Physics News Update The American Institute of Physics Bulletin of Physics News Number 157, December 23, 1993 by Phillip F. Schewe and Ben Stein 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.H. (not J.D.) 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).