While superstring theory (or M theory, or GUT-of-the-day) is certainly important, something is amiss with the idea that solving the equations, or even determining that we have the right set of equations, will provide us with any understanding.
We have the equations (as far as we know) to accurately and essentially perfectly describe classical phenomena (fluids, plasmas, day-to-day things) -- kinetic theory, in its most primal and ugly form, whichs tracks every goddamn particle and interaction. This is unfortunately useless, as the system of equations is then far too large for our puny brains or computers to deal with. Therefore, we replace the correct equations with approximations -- newtonian mehcanics, statisical mechanics, fluid dynamics, chaotic systems, etc.
Nature is quite possible just too large and varied to be understood through possession of the proper equations and solutions. Depressing, huh?
Despite the often choppy and bad sound quality streaming MP3 servers provide me with much better access to unknown indie music than napster did. (eg indiepopradio.com) So when will the FCC (or corresponding agency) start shutting it down, because it is competition with the broadcast corporations?
Maybe when the sound quality is good enough, or there is money to be made?
I suppose they could really be afraid of people capturing the songs from the stream, much like I would tape the radio when I was young because I couldn't afford to buy every goddamn album I wanted.
Anyway, the same issue will come up again and again, because goddammit the people with control don't wanna lose it. I don't blame them, much.
Possbily I haven't lost anything that I 'have a right to', but I have lost (until I start up another service) one of the few places where I learn new music that I will actually buy. Radio stations, now, tend to suck horribly, and I can't even listen to the college/independent stations for what I want more than a few hours a week. (I guess i'm not young enough for most of the music they're playing...) But with napster, I could go look at other people's choices, find similar tastes, etc.
And some indie musicians will loose me buying their CDs and going to shows, until I find other sources to hear them. I'm sure i'm not the only one.
The result of this decision, in the short term at least, is to criminalize that trading not organized by the record labels. Maybe it cannot be prevented, blah blah blah, but this puts it one more step towards a prosecutable crime, and more towards me not doing it.
So I lost something. Whether I had a right to that thing or not is what is being decided in court, unfortunately.
You're essentially right -- the guy down the hall (worked with CO2 lasers) says they work through a combination of gases, (nitrogen/hydrogen and CO2). The nitrogen is ionized through some technique -- a glow discharge in this case -- and either the ions or electrons created then excite a particular CO2 state (we don't remember if it is rotational or vibrational.) This takes place in a tuned cavity (a quartz or glass tube of order 1m with mirrors at either end) which selects the wavelength of that particular state's transition eneregy, thus created a surplus of directed energy which excites more and more of the same radiation by resonating with the CO2. Frequency is tunable, to some degree, by changing the cavity length.
He also says efficiency is no concern. I only know that the CO2 laser beam was invisible, and could give you a nasty burn. The cavity for it had a purple (probably nitrogen) glow.
Of course, this topic has probably decayed past the care threshold, given the/. fickle-ity, but the websites for the research groups doing the plasma sheilding work are
Since NASA is always working on propulsion techniques (the tether, plasma thrusters) to overcome atmospheric friction for a minimal mass expense rather than the inefficient chemical rockets typically used, you would think this would make a rather poor shielding device. Also, the plasma density can no doubt be expressed as a percentage of the gas density--likely a fairly low percentage.
They probably don't mention CO2 because of the large ionization energies involved (for an atomic plasma -- molecular plasmas are beyond my expertise.) I'm not sure that you get a gain in a laser from this -- the CO2 laser transition is a molecular transition that may not exist once the gas is ionized, and the thermal heating due to the RF is not generating the organized state inversion necessary to 'lase'.
Low temperature plasmas are currently used to shield the contact surfaces in fusion experiments (i.e. tokamaks), in several versions, with the radiative divertor being the most common technique. Essentially, a high density (relative to the core neutral density) gas is puffed at the point at which the plasma would heath the wall most strongly. This gas then heats and ionizes, and radiates the excess heat rather than letting the wall melt. Unfortunately, a plasma won't absrob the high neutron flux present in all of the current reactor scenarios, so radiative divertors are only a partial solution. The direct conversion of this excess energy to electrical currents through an increase in stored magnetic field/plasma energy is rather more complicated. It would have to involve something like an MHD (magnetohydrodynamic) generator, which is certainly a real idea. In the case of absorbing energy from the edge plasma though, you need to find some trick to create an organized plasma flow (low entropy) of some sort from the pretty high entropy state of the plasma edge. Not entirely unreasonable (tokamaks do self-generate current flows) but beyond the current state of the research. Rest assured, though, people are working on it...
Slashdot Mirror
While superstring theory (or M theory, or GUT-of-the-day) is certainly important, something is amiss with the idea that solving the equations, or even determining that we have the right set of equations, will provide us with any understanding.
We have the equations (as far as we know) to accurately and essentially perfectly describe classical phenomena (fluids, plasmas, day-to-day things) -- kinetic theory, in its most primal and ugly form, whichs tracks every goddamn particle and interaction. This is unfortunately useless, as the system of equations is then far too large for our puny brains or computers to deal with. Therefore, we replace the correct equations with approximations -- newtonian mehcanics, statisical mechanics, fluid dynamics, chaotic systems, etc.
Nature is quite possible just too large and varied to be understood through possession of the proper equations and solutions. Depressing, huh?
Despite the often choppy and bad sound quality streaming MP3 servers provide me with much better access to unknown indie music than napster did. (eg indiepopradio.com) So when will the FCC (or corresponding agency) start shutting it down, because it is competition with the broadcast corporations?
Maybe when the sound quality is good enough, or there is money to be made?
I suppose they could really be afraid of people capturing the songs from the stream, much like I would tape the radio when I was young because I couldn't afford to buy every goddamn album I wanted.
Anyway, the same issue will come up again and again, because goddammit the people with control don't wanna lose it. I don't blame them, much.
Possbily I haven't lost anything that I 'have a right to', but I have lost (until I start up another service) one of the few places where I learn new music that I will actually buy. Radio stations, now, tend to suck horribly, and I can't even listen to the college/independent stations for what I want more than a few hours a week. (I guess i'm not young enough for most of the music they're playing...) But with napster, I could go look at other people's choices, find similar tastes, etc.
And some indie musicians will loose me buying their CDs and going to shows, until I find other sources to hear them. I'm sure i'm not the only one.
The result of this decision, in the short term at least, is to criminalize that trading not organized by the record labels. Maybe it cannot be prevented, blah blah blah, but this puts it one more step towards a prosecutable crime, and more towards me not doing it.
So I lost something. Whether I had a right to that thing or not is what is being decided in court, unfortunately.
You're essentially right -- the guy down the hall (worked with CO2 lasers) says they work through a combination of gases, (nitrogen/hydrogen and CO2). The nitrogen is ionized through some technique -- a glow discharge in this case -- and either the ions or electrons created then excite a particular CO2 state (we don't remember if it is rotational or vibrational.) This takes place in a tuned cavity (a quartz or glass tube of order 1m with mirrors at either end) which selects the wavelength of that particular state's transition eneregy, thus created a surplus of directed energy which excites more and more of the same radiation by resonating with the CO2. Frequency is tunable, to some degree, by changing the cavity length.
/. fickle-ity, but the websites for the research groups doing the plasma sheilding work are
He also says efficiency is no concern. I only know that the CO2 laser beam was invisible, and could give you a nasty burn. The cavity for it had a purple (probably nitrogen) glow.
Of course, this topic has probably decayed past the care threshold, given the
http://aprp.stanford.edu/
http://www.ece.odu.edu/~mlarouss/
and it is a real military project.
Since NASA is always working on propulsion techniques (the tether, plasma thrusters) to overcome atmospheric friction for a minimal mass expense rather than the inefficient chemical rockets typically used, you would think this would make a rather poor shielding device. Also, the plasma density can no doubt be expressed as a percentage of the gas density--likely a fairly low percentage.
They probably don't mention CO2 because of the large ionization energies involved (for an atomic plasma -- molecular plasmas are beyond my expertise.) I'm not sure that you get a gain in a laser from this -- the CO2 laser transition is a molecular transition that may not exist once the gas is ionized, and the thermal heating due to the RF is not generating the organized state inversion necessary to 'lase'.
Low temperature plasmas are currently used to shield the contact surfaces in fusion experiments (i.e. tokamaks), in several versions, with the radiative divertor being the most common technique. Essentially, a high density (relative to the core neutral density) gas is puffed at the point at which the plasma would heath the wall most strongly. This gas then heats and ionizes, and radiates the excess heat rather than letting the wall melt. Unfortunately, a plasma won't absrob the high neutron flux present in all of the current reactor scenarios, so radiative divertors are only a partial solution. The direct conversion of this excess energy to electrical currents through an increase in stored magnetic field/plasma energy is rather more complicated. It would have to involve something like an MHD (magnetohydrodynamic) generator, which is certainly a real idea. In the case of absorbing energy from the edge plasma though, you need to find some trick to create an organized plasma flow (low entropy) of some sort from the pretty high entropy state of the plasma edge. Not entirely unreasonable (tokamaks do self-generate current flows) but beyond the current state of the research. Rest assured, though, people are working on it...