I think the theoretical efficiency of cooling is 10% of the heat to be removed, where it would take 100W to remove 1000W of heat.
SEER is one incredibly botched measurement system, and I believe this statement is a direct cause of it.
The SEER numbers you see are usually about 10 to 15, however SEER is not an apples-to-apples comparison. It's BTUsOfCooling / WattHoursOfElectricityUsed. Half metric, half imperial. Who comes up with this stuff?
To turn BTUsOfCooling / WattHoursOfElectricityUsed into a sensible measurement like Cooling / ElectricityUsed, divide by 3.412.
So, a SEER of 13 becomes an efficiency ratio of 3.80. The reciprocal of 3.80 is.26, much closer to your '30% in practice' comment, so (assuming a SEER of 13) for every watt you bring into your datacenter, you need an extra.26 watts to bring it back out.
I think the difference is that many homes and businesses come pre-installed with cat5 cable to every room (or at least have already wired it up), so in those cases you WOULDN'T have to run cable.
In those situations I would rather put an analog line-level balanced signal directly over the cat5, using whatever baluns and amplifiers I needed to accomplish that. It'd likely be cheaper, I wouldn't have to worry about latency or jitter, and as long as your amp's balanced inputs had common-mode rejection (pretty much all of them do) the twists in the cat5 would prevent picking up interference over long runs.
Aircraft like the C172 I fly have wings that are specifically designed to stall in a very particular way... high precision engineering...
Very funny. Any roughly rectangular wing will stall from the inside out. It's only when the wing is tapered more strongly than an ellipse that you risk stalling at the tips first. To further minimize the risk of the tips stalling, the wingtips are usually angled down (washed out) a couple degrees (compared to the rest of the wing) or they incorporate a different airfoil at the tip that stalls a few degrees later.
What would happen if a single speaker went out? Would the plane go into an irrecoverable barrel roll?
You could easily prevent just one speaker from going out at a time by wiring opposing panels in series.
What would happen is the plane would revert to its old dynamics. The five degrees past normal stall AOA mentioned in the article would put you into a fairly deep stall, but if your plane was otherwise properly designed, you'd still have authoritative rudder control, certainly enough to keep any yaw momentum down until you can nose the plane over.
Also, stalls really aren't that big a deal if you know your ass from a hole in the ground.
Many pilots have stalled a wingtip on their landing approach by banking too tightly to make a turn, while trying to maintain altitude, while going too slowly for the wings to generate the extra lift required for that maneuver. Because one wing is already moving slower than the other, it generally puts you in a spin that you won't have altitude to recover from. You could say those pilots don't know their ass from a hole in the ground, but at that point it really is a matter of semantics.
Why are you, as a pilot of a certified aircraft, worried about new things, anyway? You might as well own a car in Cuba.
As for a 200 dB antenna, well, I'd like to see that. I suspect it would be larger than the size of the Earth for the 2.4 GHz band:)
You're right!
A google search says the formula for theoretical dish gain is 20*log(7.4*FreqInGhz*DiameterInMeters). That matches some more google searching that says Arecibo (305 meters diameter) in Puerto Rico does about 70dB at those frequencies.
Solving for diameter in meters results in 563000000 meters, which is roughly the size of the moon's orbit.
Get to space. As long as you're stuck on this step, you're going to have to have an entire planet's worth of heavy industries, energy generation, and resource extraction being performed on the surface of said planet.
Fast forward 50 years:
Colonist #1: "Woohoo! We're on Mars! For good! All seven of us!"
Colonist #2: "Sweet! Guess we can shut down all the heavy industries, energy generation, and resource extraction on the surface of Earth!"
Colonist #1: "What a great idea! Our kids won't even have to terraform it when they wanna go back!"
If I build something other people can't easily duplicate, that doesn't make my product common infrastructure.
However, if you do it because you are a government-sanctioned monopoly with sole rights to do it (in some areas) and a government mandate to do it, and you do it partially with government money, partially with your monopoly status, then the situation changes. You can't maintain the 'privately-funded stuff' argument when your private corporation has had special legal status to be the only game in town for 100 years.
The phone companies are here to serve us. Not the other way around. The rules need to reflect that. Compare it to the power/water/sewer/postal monopolies and the government regulation needed to keep that common infrastructure working for us.
I've been watching the stories on this since they started hitting news.google.com. Most of the initial headlines were "FCC eases rules" or "Phone companies get internet relief".
Is it unreasonable to expect headlines like "Local ISPs across the country doomed"? Even if the press doesn't care about the ISPs, that's a lot of people who will probably be out of work soon, and employment trends generally are something the press cares about.
I hate this ruling for several reasons:
It's the FCC wantonly overriding Congress. The line-sharing rules were set up by Congress as a main purpose, perhaps the main purpose of the 1996 Telecommunications Reform Act.
The wiring that the phone companies pretend is theirs alone really belongs to the people. It's common infrastructure - if everyone had to attempt to duplicate it to compete, the result would be an expensive mess.
It reduces us to a handful of choices for ISPs. The cable company, the phone company, maybe a WiMax ISP, some form of satellite access, etc. Those of us who consciously chose to buy our DSL service from a competitor do it for the markedly better customer service and for more options.
I think that the press is slowly starting to pick that up, thanks in part to organizations such as the Consumers Union. I hope the FCC is forced to reconsider. If they don't, I hope the local ISPs take the initiative to build some new infrastructure of their own (and I hope it's something so clearly better that it's not just an expensive mess).
The Baby Bells keep their uptime greater than 5 nines typically.
I find it incredible that no one has mentioned in this discussion the fact that that availability metric does not apply to your land line.
That's the fabled gold standard of reliability they need from their equipment to be able to promise you a completely different availability metric for their network. Network, as in, after your call makes it to the phone switch at the CO, that's the chance of the call making it to the other parties' phone switch at their CO.
the only way to theoretically overrule a decision is to amend the constitution
Only when that decision chooses to recognize the highest law in the land at the expense of regular legislation.
Congress passes and the states ratify constitutional amendments. The amended constitution takes precedence over law, as well as judicial opinions concerning that law or the previous constitution. Federal courts interpret the amended constitution.
Congress legislates federal law. The law takes precedence over old judicial opinions concerning that law. Federal courts interpret the new law.
Two levels of law, but other than one being very difficult to modify, they both work the same way. Federal courts refer to 'direction from Congress' all the time. It still seems to me that as a group, our justices strongly prefer such direction over making their own decisions.
I'd imagine the reason you feel that the SCOTUS does not have the same checks and balances is because Congress has been too cowardly to make the most controversial decisions on their own. Someone else mentioned abortion - can you imagine the trouble a representative would have getting reelected if he/she proposed a bill either for or against abortion?
A little difficult to fly from New York to Tokyo in six hours if you've gotta go around South America, isn't it?
Only a few hundred miles of a New York<->Tokyo path is over US soil, at least if you divert ever so slightly north of Alaska. Most of it is uninhabited areas of Canada, the Arctic Ocean, and Siberia.
But there was always a lot of effort involved in getting it to work, and they were always precarious in operation. It was scarey to do upgrades. It was scarey to have hard drives fail.
Here's another approach: put Linux on a CompactFlash card instead of a hard drive. Keep the filesystem mounted read-only for normal operation. Test upgrades on a different computer and CF card. Upgrade by swapping out CF cards. If you can build a PC that doesn't need fans, then you've removed all moving parts from the equation. For smaller installations, single-board computers such as the Soekris are very reliable. For larger installations, you can usually find a 1U system with the level of performance you need.
It was always just so much simpler to get a more expensive Cisco box in the long run due to its design, documentation, an performance.
It always depends on what you're doing, of course, and also what you're familiar with, but for my routing/firewalling/VPN/load balancing/ etc needs I've simply found Linux to be more flexible.
Cisco uses two factor one time passwords for remote access. I don't see how planting a trojaned copy of SSH on the lab computers would give the hacker access to Cisco's systems.
I don't know how Cisco has their stuff set up, but it's easy to imagine such a breach playing out:
Black hat replaces ssh client at University lab computer.
Authorized but unwitting user uses University computer to VPN into Cisco's network and then uses the trojaned ssh client to connect to a computer on Cisco's network.
The trojaned ssh client is now able to execute arbitrary code as the unwitting user on an internal Cisco computer. It uploads an executable to the internal Cisco computer that regularly makes outgoing TCP connections (they could even look like web browser traffic) to a computer under the black hat's control. The black hat sends control commands through these connections which the executable gladly obeys.
The black hat is now free to scan the internal network to look for a host they can get root on, or hope that the user's account on the internal server they control will be used to connect to other internal systems, perhaps using more highly privileged accounts. (Any admins ever had to sit down at a users' computer and ssh into a server to fix something?) The longer the initial breakin is left unidentified, the better the chances of this occurring.
Eventually the black hat will strike paydirt and get root on a system. From then on, the rootkit that the black hat installs can use any credentials anyone uses to access any systems remotely. Ssh into something? It can run commands on the remote host. Connect to a file server? It can replace executables that you have write access to and wait for someone else to run them.
While an attacker would need a fairly deep understanding of the software infrastructure he is attacking and of the usage habits of the users there to pull this off, the same basic strategy is applicable to UNIX, Windows, anything. I remember reading several years ago that the breakins at Exodus and VA Linux happened this way.
We're only used to the stuff we hear about not doing any real damage, because it's all dumb worms running without anyone at the controls. Just because we can fend off that stuff doesn't mean that someone with determination, knowledge, and patience won't get in and stay in.
Whenever I plug ear-phones into my speaker's earphone jack, I get the fucking radio on it. Same goes for the phone.
If you're receiving FM radio on your speakers without an actual radio attached, it's probably due to interference from another radio receiver (not necessarily a radio transmitter) nearby.
Almost all tunable radio receivers since the 1920's have been built around a principle called superheterodyning - reducing and tuning the received signal by mixing it with another signal.
This process causes the receiver to weakly transmit the received signal at a lower frequency (FM broadcast receivers have standardized on 10.7 MHz, AM broadcast receivers have standardized on 455kHz). Poorly-built receivers can retransmit with a signal that can be picked up with hundreds or thousands of feet away.
Any circuit with an inductor, a capacitor, a diode, and audio outputs (such as your phone and speakers) will act as an AM crystal radio, which is all you need to pick up such a retransmission.
The radio stations you hear as interference reflect the demographics of those who own shoddy radios.
The cells drain unequally but charge equally, meaning you will overcharge the cells you don't use, and likely you'll never fully charge the cells you do use. The pack will die more quickly. (For this reason, even with conventional designs, some people who assemble battery packs will put in the effort to sort cells by their tested capacity and match them.)
Other issues are that you only get the available power from the cells you use, and you have differing ground potentials between equipment.
Oh, and lead-acid batteries are nominally 2.0 volts per cell, not 1.5 volts.
In this context he was paying a debt. While Best Buy still has the option to refuse the payment tendered, they can't legally make him pay in some other form. For Best Buy, it's take it or leave it.
That's why currency reads "this note is legal tender for all debts, public and private."
Just how big a car are we talking about that we can put sphere that's at least three feet in diameter under the hood?;)
What kind of flywheels are people talking about putting in cars that are three feet in diameter? Flywheel energy goes up linearly with mass but squarely with rotational speed, which is why people talk about spinning them at 100000rpm and making them out of carbon fiber.
Another problem of large flywheels would be the gyroscopic effect.
It is possible (granted, often not practical) to negate this by either using two counterrotating flywheels, or mounting the flywheel in gimbals like a gyroscope.
This number sounds low. While it wouldn't surprise me if there are plants still operating at that efficiency level, you can get 45-50% efficiency with external combustion Ranking cycle steam turbines, and up to 60% efficiency with the new Kalina cycle designs.
I don't think it's particularly helpful to compare old power plants to new cars, at least when we are debating what the masses should do.
You need to examine what is known as 'well to wheel' efficiency to make a rational comparison
Absolutely. One also should factor in the resources used to manufacture the equipment or infrastructure. Arguably the best way for us non-omniscient mortals to estimate that is by looking at the price tag.
overall I think you'll find there is very little in it.
Almost all efficiency gains these days come from evolutionary rather than revolutionary improvements, but they certainly add up.
The thing is, I can't trust you regarding your apparent conclusion that it's OK to use car batteries for UPS applications, because not only do your experiences differ from mine, but they also contradict just about everything I've read.
To get to your point about reduction in voltage, if a cell were truly reversed and somehow stayed that way even through a charge cycle (not sure that's even possible unless you purposely disconnected it and charged it separately with a reverse bias) you would actually see a 4v reduction as it would not only be failing to contribute it's own 2v but that reversed 2v would effectively cancel out 2v worth provided by one of the other cells.
I'm left to assume you've never actually experienced this for yourself. A reversed cell in a battery never reaches anything near full voltage. It adds to the internal resistance of the battery (the opposite of what would happen if the cell shorted out). It happens much faster than sulfation.
Normal lead-acid batteries are actually surprisingly resilient...
Car batteries aren't normal lead-acid batteries. They are designed to deliver and accept incredible amounts of current for short periods of time. The lead plates in each cell are much thinner, made of sponge lead, and have a lot more total surface area than plates in normal lead-acid batteries. A car battery can put out hundreds of amps, but because of these thin plates, you risk reversing a cell any time you discharge below 80%. Reverse a cell in a 12V battery and you suddenly have a 10V battery. Reverse another one and it's an 8V battery.
I'd bet that the reduced capacity of your batteries just became easily noticable after a few years.
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SEER is one incredibly botched measurement system, and I believe this statement is a direct cause of it.
The SEER numbers you see are usually about 10 to 15, however SEER is not an apples-to-apples comparison. It's BTUsOfCooling / WattHoursOfElectricityUsed. Half metric, half imperial. Who comes up with this stuff?
To turn BTUsOfCooling / WattHoursOfElectricityUsed into a sensible measurement like Cooling / ElectricityUsed, divide by 3.412.
So, a SEER of 13 becomes an efficiency ratio of 3.80. The reciprocal of 3.80 is .26, much closer to your '30% in practice' comment, so (assuming a SEER of 13) for every watt you bring into your datacenter, you need an extra .26 watts to bring it back out.
In those situations I would rather put an analog line-level balanced signal directly over the cat5, using whatever baluns and amplifiers I needed to accomplish that. It'd likely be cheaper, I wouldn't have to worry about latency or jitter, and as long as your amp's balanced inputs had common-mode rejection (pretty much all of them do) the twists in the cat5 would prevent picking up interference over long runs.
Very funny. Any roughly rectangular wing will stall from the inside out. It's only when the wing is tapered more strongly than an ellipse that you risk stalling at the tips first. To further minimize the risk of the tips stalling, the wingtips are usually angled down (washed out) a couple degrees (compared to the rest of the wing) or they incorporate a different airfoil at the tip that stalls a few degrees later.
What would happen if a single speaker went out? Would the plane go into an irrecoverable barrel roll?
You could easily prevent just one speaker from going out at a time by wiring opposing panels in series.
What would happen is the plane would revert to its old dynamics. The five degrees past normal stall AOA mentioned in the article would put you into a fairly deep stall, but if your plane was otherwise properly designed, you'd still have authoritative rudder control, certainly enough to keep any yaw momentum down until you can nose the plane over.
Also, stalls really aren't that big a deal if you know your ass from a hole in the ground.
Many pilots have stalled a wingtip on their landing approach by banking too tightly to make a turn, while trying to maintain altitude, while going too slowly for the wings to generate the extra lift required for that maneuver. Because one wing is already moving slower than the other, it generally puts you in a spin that you won't have altitude to recover from. You could say those pilots don't know their ass from a hole in the ground, but at that point it really is a matter of semantics.
Why are you, as a pilot of a certified aircraft, worried about new things, anyway? You might as well own a car in Cuba.
You're right!
A google search says the formula for theoretical dish gain is 20*log(7.4*FreqInGhz*DiameterInMeters). That matches some more google searching that says Arecibo (305 meters diameter) in Puerto Rico does about 70dB at those frequencies.
Solving for diameter in meters results in 563000000 meters, which is roughly the size of the moon's orbit.
Fast forward 50 years:
Colonist #1: "Woohoo! We're on Mars! For good! All seven of us!"
Colonist #2: "Sweet! Guess we can shut down all the heavy industries, energy generation, and resource extraction on the surface of Earth!"
Colonist #1: "What a great idea! Our kids won't even have to terraform it when they wanna go back!"
However, if you do it because you are a government-sanctioned monopoly with sole rights to do it (in some areas) and a government mandate to do it, and you do it partially with government money, partially with your monopoly status, then the situation changes. You can't maintain the 'privately-funded stuff' argument when your private corporation has had special legal status to be the only game in town for 100 years.
The phone companies are here to serve us. Not the other way around. The rules need to reflect that. Compare it to the power/water/sewer/postal monopolies and the government regulation needed to keep that common infrastructure working for us.
Is it unreasonable to expect headlines like "Local ISPs across the country doomed"? Even if the press doesn't care about the ISPs, that's a lot of people who will probably be out of work soon, and employment trends generally are something the press cares about.
I hate this ruling for several reasons:
I think that the press is slowly starting to pick that up, thanks in part to organizations such as the Consumers Union. I hope the FCC is forced to reconsider. If they don't, I hope the local ISPs take the initiative to build some new infrastructure of their own (and I hope it's something so clearly better that it's not just an expensive mess).
I find it incredible that no one has mentioned in this discussion the fact that that availability metric does not apply to your land line.
That's the fabled gold standard of reliability they need from their equipment to be able to promise you a completely different availability metric for their network. Network, as in, after your call makes it to the phone switch at the CO, that's the chance of the call making it to the other parties' phone switch at their CO.
For example, Verizon only claims 99.99% network availability.
In fact, the article we're discussing only pegged a land line's availability at 99.9%.
Only when that decision chooses to recognize the highest law in the land at the expense of regular legislation.
Congress passes and the states ratify constitutional amendments. The amended constitution takes precedence over law, as well as judicial opinions concerning that law or the previous constitution. Federal courts interpret the amended constitution.
Congress legislates federal law. The law takes precedence over old judicial opinions concerning that law. Federal courts interpret the new law.
Two levels of law, but other than one being very difficult to modify, they both work the same way. Federal courts refer to 'direction from Congress' all the time. It still seems to me that as a group, our justices strongly prefer such direction over making their own decisions.
I'd imagine the reason you feel that the SCOTUS does not have the same checks and balances is because Congress has been too cowardly to make the most controversial decisions on their own. Someone else mentioned abortion - can you imagine the trouble a representative would have getting reelected if he/she proposed a bill either for or against abortion?
Only a few hundred miles of a New York<->Tokyo path is over US soil, at least if you divert ever so slightly north of Alaska. Most of it is uninhabited areas of Canada, the Arctic Ocean, and Siberia.
Google searching for 'great circle route' provides a better illustration.
I figured it was more a metaphor for jwz as a really sorry leaky houseguest.
Here's another approach: put Linux on a CompactFlash card instead of a hard drive. Keep the filesystem mounted read-only for normal operation. Test upgrades on a different computer and CF card. Upgrade by swapping out CF cards. If you can build a PC that doesn't need fans, then you've removed all moving parts from the equation. For smaller installations, single-board computers such as the Soekris are very reliable. For larger installations, you can usually find a 1U system with the level of performance you need.
It was always just so much simpler to get a more expensive Cisco box in the long run due to its design, documentation, an performance.
It always depends on what you're doing, of course, and also what you're familiar with, but for my routing/firewalling/VPN/load balancing/ etc needs I've simply found Linux to be more flexible.
Maximum efficiency is a 15:1 mixture, maximum power is more like 12:1.
So you'd only see a simultaneous increase in both power and efficiency if you happened to start with a richer-than-12:1 mixture.
With IPv6, ISP's will route /48's to any customer, even lowly ppp dialup users. A /48 is 2^80 (1208925819614629174706176) IPs.
Good luck!
I don't know how Cisco has their stuff set up, but it's easy to imagine such a breach playing out:
While an attacker would need a fairly deep understanding of the software infrastructure he is attacking and of the usage habits of the users there to pull this off, the same basic strategy is applicable to UNIX, Windows, anything. I remember reading several years ago that the breakins at Exodus and VA Linux happened this way.
We're only used to the stuff we hear about not doing any real damage, because it's all dumb worms running without anyone at the controls. Just because we can fend off that stuff doesn't mean that someone with determination, knowledge, and patience won't get in and stay in.
If you're receiving FM radio on your speakers without an actual radio attached, it's probably due to interference from another radio receiver (not necessarily a radio transmitter) nearby.
Almost all tunable radio receivers since the 1920's have been built around a principle called superheterodyning - reducing and tuning the received signal by mixing it with another signal.
This process causes the receiver to weakly transmit the received signal at a lower frequency (FM broadcast receivers have standardized on 10.7 MHz, AM broadcast receivers have standardized on 455kHz). Poorly-built receivers can retransmit with a signal that can be picked up with hundreds or thousands of feet away.
Any circuit with an inductor, a capacitor, a diode, and audio outputs (such as your phone and speakers) will act as an AM crystal radio, which is all you need to pick up such a retransmission.
The radio stations you hear as interference reflect the demographics of those who own shoddy radios.
The cells drain unequally but charge equally, meaning you will overcharge the cells you don't use, and likely you'll never fully charge the cells you do use. The pack will die more quickly. (For this reason, even with conventional designs, some people who assemble battery packs will put in the effort to sort cells by their tested capacity and match them.)
Other issues are that you only get the available power from the cells you use, and you have differing ground potentials between equipment.
Oh, and lead-acid batteries are nominally 2.0 volts per cell, not 1.5 volts.
I can't tell if you read my earlier post, so to repeat: In this context he was paying a debt.
In this context he was paying a debt. While Best Buy still has the option to refuse the payment tendered, they can't legally make him pay in some other form. For Best Buy, it's take it or leave it.
That's why currency reads "this note is legal tender for all debts, public and private."
What kind of flywheels are people talking about putting in cars that are three feet in diameter? Flywheel energy goes up linearly with mass but squarely with rotational speed, which is why people talk about spinning them at 100000rpm and making them out of carbon fiber.
It is possible (granted, often not practical) to negate this by either using two counterrotating flywheels, or mounting the flywheel in gimbals like a gyroscope.
This number sounds low. While it wouldn't surprise me if there are plants still operating at that efficiency level, you can get 45-50% efficiency with external combustion Ranking cycle steam turbines, and up to 60% efficiency with the new Kalina cycle designs.
I don't think it's particularly helpful to compare old power plants to new cars, at least when we are debating what the masses should do.
You need to examine what is known as 'well to wheel' efficiency to make a rational comparison
Absolutely. One also should factor in the resources used to manufacture the equipment or infrastructure. Arguably the best way for us non-omniscient mortals to estimate that is by looking at the price tag.
overall I think you'll find there is very little in it.
Almost all efficiency gains these days come from evolutionary rather than revolutionary improvements, but they certainly add up.
The thing is, I can't trust you regarding your apparent conclusion that it's OK to use car batteries for UPS applications, because not only do your experiences differ from mine, but they also contradict just about everything I've read.
I'm left to assume you've never actually experienced this for yourself. A reversed cell in a battery never reaches anything near full voltage. It adds to the internal resistance of the battery (the opposite of what would happen if the cell shorted out). It happens much faster than sulfation.
Car batteries aren't normal lead-acid batteries. They are designed to deliver and accept incredible amounts of current for short periods of time. The lead plates in each cell are much thinner, made of sponge lead, and have a lot more total surface area than plates in normal lead-acid batteries. A car battery can put out hundreds of amps, but because of these thin plates, you risk reversing a cell any time you discharge below 80%. Reverse a cell in a 12V battery and you suddenly have a 10V battery. Reverse another one and it's an 8V battery.
I'd bet that the reduced capacity of your batteries just became easily noticable after a few years.