The bad news is, people are going to find it a lot less convenient to make good MP3's under Windoze XP.
The good news is, a lot of those people are going to blame Microsoft for giving them shitty alternatives and turn to other codecs/software. The more people who realize that Microsoft is foisting crap onto them, the better. --
spam spam spam spam spam spam
No one expects the Spammish Repetition!
That might be the case if the bankruptcy court appoints a clueful receiver. This cannot be guaranteed; there have been examples of the assets of bankrupt brokerage firms being frozen while clients' options expired, for example. It is all too likely that a bunch of businesses are going to come to the end of their rental period and find that they have no-one
authorized to renew their license. For businesses which have deployed this software in a mission-critical application, it is going to serve as an extremely rude wake-up call.
Legislation and rental agreements should address this up front, but I doubt that's going to happen. --
Power a three-phase motor via a six-scr power stack. When the SCRs are fully phased-on (i.e. triggered at 0 degrees through 180) the motor will have full line power, minus the volt or so the SCRs drop the line. By "reduce the phase angle" I mean to start phasing back the SCRs... instead of turning on at 0 degrees, turn them on at 45 degrees (3/4 of the half-sine wave) -- If the motor is driving something like a pump or a high inertia load the current will rise quite a bit.
That's a lot clearer. From your description it's pretty obvious that the harmonic content of the applied power increases radically as you begin chopping out the rising part of the sine curve. I'd have to do an analysis to check (and I'm not being paid to do this, so it isn't likely to get done anytime soon), but I suspect that the third harmonic is going to ground and the fifth harmonic is behaving like what you'd expect: trying to drive the motor at 300 Hz when it's turning at < 60 Hz, leading to behavior like it's running at a slip factor of 4 to 6 (consider the backward component of the 5th harmonic). You'd expect it to pull huge amounts of reactive current under those conditions, no?
We're not running backwards; the load is turning the motor in the same direction it was originally going...
I thought you were referring to a conveyor belt, which can typically move in either direction if the mechanicals aren't designed to forbid it. Sorry for any misconceptions.
I agree but if you're using PWM waveforms to generate a sinusoidal current waveform you are going to have very steep edges (as you switch from +bus to gnd and back) and the only way to get nice steep edges is to have lots of harmonic content.
If I recall correctly, there are resonant power-converter designs which allow switching of the power components at near-zero voltage. This would avoid most problems with steep edges. (I have not studied them much so I can't make any judgements about their suitability for any particular purpose.)
Thanks for the pointer to Magic Sinewaves. I was going to cite them yesterday, but I couldn't remember exactly who was pushing them or what they were called so my quick Google search turned up nothing of interest. --
Sorry, wrong. An induction motor will only generate power if it is turning faster than synchronous speed.
Hmmm, I guess that's why we have the current go through the roof when you're driving a pump and go to reduce phase angle, right?
Explain "reducing phase angle" in English. If the motor were supplying power back to the mains your current would drop, as the sign of the real power component went through zero (then it would rise again). If you run the motor backwards the effective inductance of the motor drops and your reactive current goes way up; your slip ratio is climbing beyond 1 and you're probably way down the tail of the real-power curve (unless you've got a wound-rotor motor and are playing games with the resistors).
I know a mining engineer who got around regulations requiring "powered descent" capabilities for his ancient mine lift by upping the resistance on his rotor until the slip at loaded torque was > 1. (Loads normally went down on the brake.) The inspector shook his head and said something like "That's not how you're supposed to do it, but...." and signed him off. Clever guy.
Perhaps it's because I'm in large industrial controls but would a 700W filter not be rather large and bulky?
Depends on the what you have to filter, doesn't it? Depending on the harmonic output of the inverter, I could see the filter being smaller than a car-alternator hash filter. They'd have to pass similar amounts of power, and the hash filter doesn't have the luxury of having to only remove a small set of frequencies (odd multiples of 60 Hz). --
Simple, really: the PWM voltage output has lots of nice sharp edges and causes all kinds of ringing in any length of cable.
I can't speak for the designers of all UPS's, but any unit with either a pi-network or L-network (inductor input) output filter is going to soak up those spikes before they leave the box.
A 130 volt MOV connected to a 120 VAC (RMS) outlet is going to blow within a few tenths of a second. I have never seen such a device on the line side of a power supply. I have real difficulty taking the rest of your piece seriously after reading this.
The only time that an AC motor will cause grief to a UPS is if you're powering it and your load is actually driving the motor; i.e. you're using a motor to power an uphill conveyor and the load on the conveyor gets to great as to start moving the belt downhill and drive the motor. This causes the motor to generate instead of.. uh.. "motorate" and raises the bus voltage on your poor UPS which was NOT designed to do so.
Sorry, wrong. An induction motor will only generate power if it is turning faster than synchronous speed. If you are turning it in the backward direction, you are going to have current draw (both power and power factor) typical of a stall*. If you are powering it from an inverter and the inverter cannot handle a stalled motor on continuous duty, something's going to quit in the inverter (unless the motor's thermal cutout trips first).
*Unless it is a single-phase motor and you get it up to the speed where the start winding disconnects. If that happens, a single-phase induction motor will happily run backwards. --
Let me get this right: When you have a power outage, you want to make sure that you can watch your really big TV, and use your "large speaker amp"?
If he lives in California, it would be a great geeky thing to have all your electronics going even when the rolling blackouts hit your neighborhood. You could even host "blackout parties" and be the life of your block. It wouldn't be all that expensive to do; deep-cycle batteries are reasonably priced.
For your purposes, I recommend an old mainstay of power backups: a nuclear reactor. That way, you only have to refuel it every 20 years or so...
I hate to break this to you, but commercial nuke plants (PWRs) are refuelled on roughly a 2-year cycle. Then again, that's when they're cranking out a few GWthermal most of the time... if you had a Babcock and Wilcox unit all to yourself you could probably stretch it longer. --
This article does not deserver dissemination. It is a lot of hot air. It's, in the plainest terms, a lot of bullshit.
More significantly, the K5 editorial misses the point. There is no real distinction between a right to (your own) life and the right to property; if someone can take away your home and your clothes in a Minnesota winter because "it's only property" you will be dead in short order, perhaps minutes. If someone can take away your means of making a living (which is almost always property, like a computer), you're that ->||<- close to losing your home etc. Where's the beef?
The editorial would have been insightful if it had drawn a distinction between physical property (objects), real property (land) and "intellectual property" (data), and how the last is the fuzziest and most socially constructed. Even the "propertyless" Native Americans recognize property rights in tools and clothes, not to mention dwellings. If they had no concept of ownership of land save by the tribe, it's because they had no regime or technology which required it. We have a firm system of rights in real property (land and buildings) because capitalist societies depend on loans, bonds and other forms of ownership to get buildings built, advance money for farm machinery or to plant the next crop, etc. Society ignores these things at their peril (witness the utter collapse of agriculture in the old USSR).
rusty is right that our concept of intellectual property is bending. This is because it was never firm in the first place, and the whole idea of copyright is both socially constructed from the word go ("fair use", anyone?) and utterly dependent on technology (it did not exist before the printing press and now it is eroding on some fronts under the influence of the Internet). What do we call posts which are so one-sided that they lend themselves to - nay, beg for - heated instead of thoughtful responses? Okay, maybe it's flamebait instead of a troll, but my point stands. --
Of course, WHY anyone needs to control their airconditioner from a remote location is beyond me. Leaving it on if you go out for the day isn't that big a deal, since its probably most cost efficient to let it run then let the room warm up and then try to cool it again.
No it isn't. A heat pump (A/C, refrigerator... they all pump heat) is most efficient when the temperature difference is small. When you are pumping vapor, you also have the greatest vapor density in the evaporator (the part that gets cold) when it is warmer; more vapor density means you push more vapor into the compressor per cycle and move more heat. If you let your space warm up, you also have less total heat to move (because the flow of outside heat into the space slows down as the temperature difference decreases).
All in all it is more efficient to turn the air conditioner off when you leave, and turn it on just in time to have it where you want it when you get back. This may make no sense from the perspective of demand management (lots of people kicking on their A/C units just as they leave work could trigger rolling blackouts in places like California), but it would save energy on the whole. --
But let's keep this in proportion; any exploits found are going to have minimal effect on this country's operations. It's not like linux clusters running NSA Linux are going to handle CNWDI stuff (Critical Nuclear Weapons Design Information).
That information wouldn't affect the USA's operations even if it was shown on prime-time television; those are strategic issues. The issue is that an attacker could take down the Internet "storefronts" of lots of businesses and other essential or important parts of many more. Imagine a blizzard which shuts down New York City...
... only it hits the entire nation...
... and it keeps coming down in different types of snow as soon as you learn how to plow the last one. That's what the problem is: it's the economic impact of the disruption of something we rely on for more and more.
I stand by my judgement that the NSA would be suicidal to leave a backdoor in this system. First, the NSA doesn't need back doors; they have enough computing power to brute-force many things. Second, if this "blizzard" scenario came about because a hostile group found a back door inserted by the NSA, the NSA would take enough heat to incinerate whole cabinet-level departments. I doubt that they would be that dumb. --
My employers provide me with very little, but they still have me by the short and curlies. And there was me thinking that the IP law was supposed to support innovation?
That's just the sales hype. If you wanted to know who it was really supposed to benefit look at who paid for it (buying the lobbyists, etc.) and then ask yourself, cui bono (who benefits)? --
Maybe not this time. If you consider the vulnerability of the IT infrastructure to various modes of attack and the damage this could do to the USA, it's entirely possible that the NSA is absolutely serious about trying to help people lock down their systems. Look at it this way; if the NSA can't figure an automated crack against the systems, it's unlikely that an enemy could either. This radically reduces the possible damage.
Leaving a backdoor in would be pretty stupid, because the impact (to the nation and the NSA itself) if it was found and exploited would be enormous. You may think of the NSA as a bunch of goons, but they do have a sense of self-preservation; they'd have to be suicidal to do what you're proposing. --
I think (it's been a long time) that there was speculation that the NSA had found a backdoor in the RSA algorithm itself when they stopped trying to get the original Rivest, Shamir and Adelman paper classified. --
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.
Maybe for that one, but not in general.
Back of the envelope: Let's take a sheet of aluminum foil 1 kilometer square and 5 micrometers thick. The total volume is 5 cubic meters, total mass about 13,500 kg. It receives about 1.35 gigawatts of sunlight at 1 AU. If it has 100% reflectivity, by P=E/c it can develop a best-case thrust of 2.7*10^9/3*10^8 = 9 N (4.5 N at a 45 degree angle, of which 3.2 N would be outward and 3.2 N would be tangential).
4.5 N doesn't sound like much, but it's an acceleration of about 0.33 mm/sec^2. By a = w^2r, the acceleration of Sol's gravity at 1 AU is only about (2*pi/(365.25*86400s))^2*150,000,000,000m = 5.9 mm/s^2. More to the point, Earth's orbital velocity around the Sun is about 30 km/sec. To get to solar escape velocity, you need about 42 km/sec. 12,000m/s/.00033m/s^2 = 36 million seconds = 421 days, ignoring the decrease of sunlight with distance. If you dropped in to the distance of Venus you could cut that in half, if you built your orbit into an ellipse that took you in to about the orbit of Mercury and then boosted like hell on the way out you could shave even more. You wouldn't get to another star in any reasonable amount of time, but you could sent a probe to literally anywhere in the solar system in a few years without any fancy gravity assists (flyby, not rendezvous). --
Give a man a fish and he eats for a day.
Since the deflected photons act as a force in themselves though, that does change things. I just don't really understand how a deflected photon can provide any additional force, since the inertia appears to be transferred at impact.
Think of playing pool with a cueball made of modelling clay. (Use a slingshot instead of a cue, of course.) You throw it at the target ball, and when it hits, it sticks. The target ball takes on the momentum of the clay. If you use a real, elastic cueball instead, when it hits it bounces. From the perspective of momentum, you could consider this as a lump of clay hitting and sticking to the target, then expelling the clay in another direction (giving another boost to the target). Or you can just measure the difference in momentum (mass * velocity) of the cueball before and after and by conservation of momentum you know what was transferred to the target ball.
Photons are no different. Photons carry momentum P=E/c. If you shine photons onto a blackbody they transfer momentum on impact (and make the blackbody hotter); if they bounce off instead it's equivalent to re-emitting the photon in another direction, with the momentum changed. The delta-P is transferred to the mirror. Does that help? --
Give a man a fish and he eats for a day.
The problem with the standard magsail (and artificial magnetosphere devices) is that they are pretty much pure drag devices. They can push you along the solar-wind vector, and that's just about it. You have to do something fancier to add or subtract velocity to circularize your new orbit, or to change your orbital plane. This is something a solar sail can do easily.
Artificial magnetosphere gadgets have the further disadvantage that they require a source of plasma to inflate the magnetic field, so they consume their mass over time. Again, not a problem for a lot of missions, but hardly the be-all and end-all of propulsion technology. --
Give a man a fish and he eats for a day.
I would be curious to see information on these designs. Certainly with such a design one could leave the solar system (although it would take an awfully long time to get to another star...).
You can find some short info on heliogyros here, and the history here. (The sites aren't loading well at the moment, look in Google's cache.)
Google says that Drexler's "lightsail" paper is at http://www.aeiveos.com/~bradbury/Authors/Engineeri ng/Drexler-KE/MMfSSAO.html, but I'm having difficulty getting the page to load right now (try Google's cache). Anyway, Drexler writes "A 20 nm thickness of aluminium has a reflectivity approaching that of the bulk material (~ 0.9). Lightsails constructed on the multikilometre scale can have structural masses that are small compared to the reflector mass, if a suitable pure-tension structure is employed to transmit forces from the sail to the payload. At Earth's distance from the Sun, the outward acceleration of an unloaded sail using 20 nm aluminium reflectors is ~0.16 m/s^2, or ~ 14 km/s per day." The acceleration of the Sun's gravity at Earth is only 0.0059 m/sec^2, unless I slipped a decimal point.
I'm looking but haven't found any helpful info on the Halley rendezvous probe, but what you're describing sounds like the probe would slingshot around either a planet or the comet itself...
No, that wouldn't have worked anyway because Halley's orbit is inclined too far to the ecliptic. The maneuver went something like this:
Thrust out and change plane to get into the plane of Halley's orbit.
From the top of this ellipse, thrust back to get into a very elliptical retrograde orbit.
Fall in toward the Sun, edge-on to minimize thrust.
Once past perihelion, thrust to match velocities with the comet which is just about to come by.
You can do this with arbitrarily little thrust so long as you start long enough in advance and have no limit on total impulse. That describes a solar sail pretty well.
However, if you wanted to leave the solar system, it seems unlikely that you could get enough energy for it by slingshotting around planets...
Excuse me? That's exactly how Pioneers 10 and 11 and Voyagers 1 and 2 have already left the solar system: slingshotting Jupiter. Are you having a really bad day at the keyboard, or have I just been trolled?
--
Give a man a fish and he eats for a day.
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.
Not true. If you reflect directly back at the Sun the thrust will offset gravity and will cause the orbit to expand, as if gravity had decreased. As gravity and photon pressure both scale as the inverse square of R, that can be taken as a rule.
This is because regardless of your distance from the sun, the gravitational force will always be greater than the light force.
Not necessarily. There are designs for sails which will have a "lightness" as high as 3 (lightness = photon pressure / gravitational force). Nobody's built one yet, of course.
This also means they won't be practical for leaving the solar system, since they would have to spiral out rather slowly.
You should look up the heliogyro concept for the Halley rendezvous probe, with careful attention paid to the planned trajectory. It makes a jog out, falls back in, and catches the comet shortly after perihelion... and stays with it. That's not "spiralling out slowly" by any definition, and that probe could have been built 20 years ago. (Should have been, too.) --
Give a man a fish and he eats for a day.
1. The further you are from the sun, the less force is exerted on the sails, until the forces from other stars/suns outweighs the force of our sun.
True. However, this occurs at such an absurdly vast distance from Sol that it is not a factor for any near-term mission.
2. Travelling towards the sun is difficult and requires some sort of "tacking" process.
False. All you have to do is reflect light in the direction of orbital motion, which causes a braking thrust. This causes the orbit to move closer to the Sun.
3. Travelling in any direction other than away from the sun [a] requires a centerboard and rudder for maintaining a direction [b]. Both these systems rely on resistance [c]. In space there is no resistance [d]. There sill need to be something to exert force away from the sun to keep the correct heading [e].
You can generate thrust in any direction in the half-sphere centered on the Sun-spacecraft line, with the thrust falling off according to cos^2 theta. So long as your trajectory changes can be performed without a thrust vector aiming away from the Sun, you can (theoretically) perform them with a solar sail. In space, gravity (especially from a third body, like Earth) and inertia allow tack-like maneuvers.
4. Sun-spots change the intensity of the solar winds, creating 'gusts'. Gusts will be difficult to control.
Solar sails use the pressure of the photons, not the plasma wind. There may be some small influence from plasma impingement, but it is just that: small.
From what I can see, there is only one direction the vessel can travel, and that will be determined by the release time from the earth, and the velocity at releas.
You should look up the "heliogyro" concept for a Comet Halley rendezvous probe (it was never built, of course). The details will show you where your thinking is faulty.
--
Give a man a fish and he eats for a day.
Maneuvering a solar-sail spacecraft requires balancing two factors: the direction of the solar sail relative to the sun and the orbital speed of the spacecraft."
That should be the direction of motion of the spacecraft; its orbital speed is a function of the altitude and eccentricity of the orbit. The attitude of the sail vs. the line to the sun determines the direction of thrust, the orbit is raised, lowered or changes plane depending on whether the thrust adds to, subtracts from, or is crosswise to the spacecraft velocity vector. --
Give a man a fish and he eats for a day.
I think you missed a critical distinction
on
Republic.Com
·
· Score: 1
the 'net has at its bedrock the principle of freedom of something: namely, information.
There are three basic categories here:
Information,
Data, and
Noise.
Only information is immediately useful. One person's information is another person's noise; it depends what you are looking for. Requiring the inclusion of certain material will just increase the noise from the perspective of many readers, and they will go to considerable effort to filter it out. You'd have to be hopelessly naive or an idiot to think that something like this would work; whether Sunstein is naive or cynical and two-faced is a good question. I have never read his writings to see if he has a talent for double-think, but given the obvious flaws in Republic.com I'm not likely to bother. I already have enough noise being thrown at me by people who think I should rate their priorities higher than my own. --
Give a man a fish and he eats for a day.
Here's what's wrong with this:
on
Republic.Com
·
· Score: 2
Compelled speech is un-Constitutional.
People would just filter it anyway, either the way you already ignore banner ads or via anti-compulsion filters akin to WebWasher.
On the other hand, if libel law were modified to limit or remove the safe-harbor provisions when inaccurate or selective quotes did not include a link to the context (if said context was available on-line and at a linkable address - none of this "have to go through the main page and then search" crap), that might address many of Sunstein's objections. --
Give a man a fish and he eats for a day.
Should we be required to publish the... underlying designs of all our software so that anyone can copy it? I would hope not - much the same that companies in other industries have the right to build products and retain the intellectual property rights associated with those products.
In other words, Doug wants Microsoft to be able to use the hard work of others involved in creating architectures and protocols to engineer his own proprietary, incompatible protocols which he then refuses to share with the people whose work he exploited. Did anyone expect any better from him?
I'll accept that Microsoft plays fair when they publish all their file formats and protocols for all their products, make their own products adhere to the published formats and protocols, and allow anyone and everyone to use the published standards to produce competing products. Fair's fair, and that's what interoperability is about. --
Give a man a fish and he eats for a day.
As for the "delete every file on your drive" BS, do you think they'd be around for more than 10 minutes if that happened?
The point is that they're engaging in a for-profit effort but disclaiming any responsibility for damage their software might do to you. They get all the profits, you get all the liabilities, and if you happen to run your business on that computer and it corrupts or deletes your essential files, you have no way to recover from them even if they make a billion dollars off of your CPU cycles.
I'd give CPU cycles to a bunch of researchers who will publicly publish their results and make them available royalty-free to the world, but not to people like these. --
Give a man a fish and he eats for a day.
What good, besides from a few inventions that were developed in space and are now used by us, do we get from billionaire space exploration?
Here's a partial list:
Going to the Moon, we got insight into the formation of the Earth-Moon system and refinement of the bombardment history of same, which figures prominently into any idea of protecting Earth from future asteroid strikes. (Saving your butt, and the butt of just about everyone and everything on Earth, sounds like helping people to me.)
Going to Mars, Venus, & Jupiter we got plenty of analysis of weather in atmospheres unlike our own. This highlighted phenomena which aren't easily observable here and allowed the refinement of weather models for Earth. Figure what a timely tornado warning is worth in terms of helping people.
Landing on and exploring another planet will give us experience with geology unlike Earth's. What we find will make it easier to understand Earth's geology, similar to analysis of alien weather patterns. What we get from that could lead to better ways to find minable ores and teach us things about aquifers that might help us get more and better water out of them, keep them from getting polluted or clean up existing pollution. This sounds like making people's lives better.
All of that's aside from all the use we get out of new ideas developed for solving problems associated with sending things to other planets and doing sciece there. If that benefit amounts to "none", you've got a funny definition. --
Give a man a fish and he eats for a day.
The Moon is moving away from the Earth. This has been known from first principles for centuries and has been measured directly by laser ranging ever since Apollo 11 placed retroreflectors on the surface.
The cause has nothing to do with any change in gravity. The gravitational pull between Earth and Moon is decreasing because of the increase in Earth-Moon distance.
The reason the Earth-Moon distance is increasing is because the Earth's spin is being transferred to the Moon via tidal forces.
The faster-spinning object (Earth around its own axis) is slowed down,
the slower-spinning object (Moon around Earth) is accelerated, and
the acceleration raises the Moon into a higher and slower orbit.
There is plenty of historical evidence for the slowing of the Earth's rotation; there are fossils showing daily and annual cycles from a few billion years ago, and at least one of these shows a 400-day year; Earth was spinning about 11% faster in those days.
I hope that clears up a few things. --
Give a man a fish and he eats for a day.
Slashdot Mirror
The good news is, a lot of those people are going to blame Microsoft for giving them shitty alternatives and turn to other codecs/software. The more people who realize that Microsoft is foisting crap onto them, the better.
--
spam spam spam spam spam spam
No one expects the Spammish Repetition!
Legislation and rental agreements should address this up front, but I doubt that's going to happen.
--
Thanks for the pointer to Magic Sinewaves. I was going to cite them yesterday, but I couldn't remember exactly who was pushing them or what they were called so my quick Google search turned up nothing of interest.
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I know a mining engineer who got around regulations requiring "powered descent" capabilities for his ancient mine lift by upping the resistance on his rotor until the slip at loaded torque was > 1. (Loads normally went down on the brake.) The inspector shook his head and said something like "That's not how you're supposed to do it, but...." and signed him off. Clever guy.
Depends on the what you have to filter, doesn't it? Depending on the harmonic output of the inverter, I could see the filter being smaller than a car-alternator hash filter. They'd have to pass similar amounts of power, and the hash filter doesn't have the luxury of having to only remove a small set of frequencies (odd multiples of 60 Hz).--
A 130 volt MOV connected to a 120 VAC (RMS) outlet is going to blow within a few tenths of a second. I have never seen such a device on the line side of a power supply. I have real difficulty taking the rest of your piece seriously after reading this.
Sorry, wrong. An induction motor will only generate power if it is turning faster than synchronous speed. If you are turning it in the backward direction, you are going to have current draw (both power and power factor) typical of a stall*. If you are powering it from an inverter and the inverter cannot handle a stalled motor on continuous duty, something's going to quit in the inverter (unless the motor's thermal cutout trips first).*Unless it is a single-phase motor and you get it up to the speed where the start winding disconnects. If that happens, a single-phase induction motor will happily run backwards.
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The editorial would have been insightful if it had drawn a distinction between physical property (objects), real property (land) and "intellectual property" (data), and how the last is the fuzziest and most socially constructed. Even the "propertyless" Native Americans recognize property rights in tools and clothes, not to mention dwellings. If they had no concept of ownership of land save by the tribe, it's because they had no regime or technology which required it. We have a firm system of rights in real property (land and buildings) because capitalist societies depend on loans, bonds and other forms of ownership to get buildings built, advance money for farm machinery or to plant the next crop, etc. Society ignores these things at their peril (witness the utter collapse of agriculture in the old USSR).
rusty is right that our concept of intellectual property is bending. This is because it was never firm in the first place, and the whole idea of copyright is both socially constructed from the word go ("fair use", anyone?) and utterly dependent on technology (it did not exist before the printing press and now it is eroding on some fronts under the influence of the Internet). What do we call posts which are so one-sided that they lend themselves to - nay, beg for - heated instead of thoughtful responses? Okay, maybe it's flamebait instead of a troll, but my point stands.
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All in all it is more efficient to turn the air conditioner off when you leave, and turn it on just in time to have it where you want it when you get back. This may make no sense from the perspective of demand management (lots of people kicking on their A/C units just as they leave work could trigger rolling blackouts in places like California), but it would save energy on the whole.
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I stand by my judgement that the NSA would be suicidal to leave a backdoor in this system. First, the NSA doesn't need back doors; they have enough computing power to brute-force many things. Second, if this "blizzard" scenario came about because a hostile group found a back door inserted by the NSA, the NSA would take enough heat to incinerate whole cabinet-level departments. I doubt that they would be that dumb.
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Leaving a backdoor in would be pretty stupid, because the impact (to the nation and the NSA itself) if it was found and exploited would be enormous. You may think of the NSA as a bunch of goons, but they do have a sense of self-preservation; they'd have to be suicidal to do what you're proposing.
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I think (it's been a long time) that there was speculation that the NSA had found a backdoor in the RSA algorithm itself when they stopped trying to get the original Rivest, Shamir and Adelman paper classified.
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Back of the envelope: Let's take a sheet of aluminum foil 1 kilometer square and 5 micrometers thick. The total volume is 5 cubic meters, total mass about 13,500 kg. It receives about 1.35 gigawatts of sunlight at 1 AU. If it has 100% reflectivity, by P=E/c it can develop a best-case thrust of 2.7*10^9/3*10^8 = 9 N (4.5 N at a 45 degree angle, of which 3.2 N would be outward and 3.2 N would be tangential).
4.5 N doesn't sound like much, but it's an acceleration of about 0.33 mm/sec^2. By a = w^2r, the acceleration of Sol's gravity at 1 AU is only about (2*pi/(365.25*86400s))^2*150,000,000,000m = 5.9 mm/s^2. More to the point, Earth's orbital velocity around the Sun is about 30 km/sec. To get to solar escape velocity, you need about 42 km/sec. 12,000m/s/.00033m/s^2 = 36 million seconds = 421 days, ignoring the decrease of sunlight with distance. If you dropped in to the distance of Venus you could cut that in half, if you built your orbit into an ellipse that took you in to about the orbit of Mercury and then boosted like hell on the way out you could shave even more. You wouldn't get to another star in any reasonable amount of time, but you could sent a probe to literally anywhere in the solar system in a few years without any fancy gravity assists (flyby, not rendezvous).
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Give a man a fish and he eats for a day.
Photons are no different. Photons carry momentum P=E/c. If you shine photons onto a blackbody they transfer momentum on impact (and make the blackbody hotter); if they bounce off instead it's equivalent to re-emitting the photon in another direction, with the momentum changed. The delta-P is transferred to the mirror. Does that help?
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Give a man a fish and he eats for a day.
Artificial magnetosphere gadgets have the further disadvantage that they require a source of plasma to inflate the magnetic field, so they consume their mass over time. Again, not a problem for a lot of missions, but hardly the be-all and end-all of propulsion technology.
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Give a man a fish and he eats for a day.
Google says that Drexler's "lightsail" paper is at http://www.aeiveos.com/~bradbury/Authors/Engineeri ng/Drexler-KE/MMfSSAO.html, but I'm having difficulty getting the page to load right now (try Google's cache). Anyway, Drexler writes "A 20 nm thickness of aluminium has a reflectivity approaching that of the bulk material (~ 0.9). Lightsails constructed on the multikilometre scale can have structural masses that are small compared to the reflector mass, if a suitable pure-tension structure is employed to transmit forces from the sail to the payload. At Earth's distance from the Sun, the outward acceleration of an unloaded sail using 20 nm aluminium reflectors is ~0.16 m/s^2, or ~ 14 km/s per day." The acceleration of the Sun's gravity at Earth is only 0.0059 m/sec^2, unless I slipped a decimal point.
No, that wouldn't have worked anyway because Halley's orbit is inclined too far to the ecliptic. The maneuver went something like this:- Thrust out and change plane to get into the plane of Halley's orbit.
- From the top of this ellipse, thrust back to get into a very elliptical retrograde orbit.
- Fall in toward the Sun, edge-on to minimize thrust.
- Once past perihelion, thrust to match velocities with the comet which is just about to come by.
You can do this with arbitrarily little thrust so long as you start long enough in advance and have no limit on total impulse. That describes a solar sail pretty well. Excuse me? That's exactly how Pioneers 10 and 11 and Voyagers 1 and 2 have already left the solar system: slingshotting Jupiter. Are you having a really bad day at the keyboard, or have I just been trolled?--
Give a man a fish and he eats for a day.
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Give a man a fish and he eats for a day.
You can generate thrust in any direction in the half-sphere centered on the Sun-spacecraft line, with the thrust falling off according to cos^2 theta. So long as your trajectory changes can be performed without a thrust vector aiming away from the Sun, you can (theoretically) perform them with a solar sail. In space, gravity (especially from a third body, like Earth) and inertia allow tack-like maneuvers.
Solar sails use the pressure of the photons, not the plasma wind. There may be some small influence from plasma impingement, but it is just that: small. You should look up the "heliogyro" concept for a Comet Halley rendezvous probe (it was never built, of course). The details will show you where your thinking is faulty.--
Give a man a fish and he eats for a day.
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Give a man a fish and he eats for a day.
- Information,
- Data, and
- Noise.
Only information is immediately useful. One person's information is another person's noise; it depends what you are looking for. Requiring the inclusion of certain material will just increase the noise from the perspective of many readers, and they will go to considerable effort to filter it out. You'd have to be hopelessly naive or an idiot to think that something like this would work; whether Sunstein is naive or cynical and two-faced is a good question. I have never read his writings to see if he has a talent for double-think, but given the obvious flaws in Republic.com I'm not likely to bother. I already have enough noise being thrown at me by people who think I should rate their priorities higher than my own.--
Give a man a fish and he eats for a day.
- Compelled speech is un-Constitutional.
- People would just filter it anyway, either the way you already ignore banner ads or via anti-compulsion filters akin to WebWasher.
On the other hand, if libel law were modified to limit or remove the safe-harbor provisions when inaccurate or selective quotes did not include a link to the context (if said context was available on-line and at a linkable address - none of this "have to go through the main page and then search" crap), that might address many of Sunstein's objections.--
Give a man a fish and he eats for a day.
I'll accept that Microsoft plays fair when they publish all their file formats and protocols for all their products, make their own products adhere to the published formats and protocols, and allow anyone and everyone to use the published standards to produce competing products. Fair's fair, and that's what interoperability is about.
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Give a man a fish and he eats for a day.
I'd give CPU cycles to a bunch of researchers who will publicly publish their results and make them available royalty-free to the world, but not to people like these.
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Give a man a fish and he eats for a day.
- Going to the Moon, we got insight into the formation of the Earth-Moon system and refinement of the bombardment history of same, which figures prominently into any idea of protecting Earth from future asteroid strikes. (Saving your butt, and the butt of just about everyone and everything on Earth, sounds like helping people to me.)
- Going to Mars, Venus, & Jupiter we got plenty of analysis of weather in atmospheres unlike our own. This highlighted phenomena which aren't easily observable here and allowed the refinement of weather models for Earth. Figure what a timely tornado warning is worth in terms of helping people.
- Landing on and exploring another planet will give us experience with geology unlike Earth's. What we find will make it easier to understand Earth's geology, similar to analysis of alien weather patterns. What we get from that could lead to better ways to find minable ores and teach us things about aquifers that might help us get more and better water out of them, keep them from getting polluted or clean up existing pollution. This sounds like making people's lives better.
All of that's aside from all the use we get out of new ideas developed for solving problems associated with sending things to other planets and doing sciece there. If that benefit amounts to "none", you've got a funny definition.--
Give a man a fish and he eats for a day.
The long and the short of it is:
- The Moon is moving away from the Earth. This has been known from first principles for centuries and has been measured directly by laser ranging ever since Apollo 11 placed retroreflectors on the surface.
- The cause has nothing to do with any change in gravity. The gravitational pull between Earth and Moon is decreasing because of the increase in Earth-Moon distance.
- The reason the Earth-Moon distance is increasing is because the Earth's spin is being transferred to the Moon via tidal forces.
- The faster-spinning object (Earth around its own axis) is slowed down,
- the slower-spinning object (Moon around Earth) is accelerated, and
- the acceleration raises the Moon into a higher and slower orbit.
- There is plenty of historical evidence for the slowing of the Earth's rotation; there are fossils showing daily and annual cycles from a few billion years ago, and at least one of these shows a 400-day year; Earth was spinning about 11% faster in those days.
I hope that clears up a few things.--
Give a man a fish and he eats for a day.