In case anyone's interested, I worked out some numbers on the force of the light on this thing relative to that of the sun's gravity. Both forces drop as inverse squares of the distance from the sun, so the ratio between them remains constant.
The force due to the light is determined by the area of the sail and the luminosity of the sun (which I looked up), while the force due to gravity is just determined by the mass of the spacecraft and the mass of the sun.
When you work out the numbers using the area and mass quoted in the article, the force of gravity from the sun turns out to be about 200,000 times greater than that of the light.
This means (as the article states) that the best such a spacecraft can do is remain in orbit around the sun, and angle the light in such a way as to gradually spiral out to a higher orbit.
Alas, no interstellar travel with one of these guys, since we can never break out of solar orbit. For a spacecraft with this size solar sail to achieve interstellar travel, it would need to have a mass of less than 0.3 grams! That would require quite an impressive materials breakthrough, I'm afraid.
Actually, you are forgetting about the fact that a spacecraft would be in orbit around the sun. It is true that there will be no keel, and you won't be able to tack to control your direction.
However, you will still be able to go towards the sun just as easily as going away from it, because the sun's gravity will still be the dominant force in play. To travel towards the sun, you angle your sail to slow you down, while to travel away from the sun you angle it to increase your orbital velocity.
If you reflect the sunlight directly back at the sun, you won't travel away from it at all, even though the light will be exerting a maximum force on your spacecraft.
This is because regardless of your distance from the sun, the gravitational force will always be greater than the light force. Actually, the ratio between the two is determined by the area/mass ratio of your spacecraft, but for those that are proposed, gravity will dominate. This also means they won't be practical for leaving the solar system, since they would have to spiral out rather slowly.
Actually this is new (or rather, was new last year), since the index of refraction is the sqrt of the product of dielectric constant and the permeability.
If only one of them is negative, you have an imaginary index of refraction, and no travelling waves, which is why AM radio is reflected by the ionosphere...
On the contrary, it is even worse than the original poster suggested. Where do you think the oil comes from? If is a result of the anaerobic decay of plant matter (a.k.a. sugar). Therefore, it must be a lower free energy state than the original plant matter.
So it would seem that we'd be taking one step forward and two steps backward...
That's true. The speckles you see from laser light are are result of interference of the coherent light. I'm not sure how the resolution of your eye would come into play, as it would seem to me that the dominant effect of moving your head would be to change the interference pattern.
I read all about this a month or two ago, and the catch is that it has an incredibly short focal length. Specifically, the focal length is just the thickness of the lens. This is not your ordinary lens, and really can only be used for near field work. Actually the total distance between the object and the image is twice the thickness of the lens.
Anyhow, so it isn't too practical for most of the things we use lenses for, although it is still a very impressive piece of work.
I would imagine for things like quizes at the beginning of class, possibly even tests. I have a friend who went to a med school where they required laptops, and there it was quite useful. They had network/power connections at each seat, and for things like anatomy tests it was very helpful to be able to show the students full color photos (and have them go at their own paces).
Of course, that sort of stuff requires lots of work and infrastructure, but even here at Cal they are doing online prelabs over the web. This means that Chem 1 students who don't have access to computers need to come into a computer lab each week which must be a pain.
They (the black lab folks) do offer G4s as an option, still using imac motherboards. They even offer a couple of different speeds.
And altivec is next to worthless for most mathematical computation. It only works on single precision floats, and even then doesn't even give you a factor of two speedup, since there is (as I recall) only one altivec unit so you can't pipeline the altivec calls. On the other hand, the G4 has more floating point units than the G3, and faster ones, so it definitely would be much better.
If you mean by "authentic" source, that your trusted friend emails you his key, this is not safe. Email is alterable. An adversary can insert an ADK into the mailed key, that will not be visible to you without specific scrutiny with a hex editor or special GPG incantations.
Presumably if you are bothering to use PGP your friend would either encrypt the key when he emails it to you, or would sign it (preferably both). Either way it should be fine, as long as you don't rely on the self-signature of the key itself.
You wouldn't want a cluster of clusters, but you could set up a unified queue system. This is what they do at NCSA in IL. You log onto the interactive machine, modi4, and submit jobs to the queue. It then sends them off to any one of a slew of other machines. These are all Origin 2000 systems with either 64 or 128 nodes each, and either a quarter or half a gig of ram per node.
It is quite a nice little system when you have enough users to keep it busy, and I imagine is quite easily scalable. The only trick is that if there are differences between the various machines you can have really annoying and hard to track down bugs. Fortunately consult is very responsive. Once they even contacted me about a bug in my code, because they saw the error in the system logs and thought it might be their fault!
My relativity is probably a bit less rusty, since I'm still in graduate school.
You are right about spacelike and timelike intervals, and this would definitely be an example of a timelike interval. It would correspond to weird stuff that would violate causality if information were able to travel faster than the speed of light.
But fortunately, there is a limit to how far the speeded up light can travel, since it can't go further than the tail preceding the pulse. This technique wouldn't work at all (as I understand it) for a perfect square pulse, becuase the wave front can't travel faster than the speed of light.
I have heard of that earlier work, which was by Raymond Chiao, whose office is down the hall from me. Your understanding is essentially correct, and I think that the main difference with this new work is that of adding in an amplifying element.
Imagine taking the smaller hump you mentioned and amplifying it. Now you have a hump that is the same size (and maybe shape) and is ahead of the vacuum one.
Of course it is much trickier than that, but I think that the issues of information travelling faster than the speed of light are the same. Essentially, if you had a square wave front, that wave front would not travel faster than the speed of light.
Actually, you'd have to be pretty careful even in the US. I don't know how you'd distinguish local toll calls from true local calls, as they both have the same area code (although local toll calls are to people who live further away).
And local toll calls are usually more expensive than long distance calls because the local phone company has a monopoly (and to be fair, they also have government restrictions on their base rate, which they have to recoup somehow).
Did they take special training, or is it easy to pick up for any programmer?
I work with parallel computers doing physics stuff. We use mpi exclusively (except on the T3E where we also use their shmem primitives in the most intensive part).
Most supercomputing centers offer free training courses a couple of times a year. In our group, most of us aren't even trained programmers, let alone trained in parallel programming. It's not that hard, although I try to avoid programming in parallel as much as possible, since it's a lot of work. mpi is actually very nice because it is so portable.
I think you have misunderstood what this is. It is a monitor with two layers of display, one behind the other, so the surface is still smooth and flat.
But I do agree with you that a tactile display would be extremely cool.
But I'm looking forward to when we get transparent displays with resolutions of tenths of microns (ok, this is a bit far in the future) so we can have real 3-D holographic displays. That would be even cooler (at least for those of us with eyes).
The CPUs only run a few hundrad Mhz (last year 300Mhz to 400Mhz was extreamly fast for them).
Caveat: I know absolutely nothing about the S/390.
This doesn't relate to how fast the actual computers are. Most of the supercomputers I use run under 300 MHz (even the ones purchased this year). Of course, most of those supercomputers are actually glorified clusters...
I haven't compiled my code for intel (it's in f90, and I have no intel f90 compiler for linux), but I would guess that they would easily kick the pants off of our 600 MHz linux boxen. I'll see if I ever bother with a linux port.
Of course, speed all depends on what the job is. In my case I run memory/floating point intensive quantum mechanics calculations.
At uni I actually use a X terminal, i.e. a fairly dumb device that connects to a server, they still exist and they still do a decent job.
Actually, I have a dumb X terminal at my desk (in my office) which I use every day, and am typing on right now. It's pitiful on RAM, but it gets the job done.
Although with the price of cheap linux boxes now, I would never recommend that anyone buy one. But I don't see any problem with configuring a linux box to act as an X terminal.
This requires that an X server have knowledge of other output devices besides itself, but this is not so stupid an idea.
Wouldn't this rather require a separate X server for printing? I don't see why the computer I'm typing at should do any processing of a print job. It seems to me that that should be between the computer I'm running on (the X client) and the computer the printer is on.
It seems to me that this is the big advantage of the client server architecture of X. Why should every user have to upgrade the X server on their box just to use the printer?
Personally I like the idea of X as a dumb display device. Although antialiasing and alpha would be nice.
Ever since I read Mostly Harmless, I have been troubled by the question of what happened to Arthur Dent's watch. In Hitchhiker's Guide, he clearly had a digital watch ("Oh no, now how will I operate my digital watch" -- as one arm flies off), but by the last book he had an self-winding analog watch given him by his uncle before the original destruction of Earth.
When did he switch watches? Was it in his pocket when he fled Earth with Ford Prefect in the first place?
Was he wearing one watch on each arm? Then the arm that flew off must have been the one wearing the analog watch...
Or was this an effect of the strange parallel Earth business?
I have been wanting to know the answer to these questions for some time!
They could have given him one bodyguard, or a magic sword of his own, or at the very least a freakin' map, but they actually hung him out to dry.
They did give him a guide, who had a magic sword (ok, ok, it was broken...), along with the most powerful good wizard in existence, along with a few others. The guide they gave him was perhaps the only good person to ever have snuck into Mordor before. It just turned out that the companions were forced to separate due to the divisive influences of the ring.
This research was done at UC Berkeley, which means the money will mostly go to UC Berkeley, where it will either support more research (a Good Thing) or education (another Good Thing). I don't know how they earmark the money.
They make you sign a form giving them a certain (large) cut of the royalties from any patents you get from work done hear. I signed one myself. So you don't need to worry about this getting into the hands of an Evil Corporation. Although the university was involved in the development of the bomb...
AFAIK, Be doesn't have very many apps, and that may be a downer to regular Joes.
I have used BeOS (although admittedly that was a year or two ago), and I'm afraid I would hesitate to recommend it. It really didn't have many apps available, and since I don't use word processors I don't know if those it had were any good. But you make a good point.
If BeOS becomes a viable option (as far as availability of software goes), then it would be a good thing to recommend, although the Be people didn't seem to have put much thought into the user interface (no guidelines) at the time I had looked into it. This makes as much a difference as anything.
Re:Look for something amazing from this project
on
New Desktop for Linux
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· Score: 2
Why is it seen that it "must" appeal to the desktop luser as well as everyone else?
I have many friends and relatives who you would probably put into the category of "desktop lusers."
Just because someone doesn't care about their computer for its own sake doesn't mean they should be forced to use an inferior operating system. I would very much like to be able to recommend linux to my friends, but right now although I use it myself, I would definitely not recommend it to most of my friends.
It seems to me that fair use would cover the use in/., since in this case the Apple logo is used to refer to Apple itself. If I were to start making computers with the Apple logo on them, that would be a trademark violation.
It seems reasonable to me that themes should be able to imitate the look of the MacOS, but to use its logos would be falsely pretending to be the MacOS. But IANAL.
Slashdot Mirror
In case anyone's interested, I worked out some numbers on the force of the light on this thing relative to that of the sun's gravity. Both forces drop as inverse squares of the distance from the sun, so the ratio between them remains constant.
The force due to the light is determined by the area of the sail and the luminosity of the sun (which I looked up), while the force due to gravity is just determined by the mass of the spacecraft and the mass of the sun.
When you work out the numbers using the area and mass quoted in the article, the force of gravity from the sun turns out to be about 200,000 times greater than that of the light.
This means (as the article states) that the best such a spacecraft can do is remain in orbit around the sun, and angle the light in such a way as to gradually spiral out to a higher orbit.
Alas, no interstellar travel with one of these guys, since we can never break out of solar orbit. For a spacecraft with this size solar sail to achieve interstellar travel, it would need to have a mass of less than 0.3 grams! That would require quite an impressive materials breakthrough, I'm afraid.
Actually, you are forgetting about the fact that a spacecraft would be in orbit around the sun. It is true that there will be no keel, and you won't be able to tack to control your direction.
However, you will still be able to go towards the sun just as easily as going away from it, because the sun's gravity will still be the dominant force in play. To travel towards the sun, you angle your sail to slow you down, while to travel away from the sun you angle it to increase your orbital velocity.
If you reflect the sunlight directly back at the sun, you won't travel away from it at all, even though the light will be exerting a maximum force on your spacecraft.
This is because regardless of your distance from the sun, the gravitational force will always be greater than the light force. Actually, the ratio between the two is determined by the area/mass ratio of your spacecraft, but for those that are proposed, gravity will dominate. This also means they won't be practical for leaving the solar system, since they would have to spiral out rather slowly.
Actually this is new (or rather, was new last year), since the index of refraction is the sqrt of the product of dielectric constant and the permeability. If only one of them is negative, you have an imaginary index of refraction, and no travelling waves, which is why AM radio is reflected by the ionosphere...
On the contrary, it is even worse than the original poster suggested. Where do you think the oil comes from? If is a result of the anaerobic decay of plant matter (a.k.a. sugar). Therefore, it must be a lower free energy state than the original plant matter.
So it would seem that we'd be taking one step forward and two steps backward...
That's true. The speckles you see from laser light are are result of interference of the coherent light. I'm not sure how the resolution of your eye would come into play, as it would seem to me that the dominant effect of moving your head would be to change the interference pattern.
I read all about this a month or two ago, and the catch is that it has an incredibly short focal length. Specifically, the focal length is just the thickness of the lens. This is not your ordinary lens, and really can only be used for near field work. Actually the total distance between the object and the image is twice the thickness of the lens.
Anyhow, so it isn't too practical for most of the things we use lenses for, although it is still a very impressive piece of work.
The point would be that because tripwire is no longer semi-fre you could now use either.
I would imagine for things like quizes at the beginning of class, possibly even tests. I have a friend who went to a med school where they required laptops, and there it was quite useful. They had network/power connections at each seat, and for things like anatomy tests it was very helpful to be able to show the students full color photos (and have them go at their own paces).
Of course, that sort of stuff requires lots of work and infrastructure, but even here at Cal they are doing online prelabs over the web. This means that Chem 1 students who don't have access to computers need to come into a computer lab each week which must be a pain.
And altivec is next to worthless for most mathematical computation. It only works on single precision floats, and even then doesn't even give you a factor of two speedup, since there is (as I recall) only one altivec unit so you can't pipeline the altivec calls. On the other hand, the G4 has more floating point units than the G3, and faster ones, so it definitely would be much better.
Presumably if you are bothering to use PGP your friend would either encrypt the key when he emails it to you, or would sign it (preferably both). Either way it should be fine, as long as you don't rely on the self-signature of the key itself.
It is quite a nice little system when you have enough users to keep it busy, and I imagine is quite easily scalable. The only trick is that if there are differences between the various machines you can have really annoying and hard to track down bugs. Fortunately consult is very responsive. Once they even contacted me about a bug in my code, because they saw the error in the system logs and thought it might be their fault!
You are right about spacelike and timelike intervals, and this would definitely be an example of a timelike interval. It would correspond to weird stuff that would violate causality if information were able to travel faster than the speed of light.
But fortunately, there is a limit to how far the speeded up light can travel, since it can't go further than the tail preceding the pulse. This technique wouldn't work at all (as I understand it) for a perfect square pulse, becuase the wave front can't travel faster than the speed of light.
Imagine taking the smaller hump you mentioned and amplifying it. Now you have a hump that is the same size (and maybe shape) and is ahead of the vacuum one.
Of course it is much trickier than that, but I think that the issues of information travelling faster than the speed of light are the same. Essentially, if you had a square wave front, that wave front would not travel faster than the speed of light.
And local toll calls are usually more expensive than long distance calls because the local phone company has a monopoly (and to be fair, they also have government restrictions on their base rate, which they have to recoup somehow).
I work with parallel computers doing physics stuff. We use mpi exclusively (except on the T3E where we also use their shmem primitives in the most intensive part).
Most supercomputing centers offer free training courses a couple of times a year. In our group, most of us aren't even trained programmers, let alone trained in parallel programming. It's not that hard, although I try to avoid programming in parallel as much as possible, since it's a lot of work. mpi is actually very nice because it is so portable.
But I do agree with you that a tactile display would be extremely cool.
But I'm looking forward to when we get transparent displays with resolutions of tenths of microns (ok, this is a bit far in the future) so we can have real 3-D holographic displays. That would be even cooler (at least for those of us with eyes).
Caveat: I know absolutely nothing about the S/390.
This doesn't relate to how fast the actual computers are. Most of the supercomputers I use run under 300 MHz (even the ones purchased this year). Of course, most of those supercomputers are actually glorified clusters...
I haven't compiled my code for intel (it's in f90, and I have no intel f90 compiler for linux), but I would guess that they would easily kick the pants off of our 600 MHz linux boxen. I'll see if I ever bother with a linux port.
Of course, speed all depends on what the job is. In my case I run memory/floating point intensive quantum mechanics calculations.
Actually, I have a dumb X terminal at my desk (in my office) which I use every day, and am typing on right now. It's pitiful on RAM, but it gets the job done.
Although with the price of cheap linux boxes now, I would never recommend that anyone buy one. But I don't see any problem with configuring a linux box to act as an X terminal.
Wouldn't this rather require a separate X server for printing? I don't see why the computer I'm typing at should do any processing of a print job. It seems to me that that should be between the computer I'm running on (the X client) and the computer the printer is on.
It seems to me that this is the big advantage of the client server architecture of X. Why should every user have to upgrade the X server on their box just to use the printer?
Personally I like the idea of X as a dumb display device. Although antialiasing and alpha would be nice.
When did he switch watches? Was it in his pocket when he fled Earth with Ford Prefect in the first place?
Was he wearing one watch on each arm? Then the arm that flew off must have been the one wearing the analog watch...
Or was this an effect of the strange parallel Earth business?
I have been wanting to know the answer to these questions for some time!
They did give him a guide, who had a magic sword (ok, ok, it was broken...), along with the most powerful good wizard in existence, along with a few others. The guide they gave him was perhaps the only good person to ever have snuck into Mordor before. It just turned out that the companions were forced to separate due to the divisive influences of the ring.
They make you sign a form giving them a certain (large) cut of the royalties from any patents you get from work done hear. I signed one myself. So you don't need to worry about this getting into the hands of an Evil Corporation. Although the university was involved in the development of the bomb...
I have used BeOS (although admittedly that was a year or two ago), and I'm afraid I would hesitate to recommend it. It really didn't have many apps available, and since I don't use word processors I don't know if those it had were any good. But you make a good point.
If BeOS becomes a viable option (as far as availability of software goes), then it would be a good thing to recommend, although the Be people didn't seem to have put much thought into the user interface (no guidelines) at the time I had looked into it. This makes as much a difference as anything.
I have many friends and relatives who you would probably put into the category of "desktop lusers."
Just because someone doesn't care about their computer for its own sake doesn't mean they should be forced to use an inferior operating system. I would very much like to be able to recommend linux to my friends, but right now although I use it myself, I would definitely not recommend it to most of my friends.
It seems to me that fair use would cover the use in /., since in this case the Apple logo is used to refer to Apple itself. If I were to start making computers with the Apple logo on them, that would be a trademark violation.
It seems reasonable to me that themes should be able to imitate the look of the MacOS, but to use its logos would be falsely pretending to be the MacOS. But IANAL.