Speed isn't only determined by on-state resistance. Capacitance & inductance matter too and will be the limiting factors for a theoretical transistor that's 0 resistance on and infinite resistance off. Such a theoretical transistor won't dissipate heat, so it won't get hot. However, heat will be dissipated somewhere else because current still must flow from high potential to low potential. Furthermore, transition times aren't arbitrarily fast, and during the transition, the transistor will dissipate resistive power; this could be a big problem for systems cooled below 4 K.
There's no such thing as a universally tunable laser, or even an universal spectrometer, although it's easier to come close with the detection side of things...
Anyhow, the big problem is the laser. If you want an "universal surface sensor" you might want a laser that tunes from 500 micrometers to 200 nm. Fat chance. It's really annoying how these university press releases overhype the technology. You could use this technology to make a nice sensor that targets a specific set of molecules with well-defined spectral features, but forget about a single sensor that does everything.
if it's just down to detecting the frequency of the light emitted, couldn't some sort of photovoltaic or photoelectric sensor be designed so that you wouldn't have to chemically engineer receptors for different kinds of surfaces, but rather just program the software to identify the surface material?
This is clearly their intention. However, for a spectroscopic solution to work, they must have clear spectral features for their target species, they must have a laser that can cover all the possible frequencies of interest, and a detector that will detect all the relevant frequencies. So, if they combine a universal laser with a universal spectrometer, their universal surface sensor will be complete.
For some target materials, the problem of distinct and unique spectral features can be a big one. For things like bacteria, containing a multitude of molecules with similar spectral features but slightly different function, you end up with spectral soup. I believe that there are some spectral features that indicate that you have bacteria, and not some other generic background material, such as pollen. However, you then need to say that you have some nasty material, and not just the usual microbes that are everywhere. I don't know how you do that without chemical receptors. Finally, if the receptors rely on DNA, you need to do a bit of biochemistry to actually get to the DNA.
Explosives could work, since you're dealing with specific molecules. However, in many scenarios if you need to touch the sample you're too damn close.
Great. Now you need to explain why by accident vast quantities of the organic material hydrocarbons were converted to napthalene in sufficient quantity to be detected at a range of 400 lightyears, and then explain how this event is locally unique so that it didn't happen in every corner of the universe.
OK. I'll have a go at it.
The theory is that polycyclic aromatic hydrocarbons (PAHs) are end-of-the-food-chain survivors in the photochemistry that is thought to occur in certain types of nebulae where interstellar dust clouds are illuminated by hot stars. If a nearby star is hot enough, it's spectrum will extend deep into the UV, and it will generate a considerable flux of high energy photons. Some organic molecules will efficiently fluoresce when excited into specific states following absorption of UV photons within certain energy ranges. When these molecules fluoresce, most of the energy goes away. However, if fluorescence doesn't occur, all the energy from photon will eventually end up in the ground electronic state, heating the molecule vibrationally. In space, the molecules can only cool through IR radiation and this is slow. In many cases, the molecule will dissociate before it can cool through radiation of IR photons.
PAHs are unique because they are robust and large. Every carbon atom has multiple carbon-carbon bonds. Even if the photon energy is sufficient to break one or two of these bonds, the molecule won't fall apart. (If it looses an H atom, that's OK. It will find another one since hydrogen is the most abundant thing out there.)
Finally, these UV photons can also ionize these molecules, which is potentially a good thing for helping them grow. With the low densities in these clouds, random collisions are infrequent, and the charge can increase the cross-section leading to more collisions with uncharged species such as H, H2, and C2. It's been a while since I have studied this stuff, but there's probably at least one dissertation out there covering the balance between ion-molecule reaction rates leading to PAH formation and the photodissociation rates in nebulae with nearby hot stars.
So what's the bottom line?
on
Plane Simple Truth
·
· Score: 3, Interesting
What I want to know is how much fuel does it take to travel from San Francisco to New York City by the following methods: A modern plane A Prius A generic 6 cylinder sedan An Escalade Amtrak
Of course, the extra 4 days on the road really make me favor the plane, but I want to know how guilty I should feel.
That's why you need sharks to go with your lasers. You think you can defend yourself with mirrors, do you? Don't you know that sharks like to eat shiny things?
Horowitz and Hill is the best book on electronics that I know of. It does have some handy circuit examples that you can build, but don't think of it as an instruction book for a kit. If you read Horowitz and Hill, you will be ready to go out and design your own circuits.
Do you mean Video on Demand? Otherwise, you're also railing against how TV works. Well, actually, he's railing against how TV used to work before Tivo.
The parent comment is modded "funny," but it could equally be modded "informative." When an intense femtosecond pulse is focused into many materials, including water, nonlinear effects will lead to fillamentation and continuum generation. Here are some pictures from lasers with roughly an order of magnitude less power focused in air.
(I corrected a link. Please mod my previous comment down)
The parent comment is modded "funny," but it could equally be modded "informative." When an intense femtosecond pulse is focused into many materials, including water, nonlinear effects will lead to fillamentation and continuum generation. Here are some pictures from lasers with roughly an order of magnitude less power focussed in air.
If no Windows version is present on the hard disk, it asks you to briefly insert a disk of a qualifying version
Most consumers don't have a qualifying Windows install disk. They have the system restore CDs supplied by their OEM. Let's say you install Vista on one of these machines and later decide that you want to do a clean install or maybe the HD dies and you need to start fresh with a new HD. If they were to close this back-door they would have plenty of pissed off customers who cant install the upgrade that they legitimately purchased because it won't recognize the disks provided by the OEM.
I am also perplexed. I to am not an expert on relativity & cosmology, but I know a thing or two about nonlinear optics. An intense light field can modify the index of refraction of the medium through which it's propagating. This is known as the AC or optical Kerr effect. http://en.wikipedia.org/wiki/Kerr_effect/ The second light pulse will gradually encounter a higher index as it approaches the first pulse and therefore slow down. While I know nothing about Hawking radiation, it seems like gravity must be somehow involved, and this experiment is all about electromagnetic forces.
Does this make Christians better? I would argue that the Hindus have the most literal interpretation of the phrase "up in arms," but I don't have any problems with that.
The previous posters responding to this comment have correctly identified different elements of the problem. A high index is necessary, so that there are strong reflections from the facets. Furthermore, the large index helps generate large refractive angles when the diamond is cut correctly. A large dispersion is necessary in order to generate the rainbow effect when the light undergoes refraction.
However, the crystal structure alone does not guarantee these properties. Diamond, silicon, and germanium all share the came crystal structure. All are semiconductors. The reason why diamond is transparent is because the bandgap is above the energy of a visible photon. The crystal structure alone does not determine the electronic properties of a material and optical properties such as index of refraction and dispersion. There is no guarantee that a material with this hypothetical crystal structure would be transparent at visible wavelengths. If it is transparent, there is no guarantee that it would have a large diffractive index and high dispersion.
If you're a US citizen, you paid for this research. If you want to read the article, you need to pay the copyright holder.
If you're a scientist, it's even worse. You might also be asked to referee the article before it's published, for no compensation and on your own time. If you want to see the final product, you still have to pay the copyright holder.
Slashdot Mirror
Speed isn't only determined by on-state resistance. Capacitance & inductance matter too and will be the limiting factors for a theoretical transistor that's 0 resistance on and infinite resistance off. Such a theoretical transistor won't dissipate heat, so it won't get hot. However, heat will be dissipated somewhere else because current still must flow from high potential to low potential. Furthermore, transition times aren't arbitrarily fast, and during the transition, the transistor will dissipate resistive power; this could be a big problem for systems cooled below 4 K.
Adobe is one of the best when it comes to cross-platform compatibility and the hole is based on Javascript...
And yes, I did RTFA.
There's no such thing as a universally tunable laser, or even an universal spectrometer, although it's easier to come close with the detection side of things...
Anyhow, the big problem is the laser. If you want an "universal surface sensor" you might want a laser that tunes from 500 micrometers to 200 nm. Fat chance. It's really annoying how these university press releases overhype the technology. You could use this technology to make a nice sensor that targets a specific set of molecules with well-defined spectral features, but forget about a single sensor that does everything.
This is clearly their intention. However, for a spectroscopic solution to work, they must have clear spectral features for their target species, they must have a laser that can cover all the possible frequencies of interest, and a detector that will detect all the relevant frequencies. So, if they combine a universal laser with a universal spectrometer, their universal surface sensor will be complete.
For some target materials, the problem of distinct and unique spectral features can be a big one. For things like bacteria, containing a multitude of molecules with similar spectral features but slightly different function, you end up with spectral soup. I believe that there are some spectral features that indicate that you have bacteria, and not some other generic background material, such as pollen. However, you then need to say that you have some nasty material, and not just the usual microbes that are everywhere. I don't know how you do that without chemical receptors. Finally, if the receptors rely on DNA, you need to do a bit of biochemistry to actually get to the DNA.
Explosives could work, since you're dealing with specific molecules. However, in many scenarios if you need to touch the sample you're too damn close.
You never heard of an on-line sex toy? They're a crucial component of modern interweb maintenance. You got to keep those tubes well lubricated.
So does this mean that the state of Alabama could seize the domains names of all vendors of on-line sex toys?
If asking nicely doesn't work, we could get tough...
We could tell the Russians we won't take her back.
OK. I'll have a go at it.
The theory is that polycyclic aromatic hydrocarbons (PAHs) are end-of-the-food-chain survivors in the photochemistry that is thought to occur in certain types of nebulae where interstellar dust clouds are illuminated by hot stars. If a nearby star is hot enough, it's spectrum will extend deep into the UV, and it will generate a considerable flux of high energy photons. Some organic molecules will efficiently fluoresce when excited into specific states following absorption of UV photons within certain energy ranges. When these molecules fluoresce, most of the energy goes away. However, if fluorescence doesn't occur, all the energy from photon will eventually end up in the ground electronic state, heating the molecule vibrationally. In space, the molecules can only cool through IR radiation and this is slow. In many cases, the molecule will dissociate before it can cool through radiation of IR photons.
PAHs are unique because they are robust and large. Every carbon atom has multiple carbon-carbon bonds. Even if the photon energy is sufficient to break one or two of these bonds, the molecule won't fall apart. (If it looses an H atom, that's OK. It will find another one since hydrogen is the most abundant thing out there.)
Finally, these UV photons can also ionize these molecules, which is potentially a good thing for helping them grow. With the low densities in these clouds, random collisions are infrequent, and the charge can increase the cross-section leading to more collisions with uncharged species such as H, H2, and C2. It's been a while since I have studied this stuff, but there's probably at least one dissertation out there covering the balance between ion-molecule reaction rates leading to PAH formation and the photodissociation rates in nebulae with nearby hot stars.
What I want to know is how much fuel does it take to travel from San Francisco to New York City by the following methods:
A modern plane
A Prius
A generic 6 cylinder sedan
An Escalade
Amtrak
Of course, the extra 4 days on the road really make me favor the plane, but I want to know how guilty I should feel.
That's why you need sharks to go with your lasers. You think you can defend yourself with mirrors, do you? Don't you know that sharks like to eat shiny things?
I don't get it. If you're constipated, how could you possibly use it?
Oh, wait...that's facial recognition, not fecal recognition.
Never mind.
Horowitz and Hill is the best book on electronics that I know of. It does have some handy circuit examples that you can build, but don't think of it as an instruction book for a kit. If you read Horowitz and Hill, you will be ready to go out and design your own circuits.
The parent comment is modded "funny," but it could equally be modded "informative." When an intense femtosecond pulse is focused into many materials, including water, nonlinear effects will lead to fillamentation and continuum generation. Here are some pictures from lasers with roughly an order of magnitude less power focused in air.
(I corrected a link. Please mod my previous comment down)The parent comment is modded "funny," but it could equally be modded "informative." When an intense femtosecond pulse is focused into many materials, including water, nonlinear effects will lead to fillamentation and continuum generation. Here are some pictures from lasers with roughly an order of magnitude less power focussed in air.
I am also perplexed. I to am not an expert on relativity & cosmology, but I know a thing or two about nonlinear optics. An intense light field can modify the index of refraction of the medium through which it's propagating. This is known as the AC or optical Kerr effect. http://en.wikipedia.org/wiki/Kerr_effect/ The second light pulse will gradually encounter a higher index as it approaches the first pulse and therefore slow down. While I know nothing about Hawking radiation, it seems like gravity must be somehow involved, and this experiment is all about electromagnetic forces.
Does this make Christians better? I would argue that the Hindus have the most literal interpretation of the phrase "up in arms," but I don't have any problems with that.
The previous posters responding to this comment have correctly identified different elements of the problem. A high index is necessary, so that there are strong reflections from the facets. Furthermore, the large index helps generate large refractive angles when the diamond is cut correctly. A large dispersion is necessary in order to generate the rainbow effect when the light undergoes refraction.
However, the crystal structure alone does not guarantee these properties. Diamond, silicon, and germanium all share the came crystal structure. All are semiconductors. The reason why diamond is transparent is because the bandgap is above the energy of a visible photon. The crystal structure alone does not determine the electronic properties of a material and optical properties such as index of refraction and dispersion. There is no guarantee that a material with this hypothetical crystal structure would be transparent at visible wavelengths. If it is transparent, there is no guarantee that it would have a large diffractive index and high dispersion.
If you're a US citizen, you paid for this research. If you want to read the article, you need to pay the copyright holder.
If you're a scientist, it's even worse. You might also be asked to referee the article before it's published, for no compensation and on your own time. If you want to see the final product, you still have to pay the copyright holder.
Somebody had to say it.
I forgot to set the tounge-in-cheek flag. Sorry about that.
Now that everybody has made the shift to ROHS electronics, who cares if the heat melts lead? They should be able to do it with all COTS parts.
I would tell you, but then I would have to kill you.