It's all software, but I believe it's a PID controller at heart. I know they do things that aren't strictly PID, like dead bands in the roll control, but I don't think it's terribly complicated. If you read through their updates they have a fair bit of information, in varying levels of detail.
I know they've moved more and more to having broader control loops: instead of one loop that sets a thrust level in order to maintain position, and another that tweaks the throttle to hit the target thrust, they just wrap it into one loop that moves the throttle valve in order to maintain altitude.
The Google X-Prize is silly. The hard part of that prize is not the lander. The hard parts are getting your lander there in the first place, and the requisite high-bandwidth communications link back to Earth. Guidance when you can't use GPS is tricky, but easier than those two. (Detail work can be done inertially, but you also need a star tracker or similar baseline reference to work from.)
Any serious contender for the GXP needs to be planning to do a couple test flights if they want a serious hope of winning the prize. Right now there is no way to put a significant payload in Low Earth Orbit on a budget that would make that feasible, let alone on a Lunar transfer orbit. Therefore, if you want to make back any reasonable fraction of your budget with the prize, you *also* have the distinctly nontrivial task of building your own launcher capable of getting to a Lunar transfer orbit.
Now, that said, I fully expect to see Carmack and company build an orbital launcher one day. I expect that, after some development test flights, they'll get it working. But they won't do it on a schedule and budget that makes the GXP look anything other than laughably short-term.
Yep, the main engine is thrust vectoring. Roll control is handled by small cold-gas thrusters that use the same helium supply that pressurizes the main propellant tanks.
Note also that "it most certainly looks top-heavy" is actually an example of the pendulum fallacy. It doesn't matter whether the center of mass is far above, a little above, or below the rocket engine, you need active stabilization on a hovering rocket. (On a rocket flying a vertical trajectory, passive stabilization via fins will suffice to hold it basically straight.)
You can't blame it on the tool, but you most certainly can blame it on the company making it and their marketing tactics, in addition to the users.
You must be one of those people that thinks it's ok to sue Smith and Wesson if some thug blows away your child using one of their guns.
Actually, I don't. I don't recall S&W marketing their guns as appropriate to use on innocent children. If they did, then I think a lawsuit would be appropriate. Your argument is irrelevant. Taser markets their weapons as appropriate for situations calling for non-lethal force, and encourages their use without proper guidelines, training, or policies similar to the ones around police use of guns. That's not appropriate for a tool which can kill people when used in the intended manner.
These devices would never be used against people in the manner they now are in a truly free society.
That part I'd give you. It seems that there are quite a few incidents wherein police officers have reached for their TASER rather than reaching for their deescalation skills. I don't think you can blame this on the tool though -- you have to blame it on the operator. These same personalities would probably have wielded the police baton in the same inappropriate manner.
You can't blame it on the tool, but you most certainly can blame it on the company making it and their marketing tactics, in addition to the users.
Or, we could decide that we're stuck with chemical rockets for the foreseeable future, and ask why they're so expensive. It isn't because complex machinery is inherently unreliable; jet engines are more complicated than simple rockets and have high reliability. It's because NASA's rocket designers routinely decide to spend lots more money for a little extra performance and a lot less reliability. If we went back to the design phase with a plan of low-pressure, medium-high performance LOX-Kerosene engines, that would be far more interesting. Who cares if the booster weighs twice as much on the pad if it costs a tenth (or a hundredth) as much per flight?
We need to get to the point where the propellant cost is a significant fraction of the flight cost. To do that we need truly reusable vehicles. Not because a disposable vehicle is inherently that expensive, but because you can't run a sane test program on them. The safety plan needs to be such that normal failures result in mission abort without further loss of hardware, let alone life. The development program needs to be one of incremental envelope expansion. That's how you build a cheap, reliable rocket.
If the propellant costs were a significant piece of the launch costs, space flight would be merely pricey, rather than outrageously expensive. Our hypothetical rocket that was willing to trade some performance away to save cost and increase reliability might manage a 1% payload fraction (or a little less, even). If a quarter of that was passengers (short duration, ferry to something already in orbit; life support is a lot lighter if it only has to last 12 hours, and even that only in an emergency), then every kilogram of person implies 400 kg of propellant. That 400 kg of LOX-Kerosene costs about $100. That puts the cost of the propellant at $10k, and the launch cost at $20-30k for a single person. That's hardly cheap, but it's low enough that serious work could be done.
We need to be asking ourselves why we keep building expensive rockets. The answer isn't because that's the only way to do it. It might be because it's the only way NASA knows how to do it.
I'm a software engineer who can't touch type. And I can honestly say that learning wouldn't increase my productivity in any measurable way.
Logically the only way this can be true is if you think slower than you type, in which case, sorry, you may not be the best software engineer out there. I easily type 120wpm and it is still far too slow for me, whether it's coding or writing English (documents, slashdot posts, e-mails) I think much faster than I type, typing is *the* primary bottleneck in my work... if I could type 500 wpm my productivity would go through the roof.
This makes me suspect the parent poster is a better software engineer than you. He knows that Amdahl's law applies not only to the software programs he writes, but also to how he writes them. In other words, he knows that he needs to worry about optimizing the slow parts, but that optimizing the fast parts is less critical.
Headphones probably didn't create a ground loop; there isn't exactly a loop to be found in the wiring. However, that's far from the only way for AM radios to be picked up. Various forms of input nonlinearities will rectify AM and let it sneak into the output. The solution is likely the ferrite cores mentioned by the GP post.
We aren't talking about a professional recording setup that had a little bit of hum or AM pickup. We're talking about basic amplified computer speakers and a normal computer. XLR gear is expensive; I doubt there exists a set of inexpensive amplified speakers with an XLR input, or an inexpensive sound card with an XLR output (which wouldn't even fit in the standard PCI slot opening), let alone an inexpensive motherboard with onboard audio with XLR output.
We're talking about a level of interference that meant it was annoying to use the speakers at all, not one that was merely slightly degrading high end audio quality. We're also talking about a college student who had no budget to spend on the problem, and wouldn't have been interested in high end audio gear even if he did. Nicer speakers, perhaps, but not recording studio gear. So, I diagnosed a ground loop as a possible explanation, told him to carefully rearrange his cables, and he did. The problem went from highly annoying to just barely perceptible. Sometimes the right solution to offer someone isn't the one that has them throw out all their gear and buy expensive stuff that they really don't need.
Personally, I go for the in between solution. I'm of the opinion that the inside of a computer case, with its myriad switching supplies that aren't designed for their audio performance, is a horrible place to work with analog audio signals, whether they leave the case by minijack or XLR. I have a sound card with optical digital outputs, and an amp with optical inputs. No ground loop, no stupid problems from putting sensitive analog stuff where it shouldn't be, and vastly cheaper than serious recording gear I don't need or care to pay for.
Also, watch out for ground loops. If you plug your computer into your power strip, and then plug an amplifier into the analog audio out connector, and then plug your amp into the outlet, you've created a loop antenna in the ground system (there's a loop running from power strip to computer to amp to power strip, because the audio out cable has 2 single-ended signal lines plus a ground line). Getting rid of such loops can be hard (cutting the ground line in the audio cable doesn't entirely solve the problem and has its own issues, for example), but being aware of them and minimizing the area that they enclose can help dramatically.
I saw an example where the problem was exactly as above, and until they moved the power cables around to shrink the loop the local AM station always played on the speakers.
In small general aviation craft... a competent pilot is very likely to survive a rather large subset of such failures - basically anything excluding "wings fall off"
That's the problem; a flying cars don't have wings.
How is that the problem? GA aircraft wings don't fall off, much like cars don't tend to have their wheels just fall off while on the highway — which, while note guaranteed to be fatal, would certainly cause fatalities a lot of the time. And the aircraft could have a backup, in the form of a ballistic chute, whereas the car doesn't have time to do much before colliding with other cars.
Someone else mentioned control cables; it would be similarly problematic if your car's steering wheel simply stopped working on the highway. Or brakes. Either of those is an instant, critical emergency. Neither one is guaranteed fatal, but they certainly could be if not handled well.
Really, claiming you're scared of the wings just falling off is rather absurd. Some sorts of mechanical things we simply build robustly enough. Others, we provide backups for, or ensure that the failures are survivable. You defend against failure in depth, whether on the highway or in the air.
Really, I think cost and air traffic control are much bigger impediments to flying cars than mechanical safety.
A broken control cable will kill you really quick.
That depends on which control cable, the situation, and what state the thing it was connected to decided to get stuck in. Even in the worst case, if you seriously care about safety over cost and weight (and you would if you were talking about mass-market aircars that have normal automobile maintenance standards applied to them rather than aircraft standards), the ballistic chute will probably give you a crash that you walk away from, even if your airplane needs some serious overhaul.
As for your flying car, you'll start seeing it when we have drivers who can safely drive on 3 dimensional roads, and for that, you have to be able to do it safely on 2 dimensional roads first, which can be far, far away...
Not to mention a flying car that can fail safe, so that a mechanical mishap or minor accident doesn't prove invariably fatal from, ya know, falling out of the sky.
You mean the way it does with small single-engine airplanes today?
In small general aviation craft, an engine failure, electrical failure, or mechanical failure is frequently a serious emergency, with potentially fatal consequences. However, unless you're doing something seriously stupid, a competent pilot is very likely to survive a rather large subset of such failures — basically anything excluding "wings fall off". Landing with engine out is expected; it only gets really interesting if there isn't a runway or suitable road within glide range. Handling the airplane with mechanical or electrical malfunctions is something flight instructors routinely test on (you can simulate a rather large range of electrical failures by pulling fuses, for example).
There are plenty of reasons there aren't flying cars; safety in response to malfunctions is certainly on the list. But that does not even remotely mean that an engine failure has to be a fatal problem.
The helmet could well be preventing acute injury resulting in death (shrapnel through the skull), but increasing the diffuse brain damage to other parts of the brain. However, the death due to acute injury would make the diffuse injury rate difficult to determine. Preventing death but causing brain damage is clearly an improvement, but it doesn't mean the helmet merely "failed to completely prevent" the brain damage, if the brain damage wouldn't have occurred without it.
Maybe it's just my layman's naivety, but I would think that a sharp piece of metal piercing your skull would qualify as "brain damage".
Which is why I was careful to use qualifier words. Shock waves tend to cause diffuse brain damage of a qualitatively different sort than shrapnel. The helmet prevented the acute brain damage from the shrapnel, but caused or contributed to the diffuse damage from the shock wave by making it worse than it would have been. The helmet prevented one sort, but caused another. It's still accurate to say it caused the [increase in] diffuse shockwave-induced damage.
And this idea of making predictions based on models, and then seeing whether you observe those results in the real world, is different from making a model of how a helmet might cause brain damage, and then looking for brain damage in the real world?
Precisely. The corollary, though, is that the answer needs to be age-appropriate. Recognize that young children often want the simple version of the answer; if they want more, they'll ask. Often they don't, or don't want it right away. The overly complex answer is less helpful.
You know, observational studies are still scientific. There are plenty of hypotheses that can be tested without randomized controlled trials.
You're not going to claim that if astronomers really wanted to be scientific, they would start their research by gathering up a bunch of hydrogen and piling it together in empty space and then watching what happens, are you?
It's also entirely possible your test methodology would fail. The helmet could well be preventing acute injury resulting in death (shrapnel through the skull), but increasing the diffuse brain damage to other parts of the brain. However, the death due to acute injury would make the diffuse injury rate difficult to determine. Preventing death but causing brain damage is clearly an improvement, but it doesn't mean the helmet merely "failed to completely prevent" the brain damage, if the brain damage wouldn't have occurred without it.
Sometimes science is hard. It's still science, though, even if your "ideal" test methodology is impractical.
Hence the part about "four of the most reliable." Trust me, medical professionals are aware of the base rate problem and the difference between type I and type II errors.
Study thermo much? I thought not. The thermal resistance of either sort of piping is tiny in comparison to the concrete. The water has to be thermally coupled to a very large volume of concrete in order to get the heat sink effect, and conduction through the concrete into the ground. That's why you need a lot of pipe length -- plenty of contact area. Consider how much thermal resistance there is involved in transporting the heat through 12" or more of concrete; the thermal resistance of 1/16" of plastic is negligible in comparison. The plastic pipe is enough cheaper that, for the same money, you can buy a (much) longer length of plastic than the copper pipe, and get more contact area, and thus less total resistance.
Copper only makes sense when you're limited in the *area* of your heat transport zone -- for example, when trying to spread the heat away from a hot CPU core out to the heat sink fins. In this case, there is no such limit, so you should optimize for conductivity per dollar (corrected for the difference in pipe wall thickness, of course, and selecting optimal size pipes for each case). Don't forget to include installation costs; a long roll of flexible plastic pipe or tube may be much cheaper to install than copper that requires fittings.
You don't have to set the place on fire. It suffices to offer a monetary reward for getting out soon enough. Of course, you still have the problem of people hurting themselves / each other in the experiment, but that does show it's realistic enough for most purposes.
The analgesics like ibuprofen and aspirin are operating on a different set of receptors. My limited understanding of neurochemistry is that pain caused by a lack of opioids is a different part of the same mechanism -- basically the threshold on the relevant nerves is lower, so they fire when they shouldn't. Your body is no longer producing as many opiates, which makes you hurt everywhere; you're going through withdrawl in a very literal sense.
Basically, there's no cure for opiate withdrawl, whether endogenous opiates or drugs, except to either tough it out or get more opiates. Note that getting more opiates doesn't have to mean cooking up heroin; your body can be induced to produce more through other mechanisms. The usual trite advice about going out finding something to take your mind off it works. Best is to choose something like exercise, that naturally causes the release of such chemicals.
In short: analgesics won't do much. Going out and exercising might. (I've been there, and I won't pretend it will solve your problems; it won't. It will mitigate some aspects of them somewhat, though. Also, no need for it to be specifically "exercise"; anything that gets your heart rate up counts.) Finding some other activity to spend time on may help, but more by distracting you and helping you get over it than by direct neurochemistry. Going and acquiring an addiction to pharmaceutical or illicit opiates would probably help, but it certainly wouldn't fix it completely; it just isn't worth it, though.
No. The article is about using some intervening steps, like uranium energy -> thermal energy -> electric energy -> electrolysis of water. That would be what the parent post was complaining about.
That's not fundamentally better. The "and heat" step means you're still subject to the Carnot limit, for starters. Secondly, I don't think thermochemical splitting is any better than high-temperature electrolysis (though my knowledge of both is limited, so I could be mistaken). The major difference between the two basic schemes is which one is more practical, not any big theoretical advantage.
When you come up with a way to make the jet fuel directly out of CO2, water, and the energy in the uranium, let us know. I'm sure someone can find a use for that somehow.
That sounds suspiciously like saying no one needs thousand-digit primes because there aren't more than a few dozen digits worth of things to count in this universe.
It's obvious that the only use we've found for calculating lots of digits of Pi is testing our computers. That doesn't mean there aren't other uses.
Slashdot Mirror
It's all software, but I believe it's a PID controller at heart. I know they do things that aren't strictly PID, like dead bands in the roll control, but I don't think it's terribly complicated. If you read through their updates they have a fair bit of information, in varying levels of detail.
I know they've moved more and more to having broader control loops: instead of one loop that sets a thrust level in order to maintain position, and another that tweaks the throttle to hit the target thrust, they just wrap it into one loop that moves the throttle valve in order to maintain altitude.
The Google X-Prize is silly. The hard part of that prize is not the lander. The hard parts are getting your lander there in the first place, and the requisite high-bandwidth communications link back to Earth. Guidance when you can't use GPS is tricky, but easier than those two. (Detail work can be done inertially, but you also need a star tracker or similar baseline reference to work from.)
Any serious contender for the GXP needs to be planning to do a couple test flights if they want a serious hope of winning the prize. Right now there is no way to put a significant payload in Low Earth Orbit on a budget that would make that feasible, let alone on a Lunar transfer orbit. Therefore, if you want to make back any reasonable fraction of your budget with the prize, you *also* have the distinctly nontrivial task of building your own launcher capable of getting to a Lunar transfer orbit.
Now, that said, I fully expect to see Carmack and company build an orbital launcher one day. I expect that, after some development test flights, they'll get it working. But they won't do it on a schedule and budget that makes the GXP look anything other than laughably short-term.
Yep, the main engine is thrust vectoring. Roll control is handled by small cold-gas thrusters that use the same helium supply that pressurizes the main propellant tanks.
Note also that "it most certainly looks top-heavy" is actually an example of the pendulum fallacy. It doesn't matter whether the center of mass is far above, a little above, or below the rocket engine, you need active stabilization on a hovering rocket. (On a rocket flying a vertical trajectory, passive stabilization via fins will suffice to hold it basically straight.)
You can't blame it on the tool, but you most certainly can blame it on the company making it and their marketing tactics, in addition to the users.
You must be one of those people that thinks it's ok to sue Smith and Wesson if some thug blows away your child using one of their guns.
Actually, I don't. I don't recall S&W marketing their guns as appropriate to use on innocent children. If they did, then I think a lawsuit would be appropriate. Your argument is irrelevant. Taser markets their weapons as appropriate for situations calling for non-lethal force, and encourages their use without proper guidelines, training, or policies similar to the ones around police use of guns. That's not appropriate for a tool which can kill people when used in the intended manner.
These devices would never be used against people in the manner they now are in a truly free society.
That part I'd give you. It seems that there are quite a few incidents wherein police officers have reached for their TASER rather than reaching for their deescalation skills. I don't think you can blame this on the tool though -- you have to blame it on the operator. These same personalities would probably have wielded the police baton in the same inappropriate manner.
You can't blame it on the tool, but you most certainly can blame it on the company making it and their marketing tactics, in addition to the users.
Or, we could decide that we're stuck with chemical rockets for the foreseeable future, and ask why they're so expensive. It isn't because complex machinery is inherently unreliable; jet engines are more complicated than simple rockets and have high reliability. It's because NASA's rocket designers routinely decide to spend lots more money for a little extra performance and a lot less reliability. If we went back to the design phase with a plan of low-pressure, medium-high performance LOX-Kerosene engines, that would be far more interesting. Who cares if the booster weighs twice as much on the pad if it costs a tenth (or a hundredth) as much per flight?
We need to get to the point where the propellant cost is a significant fraction of the flight cost. To do that we need truly reusable vehicles. Not because a disposable vehicle is inherently that expensive, but because you can't run a sane test program on them. The safety plan needs to be such that normal failures result in mission abort without further loss of hardware, let alone life. The development program needs to be one of incremental envelope expansion. That's how you build a cheap, reliable rocket.
If the propellant costs were a significant piece of the launch costs, space flight would be merely pricey, rather than outrageously expensive. Our hypothetical rocket that was willing to trade some performance away to save cost and increase reliability might manage a 1% payload fraction (or a little less, even). If a quarter of that was passengers (short duration, ferry to something already in orbit; life support is a lot lighter if it only has to last 12 hours, and even that only in an emergency), then every kilogram of person implies 400 kg of propellant. That 400 kg of LOX-Kerosene costs about $100. That puts the cost of the propellant at $10k, and the launch cost at $20-30k for a single person. That's hardly cheap, but it's low enough that serious work could be done.
We need to be asking ourselves why we keep building expensive rockets. The answer isn't because that's the only way to do it. It might be because it's the only way NASA knows how to do it.
I'm a software engineer who can't touch type. And I can honestly say that learning wouldn't increase my productivity in any measurable way.
Logically the only way this can be true is if you think slower than you type, in which case, sorry, you may not be the best software engineer out there. I easily type 120wpm and it is still far too slow for me, whether it's coding or writing English (documents, slashdot posts, e-mails) I think much faster than I type, typing is *the* primary bottleneck in my work ... if I could type 500 wpm my productivity would go through the roof.
This makes me suspect the parent poster is a better software engineer than you. He knows that Amdahl's law applies not only to the software programs he writes, but also to how he writes them. In other words, he knows that he needs to worry about optimizing the slow parts, but that optimizing the fast parts is less critical.
Headphones probably didn't create a ground loop; there isn't exactly a loop to be found in the wiring. However, that's far from the only way for AM radios to be picked up. Various forms of input nonlinearities will rectify AM and let it sneak into the output. The solution is likely the ferrite cores mentioned by the GP post.
We aren't talking about a professional recording setup that had a little bit of hum or AM pickup. We're talking about basic amplified computer speakers and a normal computer. XLR gear is expensive; I doubt there exists a set of inexpensive amplified speakers with an XLR input, or an inexpensive sound card with an XLR output (which wouldn't even fit in the standard PCI slot opening), let alone an inexpensive motherboard with onboard audio with XLR output.
We're talking about a level of interference that meant it was annoying to use the speakers at all, not one that was merely slightly degrading high end audio quality. We're also talking about a college student who had no budget to spend on the problem, and wouldn't have been interested in high end audio gear even if he did. Nicer speakers, perhaps, but not recording studio gear. So, I diagnosed a ground loop as a possible explanation, told him to carefully rearrange his cables, and he did. The problem went from highly annoying to just barely perceptible. Sometimes the right solution to offer someone isn't the one that has them throw out all their gear and buy expensive stuff that they really don't need.
Personally, I go for the in between solution. I'm of the opinion that the inside of a computer case, with its myriad switching supplies that aren't designed for their audio performance, is a horrible place to work with analog audio signals, whether they leave the case by minijack or XLR. I have a sound card with optical digital outputs, and an amp with optical inputs. No ground loop, no stupid problems from putting sensitive analog stuff where it shouldn't be, and vastly cheaper than serious recording gear I don't need or care to pay for.
Also, watch out for ground loops. If you plug your computer into your power strip, and then plug an amplifier into the analog audio out connector, and then plug your amp into the outlet, you've created a loop antenna in the ground system (there's a loop running from power strip to computer to amp to power strip, because the audio out cable has 2 single-ended signal lines plus a ground line). Getting rid of such loops can be hard (cutting the ground line in the audio cable doesn't entirely solve the problem and has its own issues, for example), but being aware of them and minimizing the area that they enclose can help dramatically.
I saw an example where the problem was exactly as above, and until they moved the power cables around to shrink the loop the local AM station always played on the speakers.
In small general aviation craft... a competent pilot is very likely to survive a rather large subset of such failures - basically anything excluding "wings fall off"
That's the problem; a flying cars don't have wings.
How is that the problem? GA aircraft wings don't fall off, much like cars don't tend to have their wheels just fall off while on the highway — which, while note guaranteed to be fatal, would certainly cause fatalities a lot of the time. And the aircraft could have a backup, in the form of a ballistic chute, whereas the car doesn't have time to do much before colliding with other cars.
Someone else mentioned control cables; it would be similarly problematic if your car's steering wheel simply stopped working on the highway. Or brakes. Either of those is an instant, critical emergency. Neither one is guaranteed fatal, but they certainly could be if not handled well.
Really, claiming you're scared of the wings just falling off is rather absurd. Some sorts of mechanical things we simply build robustly enough. Others, we provide backups for, or ensure that the failures are survivable. You defend against failure in depth, whether on the highway or in the air.
Really, I think cost and air traffic control are much bigger impediments to flying cars than mechanical safety.
A broken control cable will kill you really quick.
That depends on which control cable, the situation, and what state the thing it was connected to decided to get stuck in. Even in the worst case, if you seriously care about safety over cost and weight (and you would if you were talking about mass-market aircars that have normal automobile maintenance standards applied to them rather than aircraft standards), the ballistic chute will probably give you a crash that you walk away from, even if your airplane needs some serious overhaul.
Not to mention a flying car that can fail safe, so that a mechanical mishap or minor accident doesn't prove invariably fatal from, ya know, falling out of the sky.
You mean the way it does with small single-engine airplanes today?
In small general aviation craft, an engine failure, electrical failure, or mechanical failure is frequently a serious emergency, with potentially fatal consequences. However, unless you're doing something seriously stupid, a competent pilot is very likely to survive a rather large subset of such failures — basically anything excluding "wings fall off". Landing with engine out is expected; it only gets really interesting if there isn't a runway or suitable road within glide range. Handling the airplane with mechanical or electrical malfunctions is something flight instructors routinely test on (you can simulate a rather large range of electrical failures by pulling fuses, for example).
There are plenty of reasons there aren't flying cars; safety in response to malfunctions is certainly on the list. But that does not even remotely mean that an engine failure has to be a fatal problem.
The helmet could well be preventing acute injury resulting in death (shrapnel through the skull), but increasing the diffuse brain damage to other parts of the brain. However, the death due to acute injury would make the diffuse injury rate difficult to determine. Preventing death but causing brain damage is clearly an improvement, but it doesn't mean the helmet merely "failed to completely prevent" the brain damage, if the brain damage wouldn't have occurred without it.
Maybe it's just my layman's naivety, but I would think that a sharp piece of metal piercing your skull would qualify as "brain damage".
Which is why I was careful to use qualifier words. Shock waves tend to cause diffuse brain damage of a qualitatively different sort than shrapnel. The helmet prevented the acute brain damage from the shrapnel, but caused or contributed to the diffuse damage from the shock wave by making it worse than it would have been. The helmet prevented one sort, but caused another. It's still accurate to say it caused the [increase in] diffuse shockwave-induced damage.
And this idea of making predictions based on models, and then seeing whether you observe those results in the real world, is different from making a model of how a helmet might cause brain damage, and then looking for brain damage in the real world?
Precisely. The corollary, though, is that the answer needs to be age-appropriate. Recognize that young children often want the simple version of the answer; if they want more, they'll ask. Often they don't, or don't want it right away. The overly complex answer is less helpful.
You know, observational studies are still scientific. There are plenty of hypotheses that can be tested without randomized controlled trials.
You're not going to claim that if astronomers really wanted to be scientific, they would start their research by gathering up a bunch of hydrogen and piling it together in empty space and then watching what happens, are you?
It's also entirely possible your test methodology would fail. The helmet could well be preventing acute injury resulting in death (shrapnel through the skull), but increasing the diffuse brain damage to other parts of the brain. However, the death due to acute injury would make the diffuse injury rate difficult to determine. Preventing death but causing brain damage is clearly an improvement, but it doesn't mean the helmet merely "failed to completely prevent" the brain damage, if the brain damage wouldn't have occurred without it.
Sometimes science is hard. It's still science, though, even if your "ideal" test methodology is impractical.
Hence the part about "four of the most reliable." Trust me, medical professionals are aware of the base rate problem and the difference between type I and type II errors.
Study thermo much? I thought not. The thermal resistance of either sort of piping is tiny in comparison to the concrete. The water has to be thermally coupled to a very large volume of concrete in order to get the heat sink effect, and conduction through the concrete into the ground. That's why you need a lot of pipe length -- plenty of contact area. Consider how much thermal resistance there is involved in transporting the heat through 12" or more of concrete; the thermal resistance of 1/16" of plastic is negligible in comparison. The plastic pipe is enough cheaper that, for the same money, you can buy a (much) longer length of plastic than the copper pipe, and get more contact area, and thus less total resistance.
Copper only makes sense when you're limited in the *area* of your heat transport zone -- for example, when trying to spread the heat away from a hot CPU core out to the heat sink fins. In this case, there is no such limit, so you should optimize for conductivity per dollar (corrected for the difference in pipe wall thickness, of course, and selecting optimal size pipes for each case). Don't forget to include installation costs; a long roll of flexible plastic pipe or tube may be much cheaper to install than copper that requires fittings.
You don't have to set the place on fire. It suffices to offer a monetary reward for getting out soon enough. Of course, you still have the problem of people hurting themselves / each other in the experiment, but that does show it's realistic enough for most purposes.
The analgesics like ibuprofen and aspirin are operating on a different set of receptors. My limited understanding of neurochemistry is that pain caused by a lack of opioids is a different part of the same mechanism -- basically the threshold on the relevant nerves is lower, so they fire when they shouldn't. Your body is no longer producing as many opiates, which makes you hurt everywhere; you're going through withdrawl in a very literal sense.
Basically, there's no cure for opiate withdrawl, whether endogenous opiates or drugs, except to either tough it out or get more opiates. Note that getting more opiates doesn't have to mean cooking up heroin; your body can be induced to produce more through other mechanisms. The usual trite advice about going out finding something to take your mind off it works. Best is to choose something like exercise, that naturally causes the release of such chemicals.
In short: analgesics won't do much. Going out and exercising might. (I've been there, and I won't pretend it will solve your problems; it won't. It will mitigate some aspects of them somewhat, though. Also, no need for it to be specifically "exercise"; anything that gets your heart rate up counts.) Finding some other activity to spend time on may help, but more by distracting you and helping you get over it than by direct neurochemistry. Going and acquiring an addiction to pharmaceutical or illicit opiates would probably help, but it certainly wouldn't fix it completely; it just isn't worth it, though.
No. The article is about using some intervening steps, like uranium energy -> thermal energy -> electric energy -> electrolysis of water. That would be what the parent post was complaining about.
That's not fundamentally better. The "and heat" step means you're still subject to the Carnot limit, for starters. Secondly, I don't think thermochemical splitting is any better than high-temperature electrolysis (though my knowledge of both is limited, so I could be mistaken). The major difference between the two basic schemes is which one is more practical, not any big theoretical advantage.
When you come up with a way to make the jet fuel directly out of CO2, water, and the energy in the uranium, let us know. I'm sure someone can find a use for that somehow.
That sounds suspiciously like saying no one needs thousand-digit primes because there aren't more than a few dozen digits worth of things to count in this universe.
It's obvious that the only use we've found for calculating lots of digits of Pi is testing our computers. That doesn't mean there aren't other uses.