How efficient is a power generation plant that throws away gigawatts of power as waste heat?
From the heat source to electrical power output is usually in the range 35--50%, depending on the plant design. A fundamental problem is the theoretical limit of the efficiency of a heat engine, a device that converts a temperature difference into mechanical power. It is 1 - Tcold/Thot, where Tcold and Thot are the temperatures of the cold and hot parts, in kelvin. For a steam-operated heat engine, the cold end is around the boiling point of water (373 K), and the hot end might be 1000 K, which limits the efficiency to 63% if there are no other losses. But one can use the waste heat for other purposes in a cogeneration plant, for example for residential heating in cold climates or for the industry.
he was a top student in elementary school (Rosenkranz 2005, p. 29).... ...introduced the ten-year-old Albert to key science and philosophy texts, including Kant's Critique of Pure Reason and Euclid's Elements (Einstein called it the "holy little geometry book").[7] From Euclid, Albert began to understand deductive reasoning (integral to theoretical physics), and by the age of twelve, he learned Euclidean geometry from a school booklet. Soon thereafter he began to investigate calculus. ... when Einstein was fifteen [...] Albert wrote his first scientific work, "The Investigation of the State of Aether in Magnetic Fields".[8]
But then you say:
It does somewhat dent the conclusion when one notes that the stories are certainly exaggerated, if not outright untrue
I don't see how this conclusion is at all possible based on Einstein's youth.
... However if you look into the details, you'll see that the pulse is made up of photons with a variety of arrival times. All the photons are traveling at light-speed. At the beginning, the peak of the pulse envelope is, say, in the center of the distribution of photons...
Your terminology is very confusing - or confused. "Made up of photons"??? A photon is a delocalized excitation of the electromagnetic field, and not some kind of classical particle. What I suspect that you are trying to say has nothing to do with the quantum-mechanical nature of light: a wave packet that is subject to dispersion undergoes distortion during propagation. This distortion might be such that the the peak of the wave packet travels slightly faster than light, but it is the leading edge (where it starts to deviate from zero) of the wave packet that counts rather than the peak, and that leading edge will never travel faster than light.
It seems more was (audibly) lost on the digital to analogue conversion by the old DAC than was by discarding 3/4 of the data.
Indeed. I've always been told that the earliest cd players had 14-bit DACs because the 16-bit ones were too expensive. Some even had just one DAC that was interleaving the left and right channel. Also, they didn't have the advanced oversampling that the players have nowadays. There is quite a lot of digital signal processing in modern DACs to ensure that all the intended spectral content below 20 kHz is still there, while all the noise above 22 kHz (half of the sampling rate) is filtered out. I remember that the more expensive CD players in 1989 were advertised with "4x oversampling". That's 5 years after the introduction. It wouldn't surprise me if the first CD players didn't do any oversampling, but rather sent the "staircase" electrical signal through a simple analog lowpass filter, with likely audible distortions as a result.
I don't have stats, but in Amsterdam we consider tourists on rental bikes to be rather dangerous.:) I've lost balance at high speed (30+ km/h) a couple of times and once had a collision with a car that launched my body across the street. All times without even touching my heads and just a few scratches and bruises. The trick is to convert the momentum into a rolling motion rather than trying to absorb it with your arms. I developed reflexes for falling in the judo martial arts lessons I had as a kid. It probably wouldn't help me in a frontal collision with a car or, worse, SUV.
Supposedly because when you fall sideways and slide with your head over the ground, with a helmet -- especially the fancy ones with ventilation holes everywhere -- there's a fair chance that the helmet catches something and forces your head to turn faster than the brain tissue can follow.
could a contact lens work? If it blocks the light via absorption, then you've just moved the hot-spot from the retina to the cornea.
The difference is that on the retina it will be a 10x10 micrometer spot (worst case), while at the cornea it is 5x5 mm. That's a 250-thousand-fold increase in intensity. It will still heat up, but you'll probably blink from the bit that passes through before it burns. A problem is that there aren't many dyes that absorb within a very narrow band around 650 nm (or whatever it is) while letting everything else pass through. Laser safety eyewear for that wavelength range typically has a deep blue-green color. See e.g. here: http://www.noirlaser.com/filters/rb2.html .
Damage occurs that quickly? Hmm... most people tell me I couldn't possibly have this little blind spot in my right eye, where I got caught by a supermarket scanning laser.
See my other post. The damage time scales very nonlinearly with the power of the laser. A barcode reader is no more than a few mW and because the beam is moving all the time you wouldn't be exposed to more than a couple of microseconds at a time anyway. Unless of course you managed to stop the rotating mirrors without shutting down the laser.
I don't think it scales like that (or even linearly).
I just put the MPE numbers on Wikipedia. I assumed that the pupil is 0.5 cm2, so for 500 mW/cm2 versus 50 mW/cm2 you can read from the plots that these are the MPEs for 1 and 10 microseconds. Actually, between 1 ns and 10 microseconds, the MPE is 50 nJ regardless of the duration. For shorter times, nonlinear effects kick in, such as two-photon absorption, while for longer exposure times, heat diffusion in the retina will limit the temperature increase.
Personally I'd say the danger is somewhat exagerated. I have looked into red keyring laser pointers plenty of times with no ill effects. A seconds exposure from that kind of a laser will not harm you in any way.
So did I, to be honest, although never several seconds. But: at 1 mW (visible light), the MPE (maximum permissible exposure) is about 1 second. The MPE represents the largest exposure which under worst-case circumstances does not lead to eye injury for 90% of the population. Worst case means that the eye and the laser source are stationary over the given exposure time, and that the eye lens is focused such that the laser light is concentrated onto the smallest possible spot size on the retina. If the eye lens is a bit out of focus, resulting in a blurry spot, you have some extra margin. I think the MPE values take into account that the eye is never completely motionless.
Yes. But the main problem is that you need some way to limit the electric current through the diode. Laser diodes behave a bit like LEDs, electrically: below a threshold (2.5 V or so) there is little current and they don't do much, and above that threshold, every 0.1 V you add will increase the current and light output enormously. Too much current and the diode will die in a matter of seconds. Apparently the laser diode he used was just right at 3 V from two penlites, although I doubt that he had a calibrated laser power meter to measure whether the output power matched the nominal power rating for the diode. The simplest way to limit the current is to use a higher voltage and a series resistor. Something else is that the laser assembly in different optical writers sometimes doesn't have the collimating lens attached to the laser diode itself: without lens a laser diode produces a very divergent beam.
Now for safety: I work with fairly high-power lasers (up to 25 W) for a living and consider a hand-held 250 mW laser in the hands of someone without appropriate training in laser safety hugely irresponsible. According to the IEC60825 standard on laser safety, 200 mW will lead to permament eye damage within 1 microsecond (!) of exposure. The reason laser pointers are restricted to 1 or 5 mW (depending on the country) is that for those powers, eye damage will occur after 0.3 seconds, which is about the time for the blinking reflex to close your eyes in the event of accidental exposure. Unexpected reflections from things like glass can be up to 10% of the beam power - 20 mW (eye damage in 10 microseconds).
If I get 11Mb/s total (I do, 10Mb/s down and 1Mb/s up), let me adjust the caps myself. If I want 5.5/5.5, or 9/2, let me have it.
There's a technological reason that ADSL is asymmetric. The signal strength decreases with distance from the transmitter, and at the receiving end, the signal must be above the background noise. Up to here the problem is symmetric. However, at the customer side, there's only one wire to deal with, while at the network side, there are hundreds of wires from all customers close to each other, together with all the other equipment, so the background noise level is much higher on the network side. Hence, if you give up 1 Mb/s down, you won't be able to trade it for a full 1 Mb/s up, but less, although I'm not sure exactly how much. I assume that a similar principle affects cable internet.
Colour is a faster and arguably more intuitive way of ranking something,
Well, for me it took a while before I had figured out what the color scale was representing. I'd prefer numbers or a bar that can be filled from 0 to 100%. And I'm not colorblind.
If you have a solid immovable floor the energy you impart onto the surface through friction gets dissipated as heat (slight bending of the material, compacting of the earth...)
No. At normal walking speed, relatively little energy is wasted since the point of gravity of the walker does not go up and down a lot and the legs swing back and forth as a pendulum, close to their natural frequency. When you're running, energy is indeed dissipated, but it happens in the leg muscles each time they pull the legs to make them change direction from backwards to forwards and vice versa. In those cases, the force of the muscle is opposite to the direction of the movement, which means that mechanically, the muscle performs negative work. Unfortunately, negative work by a muscle does not convert CO2 and water back into glucose, so the energy is really wasted.
That's why animals that are good at running, such as horses, have thin lower legs that carry less kinetic energy during running.
Hmm, the screens are Samsung 460p with MagicNet support. Apparently, it's possible to upload images or powerpoint files to these screens. It doesn't make sense why they would display a Windows error message, though.
It would be nice for airport displays. A single server can drive all displays and no restrictions on video cable lengths. Apparently, it currently is one server, one video card per display. But maybe I'm mistaken.
Cellulose and Ligno-cellulose is desinged by trees to be indigestible and energetically inaccessible. If it were easy to digest the bacteria and termites would have eaten the whole forest a long time ago.
I think that has more to do with natural predators and lack of other conditions. In a humid climate like Netherlands, everything made out of wood will disintegrate in a few years unless protected by paint or made of tropical hardwood. Grind the wood, supply the right amount of oxygen and moisture, and fungi will eat it within a fraction of the time. That's incidentally how oyster mushrooms are grown commercially (on cellulose-rich straw).
The problem might be how to combine a (probably) aerobic decomposition process with anaerobic fermentation into ethanol. Yeast will only produce alcohol under anaerobic conditions. If the energy to break up cellulose is larger than could be obtained from anaerobic metabolizing of the resulting glucose units, then there is a fundamental problem.
Sample photos of IR and sunglasses and other materials... kaya-optics.com
That must be a hoax. Silicon-based sensors (like in all nonscientific cameras) work up to 1100 nm and no way that is going to pass through fabric without being scattered. The only exception might be very thin synthetic fabrics such as lycra that are basically transparent except for a black dye that is doesn't absorb near-IR. For example, cotton fibers are, like sugar, transparent to visible light, but because there are so many of them, it appears white. At least, until you fill the air gaps between the fibers with water as in a wet T-shirt contest.;-)
Just to check, I just tried walking around in the lab with a special IR camera (up to 1400 nm) with an IR filter in front and indeed no way it will see through t-shirts.:-)
Or decrease your battery time since FLAC uses less processing power than most, if not all, lossy decoders.
... if true, it is more than compensated by the fact that the hard disk has to spin up much more often at lossless (700 kbps) bitrates than at 128-ish bitrates.
Is it that the razor blade companies change the form factors fast enough that patents protect the properly-fitting blades until they're irrelevant?
Exactly. A patent can be extended for some 17 years, and a couple of patents on the system which clicks the blades to the holder will ensure that competitors can't legally make compatible blades.
it will only require one.. a method for freezing water that doesn't cause it to expand.
It already exists. Cooling water to 250 K (-23 C) at 3000 bars will do the job. Unfortunately, the pressure rather than the ice crystals will kill a human being at that type of pressure.
3. Can I obfuscate my code (e.g. encode it)?
Isn't compiling it enough? You can strip the compiled code or debugging symbols if you really want, but you only hurt your own ability to debug your users problems.
I suppose obfuscation serves a purpose if it is about handling license keys. You don't want to make it too easy for a cracker to overwrite a single subroutine call to check_license() with NOP instructions. But it is rather unclear what he's thinking of with the term 'obfuscate'.
He just needs to know enough techno-babble to convince the patent reviewer that he can invent one (and often he doesn't even need that). Then he can sit on the patent and wait for someone else to do something similar (and make money off it), and sue the pants off the actual inventor.
The first half is unfortunately correct. But the patent can be invalidated even after being granted if it becomes clear that the patent description was lacking essential information. Although that is also theory...
At a bare minimum, a patent application should require a functional prototype.
According to the rules, the patent application should contain enough information for someone skilled in the art to build the device or whatever it is that is patented.
One of the nice things of the patent system is that an inventor can freely talk to investors in order to build the prototype without risking that the idea is stolen and commercially exploited by someone else.
Slashdot Mirror
From the heat source to electrical power output is usually in the range 35--50%, depending on the plant design. A fundamental problem is the theoretical limit of the efficiency of a heat engine, a device that converts a temperature difference into mechanical power. It is 1 - Tcold/Thot, where Tcold and Thot are the temperatures of the cold and hot parts, in kelvin. For a steam-operated heat engine, the cold end is around the boiling point of water (373 K), and the hot end might be 1000 K, which limits the efficiency to 63% if there are no other losses. But one can use the waste heat for other purposes in a cogeneration plant, for example for residential heating in cold climates or for the industry.
From Wikipedia:
But then you say: I don't see how this conclusion is at all possible based on Einstein's youth.If you had RTFA, you would have noticed the link to Portable Application Description.
Your terminology is very confusing - or confused. "Made up of photons"??? A photon is a delocalized excitation of the electromagnetic field, and not some kind of classical particle. What I suspect that you are trying to say has nothing to do with the quantum-mechanical nature of light: a wave packet that is subject to dispersion undergoes distortion during propagation. This distortion might be such that the the peak of the wave packet travels slightly faster than light, but it is the leading edge (where it starts to deviate from zero) of the wave packet that counts rather than the peak, and that leading edge will never travel faster than light.
Indeed. I've always been told that the earliest cd players had 14-bit DACs because the 16-bit ones were too expensive. Some even had just one DAC that was interleaving the left and right channel. Also, they didn't have the advanced oversampling that the players have nowadays. There is quite a lot of digital signal processing in modern DACs to ensure that all the intended spectral content below 20 kHz is still there, while all the noise above 22 kHz (half of the sampling rate) is filtered out. I remember that the more expensive CD players in 1989 were advertised with "4x oversampling". That's 5 years after the introduction. It wouldn't surprise me if the first CD players didn't do any oversampling, but rather sent the "staircase" electrical signal through a simple analog lowpass filter, with likely audible distortions as a result.
I don't have stats, but in Amsterdam we consider tourists on rental bikes to be rather dangerous. :) I've lost balance at high speed (30+ km/h) a couple of times and once had a collision with a car that launched my body across the street. All times without even touching my heads and just a few scratches and bruises. The trick is to convert the momentum into a rolling motion rather than trying to absorb it with your arms. I developed reflexes for falling in the judo martial arts lessons I had as a kid. It probably wouldn't help me in a frontal collision with a car or, worse, SUV.
See also Some links on bicycle helmet safety
Supposedly because when you fall sideways and slide with your head over the ground, with a helmet -- especially the fancy ones with ventilation holes everywhere -- there's a fair chance that the helmet catches something and forces your head to turn faster than the brain tissue can follow.
The difference is that on the retina it will be a 10x10 micrometer spot (worst case), while at the cornea it is 5x5 mm. That's a 250-thousand-fold increase in intensity. It will still heat up, but you'll probably blink from the bit that passes through before it burns. A problem is that there aren't many dyes that absorb within a very narrow band around 650 nm (or whatever it is) while letting everything else pass through. Laser safety eyewear for that wavelength range typically has a deep blue-green color. See e.g. here: http://www.noirlaser.com/filters/rb2.html .
See my other post. The damage time scales very nonlinearly with the power of the laser. A barcode reader is no more than a few mW and because the beam is moving all the time you wouldn't be exposed to more than a couple of microseconds at a time anyway. Unless of course you managed to stop the rotating mirrors without shutting down the laser.
I just put the MPE numbers on Wikipedia. I assumed that the pupil is 0.5 cm2, so for 500 mW/cm2 versus 50 mW/cm2 you can read from the plots that these are the MPEs for 1 and 10 microseconds. Actually, between 1 ns and 10 microseconds, the MPE is 50 nJ regardless of the duration. For shorter times, nonlinear effects kick in, such as two-photon absorption, while for longer exposure times, heat diffusion in the retina will limit the temperature increase.
So did I, to be honest, although never several seconds. But: at 1 mW (visible light), the MPE (maximum permissible exposure) is about 1 second. The MPE represents the largest exposure which under worst-case circumstances does not lead to eye injury for 90% of the population. Worst case means that the eye and the laser source are stationary over the given exposure time, and that the eye lens is focused such that the laser light is concentrated onto the smallest possible spot size on the retina. If the eye lens is a bit out of focus, resulting in a blurry spot, you have some extra margin. I think the MPE values take into account that the eye is never completely motionless.
Yes. But the main problem is that you need some way to limit the electric current through the diode. Laser diodes behave a bit like LEDs, electrically: below a threshold (2.5 V or so) there is little current and they don't do much, and above that threshold, every 0.1 V you add will increase the current and light output enormously. Too much current and the diode will die in a matter of seconds. Apparently the laser diode he used was just right at 3 V from two penlites, although I doubt that he had a calibrated laser power meter to measure whether the output power matched the nominal power rating for the diode. The simplest way to limit the current is to use a higher voltage and a series resistor. Something else is that the laser assembly in different optical writers sometimes doesn't have the collimating lens attached to the laser diode itself: without lens a laser diode produces a very divergent beam.
Now for safety: I work with fairly high-power lasers (up to 25 W) for a living and consider a hand-held 250 mW laser in the hands of someone without appropriate training in laser safety hugely irresponsible. According to the IEC60825 standard on laser safety, 200 mW will lead to permament eye damage within 1 microsecond (!) of exposure. The reason laser pointers are restricted to 1 or 5 mW (depending on the country) is that for those powers, eye damage will occur after 0.3 seconds, which is about the time for the blinking reflex to close your eyes in the event of accidental exposure. Unexpected reflections from things like glass can be up to 10% of the beam power - 20 mW (eye damage in 10 microseconds).
There's a technological reason that ADSL is asymmetric. The signal strength decreases with distance from the transmitter, and at the receiving end, the signal must be above the background noise. Up to here the problem is symmetric. However, at the customer side, there's only one wire to deal with, while at the network side, there are hundreds of wires from all customers close to each other, together with all the other equipment, so the background noise level is much higher on the network side. Hence, if you give up 1 Mb/s down, you won't be able to trade it for a full 1 Mb/s up, but less, although I'm not sure exactly how much. I assume that a similar principle affects cable internet.
Well, for me it took a while before I had figured out what the color scale was representing. I'd prefer numbers or a bar that can be filled from 0 to 100%. And I'm not colorblind.
No. At normal walking speed, relatively little energy is wasted since the point of gravity of the walker does not go up and down a lot and the legs swing back and forth as a pendulum, close to their natural frequency. When you're running, energy is indeed dissipated, but it happens in the leg muscles each time they pull the legs to make them change direction from backwards to forwards and vice versa. In those cases, the force of the muscle is opposite to the direction of the movement, which means that mechanically, the muscle performs negative work. Unfortunately, negative work by a muscle does not convert CO2 and water back into glucose, so the energy is really wasted.
That's why animals that are good at running, such as horses, have thin lower legs that carry less kinetic energy during running.
Hmm, the screens are Samsung 460p with MagicNet support. Apparently, it's possible to upload images or powerpoint files to these screens. It doesn't make sense why they would display a Windows error message, though.
It would be nice for airport displays. A single server can drive all displays and no restrictions on video cable lengths. Apparently, it currently is one server, one video card per display. But maybe I'm mistaken.
I think that has more to do with natural predators and lack of other conditions. In a humid climate like Netherlands, everything made out of wood will disintegrate in a few years unless protected by paint or made of tropical hardwood. Grind the wood, supply the right amount of oxygen and moisture, and fungi will eat it within a fraction of the time. That's incidentally how oyster mushrooms are grown commercially (on cellulose-rich straw).
The problem might be how to combine a (probably) aerobic decomposition process with anaerobic fermentation into ethanol. Yeast will only produce alcohol under anaerobic conditions. If the energy to break up cellulose is larger than could be obtained from anaerobic metabolizing of the resulting glucose units, then there is a fundamental problem.
That must be a hoax. Silicon-based sensors (like in all nonscientific cameras) work up to 1100 nm and no way that is going to pass through fabric without being scattered. The only exception might be very thin synthetic fabrics such as lycra that are basically transparent except for a black dye that is doesn't absorb near-IR. For example, cotton fibers are, like sugar, transparent to visible light, but because there are so many of them, it appears white. At least, until you fill the air gaps between the fibers with water as in a wet T-shirt contest. ;-)
Just to check, I just tried walking around in the lab with a special IR camera (up to 1400 nm) with an IR filter in front and indeed no way it will see through t-shirts. :-)
... if true, it is more than compensated by the fact that the hard disk has to spin up much more often at lossless (700 kbps) bitrates than at 128-ish bitrates.
Exactly. A patent can be extended for some 17 years, and a couple of patents on the system which clicks the blades to the holder will ensure that competitors can't legally make compatible blades.
It already exists. Cooling water to 250 K (-23 C) at 3000 bars will do the job. Unfortunately, the pressure rather than the ice crystals will kill a human being at that type of pressure.
I suppose obfuscation serves a purpose if it is about handling license keys. You don't want to make it too easy for a cracker to overwrite a single subroutine call to check_license() with NOP instructions. But it is rather unclear what he's thinking of with the term 'obfuscate'.
The first half is unfortunately correct. But the patent can be invalidated even after being granted if it becomes clear that the patent description was lacking essential information. Although that is also theory...
According to the rules, the patent application should contain enough information for someone skilled in the art to build the device or whatever it is that is patented.
One of the nice things of the patent system is that an inventor can freely talk to investors in order to build the prototype without risking that the idea is stolen and commercially exploited by someone else.