Actually 44khz was chosen for more practical reasons. Since audio signals at 44khz were originally designed for recording TV video to tape. To squeeze audio into a video stream:
Like 8-bit colour components, it represents a convenient value. But, like 8-bit colour components, it hasn't been replaced because it's close enough to perception limits to be indistinguishable for practical purposes. This is especially true for sound, as there would be no reason not to go to 4 samples per line if needed (while making higher-fidelity colour components requires sacrificing either ease of use of graphics cards (non-power-of-two sizes for RGBA pixels) or sacrificing the alpha channel).
[ObDisclaimer about high-fidelity equipment being needed for sound/image processing/compositing, where errors stack and sounds and colour values are rescaled/resampled.]
You make a good point re. non-ideal hardware; I hadn't thought of that. However, after thinking about it, I don't see how the monitor or graphics card could have removed banding.
There are three types of artifact that could be imposed: quantization, low-pass filtering, and slew-rate limiting. Quantization would result if the DAC on the video card could generate fewer than 256 levels. While this could make any given pair of bands the same colour, contrast between other bands would have been worse, so I think it can be dismissed without further consideration.
Slew-rate limiting occurs if there is a limit to the speed at which a signal can be changed. However, this would affect high-contrast edges first. The fact that I can see a grid pattern or the text I'm typing suggests that it is not a factor in seeing or not seeing banding on smooth gradients.
The more important artifact is low-pass filtering. This tends to average the colours of adjacent pixels, smoothing gradients. This would indeed remove or reduce banding. As the eye does differential processing, the perceived effect would be worse for low-contrast edges (the type I'm trying to measure). However, two factors suggest that this is not what limits my ability to perceive banding. Firstly, the DACs on modern video cards are rated to 300+ MHz sampling rates, while conventional desktop modes use far lower sampling rates (1024x768x85 has a dot clock of around 95 MHz, even after adding the horizontal and vertical blanking interval contributions). This means that if there is filtering, it's unlikely to be in the graphics card (leaving the monitor and monitor cable as options). Secondly, I can see banding with 18-bit colour even at high resolutions (where filtering problems are worst, due to high dot clocks), but I can't see banding with 24-bit colour even at low resolutions (where filtering problems are least severe). If low-pass filtering was limiting contrast at low resolutions, the problem should be bad enough at high resolutions to be noticeable with higher-contrast edges. Ditto for varying refresh rates with a low-resolution mode instead of varying resolution, though that only lets you change the dot clock by a factor of two or three due to monitor vsync limits.
The fact that I can't see banding in low resolution modes also suggests that dot pitch of the monitor is not an issue (I buy monitors with overspecced resolution capability out of habit anyways).
In short, I'm not convinced it's the hardware that prevents me from seeing banding. If you can think of a source of smoothing that I'm missing, I'll certainly reconsider my view.
I can believe that there are exceptional humans able to perceive contrasts more accurately, but I'm not one of them, and I doubt most other people are either.
Although humans have more sensitivity to grayscale, the dynamic range of color vision is higher than for distinguishing shades of gray. Sensitivity has nothing to do with dynamic range in this context.
Good point. However, I do recall being told that the dynamic range for greyscale was higher as well.
I am too lazy to look it up, but the reference is in the color chapter in Computer Graphics.
Thank you for the reference. I'll look it up if this thread drags on for more than a week:).
24 bits is used because there are three channels and a byte of 8 bits is convenient on most architectures.
If the quality change was noticeable enough to be useful for marketing, I'm confident we'd be using an 11/11/10 mode for 32-bit colour by now (with alpha channels stored somewhere else, or not used at all, outside of game mode). Remember the whole 32-vs-16 PR battle between 3dfx and nVidia a while back.
If you have 1 color change per pixel in a gradient, no banding can be seen, but try to repeat a color once or try to fit a 24-bit gray gradient across 300 pixels, and you'll see bandling galore.
Not when I tried it. These were images that didn't cover the whole gradient, and had tens of pixels per band (Mandelbrot sets with fun colour maps to iteration counts, if you're curious).
Regarding the nyquist rate of CD-Audio:
How do you represent a 22kHz sawtooth wave?
A sawtooth wave is a sine wave at the fundamental frequency plus a bunch of harmonics at higher frequencies. If you can hear the difference between a 22 kHz sawtooth wave and a 22 kHz sine wave, you're not from this planet, because the harmonics are about a factor of two out of human hearing range.
By all means get a signal generator and try it. Or bring a piezo speaker into your local university's electronics lab to perform the test.
If you can hear a 22 kHz *anything*, you have exceptional hearing to begin with.
How can you accurately represent a 18kHz wave without harmonic distortions?
Answer: You can't, because you get an interference/moire like pattern since 18kHz doesn't fit properly into 22kHz.
Nope. Break out that signal theory book - as long as the original signal was a pure tone, you have no aliasing. Sampling aliases higher frequencies down to lower on recording (which is why you need a low-pass input filter on any digital recording device). No high frequencies, no aliased signals at lower frequencies. Reconstruction causes higher-frequency harmonics if your output filtering is bad, but a) output filtering on sound cards is decent, and b) the harmonics are above your hearing range unless you're playing back at less than 10 kHz.
In summary, you made an assumption that I didn't re. colour, and don't seem to be working through the math re. sound.
And 16 million colours is more than the eye can see, and 44,100 samples per second is more than the ear can hear . Throughout the march of technology we've heard these ridiculously arbitrary "limits" of our senses, and invariably they are discounted at a future time. In essence you can consider them a sort of justification.
These limits aren't arbitrary. You can test them the same way you proposed that frame rate limits be tested.
For colour gradations, make a picture that has a very gradual colour ramp from 0-255 in each colour (or one that sweeps across colour tones, but that changes at most one component by at most one between adjacent bands).
When I tried this with an old VGA card that used 18-bit colour, I could see banding. I had to stare for a while to let my eyes adjust, but I could see it.
When I try it on a modern card with 24-bit colour, I see no bands if the monitor's gamma correction is properly adjusted.
A monitor without gamma correction will end up expanding some brightness ranges and compressing others, with the result that gradations will not be visible at all in some areas and will be (barely) visible in others. Check your configuration before complaining.
The 24-bit argument applies to distinguishing colours. Similar experiments (not performed by me) have shown that you get about 10 bits of depth in greyscale, as humans have more sensitive black and white vision than colour (which is why everything appears in shades of grey at night with poor lighting; go for an evening walk and look for badly-lit stop signs some time).
You can do the same kind of tests with sound. It's actually more difficult with modern sound cards, as they have low-pass filters that cut off everything above about 22 kHz (nyquist rate of 44 kHz), but a PC speaker works. Or use a piezo buzzer and a signal generator if you're worried about the speaker efficiency dropping at high frequencies. My hearing, last time I tested it (and last time it was tested by a doctor), dropped out about about 18 kHz.
The reason why higher frequencies are relevant at all is because of nonlinear behavior both in the speakers and in the human ear. Beat frequencies between high-frequency tones can turn into audible frequencies when interacting with nonlinear systems (this is how that two-tone ultrasonic speaker linked to a while back worked). However, the key is that the final tone you hear is in the audible frequency range. This means you can duplicate the sound perfectly by using a microphone that acts more like the human ear when recording (i.e. that has similar nonlinear effects), or by recording at high frequencies and applying appropriate transformations before downsampling. The fact remains that if I played a 20 kHz pure tone at you right now, you wouldn't hear it. And this is easy to verify by experiment.
In summary, while you're most definitely right about frame rates, your other objections about limits are unfounded.
1600x1200 on a 19" monitor is hardly "microscopic" pixels
Wow, I'd like to have your eye sight.:-)
I use 1280x1024 on my 19" usually and even then the pixels are pretty small to me.:-) Sure, they are noticeable on a static display, but I wouldn't notice them if they changed at a rate of something like 70 fps.
In first-person shooters, you're typically looking for small visual details in known locations (when you're not just in a twitch-reflex situation). In Tribes 2, at least, it's nice to be able to spot an enemy without having to pick out the one off-colour pixel in a grainy mountainside texture map, and even better to see what kind of gun he's holding, or that he's repairing something.
Features like zooming help you with the latter case but not the former (noticing the enemy in the first place).
While high-resolution displays aren't vital, they definitely are helpful.
The essential issue with the Shuttle is that it has no real mission. Just try to answer this question: Where is the shuttle supposed to go?
The notion of creating cheaper, safer ways to get into orbit is, of course, a no-brainer. Would you want to create more expensive, dangerous paths to orbit?
If I understand correctly, a few factors made the shuttle look like a good idea when the program was intiated:
It was supposed to be cheaper than disposable boosters.
In principle, this seems reasonable, as you don't have to throw away the investment made in building the craft. In hindsight, we know that the added complexity and maintenance requirements overwhelmed this advantage, but this wasn't necessarily obvious going into the project. People evidently still believe that the goal is attainable, as proposals for reusable craft are regularly floated.
Facility cost was supposed to be much lower.
The cost of the support facilities for the shuttle are amortized over the shuttle launches taking place. At the original proposed launch frequency - on the order of once a week or more, if I recall correctly - the impact on payload cost of paying for the launch and maintenance facilities would have been much lower.
Unfortunately, this required a craft reliable and easily maintained enough to launch on a weekly basis, and enough people willing to pay for shuttle payloads to launch at that frequency.
The shuttle is very useful for moving humans to and from orbit, and letting them do things there.
I've heard allegations that this was originally supposed to be the shuttle's only job. It's a craft that can go just about anywhere in low orbit, match courses with stations or satellites, transfer crew, perform repairs, retrieve malfunctioning satellintes, and so forth. As a cargo vehicle, it's horrible, but in other respects it's a very flexible and potentially useful craft.
Of course, its usefulness assumes that there are enough satellites and space stations to require regular shuttle service.
It showed technological superiority over the USSR.
In the political climate of the time, this was important and could be argued to have enough political effect to make it worthwhile to pursue regardless of other merits.
In short, I think the shuttle falls into the "it seemed like a good idea at the time" category. Assumptions that were made turned out not to hold, and costs turned out to be much higher than expected. Thus, the craft we're now stuck with.
Space travel is about going someplace. Someone needs to pick a destination for NASA.
I'm not sure about this. The goal of the manned space program also involves establishing human presence in space. This goal is best accomplished by building more facilities in the areas we can reach easily and know a lot about, as opposed to sending humans to every object we can find. Exploration is a goal too; however, it's not the only goal, and manned expeditions are arguably less useful for this aspect.
Anything science-related is most efficiently performed by unmanned devices. If we're sending people into space, it's for other reasons than science ("because we think it's cool" is, in my opinion, a valid reason).
And, of course, remember that tthe station is not yet complete. Only the Shuttle can do that job.
As opposed to just lifting units on any of the variety of disposable boosters in service?
Modules would be limited to 10 tonnes instead of 30 (unless a new heavy-lift booster was designed or the Saturn V was put back into production), but this would still certainly be adequate.
The main change needed would be the addition of small attitude control thrusters to the cargo to match orbits precisely with the space station and come close enough to docking that the new segments could either be hauled in by astronauts or moved using the station's manipulator arm.
I do not think that the shuttle is required for space station construction. It's _convenient_, but not required.
I'd worry more about space junk, myself. More of the tether could fall.
So what would you do to protect the tether from space junk?
Make it multi-stranded, per my previous post. A paint fleck will take out at most one strand. As your strands will be separated by at least tens of centimetres (and maybe tens of metres), it would take a very, very large object to sever more than one strand. Such objects are very rare and very easy to detect.
Secondly, in the event of military conflict, how do you propose to defend the tether from "space junk" that has been purposively deployed by an adversary for the purpose of breaking the tether?
If there's enough to be a problem, you'll see it coming. Haul up a large block of styrofoam, spool up the cable, and wait for all of the debris to impact on the styrofoam. Either capture the shield and dispose of it as you will, or just de-orbit it.
You say that if a tether is clipped at the bottom, it will continue to hang from space down to the point where it was clipped. On the other hand, quasi_stellar says [slashdot.org] that if it is clipped near the bottom, the tether assembly will fly off into space. It would appear that the tether community is not in agreement on this crucial issue.
Spend more than half a second thinking about it, and you'll see that losing part of the tether moves the center of mass of the structure up by some small amount. This puts it in a slightly elliptical orbit with a perigee (lowest point) at the original position of the tether.
If you're using a counterweight with a single-ended tether, no possible cut will cause any of it to fly off into space (lose the whole thing, and the counterweight will occupy an elliptical orbit). If you're using a double-ended tether and cut it close to the middle, you'll get one piece with escape velocity, but clipping any part close to Earth won't even come close to doing this.
The argument in your post is unpersuasive.
Persuaded now?
One last point. A reason why I'm unconvinced that the tether would burn up in the atmosphere, were it to come down, is the conduction of heat. Most of the tether would be in space. The part of the tether that was falling through the atmosphere would be subjected to great heat, but it seems like much of that heat would be conducted upwards to that part of the tether in frigid vacuum, where the heat would dissipate.
This is only true if the tether is a) a superconductor of heat and b) conducts it instantly. Neither is true for any tether likely to be built.
Any non-ideal conductor won't have enough heat transport (look up "Newton's Laws of Heating and Cooling", and remember that the tether is very thin and thousands of kilometres long).
If the tether is built out of magical materials and doesn't burn up, you still don't have a big problem, due to the total impact energy arguments in my previous post.
The most successful laser launch to date, using the biggest continuous laser in the US [fas.org], lifted a 50 gram vehicle two meters. And that took a laser that cost $800 million to build.
Your data appears to be inconsistent with press releases on the subject. The release at spacedaily.com says that the test used a 10 kW pulsed CO2 laser. You can buy these off the shelf as industrial cutting lasers, for substantially less than $800M.
A MIRACL-style chemical laser would actually be poorly suited to laser launching, as the laser launch schemes I've heard of use a 10-100 Hz pulse rate. The MIRACL would be difficult to pulse (I suppose q-switching might work, but that's typically done at much higher frequency).
High-powered CO2 and chemical lasers are now substantially cheaper than $800M to build, also, largely in part to the basic research done for projects like MIRACL.
We either have to go to nuclear propulsion or give it up. Those are the options.
I doubt that nuclear propulsion for ground-to-orbit will ever be practical, for reasons outlined in other messages.
Methods that work around the problem you noted - low energy density - are any of a variety of methods that supply the energy externally.
The space elevator is the most elegant, though difficult to build, solution. Mass going up makes the center of mass sink a bit. Add ion thrusters or other high-Isp drives at the center of mass, and you can reposition the cable. The net result is the cargo getting a ground-to-orbit trip using in-orbit Isp ranges.
A magnetic launcher (or even a compressed-gas launcher like the "super gun") works well for cargo. It can't be used for humans, because the gun size for reasonable accelerations is ridiculous (thousands of kilometres), and the radius of curvature for survivable radial acceleration is similarly impractical. Still, that lets you build very large structures in space more cheaply.
A laser-launcher scheme would provide an arbitrarily long acceleration path, as long as you had multiple stations along the (mostly lateral) launch route. This would make it potentially practical for humans. A laser launch scheme is basically an externally powered space plane. Because there is no combustion, you don't have the blowout problems you have with scramjets.
In summary, I see several options besides nuclear.
Most of the risks you list for a tether turn out to not be as serious as you paint them, or to have far less drastic consequences than you seem to be assuming.
A space tether would be a huge structure. Yes, it would be thin. It would nevertheless be very tall. As a result, it would be easy to hit. A cruise missile, ICBM, or an airplane that struck the tether would break it. An explosive device, including either a conventional explosive or a nuclear device, would break it. If the tether were stationed at sea, a submarine could clip the tether, or shoot a torpedo at it.
Clipping the bottom of the tether, or firing a missile at it, would do next to nothing. The single-ended tether (with counterweight) is 40,000 km long; the double-ended one is twice that. Low earth orbit - which is the maximum practical range for things like ICBMs, unless they're built specifically to be anti-geostationary missiles - is in the 200-300km regime. Lose the bottom of the tether? Just send down a replacement segment from the hub, and you're back in business.
There would be no way to defend the tether from terrorists. You would have to create a large no-fly zone and a no-sail zone around the perimeter. This would create a humongous, circular no-commerce zone that would harm the global economy.
Not really. What is the maximum distance a hostile craft could travel from detection to interception? That's the radius of your no-fly zone. This is tens of kilometres at most if you're dealing with civilian craft. Antimissile interception range is left as an exercise for people with more military background than I have. Either way, impact on trade is next to nil. Commercial flights fly *thousands* of kilometres - why would a 10-km detour have any effect at all?
Natural events are also dangerous. A lightning strike could break it. An earthquake or volcanic activity could result in enough stress on the tether to break it. A tornado, with winds in excess of 400 mph, could damage the tether.
Extreme weather only exists in the lowest 10km or so of the atmosphere. 99.97% of your tether is above this level. If you see the storm coming, pull up the bottom 20km or so until it passes. If you get blindsided, send down another small segment as a replacement.
I'd worry more about space junk, myself. More of the tether could fall.
If a tether ever became damaged or underperformed its design specs, there would be no way to repair it. Should we ever decide to remove the tether, there would be no way to take it down without it causing a catastrophe on the ground.
How do you figure this? You can just spool the darn thing back up to the counterweight/hub in geostationary orbit! That's where its center of mass is.
As for repair - how do you think the cable would be built in the first place? You aren't going to lift a full-thickness cable on chemical rockets - you'll lift a very thin leader cable, and send crawlers up it with extra strands/ribbons to thicken it with.
To repair a damaged (but still holding) cable, send down a patch, connect above and below the damaged section, and remove the damaged section. Or, if multistranded, remove the damaged strands and send down replacement strands. You've overspecced the cable strength, so the undamaged strands will hold. Any given strand breaking isn't a big deal with a multistranded design.
Even if you're foolish enough to build a difficult-to-repair elevator, there's nothing to stop you from lifting materials for a new one up ahead of time. Keep a backup elevator - spooled up - in geostationary orbit for use as a replacement if anything happens to one of the elevators currently in service. Only the first elevator will be expensive to build - cost of lifting matter goes down drastically once that one's done.
In summary, I find your claim that an elevator would be fragile or impossible to repair puzzling.
Any breakage of the tether would result in catastrophe. First, there would be damage to the ground. Anything that big (about as long as the circumference of the Earth) is not going to totally burn up in the atmosphere.
Firstly, since it'll wrap around like twine as it orbits (speeding up tangentially as it falls to conserve angular momentum), it could easily burn up - it's impacting over a very large area.
Secondly, there's a strong upper limit on the amount of damage it can do - that limit being the gravitational potential energy of the cable. Potential energy per unit mass for something most of the way outside the gravity well is on the order of 10 times its equivalent weight in TNT or other high explosive. Declare a maximum acceptable explosive yield for the whole cable coming down, and that gives you the maximum weight of the cable. Simple enough.
Any real disaster would be far _less_ severe, as a) it's unlikely the whole cable would come down; most logical point of breakage is within easy reach of the surface, and b) even if the whole cable from geosynch onwards came down, it would impact over a large and mostly-uninhabited area (if you've placed your cable with any sense at all). Only the fraction that hits populated areas matters.
Our economic security and probably our military security and national security would come to depend on this tether.
The big problem is that once the tether is destroyed, you're probably looking at years before a replacement tether could be erected.
If the tether's that important to the economy, you'd a) have more than one in service at any given time, and b) have replacements stashed in geosynch, ready to unspool. If space travel is that widespread, then you also have the manufacturing facilities off-planet to produce a new one. Build it, send it to geosynch from wherever else it's built, and spool it down.
In summary, all of the risks you've pointed out have easy workarounds.
Lastly, there's a very compelling argument for a tether being much better in the long run than a space plane. An *ideal* space plane would have a specific impulse of perhaps three times that of chemical rockets. Lifting cargo is still expensive with such a beast - on the order of thousands of dollars per kilo even under ideal conditions (and likely much more, given the industry's track record with other launch vehicles). Lifting cargo with a space elevator is orders of magnitude cheaper, if you have high volume. The theoretical limit (cost of the gravitational potential energy paid in electricity) is absurdly low (on the order of $1/kg). The practical limit is determined by how fast you can haul cargo up the cable (no more than, say, an amount equal to the cable's weight can be in transit at any given time, and it has 40,000 km to travel before being unloaded). Haul fast enough, and you can make the cost per unit weight as low as you please. All of your hauled weight is cargo, because your fuel can either be burned on the ground with electricity sent up the cable, or (more likely) produced at the counterweight by solar or nuclear generation, and sent down.
The long-term rationale for building a tether is clear.
what is the theory of the scram jet? you get enough speed through conventional rockets and at the critical speed the scramjet kicks in? isn't there a problem of the lack of enough oxygen at the point where you would want it? and where there is enough power for it, you run into friction problems?
A scramjet is a ramjet that works above about Mach 5 (it's a ramjet with Supersonic Combustion; hence, the name). You use it _instead_ of a rocket for as much of your early launch as you can, because three quarters of the weight of rocket fuel is oxidizer. If you can get oxygen from the atmosphere instead, your specific impulse goes up by a very large amount (so you need less fuel per unit craft weight).
As Moofie pointed out, though, nobody's been able to build one that works (yet).
Friction is a problem, but it's a manageable one. If you can survive dropping back down into the atmosphere at orbital speeds, you can survive friction on the way out. It just slows you down (i.e. above a certain speed, drag will equal scramjet thrust, and further air-breathing boosting doesn't help you).
To recap, the benefit of doing any of this is to use air as the oxidizer instead of carrying oxygen with you. Altitude isn't the issue (from orbital height you'll still fall like a rock if you aren't moving very, very fast *sideways*).
what about a nuclear powered plasma system? it works in space (theoreticly) would it not work in the atmosphear?
All electric propulsion drives studied to date (ion, and many plasma variants) have thrust far, far too low to use for launch. They're designed to work at moderate power and very low thrust for a very long time. Specific impulse is great (lots of delta-v for a small amount of mass), but thrust isn't (thousandths of a gravity).
Other nuclear drives have been investigated for launch, but they have problems, and are very messy. NERVA style drives - where you feed gas through a reactor core to heat it instead of forming hot gas by burning fuel - work, but because of temperature limits specific impulse is at best about twice that of chemical fuels. You also have to lug a lot of very heavy shielding and other reactor material, so the effectiveness for launch starts looking questionable. You're *also* spraying radioactive crud out behind you, because the flowing gas is hot enough to etch the reactor away over time.
In space, NERVA drives are a bit more practical, but you're better off using the nuclear plant to power an electric drive (better specific impulse).
The other ground-to-orbit scheme proposed for launch was to detonate fission bombs beneath the craft and let the shock wave drag you along, but a) minimum craft size is _large_, and b) this is messy enough to not have a prayer of being used.
In short, nuclear drives won't be useful for ground-to-orbit in the forseeable future. Wait a century, and we'll have a space elevator. Until then, chemical will be good enough (and very good if we get scramjets working).
Shortly after the release of the 2600, they realized that 4K wasn't enough for future games. To rectify the problem, a mini comuputer was built into cartrages to expose only 4K to the atari at a time.
It wouldn't take a "mini computer"; a register chip tied to the high-order address lines would do.
I've wanted to try making an Atari cartridge for a long time. The parts are very cheap, and it would be quite a challenge to wrap my mind around (for programming-model reasons others have described).
from about march-november we see thunder about once a week on average. on more than one occasion i'd convince a girl you could see the bones in your hand if you held it in front of you when lightning stuck.
You can do this with an ordinary flashlight, if you turn off the lights and let your eyes adjust, and if you make sure your hand covers all of the aperture.
Similar techniques were proposed for medical imaging, though both the equipment and the principles were more complicated. They looked for light that passed through you without scattering, in order to give a sharp image. It takes much fiddling to distinguish this from the scattered light that arrives just behind it.
Seriously, though, how do you shield your X-ray detector so you can prove to yourself that what you are seeing is not just the effect of power spikes and RF interference in your instruments?
Almost certainly just by putting the instruments and a few batteries in a metal cage or inside a thin metal shell. Plenty of things will block radio noise without blocking X-rays.
You could get readings without any electronics at all by using something akin to the radiation sensing badges worn at nuclear power stations, but that would only tell you the total exposure, not give you intensity-vs-time information.
Same setup earlier: soda cans with tennis balls, only back then you could use rubbing alchohol. It made a really nice flame, at dusk especially.(They've changed the concentration of alchohol in the stuff they sell now, so you can't use that any more. What is this freaking world coming to?)
I've seen 99% ethanol and isopropanol in drug stores around here. It's not *all* 70%.
When we tried flaming projectiles, the wind from firing blew them out.
So, even if the RIAA only goes after the most hardcore P2Pers, the fact is that the group as a whole will see it as a personal attack by established corporate interests.
In short, the RIAA will seriously piss off a huge part of their customer base. It'll kill them.
I doubt it.
They'll whine and gnash their teeth and buy the CDs anyways. This is the same demographic that says "music group X has sold out!" and buys all of their stuff anyways, and who will watch TV for hours on end while complaining that there's nothing good on.
As for prosecution, the only people hit will be the suppliers with gigabytes of music or hundreds of movies. Most people won't be directly under attack, and so will barely notice. Remember pirate boards in BBS days? The boards, not the users, were the ones hit. It was actually even more selective than that; the boards specializing in credit card fraud and kiddie porn were hit, while the smaller fish were ignored. This is a natural consequence of the prosecuting organization's resources being limited. Joe User didn't really care; there were always more boards.
What happens for Joe User is that their favourite boards go down, it becomes harder for them to find what they want online, so they pester their parents to buy $item instead of spending hours looking for it.
Sharing can't be eliminated, but it can be made inconvenient, which is good enough. And people will still buy things no matter what.
I didn't think most tissue would be 'printable' it's to complex. so don't expect a new set of lungs any time soon.
I'm not sure this argument holds. Any 2400-dpi printer that's actually 2400-dpi can place dots accurately enough to place cells, so placement's not an issue for a specialty printer. You can keep data requirements sane by algorithmically generating the tissue structure map as you print. We already both seem to be assuming that you can store enough types of cell; the limit to the number of inks you can store is a cost/engineering problem, not a strong limit.
In summary, I don't think complexity is a serious roadblock.
The main limits I see are more fundamental. Cells are flexible enough not to deposit easily into well-controlled 3D structures even if you do have a way to form connective tissue on contact (which we don't), and you're going to have an interesting time printing open spaces like blood vessels (water doesn't like staying in one place at *all*). I'm undoubtedly overlooking many other important problems in addition to these.
Because it's so damn deep, I can't put my input devices in front of it! I just happened to be at that stupid trendy (but cheap) quasi-swedish furniture store today measuring up desks. The standard depth was 28", on almost every single desk. That ViewSonic monitor I mentioned is 24" deep including cable relief - so unless I can find a 4" keyboard, I'm screwed..
My solution: Put the big monitor on a corner of the desk. That leaves over a foot in front of it, and fills a desk section that just collects cruft (especially if it's the corner that's in the corner of the room).
A desk that's designed as an L-shaped corner desk is even better for this, but I do it on standard desks as well.
I've had the privilege of using APC products for the network used by a home business run by a relative.
Most of them have worked admirably for years.
One, however, didn't. When looking for the cause of strange computer behavior, I found the UPS half-melted, just as the article describes. I don't recall the model offhand; it had a form factor similar to the VS line, but was pitched as an "office" UPS.
Needless to say, I haven't touched that particular line since.
I've had similar things occur with multi-purpose wall warts (specified current ratings apparently aren't).
Actually, if gravity is instantaneous, then you would percieve the sun as moving away from the earth instantaneously after it vanished due to the earth moving quickly out of orbit. The earth would fling off in a straight line from the sun as soon as it vanished at incredible speed, and the light from where the sun WAS would take longer to reach the earth as the earth moves away.
While you are correct in pointing out that we'd see the light for slightly longer than 8 minutes (with a slight accompanying redshift), the time (and distance) difference is very small.
The time between gravity shutoff and light shutoff is 8 minutes. The Earth's orbital period is about 526,000 minutes. That gives an angle of about 9.6e-5 radians. Over that small an angle, the Earth's orbit is close enough to being straight already that divergence from the path would be negligeable.
CERN's also been working on this.
on
Visiting the Big Bang
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· Score: 5, Informative
CERN has also been trying to produce a quark/gluon plasma (and may have already done it).
The problem with the current ICMP standards are that it's too damn easy to spoof the original addresses, so you can send crap and nobody would know were it came from.
This will unfortunately remain a problem for the same reason it'll remain a problem with email - unless all possible nodes that traffic can be routed through are known and trusted, you have to take much of your routing information on faith.
There is no strong force. It's a myth. Just like Neutrons are a myth. No, I'm not joking. Anytime you extract a neutron from an atom, it breaks into a proton and an electron (hydrogen). A Neutron is not a true particle, it's simply a compressed proton and electron.
First of all, you're still going to have an interesting time explaining how all of those nice, positively-charged protons are bound into an incredibly tiny space without the strong force holding them together.
Secondly, the production and decay of neutrons is mediated by the weak force, not the strong force.
Thirdly, your model fails to explain mesons and the zoo of other particles that can be produced even in relatively low-energy accelerators, while the quark model explains it nicely.
Protons become neutrons when an electron and an "up" quark interact to produce a "down" quark and an electron neutrino. The inverse process - decay of neutrons into protons and electrons - happens when a "down" quark decays into an "up" quark, emitting an electron antineutrino and an electron.
The neutrino emitted during the decay has significant momentum. Its existence can be shown - and was originally inferred - by tracking the charged particles emitted when a neutron decays into a proton and an electron. In many cases, both of the charged particles are going in the same direction. To conserve momentum, something else had to be fired off in the opposite direction during the decay. That "something" is the neutrino. If a neutron was a bound proton/electron pair, there would be no third particle to explain the momentum discrepancy.
You're also overlooking the fact that a bound system has less energy than an unbound one. Which would mean that in your proposed scenario, _neutrons_ should be the stable nucleon, which is at odds with observations.
Or, you may have written that post as sarcasm. Either way, moderators have been falling for it.
The rest of your post is even sillier, so I'm not going to bother with it.
In summary, your proposed model is demonstrably incorrect.
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Actually 44khz was chosen for more practical reasons. Since audio signals at 44khz were originally designed for recording TV video to tape. To squeeze audio into a video stream:
3 samples * 490/2 lines (interlaced) * 60hz = 44100 Hz.
How is that for arbitrary?
Like 8-bit colour components, it represents a convenient value. But, like 8-bit colour components, it hasn't been replaced because it's close enough to perception limits to be indistinguishable for practical purposes. This is especially true for sound, as there would be no reason not to go to 4 samples per line if needed (while making higher-fidelity colour components requires sacrificing either ease of use of graphics cards (non-power-of-two sizes for RGBA pixels) or sacrificing the alpha channel).
[ObDisclaimer about high-fidelity equipment being needed for sound/image processing/compositing, where errors stack and sounds and colour values are rescaled/resampled.]
You make a good point re. non-ideal hardware; I hadn't thought of that. However, after thinking about it, I don't see how the monitor or graphics card could have removed banding.
:).
There are three types of artifact that could be imposed: quantization, low-pass filtering, and slew-rate limiting. Quantization would result if the DAC on the video card could generate fewer than 256 levels. While this could make any given pair of bands the same colour, contrast between other bands would have been worse, so I think it can be dismissed without further consideration.
Slew-rate limiting occurs if there is a limit to the speed at which a signal can be changed. However, this would affect high-contrast edges first. The fact that I can see a grid pattern or the text I'm typing suggests that it is not a factor in seeing or not seeing banding on smooth gradients.
The more important artifact is low-pass filtering. This tends to average the colours of adjacent pixels, smoothing gradients. This would indeed remove or reduce banding. As the eye does differential processing, the perceived effect would be worse for low-contrast edges (the type I'm trying to measure). However, two factors suggest that this is not what limits my ability to perceive banding. Firstly, the DACs on modern video cards are rated to 300+ MHz sampling rates, while conventional desktop modes use far lower sampling rates (1024x768x85 has a dot clock of around 95 MHz, even after adding the horizontal and vertical blanking interval contributions). This means that if there is filtering, it's unlikely to be in the graphics card (leaving the monitor and monitor cable as options). Secondly, I can see banding with 18-bit colour even at high resolutions (where filtering problems are worst, due to high dot clocks), but I can't see banding with 24-bit colour even at low resolutions (where filtering problems are least severe). If low-pass filtering was limiting contrast at low resolutions, the problem should be bad enough at high resolutions to be noticeable with higher-contrast edges. Ditto for varying refresh rates with a low-resolution mode instead of varying resolution, though that only lets you change the dot clock by a factor of two or three due to monitor vsync limits.
The fact that I can't see banding in low resolution modes also suggests that dot pitch of the monitor is not an issue (I buy monitors with overspecced resolution capability out of habit anyways).
In short, I'm not convinced it's the hardware that prevents me from seeing banding. If you can think of a source of smoothing that I'm missing, I'll certainly reconsider my view.
I can believe that there are exceptional humans able to perceive contrasts more accurately, but I'm not one of them, and I doubt most other people are either.
Although humans have more sensitivity to grayscale, the dynamic range of color vision is higher than for distinguishing shades of gray. Sensitivity has nothing to do with dynamic range in this context.
Good point. However, I do recall being told that the dynamic range for greyscale was higher as well.
I am too lazy to look it up, but the reference is in the color chapter in Computer Graphics.
Thank you for the reference. I'll look it up if this thread drags on for more than a week
24 bits is used because there are three channels and a byte of 8 bits is convenient on most architectures.
If the quality change was noticeable enough to be useful for marketing, I'm confident we'd be using an 11/11/10 mode for 32-bit colour by now (with alpha channels stored somewhere else, or not used at all, outside of game mode). Remember the whole 32-vs-16 PR battle between 3dfx and nVidia a while back.
If you have 1 color change per pixel in a gradient, no banding can be seen, but try to repeat a color once or try to fit a 24-bit gray gradient across 300 pixels, and you'll see bandling galore.
/moire like pattern since 18kHz doesn't fit properly into 22kHz.
Not when I tried it. These were images that didn't cover the whole gradient, and had tens of pixels per band (Mandelbrot sets with fun colour maps to iteration counts, if you're curious).
Regarding the nyquist rate of CD-Audio:
How do you represent a 22kHz sawtooth wave?
A sawtooth wave is a sine wave at the fundamental frequency plus a bunch of harmonics at higher frequencies. If you can hear the difference between a 22 kHz sawtooth wave and a 22 kHz sine wave, you're not from this planet, because the harmonics are about a factor of two out of human hearing range.
By all means get a signal generator and try it. Or bring a piezo speaker into your local university's electronics lab to perform the test.
If you can hear a 22 kHz *anything*, you have exceptional hearing to begin with.
How can you accurately represent a 18kHz wave
without harmonic distortions?
Answer: You can't, because you get an interference
Nope. Break out that signal theory book - as long as the original signal was a pure tone, you have no aliasing. Sampling aliases higher frequencies down to lower on recording (which is why you need a low-pass input filter on any digital recording device). No high frequencies, no aliased signals at lower frequencies. Reconstruction causes higher-frequency harmonics if your output filtering is bad, but a) output filtering on sound cards is decent, and b) the harmonics are above your hearing range unless you're playing back at less than 10 kHz.
In summary, you made an assumption that I didn't re. colour, and don't seem to be working through the math re. sound.
And 16 million colours is more than the eye can see, and 44,100 samples per second is more than the ear can hear . Throughout the march of technology we've heard these ridiculously arbitrary "limits" of our senses, and invariably they are discounted at a future time. In essence you can consider them a sort of justification.
These limits aren't arbitrary. You can test them the same way you proposed that frame rate limits be tested.
For colour gradations, make a picture that has a very gradual colour ramp from 0-255 in each colour (or one that sweeps across colour tones, but that changes at most one component by at most one between adjacent bands).
When I tried this with an old VGA card that used 18-bit colour, I could see banding. I had to stare for a while to let my eyes adjust, but I could see it.
When I try it on a modern card with 24-bit colour, I see no bands if the monitor's gamma correction is properly adjusted.
A monitor without gamma correction will end up expanding some brightness ranges and compressing others, with the result that gradations will not be visible at all in some areas and will be (barely) visible in others. Check your configuration before complaining.
The 24-bit argument applies to distinguishing colours. Similar experiments (not performed by me) have shown that you get about 10 bits of depth in greyscale, as humans have more sensitive black and white vision than colour (which is why everything appears in shades of grey at night with poor lighting; go for an evening walk and look for badly-lit stop signs some time).
You can do the same kind of tests with sound. It's actually more difficult with modern sound cards, as they have low-pass filters that cut off everything above about 22 kHz (nyquist rate of 44 kHz), but a PC speaker works. Or use a piezo buzzer and a signal generator if you're worried about the speaker efficiency dropping at high frequencies. My hearing, last time I tested it (and last time it was tested by a doctor), dropped out about about 18 kHz.
The reason why higher frequencies are relevant at all is because of nonlinear behavior both in the speakers and in the human ear. Beat frequencies between high-frequency tones can turn into audible frequencies when interacting with nonlinear systems (this is how that two-tone ultrasonic speaker linked to a while back worked). However, the key is that the final tone you hear is in the audible frequency range. This means you can duplicate the sound perfectly by using a microphone that acts more like the human ear when recording (i.e. that has similar nonlinear effects), or by recording at high frequencies and applying appropriate transformations before downsampling.
The fact remains that if I played a 20 kHz pure tone at you right now, you wouldn't hear it. And this is easy to verify by experiment.
In summary, while you're most definitely right about frame rates, your other objections about limits are unfounded.
1600x1200 on a 19" monitor is hardly "microscopic" pixels
:-)
:-) Sure, they are noticeable on a static display, but I wouldn't notice them if they changed at a rate of something like 70 fps.
Wow, I'd like to have your eye sight.
I use 1280x1024 on my 19" usually and even then the pixels are pretty small to me.
In first-person shooters, you're typically looking for small visual details in known locations (when you're not just in a twitch-reflex situation). In Tribes 2, at least, it's nice to be able to spot an enemy without having to pick out the one off-colour pixel in a grainy mountainside texture map, and even better to see what kind of gun he's holding, or that he's repairing something.
Features like zooming help you with the latter case but not the former (noticing the enemy in the first place).
While high-resolution displays aren't vital, they definitely are helpful.
The notion of creating cheaper, safer ways to get into orbit is, of course, a no-brainer. Would you want to create more expensive, dangerous paths to orbit?
If I understand correctly, a few factors made the shuttle look like a good idea when the program was intiated:
In principle, this seems reasonable, as you don't have to throw away the investment made in building the craft. In hindsight, we know that the added complexity and maintenance requirements overwhelmed this advantage, but this wasn't necessarily obvious going into the project. People evidently still believe that the goal is attainable, as proposals for reusable craft are regularly floated.
The cost of the support facilities for the shuttle are amortized over the shuttle launches taking place. At the original proposed launch frequency - on the order of once a week or more, if I recall correctly - the impact on payload cost of paying for the launch and maintenance facilities would have been much lower.
Unfortunately, this required a craft reliable and easily maintained enough to launch on a weekly basis, and enough people willing to pay for shuttle payloads to launch at that frequency.
I've heard allegations that this was originally supposed to be the shuttle's only job. It's a craft that can go just about anywhere in low orbit, match courses with stations or satellites, transfer crew, perform repairs, retrieve malfunctioning satellintes, and so forth. As a cargo vehicle, it's horrible, but in other respects it's a very flexible and potentially useful craft.
Of course, its usefulness assumes that there are enough satellites and space stations to require regular shuttle service.
In the political climate of the time, this was important and could be argued to have enough political effect to make it worthwhile to pursue regardless of other merits.
In short, I think the shuttle falls into the "it seemed like a good idea at the time" category. Assumptions that were made turned out not to hold, and costs turned out to be much higher than expected. Thus, the craft we're now stuck with.
Space travel is about going someplace. Someone needs to pick a destination for NASA.
I'm not sure about this. The goal of the manned space program also involves establishing human presence in space. This goal is best accomplished by building more facilities in the areas we can reach easily and know a lot about, as opposed to sending humans to every object we can find. Exploration is a goal too; however, it's not the only goal, and manned expeditions are arguably less useful for this aspect.
Anything science-related is most efficiently performed by unmanned devices. If we're sending people into space, it's for other reasons than science ("because we think it's cool" is, in my opinion, a valid reason).
And, of course, remember that tthe station is not yet complete. Only the Shuttle can do that job.
As opposed to just lifting units on any of the variety of disposable boosters in service?
Modules would be limited to 10 tonnes instead of 30 (unless a new heavy-lift booster was designed or the Saturn V was put back into production), but this would still certainly be adequate.
The main change needed would be the addition of small attitude control thrusters to the cargo to match orbits precisely with the space station and come close enough to docking that the new segments could either be hauled in by astronauts or moved using the station's manipulator arm.
I do not think that the shuttle is required for space station construction. It's _convenient_, but not required.
I'd worry more about space junk, myself. More of the tether could fall.
So what would you do to protect the tether from space junk?
Make it multi-stranded, per my previous post. A paint fleck will take out at most one strand. As your strands will be separated by at least tens of centimetres (and maybe tens of metres), it would take a very, very large object to sever more than one strand. Such objects are very rare and very easy to detect.
Secondly, in the event of military conflict, how do you propose to defend the tether from "space junk" that has been purposively deployed by an adversary for the purpose of breaking the tether?
If there's enough to be a problem, you'll see it coming. Haul up a large block of styrofoam, spool up the cable, and wait for all of the debris to impact on the styrofoam. Either capture the shield and dispose of it as you will, or just de-orbit it.
You say that if a tether is clipped at the bottom, it will continue to hang from space down to the point where it was clipped. On the other hand, quasi_stellar says [slashdot.org] that if it is clipped near the bottom, the tether assembly will fly off into space. It would appear that the tether community is not in agreement on this crucial issue.
Spend more than half a second thinking about it, and you'll see that losing part of the tether moves the center of mass of the structure up by some small amount. This puts it in a slightly elliptical orbit with a perigee (lowest point) at the original position of the tether.
If you're using a counterweight with a single-ended tether, no possible cut will cause any of it to fly off into space (lose the whole thing, and the counterweight will occupy an elliptical orbit). If you're using a double-ended tether and cut it close to the middle, you'll get one piece with escape velocity, but clipping any part close to Earth won't even come close to doing this.
The argument in your post is unpersuasive.
Persuaded now?
One last point. A reason why I'm unconvinced that the tether would burn up in the atmosphere, were it to come down, is the conduction of heat. Most of the tether would be in space. The part of the tether that was falling through the atmosphere would be subjected to great heat, but it seems like much of that heat would be conducted upwards to that part of the tether in frigid vacuum, where the heat would dissipate.
This is only true if the tether is a) a superconductor of heat and b) conducts it instantly. Neither is true for any tether likely to be built.
Any non-ideal conductor won't have enough heat transport (look up "Newton's Laws of Heating and Cooling", and remember that the tether is very thin and thousands of kilometres long).
If the tether is built out of magical materials and doesn't burn up, you still don't have a big problem, due to the total impact energy arguments in my previous post.
The most successful laser launch to date, using the biggest continuous laser in the US [fas.org], lifted a 50 gram vehicle two meters. And that took a laser that cost $800 million to build.
Your data appears to be inconsistent with press releases on the subject. The release at spacedaily.com says that the test used a 10 kW pulsed CO2 laser. You can buy these off the shelf as industrial cutting lasers, for substantially less than $800M.
A MIRACL-style chemical laser would actually be poorly suited to laser launching, as the laser launch schemes I've heard of use a 10-100 Hz pulse rate. The MIRACL would be difficult to pulse (I suppose q-switching might work, but that's typically done at much higher frequency).
High-powered CO2 and chemical lasers are now substantially cheaper than $800M to build, also, largely in part to the basic research done for projects like MIRACL.
We either have to go to nuclear propulsion or give it up. Those are the options.
I doubt that nuclear propulsion for ground-to-orbit will ever be practical, for reasons outlined in other messages.
Methods that work around the problem you noted - low energy density - are any of a variety of methods that supply the energy externally.
The space elevator is the most elegant, though difficult to build, solution. Mass going up makes the center of mass sink a bit. Add ion thrusters or other high-Isp drives at the center of mass, and you can reposition the cable. The net result is the cargo getting a ground-to-orbit trip using in-orbit Isp ranges.
A magnetic launcher (or even a compressed-gas launcher like the "super gun") works well for cargo. It can't be used for humans, because the gun size for reasonable accelerations is ridiculous (thousands of kilometres), and the radius of curvature for survivable radial acceleration is similarly impractical. Still, that lets you build very large structures in space more cheaply.
A laser-launcher scheme would provide an arbitrarily long acceleration path, as long as you had multiple stations along the (mostly lateral) launch route. This would make it potentially practical for humans. A laser launch scheme is basically an externally powered space plane. Because there is no combustion, you don't have the blowout problems you have with scramjets.
In summary, I see several options besides nuclear.
Most of the risks you list for a tether turn out to not be as serious as you paint them, or to have far less drastic consequences than you seem to be assuming.
A space tether would be a huge structure. Yes, it would be thin. It would nevertheless be very tall. As a result, it would be easy to hit. A cruise missile, ICBM, or an airplane that struck the tether would break it. An explosive device, including either a conventional explosive or a nuclear device, would break it. If the tether were stationed at sea, a submarine could clip the tether, or shoot a torpedo at it.
Clipping the bottom of the tether, or firing a missile at it, would do next to nothing. The single-ended tether (with counterweight) is 40,000 km long; the double-ended one is twice that. Low earth orbit - which is the maximum practical range for things like ICBMs, unless they're built specifically to be anti-geostationary missiles - is in the 200-300km regime. Lose the bottom of the tether? Just send down a replacement segment from the hub, and you're back in business.
There would be no way to defend the tether from terrorists. You would have to create a large no-fly zone and a no-sail zone around the perimeter. This would create a humongous, circular no-commerce zone that would harm the global economy.
Not really. What is the maximum distance a hostile craft could travel from detection to interception? That's the radius of your no-fly zone. This is tens of kilometres at most if you're dealing with civilian craft. Antimissile interception range is left as an exercise for people with more military background than I have. Either way, impact on trade is next to nil. Commercial flights fly *thousands* of kilometres - why would a 10-km detour have any effect at all?
Natural events are also dangerous. A lightning strike could break it. An earthquake or volcanic activity could result in enough stress on the tether to break it. A tornado, with winds in excess of 400 mph, could damage the tether.
Extreme weather only exists in the lowest 10km or so of the atmosphere. 99.97% of your tether is above this level. If you see the storm coming, pull up the bottom 20km or so until it passes. If you get blindsided, send down another small segment as a replacement.
I'd worry more about space junk, myself. More of the tether could fall.
If a tether ever became damaged or underperformed its design specs, there would be no way to repair it. Should we ever decide to remove the tether, there would be no way to take it down without it causing a catastrophe on the ground.
How do you figure this? You can just spool the darn thing back up to the counterweight/hub in geostationary orbit! That's where its center of mass is.
As for repair - how do you think the cable would be built in the first place? You aren't going to lift a full-thickness cable on chemical rockets - you'll lift a very thin leader cable, and send crawlers up it with extra strands/ribbons to thicken it with.
To repair a damaged (but still holding) cable, send down a patch, connect above and below the damaged section, and remove the damaged section. Or, if multistranded, remove the damaged strands and send down replacement strands. You've overspecced the cable strength, so the undamaged strands will hold. Any given strand breaking isn't a big deal with a multistranded design.
Even if you're foolish enough to build a difficult-to-repair elevator, there's nothing to stop you from lifting materials for a new one up ahead of time. Keep a backup elevator - spooled up - in geostationary orbit for use as a replacement if anything happens to one of the elevators currently in service. Only the first elevator will be expensive to build - cost of lifting matter goes down drastically once that one's done.
In summary, I find your claim that an elevator would be fragile or impossible to repair puzzling.
Any breakage of the tether would result in catastrophe. First, there would be damage to the ground. Anything that big (about as long as the circumference of the Earth) is not going to totally burn up in the atmosphere.
Firstly, since it'll wrap around like twine as it orbits (speeding up tangentially as it falls to conserve angular momentum), it could easily burn up - it's impacting over a very large area.
Secondly, there's a strong upper limit on the amount of damage it can do - that limit being the gravitational potential energy of the cable. Potential energy per unit mass for something most of the way outside the gravity well is on the order of 10 times its equivalent weight in TNT or other high explosive. Declare a maximum acceptable explosive yield for the whole cable coming down, and that gives you the maximum weight of the cable. Simple enough.
Any real disaster would be far _less_ severe, as a) it's unlikely the whole cable would come down; most logical point of breakage is within easy reach of the surface, and b) even if the whole cable from geosynch onwards came down, it would impact over a large and mostly-uninhabited area (if you've placed your cable with any sense at all). Only the fraction that hits populated areas matters.
Our economic security and probably our military security and national security would come to depend on this tether.
The big problem is that once the tether is destroyed, you're probably looking at years before a replacement tether could be erected.
If the tether's that important to the economy, you'd a) have more than one in service at any given time, and b) have replacements stashed in geosynch, ready to unspool. If space travel is that widespread, then you also have the manufacturing facilities off-planet to produce a new one. Build it, send it to geosynch from wherever else it's built, and spool it down.
In summary, all of the risks you've pointed out have easy workarounds.
Lastly, there's a very compelling argument for a tether being much better in the long run than a space plane. An *ideal* space plane would have a specific impulse of perhaps three times that of chemical rockets. Lifting cargo is still expensive with such a beast - on the order of thousands of dollars per kilo even under ideal conditions (and likely much more, given the industry's track record with other launch vehicles). Lifting cargo with a space elevator is orders of magnitude cheaper, if you have high volume. The theoretical limit (cost of the gravitational potential energy paid in electricity) is absurdly low (on the order of $1/kg). The practical limit is determined by how fast you can haul cargo up the cable (no more than, say, an amount equal to the cable's weight can be in transit at any given time, and it has 40,000 km to travel before being unloaded). Haul fast enough, and you can make the cost per unit weight as low as you please. All of your hauled weight is cargo, because your fuel can either be burned on the ground with electricity sent up the cable, or (more likely) produced at the counterweight by solar or nuclear generation, and sent down.
The long-term rationale for building a tether is clear.
what is the theory of the scram jet? you get enough speed through conventional rockets and at the critical speed the scramjet kicks in? isn't there a problem of the lack of enough oxygen at the point where you would want it? and where there is enough power for it, you run into friction problems?
A scramjet is a ramjet that works above about Mach 5 (it's a ramjet with Supersonic Combustion; hence, the name). You use it _instead_ of a rocket for as much of your early launch as you can, because three quarters of the weight of rocket fuel is oxidizer. If you can get oxygen from the atmosphere instead, your specific impulse goes up by a very large amount (so you need less fuel per unit craft weight).
As Moofie pointed out, though, nobody's been able to build one that works (yet).
Friction is a problem, but it's a manageable one. If you can survive dropping back down into the atmosphere at orbital speeds, you can survive friction on the way out. It just slows you down (i.e. above a certain speed, drag will equal scramjet thrust, and further air-breathing boosting doesn't help you).
To recap, the benefit of doing any of this is to use air as the oxidizer instead of carrying oxygen with you. Altitude isn't the issue (from orbital height you'll still fall like a rock if you aren't moving very, very fast *sideways*).
what about a nuclear powered plasma system? it works in space (theoreticly) would it not work in the atmosphear?
All electric propulsion drives studied to date (ion, and many plasma variants) have thrust far, far too low to use for launch. They're designed to work at moderate power and very low thrust for a very long time. Specific impulse is great (lots of delta-v for a small amount of mass), but thrust isn't (thousandths of a gravity).
Other nuclear drives have been investigated for launch, but they have problems, and are very messy. NERVA style drives - where you feed gas through a reactor core to heat it instead of forming hot gas by burning fuel - work, but because of temperature limits specific impulse is at best about twice that of chemical fuels. You also have to lug a lot of very heavy shielding and other reactor material, so the effectiveness for launch starts looking questionable. You're *also* spraying radioactive crud out behind you, because the flowing gas is hot enough to etch the reactor away over time.
In space, NERVA drives are a bit more practical, but you're better off using the nuclear plant to power an electric drive (better specific impulse).
The other ground-to-orbit scheme proposed for launch was to detonate fission bombs beneath the craft and let the shock wave drag you along, but a) minimum craft size is _large_, and b) this is messy enough to not have a prayer of being used.
In short, nuclear drives won't be useful for ground-to-orbit in the forseeable future. Wait a century, and we'll have a space elevator. Until then, chemical will be good enough (and very good if we get scramjets working).
Shortly after the release of the 2600, they realized that 4K wasn't enough for future games.
To rectify the problem, a mini comuputer was built into cartrages to expose only 4K to the atari at a time.
It wouldn't take a "mini computer"; a register chip tied to the high-order address lines would do.
I've wanted to try making an Atari cartridge for a long time. The parts are very cheap, and it would be quite a challenge to wrap my mind around (for programming-model reasons others have described).
from about march-november we see thunder about once a week on average. on more than one occasion i'd convince a girl you could see the bones in your hand if you held it in front of you when lightning stuck.
You can do this with an ordinary flashlight, if you turn off the lights and let your eyes adjust, and if you make sure your hand covers all of the aperture.
Similar techniques were proposed for medical imaging, though both the equipment and the principles were more complicated. They looked for light that passed through you without scattering, in order to give a sharp image. It takes much fiddling to distinguish this from the scattered light that arrives just behind it.
Seriously, though, how do you shield your X-ray detector so you can prove to yourself that what you are seeing is not just the effect of power spikes and RF interference in your instruments?
Almost certainly just by putting the instruments and a few batteries in a metal cage or inside a thin metal shell. Plenty of things will block radio noise without blocking X-rays.
You could get readings without any electronics at all by using something akin to the radiation sensing badges worn at nuclear power stations, but that would only tell you the total exposure, not give you intensity-vs-time information.
Same setup earlier: soda cans with tennis balls, only back then you could use rubbing alchohol. It made a really nice flame, at dusk especially.(They've changed the concentration of alchohol in the stuff they sell now, so you can't use that any more. What is this freaking world coming to?)
I've seen 99% ethanol and isopropanol in drug stores around here. It's not *all* 70%.
When we tried flaming projectiles, the wind from firing blew them out.
So, even if the RIAA only goes after the most hardcore P2Pers, the fact is that the group as a whole will see it as a personal attack by established corporate interests.
In short, the RIAA will seriously piss off a huge part of their customer base. It'll kill them.
I doubt it.
They'll whine and gnash their teeth and buy the CDs anyways. This is the same demographic that says "music group X has sold out!" and buys all of their stuff anyways, and who will watch TV for hours on end while complaining that there's nothing good on.
As for prosecution, the only people hit will be the suppliers with gigabytes of music or hundreds of movies. Most people won't be directly under attack, and so will barely notice. Remember pirate boards in BBS days? The boards, not the users, were the ones hit. It was actually even more selective than that; the boards specializing in credit card fraud and kiddie porn were hit, while the smaller fish were ignored. This is a natural consequence of the prosecuting organization's resources being limited. Joe User didn't really care; there were always more boards.
What happens for Joe User is that their favourite boards go down, it becomes harder for them to find what they want online, so they pester their parents to buy $item instead of spending hours looking for it.
Sharing can't be eliminated, but it can be made inconvenient, which is good enough. And people will still buy things no matter what.
I didn't think most tissue would be 'printable' it's to complex. so don't expect a new set of lungs any time soon.
I'm not sure this argument holds. Any 2400-dpi printer that's actually 2400-dpi can place dots accurately enough to place cells, so placement's not an issue for a specialty printer. You can keep data requirements sane by algorithmically generating the tissue structure map as you print. We already both seem to be assuming that you can store enough types of cell; the limit to the number of inks you can store is a cost/engineering problem, not a strong limit.
In summary, I don't think complexity is a serious roadblock.
The main limits I see are more fundamental. Cells are flexible enough not to deposit easily into well-controlled 3D structures even if you do have a way to form connective tissue on contact (which we don't), and you're going to have an interesting time printing open spaces like blood vessels (water doesn't like staying in one place at *all*). I'm undoubtedly overlooking many other important problems in addition to these.
Still, it's a neat concept.
But EmagGeek! Why not use the 21"!?
Because it's so damn deep, I can't put my input devices in front of it! I just happened to be at that stupid trendy (but cheap) quasi-swedish furniture store today measuring up desks. The standard depth was 28", on almost every single desk. That ViewSonic monitor I mentioned is 24" deep including cable relief - so unless I can find a 4" keyboard, I'm screwed..
My solution: Put the big monitor on a corner of the desk. That leaves over a foot in front of it, and fills a desk section that just collects cruft (especially if it's the corner that's in the corner of the room).
A desk that's designed as an L-shaped corner desk is even better for this, but I do it on standard desks as well.
YMMV.
I've had the privilege of using APC products for the network used by a home business run by a relative.
Most of them have worked admirably for years.
One, however, didn't. When looking for the cause of strange computer behavior, I found the UPS half-melted, just as the article describes. I don't recall the model offhand; it had a form factor similar to the VS line, but was pitched as an "office" UPS.
Needless to say, I haven't touched that particular line since.
I've had similar things occur with multi-purpose wall warts (specified current ratings apparently aren't).
Yet another reason to keep spares handy.
Keep going with that math. 8 light-minutes times (1-cos(9.6e-5)) is about 660 meters of deviation, which is not really "negligible."
Compared to the distance from your terminal to the break room, no.
Compared to the distance between the Earth and the Sun (about 1.5e+11 m), yes, it's most definitely insignificant.
Read the original poster's description of visual effects to see what "significant" in this context would do.
Actually, if gravity is instantaneous, then you would percieve the sun as moving away from the earth instantaneously after it vanished due to the earth moving quickly out of orbit. The earth would fling off in a straight line from the sun as soon as it vanished at incredible speed, and the light from where the sun WAS would take longer to reach the earth as the earth moves away.
While you are correct in pointing out that we'd see the light for slightly longer than 8 minutes (with a slight accompanying redshift), the time (and distance) difference is very small.
The time between gravity shutoff and light shutoff is 8 minutes. The Earth's orbital period is about 526,000 minutes. That gives an angle of about 9.6e-5 radians. Over that small an angle, the Earth's orbit is close enough to being straight already that divergence from the path would be negligeable.
CERN has also been trying to produce a quark/gluon plasma (and may have already done it).
Googling only turns up articles of questionable use. You can find better information in their list of experiments, and maybe a summary elsewhere on the CERN web site.
The problem with the current ICMP standards are that it's too damn easy to spoof the original addresses, so you can send crap and nobody would know were it came from.
This will unfortunately remain a problem for the same reason it'll remain a problem with email - unless all possible nodes that traffic can be routed through are known and trusted, you have to take much of your routing information on faith.
There is no strong force. It's a myth. Just like Neutrons are a myth. No, I'm not joking. Anytime you extract a neutron from an atom, it breaks into a proton and an electron (hydrogen). A Neutron is not a true particle, it's simply a compressed proton and electron.
First of all, you're still going to have an interesting time explaining how all of those nice, positively-charged protons are bound into an incredibly tiny space without the strong force holding them together.
Secondly, the production and decay of neutrons is mediated by the weak force, not the strong force.
Thirdly, your model fails to explain mesons and the zoo of other particles that can be produced even in relatively low-energy accelerators, while the quark model explains it nicely.
Protons become neutrons when an electron and an "up" quark interact to produce a "down" quark and an electron neutrino. The inverse process - decay of neutrons into protons and electrons - happens when a "down" quark decays into an "up" quark, emitting an electron antineutrino and an electron.
The neutrino emitted during the decay has significant momentum. Its existence can be shown - and was originally inferred - by tracking the charged particles emitted when a neutron decays into a proton and an electron. In many cases, both of the charged particles are going in the same direction. To conserve momentum, something else had to be fired off in the opposite direction during the decay. That "something" is the neutrino. If a neutron was a bound proton/electron pair, there would be no third particle to explain the momentum discrepancy.
You're also overlooking the fact that a bound system has less energy than an unbound one. Which would mean that in your proposed scenario, _neutrons_ should be the stable nucleon, which is at odds with observations.
Or, you may have written that post as sarcasm. Either way, moderators have been falling for it.
The rest of your post is even sillier, so I'm not going to bother with it.
In summary, your proposed model is demonstrably incorrect.