same it's the same for bee stings [15][16] while wasp stings are usually alkali (not sure what they contain). But in both cases, the same as with fire ants it's not really the key mechanism of action of their stings. Formic acid is also used by a number of other insects it appears [17]. As far as I'm aware, in none of these cases are the substances mixed outside the body, they're just (I presume) stored in specialised glands. Finally another example snake venom usually has digestive enzymes, would you consider them corrosive? Nil Einne (talk) 12:53, 20 April 2009 (UTC)[reply]
Well, if you put it that way... Yeah, gulls and fulmars can also spray their vomit at will when threatened. I guess that I was thinking more along the lines of species with defence mechanisms that work *primarily* by inflicting corrosive chemical burns upon a potential predator. --Kurt Shaped Box (talk) 00:06, 21 April 2009 (UTC)#[reply]
Hi, I am doing a physics problem, I am given values of , and T for some gas (assumed ideal) (note: it is done by web interface, values change every time) and asked to find the total translational kinetic energy of the atoms. The answer works out to be every time, and I'm not sure where that extra factor of 1/8 is coming from, could someone please help me? --130.216.30.234 (talk) 08:23, 20 April 2009 (UTC)[reply]
Also: related question (the one immediately following) is I am told that the balloon in the first part of the question (the one with of gas at and T) has been filled from some container containing of the same gas at and T, and asked how many of those same balloons could be filled using all the gas. The correct answer is always , or . There's that 1/8 again!! I have no idea where it's coming from! --130.216.30.234 (talk) 08:46, 20 April 2009 (UTC)[reply]
It is the correct answer. Either the answer you've been given is wrong, or there's some relevant feature of the question you're not telling us. Can you give us the exact wording, or just a link to the problem? Algebraist10:32, 20 April 2009 (UTC)[reply]
Okay, I was seconds away from posting it here when I just realised that I'm an idiot. In the original question, you had to calculate the volume of the spherical container using diameter, and I was not halving it before calculating volume, which of course would add an extra to my answers. Problem solved. Thanks for your time, everybody! --130.216.30.234 (talk) 11:34, 20 April 2009 (UTC)[reply]
Azimuth sweep angle?
In the game Call of Duty 4, in one mission we control the guns on a C-130 Spectre Gunship. A guy on the plane says a couple of times: "Recalibrate azimuth sweep angle, adjust elevation scan." What does it mean? And yes I'm the guy who asked the Coriolis effect and sniping question . Just a big fan of COD4. And thanks for your answers. āPreceding unsigned comment added by 116.71.54.217 (talk) 08:52, 20 April 2009 (UTC)[reply]
I first thought of posting this on the Language ref desk, then changed my mind. Isn't something grammatically wrong with this line from Speed of light:
"Francis Bacon argued that the speed of light was not necessarily infinite, since something can travel too fast to be perceived."Jay (talk) 10:43, 20 April 2009 (UTC)[reply]
The grammar is ok but the logic is questionable because the underlying hypothesis about "something" is not explicit. The OP could bring this up on the article discussion page to see what others think. Would the following sentence be better? "Francis Bacon argued that the speed of light was not necessarily infinite, since it could just be travelling too fast to be perceived."Cuddlyable3 (talk) 11:12, 20 April 2009 (UTC)[reply]
Yes, sorry about that. I should have said logically wrong instead of grammatically wrong. Cuddlyable3's version is making sense to me now. The meanings I had in mind were: "Francis Bacon argued that the speed of light was not necessarily infinite, since nothing can travel too fast to be perceived.", and "Francis Bacon argued that the speed of light was not necessarily infinite, since something cannot travel too fast to be perceived.", both meanings are opposite of the original line. Jay (talk) 11:29, 20 April 2009 (UTC)[reply]
I think it's vague about what is being perceived; I mean, light is definitely perceived so he can't be referring to that. I assume he's referring to the finite speed being perceived i.e it's really fast and we can't tell the difference between that and infinite speed. How about
"Francis Bacon argued that the speed of light was not necessarily infinite, since it could be travelling at a very large but finite speed which was beyond the scope of contemporary experimental accuracy."
I think you nailed it. Light is perceived as something instantaneous in all "normal" situations, but that is just an artifact of imperfect observation - and that was the point Bacon was making. --Stephan Schulz (talk) 11:49, 20 April 2009 (UTC)[reply]
It seems like the original quote implies that Bacon argued that it's possible to imagine a thing that travels imperceptibly fast but not infinitely fast, and that light might be one of those things. User:cuddlyable3's version could be less clear depending on what Bacon actually said. Cuddlyable3's version implies that he specifically theorized that light could travel very fast, but doesn't specify whether Bacon thought this was a special case or whether other items could also attain imperceptible speeds. I have no idea which is correct, but they don't mean exactly the same thing.
This guy at least included a direct quotation from (Francis) Bacon and a citation: "'Even in sight, whereof the action is most rapid, it appears that there are required certain moments of time for its accomplishment...things which by reason of the velocity of their motion cannot be seenāas when a ball is discharged from a musket' (Philosophical Works of Francis Bacon; J.M. Robertson, Ed.; London, 1905; p. 363)." The ellipsis is awkwardly placed, though, and I don't happen to have a copy of the Philosophical Works lying around in which to examine Bacon's full argument. Deor (talk) 17:01, 20 April 2009 (UTC)[reply]
I should have guessed that Google Books would have snapped this up. If one reads the whole chapter, one can say only that Bacon seems to be rather unclear whether he's discussing physics or physiology. Sometimes he seems to be maintaining that light has a finite speed; at other times, he seems to argue that it's our visual impressions that require time for their formation. And I admit to not being able to make much sense of his discussion of the idea that starlight takes time to reach us: he seems to say that he has discarded his initial suspicions that this is so, and now believes that our perception of stars is instantaneous. Deor (talk) 18:00, 20 April 2009 (UTC)[reply]
I don't think it's the light that's being not-perceived it's the speed of light. If you have a friend standing on a far distant hilltop with a mirror and you light a candle - the time it takes for the light from the candle to travel to the mirror and back again is too fast to perceive. Bacon argues that the time might not be zero - but merely so short that you can't perceive the delay...smart guy...he turned out to be correct! SteveBaker (talk) 16:58, 20 April 2009 (UTC)[reply]
Scooter electric motors
I know how electric motors work (I've had to build them by coiling wires by hand). I was discussing scooters the other day and I thought about coasting. A motor with high torque is hard to turn by hand if there is no power. So, assuming scooters use high torque motors to move a lot of weight with one small motor, are those scooters able to coast (free-spinning axle with no power applied to the motor)? If so, is there a special type of electric motor that allows for a free-spinning axle or is my memory of electric motors completely wrong? -- kainawā¢14:14, 20 April 2009 (UTC)[reply]
I would do it with a clutch - somewhat backwards than a slipper clutch. I was just wondering how it is done in real scooters (and I'd rather not hunt one down and take it apart). -- kainawā¢18:39, 20 April 2009 (UTC)[reply]
Unless there is some load on the engine, I don't see why it should be hard to turn. Where would the energy be going? Electric motors can be tough to start spinning, because the rotor settles in a low-energy state. But once you're out of the bottom of the potential well, you get back the energy if you slip into the next. It's hard to notice if you turn the axle by hand, but obvious if you install e.g. a flywheel. You can see a similar effect with hub generators in bicycles - if you do not attach a load, a free spinning wheel will go a long time. --Stephan Schulz (talk) 08:54, 21 April 2009 (UTC)[reply]
When you spin an electric motor, it acts like a generator - so if you have a load (like the battery of the scooter) connected to the motor - then it may be harder to turn. For coasting, all that should be necessary is to install a switch that disconnects one of the wires leading to the motor - and it should free-run without problems. SteveBaker (talk) 19:42, 21 April 2009 (UTC)[reply]
How is "coasting" on an electric scooter different from cruising at constant speed? Is the questioner referring to an electric bicycle, where the harder you pedal the faster the motor makes it go to supplement your efforts, or an electric motorcycle where the battery provides all the propulsion? Regenerative braking uses the motor like a generator to put energy back into the battery (way less than 100% efficiency) rather than slowing by friction in a brake which turns the energy into waste heat. I agree that an electric motor should turn freely unless the bearings are shot or a winding is connected to something to brake electrically. Edison (talk) 22:52, 21 April 2009 (UTC)[reply]
When 'coasting' (at least on level ground) your speed doesn't stay constant. It slowly decreases due to friction & drag. In order to cruise at constant speed, you have to supply energy to the motor. SteveBaker (talk) 01:42, 22 April 2009 (UTC)[reply]
If you live in flatland, there is little need for coasting. With hills, you use battery power by turning the accelerator to get up one side of the hill. Then, you coast down the other without any accelerator at all. Similar to a car - you press on the gas to go up a hill and take your foot off the gas to coast down the other side.
Steve mentioned something that caused my initial concern. An electric motor is also a generator. If you force the axle to spin, it creates electricity. Part of the energy is used to create the electricity. My understanding is that the electrical potential is there with or without a battery connected. As reference - try spinning a starter motor for a car by hand. It is very hard. So, if that was the motor for your scooter, when you let off the accelerator, the scooter would quickly come to halt. That is assuming that the motor is directly connected to the wheel with no clutch or slip gear of any kind. -- kainawā¢16:55, 22 April 2009 (UTC)[reply]
No, you're missing the point. It's only hard to turn a car starter if it's connected to something. If you unhook all of the wires, it spins quite easily (unless it's broken or something!). SteveBaker (talk) 19:52, 22 April 2009 (UTC)[reply]
Yes - that is exactly my question... I thought it was always hard to turn. Being easy to turn when disconnected means that it is possible (though may not be the case) that you could connect an electric motor directly to a wheel and when power is disconnected it will allow the vehicle to coast along. Perhaps a fancy circuit could be in place to recharge a battery while it coasts, as long as the load of the battery doesn't kill the ability to coast. That, however, is a completely different topic. I was only wondering about the motor's ability to allow for free spin. -- kainawā¢00:32, 23 April 2009 (UTC)[reply]
disappearance of gills in higher vertebrates and evolution of lungs (comparison with embryonic tadpole -> frog transition)
The whole process of an evolutionary mechanism in which the gills could be lost while the lungs developed seems kind of complex, because IIRC the gills are not evolutionarily homologous (or embryonically homologous) to lungs. So how would this sort of thing come about? Especially with the development of the circulatory system, since this would suggest a sort of fantastical rewiring that seems amazing to me -- suddenly you have to rerout the systemic and gill circulations back to the heart (whereas the gill circulation used to flow into the systemic circulation)? Can someone just clarify the whole process with me? Thanks. John Riemann Soong (talk) 17:45, 20 April 2009 (UTC)[reply]
(uh, What are you asking for clarification on? The maturation of tadpoles? Or the evolution of lungs? My reply here assumes that you're asking about evolution.)
Lungs and swim bladders did indeed evolve in addition to gills, probably in response to an environment featuring frequent oxygen-depleted water (such as lungfish inhabit today) to enable the fish involved to literally swallow air and absorb additional oxygen. However, lungs did not develop from earlier swim bladders: either the two homologous structures evolved as near parallel alternatives in two separate lineages, or (so I have seen suggested) lungs evolved first and then in some lineages that no longer needed so much supplementary oxygen (having returned to deeper waters?) they became swim bladders, still sometimes with oxygen absorbing capabilities but primarily now employed for buoyancy control. I love how often evolution repurposes organs for new tasks. 87.81.230.195 (talk) 22:59, 20 April 2009 (UTC)[reply]
Heart formation in a tadpole is a pretty damn complicated process. As far as I remember, it starts with one chamber and ends with three. For details, you can see, for example, Mohun et.al. "The Morphology of Heart Development in Xenopus laevis", Developmental Biology 218, 74ā88 (2000). --Dr Dima (talk) 04:58, 21 April 2009 (UTC)[reply]
Now, regarding your original question, the appearance of lungs and disappearance of gills occurred naturally with the transition from aquatic to terrestrial lifestyle. Some transitional, semiaquatic, or mud-dwelling species possess both lungs and gills. Axolotl - neotenicsalamander - has both lungs and gills, for example. By the way, vertebrates are not "special" in this respect. Coconut crab, too, has both gills and lungs, although gills are largely useless in an adult. --Dr Dima (talk) 05:14, 21 April 2009 (UTC)[reply]
As an aside - Coconut crabs are VERY cool. They often grow to three feet across and there are reports of six-foot coconut crabs - which are the kinds of thing you'd expect to see in old sci-fi movies! Kids in the area where they live keep them as pets and they can live for 30 years! Check out the article. SteveBaker (talk) 19:39, 21 April 2009 (UTC)[reply]
Witnessing evolution
I'm very interested in evolution, and I basically want to ask whether it's possible for someone who is not a scientist (I'm a university student though) to see evolution take place, and if so what would be the best way? Keep in mind that my knowledge of biology is rather limited but you would probably want to growing something like bacteria (possibly in a chemostat?), flies or fungi? I've heard of a fly experiment where a fly was given a different diet and in some 8 generations it had evolved. --BiT (talk) 18:30, 20 April 2009 (UTC)[reply]
Well, there are certainly experiments you can do with bacterial cultures that allow you to see evolution happening before your very eyes - but without some practical knowledge of lab techniques, I think they'd be hard for you to perform. 8 generations sounds a little short for the fly experiment - and in order for any evolution to happen at all, you'd need a very large number of flies to ensure a sufficiently diverse gene-pool. There are computer simulations of evolution that work fairly well. Richard Dawkin's "biomorphs" for example (see Weasel program). Google for "biomorphs" and you'll find several online versions of the program - and a bunch more that you can download for free. SteveBaker (talk) 21:05, 20 April 2009 (UTC)[reply]
Not sure how you would get access to a lab strain of E. Coli, but I agree that it's probably the easiest/most visible experiment you could try (the wiki page for it is here), due to the small size of bacteria and the extremely quick rate of reproduction, as well as the relative ease of culturing and "harmlessness" of the E. Coli itself. There are some other bacteria listed at Model organism. 124.154.253.25 (talk) 02:35, 21 April 2009 (UTC)[reply]
Yes, you could...theoretically. But one round of that test doesn't demonstrate evolution at all. A skeptic would rightly say that while 'Roundup' only kills 99% of plants, it's perfectly possible that the 1% survive by pure luck for environmental rather than genetic reasons. You'd have to go on and collect seeds from the survivors of that crop - grow them into plants and spray THEM with roundup in order to demonstrate a significant statistical improvement in the survival of the second generation - and thereby get any idea whether the roundup-resistance is inheritable. In fact, since it's highly likely that some plants are indeed surviving for environmental rather than genetic reasons - you'd probably need to do this over many generations in order to show a really convincing effect where 100% of plants survive being sprayed. You really need to prove a substantial increase in the percentage of plants that survive AND that this trait is inherited - or else all you've done is shown that some plants survive Roundup rather than that they EVOLVED a natural resistance to the herbicide. You might also need a VAST number of plants in each generation. If only one plant in a million carries some random mutation for roundup-resistance then you'll need to grow several million plants in order to have enough of them survive to make a million seeds for the second generation of the trials. Since the plants might take a year to grow to maturity and produce seed - this experiment could easily require acres of land and dozens of years in order to produce results.
That's why we do these kinds of experiments with bacteria - where an experimenter can easily have a few million bacteria available - and they reproduce and mature over hours rather than years. That's not to say that the experiment wouldn't work - just that you'd need to dedicate a LOT of money and years of your life to doing it using plant seed. SteveBaker (talk) 13:46, 21 April 2009 (UTC)[reply]
You would also need to be careful where you got your seeds - if they all come from the same, or a small number of, plants then there might not be sufficient genetic variation for any of them to survive due to genetic reasons (if you want to rely on random mutations, you need far more generations and a far larger population). --Tango (talk) 14:23, 21 April 2009 (UTC)[reply]
I was reading this. It says that one bit of semiconductor memory contains about 60,000 electrons. It struck me that that's a finite number of qubits. A qubit can only be determined once, so a bit of memory can only be read a finite number of times. You can use classical error correction to copy the bit of memory a bunch of times, but that just uses up your number of reads. This makes me suspect:
Any particular piece of information available on the Internet "degrades" (becomes less well-defined) over time as it's read. The more the information is distributed (Wikileaks :D) the less sure we can be of the integrity of the original and its copies.
Eventually we'll run out of information! Fortunately we have people typing on their keyboards and people uploading porn to 4chan, adding bits to the system. It's like Shannon entropy: my Linux box uses the unpredictable movements of my mouse cursor to increase the complexity of the parameters to its pseudorandom number generator. No outside input is a very bad idea. Without input the information on the hard drives and semiconductor memories of the Internet would degrade until they pass the manufacturer-guaranteed tolerances of their restoring logic and then you start losing information.
These are first impressions; what do you think? Can you only read a book a finite number of times before the information degrades? If you've already memorized it, is it really a "read" of the qubits? Is the repeated operation of a half adder (or a calculator, or a router) "reading" procedural information that will eventually degrade? .froth. (talk) 20:29, 20 April 2009 (UTC)[reply]
You're atempting to apply qubit theorems, like the No cloning theorem to classical bits. That's not really correct. There is really no limit to the number of times you can copy a classical bit. Dauto (talk) 20:44, 20 April 2009 (UTC)[reply]
And it's certainly the case that as a practical matter some bits in some computers are read trillions of times a day for years on end without problems and most of the bits on (say) Wikipedia are read maybe a few times a day at most...so the practical answer is also that this certainly isn't a problem. SteveBaker (talk) 20:57, 20 April 2009 (UTC)[reply]
There's no classical limit but classical bits are an idealization, right? The real world works in qubits, does it not? I know I'm mixing levels, that's the whole question: what do the qubit theorems mean for classical information theory? .froth. (talk) 01:25, 21 April 2009 (UTC)[reply]
A classical bit is consistent with many different quantum states. Quantum decoherence isn't a problem and the act of reading the classical bit will not change the bit (eventhough the quantum state will be changed), and you can read the bit as many times as you want. The qubit theorems have very little to do with classical information thory. Dauto (talk) 03:00, 21 April 2009 (UTC)[reply]
A qubit can be read any number of times and it will always give you the same result (in theory). Reading destroys the quantum properties of the qubit, but it doesn't destroy its classical value (0 or 1). Cloning and copying are different things. Copying means that if you started with a probability p of having a 0 and a probability q (=1āp) of having a 1, then you end up with a probability p of having two zeros and a probability q of having two ones. Cloning means that you end up with a probability p2 of having two zeros, a probability q2 of having two ones, and a probability 2pq of having a zero and a one. Both classical bits and qubits can be copied; neither classical bits nor qubits can be cloned. If classical cloning were possible then you could just read a single random bit from /dev/random and clone it to get as many random bits as you needed. In reality, if you need n random bits then you need to read at least n bits from /dev/random. The /dev/random driver has the same problem: it can't invent random bits to give you, it has to get them from somewhere. So there is a limited supply of randomness, and I think this is what you were talking about in your initial post. The randomness supply can run dangerously low on a standalone machine without good sources to replenish it (like a Winchester hard drive or a keyboard in active use). -- BenRG (talk) 13:25, 21 April 2009 (UTC)[reply]
Thanks for then clarification on the difference between cloning and copying. It is a relief to see that two completely different operations such as the reproduction of a qubit (cloning) and the reproduction of a classical bit (copying) receive different names. Dauto (talk) 14:49, 21 April 2009 (UTC)[reply]
I think you've misunderstood what BenRG was saying - he specifically talked about both quantum and classical bits being both cloned and copied, not one term for one and one term for the other. --Tango (talk) 22:17, 21 April 2009 (UTC)[reply]
I hear you. I heard him too. I just don't think what he said about cloning a classical bit makes any sense. A classical bit is either definitaly 0 or it is definitaly 1. It cannot be either one or the other with probabilities p and q=1-p. A quantum bit, on the other hand, cannot be copyed unless it's read first. And once it's read, the wavefunction colapses and it becomes a classical bit anyways. Dauto (talk) 22:43, 21 April 2009 (UTC)[reply]
"the Shannon entropy is a measure of the average information content one is missing when one does not know the value of the random variable" Yes classical bits too can have probabilities. And thanks BenRG that helps a lot. Basically you can copy bits, you just can't create new bits. Interesting.. algorithms can't create new information no matter how much procedural information the steps of the algorithm contain.. right? Can't map 5 bits of input into 6 bits of output. Fits in nicely with information entropy only increasing or standing still. .froth. (talk) 23:35, 21 April 2009 (UTC)[reply]
The inability to create information is well-known in information-theory - and mostly pre-dates all of this quantum stuff. If you think about it, that's not surprising because you can use some algorithm to take some set of source data and transform it into more bits of output data - but you could then compress redundant information out of the output by replacing it with the input - using whatever your algorithm is to uncompress it again on demand. So the actual information content of the output is no larger than the input. This is why computers can't generate proper random numbers without relying on some external input. It's been argued that this is why computers can never become intelligent - but that misses the point that humans are equally unable to create new information...it just seems like we can. SteveBaker (talk) 01:37, 22 April 2009 (UTC)[reply]
April 21
Bacteria passed on at birth: what about cloning?
I guess this question is equally valid for many species probably to be cloned in the near future, but it most directly concerns the Spanish Ibex previously "cloned" into a goat, and the Woolly Mammoth. I'm aware that the human body is host to a great deal more bacteria than there are cells in our body, and without most of those we wouldn't be able to survive, we may not even be able to call ourselves "human". Now I assume a lot of these are transmitted through the atmosphere, or possibly what we consume, but I can only assume that a lot of the more essential bacteria are passed on through the mother in the early stages of growth. When human cloning is concerned I don't see a problem as long as there is a surrogate mother, but with the Ibex and the Mammoth supposedly best cloned into some sort of a goat and an elephant, doesn't that cause major problems? I'm assuming that cultured bacteria are very different between species, but is that too much of an assumption? Also, even if it is possible in the future to clone and nurture to size an animal without some sort of surrogate, will the fact that they don't have access to native bacteria cause problems? Thanks! 124.154.253.25 (talk) 01:54, 21 April 2009 (UTC)[reply]
I seriously doubt that's a problem. For one thing, I believe your assumption that bacteria pass from mother to baby while the baby is still a fetus is incorrect. Most bacteria probabily colonise the baby after s/he's born. Besides the bacteria are different from person to person and that doesn't cause a problem, so I don't see how that's a problem. Dauto (talk) 02:44, 21 April 2009 (UTC)[reply]
I see. I guess I was under the mistaken assumption that there were bacteria essential (to the human digestive system), but apparently that's not the case, and we can live in sterile environments. (Now that I think of it, actually... that's pretty obvious!) According to gut flora though, some bacteria probably do pass from the mother to the baby during birth, but they are all incidental, and they will colonise the baby within the next few years anyway. Alright, thanks for the quick answer! 124.154.253.25 (talk) 03:05, 21 April 2009 (UTC)[reply]
I think bacteria in the gut are essential to the human digestive system (if you take lots of antibiotics you can get horrible stomach cramps due to the bacteria being killed off), but newborn babies only digest milk and aren't capable of digesting anything else - perhaps bacteria aren't required for digesting milk. There is plenty of time for bacteria to colonise the baby before they start eating solid food. --Tango (talk) 13:04, 21 April 2009 (UTC)[reply]
Columbus's New World "nightingale"
Christopher Columbus thought he heard the song of a nightingale not long after he landed in the Americas, where there are no nightingales. What kind of bird might he have mistaken for one? 69.224.37.48 (talk) 02:05, 21 April 2009 (UTC)[reply]
Possibly Catharus sp., not sure. In fact, I am not even sure the story is true. The version I know is Columbus saying "the only thing missing is a nightingale song", meaning he's confident the land is close. The two stories are not necessarily contradictory, though. Sorry. I wish I could help more. All the best, --Dr Dima (talk) 04:45, 21 April 2009 (UTC)[reply]
Gut flora
My wife and I were having a conversation today about gut flora, so I decided to read the article here. One bit in particular confused me a bit and I'd appreciate an explanation if you could...
The article states:
Immediately after vaginal delivery, babies have bacterial strains in the upper gastrointestinal tract derived from the mothersā feces.
Since I don't have any kids, I'm a little unclear on how bacteria from the mother's feces could get into the baby. I thought that expectant mothers were given a laxative to flush the bowels so that they don't eliminate during the birth. I also thought that the vaginal area in general, including the anus, would be cleaned before delivery. So, could someone clear up my confusion? (I realize that birthing procedures are different around the world due to varying sanitary conditions and such but I'm guessing that the reference (which I can't read from where I am) for this sentence deals with babies born in modern hospitals.) Thanks, Dismas|(talk)05:31, 21 April 2009 (UTC)[reply]
And having just read up from my question, I didn't realize that we had another, though different, gut flora question here today. Dismas|(talk)05:33, 21 April 2009 (UTC)[reply]
It was in relation to our new puppy and his diarrhea. When you have as many animals as we do, you get into some interesting conversations. Ā :-P Dismas|(talk)08:42, 21 April 2009 (UTC)[reply]
I think that there will be some (probably very few) faecel bacteria in the birth canal. I remember hearing that children born by caesarean have a higher occurence of allergies which is possibly associated with the lack of bacteria during delivery. Smartse (talk) 12:49, 21 April 2009 (UTC)[reply]
Actually, there are three parts to this: the existance of the gut bacterias, the transferring into the baby and the cleaning away of them that you describe. Naturally, some gut bacteria is present on the skin of the mother. There are so many zillion bacteria, that getting every single one off after a normal visit to the toilet is impossible with just wiping. These are in or close enough to the birth canal to be transferred to the baby either directly when the face passes or inderectly via hands, towels etc. In "modern" hospitals you say, mothers are cleaned. As a matter of fact, with the knowledge that bacteria is indeed most often healthy in these circumstances, Swedish hospitals have stopped sterilizing the mother with alcohol ahead of delivery. If some feces are pressed out during delivery (laxative is optional), it is simply wiped off. For the same reason, the baby is not cleaned after delivery, but just wiped off to keep the natural fat, bacteria and mucus on the skin - and nipples should not be sterilized either. -Mummy āPreceding unsigned comment added by 195.67.112.146 (talk) 12:11, 22 April 2009 (UTC)[reply]
I think it is zero for Spur gear and it could be anything less than 90 degrees for helical gears, although for practical purposes it is never even close to 90 degrees. It is the angle which the helix of the gear makes with the plane perpendicular to the longitudinal axis of the gear. Correct me if I am wrong. - DSachan (talk) 19:04, 21 April 2009 (UTC)[reply]
A quick Google check says that these are German standards. You'd probably have to be lucky to find anybody here who knows about them. Looie496 (talk) 21:09, 21 April 2009 (UTC)[reply]
What factors impose the ~550 m limit on the length of a 1000BASE-SX link? Is it modal dispersion, attenuation? What is the influence of chromatic dispersion in this kind of transmission? What is the bandwidth of a 1000BASE-SX signal? What are the alternatives? I've already read the Gigabit Ethernet article. Thanks in advance for your answers. 93.108.139.109 (talk) 11:07, 21 April 2009 (UTC)[reply]
Normally the range is limited by modal dispersion in multimode fibre. The range can be down to as low as 300m. Different paths of light in the fibre results in a bit being smeared out in time, and running over following bits. You can get increased range by using OM3 fibre rather than OM2. Or you slow down to 100meg and get 2km range. If you go single mode, by using single mode laser GBICs and single mode fibre, you can get much longer range, 10 km at 1310nm or further at 1550nm wavelengths. Graeme Bartlett (talk) 21:21, 21 April 2009 (UTC)[reply]
The encoding uses 8b/10b encoding which expands data rate to 1250 Mbps. The Nyquist theorem says that the minum bandwidth is half this. Just imagine a 1 and a 0 in a square wave making up one cycle of a wave. So that is 625MHz bandwidth. In practice it is a square wave and there will be odd harmonics as well. Graeme Bartlett (talk) 03:24, 22 April 2009 (UTC)[reply]
Which makes it a bit more difficult to cram for my orgo final ... I'm trying to keep track on when you would have to use aqueous solvents and what polar aprotic solvents to use, especially when you're using hydrogen halide gases. Would methylene chloride be suitable here? But you're adding peroxide, which I imagine may want aqueous solution, or would methylene chloride be suitable for distributing the peroxide too?
You are using Wikipedia articles to cram for your final exam? Man, you are in real trouble. A suggested order of preference for cramming for a course is a) your own notes b) the notes of someone else in your class c) the notes of anyone who has ever taken the course d) your textbook e) someone else's textbook f) any textbook on the same subject g) online lecture notes on the same subject h) Wikipedia i) X-men comics. DJ Clayworth (talk) 14:22, 21 April 2009 (UTC)[reply]
Protic solvent talks about some reaction solvent effects. It would be great if someone added info about solvent effects to the major orgoI/II-level reaction pages themselves. But here's the key: if you actually know a reaction mechanism (and there are only really like a half-dozen of them in all of organic chemistry!), it's easy to figure out what types of solvents are good or bad and you don't have to memorize these last-minute details...it really is easier to learn along the way! I'm with DJC here...if you're cramming, getting a broader perspective, learning about related ideas, etc are totally not what you're looking for, You just need to get 70% (I assume) of the the bare minimum info required for this specific exam. You don't care about anything except what is exactly part of the course as taught, so anything other than "stuff that is part of the course" (textbooks, notes, etc.) is only going to have the info you do want scattered among stuff you don't, and might not have the minute details or some special case that your prof has chosen as important for your course. DMacks (talk) 15:02, 21 April 2009 (UTC)[reply]
DNA sequencing
Hi all I am having trouble trying to understand the process of DNA sequencing. I've read the article on DNA sequencing but I am still a little confused so I hope that someone can help explain a few things to me. I understand that at the beginning there is a single strand of DNA and a primer joins on. The primer tells DNA polymerase where to begin transcription. The growth of the chain which begins with the primer is halted due to a dideoxynucleotide being incorporated into the sequence. Thats about all I do understand. Is there just one strand of single stranded DNA or lots of little single strands at the start? How does using radioactive or fluorescent nucleotides result in being able to tell the sequence of bases? If someone could give a brief explain DNA sequencing or tell me about any websites which may be of use that would be great. Thanks. āPreceding unsigned comment added by 92.18.166.121 (talk) 15:06, 21 April 2009 (UTC)[reply]
There are numerous primers and single strands in the mix at the beginning of the reaction. It proceeds essentially like PCR. Due to the presence of the terminating nucleotide, every conceivable length of polynucleotide based on size will be produced in the reaction. Because there are different color fluorescence probes for each nucleotide, an analyzer can read the bands on a gel. Each band represents a different size length. The machine simply reads from smallest to largest using the colors for the nucleotide. Wisdom89(T / C)15:11, 21 April 2009 (UTC)[reply]
Just a comment (slightly offhand), but Viruses aren't really considered alive..it's the whole obligate intracelluar parasite definition. That may be a reason why they do not exist in the fossil record. Wisdom89(T / C)15:55, 21 April 2009 (UTC)[reply]
Well, the reason they don't exist in the geological record is because they are too small to form recognizable fossils and their molecular components can't survive for geological times, even in the rare LagerstƤtte that preserve soft tissues. There are "genetic fossils" consisting of viral DNA that has been incorporated to the genomes of living organisms, but it's hard to see how that can be used to date viruses further back than 500 million years at the very most. Looie496 (talk) 16:13, 21 April 2009 (UTC)[reply]
Yup, excellent point - I was going to mention the small size, but my first instinct was "alive"? That seems to be the first thing people think of when viruses are mentioned.Ā : ) Wisdom89(T / C)16:21, 21 April 2009 (UTC)[reply]
And classification is based on things such as the nucleic acid composition/sero markers/envelope etc.. and actual morphology - the latter only being successful with the advent of electron microscopy me thinks, and the former with molecular genetics. Wisdom89(T / C)16:37, 21 April 2009 (UTC)[reply]
If the furthest back that viruses can be dated is 500M years, where does the assertion that they probably existed as long as living cells come from? 65.121.141.34 (talk) 18:23, 21 April 2009 (UTC)[reply]
There is no evidence of when the first viruses arrived, and only indirect evidence for viruses on any timescale that isn't virtually now. That said, viruses are so simple (evolutionarily speaking) that it seems logical to predict that they would have arisen not long after the evolution of the first cells. Dragons flight (talk) 18:58, 21 April 2009 (UTC)[reply]
For sure we're not likely to find direct evidence for them. To the degree that they inadvertently dump pieces of their DNA as 'junk' sequences into that of 'normal' lifeforms, we can look back and say things like "this exact sequence of base-pairs appears in horses, dogs, people, koala bears and elephants - so it must have been from a virus that was around before the common ancestor of all of these animals"...if (for example) we found the same "junk" viral snippet in all plants AND all animals AND all Fungi, Bacteria, etc - then we'd be in a position to strongly suspect that this virus was around at the very beginning of life. But that is rather indirect evidence. SteveBaker (talk) 19:26, 21 April 2009 (UTC)[reply]
Or alternately instead of a common ancestor, perhaps a virus infection has transferred the genes from one species to another. This would appear more likely if the gene was missing from most other organisms. This happens with bacteria transferring genes to unrelated bacteria. Graeme Bartlett (talk) 21:02, 21 April 2009 (UTC)[reply]
The best chance to trace back viruses would be by their pathogenesis. It is not uncommon to find signs of disease or trauma in the fossils. I am not aware of any fossils that exhibit clear effects of viral disease of any sort, but that certainly does not mean there aren't any. In any case, I am talking about plants and animals that actually leave fossils large enough to be studied for the signs of any pathology. Viruses probably evolved long before that. --Dr Dima (talk) 20:22, 21 April 2009 (UTC)[reply]
Your argument doesn't make sense. Not all DNA comes from viruses, so the DNA shared between those species could just have come from a common ancestor originally. If two species share a bit of DNA but another species known to be in the smallest clade containing the first two species, then that might be evidence that both species were infected by the same virus some time after all three species split. (It could also be explained by mutation in the 3rd species, of course, examining more species would be required to get a conclusive result.) --Tango (talk) 12:21, 22 April 2009 (UTC)[reply]
To me, the most compelling evidence is the tropism that different viruses have for certain organisms, suggesting a very long period of coexistence.
Mimivirus is a virus found in infect primitive unicellular organisms like amoeba
There are numerous examples of viruses that affect only animals (and sometimes very specific species)
One possible explanation for this finding is that viruses existed as early as the primitive cells that were the common ancestors of all major branches of the tree of life, and then evolved in parallel with a group of organisms, gradually becoming selective for the replicative machinery or cellular physiology of that specific group. An alternative explanation is that viruses popped into existence at some point when all the major taxonomic groups were established, and somehow then became specific for those distinct kingdoms and phyla. The first of these is the simplest explanation (which as scientists we tend to like the best) -- that viruses "have probably existed since living cells first evolved." The mimivirus article suggests that it may even predate cellular organisms. --- Medical geneticist (talk) 21:02, 21 April 2009 (UTC)[reply]
Are all viruses harmful? Because if they were, and viruses just popped into existence wouldn't they basically kill species too fast for them to develop an immunity to them? An immune system wouldn't even know what a virus was. So I think the spontaneous virus appearance could be discounted. 65.121.141.34 (talk) 13:24, 22 April 2009 (UTC)[reply]
Right, this is my point -- there's a balance between the ability of the virus to enter the cell, replicate itself, and destroy the host cell (what you might consider being "harmful") with the ability of the organism to detect and destroy the virus before too much damage is done -- and this balance has been achieved over millenia of evolutionary "warfare" between viruses and their hosts. Often the viruses are so specific for the cell surface molecules expressed in their natural host species that they are completely incapable of gaining entry into cells from another species. However, consider what happens when a virus is able to move from its normal host into a host from a different species, usually the new host doesn't cope very well with the infection because the immune system has never "seen" anything like it (examples include bird flu and other zoonotic diseases). I only proposed the "alternative explanation" of viruses "popping into existence" to show how poorly this would explain the observed situation of host tropism. --- Medical geneticist (talk) 13:40, 22 April 2009 (UTC)[reply]
Things like viruses and bacteria that make a living by making other lifeforms sick have to be very careful not to kill off their hosts too rapidly or else they'll be unable to spread. I saw a study a few years ago about how "new" diseases are often extremely lethal for the first year or so - but then gradually lose their potency. That's because the disease organism is evolving. The bacteria/virusses that kill their hosts within hours have a very tough time spreading because the host doesn't have time to get close to enough others of it's kind to pass on the illness before it drops dead. Those bacteria/virusses have a hard time passing on their genes once the host dies - so the less virulent amongst them that allow their host to continue to live and (importantly) get close to others of it's kind - will be the survivors. So I don't think you can assume that all of life would be annihilated on the very first occasion it encountered a disease virus...evolution doesn't work like that. SteveBaker (talk) 19:49, 22 April 2009 (UTC)[reply]
I don't think anyone made the assumption that "all of life would be annihilated on the very first occasion it encountered a disease virus". But when viruses jump from their normal host (in which they've evolved to balance their ability to propagate versus the damage to the host, as you very correctly point out) into a new species, we often see horrible, horrible diseases like SARS, West Nile encephalitis, hemorrhagic fever, or Ebola. NOTE, however, that even in these terrible illnesses only a fraction of the infected individuals actually die, it's just that the fraction of people that DO die is much higher than other viral illnesses to which our immune systems have evolved to cope with. --- Medical geneticist (talk) 14:27, 23 April 2009 (UTC)[reply]
It is a common misconception that viruses are either inherently pathogenic or cytopathic. Viruses with those properties have been studied intensely for obvious reasons, and historically it was hard to discover and study viruses so efforts were focused on the ones that caused disease (pathogenic) or easy to identify (killed/injured cells in culture = cytopathic). More recently, it's become clear that we're awash in viruses that cause no apparent disease. Notable examples include GB virus C and TTV. These viruses don't appear to kill the cells they infect, and don't harm the people whom they infect (to our knowledge). In the past, we'd never have known about them, but with PCR it appears that most of us harbor TTV, for example. So, virus does not intrinsically equal disease or cell death. It seems likely to me that most viruses don't cause any disease - they just propogate quietly. --Scray (talk) 04:59, 23 April 2009 (UTC)[reply]
This is an excellent point, and it is another great piece of evidence that viruses (not to mention bacterial commensals) have been co-evolving with their hosts for millenia. --- Medical geneticist (talk) 14:27, 23 April 2009 (UTC)[reply]
Increase in rolling resistance on a wet road?
This question has been bugging me for a while, and I'm unable to find any figures on the net about this. When a car travels along a wet road, the tyre acts as a "pump" to move water away from the contact patch of the tyre. This uses some of the kinetic energy of the car, although some presumably is recovered as the water flows back in to the space behind the tyre, pushing it a little. Also, presumably, the majority of this energy is used in the process of moving this water out of the way of the tyre, heating the water, atomizing it into a spray and producing the characteristic noise associated with cars on wet roads. Not to mention the "stickyness" of water causing extra friction.
Does anyone have any figures for how much energy this process takes? For example, what kind of economy penalty can I expect in an average car at a given speed?
Certainly it's very noticable how a car slows down faster if you put it into neutral on a wet road than on a dry one - and if you run through a deep puddle in a small car, you can really feel it slowing you down. So there is certainly an effect - and for water in maybe the quarter-inch-or-deeper range, it's gotta be pretty significant. As for quantifying it...I've never seen anything like that out there and a Google search on likely terms didn't turn up anythink of use. The figures for aircraft tyres may not be comparable. Aircraft tyres are optimised for going in a straight line and not imposing too much drag on takeoff - where car tyres have to cope with the much more tricky business of cornering. If you look at an aircraft tyre, you'll see it has a simple circumpherential tread pattern with none of the fancy zig-zag or diagonal grooves you see in the tread patterns of cars - and that suggests to me that pumping water out from under the tyre isn't so important to them. So I don't have a good numerical answer for you - beyond that it must be reasonably large because of the degree of deceleration you feel when you coast through even a half-inch-deep puddle and that you can't use the aircraft figures. SteveBaker (talk) 20:07, 21 April 2009 (UTC)[reply]
Another difference between cars and planes which may be relevant is that the wheels of a car are its means of propulsion, they aren't on a plane. (Which is why, as we all know by now, planes can takeoff on a treadmill running backwards at takeoff speed.) --Tango (talk) 23:34, 21 April 2009 (UTC)[reply]
Just one data point.. I've noticed a decrease in highway mileage, often significant, in rain. Say, down to 28mpg from a more normal 32. Friday(talk)20:09, 21 April 2009 (UTC)[reply]
Yes - although some of that would be increased drag due to the raindrops effectively increasing the density of the air...also, you're running your wipers and (hopefully) your headlights - although that won't make a lot of difference to your mpg numbers. SteveBaker (talk) 01:16, 22 April 2009 (UTC)[reply]
Tire treads have aggressive cross-cuts or grooves to provide a place for the surface water to go so that "the rubber meets the road" and provides traction. Does this cause the tire to do work by lifting water from the pavement and presumably throwing it out sideways to make room for the water in the next rotation? If so, then the tire is acting as a pump, and the car engion or the kinetic energy of the car is the source of the energy, causing the car to slow down or requiring greater fuel per distance driven. Edison (talk) 14:10, 22 April 2009 (UTC)[reply]
Yes - that's exactly the mechanism - but it's hard to estimate the magnitude of it in order to answer the OP's question. Knowing the depth of the water and the speed of the car and the width of the tyres - we can figure out the amount of water that's being "pumped" away by the tyres - but we don't know how much kinetic energy that water leaves with - so we can't really figure out how much energy the car loses in doing that. We certainly know it's bigger than zero...but beyond that??? SteveBaker (talk) 19:42, 22 April 2009 (UTC)[reply]
The Beauty of the Universe
I might have the wrong section, please direct me to the right area if I do.
I was looking at photos of the Universe, specifically of Saturn's moon and rings, and I was completely awe-struck by it. You know, a deep down feeling that something is incredibly beautiful. I was not alone. The website's commentators made many similar remarks. They too don't seem to be alone. In general, it seems like most people find "beauty" in outer space. Here's my question, and it deals with the anthropology side of evolution. If humans evolved beauty in response to let's say conditions that promoted life (ex. a lake provides water ... landscape of a lake looks beautiful), why is it that things beyond our world, things that can't provide any form of subsistence strike such a note inside of many humans? āPreceding unsigned comment added by 24.131.131.5 (talk) 20:52, 21 April 2009 (UTC)[reply]
Is it beauty you are perceiving or awe? You use the term "awe-struck", which is how I would describe myself when, for example, I first saw the moon through a telescope. I think there is a difference between awe and beauty. Beauty (in this context) is a purely visual thing, but I think in order to be awe-struck by celestial objects you need a certain amount of understanding of what they are. You have, however vague and imprecise, a sense of the size and distance of the thing you are looking at - I think that is an important factor. I'm not sure what the evoluntionary benefit of awe is, though, so I can't really answer your question, just ask a slightly different one! --Tango (talk) 21:56, 21 April 2009 (UTC)[reply]
The question is pertinent in matters closer to home, I think. When did a person first look at a range of snow-capped mountains and find it beautiful, rather than simply forbidding? What was up with that?
I once read an account of a troop of chimpanzees, working their way through a jungle. They emerged into a sudden clearing, and beheld a humongous waterfall with water cascading great distances over rocks. Very dangerous. They started shouting, and jumping, and looking at it, and reacting with... what was that? Is it somewhere on the continuum towards an aesthetic sense? Impossible to say, I'm sure. -GTBacchus(talk)22:02, 21 April 2009 (UTC)[reply]
I believe I came across something a while ago that said the Romans and Greeks normally regarded forests and nature generally as threatening rather than beautiful, and the modern thing in the West of seeing nature as beautiful started quite recently with Romanticism in the 18th century. Dmcq (talk) 22:40, 21 April 2009 (UTC)[reply]
You respect and fear the enemy's strength; fearing big dangers is obviously advantageous. It turns to beauty and awe when you fear and admire your alpha male or chief, and promote the most fearsome warriors to high position. Being fearsome becomes favored (aesthetically pleasing)... so huge objects convey might and you hold them in awe. 72.236.192.238 (talk) 23:18, 21 April 2009 (UTC)[reply]
astronaughts
Well, to rain on the parade a bit, there are vast numbers of things in space that are utterly boring. You don't generally see pictures of them. And even for the things you do see pictures of, the colors are often greatly enhanced. Looie496 (talk) 00:15, 22 April 2009 (UTC)[reply]
To me, there was no danger in viewing the object. I understand my own feelings of danger or vulnerability. I've seen photos of astronauts in space juxtaposed to the looming Earth. There a simple sense of vulnerability and empathy for that man consumed my thoughts. Rather, when I saw the picture of Saturn's moon, with its craters and pale white color, without any coaxing, I felt that it was beautiful and like I said I was awe-struck. The image was viewed upon a 17 inch monitor, consuming maybe 1/2 of the screen. I don't think I feared its size, nor felt in anyway that it resembled a human that I might fear.
I think it's mostly observer bias. If you are an astronomer - in any given year, maybe you'll take hundreds of thousands of photos that are basically white dots scattered at random on a black background - and a couple of gaseous nebulae with unusual dust formations, etc. Which ones get nice names like "The Horsehead nebula" and go on your web site...and which ones get some six digit serial number with the date on the end and are kept in your large collection of other similar pictures that nobody ever sees?
Also, they have a lot of control over the look of the things. Most scientific data is collected in regions of the electromagnetic spectrum that humans can't see - so the "photos" aren't really photos at all - they are the result of running a bunch of computer programs on a string of numbers. You can make the colors come out any way you want - you can enhance the 'pretty' bits and tone down the 'ugly' bits. While you probably won't do that for the purpose of extracting scientific information - when you are preparing an image to put on your web site or the cover of your next book - you're very likely to set the software up with some pretty pastel colors and tweak them until it does look beautiful. There is no "right" or "wrong" when it comes to using "false color" techniques. So what you are seeing isn't that all of space is somehow beautiful - you're seeing just the bits that someone who stares at these things all day long finds beautiful...tweaked to make them look even more beautiful. It's no surprise that the results are usually pleasing. SteveBaker (talk) 01:12, 22 April 2009 (UTC)[reply]
Erm. I'm 100% sure these weren't enhanced by the computer. I was looking at a picture of Saturn's moon. It might have been cropped for dramatic effect, but it still doesn't change the emotional response I observed. āPreceding unsigned comment added by 24.131.131.5 (talk) 01:34, 22 April 2009 (UTC)[reply]
I'd be VERY surprised if the image you're thinking of was taken in Red/Green/Blue light at normal intensities and displayed with nothing more than cropping - they simply don't put that kind of instrument onto deep space probes because RGB photographs simply don't contain much that's of scientific benefit. The image was probably taken in IR or UV or with a monochrome camera using some combination of polarizing filters or something. If you're "100% sure" - tell us (in detail) how come you're so sure - because I'm REALLY sure you're 100% wrong! SteveBaker (talk) 04:02, 22 April 2009 (UTC)[reply]
Care to tell us what image you're talking about? To me, most pictures of Saturn's moons look like relatively boring lumps of rock. Sometimes lumps of rocks with an equally boring gray line behind them. (Except the one that looks like the Deathstar.)
One things that moon and asteroid pictures usually do have going for them is that they typically have pretty dramatic lighting. I'm not sure if that makes them "beautiful", but it certainly makes them striking. APL (talk) 03:35, 22 April 2009 (UTC)[reply]
Oh, actually, there's a very dramatic image of Mimas (The deathstar look-alike) that's just as you described, right on the Mimas page. It is a great image. It's aspect ratio will make it a good background image for my tablet PC. However, be aware that this is not a natural color image. Instead of Red/Green/Blue, it was taken in IR/Green/UV. The colors had to be adjusted to look approximately correct. (Here's a similar image in true color.]) APL (talk) 03:51, 22 April 2009 (UTC)[reply]
Yeah - there is no way an image like that has not been processed in some way. As our caption says - it was photographed in IR, Green and UV light - not Red, Green, Blue - and the interpretation of those three frequencies into light that we can see is largely an artistic matter. SteveBaker (talk) 04:02, 22 April 2009 (UTC)[reply]
Cassini's "red, green and blue" filtersI've been curious for a while about how true NASA's true-color images really are, so I went and tracked down the actual spectral response curves for Cassini's filters. They're available here. The description of "Nature's Canvas" (which APL linked above) says that it's a true color image made using red, green and blue filters. The source images are [19][20] and [21], which were taken through the RED+CL2, CL1+GRN, and BL1+CL2 filter pairs respectively. (CL1 and CL2 are clear filters.) On the right is a plot of the camera's frequency response curve with those filter pairs in place. The horizontal scale is wavelength in nanometers. I'm not sure what the vertical units are but I think they're CCD electrons per incoming photon. The vertical scale is linear and the maximum is around 0.23.
One interesting thing about these filters is that, compared to the human eye, they have very little ability to distinguish monochromatic colors. For example, they can't tell the difference between blue and violetāthey both show up as a nonzero value in the BL1 channel and zero in the other two channels. There might be a little bit of variation in the brightness of the BL1 channel, but that doesn't help because there's no way to tell the difference between a change of wavelength and an actual change of brightness. There's also no frequency discrimination in the 500ā570 nm and 640ā730 nm ranges, and very little in the red-yellow range where the RED and GRN filters overlap. If the value in the BL1 channel is zero and the values in the GRN and RED channels are nonzero and roughly equal, the spectrum might have a single peak somewhere in the red-yellow range (which a human would perceive as red/orange/yellow) or it might have a peak in the infrared and another in the 500ā570 nm range (which a human would perceive as green or cyan). There's no way to be sure. So you can't, strictly speaking, produce a true-color image from these filters.
On the other hand, real-world spectra are pretty predictableāthey don't vary much across the visible range. If you can come up with a model with only three adjustable parameters that approximates the spectra you actually expect to find in the scene, then the values from the BL1, GRN, and RED channels together fix the parameters of the model, and from that you can work out sRGB coordinates. A simple example would be to model the spectrum (in units of photons/mĀ²/s/nm) as a quadratic function of the wavelength. I actually tried doing this and got
(where I've applied an overall normalization to the matrix so that the largest entry is 1). So in this simplistic model you can pretty much plonk the BL1 data into the blue channel, but the red and green channels are more complicated. There's also the fact that I don't know how the CCD electron counts are related to the pixel brightness in the raw JPG/TIFF images, and this calculation gives you linear sRGB values which need to be gamma corrected, and my model isn't very good, and I probably made a mistake in the calculation. But anyway this gives the general idea of what you have to do to compose the raw images into something that might (if you used the right model) resemble true color. Note that you can get better color accuracy by using more than three filters, even though there are only three output channels, because with more inputs you can fit more parameters. The only exceptions are if your model is perfect already or you have three filters that are independent linear combinations of the human cone responses (in which case the model is irrelevant). You could produce a true color image from IR/Green/UV channels by this technique if you had a good enough model. I have no idea whether the official NASA images are really produced this way, though. I get the impression they do a lot of retouching to get the colors right, though in that case I don't understand why they use three source imagesāif they know the right colors beforehand, couldn't they just colorize a single one?
Incidentally, if you look at the three source images you'll notice that Mimas moves significantly against the background rings, so there was a fair amount of non-color-related Photoshopping required here too. Even more so with the sources for "Mimas blues" ([22][23][24]). Not that there's anything wrong with that, it's just interesting. -- BenRG (talk) 00:48, 23 April 2009 (UTC)[reply]
One reason why we think some astronomical objects are pretty is symmetry. Saturn's rings are rather symmetrical, as are the arms of a spiral galaxy. A planet or moon in a pic that shows no detail looks pretty, too. When you get to a resolution that shows the pockmarked craters and such, they don't look quite so pretty any more. So, then, why do we have this preference for symmetryĀ ? Since many biological systems use symmetry, a symmetrical plant, animal, or person is more likely to be healthy, so a better choice to eat, own, and/or mate with. StuRat (talk) 15:40, 22 April 2009 (UTC)[reply]
how much biological output is produced (by either weight or volume) daily by all of the world's population combined?
I've tried not to be too direct, but you can skip this question if you are having dinner or something. My question is: how much biological output is produced daily by all the people of the world combined, per "type". Either by weight or by volume.
This is surprisingly hard to find, I tried googling both total, and average production for both types using several phrases but could not find any numbers at all. Any ideas? 94.27.218.161 (talk) 21:28, 21 April 2009 (UTC)[reply]
By "biological output", do you mean feces and urine? And by "world's population" do you mean human population? If so, according to urine: "In adult humans the average production is about 1 - 2 L per day." Since there are about 6.8 billion people in the world, that comes to a total of about 7-14 litres/kgs of urine per day (actually, it's probably a little less since children presumably produce less than adults). I can't seem to find the appropriate numbers for feces, though... --Tango (talk) 21:46, 21 April 2009 (UTC)[reply]
I think you missed a rather important "billion" in your answerĀ :) In terms of faeces a roundabout figure would be 500g/person/day which gives about 3.5 million tonnes per day... NICE! Smartse (talk) 21:16, 22 April 2009 (UTC)[reply]
The OP said "both types", so we're looking for just two types. Feces and urine seem to be the most obvious two. --Tango (talk) 21:52, 21 April 2009 (UTC)[reply]
Food statistics might be easier to find (and nicer to contemplate) than waste statistics. I would assume that the total mass excreted as feces is less than the total mass ingested as food. If you assume that my daily poo weighs... one half as much as my daily bread? You'd probably be accurate within an order of magnitude, and this kind of calculation isn't going to be much more precise than that anyway, right?
More direct information about volume of waste might be available by considering a city and how much waste is treated daily - something else you could probably look up. -GTBacchus(talk)21:54, 21 April 2009 (UTC)[reply]
The total excreted as feces and urine will be less than the total consumed as food and drink, I'm not sure you can simply separate the two, though. Feces is mostly water, whether that is water that comes from the food, or whatever that comes from drink is difficult to determine (or even define). The waste processed by a city will be mixed up with lots of other stuff (mostly water from the mains supply and rain), so I doubt you'll get useful figures from that. --Tango (talk) 22:14, 21 April 2009 (UTC)[reply]
What about handling the question as if it were asked like How much inorganic matter is turned into organic matter by the Earth's biosphere daily?āPreceding unsigned comment added by 131.188.3.20 (talk) 00:27, 23 April 2009 (UTC)[reply]
Cancer
Obviously, everything that exists in this world consists of specific elements, thus giving us it's molecular, or empirical formula. Now if we look at anything along with it's molecular/empirical formula, that certain thing consists of a "geometrical chemical shape." So, if everything has it's own shape, everything can be cured with some form of conversive, contradicted, form of that matter, which is what we call medicine.
--
So, TO MY QUESTION, does cancer have a molecular, or empirical formula? and if so, can you lead me to a site with it's geometrical shape?
No. Cancer is made up of cells, just like any other living tissue. The difference between cancer cells and other cells is just that cancer cells reproduce out of control. The difficulty with curing cancer is that the cancer cells are very similar to the non-cancer cells and you have to come up with a way to kill the cancer without killing the patient, which is very hard to do. --Tango (talk) 22:11, 21 April 2009 (UTC)[reply]
You have a basic idea, which is correct, that every substance is composed of specific elements which form molecules. However, the point you appear to be missing is that cells are made up from billions and billions of these molecules. Cancer is a process which affects cells as a whole, and cannot be treated by a lock-and-key mechanism which you appear to be describing. Instead, cancer must be treated by either limiting damaged, uncontrollable cells replication, or by killing off those cells which are damaged. I recommend you read up on cell (biology) which should give you an insight to what cells are composed of. If you have further questions, feel free to come back. Regards, --āCyclonenim |Ā ChatĀ 22:44, 21 April 2009 (UTC)[reply]
Okay, but even if cancer is made up of cells, don't these cells contain specific elements? And just like other viruses or bacteria, can medicine not be produced to react with these compounds that would cause the inactive cells in cancer to "undo" their inactiveness, and make them re-active, or turn them into another type of matter that would be helpful and plentiful to the body? If we could find the molecular formula, could we not change these cells into matter that would nuture the body instead of destroying it? (i.e. Some type of protein, sugar, hormone, etc...I'm not definite on the subject, it is just interesting, so I'm only throwing out some creative ideas!)
The problem is that the cancer cells are made up of exactly the same elements as the non-cancer cells. The differences are really tiny - a couple of protein molecules in a slightly different place, that sort of thing. We can do all kinds of things to cells, but we need to find ways of doing them to just cancer cells, which is hard. We do have ways of combating cancer and are inventing new ways all the time, but it is a really difficult problem to solve so we haven't got any perfect solutions yet. --Tango (talk) 00:17, 22 April 2009 (UTC)[reply]
All biological tissue is made almost entirely from carbon, hydrogen, oxygen and nitrogen - with a few bits and pieces of other elements. But the amounts and ratios of those things are very similar between (say) a lung cancer cell and a healthy lung cell. In fact, they might have utterly identical amounts of those elements - the only difference being something very subtle about the arrangement of them...and even then, the mis-arrangement is just in the DNA and that's a microscopically tiny fraction of all of the chemicals in the cell - just a few misplaced atoms in just the wrong place is enough. Worse still - a healthy muscle cell is way different to a healthy lung cell - but a cancerous lung cell is much more similar to a healthy one than the muscle cell is. These difficulties probably explain why we have not yet evolved a way for our bodies to cure themselves of cancer just as we can cure ourselves of the common cold. Most of the treatments for Cancer depend on targetting the way they behave. So when they go nuts and start reproducing like crazy, they don't build things like the blood vessels they need to get nutrients...so there are tricks like treating the patient with drugs that slow the development of new blood vessels that'll starve out the cancer cells and hopefully reduce their numbers. Sadly, doing that also prevents new blood vessels that you actually NEED from forming - hence the treatment can make you even sicker than the cancer did. SteveBaker (talk) 00:54, 22 April 2009 (UTC)[reply]
As others pointed out, the difficulty lies on the fact that cancer cells are so similar to normal cells. They are descendant from normal cells after all. But there are subtle methabolic differences that can be used to attack them. The lock and key idea is actually a good one and our own body makes use of some of those sublte methabolic differences to find the cancer cells and kill them. But there are no magic silver bullets and sometimes things get off hand. Dauto (talk) 01:03, 22 April 2009 (UTC)[reply]
Is it not possible through research that we could identify these microscopic, subtle changes in the inactive, harmful cancer cells to reverse the process by means of injecting some sort of "medicine" into the general area of the cancer? Or, is this what all the research for cancer is searching for? Since the alterations in the DNA sequences are microscopic, does this mean that the "lock and key" idea would not work because it would be impossible to specifically locate infected, maladaptive atoms (molecules) inside of the DNA sequences?
Indeed cancer research is directed toward finding shared characteristics of cancers that might represent therapeutic targets. There is no single simple DNA sequence change that is shared by cancers, not even for a single type of cancer. Sometimes there are themes that are shared, like suppression or mutation of tumor suppressor genes like P53, or over-expression of a protooncogene like myc, but these are neither uniform nor easy targets - they are "normal" genes being expressed at the wrong level for a particular cell type. Extremely bright and highly motivated people, many of whom have friends or family affected by cancer, are heavily engaged in this work. --Scray (talk) 02:21, 22 April 2009 (UTC)[reply]
All cancer treatments are dependent on exploiting the effects on the cell that the changes in its DNA has on it. The entire concept of chemotherapy is to develop toxins that kill cancer cells faster than normal cells. The problem with what you want is that the immutable differences between cancer and normal tissue (the changes in the DNA code) cannot be targetted by any developed method. This paper describes a fascinating (and theoretical) way of doing it, but at the moment, we're stuck with toxins, radiation, and cutting it out. Someguy1221 (talk) 02:15, 22 April 2009 (UTC)[reply]
I would hope that, at some point in the future (decades perhaps), a cure for all cancers could be developed which would work like this:
1) Take a sample of cancer from the affected individual, and also a sample of the same tissue without cancer from that individual (the "control").
2) Run both samples (with thousands of cells in each sample) through a computer which will analyze the genetic code and find the difference in the cancerous cells.
3) Program a virus to search for those cells which contain the cancerous genetic code. When it finds them, it can repair them, kill them, or mark them in some way so other agents (the person's own immune system or chemotherapy drugs) can then kill them. It would also be a good idea to make this virus incapable of reproduction once introduced to the patient's body, so the rate at which it works could be controlled. The virus could also be programmed to self-destruct once it finds a cancerous cell and does it's thing. If this control isn't present, so much cancerous tissue could be killed all at once that this would cause a new problem, a mass of decomposing tissue too large for the patient's body to clean it up quickly.
If the cancer has metastasized (spread to other organs/systems), then it may be necessary to repeat this process for each organ/system. StuRat (talk) 15:23, 22 April 2009 (UTC)[reply]
Good idea StuRat. That's pretty much what my idea was, which I titled "the lock and key." If we could track the genetic variations inside of the DNA samples, then we could find the "key" that would fit into the "lock" that would then reverse the process of the cancer, either [like you said] killing it, healing it, and/or making it beneficial to the body.
Lock-and-key isn't really a new idea, it's used in regards to enzymes and their substrates too. This method for curing cancer, however, it a pretty futuristic idea since at the moment we do not have a way to repair individual cells. The idea that they could be killed, perhaps by nanorobots when they are developed, is an interesting one that may be possible in the very long term future. That said, I prefer the idea marking cells with chemical markers so that the immune system can destroy them. That sounds the most plausible in time scale terms, but it's still a long way off. Regards, --āCyclonenim |Ā ChatĀ 07:04, 23 April 2009 (UTC)[reply]
StuRat makes an interesting point, but the idea of programming a virus to detect "the cancerous genetic code" is a bit far-fetched. The approach that seems to have people excited right now is to try to detect a gene expression profile that can uniquely identify a cancer cell; or even better a cell surface protein that is only expressed on cancer cells, and use drugs that can either target a key pathway that's abnormal in cancer cells or take advantage of the cancer cell surface marker to kill cancer cells more directly (rather than using systemic cell poisons). See Gleevec and Herceptin for current approaches that are based on these ideas. --- Medical geneticist (talk) 14:35, 23 April 2009 (UTC)[reply]
Hiding from thermographic camera view by covering oneself in thick mud from head to toe...
...malarkey or effective way? Yes, I'm a Predator fanboy.
That wouldn't actually work in Real Life, would it? Yep, I'm aware that the Predator's visual filter mask is alien technology and may not (in the story) *actually* be a thermographic camera, in the way that we think of one. --Kurt Shaped Box (talk) 23:17, 21 April 2009 (UTC)[reply]
You might be able to get it to work for a short amount of time, but if it worked over a long period it would kill you. The human body produces a significant amount of heat and if that heat isn't allowed to escape the body rapidly overheats. If the heat is escaping, then it is visible to a thermographic camera. A better option is heating the surroundings up to body temperature (uncomfortably hot, but not fatally so, at least if you keep the humidity low). I believe both these options were discussed in a Mission Impossible film, or similar (although they didn't use mud but a special foam suit) - for the reasons I've stated, they went with the heating up the room option. --Tango (talk) 23:28, 21 April 2009 (UTC)[reply]
(after edit conflict) Thinking about it, the movie is set in the jungles of Central America, so the ambient temperature is going to be pretty high anyway. Slap on some thick wet mud to bring down your own surface temperature and it might work for a time (as you say). The black ops guys in Predator 2 used insulated foil suits when attempting to capture the creature. IIRC, they were tethered by hose to some sort of central refrigeration unit. --Kurt Shaped Box (talk) 23:57, 21 April 2009 (UTC)[reply]
The Pierce Brosnan remake of the Thomas Crown Affair used exactly this method of increasing ambient air temperature to "blind" the thermal cameras in the art museum.Ā :-) 61.189.63.224 (talk) 23:51, 21 April 2009 (UTC)[reply]
Yeah - but that's fiction - so we may safely ignore it. OTOH - the Mythbusters tried a whole bunch of ways to get past thermal sensing alarms and found that a white bed-sheet held up in front of you was entirely effective (and a darned sight less messy!). Evidently, something that's highly reflective of IR energy allows your body heat to be reflected back away from the camera. SteveBaker (talk) 00:35, 22 April 2009 (UTC)[reply]
Even if it is effective, what about Schwarzenegger's eyes? He doesn't put mud over his eyes (for obvious reasons), but shouldn't the preditor been able to detect the heat coming from his eyes? A Quest For Knowledge (talk) 00:44, 22 April 2009 (UTC)[reply]
Insufficient resolution on his HUD perhaps? I don't recall him being stood particularly close to Arnold in that scene. A lot of the Predators' gear seems to have technical limitations (e.g. a cloaking device that provides less than perfect invisibility when moving and malfunctions when wet, or an auto-tracking plasma cannon that struggles to acquire an accurate lock on a moving target). Or maybe he was looking for and expecting a human-sized heat source? Not finding one and dismissing the notion that a human could be smart enough to figure out the limitations of his thermal imaging (the mud thing was a lucky accident anyway), maybe he just figured that Dutch had somehow given him the slip and run off before he got there? --Kurt Shaped Box (talk) 01:23, 22 April 2009 (UTC)[reply]
Military anti-thermal-detection suit
This Q inspired me to ask one I've had on my mind. Is there a suit that could be designed to fool a thermal detection camera, over long time periods (many hours)Ā ? I'm going to assume that heating up the environment to body temp isn't an option here, and neither is holding a sheet in front of yourself. Here's a couple of thoughts I had to overcome the build-up of heat problem:
1) Have the suit carry a coolant to fight the build-up of heat. This could be a very simple design, with inside pockets holding the coolant close to the body, and thermal insulation on the outside of the suit. No circulation system would be needed. When the solider returns to base, he could replace the warm coolant packs with cold ones. The trick would be a finding a light-weight coolant which has a high thermal capacity.
2) Have the suit heat some liquid, such as water, then inject it far enough underground to hide the thermal trace. A large downward pointing needle could be affixed to the calf of the soldier, which would periodically inject the hot water into the ground. This would only work on soft terrain. Alternatively, the soldier could dump warm water on the ground when he judges himself to be safe from thermal cameras. If a source of cold water is available (river or lake), then a tank of cooling water could be loaded up inside the suit and the warm water released into the river or lake periodically. Such a suit would require a circulation system, but it might be possible to install one-way valves such that normal body movements would circulate the fluid.
There are a few tricky bits to get around. How to cover the face and hands without limiting maneuverability or limiting vision comes to mind. Also, The suit could not limit hearing or be noisy to use (crinkly aluminum sheets for example). Weight of course could be an issue. The more coolant you can carry, the more weight, but the longer the suit can go before a recharge. I don't think the needle idea would work because it would probably get broken while moving around, or else it might make you trip. Maybe it could be retracted or something. It is really going to depend on what you are doing while wearing the suit. If you are just standing in 1 place, it should be fairly easy. If you are in a special ops unit of the military, then it would be a lot harder to design. 65.121.141.34 (talk) 15:19, 22 April 2009 (UTC)[reply]
You're want to make sure that you didn't show up as a mysterious cool spot. The Predator would figure that out pretty quickly. APL (talk) 15:59, 22 April 2009 (UTC)[reply]
For military use - it's a lot harder. To fool a sensor, you only have to fool the kinda crappy image processing system that's hooked up to a cheap camera and saying something like: "If you see heat above 80 degF covering more than 10% of your pixels - ring the alarm". To fool human eyes (albeit looking through an infra-red camera or night vision goggles) is vastly harder. Having cool-packs isn't enough - you'd have to spread the body heat out uniformly - but you're still blocking the heat from whatever is behind you. When you look through night vision goggles, you see all the details of the trees and the grass and the road and vehicles, etc - and a human-shaped blob of any temperature whatever will look like a guy in a suit trying not to be notice! It's the EXACT same problem as trying to be invisible in daylight - you can't just be black or grey or the exact same AVERAGE color/temperature as the rest of your environment - you actually have to be an exact match for your environment - as seen from the point of view of the observer. Having said that, there are people who are trying to figure out how to make invisibility 'cloaks' - and if they ever succeed, then whatever they do will probably work perfectly well for IR imaging too...and of course you could merely seek to 'break up the shape' using camoflage techniques (but in the IR domain) and have some improvement. But as far as I know, this isn't a serious issue for the military right now. Most of the people that 'modern' armies are fighting are using techniques from 50 years ago - and they don't typically have night vision so going to a lot of trouble to hide from night vision devices isn't a huge deal right now. SteveBaker (talk) 19:37, 22 April 2009 (UTC)[reply]
Well, you'd still expect the special ops soldiers to keep hidden behind trees, in ditches, etc. However, if they are glowing brightly in infrared, that won't be enough. But, using an IR-suppression suit, in combination with standard stealth techniques, they should be able to avoid detection. As for "the enemy" not having IR scopes, they are cheap enough now that the military should consider them to be available to the terrorists. StuRat (talk) 03:15, 23 April 2009 (UTC)[reply]
You could try something like a thermocouple, which would cool the body by using the heat difference between it and the outside world to generate electricity which could then by used to power your equipment, or just dissipated in some invisible way. Done correctly, this could give you a suit that allows you to control the temperature at different points on the outside allowing you to create an IR version of the standard camouflage pattern. You would probably want something that can be adjusted depending on the time of day, ambient temperature, terrain etc. (you might have some of the suit the temperature of the sky and some the temperature of the trees, for example). --Tango (talk) 19:48, 22 April 2009 (UTC)[reply]
Gaussian random motion occurs when the probability distribution of the displacement between now and any later time is Gaussian. It basically means completely random motion: if you take an object that in every time increment moves a random amount in a randomly chosen direction, as long as the time increments are short enough the motion closely approximates a Gaussian random motion. It is, for example, a useful model of the movement of molecules in a gas. Looie496 (talk) 04:08, 22 April 2009 (UTC)[reply]
How do dot diagrams with little crosses or x's in place of some of the dots work? I see this in some diagrams and I'm not entirely sure what it means. 98.165.40.158 (talk) 04:32, 22 April 2009 (UTC)[reply]
I am, yes. I can't find anything on that page, but I've seen where some of the dots are replaced with crosses. What does this mean? āPreceding unsigned comment added by 98.165.40.158 (talk) 04:56, 22 April 2009 (UTC)[reply]
Do you mean all of the dots are replaced by crosses/plus signs, or a mixture? If it's the former, that's just stylistic - if not, the only time I've seen + signs is in relation to the valence of an ion. Wisdom89(T / C)05:01, 22 April 2009 (UTC)[reply]
The dot-and-cross diagram is a variation on the Lewis diagram that shows the electrons shared within each covalent bond. Dots and crosses are used to distinguish electrons donated by one atom from those donated by the other atom in the bond - electrons in the outer shell of one atom are shown by crosses, electrons in the outer shell of the other atom are shown by dots. In a normal covalent there will be one electron from each atom, so this is represented by a dot and a cross. In a dative covalent bond both electrons come from the same atom, so this is represented by two dots (or two crosses). You can see some examples of dot-and-cross diagrams on this BBC Bitesize page. Gandalf61 (talk) 10:52, 22 April 2009 (UTC)[reply]
Bruce Lee martial arts glowing light energy field
Perhaps more pseudo-science than science, but the science page is where are the smart geeky people are, so...here is my question... There is a(n apocryphal) tale that Bruce Lee had attained such an advanced level in his Martial Arts practice that at certain times he emitted a (green) glowing aura / energy field around his body. Does anyone know what this field is purportedly called or has anyone heard this story? I already looked at Tummo. Merci d'avance, Saudade704:50, 22 April 2009 (UTC)[reply]
Oddly enough, people who believe in this call it an aura: see aura (paranormal). --Anonymous, 05:00 UTC, April 22, 2009.
Yes, but this is something else...people who believe in Auras believe that everyone has one. But this is a special field of glowing energy that only envelopes certain high-level martial arts practitioners when they are in the zone / at the top of their game / about to kick ass. Apparently Bruce Lee had it. I found the name on the Internet 10 years or so ago, (I feel like it was a Chinese-sounding word) but now everything I Google turns up yoga stuff. I feel like BL's field was said to be green. Thanks Saudade706:12, 22 April 2009 (UTC)[reply]
Well, there was a movie called The Last Dragon in which the main character was inspired by Bruce Lee to attain an ability called "The Glow" which is essentially what you're describing, but this is fiction of course, no one in their right mind would believe it was based on something Bruce Lee could actually do. Truthforitsownsake (talk) 12:35, 22 April 2009 (UTC)[reply]
There is an awful lot of bullshit pseudo-science relating to auras. However, no properly designed experiment has ever shown that they exist - and since a ton of laws of physics would have to be overturned if they really DID exist, we have to employ Occam's Razor and say that since extraordinary claims (which aura's are) require extraordinary evidence (and we have ZERO evidence) - then we should simply say that they are bullshit and move on. Which is what I'm going to do now. SteveBaker (talk) 19:25, 22 April 2009 (UTC)[reply]
POSTED THIS QUESTION ON THE MATHAMATICS PAGE AND WAS SUGGESTED I POST IT HERE
I would like to add if i may that i do not have a great understanding or math and mistakenly as was pointed out asked if there was an equation that fits the model...Equation is the wrong word please ignore that but i would like a good solid answer.
I was bored sitting in work and a colleauge said look up Schrƶdinger's cat.... While reading it...... it seemed as if the only way to explain Quantum mechanics is "the end product of any situation is allready predetermined"; applying this to the riddle, as far as i see it would explain the answer to the Schrƶdinger's cat experiment...the cat is either pre destined to be dead or alive this was pre determined right back to the big bang hence all future things are all ready predestined....(god knows what that makes to a time theory?) For example we know the Sun will burn out but it hasnt happened yet' its fule will be used up it will swell then cool ECT....this is all ready predetermined.So my question is if the universe surrounding us is all ready played out and the end states are known (but not by the human race) is there an equation that would fit this model? Ok i dont want you to look at this and think this guy is a nutter 'which i am sure you will' but it makes sense to me....we just need to be able to see the future is allĀ :) Adrian O'Brien āPreceding unsigned comment added by 214.13.113.138 (talk) 12:29, 21 April 2009 (UTC)
I'm not sure but I think there is. Even if there is, the equation has to be really complicated. Also, I recommend you on posting this question on the science reference desk instead. Superwj5 (talk) 13:18, 21 April 2009 (UTC)
It is nice that you are interested in this - I suggest you read the article Quantum mechanics. Especially, it is recommended that you read the "overview" section and the beginning of the introduction. Just read what you understand and ignore what you don't. The other thing I wish to comment upon is your belief that mathematics is described by "equations". This is false. Group theory does indeed apply in quantam mechanics as well as probability theory, and the deep purpose of either subject has nothing to do with equations. Just let me stress that mathematics is not equations. If you are referring to the uncertainty principle, then:
Also, I recommend that you read Introduction to quantum mechanics first as this is (apparently) more accessible. I do not wish to discourage you from asking questions but I just wish to stress the mathematics that applies to theoretical physics is much deeper than you think (for example the application of knot theory (a branch of mathematics) to string theory (a branch of physics)). --Point-set topologist (talk) 14:14, 21 April 2009 (UTC)
All equations including mistaken ones fit the OP's notion of predetermination. It made me post this. Cuddlyable3 (talk) 14:25, 21 April 2009 (UTC)
I was under the impression that it was classical mechanics that deals with a deterministic world, while quantum mechanics deals with a probabilistic one. What I mean to say is that if the position and momentum of every particle in the world were known at one instant, the state of the universe at any future instant is easily obtained by applying Hamilton's (or Lagrange's) equations. However in quantum mechanics it is intrinsically impossible to know the position and momentum of even one particle to arbitrary precision, let alone all of them. I would disagree with the OP's statement that the end result of any situation is predetermined, as we can only state the probability of obtaining any particular end. mislih 23:08, 21 April 2009 (UTC)āPreceding unsigned comment added by 214.13.113.138 (talk)
Please use the proper, above-outlined method to post things instead of adding on to other people's questions. Then there will be no conflict. Saudade706:12, 22 April 2009 (UTC)[reply]
Nope, there is no predetermination. See Bell's theorem and Bell test experiments. Unobserved measures truly don't exist yet. You see, the trick is to just dispell your classical notion that a particle must have a single unique position and velocity at any given time. In the real world, a particle simultaneously occupies many positions, with a probability of being found at any given one upon being observed (whatever "observed" means). Although, of course, the Schrodinger cat has any number of issues, which I'm sure further responders will nitpick. Someguy1221 (talk) 06:16, 22 April 2009 (UTC)[reply]
Ok Saudade7 this was my question from the maths portal i just pasted the same question on here so there is no conflict.
The part of your answer if i may i struggle with is, we may not know what the predetermined out come is, or be able to see it but this does not mean it doesnt have one...push a rock off the cliff it will hit the floor this is predetermined even if it hasnt hit the floor yet...If the rock is in many diffrent places at the same time we still know at that place it will hit the floor. there can be many variables i.e. somebody catches the rock ect... but that could be a predetermination somebody was always going to catch the rock if you see what i mean? Please excuse my lack of knowledge of science and math but i am trying to understand:)As i see it probability rather than predetermination seems to fit but the particle/rock/cat is allready doing what it was predestined to do we just dont no it.... āPreceding unsigned comment added by 214.13.113.138 (talk) 06:39, 22 April 2009 (UTC)[reply]
Your idea that everything is predetermined, was, indeed, believed by scientists hundreds of years. This comes from classical mechanics, or common sense, and nobody dared to question it. Then in the last hundred years or so, great reforms began to occur based on experiments and sheer brilliance, culminating in Quantum Mechanics. At the heart of Quantum Mechanics lies the uncertainty principle. According to this outrageous fact, we can NOT even measure things around us as we like. There is always an uncertainty in measurement, inherent in the system. This has nothing to do with the faults of our measuring apparatus. For example, it may be possible to measure the length of a block of wood with a scale say down to an error of 1 mm. If we have an even better scale( say a vernier caliper) we might be able to measure it more accurately, say to .01mm. In PRINCIPLE, it is possible to measure with as much accuracy as we want, though it may not be practical. But in the realm of Quanto, there are fundamental restrictions even in principle. What's more, you the the length of a block is say 1 meter, whether or not you measure it, ie it is deterministic - already determined. The whole idea of determinism is gone in Quanto. Before the act of measurement, everything is just in a confused superposed state. The act of measurement forces it to take a value, which is then approximately measured. This might need some rereading and might be outrageous at first sight, but that is the way nature behaves. So if we assume Quanto uncle to be right, then determinism is just chucked out the window.... Rkr1991 (talk) 07:34, 22 April 2009 (UTC) āPreceding unsigned comment added by Rkr1991 (talk ā¢ contribs) 07:30, 22 April 2009 (UTC)[reply]
I meant you should have begun the process of asking your question by clicking on the "ask a new question by clicking here" link at the top of the page, rather than coming down here to the bottom of the page, clicking on the edit, and adding your question. It is just a simple a courtesy to others, like myself, who might be posting in a situation with sketchy Internet connection (I was at a cafe and needed to pirate an intermittent open signal). I had to wait for a new signal to re-post because your post time conflicted with mine as a result of your method. So I was cranky. The math portal has nothing whatsoever to do with the conflict. Saudade7 07:53, 22 April
\2009 (UTC)
Ok thats great thanks for the answers makes a lot more sense now, ill come forward 100 years and try to catch upĀ :) just like to add some great minds on here brilliant to see. Keep it upĀ :) NP's Saud i was on my third coffeeĀ :)
It may be surprizing to some people to realize that quantum mechanics, despite the uncertaity principle, is actually just as deterministic as classical mechanics, except for the wave function collapse that happens when an observation is performed. This is somewhat contradictory and to this day there is still some debate about whether the colapse is a fundamental phenomenon or just an epiphenomenon of quantum decoherence. The latter is considered more self-consistent and leads to an entirely deterministic theory. Dauto (talk) 14:53, 22 April 2009 (UTC)[reply]
April 22
GLOBAL WARMING
Ok; the idea of global warming is consistant with it being a natural process all we do as humans is speed up that process...
Has there been thought on the idea of creating a large volcanic eruption which would place large amounts of what ever into the atmosphere and thus help cool the earth...Simlar effect in Victorian times when global temp was reduced due to an eruption. The Year Without a Summer 1800 and something? To control this even would be extremly difficult of course but would it work? āPreceding unsigned comment added by 214.13.113.138 (talk) 08:41, 22 April 2009 (UTC)[reply]
Or maybe there could be a way to divert an asteroid (nuclear blasts?) so it falls into Earth, the impact of which will result in blocking out of the sun like it's frickin dinosaur extinction time. That might also achieve your goal.āPreceding unsigned comment added by 94.27.153.3 (talk) 10:00, 22 April 2009 (UTC)[reply]
I am afraid that your second method is just silly. Life on Earth would not exist without sunlight and furthermore, the impact of an asteroid on the Earth's surface would result in many deaths. --PST10:10, 22 April 2009 (UTC)[reply]
First, what do you mean by "natural process"? "Natural" like in "without human intervention"? We have caused this by releasing greenhouse gases into the atmosphere that disturbed the balance, and now the system is "readjusting", so the mean temperature will rise until a new equilibrium in energy received/energy lost is reached. It is true that in the past "natural" warmings occured (over thousands of years), but as far as we know nothing even roughly comparable to the situation today ever happened (warming the planet in centuries or even decades). We are to blame! Now coming to the question: What makes you think that we are able to trigger a volcanic eruption? I don't say it is impossible, but at least nothing like this has been tried before (for good reasons, I'd think), so it would at least be a really uncontrollable, dangerous experiment. But now to the main caveat: You are confusing climate change with the actual weather. Climate is something that happens on the scale of several years, but the cooling you mentioned mainly affected a single year and then quickly (in climate scales) disappeared. To the contrary, a much discussed theory is that vulcanic eruptions in the past could have triggered massive climate changes which added to or even caused mass extinctions, because many lifeforms could not adapt fast enough to the changing world. This is because vulcanos also emit greenhouse gases, and large vulcanos can put an awful lot of them into the atmosphere in a short time. So in summary: I think it would be a real bad idea to try something we don't understand (vulcanic eruptions) to cure something we don't understand (the climate). TheMaster17 (talk) 10:08, 22 April 2009 (UTC)[reply]
To the second question with the meteor: I hope this is irony, because the answer has to be nearly the same: we have no idea how to divert an asteroid, because of very many practical problems on the way. And even if we could, we would bring an incalculable element into an already incalculable situation. TheMaster17 (talk) 10:17, 22 April 2009 (UTC)[reply]
(Reply to both PST and TheMaster) I could be wrong, but it looks to me like those two anons are unrelated. I'm pretty sure 94 was trying to be sarcastic indicating that the first idea was likely to be very difficult to achieve and to have serious side effect and so was (almost?) as silly as the second idea which I guess he/she hoped the OP could more easily see as an idea which would never work. Nil Einne (talk) 13:52, 22 April 2009 (UTC)[reply]
Well, of course the Earth has warmed and cooled before, but the current process is, as far as we know, different in that a) it's primarily driven by greenhouse gases (instead of them acting as a feedback to amplify an otherwise triggered warming trend) and b) it's a lot faster that anything we have seen before. So calling it "a natural process" that we "only speed up" is a very arguable position. What cools the Earth after a large volcanic eruption are aerosols, mostly sulfur-aerosols in the atmosphere. We have indeed injected a large number of those via industrial processes, and they have masked the early warming trend. Warming only became very notable when Europe and the US installed scrubbers to reduce acid rain and other negative effects of sulfur emissions. There also have been some proposals to actively introduce aerosols to reduce the warming. However, there are serious technical challenges and ecological side effects - and, since it's a global problem, it will be very hard to find a politically acceptable solution. Just imagine Mexico emitting large aerosol clouds that rain out as acid rain over Yosemite National Park, or emissions in Germany causing respiratory diseases in Poland and the Czech Republic. A final problem is that CO2 accumulates over a long time, while aerosols have a short atmospheric lifetime. So to counteract the effect of inreasing CO2 concentration, one would need ever-increasing aerosol emissions. There is some discussion at Mitigation of global warming. --Stephan Schulz (talk) 10:23, 22 April 2009 (UTC)[reply]
I think your point b is pretty worthless. Saying that the temperature is changing faster then anything we have ever seen before completely ignores the fact that written human history runs for thousands of years, and thermometers that operate independent of air pressure have only been around for 400 years tops. And do we have documents showing a daily temperature record for hundereds or thousands of locations so that we have a basis of comparison? I would say we don't have anything like that until the 19th century. So saying we have never seen anything like this before does not mention that we had our eyes closed the other 23 hours of the day. 65.121.141.34 (talk) 13:06, 22 April 2009 (UTC)[reply]
We don't have human recorded measurements but we do have quite good estimates of previous temperatures from ice core samples for example. Take a look at temperature record for more detail. We may have closed our eyes for the other 23 hours, fortunately there were cameras recording the 23 hours while our eyes were closed which we can now review. Nil Einne (talk) 13:52, 22 April 2009 (UTC)[reply]
In fact, the icecore registers the temperature at the place where the evaporation happened, not the place where the snow fell. Since there is a lot og mixing between one and the other, The ice core turn out to be an excellent proxy for the past global average temperatures. Dauto (talk) 19:42, 22 April 2009 (UTC)[reply]
But temperature changes exist all over the planet, not just at one location. If anything, the temps at the poles vary more than on the rest of the planet, so any global temp changes would be well-preserved in ice cores. Thus, Antarctic ice cores are a good indication of the global temperature. Also, we can go back a few thousand years by looking at tree rings. Rapidly warming weather would favor some trees and hurt others, and the tree rings from those years would reflect that. StuRat (talk) 14:36, 22 April 2009 (UTC)[reply]
But things other then temperature can have a big impact on tree rings, like drought or flooding or fire. Is there a way to differentiate? 65.121.141.34 (talk) 15:11, 22 April 2009 (UTC)[reply]
Yes, but not perfectly. The general idea is that drought and flooding are local effects that last a small number of years. By looking at tree rings over wide geographic areas and over longer time periods you get plot a general trend. See Dendroclimatology. APL (talk) 15:56, 22 April 2009 (UTC)[reply]
"However, coverage of these proxies (tree rings and ice cores) is sparse: even the best proxy records contain far fewer observations than the worst periods of the observational record. Also, problems exist in connecting the proxies (e.g. tree ring width) to the variable of interest (e.g. temperature)." I am not saying global warming does not exist, I am just saying that the evidence supplied is less conclusive then most people are lead to believe. 65.121.141.34 (talk) 16:15, 22 April 2009 (UTC)[reply]
I'm not sure what you are saying. Are you saying you don't believe global warming is happening or are you saying that because the record of the past is less accurate than the present there is a possibility that something like what is happening now might have happened before and therefore it cold be natural and not man made? By the way the PaleoceneāEocene Thermal Maximum only 55 million years ago looks like it had spikes of 3Ā°C increases in less than a thousand years so there is a possibility that it was as bad as is happening now so that would bolster the second point of view if that is what you are saying. Dmcq (talk) 16:42, 22 April 2009 (UTC)[reply]
I am saying that there are holes in the theory that are not addressed well and thus it is not the scientific fact it is often purported to be. 65.121.141.34 (talk) 16:51, 22 April 2009 (UTC)[reply]
There may be holes in the theory, but your atempts here fall in the naive category. Denial isn't a scientifically acceptable alternative. Dauto (talk) 19:45, 22 April 2009 (UTC)[reply]
Just because coverage is more sparse doesn't mean that it is inadequate. The question is, would we detect the current rise from the ice core? If we would, then the fact that the record is more sparse is largely irrelevant. Our excellent modern observation is good because we can see more carefully what is going on, it doesn't mean it's necessary to detect massive global warming Nil Einne (talk) 03:50, 23 April 2009 (UTC)[reply]
These kinds of ideas are what is increasingly being called "Plan B" amongst climatologists. If it's truly too late to stop emitting CO2 - or if we can't get international agreement - or if the 'runaway' scenario has truly kicked in - is there anything we can do to make the planet cooler and thus circumvent the worst of the danger? Well, volcano's definitely aren't it because they are actually a major contributor of greenhouse gasses. While the smoke from the ash plume would reduce temperatures for days, weeks, months or even perhaps a year or two - the CO2 it emits will still be in the upper atmosphere in 10,000 years time. So that particular trick certainly won't work. But there are other possibilities. It's known that the contrails from the exhausts of high altitude airliners is reflecting heat away from the earth to a small degree (it was noted that after the 9/11 attacks when all North American aircraft were grounded - the temperature shot up a couple of degrees!). So maybe we could make some more big white clouds up there and block sunlight that way? The really big problem with all "Plan B" approaches is that we really don't understand the complicated inner-workings of the whole planet to know whether one of these "cunning plans" would actually do more harm than good. For example - if we reflect away sunlight to make the earth cooler, plants that use sunlight to perform photosynthesis would do less well - this might result in disasterous world-wide crop failures - and since plants consume CO2 and output oxygen during photosynthesis - we might easily make MORE CO2 than we do now! In fact, it's hard (or perhaps, impossible) to imagine any kind of "Plan B" that might not have disasterous consequences. Worse still, these things have to be world-wide events - we're modifying the atmosphere for the entire planet - and you really can't go around doing that kind of thing without (at least) the agreement of all of the major governments of the world. While we may ultimately have no choice but to attempt something that wreckless - it would have to be a last-ditch effort when we know for 100% sure that we're doomed if we don't do it. But there are LOTS of "Plan B" ideas out there...covering large areas of the ocean with white foam polystyrene beads to make it reflect sunlight away...launching massive sun-screens into earth orbit to block sunlight...there are MANY choices! SteveBaker (talk) 19:19, 22 April 2009 (UTC)[reply]
As for aerosols such as sulfur dioxide, a better alternative is to launch them up to the stratosphere, where it doesn't interact with our weather. As for warming/cooling being part of a natural cycle, yes there has been a period of warming since the Younger Dryas, but that warming is no longer a part of the trend seen today. As for rapid climate change in the past, some of those events may have been caused by methane clathrate collapses (which are starting to occur today), but now instead of 3C of warming in several centuries (under 1,000 years), it could be 3C in several decades (less than 100 years). ~AH1(TCU)23:05, 22 April 2009 (UTC)[reply]
Hi everyone just I have a couple of quick questions - Would I be correct in saying that B cells don't have to be activated by a helper T cell before they can produce antibodies? If they don't need helper T cells to activate them how are they activated in the absence of helper T cells - does another type of cell activate them into producing antibodies/forming plasma cells etc. or can they can activate themselves? If they can activate themselves (I don't know if they can or not)then wouldn't that render the helper T cell uneccessary in this sense? (I realise helper T cells probably have other functions aside from activating B cells.) Sorry if my questions are badly worded and thanks in advance to all who help! āPreceding unsigned comment added by 92.21.237.143 (talk) 11:21, 22 April 2009 (UTC)[reply]
"Some textbooks state that electricity within wires flows at nearly (or even exactly) the speed of light,[1] which can give the impression that electrons themselves move almost instantly through a circuit. The electrons in a typical wire actually move at a drift velocity on the order of centimeters per hour[2] (much slower than a snail). The random thermal motions of the electrons are much faster than this, but still much slower than light, and with no tendency to occur in any particular direction. It is the electrical signal that travels almost at the speed of light. The information that a light switch has been turned on propagates to the bulb very quickly, but the charge carriers move slowly.[citation needed]"
Wow, misconceptions are everywhere, including the Speed of electricity article and most of the things on the web that discuss this. When somebody asks for the "speed of electricity", what they usually mean is something like "If I switch on a light, how quickly does the signal travel from switch to light", or "if I send a signal along a wire, how quickly does it reach the receiver". To answer these questions requires cable theory. The answer you get depends greatly on the conductivity, boundary impedance, and capacitance of the wire, but it is always far slower than the speed of light. This article, for example, calculates the speed of signal transmission for a telegraph cable across the Atlantic -- a very fast carrier -- and gets a result of about 2x106 m/sec, or about 1/10000 of the speed of light. In other words, very fast in human terms (two seconds to cross the Atlantic), but very slow compared to light. The wires in your home are typically hundreds or thousands of times slower. For computer equipment, conduction speeds along wires are often an important design factor. Looie496 (talk) 18:21, 22 April 2009 (UTC)[reply]
The calculation for transatlantic cables may have been accurate in the days of the telegraph, but is not even close when most telephone cables are considered. Up until the mid-70s, transatlantic telephony used either satellite or copper cable. Satellite experienced noticeable delay, and cable did not. We can therefore estimate that the round-trip time was less than 100ms. Therefore for the signal to cross the atlantic, we can estimate a time of 50ms maximum, which is a speed of about 1x108 m/s, or about 1/3 the speed of light. --Phil Holmes (talk) 09:12, 23 April 2009 (UTC)[reply]
In a physics lab, we would send pulses down 200' coax cables and measure velocities of 2/3 c. Of course the pulse got smeared some and there are other issues to consider, but Looie's assertion that most wiring would be many orders of magnitude less than c seems unlikely to me too. Dragons flight (talk) 09:36, 23 April 2009 (UTC)[reply]
The way to imagine this (crudely) is to imagine an almost frictionless 200' long garden hose and some half-inch ball-bearings. If you stretch out the hose on level ground and roll a ball-bearing down the length of it - it might take 30 seconds to pop out of the other end. But if you fill the hosepipe full of ball bearings from end to end then if you try to push one ball in at one end - then another one pops out of the other end almost instantaneously. So even though the individual balls move fairly slowly - the time between stuffing one in one end and a DIFFERENT ball popping out of the other is quite short. The hose is a wire, the balls are electrons. The electrons move incredibly slowly - like watching the minute hand move on an analog clock. But when you push an electron into one end of the wire - a different one pops out the other end with a delay that's about equal to the speed of light. SteveBaker (talk) 19:06, 22 April 2009 (UTC)[reply]
Neat! Thanks for answers. The one I understand the best is from SteveBaker. That one I grasp the best and it makes sense on how the "speed of electricity" happens. --LordGorval (talk) 21:15, 22 April 2009 (UTC)[reply]
wikipedia article on E.D.T.A.[ethylene diamine tetra acetic acid]
in the above article,Uses in Medicine,Last entry is Use in Thalassemia Major to remove excess iron.Pl.indicate the reference of source i.e journal etc.thanks āPreceding unsigned comment added by 117.198.195.147 (talk) 12:59, 22 April 2009 (UTC)[reply]
Well to be fair to the OP, if our article says something (and it does "This therapy is used to treat the complication of repeated blood transfusions, which used in cases of severe thalassaemia") then it should be referenced (which it isn't). However that should be dealt with on the article talk page (which I've copied it to), not here Nil Einne (talk) 13:42, 22 April 2009 (UTC)[reply]
Yes, I know all challenged claims require a citation and are subject to removal if none is provided - but I got the impression that the anon was also interested in the veracity of the statement apart from just the quality of Wikipedia. Wisdom89(T / C)14:53, 22 April 2009 (UTC)[reply]
How to insulate an old homeĀ ?
My current house was built in the 1920s (I know, that's not old by European standards). The windows have all been replaced with triple-pane insulated windows. Now the problem is the walls. They are cold all winter long and hot all summer long. I don't believe there's any insulation at all (other than the bricks and wood of which the house is constructed, which offer minimal insulation value). The obvious answer is blown-in insulation. However, the wiring in the walls is sub-par and gets warm now. If it was buried under layers of insulation it might get hot enough the cause a fire. So, is there any way to insulate the walls, short of ripping all the walls apart to replace the wiringĀ ? One thought we had was to disconnect the existing wiring, leave it in place, and install exterior mounted wiring to replace the wall wiring. This would then allow for blown-in wall insulation. Is this idea feasibleĀ ? Has anyone done thisĀ ? Any other ideasĀ ? StuRat (talk) 14:11, 22 April 2009 (UTC)[reply]
Those sound like some possibilities. Do you know how much of an insulation value (R-factor) the thermal wallpaper providesĀ ? StuRat (talk) 20:11, 22 April 2009 (UTC)[reply]
If your wiring is getting hot, you should definitely replace it. (5-10% of all deadly house fires in the U.S. involve electrical causes[29]) Wiring from that era probably has degraded insulation (mine certainly did) but more importantly as code standards and appliance usage have changed, the system may not be laid out to properly handle the much higher electrical loads we now use leading to overheating of the wires. Rmhermen (talk) 16:02, 22 April 2009 (UTC)[reply]
It should definitely be rewired to start with. The old wiring can usually be used to pull through the new wiring; it certainly won't mean ripping any walls apart, and your house will be a lot safer.--Shantavira|feed me15:59, 22 April 2009 (UTC)[reply]
My thoughts too exactly. The insulation on ancient wiring can quite easily crumble and cause a fire, never mind the possibility of shocks. Do it now before it does you in. Dmcq (talk) 16:07, 22 April 2009 (UTC)[reply]
When you do get to the insulation I think your idea of blow in is best to start with. The problem with having thin insulation trying to do the whole job is with any bits which have to stick through may tend to get condensation at times, but they can be good supplementing the main business. Dmcq (talk) 16:18, 22 April 2009 (UTC)[reply]
To do a good job of blowing in insulation, you will need to make holes in the plaster or wallboard anyway, and patch and paint as part of the job. Therefore, the incremental cost of putting the new wiring inside the walls rather than outside the walls is much lower: the incremental cost is mostly in the wall repair. Depending on where you live, you may want to make the walls thicker to hold more insulation. This involves removing the plaster or wallboard and adding studs another set of studs, which should be offset from the existing studs. Of course, with the walls open you are no longer restricted to blown insulation. -Arch dude (talk) 20:13, 22 April 2009 (UTC)[reply]
Everyone seems to think new wires can be pulled through the walls using the old wiring. I'm far more skeptical that thin, 90 year old wires with deteriorating insulation wouldn't just break. Also, the builders may well have attached the wiring to studs using staples. And the walls are made of wet plaster, so the thought of tearing them open is horrifying. What about my idea of leaving the old wiring in place, disconnecting it, and putting new surface mounted wiring in placeĀ ? Has anyone done thisĀ ? StuRat (talk) 20:08, 22 April 2009 (UTC)[reply]
In addition to the fragility, a 90 year old home with the original wires would likely have knob and tube wiring instead of free-floating Romex-style power cable. (Applicable words from the article "Currently the United States NEC forbids use of loose, blown-in, or expanding foam insulation over K&T wiring. This is because K&T is designed to let heat dissipate to the surrounding air.") -- 128.104.112.117 (talk) 22:29, 22 April 2009 (UTC)[reply]
There are ways of "snaking" wire through walls without pulling on the existing wire (which being metal should not have gotten any weaker - if it has it is an even greater fire hazard) Another problem with knob and tube (which was less common already by the 20s) is that some insurers refuse to write policies for houses that still use it. Rmhermen (talk) 00:49, 23 April 2009 (UTC)[reply]
My house is also of that period, but the previous owner did a major renovation. Where the original double brick walls are still in place, they are now lined with another layer of wall of standard frame construction, which allowed space for insulation and new wiring. All wiring and plumbing in the house was replaced. That's the sort of job you'd need to do things properly, but as you can imagine, it can be awfully expensive. I think you need to talk to a renovation contractor (or rather, several of them) to talk about what is possible and what it might cost. --Anonymous, 23:23:23 UTC, April 22, 2009.
Hi there, I've been revising Dynamics for a few days now and come across this question, and I'm not too sure where to go for the final part.
Two particles of masses m1 and m2 move under their mutual gravitational attraction. Show from ļ¬rst principles that the quantity is constant, where r is the position vector of one particle relative to the other and M = m1 +m2 .
The particles are released from rest a long way apart, and fall towards each other. Show that the position of their centre of gravity is ļ¬xed, and that when they are a distance r apart their relative speed is .
When the particles are a distance a apart, They are given equal and opposite impulses, each of magnitude I , and each perpendicular to the direction of motion. Show that subsequently , where Ļ is the angular speed of either particle relative to the centre of mass and Āµ is the reduced mass of the system.
Show further that the minimum separation, d, of the two particles in the subsequent
motion satisļ¬es .
That's all okay until I get to the minimum separation bit, at which point I get a bit confused - could anyone let me know how to go about finishing this part of the question please? Thanks!Ā :) Otherlobby17 (talk) 14:44, 22 April 2009 (UTC)[reply]
It is possible to rearrange the angular momentum as an Effective Radial Potential. This is a "pseudo"-potential energy field. When added to the gravitational potential, there is a minimum of potential energy (this is the optimal radius for stable circular orbit); and another point at even lower radius, where effective potential is equal to the gravitational potential at infinite radius (this is the minimum separation for the scenario you described). This derivation is detailed in Marion & Thornton's dynamics textbook. I will try to dig out my notes on the subject. Nimur (talk) 15:56, 22 April 2009 (UTC)[reply]
No need - here's Effective potential (which should probably be renamed to something less general, like "Effective potential due to angular momentum"). To find the minimum separation, just locate the point where initial energy equals the potential energy. The particle can go no further (so it is at the minimum radius) unless new energy is added from another source. Nimur (talk) 16:00, 22 April 2009 (UTC)[reply]
While the effective potential idea works, it is not the simplest way to solve that problem. Before the Impulses, the system had both energy and angular momentum equal to zero. The Impuses transfer energy and angular momentum given by the formulae:
and both are conserved thereafter.
At the point of minimun separation, the velocity has no radial component
, and
which gives us energy and anguloar momentum
Solving the system of equations we get from this it is easy to show that
Adverts for toilet cleaning products always boast about how they kill "99.99% of all germs" in the toilet (in the UK, at least). Now, correct me if I'm wrong, but people don't go around licking toilet bowls regularly, do they? Exactly what would be the problem with germs inside a toilet? Is this just more advertising BS designed to sell products to ignorant consumers, or do germs inside a toilet pose a genuine threat of which I'm ignorant? Vimescarrot (talk) 14:50, 22 April 2009 (UTC)[reply]
I am reminded of a study on household germ contamination I read. They found that the most contaminated places in most houses were the cloth or scrubber used to clean kitchen surfaces, and the chopping board; the latter having some particularly nasty germs. The head of the study was quoted as saying "In the average house if I was forced to lick either the toilet seat or the chopping board, I'd choose the toilet seat every time". DJ Clayworth (talk) 15:43, 22 April 2009 (UTC)[reply]
And I would answer that he obviously does not know what he is even doing with this study. Just because you find bacteria on a surface, does not mean that anybody will become sick from licking it. I, as a biologist with training in immunology, would rather stick with Vimescarrot's explanation: Nobody eats out of the toilet, but everybody prepares food on kitchen surfaces. To what germs will our body be more resistent? And the problem, in reality, is the other way round: By cleaning all those bacteria which normally live there, you pave the way for bacteria that normally cannot grow there (because the "normal bacteria" outcompete them) and which could be "real" pathogens (meaning they can really make you sick, because your body has no immunity for them). There are few surfaces, in a hospital for example, that really need to be sterile. Most other things are perfectly "healthy" in everyday live even when they are covered with germs, unless your immunesystem is severely compromised. TheMaster17 (talk) 16:02, 22 April 2009 (UTC)[reply]
So microwaving my dishcloths to kill the germs on them is a bad idea? What about the fact that my mother wipes bloodstained hands on a cloth meant for drying hands that have just been washed? =p Vimescarrot (talk) 17:44, 22 April 2009 (UTC)[reply]
The chopping board may be a special case. The expert may have been concerned about getting germs from raw poultry. I wonder how he'd feel about a dry counter top? (compared to a dry toilet seat) APL (talk) 17:46, 22 April 2009 (UTC)[reply]
The stuff inside the toilet bowl can contribute to foul smelling odors. Also, doesn't flushing release a small aerosol of bacteria in to the air above the toilet? I remember reading that somewhere, I'm sure someone will prove me wrong. Livewireo (talk) 18:05, 22 April 2009 (UTC)[reply]
The dishcloth one always gets me. Is that measured before you place it in hot water (to get it wet ready to wipe a side), just after and before using to clean or after cleaning? I guess my point is - the circumstances will matter as much to the number of bacteria as the place you are measuring. I would expect that the reason for most people to want rid of germs from toilet seats is that they A) sit on them with a part of their body they otherwise only wash daily (or potentially less) compared to touching something with your hands (which would be washed numerous times a day by most). Also toilets are a place where people go to get rid of their 'waste' so they associate them with being dirty/unhygienic as a result it'd make perfect sense for a marketing/branding dept to make a point about their product killing germs there. After all that it still matters whether the bacteria is harmful or not. Numbers alone are a bit of a con in comparison to the type of bacteria? ny156uk (talk) 19:11, 22 April 2009 (UTC)[reply]
It's true that in the UK these adverts make us feel like we are surrounded by monsters, and that we should get rid of them before it's too late. However, if they wanted to be honest, they'd say "kill 99.99% of germs (99.9999999% of those being harmless)". Laurent (talk) 19:28, 22 April 2009 (UTC)[reply]
Toilet bowls normally contain far more "germs" than toilet seats. And they can be harmful to you if someone else in your household has a communicable disease which you don't want to catch. They also look and smell bad when you get ugly growths on the sides of the bowl. It's true that you aren't likely to be exposed to those germs though, with exceptions for pets or small children which happily drink from and play in the toilet bowls. However, nothing fancy is needed to kill those germs, bleach will do the job, although you need to scrub the bowl to get the bleach on all the microbes. Bleach in a thick gel would be even better, as that can stick to the sides of the bowl long enough to kill whatever needs killing. Many toilet bowl cleaners are just that, bleach in a thick gel in a bottle with an angled neck for ease of delivery. Note, however, that bleach and other cleansers may be worse for the children and pets than the original germs were, so keep them out of the bathroom during cleaning. StuRat (talk) 19:45, 22 April 2009 (UTC)[reply]
Products that kill "99.99%" of germs are likely to leave behind ones that are now more resistant to the antibiotic spray, creating what are sometimes called "superbugs". Also, humans don't usually drink from a toilet bowl, but a pet dog might. Another thing, MythBusters confirmed that flushing the toilet brings a small number of the fecal germs up into the air, thus landing on other items such as your toothbrush (in very detectable amounts, even if placed in enclosed containers). ~AH1(TCU)22:48, 22 April 2009 (UTC)[reply]
Such products are not antibiotics and thus there is minimal risk of inducing the formation of resistant strains of anything - Disinfectants such as benzalkonium chloride generally do not produce tolerance. Wisdom89(T / C)22:56, 22 April 2009 (UTC)[reply]
I've noted much more guarded language from advertisers of these products of late - one I noticed a couple of evenings ago said "Kills up to 99% of known germs that may do you harm"...which is pretty much saying "It might kill some bacteria"! The word "germ" is carefully vague - is this bacteria? fungi? viruses? The advertiser's favorite get-out-clause "up to" is a good one. If there are some really virulent bugs, then 1% of them will plenty enough to harm you. Evidently it only kills "known" germs (known by whom?) - and it might only kill the ones that would do me harm...what about my pets or whatever? SteveBaker (talk) 00:08, 23 April 2009 (UTC)[reply]
Are you really serious about microwaving a dishcloth to kill bacteria? What makes you think that this will work? As far as I know, microwaves only really heat water, and most spores of bacteria are water poor, plus they have a small volume, are very damage resistant and repair capable. I would assume microwaving for a long time will reduce the number of viable bacteria, but kitchen microwaving is not capable of sterilizing something. My main argument stays the same: For 99.99999999...Ā % of time that life on earth existed, there were no artificial antibiotics and no really sterile surfaces. Even considering that we have changed the rules lately (moving around the globe faster and changing the patterns of germs that can infect us, by changing the environment we live in), I'm totally fine with my immunesystem coping with the "usual" suspects like bacteria dwelling in my home, the soil, the food, the water or whatever I encounter on a regular basis. I think cleaning your home from 99.99% of bacteria on a regular basis does more harm than good, because you disturb the established pattern of microorganisms and so create a situation where really nasty things can creep into your home, that in addition are new to your immunesystem. I'm not saying that you shouldn't clean your home, but trying to keep it near-sterile every week is really overdoing it, without a clear justification why those things you try to eradicate should not peacefully coexist with you. TheMaster17 (talk) 08:12, 23 April 2009 (UTC)[reply]
I would assume that the idea is to heat the water in a damp dishcloth to boiling point (or so) and to keep it there long enough to sterilise it. But I'd be pretty surprised if that actually worked. If you merely warm it up to a nice comfy body-heat, you may actually be encouraging the bacteria to multiply. I strongly agree that an overly sensitive person can do more harm than good. Continually killing only 99% of bacteria simply encourages the remaining 1% to evolve to the point where you can't kill them that way. Better to reserve that killing capability until you actually need it for something. Also, it's been well documented that children NEED exposure to a wide variety of bacteria in order to develop immune responses to them. Children who are born into families of "neat freaks" get sick far more often than those of people with a more relaxed attitude to cleanliness. So, keep things clean - yes. Pay a heck of a lot of attention to places where you prepare chicken and such - but otherwise, chill out. We are able to withstand most of what the bacteria can throw at us without even noticing that we're doing it - and when we do get sick, modern medicine is there to help. Of course different rules come into play if you're actually immuno-compromised in some way (eg with AIDS or something). SteveBaker (talk) 11:53, 23 April 2009 (UTC)[reply]
No. White vinegar is distilled, and is basically pure, dilute acetic acid. White wine vinegar is vinegar made from white wine, and it retains some of the complex flavors associated with wine. IMO, white vinegar is not very useful for cooking due to its simple flavor (but can be useful for cleaning coffeemakers, etc.), while white wine vinegar is quite useful for sauces, vinaigrettes, etc. -- Coneslayer (talk) 17:05, 22 April 2009 (UTC)[reply]
White (distilled) vinegar can be used for cooking, but would be used in pickling or acidifying something (like the water used to cook poached eggs) when you don't want to add any additional flavors. I wouldn't use distilled vinegar in something like a vinaigrette or sauerbraten, where the flavor of the vinegar is a major component of the dish. -- 128.104.112.117 (talk) 22:23, 22 April 2009 (UTC)[reply]
I think I am probably just not trying the right search terms, but where can I learn more about the tendency of some birds to collect (e.g. steal) shiny things and other man made objects for use in their nests? I'd like to know more about which birds do this and what types of things they go after. Dragons flight (talk) 23:38, 22 April 2009 (UTC)[reply]
Magpies hoard food; that behavior is well documented. I know magpies are also said to steal and hoard shiny objects, but I'm not sure there is any rigorous scientific study of that. If they do that at all, I guess it must be an extension of the food hoarding behavior. Now the bowerbird that Steve mentioned is a different story altogether. In bowerbirds, collecting colorful objects is a part of a (pretty damn impressive) courtship ritual. --Dr Dima (talk) 05:14, 23 April 2009 (UTC)[reply]
NRPG. I'm uncertain as to what it means, and don't know where it is located in the CNS. Possibly called the Nucleus reticularis paragigantoceullaris, it definately excites the Raphe magnus and is involved in opiod modulation of pain transmission. Is that what its called and am I correct in assuming its next to the gigantocellular nucleus. Any help would be most appreciated, many thanks MedicRoo (talk) 01:15, 23 April 2009 (UTC)[reply]
Light through optical centre
Imagine that a light ray passes towards the direction of the optical centre of a convex lens.
when the light ray strikes the lens from air, it is not normally incident. So, it must be bent towards the normal at that point. It means that it will not pass through the optical centre. Even if it does, as it emerges out of the lens, it is not normally incident on the glass-air boundary. So it will be shifted away from the normal. It means that the light ray will emerge parallel to the incident ray. But the wiki article says that it will not get deviated. Please Explain with diagrams--harish (talk) 01:28, 23 April 2009 (UTC)[reply]
You didn't say what article you're talking about, but in any case, the ray will only emerge parallel to the incident ray if the angles of bending are exactly opposite when it enters and leaves the glass, which will only happen if the glass surfaces are parallel on both sides. For a convex lens as shown in the figure, the two sides of the glass are not parallel. Looie496 (talk) 02:46, 23 April 2009 (UTC)[reply]
The two surfaces are papallel at the center of the lens which seems to be the point of the question, though that is not entirely clear to me. Dauto (talk) 04:22, 23 April 2009 (UTC)[reply]
I heard of the news today that medical research has shown that the use of Bonjela and similar over-the-counter treatments contain salts which could cause liver and/or brain damage in children under the age of 16. I'm curious in knowing which chemicals in Bonjela cause these side effects, and why the risk of damage to adults doesn't exist. Is it due to a more developed blood-brain barrier or maybe a metabolic deficiency that disappears over the age of 16? I can't find much reason why the same salts wouldn't cause toxic effects in adults. Regards, --āCyclonenim |Ā ChatĀ 07:08, 23 April 2009 (UTC)[reply]
Bonjela contains similar ingredients to aspirin, whose use is strongly correlated with Reye's syndrome in small children. That article itself mentions that the cause really is unknown, and my quick search of google scholar shows that this is still a very active area of research with little concrete evidence on any reason for the link, although the link itself is very firmly established for at least injested pills. Someguy1221 (talk) 07:41, 23 April 2009 (UTC)[reply]
I understand that the resolution or amount of detail that can be seen by telescopes, both optical and radio wave, increases with their width. And that very wide telescopes can be simulated by joining up two or more widely-spaced telescopes in an array. I know such arrays have been formed of radio telescopes at least. I'm not sure if optical telescopes have been linked like this yet, or if that is something for future technology.
My question is, if you had a very long baseline for two or more telescopes, such as one telescope being on earth and another on the moon or even on Neptune or Pluto, would the amount of detail be enough to see planets orbiting stars, or even see some surface detail on those planets? And is there any theorectical limit to the length of the baseline? 89.242.82.4 (talk) 10:56, 23 April 2009 (UTC)[reply]
What becomes tricky on very large scales is the speed-of-light limitations in the communications path between telescopes. Also, no matter how far apart you put your telescopes, their light-gathering abilities don't get any better - so imaging very dim objects doesn't really improve. SteveBaker (talk) 11:42, 23 April 2009 (UTC)[reply]
(ec) The technique is a type of astronomical interferometry called aperture synthesis. It's been done for a long time in radio astronomy; Very Long Baseline Interferometry can link radio telescopes across the entire face of the Earth. High-precision atomic clocks allow radio astronomers to synchronize and combine radio signals from widely separated telescopes.
The problem is quite a bit more difficult at optical wavelengths. Because radio waves are typically a million times (or more) longer than visible and near-infrared light waves, the problem of 'lining up' the data from multiple radio telescopes is correspondingly much easier than it would be for a similar array of optical telescopes. (On the plus side, the much-shorter optical wavelengths mean that comparable resolution can be obtained with a much smaller baseline size.)
Nevertheless, a substantial number of optical interferometers now exist: List of astronomical interferometers at visible and infrared wavelengths. One of the largest is the CHARA array in California; its six telescopes are linked optically through a series of vacuum-filled pipes to generate a 330-meter (1100-foot) baseline. Together, they can resolve features down to 0.0005 arcseconds (0.5 milliarcseconds) ā in 2007 they generated images of the surface of the star Altair, 17 light years away.
The twin 10-meter Keck telescopes in Hawaii can be linked optically to generate a very sensitive nulling interferometer with an 85-meter baseline. In that configuration, they are aimed at a star and configured so that the light from that star is optically cancelled-out between the two telescopes. Off-center light ā as from an extrasolar planet ā doesn't get cancelled out. In principle, the planet should become visible once it's no longer drowned out by the glare of its star.
Off the top of my head, I don't think there's any upper limit imposed by physics on the size of an interferometer array. The real bounds are the limitations of engineering. For an optical interferometer to work, you need to know and maintain the relative positions of the components with a precision of less than one micron (smaller than the wavelength of the light you're collecting). It's painstaking but possible to do when you've got a group of telescopes all together on the same mountain; it's a nightmare to manage if you want to put the telescopes further apart. Proposals exist for space-based optical interferometers as well, though as far as I know none are currently under construction. TenOfAllTrades(talk) 12:10, 23 April 2009 (UTC)[reply]
I don't want to spoil your wonderful answer, Ten, but I have to say that "vacuum-filled" made me do a double-take. Deor (talk) 13:08, 23 April 2009 (UTC)[reply]
The subjective experience of being blind
Does it seem like perpetual black night? Or might it even be whiteness, or nothingness? The blind spot on the eye is more like nothingness or whiteness rather than blackness, with the brain seeming to fill in what is there from the surrounding image. See http://www.colorcube.com/illusions/blndspot.htm As there are various causes of blindness, so the subjective experience may differ. 89.242.82.4 (talk) 11:07, 23 April 2009 (UTC)[reply]
For people who have been utterly blind since conception, whole areas of the brain related to vision don't develop so I doubt there would be any sense of 'blackness' - just no vision sense at all. That's impossible for a sighted person to even imagine and discussing what that means with a blind-since-birth person results in no common terms of reference. They can't explain what it's like to not have a sense that they never had. Can you explain to a dolphin what it's like to have no echolocation sense? Or to a fish, how it feels to have no lateral-line electrical sense? I don't think so. People who have become blind after being sighted will doubtless have a different sense of what it's like. SteveBaker (talk) 11:40, 23 April 2009 (UTC)[reply]
I once heard someone saying (I am not blind) that a completely blind person can see just as much with their eyes as I can see with my knees. That makes it pretty clear for me... -M āPreceding unsigned comment added by 195.67.112.146 (talk) 12:21, 23 April 2009 (UTC)[reply]
There is a phenomenon in perception (I'm blanking on the name right now, but it's related to change blindness and inattentional blindness) where the mind subtracts out a constant stimulus. It still may be registering at the sensory nerves, but after a while it is no longer perceived consciously. You've probably experienced this yourself. If there's a humming fan, after awhile it no longer registers, but when it turns off you can "hear" the silence. Likewise with scents - after a short period in a strongly scented room, you no longer can smell anything "off", but leave and reenter and the smell hits you. I would imagine the same would happen with a blind person. Immediately after becoming totally blind they might register a strong white/strong black perception. But after a while with that constant stimulus, the brain would ignore the signals coming from the optic nerves completely, and they wouldn't "see" anything at all. -- 128.104.112.117 (talk) 14:38, 23 April 2009 (UTC)[reply]
Why do people collect things / derive satisfaction from completing sets of objects?
I am well aware of hoarding, but I'm interested in the more mundane and widespread human compulsion to collect things. I know we're not the only animal to do this, but I'm having a hard time seeing the evolutionary value of such a finely honed desire to accumulate things.
I'm sure there are occasional cases where an impressive collection of _____ resulted in the acquisition of a mate, but I doubt that that was the conscious goal of the collection to begin with.
So... why do (most) humans feel a need and derive satisfaction from collecting things? What is it about a complete set that soothes the mind? Oftentimes these objects serve no use other than to occupy space (and please the collector...)
61.189.63.224 (talk) 13:00, 23 April 2009 (UTC)[reply]
Not all human desires/traits are linked (clear or otherwise) to an evolutionary reason. We could speculate that things that are collectable have their roots in effort/time/reward. It takes time and effort to get a complete set of something, so the satisfcation is the reward. If you receive a complete set instantly it wouldn't have your emotional journey attached to it. I'm not sure that everything needs to have an evoluntionnary reason for existence. 194.221.133.226 (talk) 13:52, 23 April 2009 (UTC)[reply]
Just a guess: In prehistoric times collecting nuts and berries (food) may, on occasions, have made a difference between survival or not. Equally, gathering bits of timber (fire) and heaps of rock fragments (defense / tools) may have given some hominids an advantage in survival. Collecting stamps, beer coasters or Van Goghs could be just a sublimation of this. --Cookatoo.ergo.ZooM (talk) 14:23, 23 April 2009 (UTC)[reply]
Is it possible that it's a learned behavior planted in our heads by society? How many times in your life have you heard the phrase "collect all six" (or whatever quantity)? Is the drive to collect a set universal in all cultures, or only in capitalistic societies? 168.9.120.8 (talk) 14:29, 23 April 2009 (UTC)[reply]
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