Physics News Update 636 (fwd)

Jim Choate ravage at einstein.ssz.com
Wed May 7 20:13:06 PDT 2003


---------- Forwarded message ----------
Date: Wed, 7 May 2003 11:48:12 -0400
From: physnews at aip.org
To: ravage at SSZ.COM
Subject: Physics News Update 636

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 636 May 7, 2003   by Phillip F. Schewe, Ben Stein, and James Riordon

ULTRA-LOW-ENERGY ELECTRONS CAN BREAK UP URACIL, a new study shows.  How
injurious is radiation (alpha, beta, and gamma rays or heavy ions) to living
cells?  This important question has been addressed in many ways.  Much
attention has centered on the secondary particles produced in the wake of the
intruding primary radiation, especially electrons (about 40,000 electrons are
produced for each MeV of energy deposited) with typical energies of tens of
electron volts.  Many of these secondary particles quickly lose their energy
and become attached (solvated) to water molecules in the cell.   What is the
general effect of electron energies below 20 eV?  A report from three years
ago (Boudaiffa et al., Science 287, 1658, 2000) showed that electrons in the
3-20 eV range are able to produce substantial genotoxic damage, including
breaking single- and double-stranded DNA?  What about secondary electrons with
even smaller energies? To look at this energy range for the first time,
Tilmann Maerk and his colleagues at the Universitat Innsbruck (Austria) and
the University Claude Bernard Lyon (France) scattered a beam of sub-eV electrons from a beam of gaseous uracil molecules.  Uracil is one of the base units of RNA molecules, and is thus a crucial component in cells.  These scientists found that uracil is efficiently fragmented by electrons with energies as small as milli-electron-volts.  It's not the electron's kinetic energy that causes the disruption, but the electron's charge, which changes the uracil's internal potential energy environment. Furthermore, in the process a very mobile  atomic hydrogen can be freed, which on its own, as a radical (a free chemical unit by itself), can do
damage to biomolecules (see a movie of this process at
http://info.uibk.ac.at/ionenphysik/ClusterGroup/Uracil.html;
schematic at http://www.aip.org/mgr/png/2003/187.htm ).
Maerk (tilmann.maerk at uibk.ac.at, 43-512-507-6240) says that this low-energy
damage seems to be a general result since his group has since performed
similar work with thymine (a DNA base) and have seen similar fragmentation.
(Hanel et al., Physical Review Letters, 9 May 2003; Innsbruck website,
http://info.uibk.ac.at/c/c7/c722/e-index.html )

PERFECT INSULIN CRYSTALS.
{SSZ: Text deleted]


THE TINIEST SOLID-STATE LIGHT EMITTER, produced by Phaedon Avouris and his
colleagues at IBM, consists of a single-walled carbon nanotube (NT) strung
between two electrodes, and controlled by a third.  The business part of this
minuscule transistor is a nanotube only 1.4 nm wide and tailored to be
semiconducting.  In this arena electrons coming from one electrode meet with
positively charged "holes" coming from the other electrode.  When the two
species meet they combine and emit a tiny burst of light.  This light is
conveniently engineered to be at a wavelength of 1.5 microns, invisible to the
human eye but perfect for photonic applications.  Why use a NT when a larger
piece of bulk semiconductor could also produce light?  Because of the
potentially much greater energy efficiency and compactness of the light
emitting region.  Single-molecule light emission has been instigated before,
but not under the auspices of solid state wiring. The NT wire also seems to be
robust: it is able to carry 6 micro-amps of current, for a current density of
more than 100 million amps per square cm.  (Misewich et al., Science 2 May
2003.)

***********
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