No. The abstract to their publication (Appl Phys Lett 85 145) begins:
We demonstrate a single-walled carbon nanotube p-n junction diode device. The p-n junction is formed along a single nanotube by electrostatic doping using a pair of split gate electrodes. By biasing the two gates accordingly, the device can function either as a diode or as an ambipolar field-effect transistor.
They "discovered" that nature behaves in a certain way. How is it not a "discovery"? You can't call it an "invention" because it's not like they're designing these particles before creating them.
Normally I am not so pedantic but the poster repeatedly misrepresented what is happening in entanglement. 4 times in the post it was said that the particles teleport or communicate, they don't.
The headline on the cover of this weeks Nature reads "Quantum Teleportation with Atoms". What was observed is known in the field as quantum teleportation. While you may dislike this term, the poster was by no means misrepresenting the content of the research.
As the other reply mentioned, part of the time error that must be corrected is from time dilation due to gravitational redshift. This is a general relativistic effect. The other part, as you suggested, is due to time dilation from the satellite's velocity. This is a special relativistic effect. IIRC, these effects contribute by an approximately equal ammount.
It's a finer line in the case of a math book though since the 'raw' text is written in a markup language called LaTeX that is essentally a programming language. You can write functions, scripts with if-then switches, etc. It's an intriguing question!
Thanks for an interesting review! The economics of college textbooks are indeed a bit nuts, and the development of free (and especially libre) courseware is exciting. I gotta say though, if there's any course for which I think it's worth plunking down cash for a nice, well-bound, colour-printed book, it'd have to be first-year calculus. In particular I'm thinking of Stewart.
Another comment - most of these books seem to cover single-variable only - if you're going to need it eventually (as i did, being a physicist), i really think it's helpful to have vector analysis/differentiation/integration covered in the same book in a unified presentation. Again I'm thinking Stewart here.
I have read a dead-tree "calculus in order of historcal development" book before and it was a bit sticky but it was intended for more advanced maths or history-of-maths students... maybe that was the intended audience of the Shchepin book?
You can do all kinds of cool things! At my old university we taught a second year physics laboratory in which the students measured the johnson noise temperature of a resistor using a low-noise amplifier plugged into the mic port of the old imacs in the lab. The amplifier transfer functions were determined by feeding the LNA's white noise from the headphone jack! I thought it was such a cool idea to use the sound card in this way.
Sure, the fact that they were approved doesn't mean anything on its own. But before they were approved, extensive studies were conducted to test for side-effects. None were found. It's not just that the side-effects were found to be tolerable; it's that they were found to be nonexistent. All the data from these studies would still be available, so if there were health risks associated with low-frequency magnetic fields, they would already be well-known.
As I said before this is just what I have been told - I have no references and should probably stop gossiping now ; )
mobile phones operate at frequencies many millions of times higher than the fields used in this study. cellular damage from exposure to low-frequency fields (if real) would surely be mediated by a different effect than cellular damage from exposure to high-frequency fields (if real).
i am skeptical of this study because a friend of mine who works in biomagnetics assures me that the effects of high B-fields on human tissue were carefully invesigated prior to the approval of MRI macines for use in biomedical imaging. any ill effects due to low-frequency or DC fields would have been found at that time. of course this is just hearsay and i am not qualified (or inclined) to assess this particular study on it's scientific merit! : )
This makes me wonder...the range of green is something like 480-520 nanometers, so since the laser beam is green, wouldn't that mean that that is the approximate wavelength of this beam?
Most high-powered green lasers make green light by doubling the 1064 nm light produced by a diode-pumped Nd:YAG laser. So it's probably 532nm - it certainly looks like it. Google confirms that doubled Nd:YAG is indeed a popular laser source for LIDAR applications. The experiment also uses IR light, so you can conveniently use the infrared pump as the source for that part of the experiment. Another group has done something similar, albeit at somewhat lower powers (i estimated in another comment that the Ball system uses about 200 W (average) of green, while the experiment i linked to uses about 10W of green).
~200 W of green light is far, far more than powerful enough to see the backscattered light with the naked eye. Even in a relatively clean laboratory, a 1 W green beam produces enough light to easily see the beam path, along with bright 'flashes' whenever a largish dust particle drifts through. Remember that green laser light is right in the 'sweet spot' as far as human vision is concerned, which is why green laser pointers look so much brighter for the same power.
I also wonder if this laser is powerfull enough to fry a bird.
The article says it's "about 40,000 times more powerful than a laser pointer", and 40k*5mW=200 watts. Since the beam diameter is "the size of a basketball hoop", nothing would be bursting into flames, although serious eye damage - to birds or pilots - could result.
Although come to think of it, for a LIDAR application I guess the beam is probably pulsed, so the situation is a bit more complicated. At any rate there's a safety shutoff mechanism as someone else pointed out.
Here in Australia mobile service is something like 40c/minute, 1 minute minimum, and SMS's are 20c apeice. That's the main reason. And once you get used to it you realise that it's a lot more convenient for certain types of messages. And you can bulk send them to heaps of people at once. There are lots of reasons.
Secondly, who decided that Anti-abortion, Pro-nazi propaganda is offensive?
Um, the people of France?
Are the french people that weak that their government decides whats offensive to them?
Nope. The French people decided for themselves, as a society, that nazi propaganda should be illegal. Good for them!
I happen to find pro-abortion sites offensive, but I don't rally for google to block those sites from their index!
Well, maybe you'd feel differently if the websites in question were actively promoting the asassination of 'pro-life' activists, giving their names and adresses and photos with crosshairs on them and so on. Most likely that's the sort of thing we're talking about here.
I often reread Feynman's autobiographical stuff for inspiration when an experiment is driving me nuts. For an illuminating look at the foundations of physics I'd recommend his _The Character of Physical Law_ (my favorite bit is where he says that although we used to think that the planets were held in place by angels pushing them out away from the sun, nowadays we know better - the angels, in fact, push _in_).
I'd recommend AVOIDING gee-whiz quantum mechanics pop science books. Sorry to all the Gribbin fans out there, but it took me the first 3 years of my degree to finally shake off some rather unhelpful ideas I'd gotten from "Schroedinger's kittens".
If you want to learn "serious" physics, especially quantum mechanics, in a meaningful way, there will be some maths involed. Serway and especially Tipler seem so make this less unpleasant than most. If you have a semi-solid maths background already, the first few chapters of _Quantum Mechanics_ by Townsend will show you how quantum mechanics actually WORKS, without any wavefunction messiness, and without any hocus-pocus. It does require basic vector calculus and linear algebra to about first-year university level, but such is the nature of the subject.
Slashdot Mirror
It's a device.
Doubtful.
They "discovered" that nature behaves in a certain way. How is it not a "discovery"? You can't call it an "invention" because it's not like they're designing these particles before creating them.
It's a bound state of two quarks. The charm quark is "heavy", i.e. relatively massive, while the the strange quark is less so.
The headline on the cover of this weeks Nature reads "Quantum Teleportation with Atoms". What was observed is known in the field as quantum teleportation. While you may dislike this term, the poster was by no means misrepresenting the content of the research.
As the other reply mentioned, part of the time error that must be corrected is from time dilation due to gravitational redshift. This is a general relativistic effect. The other part, as you suggested, is due to time dilation from the satellite's velocity. This is a special relativistic effect. IIRC, these effects contribute by an approximately equal ammount.
It's a finer line in the case of a math book though since the 'raw' text is written in a markup language called LaTeX that is essentally a programming language. You can write functions, scripts with if-then switches, etc. It's an intriguing question!
Thanks for an interesting review! The economics of college textbooks are indeed a bit nuts, and the development of free (and especially libre) courseware is exciting. I gotta say though, if there's any course for which I think it's worth plunking down cash for a nice, well-bound, colour-printed book, it'd have to be first-year calculus. In particular I'm thinking of Stewart.
Another comment - most of these books seem to cover single-variable only - if you're going to need it eventually (as i did, being a physicist), i really think it's helpful to have vector analysis/differentiation/integration covered in the same book in a unified presentation. Again I'm thinking Stewart here.
I have read a dead-tree "calculus in order of historcal development" book before and it was a bit sticky but it was intended for more advanced maths or history-of-maths students... maybe that was the intended audience of the Shchepin book?
er... so C and assembler are simple and self-explanatory? well, if you say so.... : )
You can do all kinds of cool things! At my old university we taught a second year physics laboratory in which the students measured the johnson noise temperature of a resistor using a low-noise amplifier plugged into the mic port of the old imacs in the lab. The amplifier transfer functions were determined by feeding the LNA's white noise from the headphone jack! I thought it was such a cool idea to use the sound card in this way.
he doesn't seem to be going for height, but for tricks. looks like there's a lot of compression left in that thing...
Sure, the fact that they were approved doesn't mean anything on its own. But before they were approved, extensive studies were conducted to test for side-effects. None were found. It's not just that the side-effects were found to be tolerable; it's that they were found to be nonexistent. All the data from these studies would still be available, so if there were health risks associated with low-frequency magnetic fields, they would already be well-known.
As I said before this is just what I have been told - I have no references and should probably stop gossiping now ; )
mobile phones operate at frequencies many millions of times higher than the fields used in this study. cellular damage from exposure to low-frequency fields (if real) would surely be mediated by a different effect than cellular damage from exposure to high-frequency fields (if real).
i am skeptical of this study because a friend of mine who works in biomagnetics assures me that the effects of high B-fields on human tissue were carefully invesigated prior to the approval of MRI macines for use in biomedical imaging. any ill effects due to low-frequency or DC fields would have been found at that time. of course this is just hearsay and i am not qualified (or inclined) to assess this particular study on it's scientific merit! : )
According to reverse dns, 24.86.121.228 belongs to Canadian cable tv/broadband provider Shaw Communications.
Most high-powered green lasers make green light by doubling the 1064 nm light produced by a diode-pumped Nd:YAG laser. So it's probably 532nm - it certainly looks like it. Google confirms that doubled Nd:YAG is indeed a popular laser source for LIDAR applications. The experiment also uses IR light, so you can conveniently use the infrared pump as the source for that part of the experiment. Another group has done something similar, albeit at somewhat lower powers (i estimated in another comment that the Ball system uses about 200 W (average) of green, while the experiment i linked to uses about 10W of green).
~200 W of green light is far, far more than powerful enough to see the backscattered light with the naked eye. Even in a relatively clean laboratory, a 1 W green beam produces enough light to easily see the beam path, along with bright 'flashes' whenever a largish dust particle drifts through. Remember that green laser light is right in the 'sweet spot' as far as human vision is concerned, which is why green laser pointers look so much brighter for the same power.
Actually (from the project info page):
Ball will provide an active sensor that probes the atmosphere with green and infrared laser light
They're using IR (almost certainly 1064 nm) and green (almost certainly 532 nm) beams.
Yep, it's just a normal laser, the light you see is due to scattering from dust in the atmosphere.
The article says it's "about 40,000 times more powerful than a laser pointer", and 40k*5mW=200 watts. Since the beam diameter is "the size of a basketball hoop", nothing would be bursting into flames, although serious eye damage - to birds or pilots - could result.
Although come to think of it, for a LIDAR application I guess the beam is probably pulsed, so the situation is a bit more complicated. At any rate there's a safety shutoff mechanism as someone else pointed out.
Now that I'm at work (=> broadband) I have, and you're right, it's nothing if not an 'animated comic'. I stand corrected.
...'cinematic literature' format (think animated comic).
I remember back in the day when we used to call these 'cartoons'. Maybe we should all read a little less of Wired magazine?
Wake me up when the POGO STICK to the south pole expedition gets under way.
Here in Australia mobile service is something like 40c/minute, 1 minute minimum, and SMS's are 20c apeice. That's the main reason. And once you get used to it you realise that it's a lot more convenient for certain types of messages. And you can bulk send them to heaps of people at once. There are lots of reasons.
You have 30 Moderator Points! Use 'em or lose 'em!
... but they expire on October 24th !?!?! And my karma is way up on brak as well - i likes :D
I see the same thing
Secondly, who decided that Anti-abortion, Pro-nazi propaganda is offensive?
Um, the people of France?
Are the french people that weak that their government decides whats offensive to them?
Nope. The French people decided for themselves, as a society, that nazi propaganda should be illegal.
Good for them!
I happen to find pro-abortion sites offensive, but I don't rally for google to block those sites from their index!
Well, maybe you'd feel differently if the websites in question were actively promoting the asassination of 'pro-life' activists, giving their names and adresses and photos with crosshairs on them and so on. Most likely that's the sort of thing we're talking about here.
I often reread Feynman's autobiographical stuff for inspiration when an experiment is driving me nuts. For an illuminating look at the foundations of physics I'd recommend his _The Character of Physical Law_ (my favorite bit is where he says that although we used to think that the planets were held in place by angels pushing them out away from the sun, nowadays we know better - the angels, in fact, push _in_).
I'd recommend AVOIDING gee-whiz quantum mechanics pop science books. Sorry to all the Gribbin fans out there, but it took me the first 3 years of my degree to finally shake off some rather unhelpful ideas I'd gotten from "Schroedinger's kittens".
If you want to learn "serious" physics, especially quantum mechanics, in a meaningful way, there will be some maths involed. Serway and especially Tipler seem so make this less unpleasant than most. If you have a semi-solid maths background already, the first few chapters of _Quantum Mechanics_ by Townsend will show you how quantum mechanics actually WORKS, without any wavefunction messiness, and without any hocus-pocus. It does require basic vector calculus and linear algebra to about first-year university level, but such is the nature of the subject.