Yep, and when you add up the time value of money, the end total cost is the same. Never mind that 10c/kWh is pretty darn cheap. In Europe it won't be anywhere near that low AFAIK.
I'd have thought that $50 LED light would scale its energy output to maintain a temperature at the safe operating limit (or even at a limit determined by specified lifetime). I consider them shit if they don't do that. That's actually the only way to make people dust them: light output goes down, you have to get to it, clean it up, and put it back. No "burning out". When it burns out it means that it allowed an unsafe failure. It's a step away from causing a fire.
If you do the calculation, the real thing including time value of money, you'd see that incandescents do in fact cost the least, at the moment, to own and operate, at least in the U.S. and when you're talking about residences. This may not hold in commercial settings. The "energy spent like hell" was at the factory -- that's why they cost more. They take more energy to make. That's all there's to it. Just because the energy is spent elsewhere doesn't mean it's not spent and you of course pay for it. Up front, no less. Energy = money, in the grand scheme of things. As for incandescents needing to be replaced "all the time": for me they last about half as long as CCFLs do. Due to their low purchase cost, it's not an issue. And I do keep good track of it.
The deal is: due to time value of money, all non-incandescent light sources cost actually more. They don't save shit, because money equals energy, so if you have to spend the money, the energy is expended somewhere else. Those bulbs cost more because it takes more energy to make them -- so much more, that it happens to almost exactly offset any energy savings due to using CCFLs or LED lights. When you factor in time value of money, those more expensive bulbs do actually cost more. So the entire argument about cost or energy savings is complete and utter made up bullshit. Yes, I like the CCFLs and LEDs better, because I don't like the heat being emanated in my home. That energy was spent at the factory, though.
As for storage: man, just put them in a shoe box (perhaps a plastic one) and wrap each one in crumbled newspaper. Been there, done that in exactly same circumstances. I'd have thought it's a non-issue.
What you of course failed to take into account is the time value of money. Assuming the bulb will last a year, at even a low credit card rate of 8% it costs you an extra 0.04c/hr. Or, if you look for savings, by not investing that money in AAPL you lose an extra 0.2c/hr (assuming 50% returns, and that's quite conservative). That's a lot of wasted money.
I have a little hand-held spectroscope, a 100 year old single-slit brass version of what these days looks like this. So yeah, sure you can tell the difference, you're just silly if you say otherwaise. You can tell even without any instruments -- just close your eyes and go a meter or two away from the bulb, and you can tell it's emitting heat, especially in a cold room.
That said, I'm all for CCFLs, LEDs and fluorescents. I think the incandescent lightbulb has outlived its purpose.
I dont see what is wrong with trying to stop people accessing information which is clearly only there to either assist in weapons making or to provide resources for people who want to cause widespead terror.
You're wrong, plain and simple. What information is for depends on how someone intends to use it. By being an engineer I obviously have a lot of information about how to wreck infrastructure and otherwise terrorize a whole lot of people. Most engineers have such knowledge even if they pretend otherwise. You're like a 6 year old kid who anthropomorphizes things and says "bad information!". Sorry to break your childish bubble, but there is no information that is "clearly only there to do X". It's in your mind, you seriously made up a fantasy where you have some fact (the information), and you imagine that it's bad. Information is not human, it has no feelings, desires, goals, seriously, get it out of your head or seek psychiatric help. You can use a decent highschool chemistry textbook to inflict way more damage than the 9/11 bastards did. Even reading religious texts like the bible provides plenty of ideas. I mean, thinking like you, why on Earth would you want to know the details of how to crucify someone?! Obviously it's of no other use than to run around and crucify people, right? Get real.
Winner of teh internets for today! Bravo! Gems like this appear every once in a while, and I've learned never to have any drinks near the keyboard while reading the tubes. Thanks for making my day.
If you get into a routine and do it when the baby is fed (say before feeding), and that should normally happen on fixed schedule -- at least at night, then it's no biggie. I'd fall right back to sleep afterwards. The whole feed-change thingo shouldn't take longer than 15-20 minutes when a normal baby is past the first week or two. It sure is a whole another ballgame if you have a preemie, cleft lip, etc. 20 minutes up every 3 hours -- nothing to complain about. Key rule: after feeding and burping, put the kid down. No arguments about it. They'll learn very quickly that screaming at that point is useless. Never took longer than 72 hours after birth, anyway.
So normal medical magnets don't use a stator (core)? Well then, you need 750kA-turns to get 1.5T inside a 60cm long solenoid. I'll take a bit oversize solenoid at 60cm length and 60cm inner diameter. Let's see how realistic it'd be.
Assume standard 1inch O.D. copper tubing and 33mm pitch with some insulation between each turn. We have alternating 18 and 17 turns per layer due to triangular packing of cross sections. Say we'd want a 50cm thick winding ring (outer radius - inner radius). Assuming triangular tiling, we have 28.6mm diametral layer-to-layer spacing, so we can fit 16 layers. That's 280 turns, and the current is 2.7kA.
The length of the tube is approx. 1200m. Assume type K tubing with 0.065in or 1.651mm wall thickness, operating at ~70C average temperature (due to rise in resistance, the heat load in the hotter part of pipe, closer to outlet, will be higher than in the cooler part, but that's OK -- I specify average over length). The cross-sectional area of copper is 254.9mm^2. The cross-sectional area of sodium coolant is 1772mm^2. Copper's resistivity is 20.2nOhm*m, thus its resistance is 95mOhm. Sodium's resistance at ~61nOhm*m resistivity will be 41mOhm. Those are in parallel and the resistance is 29mOhm.
Given that the dissipated power is I^2*R, we have P=(2.7kA)^2*0.001=211kW. That's 175W/m of tubing. Sure a lot of power, but it can be dealt with as far as cooling is concerned -- each layer can have its own heat exchanger, dumping 13kW. Now let's see how much would it cost. At average US 15 cents/kWh, we have $18 cost to operate per hour, assuming all the power is dumped outside. That's nothing much. Even if we'd add inefficiencies in the power supplies and pumping losses in both sodium and cooling air.
I'd need to write out the equations symbolically and figure out where is the sweet spot with power dissipation vs. pipe diameter, presumably I haven't hit the most optimum design. Too lazy to figure it out right now.
Note 1: Mercury has resistivity an order of magnitude worse than sodium, so pretty much sodium is what you need for coolant.
Note 2: With water cooling, you can't but expect galvanic corrosion, unless there's some passivation scheme that would work -- I wouldn't count on it. In such a system, hot spots would be very destructive since the power supply can pretty much dump 200kW of heat in one hot spot if you're unlucky. A split power supply, supplying each layer separately, would of course help with that, but still even a 1in O.D. pipe won't cope with 13kW in a small spot for very long, and as soon as cooling water would start to boil, you're done for. This becomes a non-issue when using sodium, but of course I don't know how well copper pipes play with sodium flowing in them...
Note 3: The power supplies won't be a walk in the park to design, since you pretty much need a switcher with synchronous rectifiers being paralleled (slow!) mosfets to keep the resistance low enough, and then you still need a linear post-regulator that would waste at least 10% of incoming power. It certainly wouldn't be cheap to design and prototype, you can't get a random appnote-copying switcher jockey to put one together;)
Just buy an ultrasound on eBay and learn how to use it. No, you don't need to have a prescription for it or anything. Say you're buying it for use in engineering. It'd have cost you way less than one hospital childbirth.
I don't know where you are, but in the U.S. home childbirths aren't unheard of. Get a midwife and do it at home, the ob-gyn has to respect your wishes in that regard. You could have made a lot of fuss about those child endangerment threats, in the U.S. at least.
Superconducting magnets don't heat up. When your field needs to be uniform in the parts per billion range, a little bit of restive heating is a big problem. And a high field resistive magnet, even if you could make one that didn't melt immediately, would suffer from a bit more than a little resistive heating.
Electric power is generally cheap. Even if that thing would be wasting tens of kilowatts, it's no biggie. I presume as long as it's cheaper than lost helium at projected helium prices, one is ahead financially, and that's what counts.
The coil is wound around a stator. Resistive drops in the wiring won't affect field uniformity, not even at ppb level I'd think. The "wiring" would be a pipe, and most of the current would flow in the copper, and there the temperature would be pretty stably distributed I'd think due to heat exchange with sodium coolant. Thus the current distribution in the pipe would be axisymmetric, and that's what counts. The exact absolute field strength doesn't need to be maintained to ppb I don't think because the gradient coils aren't that accurate (good luck generating a sine wave or in fact any amplified waveform to 1ppb). It wouldn't be all that much of a problem since we can measure field strength to such an accuracy and you could maintain a feedback loop to keep it stable to such a level if you really wanted to.
If you want to be really clever, you can recover heat from the sodium coolant and use it to locally generate some of the power needed to power the coils. Since such a system would run pretty much in thermal equilibrium, at well known operating points, it could be optimized to have thermodynamic efficiency better than, say, a car engine. 50% of discount on a power bill is always nice;)
Alternatively, there could be an option of dumping the heat into a steam circuit -- after all, large hospital campuses probably have a power plant and steam circuits, and dumping heat there would be OK. That steam powers the chillers in the summer, too, after all.
Again, those are orthogonal issues: protected free speech can run afoul of copyright laws, and in that case copyright laws win. I think there's case law to show just that. Why would that be a problem with copyright law? Have you thought through what it'd mean if free speech trumped copyright? Every cinema owner would claim exercise of free speech and would give a middle finger to the distributors in place of a check. Yeah, that'd sure as heck work.
?! So you're saying that copper piping is more expensive than superconducting alloys? Well, that's news to me. As for the energy requirement: well, pray tell, how huge would it be. As for the stability of the field: well, what's so magical about a superconducting magnet that it'd have a more stable field? I presume a superconducting magnet needs a much smaller current from the power supply (orders of magnitude smaller) to maintain the field, but you silently presume that we can't make power supplies that keep things stable within 10ppm or better.
Here's a hint as to how the MRI magnets are being cooled: there's a liquid helium bath, some insulation, and as the heat leaks into the system, the helium boils off to take the heat away. It's simply vented into the atmosphere. Given how much more helium MRI magnets use worldwide compared to all its uses as a lifting gas, combined, it's a 4:1 ratio. Per every vented helium baloon or blimp, there's 4 times as much helium vented from superconducting magnets. The only irresponsible users are those with superconductive magnets. Sorry to burst your bubbe.
Proper attribution got nothing to do with fair use, those are separate and entirely orthogonal issues. Fair use is subject to standard tests, see post above.
Slashdot Mirror
Yep, and when you add up the time value of money, the end total cost is the same. Never mind that 10c/kWh is pretty darn cheap. In Europe it won't be anywhere near that low AFAIK.
I'd have thought that $50 LED light would scale its energy output to maintain a temperature at the safe operating limit (or even at a limit determined by specified lifetime). I consider them shit if they don't do that. That's actually the only way to make people dust them: light output goes down, you have to get to it, clean it up, and put it back. No "burning out". When it burns out it means that it allowed an unsafe failure. It's a step away from causing a fire.
If you do the calculation, the real thing including time value of money, you'd see that incandescents do in fact cost the least, at the moment, to own and operate, at least in the U.S. and when you're talking about residences. This may not hold in commercial settings. The "energy spent like hell" was at the factory -- that's why they cost more. They take more energy to make. That's all there's to it. Just because the energy is spent elsewhere doesn't mean it's not spent and you of course pay for it. Up front, no less. Energy = money, in the grand scheme of things. As for incandescents needing to be replaced "all the time": for me they last about half as long as CCFLs do. Due to their low purchase cost, it's not an issue. And I do keep good track of it.
The deal is: due to time value of money, all non-incandescent light sources cost actually more. They don't save shit, because money equals energy, so if you have to spend the money, the energy is expended somewhere else. Those bulbs cost more because it takes more energy to make them -- so much more, that it happens to almost exactly offset any energy savings due to using CCFLs or LED lights. When you factor in time value of money, those more expensive bulbs do actually cost more. So the entire argument about cost or energy savings is complete and utter made up bullshit. Yes, I like the CCFLs and LEDs better, because I don't like the heat being emanated in my home. That energy was spent at the factory, though.
As for storage: man, just put them in a shoe box (perhaps a plastic one) and wrap each one in crumbled newspaper. Been there, done that in exactly same circumstances. I'd have thought it's a non-issue.
I can't agree more.
What you of course failed to take into account is the time value of money. Assuming the bulb will last a year, at even a low credit card rate of 8% it costs you an extra 0.04c/hr. Or, if you look for savings, by not investing that money in AAPL you lose an extra 0.2c/hr (assuming 50% returns, and that's quite conservative). That's a lot of wasted money.
I have a little hand-held spectroscope, a 100 year old single-slit brass version of what these days looks like this. So yeah, sure you can tell the difference, you're just silly if you say otherwaise. You can tell even without any instruments -- just close your eyes and go a meter or two away from the bulb, and you can tell it's emitting heat, especially in a cold room.
That said, I'm all for CCFLs, LEDs and fluorescents. I think the incandescent lightbulb has outlived its purpose.
I dont see what is wrong with trying to stop people accessing information which is clearly only there to either assist in weapons making or to provide resources for people who want to cause widespead terror.
You're wrong, plain and simple. What information is for depends on how someone intends to use it. By being an engineer I obviously have a lot of information about how to wreck infrastructure and otherwise terrorize a whole lot of people. Most engineers have such knowledge even if they pretend otherwise. You're like a 6 year old kid who anthropomorphizes things and says "bad information!". Sorry to break your childish bubble, but there is no information that is "clearly only there to do X". It's in your mind, you seriously made up a fantasy where you have some fact (the information), and you imagine that it's bad. Information is not human, it has no feelings, desires, goals, seriously, get it out of your head or seek psychiatric help. You can use a decent highschool chemistry textbook to inflict way more damage than the 9/11 bastards did. Even reading religious texts like the bible provides plenty of ideas. I mean, thinking like you, why on Earth would you want to know the details of how to crucify someone?! Obviously it's of no other use than to run around and crucify people, right? Get real.
If you're doing athletics in school and burn 3kCal a day, you're going to be in deep trouble if you only eat 0.85kCal for lunch. IOW, you're an idiot.
Note: 1 Cal = 1000 cal. The former are the "dietary calories" used in the U.S. Everyone else uses kcal instead of Cal.
Winner of teh internets for today! Bravo! Gems like this appear every once in a while, and I've learned never to have any drinks near the keyboard while reading the tubes. Thanks for making my day.
Point taken :)
If you get into a routine and do it when the baby is fed (say before feeding), and that should normally happen on fixed schedule -- at least at night, then it's no biggie. I'd fall right back to sleep afterwards. The whole feed-change thingo shouldn't take longer than 15-20 minutes when a normal baby is past the first week or two. It sure is a whole another ballgame if you have a preemie, cleft lip, etc. 20 minutes up every 3 hours -- nothing to complain about. Key rule: after feeding and burping, put the kid down. No arguments about it. They'll learn very quickly that screaming at that point is useless. Never took longer than 72 hours after birth, anyway.
So normal medical magnets don't use a stator (core)? Well then, you need 750kA-turns to get 1.5T inside a 60cm long solenoid. I'll take a bit oversize solenoid at 60cm length and 60cm inner diameter. Let's see how realistic it'd be.
Assume standard 1inch O.D. copper tubing and 33mm pitch with some insulation between each turn. We have alternating 18 and 17 turns per layer due to triangular packing of cross sections. Say we'd want a 50cm thick winding ring (outer radius - inner radius). Assuming triangular tiling, we have 28.6mm diametral layer-to-layer spacing, so we can fit 16 layers. That's 280 turns, and the current is 2.7kA.
The length of the tube is approx. 1200m. Assume type K tubing with 0.065in or 1.651mm wall thickness, operating at ~70C average temperature (due to rise in resistance, the heat load in the hotter part of pipe, closer to outlet, will be higher than in the cooler part, but that's OK -- I specify average over length). The cross-sectional area of copper is 254.9mm^2. The cross-sectional area of sodium coolant is 1772mm^2. Copper's resistivity is 20.2nOhm*m, thus its resistance is 95mOhm. Sodium's resistance at ~61nOhm*m resistivity will be 41mOhm. Those are in parallel and the resistance is 29mOhm.
Given that the dissipated power is I^2*R, we have P=(2.7kA)^2*0.001=211kW. That's 175W/m of tubing. Sure a lot of power, but it can be dealt with as far as cooling is concerned -- each layer can have its own heat exchanger, dumping 13kW. Now let's see how much would it cost. At average US 15 cents/kWh, we have $18 cost to operate per hour, assuming all the power is dumped outside. That's nothing much. Even if we'd add inefficiencies in the power supplies and pumping losses in both sodium and cooling air.
I'd need to write out the equations symbolically and figure out where is the sweet spot with power dissipation vs. pipe diameter, presumably I haven't hit the most optimum design. Too lazy to figure it out right now.
Note 1: Mercury has resistivity an order of magnitude worse than sodium, so pretty much sodium is what you need for coolant.
Note 2: With water cooling, you can't but expect galvanic corrosion, unless there's some passivation scheme that would work -- I wouldn't count on it. In such a system, hot spots would be very destructive since the power supply can pretty much dump 200kW of heat in one hot spot if you're unlucky. A split power supply, supplying each layer separately, would of course help with that, but still even a 1in O.D. pipe won't cope with 13kW in a small spot for very long, and as soon as cooling water would start to boil, you're done for. This becomes a non-issue when using sodium, but of course I don't know how well copper pipes play with sodium flowing in them...
Note 3: The power supplies won't be a walk in the park to design, since you pretty much need a switcher with synchronous rectifiers being paralleled (slow!) mosfets to keep the resistance low enough, and then you still need a linear post-regulator that would waste at least 10% of incoming power. It certainly wouldn't be cheap to design and prototype, you can't get a random appnote-copying switcher jockey to put one together ;)
Just buy an ultrasound on eBay and learn how to use it. No, you don't need to have a prescription for it or anything. Say you're buying it for use in engineering. It'd have cost you way less than one hospital childbirth.
I don't know where you are, but in the U.S. home childbirths aren't unheard of. Get a midwife and do it at home, the ob-gyn has to respect your wishes in that regard. You could have made a lot of fuss about those child endangerment threats, in the U.S. at least.
It is fun if you want it to be :)
Ok then, how many amp-turns does a typical 1.5T clinical scanner need? Let's crunch some numbers.
Superconducting magnets don't heat up. When your field needs to be uniform in the parts per billion range, a little bit of restive heating is a big problem. And a high field resistive magnet, even if you could make one that didn't melt immediately, would suffer from a bit more than a little resistive heating.
Electric power is generally cheap. Even if that thing would be wasting tens of kilowatts, it's no biggie. I presume as long as it's cheaper than lost helium at projected helium prices, one is ahead financially, and that's what counts.
The coil is wound around a stator. Resistive drops in the wiring won't affect field uniformity, not even at ppb level I'd think. The "wiring" would be a pipe, and most of the current would flow in the copper, and there the temperature would be pretty stably distributed I'd think due to heat exchange with sodium coolant. Thus the current distribution in the pipe would be axisymmetric, and that's what counts. The exact absolute field strength doesn't need to be maintained to ppb I don't think because the gradient coils aren't that accurate (good luck generating a sine wave or in fact any amplified waveform to 1ppb). It wouldn't be all that much of a problem since we can measure field strength to such an accuracy and you could maintain a feedback loop to keep it stable to such a level if you really wanted to.
If you want to be really clever, you can recover heat from the sodium coolant and use it to locally generate some of the power needed to power the coils. Since such a system would run pretty much in thermal equilibrium, at well known operating points, it could be optimized to have thermodynamic efficiency better than, say, a car engine. 50% of discount on a power bill is always nice ;)
Alternatively, there could be an option of dumping the heat into a steam circuit -- after all, large hospital campuses probably have a power plant and steam circuits, and dumping heat there would be OK. That steam powers the chillers in the summer, too, after all.
Say what you want, their apparent xenophobia served them well thus far. YMMV.
You're missing that it's not legal in most places in the world, unfortunately.
Again, those are orthogonal issues: protected free speech can run afoul of copyright laws, and in that case copyright laws win. I think there's case law to show just that. Why would that be a problem with copyright law? Have you thought through what it'd mean if free speech trumped copyright? Every cinema owner would claim exercise of free speech and would give a middle finger to the distributors in place of a check. Yeah, that'd sure as heck work.
?! So you're saying that copper piping is more expensive than superconducting alloys? Well, that's news to me. As for the energy requirement: well, pray tell, how huge would it be. As for the stability of the field: well, what's so magical about a superconducting magnet that it'd have a more stable field? I presume a superconducting magnet needs a much smaller current from the power supply (orders of magnitude smaller) to maintain the field, but you silently presume that we can't make power supplies that keep things stable within 10ppm or better.
What about using conducting magnets? How much power would a MRI magnet dissipate during operation if the windings were from copper?
Here's a hint as to how the MRI magnets are being cooled: there's a liquid helium bath, some insulation, and as the heat leaks into the system, the helium boils off to take the heat away. It's simply vented into the atmosphere. Given how much more helium MRI magnets use worldwide compared to all its uses as a lifting gas, combined, it's a 4:1 ratio. Per every vented helium baloon or blimp, there's 4 times as much helium vented from superconducting magnets. The only irresponsible users are those with superconductive magnets. Sorry to burst your bubbe.
Proper attribution got nothing to do with fair use, those are separate and entirely orthogonal issues. Fair use is subject to standard tests, see post above.