Number 7, November 1, 1990 by Phillip F. Schewe and Ben Stein 650,000 Z PARTICLES have been observed in the LEP electron-positron collider in Geneva, Switzerland during a five-month period ending in August. As recently as 1989, when LEP began operations, the number of Z's observed numbered only in the hundreds. The Z is one of the carriers of the weak nuclear force and can be detected only in the aftermath of high-energy collisions between particles; precise measurements (requiring plentiful events) of Z properties contribute to our knowledge of the standard model of particles physics. LEP plans to produce three times as many Z's in 1991. (CERN Courier, October 1990.) HIGH TEMPERATURE SUPERCONDUCTOR (HST) APPLICATIONS ,slow in coming, may pick up soon. For example, "melt-textured" processing, involving partial melting and then cooling the HST compounds, has resulted in better critical current densities in bulk samples, up to 105 amperes/cm2 at the University of Houston, and a higher tolerance for magnetic fields. Ease of processing and mechanical flexibility, however, must be improved. Malleability may be increased by imbedding carbon fibers in the compounds. Meanwhile, advances in HTS thin films offer the possibility of applications in the designing of superconducting quantum interference devices (SQUIDS), high-resolution antennas, and fast transistors. (Science, October 19, 1990. Contacts: Roger Koch, IBM, 914-945-2393, Marc Kastner, MIT, 617-253-4808.) A SCANNING TUNNELING MICROSCOPE WITH A GOLD TIP can deposit small hills of gold atoms only 10 nm wide by 2 nm high. In an STM setup at IBM, scientists evaporate atoms from a gold microscope tip onto a gold substrate only nanometers below. Although the "structures" (the small hills, consisting of perhaps thousands of atoms) created are not as small as those achieved by a different IBM group (which manipulated individual atoms) earlier in the year, the conditions in this case are much more favorable: the gold STM operated in air rather than at low temperatures or in high vacuum. Furthermore, the gold tip did not wear out as is the case in many other STM applications. (Physical Review Letters, Nov 5. Contact: H. John Mamin, IBM Almaden Research Center, 408-927-2027.) NEPTUNE'S MOON TRITON exhibited several interesting features to the passing eye of Voyager 2. The spacecraft observed at least four active plumes, emitting nitrogen, ice, and dark particles. Some of the emitted materials seemed to rise to an altitude of 8 km. It is unclear what the energy source for this activity may be. Triton's atmosphere is rather like that of Mars, with N2 instead of CO2 and CH4 instead of water. (Numerous Voyager 2 reports in Science, October 19, 1990.) BRAZILIAN PULSAR DISAPPEARS. Brazilian astronomers have retracted an earlier claim that they had observed a pulsar at the heart of supernova 1987A. The signal proved to be due to a mechanical problem with the telescope. (Nature, October 25.)