Perhaps I should be clearer... The minimum energy trajectory leaves the surface of the Moon at just over lunar escape velocity. The two bodies (Earth and the Moon) are relatively far apart. The simple approximation of what happens is that the rock slows down as it leaves the Moon due to the Moon's gravitational pull, eventually reaching the point where the gravitational pull from the Moon and Earth are equal with very little residual velocity. The energy required for the launch is just that required to accelerate the rock somewhat beyond lunar escape velocity. After the rock crosses the Lagrange point, it can be treated as an object with small initial velocity falling from far away -- and so it impacts the Earth at Earth's escape velocity (11.2km/s), plus a small amount for Earth's rotation and residual energy from the launch, minus small amounts for the effects of the orbital system and finite distance of the fall, but the approximation is a good one.
Effectively, the rock leaves the Moon at lunar escape velocity (a bit under 2 km/s, I don't recall the exact number) and arrives at Earth at Earth escape velocity (11.2 km/s). From a gravitational potential standpoint, there are local minimas at either end of the journey, with a hump in the middle that the launcher must supply the energy to overcome. All the energy in the rock at impact comes from its gravitational potential energy wrt the Earth; the launcher simply serves to get it over the hump so it can fall down to the Earth instead of to the Moon.
The end result is that the rock arrives at somewhere between 11 and 12 km/s, for a kinetic energy content of a bit less than double the same mass of TNT.
Attach a plow blade to the moon rover, make a flat area, and carefully lay out the ultra thin and fragile panels? It's not like they're going to get blown away by wind, and I'd be willing to bet the astronauts can be trained to respect the "don't walk on solar farm" signs.
I think the problem has more to do with nighttime energy and installation effort than it does with mass or fragility. Even with high power light weight reactors, panels would be lighter per watt generated. It's only as you head out beyond Mars that solar panels stop being viable.
Much as I loved the story, I'm disappointed that Heinlein didn't do the basic math on his rocks. Objects moving at marginally over escape velocity (12 km/s or slightly less, depending how much excess the launcher can supply) have 7.2 MJ/kg of kinetic energy (0.5*m*v^2). TNT has 4.2MJ/kg of chemical energy. So, while the rocks are certainly potent weapons if you can aim them accurately, a few tons or even tens of tons of rock, at < 2x TNT equivalent, isn't even close to the nuclear blast that Heinlein makes them out to be comparable to.
You don't necessarily need a hard drive that fast. You can buy storage that has battery-backed write caches, and can therefore legitimately confirm the write as complete in a fully recoverable fashion before it goes out to disk. Paying for enough performance to complete any transaction in 3 ms is rather rare, but then again the LSE isn't exactly a typical application.
DNA analysis will get cheaper, never more expensive. The techniques to extract signal from the data will get better, never worse.
Certainly you're correct that the techniques are too expensive today for this to be an immediate concern. So when is the appropriate time to begin worrying about the privacy implications of cheap, ubiquitous DNA techniques? Would it be better to wait until after they arrive, and are in greater use, and hurriedly try to put together policies, laws, and other safeguards?
What, pray tell, is wrong with trying to solve a problem before it gets out of hand?
Power supplies are actually complicated to engineer -- adding monitoring to every supply line would increase the component count, rather than simply add software complexity. That means it costs more per unit, as well as more design effort. So, unfortunately, you're unlikely to see it without a clear demand.
Many modern batteries are designed to fail in some safe manner; at least some of the battery problems have been due to manufacturers substituting cheaper materials than specified, which results in the safety features not working properly.
I agree, though -- I'd be willing to pay a bit extra for such features, as long as they worked reliably and with my OS. Unfortunately, that puts us in a small minority -- and small volume parts carry enough of a price premium that you wouldn't want to pay for it unless there was a substantial market. Such is life, I suppose.
Tungsten isn't heavier than gold. It's ever so slightly lighter, but for all practical purposes they're the same (and alloying agents will matter more). Iridium is denser than either.
Same can be said for Iridium. They're approximately the same density. Which is denser depends on whether you trust the measured values or the theoretical calculations (getting pure enough samples of either for a high-precision measurement is apparently difficult). Wikipedia gives the density of Iridium as 22650 kg/m^3, and Osmium as 22610 kg/m^3.
(Yeah, yeah, everyone hates the pedant getting involved in the joke. It's/., you'll survive.)
The racer flying was the XCOR plane; Carmack had theirs on display, but not flying. I don't know the details, but Carmack's engine may have a throttle -- he's done work with throttled engines for the Lunar Lander Challenge, and this engine is a related design. I believe Carmack's plane is larger, with a larger engine (but similar overall performance) compared to the XCOR plane.
I'm not up to date, but the course the RRL was talking about was basically a climbing straight past the stands, an acrobatic turn at the top, and then a power-off glide for the back stretch, before a sharp turn and relighting the engine.
For the XCOR engine, you can't leave the engine running nonstop for the full tank's worth of propellant while staying below Vne and at low altitude (ie on the race course) -- it just has too much thrust. The plan is several laps (3-6 or so, again I don't know current numbers) with the engine running ~1/3 of each lap, and then a pit stop and another round.
Suffice to say, it should be a good show.
I interned at XCOR and worked a little on their plane, but not recently; what I've said above is my recollection of what was publically available at the time, and may be wrong or out of date.
You should see that engine up close... It's loud through earmuffs (well, really you feel it in your chest as much as your ears), and it's bright enough to compete with the noon desert sun.
UAVs still have pilots. Pilot fatigue may be the limiting factor... iirc, that's how their previous demo flight (54 hours) ended. Since it's an R&D article, my guess is that time was long enough to accomplish the flight goals, and they wanted it back in the hangar to keep working on it. There are probably other reasons, but I would guess those are both significant ones.
So, have extrasolar sunspots been observed before?
I assume sunspots are far better understood than planetary formation, and that they're less interesting, but still... TFA gives no hint as to whether this is a first.
If this is a first, that's quite cool in its own right, even if there isn't a planet.
One reason many people commit copyright infringement of movies is because the p2p programs provide a simpler, faster way to find what you're looking for, all from a central location. If this really indexes everything available, and is quick and simple to use, I think it might actually see significant use.
Obviously it won't stop all infringement, but it's a much saner response than suing your customers.
It can display 500 distinct black lines on a white background. Or vice versa. When counting lines, both in the normal world and photography, you don't usually count both the lines and the spaces between them. When counting pixels, you count each pixel as a line, because it's a line of pixels separated by the miniscule gap between them. But if you're drawing with a pencil or exposing film, you only count the drawn / exposed part, not the background.
Film has a resolution, even though it isn't in the form of nice sharp-edged pixels. It's a question of how close together two objects can be and still be distinguished -- the distance is called the circle of confusion, within which the two objects are not fully distinct. Lenses, film, and printing process all play a role in the resolution of the final product. For test work, one usually uses a printed image with a very fine array of slowly converging lines, and you look for how close together the lines can get before they become indistinct. As a result, the number of (distinguishable) lines you can fit on the film is the natural way to measure its resolution. So film really does have "lines" and though they're not quite the same as in a digital system, they're remarkably close.
(Be aware there's a factor of two in there for Nyquist; a 1000 pixel wide display can only show 500 lines, obviously, and the same effect applies to analog systems.)
Of course, with better digital sensors (ie lots of megapixels), the lens quality becomes the limiting factor, and it would again make sense to speak of the imaging system in terms of lines of resolution rather than megapixels. There's a reason cheap cell phone cameras don't produce as sharp an image as a real camera with a good lens; if you want to measure the quality of the entire imaging system, you end up back with old-fashioned analog lines of resolution as one of the fundamental metrics. (Of course, there are plenty of other attributes, like various forms of noise and distortion.) If you read a good review of a digital camera, they'll point it at a test piece and measure available lines of resolution, just as they would for film.
Up to this point, photon counters were elaborate devices with scintillation media, anticoincidence detctors, veto logic, and complex timing and biasing requirements.
Now you can just apply 9.8V and an instrumentation amp and a couple analog filter/comparator chains, and off you go counting.
Single photon avalanche diodes produce rising edge times well under 1ns. You need to measure the *shape* of that rising edge to use this technique. That is a complex circuit, no matter how you look at it.
The new circuits will be vastly simpler. But they will require a fair bit more than instrument amp and a ballast resistor and a comparator.
It also uses a somewhat dated form of the word "proof" -- a meaning much closer to "test". "The test of the pudding is in the eating" would be closer to the original meaning.
That would solve it in only 2^511 operations. In actuality, factoring of large numbers is far more efficient than that. The techniques are complex, but they're quite good. That's why a 1024 bit RSA key is considered somewhat small (2048 or 4096 are the norm) but for symmetric key ciphers (where you do have to try all 2^n possible keys) use key sizes of 256 bits or less.
Known plaintext attacks are a mainstay of cryptanalysis. They tend to be more powerful than other attacks, but they still don't help much. Factoring is the best known technique for RSA, even given known plaintext or chosen plaintext.
You would be wrong. There's just not much energy in sound. A 100W sound system is quite loud -- and the speakers are only a few percent efficient. A few watts of sound is *very* loud; the energy available from covering the walls of a normal room is a couple watts at best, before you count inefficiencies.
Exactly. This article completely ignores the most interesting question -- is it cheaper or more expensive than other zero-emissions sources of energy, like solar? In some specialized applications, human power is nice. But in a supermarket or train station, power is readily available, and this should be compared on even footing in terms of $ per watt of generation capability against other options. Somehow I doubt it beats out solar power. Sure, it may be (*) cleaner than fossil fuels, but what's the point if it costs more than solar?
* Depends whether you count the marginal fossil fuel cost of food calories, which are a very expensive form of energy by the time they reach your plate. There are reasonable arguments both ways.
Getting it cold is the hard part. Hot gases don't fall on a small scale; the particle velocity is too high, so they diffuse. I don't know the details of the expirement, but the beam may be part of how they plan to cool the anti-atoms down (at least in the directions orthogonal to the beam; there might well be a significant velocity distribution within the beam).
No one is pissed about any USE of GPL2 software. It's the distribution they care about. Freedom 0 is the right to use the software, and that applies no matter how you plan to use it. Distributing it in such a way that you remove Freedom 0 from other users is a different matter.
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Perhaps I should be clearer... The minimum energy trajectory leaves the surface of the Moon at just over lunar escape velocity. The two bodies (Earth and the Moon) are relatively far apart. The simple approximation of what happens is that the rock slows down as it leaves the Moon due to the Moon's gravitational pull, eventually reaching the point where the gravitational pull from the Moon and Earth are equal with very little residual velocity. The energy required for the launch is just that required to accelerate the rock somewhat beyond lunar escape velocity. After the rock crosses the Lagrange point, it can be treated as an object with small initial velocity falling from far away -- and so it impacts the Earth at Earth's escape velocity (11.2km/s), plus a small amount for Earth's rotation and residual energy from the launch, minus small amounts for the effects of the orbital system and finite distance of the fall, but the approximation is a good one.
Effectively, the rock leaves the Moon at lunar escape velocity (a bit under 2 km/s, I don't recall the exact number) and arrives at Earth at Earth escape velocity (11.2 km/s). From a gravitational potential standpoint, there are local minimas at either end of the journey, with a hump in the middle that the launcher must supply the energy to overcome. All the energy in the rock at impact comes from its gravitational potential energy wrt the Earth; the launcher simply serves to get it over the hump so it can fall down to the Earth instead of to the Moon.
The end result is that the rock arrives at somewhere between 11 and 12 km/s, for a kinetic energy content of a bit less than double the same mass of TNT.
Attach a plow blade to the moon rover, make a flat area, and carefully lay out the ultra thin and fragile panels? It's not like they're going to get blown away by wind, and I'd be willing to bet the astronauts can be trained to respect the "don't walk on solar farm" signs.
I think the problem has more to do with nighttime energy and installation effort than it does with mass or fragility. Even with high power light weight reactors, panels would be lighter per watt generated. It's only as you head out beyond Mars that solar panels stop being viable.
Much as I loved the story, I'm disappointed that Heinlein didn't do the basic math on his rocks. Objects moving at marginally over escape velocity (12 km/s or slightly less, depending how much excess the launcher can supply) have 7.2 MJ/kg of kinetic energy (0.5*m*v^2). TNT has 4.2MJ/kg of chemical energy. So, while the rocks are certainly potent weapons if you can aim them accurately, a few tons or even tens of tons of rock, at < 2x TNT equivalent, isn't even close to the nuclear blast that Heinlein makes them out to be comparable to.
You don't necessarily need a hard drive that fast. You can buy storage that has battery-backed write caches, and can therefore legitimately confirm the write as complete in a fully recoverable fashion before it goes out to disk. Paying for enough performance to complete any transaction in 3 ms is rather rare, but then again the LSE isn't exactly a typical application.
DNA analysis will get cheaper, never more expensive. The techniques to extract signal from the data will get better, never worse.
Certainly you're correct that the techniques are too expensive today for this to be an immediate concern. So when is the appropriate time to begin worrying about the privacy implications of cheap, ubiquitous DNA techniques? Would it be better to wait until after they arrive, and are in greater use, and hurriedly try to put together policies, laws, and other safeguards?
What, pray tell, is wrong with trying to solve a problem before it gets out of hand?
Power supplies are actually complicated to engineer -- adding monitoring to every supply line would increase the component count, rather than simply add software complexity. That means it costs more per unit, as well as more design effort. So, unfortunately, you're unlikely to see it without a clear demand.
Many modern batteries are designed to fail in some safe manner; at least some of the battery problems have been due to manufacturers substituting cheaper materials than specified, which results in the safety features not working properly.
I agree, though -- I'd be willing to pay a bit extra for such features, as long as they worked reliably and with my OS. Unfortunately, that puts us in a small minority -- and small volume parts carry enough of a price premium that you wouldn't want to pay for it unless there was a substantial market. Such is life, I suppose.
Tungsten isn't heavier than gold. It's ever so slightly lighter, but for all practical purposes they're the same (and alloying agents will matter more). Iridium is denser than either.
Same can be said for Iridium. They're approximately the same density. Which is denser depends on whether you trust the measured values or the theoretical calculations (getting pure enough samples of either for a high-precision measurement is apparently difficult). Wikipedia gives the density of Iridium as 22650 kg/m^3, and Osmium as 22610 kg/m^3.
(Yeah, yeah, everyone hates the pedant getting involved in the joke. It's /., you'll survive.)
The racer flying was the XCOR plane; Carmack had theirs on display, but not flying. I don't know the details, but Carmack's engine may have a throttle -- he's done work with throttled engines for the Lunar Lander Challenge, and this engine is a related design. I believe Carmack's plane is larger, with a larger engine (but similar overall performance) compared to the XCOR plane.
I'm not up to date, but the course the RRL was talking about was basically a climbing straight past the stands, an acrobatic turn at the top, and then a power-off glide for the back stretch, before a sharp turn and relighting the engine.
For the XCOR engine, you can't leave the engine running nonstop for the full tank's worth of propellant while staying below Vne and at low altitude (ie on the race course) -- it just has too much thrust. The plan is several laps (3-6 or so, again I don't know current numbers) with the engine running ~1/3 of each lap, and then a pit stop and another round.
Suffice to say, it should be a good show.
I interned at XCOR and worked a little on their plane, but not recently; what I've said above is my recollection of what was publically available at the time, and may be wrong or out of date.
You should see that engine up close... It's loud through earmuffs (well, really you feel it in your chest as much as your ears), and it's bright enough to compete with the noon desert sun.
Does someone have a link to a medium-res copy? The thumbnail is tantalizing, but I don't want to download a 42MB TIFF.
Hey, at least it wasn't computational linguistics.
UAVs still have pilots. Pilot fatigue may be the limiting factor... iirc, that's how their previous demo flight (54 hours) ended. Since it's an R&D article, my guess is that time was long enough to accomplish the flight goals, and they wanted it back in the hangar to keep working on it. There are probably other reasons, but I would guess those are both significant ones.
So, have extrasolar sunspots been observed before?
I assume sunspots are far better understood than planetary formation, and that they're less interesting, but still... TFA gives no hint as to whether this is a first.
If this is a first, that's quite cool in its own right, even if there isn't a planet.
Mine was a Ford'); DROP TABLE Cars;--.
One reason many people commit copyright infringement of movies is because the p2p programs provide a simpler, faster way to find what you're looking for, all from a central location. If this really indexes everything available, and is quick and simple to use, I think it might actually see significant use.
Obviously it won't stop all infringement, but it's a much saner response than suing your customers.
It can display 500 distinct black lines on a white background. Or vice versa. When counting lines, both in the normal world and photography, you don't usually count both the lines and the spaces between them. When counting pixels, you count each pixel as a line, because it's a line of pixels separated by the miniscule gap between them. But if you're drawing with a pencil or exposing film, you only count the drawn / exposed part, not the background.
Film has a resolution, even though it isn't in the form of nice sharp-edged pixels. It's a question of how close together two objects can be and still be distinguished -- the distance is called the circle of confusion, within which the two objects are not fully distinct. Lenses, film, and printing process all play a role in the resolution of the final product. For test work, one usually uses a printed image with a very fine array of slowly converging lines, and you look for how close together the lines can get before they become indistinct. As a result, the number of (distinguishable) lines you can fit on the film is the natural way to measure its resolution. So film really does have "lines" and though they're not quite the same as in a digital system, they're remarkably close.
(Be aware there's a factor of two in there for Nyquist; a 1000 pixel wide display can only show 500 lines, obviously, and the same effect applies to analog systems.)
Of course, with better digital sensors (ie lots of megapixels), the lens quality becomes the limiting factor, and it would again make sense to speak of the imaging system in terms of lines of resolution rather than megapixels. There's a reason cheap cell phone cameras don't produce as sharp an image as a real camera with a good lens; if you want to measure the quality of the entire imaging system, you end up back with old-fashioned analog lines of resolution as one of the fundamental metrics. (Of course, there are plenty of other attributes, like various forms of noise and distortion.) If you read a good review of a digital camera, they'll point it at a test piece and measure available lines of resolution, just as they would for film.
Up to this point, photon counters were elaborate devices with scintillation media, anticoincidence detctors, veto logic, and complex timing and biasing requirements.
Now you can just apply 9.8V and an instrumentation amp and a couple analog filter/comparator chains, and off you go counting.
Single photon avalanche diodes produce rising edge times well under 1ns. You need to measure the *shape* of that rising edge to use this technique. That is a complex circuit, no matter how you look at it.
The new circuits will be vastly simpler. But they will require a fair bit more than instrument amp and a ballast resistor and a comparator.
It also uses a somewhat dated form of the word "proof" -- a meaning much closer to "test". "The test of the pudding is in the eating" would be closer to the original meaning.
That would solve it in only 2^511 operations. In actuality, factoring of large numbers is far more efficient than that. The techniques are complex, but they're quite good. That's why a 1024 bit RSA key is considered somewhat small (2048 or 4096 are the norm) but for symmetric key ciphers (where you do have to try all 2^n possible keys) use key sizes of 256 bits or less.
Known plaintext attacks are a mainstay of cryptanalysis. They tend to be more powerful than other attacks, but they still don't help much. Factoring is the best known technique for RSA, even given known plaintext or chosen plaintext.
You would be wrong. There's just not much energy in sound. A 100W sound system is quite loud -- and the speakers are only a few percent efficient. A few watts of sound is *very* loud; the energy available from covering the walls of a normal room is a couple watts at best, before you count inefficiencies.
Exactly. This article completely ignores the most interesting question -- is it cheaper or more expensive than other zero-emissions sources of energy, like solar? In some specialized applications, human power is nice. But in a supermarket or train station, power is readily available, and this should be compared on even footing in terms of $ per watt of generation capability against other options. Somehow I doubt it beats out solar power. Sure, it may be (*) cleaner than fossil fuels, but what's the point if it costs more than solar?
* Depends whether you count the marginal fossil fuel cost of food calories, which are a very expensive form of energy by the time they reach your plate. There are reasonable arguments both ways.
Getting it cold is the hard part. Hot gases don't fall on a small scale; the particle velocity is too high, so they diffuse. I don't know the details of the expirement, but the beam may be part of how they plan to cool the anti-atoms down (at least in the directions orthogonal to the beam; there might well be a significant velocity distribution within the beam).
No one is pissed about any USE of GPL2 software. It's the distribution they care about. Freedom 0 is the right to use the software, and that applies no matter how you plan to use it. Distributing it in such a way that you remove Freedom 0 from other users is a different matter.