the drives have other differences like a cost-reduced controller or different platter density, that makes it unsuitable for integration with the existing array.
I've mixed and matched hard drive vendors (usually intentionally) in RAID arrays for years; besides a little bit of performance, what am I missing? And if I need that little bit of performance, shouldn't I be short-stroking even more drives or using SSDs?
I haven't seen anyone with the theoretical knowledge to work out the equations to prove or disprove the concept of leeching electricity from the ground
One place this is covered is the book "Antennas and Transmission Lines" by John A. Kuecken, in chapter 23, "Directional Couplers and Hybrid Junctions".
Note that Slashdot doesn't allow for either unicode or sub/superscript so when you see "w", that means lowercase omega, and when you see "sub1" or "sup2" that means "subscripted character 1" or "superscripted character 2". The formula listed there for two sets of parallel wires (AB, the transmitting power lines, and CD, the parasitic receiver lines) is E = jIsub1wM where E in other contexts in the book is induced voltage on CD, j in other contexts in the book is a rotation operator (which appears to be identical in function to i, i.e. jsup2 = -1... in fact I'm wondering if it's really j or if that's just a confusing font), Isub1 is the current flowing through the power lines, w is 2pif, where f is the frequency (60Hz), and M is the mutual impedance per unit length AB to CD.
It goes on to say, "If line CD is properly terminated (RsubL = Zsub0) a current Isub2 = Esub2Zsub0 will flow, producing a reaction in AB: EsubR = +jIsub2wM = -Isub1(wM)sup2Zsub0. This equation is important since it leads us to the startling conclusion that the transfer of power from AB to CD proceeds not to equilibrium but to completion; that is, until the wave on AB vanishes!"
This section of the chapter also lists a couple references - "Techniques of Microwave Measurements" by C. G. Montgomery in MIT Radiation Lab Series Volume 11, "An Inside Picture of Directional Wattmeters" by W.B. Bruene in April 1959's QST magazine, "Low-Cost RF Wattmeter" by A. F. Prescott and W. C. Louden in GE Ham News, May-June 1961.
Now we have Solar thermal generation. This is pretty good tech, but it use a LOT of water.
There's no intrinsic need for that - it just makes the cooling system smaller, cheaper, and more effective (these are heat engines, operating off a temperature differential - the colder the cold side is, the more efficiently they run).
Concentrating Solar Thermal does (via heat stored in molten salt vats). However it requires specular, not diffuse light (i.e. does not work at all in overcast weather), so it's more suited to desert environments (for example, a large chunk of the southwest US). Efficiencies are also better than with PV (30-40% instead of 10-15%), it's straightforward to scale up, and the technology is well understood (you focus sunlight on a target to make it hot, generate steam with it, and turn a steam turbine with that steam).
something tells me that carbon fiber disks that are carefully stabilized and levitated in a vacuum while spinning incredibly fast...would break into a thousand pieces the second they left containment rather than rolling down the street and through someone's house
Yes, it's basically the same as a bomb with a chemical energy potential equivalent to that of the kinetic energy stored in the flywheel being detonated in the flywheel's containment. If they haven't designed the facility with this in mind, shrapnel from one disintegrated flywheel could hit another flywheel, leading to a chain reaction of disintegrating flywheels that would shut down most or all of the facility. It sounds like they've put the flywheels mostly underground which, with enough spacing, should prevent this.
As for energy levels, if the 1-megawatt-for-15-minutes number in the article is for one flywheel, then that's equivalent to 215kg of TNT. If that's for all 200 flywheels combined, then one flywheel disintegrating is equivalent to 11kg of TNT.
If more than 50% of the voters wanted the patriot act gone...
You need a higher percentage than this. Let's pretend that:
A representative lives in a semi-contested district where they've, regardless, served for several terms.
The issue in question is a big one - one that voters may make their next decision on
The issue isn't one that's aligned with either the dem or rep platform.
A change on the issue might anger voters who disagree more than it would sell voters who agree.
If only 50% of voters wanted the bill to pass, then about half of the voters who would ordinarily vote for the candidate may vote against them in the next term. While it's often true that the last bullet is just a figment of the representative's imagination, and that half the voters who wouldn't ordinarily vote for the candidate may vote for them now, if a representative has found a platform that gets them elected over and over, they won't want to risk changing it and fracturing their constituent base.
My suspicion is that you're going to wind up reimplementing a good fraction of a CNC machine's functionality, but here's an idea that might save you some time:
Implement the 1.5" increments via a ratchet-like mechanism. Allow the tube to slide down the V of some angle iron placed at a steep (say, 60 degree) angle. The drills are placed halfway down this. In the lower half of the V, there are registration pins (probably bolt heads of the appropriate size, machined to the proper diameter and with some taper for self-centering) every 1.5" for a couple repetitions. The tube is placed into the V, hits the first registration pins, is clamped to the V using electromagnets, and drilled from both directions (you have several options for moving the two drills here, but I kinda like the idea of pushing the drill away from the work with a spring and pushing it towards the work with pneumatic bellows). Once the drilling is done, some electromagnets above the tube pulse for a bit so that the tube pops up and slides down onto the next set of registration pins, and you repeat. The tube falls out of the V when it clears the last set of registration pins. Be generous with the hardware interlocking - at the very least you want to make sure one drill is out before the other drill goes in.
plus one single RPM means that you can really simplify the design of the engine so that a minimal amount of cooling is required.
No, it doesn't mean that at all. This is still a heat engine - it converts a temperature difference (between a hot side and a cold side) into mechanical energy. The smaller that difference, the less heat energy is available to extract and the less efficient the engine can be.
I hear the complaint "teachers will teach to the exam" all the time as an argument against standardized testing. Damn right they will. If this results in a poor education, it means they weren't good exams (e.g., the SAT)
I'd rather have a nation's graduates receive a wide variety of teaching experiences so that they are collectively exposed to millions and millions of different facts and concepts than have them collectively exposed to the same few thousand facts and concepts. That is something that a standardized test by its very nature simply cannot do.
Look into the efficiency of a battery sometime. Unless you buy really expensive ones you lose about half of the energy putting it into and getting it back out.
I have looked into it. There aren't many numbers on the Internet - most of the stats on Wikipedia are single-sourced from sites such as powerstream.com, but coulometric efficiency generally varies by cell chemistry type. Lead acid is about 70%, NiCd is about 83%, NiMH is about 66%, Lithium-Ion is 80-90% (and there are some sources that say it's higher than that). For large-scale grid energy storage you might look into Sodium Sulfur, which is reported to have efficiencies of 89-92% and is inexpensive but requires operating temperatures of 300-350C to work. In any case, 50% is very very pessimistic.
I still think that the solar power tower molten salt vat approach to energy storage is the most practical storage option (where hydroelectric pumping isn't available, anyway) in the short term.
Does the angle of the sun come into play here? Is it really the same at 4PM as at noon? Or is 1000 W an average?
A number like 1000W would refer to the peak power output that you'll get from it with the solar cells perpendicular to the sunlight with optimally clear skies. Since the earth receives a maximum of about 1100W/m^2 of solar energy, and ordinary silicon cells are about 12% efficient, you can expect such a system to be a little less than 10 m^2 in size.
4pm is not noon, no. First off, the lower the angle of the sun in the sky, the more atmosphere it goes through, which filters things out somewhat. Second, while you can steer the solar panels so that they are always perpendicular to the sky, most are just fixed to a south-sloped roof and more of their surface area will be going to waste.
If you google for insolation map you can get nifty maps of what areas get how much sunlight. Note that most of these maps are for plain photovoltaic installations, where diffuse light (cloudy skies) is still better than nothing. When you're using solar concentrators (mirrors), those mirrors can't focus anything but specular light (sunny skies). I don't know if any maps have been drawn taking that into account.
In order to do the same job, you would need a massive (read expensive) heat exchanger to do the same job.
And in an environment where you can assume condensation and ice buildup, rendering forced-air circulation useless, that heat exchanger can be drastically simplified - it's just a very long tube. No fins, no fans, just pumps to cover the increased pressure drop, and enough supporting structure to prevent the ice from taking it down.
Not everywhere. For air source heat pumps, the COP* (what you meant when you said efficiency) is about 1.0 at 0 degrees F
I know about COP, I was just keeping it simple for the original poster to allow them to compare to resistive heating.
The useful temperature range of a heat pump is mostly governed by your choice of refrigerant and your cold side and hot side pressures. For example, the freezer in your kitchen is designed specifically to move heat from 0 degrees F air, and it does so efficiently. The theoretical maximum COP of a heat pump with a cold side of -10C (263K) and a hot side of 40C (313K) would be 1/(1-(263/313)), or about 6.26, and it's not uncommon for ordinary consumer appliances to get at least half that. Icing simply limits the rate of heat conduction into the cold side, meaning that you need more surface area to compensate.
In the winter the old incandescent lamp has an efficiency nearing 100% because you use its heat too.
Why should anybody tell me to use CFL, harder to manufacture and dispose of and in this case less efficient?
Because unless the rest of your house is using resistive electrical heating too, it'll be cheaper by about a factor of 2 to get that same heat from natural gas (the conversion is slightly less efficient due to exhaust gas heat loss, but the natural gas chemical energy is cheaper than the electrical energy from the grid), and cheaper by about a factor of 4 to get that same heat from a heat pump (which because it moves heat from outside the building in, instead of merely converting it from electrical power, has an efficiency of 300-400%).
The L2 point (which is where JWST is headed) isn't a gravity pit - it's a gravity hill. It's a long-term unstable orbit, but it takes minimal delta-V to stay put there with active correction.
L4 and L5 (60 degrees ahead and behind the orbit of the lighter-mass object) are the gravity pits, and lots of miscellaneous stuff does collect there. But even then, it's still nearly empty space and whatever has collected there isn't moving fast relative to you.
Yes there is. Build and launch another one. It should be a heck of a lot cheaper the second time around - most of the money for these things does not pay for the parts.
I doubt the design had much to do with it, at least as far as the distance.
Exactly. The most you can hope for without active control is a stable glide in a relatively large circle (the more symmetrical the plane, the wider the circle, but there's little chance of any of the planes carving a circle larger than a mile, even if they're being folded by the best - the straightest I've ever made one fly is a several hundred foot diameter circle). Any substantial distance covered will be due to air currents.
The design looks like a basic delta wing glider - with the SD card providing balance.
The SD card is placed at the glider's existing CG. I'm sure of this because I've made the exact design they used quite a few times (a paper airplane book I read in grade school - "Wings and Things" - referred to the design as a "Blackboard Bomber") and it will fly just fine without any extra weight.
The problem is that voice over broadband doesn't come with the same kind of 99.999% uptime you have with POTS.
POTS doesn't deliver 99.999% availability. For example, Verizon promises only 99.9% availability. The goal is to have the switching equipment be 99.999% available, so that the carrier can make the (much lower) per-line dialtone availability goals.
In practice it remains a noble but unachievable goal. Show me a CO that has had 316 seconds or less of customer-affecting downtime in the past 10 years and I'll show you an Anonymous user that actually uses seven proxies.
I could see it being kind of scary to drive on the highway unless its got some serious aerodynamic down force.
It wouldn't be any worse than my first car, a Chevette (which was roughly the same curb weight). I drove that car through some pretty stiff side winds, and while you notice it more, it's not at all scary.
Efficiencies have to come from somewhere. They've made small but steady gains in engine efficiency. There won't be any quantum leaps there. The biggest things you can do to increase efficiency are make the car lighter, and make it more aerodynamic (no, not "aerodynamic styling", aerodynamic). Start talking Cd and frontal area and laminar flow. And don't stop just because you think the result is ugly.
Slashdot Mirror
I've mixed and matched hard drive vendors (usually intentionally) in RAID arrays for years; besides a little bit of performance, what am I missing? And if I need that little bit of performance, shouldn't I be short-stroking even more drives or using SSDs?
You misspelled "single manufacturing batch of drives".
One place this is covered is the book "Antennas and Transmission Lines" by John A. Kuecken, in chapter 23, "Directional Couplers and Hybrid Junctions". Note that Slashdot doesn't allow for either unicode or sub/superscript so when you see "w", that means lowercase omega, and when you see "sub1" or "sup2" that means "subscripted character 1" or "superscripted character 2". The formula listed there for two sets of parallel wires (AB, the transmitting power lines, and CD, the parasitic receiver lines) is E = jIsub1wM where E in other contexts in the book is induced voltage on CD, j in other contexts in the book is a rotation operator (which appears to be identical in function to i, i.e. jsup2 = -1... in fact I'm wondering if it's really j or if that's just a confusing font), Isub1 is the current flowing through the power lines, w is 2pif, where f is the frequency (60Hz), and M is the mutual impedance per unit length AB to CD.
It goes on to say, "If line CD is properly terminated (RsubL = Zsub0) a current Isub2 = Esub2Zsub0 will flow, producing a reaction in AB: EsubR = +jIsub2wM = -Isub1(wM)sup2Zsub0. This equation is important since it leads us to the startling conclusion that the transfer of power from AB to CD proceeds not to equilibrium but to completion; that is, until the wave on AB vanishes!"
This section of the chapter also lists a couple references - "Techniques of Microwave Measurements" by C. G. Montgomery in MIT Radiation Lab Series Volume 11, "An Inside Picture of Directional Wattmeters" by W.B. Bruene in April 1959's QST magazine, "Low-Cost RF Wattmeter" by A. F. Prescott and W. C. Louden in GE Ham News, May-June 1961.
There. Clear as mud.
As long as the music is all in a narrow frequency band, sure. For some genres this may not be that difficult.
Being right is an absolute defense for being belligerent.
Food for thought: What physical property do you believe makes it a vapor? Does that necessary physical property exist outside the bulb?
There's no intrinsic need for that - it just makes the cooling system smaller, cheaper, and more effective (these are heat engines, operating off a temperature differential - the colder the cold side is, the more efficiently they run).
Concentrating Solar Thermal does (via heat stored in molten salt vats). However it requires specular, not diffuse light (i.e. does not work at all in overcast weather), so it's more suited to desert environments (for example, a large chunk of the southwest US). Efficiencies are also better than with PV (30-40% instead of 10-15%), it's straightforward to scale up, and the technology is well understood (you focus sunlight on a target to make it hot, generate steam with it, and turn a steam turbine with that steam).
Yes, it's basically the same as a bomb with a chemical energy potential equivalent to that of the kinetic energy stored in the flywheel being detonated in the flywheel's containment. If they haven't designed the facility with this in mind, shrapnel from one disintegrated flywheel could hit another flywheel, leading to a chain reaction of disintegrating flywheels that would shut down most or all of the facility. It sounds like they've put the flywheels mostly underground which, with enough spacing, should prevent this.
As for energy levels, if the 1-megawatt-for-15-minutes number in the article is for one flywheel, then that's equivalent to 215kg of TNT. If that's for all 200 flywheels combined, then one flywheel disintegrating is equivalent to 11kg of TNT.
You need a higher percentage than this. Let's pretend that:
If only 50% of voters wanted the bill to pass, then about half of the voters who would ordinarily vote for the candidate may vote against them in the next term. While it's often true that the last bullet is just a figment of the representative's imagination, and that half the voters who wouldn't ordinarily vote for the candidate may vote for them now, if a representative has found a platform that gets them elected over and over, they won't want to risk changing it and fracturing their constituent base.
My suspicion is that you're going to wind up reimplementing a good fraction of a CNC machine's functionality, but here's an idea that might save you some time:
Implement the 1.5" increments via a ratchet-like mechanism. Allow the tube to slide down the V of some angle iron placed at a steep (say, 60 degree) angle. The drills are placed halfway down this. In the lower half of the V, there are registration pins (probably bolt heads of the appropriate size, machined to the proper diameter and with some taper for self-centering) every 1.5" for a couple repetitions. The tube is placed into the V, hits the first registration pins, is clamped to the V using electromagnets, and drilled from both directions (you have several options for moving the two drills here, but I kinda like the idea of pushing the drill away from the work with a spring and pushing it towards the work with pneumatic bellows). Once the drilling is done, some electromagnets above the tube pulse for a bit so that the tube pops up and slides down onto the next set of registration pins, and you repeat. The tube falls out of the V when it clears the last set of registration pins. Be generous with the hardware interlocking - at the very least you want to make sure one drill is out before the other drill goes in.
No, it doesn't mean that at all. This is still a heat engine - it converts a temperature difference (between a hot side and a cold side) into mechanical energy. The smaller that difference, the less heat energy is available to extract and the less efficient the engine can be.
I'd rather have a nation's graduates receive a wide variety of teaching experiences so that they are collectively exposed to millions and millions of different facts and concepts than have them collectively exposed to the same few thousand facts and concepts. That is something that a standardized test by its very nature simply cannot do.
I have looked into it. There aren't many numbers on the Internet - most of the stats on Wikipedia are single-sourced from sites such as powerstream.com, but coulometric efficiency generally varies by cell chemistry type. Lead acid is about 70%, NiCd is about 83%, NiMH is about 66%, Lithium-Ion is 80-90% (and there are some sources that say it's higher than that). For large-scale grid energy storage you might look into Sodium Sulfur, which is reported to have efficiencies of 89-92% and is inexpensive but requires operating temperatures of 300-350C to work. In any case, 50% is very very pessimistic.
I still think that the solar power tower molten salt vat approach to energy storage is the most practical storage option (where hydroelectric pumping isn't available, anyway) in the short term.
A number like 1000W would refer to the peak power output that you'll get from it with the solar cells perpendicular to the sunlight with optimally clear skies. Since the earth receives a maximum of about 1100W/m^2 of solar energy, and ordinary silicon cells are about 12% efficient, you can expect such a system to be a little less than 10 m^2 in size.
4pm is not noon, no. First off, the lower the angle of the sun in the sky, the more atmosphere it goes through, which filters things out somewhat. Second, while you can steer the solar panels so that they are always perpendicular to the sky, most are just fixed to a south-sloped roof and more of their surface area will be going to waste.
If you google for insolation map you can get nifty maps of what areas get how much sunlight. Note that most of these maps are for plain photovoltaic installations, where diffuse light (cloudy skies) is still better than nothing. When you're using solar concentrators (mirrors), those mirrors can't focus anything but specular light (sunny skies). I don't know if any maps have been drawn taking that into account.
And in an environment where you can assume condensation and ice buildup, rendering forced-air circulation useless, that heat exchanger can be drastically simplified - it's just a very long tube. No fins, no fans, just pumps to cover the increased pressure drop, and enough supporting structure to prevent the ice from taking it down.
Err, better numbers would be -25C and 40C, resulting in a max theoretical COP of about 4.81.
I know about COP, I was just keeping it simple for the original poster to allow them to compare to resistive heating.
The useful temperature range of a heat pump is mostly governed by your choice of refrigerant and your cold side and hot side pressures. For example, the freezer in your kitchen is designed specifically to move heat from 0 degrees F air, and it does so efficiently. The theoretical maximum COP of a heat pump with a cold side of -10C (263K) and a hot side of 40C (313K) would be 1/(1-(263/313)), or about 6.26, and it's not uncommon for ordinary consumer appliances to get at least half that. Icing simply limits the rate of heat conduction into the cold side, meaning that you need more surface area to compensate.
Because unless the rest of your house is using resistive electrical heating too, it'll be cheaper by about a factor of 2 to get that same heat from natural gas (the conversion is slightly less efficient due to exhaust gas heat loss, but the natural gas chemical energy is cheaper than the electrical energy from the grid), and cheaper by about a factor of 4 to get that same heat from a heat pump (which because it moves heat from outside the building in, instead of merely converting it from electrical power, has an efficiency of 300-400%).
The L2 point (which is where JWST is headed) isn't a gravity pit - it's a gravity hill. It's a long-term unstable orbit, but it takes minimal delta-V to stay put there with active correction.
L4 and L5 (60 degrees ahead and behind the orbit of the lighter-mass object) are the gravity pits, and lots of miscellaneous stuff does collect there. But even then, it's still nearly empty space and whatever has collected there isn't moving fast relative to you.
Yes there is. Build and launch another one. It should be a heck of a lot cheaper the second time around - most of the money for these things does not pay for the parts.
Exactly. The most you can hope for without active control is a stable glide in a relatively large circle (the more symmetrical the plane, the wider the circle, but there's little chance of any of the planes carving a circle larger than a mile, even if they're being folded by the best - the straightest I've ever made one fly is a several hundred foot diameter circle). Any substantial distance covered will be due to air currents.
The SD card is placed at the glider's existing CG. I'm sure of this because I've made the exact design they used quite a few times (a paper airplane book I read in grade school - "Wings and Things" - referred to the design as a "Blackboard Bomber") and it will fly just fine without any extra weight.
POTS doesn't deliver 99.999% availability. For example, Verizon promises only 99.9% availability. The goal is to have the switching equipment be 99.999% available, so that the carrier can make the (much lower) per-line dialtone availability goals.
In practice it remains a noble but unachievable goal. Show me a CO that has had 316 seconds or less of customer-affecting downtime in the past 10 years and I'll show you an Anonymous user that actually uses seven proxies.
It wouldn't be any worse than my first car, a Chevette (which was roughly the same curb weight). I drove that car through some pretty stiff side winds, and while you notice it more, it's not at all scary.
Efficiencies have to come from somewhere. They've made small but steady gains in engine efficiency. There won't be any quantum leaps there. The biggest things you can do to increase efficiency are make the car lighter, and make it more aerodynamic (no, not "aerodynamic styling", aerodynamic). Start talking Cd and frontal area and laminar flow. And don't stop just because you think the result is ugly.
Sorry, I meant "try measuring in more useful terms..."