Physics News Update
The American Institute of Physics Bulletin of Physics News
Number 308, February 20, 1997 by Phillip F. Schewe and Ben Stein
SURFACE ENHANCED RAMAN SCATTERING (SERS) can be used to detect single
molecules. In Raman spectroscopy the light scattered inelastically from
a molecule provides information about the molecule's vibrational quantum
states. The rather weak Raman effect can be greatly strengthened (by a
factor of up to 14 orders of magnitude) if the molecules are attached to
nm-sized metal structures. (The way in which the enhancement occurs is
still not known for sure.) In this way, an MIT-Berlin group (Katrin Kneipp,
100342.530@compuserve.com) has detected single dye molecules attached to
colloidal silver particles in an aqueous solution. The advantages of this
method are that it is fast, it can supply some structural information about
the molecules, and it doesn't bleach the molecules. Single-molecule detection
is of great practical interest in chemistry, biology, and medicine, and
pollution monitoring; examples include DNA sequencing and the tracing of
biomedically interesting molecules. (Kneipp et al., upcoming article in
Physical Review Letters.)
THE HUBBLE SPACE TELESCOPE UPGRADE has been successfully carried out
by Space Shuttle astronauts. The two major newly installed devices are
the Near-Infrared Camera and Multi-Object Spectrometer (NICMOS), which
will permit a look at the infrared radiation (doppler shifted from the
ultraviolet) from young stars in very early (and far out in space) galaxies,
and the Space Telescope Imaging Spectrograph (STIS), which replaces the
Faint Object Spectrograph and the Goddard High Resolution Spectrograph.
STIS will be valuable for studying exotic objects like black holes and
violent galaxies, and for searching for extrasolar planets.
A ROOM-TEMPERATURE SINGLE-ELECTRON MEMORY has been developed at the
University of Minnesota. In electronics, smaller usually means faster response,
less power consumption, and greater component density. In the tiny Minnesota
transistor a bit of information is stored in the form of a single extra
electron which, resident on a dot of silicon (acting as a "floating
gate"), has the power to influence the current flow in a silicon channel
connecting the transistor's source and drain. This single-electron arrangement
is orders of magnitude smaller than the kind of metal-oxide-semiconductor
(MOS) transistor used in conventional computer memories. (Lingjie Guo et
al., Science, 31 January 1997.)
NAKED SINGULARITIES COULD EXIST, concedes Stephen Hawking. In cosmological
terms, a singularity is a place of incalculably large---essentially infinite---mass
density. Singularities are supposed to reside inside black holes but could
never be observed because light is forever bottled up within the black
hole's event horizon. In 1991 Hawking bet Caltech physicists Kip Thorne
and John Preskill that such singularities must always be thus imprisoned
within a black hole. But a computer study has since shown that singularities
unencumbered with any event horizon could, at least in principle, exist.
Although he doubts whether a naked singularity could ever actually form,
Hawking has now paid up on his bet. (Caltech press release, 6 February
1997.)
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