[tt] advanced nanotechnology - 2 new articles
Eugen Leitl
<eugen at leitl.org> on
Sun Nov 25 08:27:50 UTC 2007
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Date: Sun, 25 Nov 2007 03:05:26 -0500
To: eugen <eugen at leitl.org>
Subject: advanced nanotechnology - 2 new articles
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"[2]advanced nanotechnology" - 2 new articles
1. [3]Economist magazine wants more spent to verify safety of
nanoparticles
2. [4]superconductors plug `terahertz gap'
3. [5]More Recent Articles
4. [6]Search advanced nanotechnology
[7]Economist magazine wants more spent to verify safety of nanoparticles
[8]The Economist has a lengthy article that suggests that more money
and effort should be sent to verify the safety of nanoparticles.
America already spends the most on EHS (environmental health and
safety) research into nanotechnology. Depending on who does the
counting, it ranges from $11m to $60m.
Safety legislation cannot be expected to work until the products of
the technology are better understood. What does it mean to regulate
nanotechnology materials when you cannot even measure their release
into the environment or agree on how to weigh a nanoparticle?
Had Dr Maynard's bag split wide open in Congress, scattering his
carbon nanotubes into the air, would any harm have been caused?
Probably not. But, as an answer, "probably" is not good enough.
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[22]superconductors plug `terahertz gap'
[23]Ulrich Welp at Argonne National Laboratory and colleagues have
discovered a simple way to synchronize the phase of these "intrinsic"
Josephson junctions in high-temperature superconductors to emit
milliwatts of power at frequencies up to 0.85 THz.
[2061110392_35fe8fb105.jpg?v=0]
Schematic of the terahertz-source, which was fabricated on the top of
an atomically layered superconducting crystal. The applied current
excites the fundamental cavity mode (solid half-wave) on the width w
of the mesa, and high-frequency electromagnetic radiation is emitted
from the side faces (red waves).
Unlike far more energetic X-rays, T-rays do not have sufficient
energy to "ionize" an atom by knocking loose one of its electrons.
This ionization causes the cellular damage that can lead to
radiation sickness or cancer. Since T-rays are non-ionizing
radiation, like radio waves or visible light, people exposed to
terahertz radiation will suffer no ill effects. Furthermore,
although terahertz radiation does not penetrate through metals and
water, it does penetrate through many common materials, such as
leather, fabric, cardboard and paper.
These qualities make terahertz devices one of the most promising
new technologies for airport and national security. Unlike today's
metal or X-ray detectors, which can identify only a few obviously
dangerous materials, checkpoints that look instead at T-ray
absorption patterns could not only detect but also identify a much
wider variety of hazardous or illegal substances.
T-rays can also penetrate the human body by almost half a
centimeter, and they have already begun to enable doctors to better
detect and treat certain types of cancers, especially those of the
skin and breast, Welp said. Dentists could also use T-rays to image
their patients' teeth.
[24]There had been a "terahertz gap" between about 0.5 and 2
terahertz, which no device has been able to fill.
Being able to produce a beam of 'T-rays' in that range could
revolutionise airport security and medical scans. They have
persuaded normally independent quantum junctions to work together.
Welp and colleagues made hundreds of junctions work together,
creating a beam of laser-like terahertz light with 10,000 times
more power (about half a microwatt).
The team used a high-temperature semiconductor called BSCCO, which
naturally contains stacks of Josephson junctions in its structure.
It comprises of superconducting sheets, a couple of atoms thick,
separated by 1.5 nanometer insulating gaps.
"We were able to pack in a huge number of Josephson junctions" in
each crystal, Welp says. In a strip of the material about one
micron tall, 100 microns wide, and 300 microns long, they fitted in
more than 600 junctions.
"If the power output were boosted up to 1 to 10 milliwatts, it
would be a very promising niche device", complementing other
devices that create terahertz radiation at other frequencies,
Yergens says.
The frequencies covered by the new device are some of the more
useful for imaging. "You have to be slightly below one terahertz to
take full advantage of such radiation," he adds.
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Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
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