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I'm trying to figure this out, and I can't: "A/A and A/a individuals are equally fertile. If 0.1 percent of the population is a/a, what selection pressure exists against a/a if the A → a mutation rate is 10^−5?" I have found online that the answer is 0.01, but I would like to know why. Any help is much appreciated. Thanks! — anon. —Preceding unsigned comment added by 141.155.31.61 ( talk) 01:41, 9 January 2008 (UTC)
Are there any theories as to the evolutionary benefit of the many neural decussations, either individually or together? Tuckerekcut ( talk) 02:11, 9 January 2008 (UTC)
How do we estimate earth's mass? From what I heard scientists don't even know exactly the composition of the earth's interior. 199.76.154.127 ( talk) 05:08, 9 January 2008 (UTC)
Do we have a list of conditions which cause people to be hypersensitive to light, sounds, odors, tastes, and touch ? The linked article in the title seems to be more about immune system over-reactions than what I have in mind. For example, someone suffering from a hangover may react badly to bright lights, loud noises, and strong smells and tastes. StuRat ( talk) 16:55, 9 January 2008 (UTC)
So there isn't any term for the condition of being hypersensitive across all the senses ? StuRat ( talk) 19:10, 10 January 2008 (UTC)
btw, Roderick Usher in the 'Fall of the House of' suffered this. In one of his novels, I think William Gibson calls the process of tuning the sensorium for high sensitivity 'to Usher'. Adambrowne666 ( talk) 10:24, 14 January 2008 (UTC)
D/Sir/Madam, For my high school project, I want some article on the above subject. Can you please help me out ?. Regards ! D.J.Sen —Preceding unsigned comment added by 220.226.37.124 ( talk) 16:57, 9 January 2008 (UTC)
I'm reading up on the history of quantum mechanics and I must confess I'm a little confused. I have a strong background in physics, having graduated with a degree in mechanical engineering from the University of Minnesota Institute of Technology, but one particular aspect of the quantum theory is bothering me.
It would seem that the precipitating factor in the development of quantum theory is that atomic emissions appear to be discrete (in terms of energy or frequency). In other words, it was observed that light is emitted from excited atoms (or rather atoms exiting an excited state) in specific frequencies, and thus the concept of energy levels was born.
However, it seems a logical leap to say that because electrons exist in an atom at discrete energy levels (and therefore the photons emitted by those electrons occur at discrete frequencies) that light itself must be quantized. Light could very well be continuous, and it's just the structure of the atom that is discrete.
What experiment or theory substantiates this leap? How do we go from the idea that atomic structure is quantized to the idea that all energy must be quantized. It's like saying because bottled water from the grocery store only comes in discrete quantities, that water itself must be organized into discrete packets. In a macro-sense, water is continuous, it is only the container that is discrete.
Thanks! FusionKnight ( talk) 17:14, 9 January 2008 (UTC)
Thank you for the responses! I appreciate it. However, I think you've just restated my original problem. The reason scientists believe energy to be quantized is because of observations of the black body problem and the photoelectric effect. However, the observed quanta are a result of atomic structure only allowing electrons to exist in specified energy levels or orbitals (and therefore only oscillating between those specific levels). I'm still missing the part where energy levels imply the quantization of energy rather than just the quantum nature of atomic structure. FusionKnight ( talk) 18:41, 9 January 2008 (UTC)
Make sure you have a look at Wave_particle_duality. In short, any matter or energy exhibits at all times both wave an packet (or quantized) behavior, except only one of those behaviors can be observed at a a time. Don't forget that it wasn't a simple or quick step from one idea to the next here but the result of a few centuries of theory, experiments, nobel prizes, and arguments which continue to today. Furmanj ( talk) 21:01, 9 January 2008 (UTC)
Without wanting to belabor a point, the introduction to photon seems to address this directly in regards to what are called the semiclassical models, whereby light is described according to Maxwell's equations (continuous) but interacts with matter in a quantized way. This was apparently an objection some had and a way some tried to "save" the classical theory, and was only later shown to be incompatible with experiments. If you are asking why Einstein would have assumed it was quantized, well, Einstein was, in those days anyway, a self-styled revolutionary and a strong Machian at that. The former quality would make him not shudder away from making as strong a statement as he felt possible, and the latter would cause him to regard any speculation about the nature of light other than how it interacted in a measurable way to be pointless metaphysical speculation. Anyway, footnote 31 in the article seems to be a reference relating to the semiclassical models, you might turn there. This isn't an aspect of the the history of physics I'm acquainted with myself, though I have a passable knowledge of the history of quantum theory. -- 24.147.86.187 ( talk) 03:10, 10 January 2008 (UTC)
So, let me see if I'm understanding correctly. The photoelectric effect showed that light must be absorbed by electrons discretely because the intensity of light had no effect on the threshold but frequency did. This meant that photons are particle-like; a single photon, if cold, won't eject an electron, but a hot one will.
If the wave theory of light had been correct, the threshold energy could be overcome either by increasing amplitude or frequency since the power of a (mechanical) wave is dictated by both its amplitude and frequency. Since the photoelectric effect was seen to be non-additive (i.e. a more intense wave or a less intense wave over time did not have the same effect as a wave of higher frequency), that meant that the "amplitude" of a light wave didn't carry energy in the same way as a sound wave or other mechanical waves.
And that was the leap. There was no luminiferous aether in which the wave propagated, because there was not "true amplitude" in a mechanics sense. So Einstein said "amplitude" for light must be something else, like... number of photons per second! Then the photoelectric effect makes sense.
So, as a previous poster said, energy quantization doesn't say that a photon's energy has to be an integer multiple of some constant, but rather that energy (photons) don't behave entirely like ordinary waves, and in fact seems to act like particles on occasion. Does that sound right? FusionKnight ( talk) 15:17, 10 January 2008 (UTC)
SIR/MADAM I HAVE STARTED TO RESEARCH ON SYSTEM DYNAMICS, BUT I AM STILL LOOKING FOR SOME USEFUL LINKS WHICH COULD HELP FRESHERS IN THIS FEILD —Preceding unsigned comment added by 202.70.201.120 ( talk) 18:28, 9 January 2008 (UTC)
I recently saw a picture of a penguin with an all-white covering, and it made me think of the question. I would guess that in the evolution of penguins, white feathers would be favored, or at least being not totally black, so as to camouflage in the snowy/icy environment. Or does the black covering help in camouflage under water? But still, I'm amazed at how much black feathers dominate in the diverse penguin population, as opposed to lighter feathers. 128.163.224.198 ( talk) 18:35, 9 January 2008 (UTC)
I was looking at the sucrose_molecule_3d_model.png/800 and I am pretty sure it is incorrectly drawn. It shows a six membered ring connected to a six membered ring. The structure directly above it is a six membered ring connected to a five membered ring. The correct number of carbon, hydrogen and oxygen are attached. However the carbon attached to the oxygen holding the rings together should have no hydrogen attached to it.
This will alter the structure correctly. —Preceding unsigned comment added by 141.154.107.189 ( talk) 20:03, 9 January 2008 (UTC)
Are there any native bears in the southern hemisphere? 202.168.50.40 ( talk) 23:13, 9 January 2008 (UTC)
Science desk | ||
---|---|---|
< January 8 | << Dec | January | Feb >> | January 10 > |
Welcome to the Wikipedia Science Reference Desk Archives |
---|
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages. |
I'm trying to figure this out, and I can't: "A/A and A/a individuals are equally fertile. If 0.1 percent of the population is a/a, what selection pressure exists against a/a if the A → a mutation rate is 10^−5?" I have found online that the answer is 0.01, but I would like to know why. Any help is much appreciated. Thanks! — anon. —Preceding unsigned comment added by 141.155.31.61 ( talk) 01:41, 9 January 2008 (UTC)
Are there any theories as to the evolutionary benefit of the many neural decussations, either individually or together? Tuckerekcut ( talk) 02:11, 9 January 2008 (UTC)
How do we estimate earth's mass? From what I heard scientists don't even know exactly the composition of the earth's interior. 199.76.154.127 ( talk) 05:08, 9 January 2008 (UTC)
Do we have a list of conditions which cause people to be hypersensitive to light, sounds, odors, tastes, and touch ? The linked article in the title seems to be more about immune system over-reactions than what I have in mind. For example, someone suffering from a hangover may react badly to bright lights, loud noises, and strong smells and tastes. StuRat ( talk) 16:55, 9 January 2008 (UTC)
So there isn't any term for the condition of being hypersensitive across all the senses ? StuRat ( talk) 19:10, 10 January 2008 (UTC)
btw, Roderick Usher in the 'Fall of the House of' suffered this. In one of his novels, I think William Gibson calls the process of tuning the sensorium for high sensitivity 'to Usher'. Adambrowne666 ( talk) 10:24, 14 January 2008 (UTC)
D/Sir/Madam, For my high school project, I want some article on the above subject. Can you please help me out ?. Regards ! D.J.Sen —Preceding unsigned comment added by 220.226.37.124 ( talk) 16:57, 9 January 2008 (UTC)
I'm reading up on the history of quantum mechanics and I must confess I'm a little confused. I have a strong background in physics, having graduated with a degree in mechanical engineering from the University of Minnesota Institute of Technology, but one particular aspect of the quantum theory is bothering me.
It would seem that the precipitating factor in the development of quantum theory is that atomic emissions appear to be discrete (in terms of energy or frequency). In other words, it was observed that light is emitted from excited atoms (or rather atoms exiting an excited state) in specific frequencies, and thus the concept of energy levels was born.
However, it seems a logical leap to say that because electrons exist in an atom at discrete energy levels (and therefore the photons emitted by those electrons occur at discrete frequencies) that light itself must be quantized. Light could very well be continuous, and it's just the structure of the atom that is discrete.
What experiment or theory substantiates this leap? How do we go from the idea that atomic structure is quantized to the idea that all energy must be quantized. It's like saying because bottled water from the grocery store only comes in discrete quantities, that water itself must be organized into discrete packets. In a macro-sense, water is continuous, it is only the container that is discrete.
Thanks! FusionKnight ( talk) 17:14, 9 January 2008 (UTC)
Thank you for the responses! I appreciate it. However, I think you've just restated my original problem. The reason scientists believe energy to be quantized is because of observations of the black body problem and the photoelectric effect. However, the observed quanta are a result of atomic structure only allowing electrons to exist in specified energy levels or orbitals (and therefore only oscillating between those specific levels). I'm still missing the part where energy levels imply the quantization of energy rather than just the quantum nature of atomic structure. FusionKnight ( talk) 18:41, 9 January 2008 (UTC)
Make sure you have a look at Wave_particle_duality. In short, any matter or energy exhibits at all times both wave an packet (or quantized) behavior, except only one of those behaviors can be observed at a a time. Don't forget that it wasn't a simple or quick step from one idea to the next here but the result of a few centuries of theory, experiments, nobel prizes, and arguments which continue to today. Furmanj ( talk) 21:01, 9 January 2008 (UTC)
Without wanting to belabor a point, the introduction to photon seems to address this directly in regards to what are called the semiclassical models, whereby light is described according to Maxwell's equations (continuous) but interacts with matter in a quantized way. This was apparently an objection some had and a way some tried to "save" the classical theory, and was only later shown to be incompatible with experiments. If you are asking why Einstein would have assumed it was quantized, well, Einstein was, in those days anyway, a self-styled revolutionary and a strong Machian at that. The former quality would make him not shudder away from making as strong a statement as he felt possible, and the latter would cause him to regard any speculation about the nature of light other than how it interacted in a measurable way to be pointless metaphysical speculation. Anyway, footnote 31 in the article seems to be a reference relating to the semiclassical models, you might turn there. This isn't an aspect of the the history of physics I'm acquainted with myself, though I have a passable knowledge of the history of quantum theory. -- 24.147.86.187 ( talk) 03:10, 10 January 2008 (UTC)
So, let me see if I'm understanding correctly. The photoelectric effect showed that light must be absorbed by electrons discretely because the intensity of light had no effect on the threshold but frequency did. This meant that photons are particle-like; a single photon, if cold, won't eject an electron, but a hot one will.
If the wave theory of light had been correct, the threshold energy could be overcome either by increasing amplitude or frequency since the power of a (mechanical) wave is dictated by both its amplitude and frequency. Since the photoelectric effect was seen to be non-additive (i.e. a more intense wave or a less intense wave over time did not have the same effect as a wave of higher frequency), that meant that the "amplitude" of a light wave didn't carry energy in the same way as a sound wave or other mechanical waves.
And that was the leap. There was no luminiferous aether in which the wave propagated, because there was not "true amplitude" in a mechanics sense. So Einstein said "amplitude" for light must be something else, like... number of photons per second! Then the photoelectric effect makes sense.
So, as a previous poster said, energy quantization doesn't say that a photon's energy has to be an integer multiple of some constant, but rather that energy (photons) don't behave entirely like ordinary waves, and in fact seems to act like particles on occasion. Does that sound right? FusionKnight ( talk) 15:17, 10 January 2008 (UTC)
SIR/MADAM I HAVE STARTED TO RESEARCH ON SYSTEM DYNAMICS, BUT I AM STILL LOOKING FOR SOME USEFUL LINKS WHICH COULD HELP FRESHERS IN THIS FEILD —Preceding unsigned comment added by 202.70.201.120 ( talk) 18:28, 9 January 2008 (UTC)
I recently saw a picture of a penguin with an all-white covering, and it made me think of the question. I would guess that in the evolution of penguins, white feathers would be favored, or at least being not totally black, so as to camouflage in the snowy/icy environment. Or does the black covering help in camouflage under water? But still, I'm amazed at how much black feathers dominate in the diverse penguin population, as opposed to lighter feathers. 128.163.224.198 ( talk) 18:35, 9 January 2008 (UTC)
I was looking at the sucrose_molecule_3d_model.png/800 and I am pretty sure it is incorrectly drawn. It shows a six membered ring connected to a six membered ring. The structure directly above it is a six membered ring connected to a five membered ring. The correct number of carbon, hydrogen and oxygen are attached. However the carbon attached to the oxygen holding the rings together should have no hydrogen attached to it.
This will alter the structure correctly. —Preceding unsigned comment added by 141.154.107.189 ( talk) 20:03, 9 January 2008 (UTC)
Are there any native bears in the southern hemisphere? 202.168.50.40 ( talk) 23:13, 9 January 2008 (UTC)