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PHYSICS NEWS UPDATE
A digest of physics news items prepared by Phillip F. Schewe, AIP
Public Information
Number 157  December 23, 1993

ATOMIC-SCALE, ULTRAFAST MOVIES of moving atoms may be
coming to a theater near you.  LBL scientists (Daniel Chemla, 510-
486-6922) have attached an ultrafast photoconductive switch to the tip
of a scanning tunneling microscope.  Bursts of 100-fsec laser light are
then used both to excite voltage pulses in a transmission line beneath
the STM tip and to open or close the optical switch.  Images of the
transmission line can be built up with a 2-psec time resolution and a
5-nm spatial resolution.  Thereby in this preliminary form, the LBL
apparatus features a time resolution some nine orders of magnitude
better than previous STM setups.  The researchers expect to achieve
movies with atom-scale spatial resolution.  (Optics & Photonics
News, Dec. 1993.)

GEOELECTRIC SIGNALS: DO THEY PRECEDE
EARTHQUAKES?  Speaking at the recent meeting of the American
Geophysical Union, Anthony Fraser Smith of Stanford (415-723-
3687) reviewed his data from four years ago which showed that local
measurements of Earth's magnetic field fluctuated much more
vigorously than usual in the days and hours before the 7.1-magnitude
Loma Prieta earthquake.  Many scientists hesitate to infer any
correction between the signals and the quake, particularly on the basis
of only one such data set.  To study the matter further, Fraser Smith
has set up several detectors around California near faults. Simon
Klemperer, also of Stanford (415-723-7344), attempts to model Fraser
Smith's signals by suggesting that in the buildup to a quake, a flexing
fault system might squeeze pockets of water together (which are
sparse at these depths--18 km), altering the electrical conductivity of
the fault, which in turn can act like an antenna to modulate the
measured magnetic field at the surface.  Other types of geoelectric
signals possibly related to quakes were reported at the AGU meeting.
Seiya Uyeda of Tokai University in Japan and Texas A&M cited data
linking four recent earthquakes in Japan with anomalies in the static
voltage differences between various measurement stations.  Jean Chu
of MIT presented a small portion of an extensive Chinese study (over
20 years) of earthquakes and possible precursors in the form of
changes in the conductivity of the Earth.

NEUTRINO TOMOGRAPHY OF THE EARTH'S INTERIOR might
be carried out soon with the DUMAND detector.  The Deep
Underwater Muon and Neutrino Detector, a series of strings of
phototubes being installed now on the ocean bottom near Hawaii,
does not observe neutrinos directly but rather the Cerenkov radiation
emitted by muons (created by interactions between neutrinos and
ordinary atoms) plowing through seawater.  DUMAND is designed
chiefly to study celestial sources of neutrinos, such as the Sun and
supernovas, but, according to Berkeley scientist Chaincy Kuo, who
spoke at the AGU meeting, variations in the observed neutrino flux
may provide information about the Earth's internal structure (Science
News, 18 Dec. 1993.)

CORRECTIONS: A temperature of 250 K is equivalent to -10 F, not
+10 F; J.D. (not J.H.) Eberly is at Rochester, not Cornell (Update
156).  The 17.6 MeV of surplus energy released in deuterium-tritium
fusion is shared between the daughter helium and neutron, and not
carried by the neutron alone (Update 155).