Sorry but I don't think the instrumentation on these probes really is advanced enough to gather what is needed to make an accurate or informed decision.
How so?
To start with, the main data of interest (probe positions and trajectories) doesn't require additional instruments to measure. They're looking at the timing and doppler-shifting of the probes' radio signals, and getting a very good estimate of their positions and velocities.
The record of the probes' trajectories over long periods of time is what suggests the effect and places limits on how it acts.
Secondly, there isn't anything *out* there to look at. At least a few of these probes have micrometeorite detectors and dust analyzers and radiation analyzers. That covers just about everything you'll run into. What extra instrumentation do you propose to add?
What kinds of instruments do you think would give us a better idea of what's going on than we already have?
How big of a power supply will I need? I am looking at an SMP (dual) Intel P-III 1ghz system, with three 80mm case fans, a high-end 7200 RPM IDE hard drive, a hard drive fan, high-end video card (possibly even Nvidia's new GeForce3), DVD, CD-RW, SBLive!, and other standard hardware. Is my current 300W ATX supply going to cut it?
It should.
The Right Way to figure this out is to look up figures for *peak* power consumption for the CPUs and the graphics cards from the various hardware review sites (Ace's, Sharkey's, etc). Then add the power ratings on all of the fans (should be on the box if you're buying them as discrete components, and you can get the store to look it up if they're building it for you). Then multiply the whole shebang by 1.3-1.5x as a safety factor.
Or, you can use the back-of-the-envelope method:
- 50W each is about the right ballpark for the processors. Spec 100W for this.
- If all of your fans together take more than 50W, I'll be very surprised. Spec 50W.
- If your graphics card takes more than 50W, the PCI bus should start smouldering. Unless you have a Voodoo 5, spec 50W.
- Hard drives and so forth aren't *horribly* power-hungry. You have a 100W margin left. You should be fine.
Heck, you'd probably be fine with a 250W supply or lower, but you don't want to risk having your computer hang when you're using it most thoroughly.
This article discusses a measurement of CP symmetry violation, which is a difference in behavior between matter and antimatter. CP-violating decay modes have been used as an explanation for the dominance of matter for many years.
The article mentions that CP violation was first detected in 1964.
The article is written in a nice, calm tone, properly painting this as a much nicer measurement of a known effect.
Where did the sensationalistic article blurb come from? Is there *any* justification for it at *all*?
actualy it depends on the electron stabilization. If you pressed the nitrogen tightly enough, you might form resonance structures and associated structures that allow electron delocalization.
Perhaps I gave the wrong impression in my previous post. I'm not saying that a solid allotrope of nitrogen couldn't exist at room temperature - just that it would be *more* stable in gaseous form, and would thus tend to revert to this form when sufficiently provoked.
It's easy to demonstrate that the gaseous form is the most stable under standard conditions - if it wasn't, the atmosphere wouldn't contain gaseous nitrogen. It's had plenty of time to be converted to an alternate form by whatever mechanisms are appropriate.
As the solid nitrogen would tend to revent to its gaseous form when provoked, and as gaseous nitrogen doesn't like being stored at solid densities, you'd almost certainly get an explosive release of stored energy if you heated or otherwise sufficiently agitated a sample of solid nitrogen.
Interesting argument, though. In your opinion, is there any chance at all of an allotrope of solid _hydrogen_ being stable much above hydrogen's freezing point, or would this not work with just a "1S" shell?
Just wondering, when it returns to normal preasure levels, they apparenlty have this new substance remaining after it forms at high preassure. Is there any chance of it returning to a gasous form and hence exploding to it's original volume?
Sure. Just heat it. It's both more entropically favourable and more energetically favourable for it to be a gas (above nitrogen's freezing point, at least), so as soon as you get over the activation energy, *boom*.
According to the article, the sample at 1 atm had to be cooled quite a bit to be stable. For all I know, they could have taken it down below nitrogen's freezing point, which would just make this an interesting allotrope of frozen nitrogen.
Material properties should change as pressure is varied, as the energy bands within the material will shift. This would be very interesting to measure experimentally to check our models of materials at high pressures (and you can bet your socks they've submitted a funding application already to do this).
Anyone know what they used to achieve such high levels of atmospheric pressure?
For the metallic hydrogen experiments I read about a while back, they used a "diamond anvil cell". This is a fairly small device that uses a screw to close a pair of lever arms. The compression cell at the base of the lever squeezes the sample between two diamonds. A metal gasket surrounds the cell.
The nice thing about this is that the diamonds pass a wide range of light frequencies, which lets you measure material properties optically.
The group that I was reading about almost, but didn't quite, succeed in making metallic hydrogen.
I have no idea whether the nitrogen semiconductor group used this apparatus or something else. I suppose that if you were clever enough to find a fast way to take the measurements, you could just set off a bomb on top of the sample and measure for a few microseconds. Pressure is difficult to control, but if you can measure pressure accurately while you do this, you can simply plot your data with pressure as one of the axes.
Some types of industrial diamond are made using explosives.
This falls into the "duh" category. If you're overstressed, take steps to change your environment by whatever means necessary. Chronic stress will do things far worse than messing up your sleep patterns.
Watch the temperature.
If I have one too many blankets, it takes me a long time to fall asleep. This is something that's difficult to notice. If you find yourself tossing and turning, chuck a blanket and see if that helps.
Asthma.
I have asthma. I rarely have full-blown attacks, but breathing will often become more difficult than usual. This is another thing that's difficult to notice, that will keep me tossing and turning for hours. Make sure you can breathe freely. Install air filters if you're having trouble - they'll save you a lot of grief during the day, too. If you have serious trouble breathing, fairly often, see a doctor. You may have asthma or another breathing disorder (or be allergic to a solvent in your carpet, or what-have-you).
Don't eat right before bed, and make sure you hit the washroom.
This is another "duh" point, but if you have to go to the bathroom, you're going to be waking up every couple of hours until you drag yourself out of bed and go. That'll wreck your night's sleep pretty effectively.
Hopefully this becomes a viable alternative to stem cells from embryos. As the article points out, that is frought with ethical problems.
Stem cells of various types exist in many places in your (living) body; in principle, there's no reason they have to be harvested from anywhere else at all.
In practice, embryo cells are nice because they haven't differentiated at *all* yet (stem cells in your body have differentiated a bit, and so only give rise to certain types of cell (e.g. blood cells for bone marrow stem cells).
Research is ongoing to try to convert these back into general-purpose stem cells. There has been some progress, some of which has been covered on slashdot.
In summary, we won't have to worry about harvesting by the time we're ready to use stem cells on a large scale.
For pure research into differentiation, there's no reason we'd have to use human stem cells. If I understand correctly, human stem cells are only used for research into medical procedures that are intended to be performed on humans, which could be delayed until the differentiation problem is solved or performed on animals instead (though both options mean it'll be longer until the techniques are perfected for use in humans).
Isn't the temperature stable down there precisely because earth is such a good heat sink? Sure, a few hundred meters of earth will insulate you from surface temperature changes, but the hot air in the mine would still lose a lot of heat to the earth.
Hot air would; however, you'd almost certainly store the compressed air at room temperature, just like you do in a compressed air tank.
When your pump actually compresses the air, you do get heating, but you'd bleed this off through a radiator before storing it (or store air in the mine slowly enough that the earth would be an adequate heat sink).
Likewise, depending on the rate at which you let the air expand, you may get cooling when taking it out again, but this is a secondary effect (and can be reduced by using a nearby lake as a heat sink/cold sink).
Consider that the energy in compressed air is in the form of heat. Unless they insulate this cavern, there is going to be appreciable heat transfer. What are the losses going to be?
Most of the energy is not stored as heat. It's stored in the fact that the air is compressed. It takes a certain amount of work to compress it in the first place, and the air is capable of performing a certain amount of work as it expands.
Heating the air will change its pressure, which will change the amount of work it can do, but the resulting energy difference will just be the amount of thermal energy gained/lost. Not a vast amount compared to the total amount you're dealing with.
Lastly, the temperature underground is quite stable. As soon as you're more than a few tens of feet below the surface, the earth above you will insulate quite well. This is why deeply buried water pipes don't freeze in the winter.
That's pretty cute... this thing we threw up there *twenty nine years ago* is still working, but the last couple probes we've slapped together can't even make it to the next planet.
You're overlooking the several probes that did work. Clementine was particularly interesting (lunar mapping probe).
That aside - this was a deliberate tradeoff. If you send out ten probes instead of one, it doesn't matter if only half work - you've still have five times as many probes out there as you otherwise would. This is the philosophy behind the "smaller, faster, cheaper" motto that Nasa has adopted.
Not sure if the Mars probes were officially part of this program or not.
If there were a conspiracy to fake the moon landings, then this conspiracy would of *course* extend to faking photographs from Clementine or any other probe allegedly sent to the moon.
This would be far more effort than it's worth, but so would faking the moon landings.
ou could perfectly well run a 0.18 or 0.13 micron process at 5V Sorry, that's just not true. If you power a process with a supply voltage that is too high, you will break the gate oxide.
For low-voltage 0.18 or 0.13 processes, you are quite correct. However, there's nothing fundamental that prevents you from using a 0.18 or 0.13 process with a thicker oxide and some doping tweaking that would work acceptably at 5V.
I'll remember this the next time I design fictional circuits. Sorry, unless your whole world is spice simulations the voltage ramps down.
*sigh*.
Look up high-voltage CMOS processes offered by your local foundaries.
The reason why you're only encountering low-voltage processes is that high-voltage processes presumably aren't useful for the applications you deal with. Arguing that you can't build deep submicron transistors that use high voltages is silly (you almost certainly know yourself what would be changed to do it).
Re:Enough speed. Where are massively parallel CPUs
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in my dream world it would be built into the OS, making the programming yokel easy.
Unfortunately, this doesn't make it easy.
To run efficiently in parallel, a program must be written to use a parallel algorithm. The best parallelized OS and hardware in the world won't save you if the algorithm is serial. Writing parallel algorithms is more difficult than writing serial algorithms (usually), and turning a serial program into a parallel program automatically is extremely difficult (some optimizing compilers try to do this when building for parallel platforms, and usually don't do very well).
To make matters even worse, many problems are intrinsically serial - impossible to reduce to parallel form. As long as even part of your program is irreducibly serial, there will be a limit to how much you can boost performance (Amdahl's Law).
In summary, trying to use a massively parallel machine to boost performance doesn't work as well as you're assuming (though it's good for many special cases).
When I started designing circuits for pay Vgs was approximately 1.8 volts, now I'm designing with a Vgs of approximately 1.2 volts. Things are excaberated by the fact that Vt hasn't decreased proportionaly.
...And this is orthogonal to the point I was shooting down. You could perfectly well run a 0.18 or 0.13 micron process at 5V. You'd just melt down the chip, if you were trying to do this with a sqare centimetre of silicon. You could also run a 1.2 micron process at 1.2 volts if you felt like it, and you'd get current driving performance just as horrible as that which you're complaining about for 0.13.
Shrinking feature size isn't responsible for reduced current. The desire to run a constant area of silicon (and hence more-or-less constant parasitic capacitance) at ever-increasing speed without melting it is responsible.
The transistor itself is smaller, but again the capacitance isn't necessarily decreasing but the ability of the transistor to drive current is.
I'm afraid this isn't the case. As you make the gate of a transister shorter, its ability to drive current increases. Shrink the entire transistor, and as the W/L ratio of the gate stays the same, the transconductance of the transistor stays (roughly) the same.
Yes, process differences and short-channel effects muck this up somewhat, but the effect is still there. This is why we're bothering to move to finer linewidths at all.
Until recently, shrinking circuits like this produced a *big* speed boost, because most of the parasitic capacitances scaled directly with device area. Same drive current with 1/x^2 the capacitance means a speedup of x^2 for a linewidth shrink of factor x. Recently, as you point out, wire delays have become relevant, but while that does limit signal propagation speed, it doesn't affect a transistor's ability to drive current.
I've been studying this in far too much detail recently:).
Just because something seems simple once somebody else thought of it doesn't mean it wasn't a good idea in the first place.
And just because they (allegedly) were the first to think of it, doesn't mean it's patentable.
Patents are supposed to be given only for things that aren't "obvious to anyone skilled in the art". In practice, this isn't assessed well by the patent office, but that's another can of worms.
you dont put your material in barrels and hope it stays there, you encase it in solid glass. that way even as it breaks up the material is still encapsulated. Also most subduction zones are a couple hundred miles off coastlines, and under alot of salt water. You arent going to be drilling there for groundwater any time soon.
I've already been assuming that the barrels are filled with glass pellets. I still wouldn't want the barrels to break. Shatter the beads, and currents will take the resulting dust all over. Disperse a pollutant in the water, and it *won't* just stay in one place - you'll eventually have to worry about it (especially if we're dumping all of a continent's waste, and not just one plant's worth).
If you have a really deep hole, and plug it really well - maybe. But I'd still feel safer with the barrels deep in the continental shield.
Re:Hydroelectric as a non-renewable resource.
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On the off chance that this wasn't just good satire:
Trivial as it may seem, energy gained by tidal power is, erg for erg, slowing down the rotation of the Earth. True right now the results are inconsequential, but if massive projects were undertaken to supply 30% of the Earth's onging power needs with tidal forces, over the long run it could have an impact, and it's not exactly like we have a way to repair the damage by speeding up the Earth's rotation...
There's on the order of 1.0e30-1.0e31 joules of energy stored in the Earth's rotation. That gives us around 30 billion terawatt-years.
I don't think we're in danger of draining it soon.
At least clean fission only eats up matter which, though not a renewable resource either, is constantly being replenished on the order of tons a day from micrometeorites.
...which are made of rock, and thus don't contain much hydrogen. Allegations of a continuing hail of ice micro-comets are as yet unsubstantiated.
Not to worry, though. Even if we just extract deuterium (which is 0.015% of all hydrogen) for fusion, we have about 1.0e13 tonnes of the stuff in the oceans. Assuming around a million times the energy yield of chemical reactions, this gives us about 5 million terawatt-years.
Switch to ordinary hydrogen, and by the time the sun burns out, we'd have used around 15% of the ocean. Assuming we don't ship in a few ice asteroids in the interim.
Re:Spent fuel MUST BE stored on site. No appeals.
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2-3% of it will always be "in the transportation tube" rolling down local railways, interstates, and highways. And if one of these trains derails? Or truck jack-knifes?
Then the heavily-armoured barrels get their paint scuffed.
I don't trust nuclear waste barrels to last a hundred thousand years, but I do trust them to survive anything short of a point-blank strike from heavy artillery.
If you *do* fire heavy artillery at point-blank range into a nuclear waste barrel, you'll get a clould of glass shrapnel - the safest transportable form of nuclear waste puts waste oxides into glass, where they stay (glass is quite durable and resistant to chemical attack). Scrape up the first foot of soil for a quarter of a mile around, put that in barrels, and sent it to the waste dump along with everything else. No additional contamination.
In summary, I don't think that accidents during transport are a concern. I'd be more worried about deliberate theft, and the risk of that can be made no worse than it already is with waste stored at power plants.
Also, storing waste at the plants is not a viable long-term solution, as they aren't in earthquake-free regions isolated from the water table. One good disaster, and *all* of the plant's waste goes into the environment.
Right, but during the time its being sucked into the molten part, its trapped under a large amount of rock, which makes a good radiation shield. Moving at a foot a year, itll be 20 feet underground in maybe 30-40 years, and thats plenty of shielding. Yes it takes a million years to be spread into the magma layer, but during that time its in a place where it cant harm humans.
The problem with this is that the subduction zone, by nature, is earthquake-prone. With your containers that close to the surface, contamination of local water will also be a problem (your containers won't last more than a couple hundred years, which puts them at a couple hundred feet...)
I suppose you could drill a deep hole in the subducting crust, seal it with clay, and then let it go down, but I wouldn't trust a filled shaft to stay impermeable to water in an earthquake zone.
The graphite-laced "pebbles" in their reactor could melt down if enough were piled in one place
No, they won't. They are designed to keep the bits of fuel far enough apart that no reaction hot enough to start burning either the fuel itself or its carbon shell could start or sustain itself.
This has actually been tested by running a pebble-bed reactor without coolant for an extended period.
I meant, a pile larger than would fit in the reactor. A large enough pile should indeed melt down. The reaction will increase exponentially if the probability of interaction (vs. escape or absorption) is greater than one divided by the number of child neutrons produced by a reaction.
The probability of absorption (by the graphite or by a nucleus) depends on how far a neutron would have to travel to escape the pile. Use a bigger pile, and there's less chance of the neutron escaping.
If fissile material was sparse enough inside the fuel balls, then you could set it up so that an arbitrarily large pile still wouldn't enter meltdown, but this would make it a lot less useful for generating power as well (a small pile would be very, very subcritical).
Re:Killing two birds with one stone
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A signifigant fraction of the heat generated is from the radioactive decay of fission products. For many reactor designs, this decay heat is enough to raise the fuel temperatures to damaging levels if it is not removed.
Noted; thanks for the tip. I'm working under the (perhaps foolish) assumption that current designs and fuel replacement policies are set up to prevent this from being a hazard.
It sounds like you are describing a negative temperature coefficient of reactivity ("negative void coefficient" if you are a civilian). In a water-moderated reactor, an increase in temperature will reduce moderator density therefore cause a tendency for power to decrease. This provides for negative feedback and causes reactor power to change to match the heat removed from the system without operator intervention. This does not prevent an over power condition - it just means that the reactor is inherently stable.
Again, this depends on the design of the reactor. One of the big selling points of the slowpoke was that there was no configuration that would lead to an overpower condition (pull all of the control rods out, and it's still in a stable regime).
Academic in this case, though, because the article wasn't talking about slowpoke reactors (I'd misunderstood initially).
Youre right, but even with alot of medium lifetime elements sitting around, were still in a better position than we are now with stuff thats going to be around for a million years.
The medium-lifetime elements are what I'd worry about, personally. Anything with a half-life of millions of years isn't going to be horribly dangerous (in low doses or for low exposure times), and so could if necessary just be spread around over a very large area as dust in the air or the ocean. Its contribution to the natural background radiation would be undetectably low.
But, if you have medium- and short-lived isotopes present, you'd triple everyone's cancer rate doing that. This is why I consider the shorter-lived elements to be the main problem.
Ultimately i think some sort of crustal sequestration method would be the best, send the radioactive particles into a fault where thell be sucked into the earth.
This was my favourite solution a while back too. Then someone pointed out that it would take millions of years for them to be sucked down (moving at maybe a foot per year, and you want it to sink several hundred miles). This unfortunately doesn't look practical.
My favourite long-term solution would be to either find a way to *safely* ship them into space (you don't want a rocket to explode), or else to feed them many times through a mass spectrometer/neutron source rig (filter out the safe elements, and send the unsafe ones back into the neutron source for transmutation). Neither approach is practical now (both could be done, but they'd either be horrifically expensive, or have unacceptable risks of contamination, or both).
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Sorry but I don't think the instrumentation on these probes really is advanced enough to gather what is needed to make an accurate or informed decision.
How so?
To start with, the main data of interest (probe positions and trajectories) doesn't require additional instruments to measure. They're looking at the timing and doppler-shifting of the probes' radio signals, and getting a very good estimate of their positions and velocities.
The record of the probes' trajectories over long periods of time is what suggests the effect and places limits on how it acts.
Secondly, there isn't anything *out* there to look at. At least a few of these probes have micrometeorite detectors and dust analyzers and radiation analyzers. That covers just about everything you'll run into. What extra instrumentation do you propose to add?
What kinds of instruments do you think would give us a better idea of what's going on than we already have?
How big of a power supply will I need? I am looking at an SMP (dual) Intel P-III 1ghz system, with three 80mm case fans, a high-end 7200 RPM IDE hard drive, a hard drive fan, high-end video card (possibly even Nvidia's new GeForce3), DVD, CD-RW, SBLive!, and other standard hardware. Is my current 300W ATX supply going to cut it?
It should.
The Right Way to figure this out is to look up figures for *peak* power consumption for the CPUs and the graphics cards from the various hardware review sites (Ace's, Sharkey's, etc). Then add the power ratings on all of the fans (should be on the box if you're buying them as discrete components, and you can get the store to look it up if they're building it for you). Then multiply the whole shebang by 1.3-1.5x as a safety factor.
Or, you can use the back-of-the-envelope method:
- 50W each is about the right ballpark for the processors. Spec 100W for this.
- If all of your fans together take more than 50W, I'll be very surprised. Spec 50W.
- If your graphics card takes more than 50W, the PCI bus should start smouldering. Unless you have a Voodoo 5, spec 50W.
- Hard drives and so forth aren't *horribly* power-hungry. You have a 100W margin left. You should be fine.
Heck, you'd probably be fine with a 250W supply or lower, but you don't want to risk having your computer hang when you're using it most thoroughly.
YMMV.
This article discusses a measurement of CP symmetry violation, which is a difference in behavior between matter and antimatter. CP-violating decay modes have been used as an explanation for the dominance of matter for many years.
The article mentions that CP violation was first detected in 1964.
The article is written in a nice, calm tone, properly painting this as a much nicer measurement of a known effect.
Where did the sensationalistic article blurb come from? Is there *any* justification for it at *all*?
actualy it depends on the electron stabilization. If you pressed the nitrogen tightly enough, you might form resonance structures and associated structures that allow electron delocalization.
Perhaps I gave the wrong impression in my previous post. I'm not saying that a solid allotrope of nitrogen couldn't exist at room temperature - just that it would be *more* stable in gaseous form, and would thus tend to revert to this form when sufficiently provoked.
It's easy to demonstrate that the gaseous form is the most stable under standard conditions - if it wasn't, the atmosphere wouldn't contain gaseous nitrogen. It's had plenty of time to be converted to an alternate form by whatever mechanisms are appropriate.
As the solid nitrogen would tend to revent to its gaseous form when provoked, and as gaseous nitrogen doesn't like being stored at solid densities, you'd almost certainly get an explosive release of stored energy if you heated or otherwise sufficiently agitated a sample of solid nitrogen.
Interesting argument, though. In your opinion, is there any chance at all of an allotrope of solid _hydrogen_ being stable much above hydrogen's freezing point, or would this not work with just a "1S" shell?
Just wondering, when it returns to normal preasure levels, they apparenlty have this new substance remaining after it forms at high preassure. Is there any chance of it returning to a gasous form and hence exploding to it's original volume?
Sure. Just heat it. It's both more entropically favourable and more energetically favourable for it to be a gas (above nitrogen's freezing point, at least), so as soon as you get over the activation energy, *boom*.
According to the article, the sample at 1 atm had to be cooled quite a bit to be stable. For all I know, they could have taken it down below nitrogen's freezing point, which would just make this an interesting allotrope of frozen nitrogen.
Material properties should change as pressure is varied, as the energy bands within the material will shift. This would be very interesting to measure experimentally to check our models of materials at high pressures (and you can bet your socks they've submitted a funding application already to do this).
Anyone know what they used to achieve such high levels of atmospheric pressure?
For the metallic hydrogen experiments I read about a while back, they used a "diamond anvil cell". This is a fairly small device that uses a screw to close a pair of lever arms. The compression cell at the base of the lever squeezes the sample between two diamonds. A metal gasket surrounds the cell.
The nice thing about this is that the diamonds pass a wide range of light frequencies, which lets you measure material properties optically.
The group that I was reading about almost, but didn't quite, succeed in making metallic hydrogen.
I have no idea whether the nitrogen semiconductor group used this apparatus or something else. I suppose that if you were clever enough to find a fast way to take the measurements, you could just set off a bomb on top of the sample and measure for a few microseconds. Pressure is difficult to control, but if you can measure pressure accurately while you do this, you can simply plot your data with pressure as one of the axes.
Some types of industrial diamond are made using explosives.
This falls into the "duh" category. If you're overstressed, take steps to change your environment by whatever means necessary. Chronic stress will do things far worse than messing up your sleep patterns.
If I have one too many blankets, it takes me a long time to fall asleep. This is something that's difficult to notice. If you find yourself tossing and turning, chuck a blanket and see if that helps.
I have asthma. I rarely have full-blown attacks, but breathing will often become more difficult than usual. This is another thing that's difficult to notice, that will keep me tossing and turning for hours. Make sure you can breathe freely. Install air filters if you're having trouble - they'll save you a lot of grief during the day, too. If you have serious trouble breathing, fairly often, see a doctor. You may have asthma or another breathing disorder (or be allergic to a solvent in your carpet, or what-have-you).
This is another "duh" point, but if you have to go to the bathroom, you're going to be waking up every couple of hours until you drag yourself out of bed and go. That'll wreck your night's sleep pretty effectively.
YMMV.
Hopefully this becomes a viable alternative to stem cells from embryos. As the article points out, that is frought with ethical problems.
Stem cells of various types exist in many places in your (living) body; in principle, there's no reason they have to be harvested from anywhere else at all.
In practice, embryo cells are nice because they haven't differentiated at *all* yet (stem cells in your body have differentiated a bit, and so only give rise to certain types of cell (e.g. blood cells for bone marrow stem cells).
Research is ongoing to try to convert these back into general-purpose stem cells. There has been some progress, some of which has been covered on slashdot.
In summary, we won't have to worry about harvesting by the time we're ready to use stem cells on a large scale.
For pure research into differentiation, there's no reason we'd have to use human stem cells. If I understand correctly, human stem cells are only used for research into medical procedures that are intended to be performed on humans, which could be delayed until the differentiation problem is solved or performed on animals instead (though both options mean it'll be longer until the techniques are perfected for use in humans).
Isn't the temperature stable down there precisely because earth is such a good heat sink? Sure, a few hundred meters of earth will insulate you from surface temperature changes, but the hot air in the mine would still lose a lot of heat to the earth.
Hot air would; however, you'd almost certainly store the compressed air at room temperature, just like you do in a compressed air tank.
When your pump actually compresses the air, you do get heating, but you'd bleed this off through a radiator before storing it (or store air in the mine slowly enough that the earth would be an adequate heat sink).
Likewise, depending on the rate at which you let the air expand, you may get cooling when taking it out again, but this is a secondary effect (and can be reduced by using a nearby lake as a heat sink/cold sink).
Consider that the energy in compressed air is in the form of heat. Unless they insulate this cavern, there is going to be appreciable heat transfer. What are the losses going to be?
Most of the energy is not stored as heat. It's stored in the fact that the air is compressed. It takes a certain amount of work to compress it in the first place, and the air is capable of performing a certain amount of work as it expands.
Heating the air will change its pressure, which will change the amount of work it can do, but the resulting energy difference will just be the amount of thermal energy gained/lost. Not a vast amount compared to the total amount you're dealing with.
Lastly, the temperature underground is quite stable. As soon as you're more than a few tens of feet below the surface, the earth above you will insulate quite well. This is why deeply buried water pipes don't freeze in the winter.
That's pretty cute... this thing we threw up there *twenty nine years ago* is still working, but the last couple probes we've slapped together can't even make it to the next planet.
You're overlooking the several probes that did work. Clementine was particularly interesting (lunar mapping probe).
That aside - this was a deliberate tradeoff. If you send out ten probes instead of one, it doesn't matter if only half work - you've still have five times as many probes out there as you otherwise would. This is the philosophy behind the "smaller, faster, cheaper" motto that Nasa has adopted.
Not sure if the Mars probes were officially part of this program or not.
Stating the obvious, but:
If there were a conspiracy to fake the moon landings, then this conspiracy would of *course* extend to faking photographs from Clementine or any other probe allegedly sent to the moon.
This would be far more effort than it's worth, but so would faking the moon landings.
ou could perfectly well run a 0.18 or 0.13 micron process at 5V Sorry, that's just not true. If you power a process with a supply voltage that is too high, you will break the gate oxide.
For low-voltage 0.18 or 0.13 processes, you are quite correct. However, there's nothing fundamental that prevents you from using a 0.18 or 0.13 process with a thicker oxide and some doping tweaking that would work acceptably at 5V.
I'll remember this the next time I design fictional circuits. Sorry, unless your whole world is spice simulations the voltage ramps down.
*sigh*.
Look up high-voltage CMOS processes offered by your local foundaries.
The reason why you're only encountering low-voltage processes is that high-voltage processes presumably aren't useful for the applications you deal with. Arguing that you can't build deep submicron transistors that use high voltages is silly (you almost certainly know yourself what would be changed to do it).
in my dream world it would be built into the OS, making the programming yokel easy.
Unfortunately, this doesn't make it easy.
To run efficiently in parallel, a program must be written to use a parallel algorithm. The best parallelized OS and hardware in the world won't save you if the algorithm is serial. Writing parallel algorithms is more difficult than writing serial algorithms (usually), and turning a serial program into a parallel program automatically is extremely difficult (some optimizing compilers try to do this when building for parallel platforms, and usually don't do very well).
To make matters even worse, many problems are intrinsically serial - impossible to reduce to parallel form. As long as even part of your program is irreducibly serial, there will be a limit to how much you can boost performance (Amdahl's Law).
In summary, trying to use a massively parallel machine to boost performance doesn't work as well as you're assuming (though it's good for many special cases).
When I started designing circuits for pay Vgs was approximately 1.8 volts, now I'm designing with a Vgs of approximately 1.2 volts. Things are excaberated by the fact that Vt hasn't decreased proportionaly.
...And this is orthogonal to the point I was shooting down. You could perfectly well run a 0.18 or 0.13 micron process at 5V. You'd just melt down the chip, if you were trying to do this with a sqare centimetre of silicon. You could also run a 1.2 micron process at 1.2 volts if you felt like it, and you'd get current driving performance just as horrible as that which you're complaining about for 0.13.
Shrinking feature size isn't responsible for reduced current. The desire to run a constant area of silicon (and hence more-or-less constant parasitic capacitance) at ever-increasing speed without melting it is responsible.
The transistor itself is smaller, but again the capacitance isn't necessarily decreasing but the ability of the transistor to drive current is.
:).
I'm afraid this isn't the case. As you make the gate of a transister shorter, its ability to drive current increases. Shrink the entire transistor, and as the W/L ratio of the gate stays the same, the transconductance of the transistor stays (roughly) the same.
Yes, process differences and short-channel effects muck this up somewhat, but the effect is still there. This is why we're bothering to move to finer linewidths at all.
Until recently, shrinking circuits like this produced a *big* speed boost, because most of the parasitic capacitances scaled directly with device area. Same drive current with 1/x^2 the capacitance means a speedup of x^2 for a linewidth shrink of factor x. Recently, as you point out, wire delays have become relevant, but while that does limit signal propagation speed, it doesn't affect a transistor's ability to drive current.
I've been studying this in far too much detail recently
Just because something seems simple once somebody else thought of it doesn't mean it wasn't a good idea in the first place.
And just because they (allegedly) were the first to think of it, doesn't mean it's patentable.
Patents are supposed to be given only for things that aren't "obvious to anyone skilled in the art". In practice, this isn't assessed well by the patent office, but that's another can of worms.
you dont put your material in barrels and hope it stays there, you encase it in solid glass. that way even as it breaks up the material is still encapsulated. Also most subduction zones are a couple hundred miles off coastlines, and under alot of salt water. You arent going to be drilling there for groundwater any time soon.
I've already been assuming that the barrels are filled with glass pellets. I still wouldn't want the barrels to break. Shatter the beads, and currents will take the resulting dust all over. Disperse a pollutant in the water, and it *won't* just stay in one place - you'll eventually have to worry about it (especially if we're dumping all of a continent's waste, and not just one plant's worth).
If you have a really deep hole, and plug it really well - maybe. But I'd still feel safer with the barrels deep in the continental shield.
On the off chance that this wasn't just good satire:
Trivial as it may seem, energy gained by tidal power is, erg for erg, slowing down the rotation of the Earth. True right now the results are inconsequential, but if massive projects were undertaken to supply 30% of the Earth's onging power needs with tidal forces, over the long run it could have an impact, and it's not exactly like we have a way to repair the damage by speeding up the Earth's rotation...
There's on the order of 1.0e30-1.0e31 joules of energy stored in the Earth's rotation. That gives us around 30 billion terawatt-years.
I don't think we're in danger of draining it soon.
At least clean fission only eats up matter which, though not a renewable resource either, is constantly being replenished on the order of tons a day from micrometeorites.
...which are made of rock, and thus don't contain much hydrogen. Allegations of a continuing hail of ice micro-comets are as yet unsubstantiated.
Not to worry, though. Even if we just extract deuterium (which is 0.015% of all hydrogen) for fusion, we have about 1.0e13 tonnes of the stuff in the oceans. Assuming around a million times the energy yield of chemical reactions, this gives us about 5 million terawatt-years.
Switch to ordinary hydrogen, and by the time the sun burns out, we'd have used around 15% of the ocean. Assuming we don't ship in a few ice asteroids in the interim.
2-3% of it will always be "in the transportation tube" rolling down local railways, interstates, and highways. And if one of these trains derails? Or truck jack-knifes?
Then the heavily-armoured barrels get their paint scuffed.
I don't trust nuclear waste barrels to last a hundred thousand years, but I do trust them to survive anything short of a point-blank strike from heavy artillery.
If you *do* fire heavy artillery at point-blank range into a nuclear waste barrel, you'll get a clould of glass shrapnel - the safest transportable form of nuclear waste puts waste oxides into glass, where they stay (glass is quite durable and resistant to chemical attack). Scrape up the first foot of soil for a quarter of a mile around, put that in barrels, and sent it to the waste dump along with everything else. No additional contamination.
In summary, I don't think that accidents during transport are a concern. I'd be more worried about deliberate theft, and the risk of that can be made no worse than it already is with waste stored at power plants.
Also, storing waste at the plants is not a viable long-term solution, as they aren't in earthquake-free regions isolated from the water table. One good disaster, and *all* of the plant's waste goes into the environment.
Right, but during the time its being sucked into the molten part, its trapped under a large amount of rock, which makes a good radiation shield. Moving at a foot a year, itll be 20 feet underground in maybe 30-40 years, and thats plenty of shielding. Yes it takes a million years to be spread into the magma layer, but during that time its in a place where it cant harm humans.
The problem with this is that the subduction zone, by nature, is earthquake-prone. With your containers that close to the surface, contamination of local water will also be a problem (your containers won't last more than a couple hundred years, which puts them at a couple hundred feet...)
I suppose you could drill a deep hole in the subducting crust, seal it with clay, and then let it go down, but I wouldn't trust a filled shaft to stay impermeable to water in an earthquake zone.
The graphite-laced "pebbles" in their reactor could melt down if enough were piled in one place
No, they won't. They are designed to keep the bits of fuel far enough apart that no reaction hot enough to start burning either the fuel itself or its carbon shell could start or sustain itself.
This has actually been tested by running a pebble-bed reactor without coolant for an extended period.
I meant, a pile larger than would fit in the reactor. A large enough pile should indeed melt down. The reaction will increase exponentially if the probability of interaction (vs. escape or absorption) is greater than one divided by the number of child neutrons produced by a reaction.
The probability of absorption (by the graphite or by a nucleus) depends on how far a neutron would have to travel to escape the pile. Use a bigger pile, and there's less chance of the neutron escaping.
If fissile material was sparse enough inside the fuel balls, then you could set it up so that an arbitrarily large pile still wouldn't enter meltdown, but this would make it a lot less useful for generating power as well (a small pile would be very, very subcritical).
A signifigant fraction of the heat generated is from the radioactive decay of fission products. For many reactor designs, this decay heat is enough to raise the fuel temperatures to damaging levels if it is not removed.
Noted; thanks for the tip. I'm working under the (perhaps foolish) assumption that current designs and fuel replacement policies are set up to prevent this from being a hazard.
It sounds like you are describing a negative temperature coefficient of reactivity ("negative void coefficient" if you are a civilian). In a water-moderated reactor, an increase in temperature will reduce moderator density therefore cause a tendency for power to decrease. This provides for negative feedback and causes reactor power to change to match the heat removed from the system without operator intervention. This does not prevent an over power condition - it just means that the reactor is inherently stable.
Again, this depends on the design of the reactor. One of the big selling points of the slowpoke was that there was no configuration that would lead to an overpower condition (pull all of the control rods out, and it's still in a stable regime).
Academic in this case, though, because the article wasn't talking about slowpoke reactors (I'd misunderstood initially).
Youre right, but even with alot of medium lifetime elements sitting around, were still in a better position than we are now with stuff thats going to be around for a million years.
The medium-lifetime elements are what I'd worry about, personally. Anything with a half-life of millions of years isn't going to be horribly dangerous (in low doses or for low exposure times), and so could if necessary just be spread around over a very large area as dust in the air or the ocean. Its contribution to the natural background radiation would be undetectably low.
But, if you have medium- and short-lived isotopes present, you'd triple everyone's cancer rate doing that. This is why I consider the shorter-lived elements to be the main problem.
Ultimately i think some sort of crustal sequestration method would be the best, send the radioactive particles into a fault where thell be sucked into the earth.
This was my favourite solution a while back too. Then someone pointed out that it would take millions of years for them to be sucked down (moving at maybe a foot per year, and you want it to sink several hundred miles). This unfortunately doesn't look practical.
My favourite long-term solution would be to either find a way to *safely* ship them into space (you don't want a rocket to explode), or else to feed them many times through a mass spectrometer/neutron source rig (filter out the safe elements, and send the unsafe ones back into the neutron source for transmutation). Neither approach is practical now (both could be done, but they'd either be horrifically expensive, or have unacceptable risks of contamination, or both).