CHAOS CONTROL OF EL NINO in a sophisticated computer simulation has been achieved by an Israel-US team. El Nino is a prolonged warming of the Pacific Ocean surface near the equator every 3 to 6 years, bringing about storms and widespread climate effects. Recent theories suggest that El Nino is chaotic: its behavior is unpredictable but sensitive to initial conditions of such variables as temperature, atmospheric pressure and winds. A Weizmann-Columbia group (Eli Tziperman, eli@beach.weizmann.ac.il; Stephen Zebiak, 914-365-8597) altered the magnitude of ocean waves reflecting from the western boundary of the Pacific Ocean, in a realistic El Nino prediction model developed at Lamont-Doherty Earth Observatory in New York. When they did this, the model produced an El Nino about every 4 years with periodic and perfectly predictable cycles of temperature, winds, and ocean currents. Although the researchers do not propose to apply chaos control directly to El Nino, they believe it may help them better understand the crucial factors governing El Nino's behavior. In addition, the research required improvements in existing chaos control methods, as the El Nino model has many more variables and parameters than previously controlled chaotic systems. (Tziperman et al., upcoming article in Physical Review Letters.)

ASTEROID MATHILDE , viewed from a distance of only 1200 km by the Near-Earth Asteroid Rendezvous (NEAR) space probe, is heavily cratered from millions of years of rough travel through the solar system. By sensing the Doppler effect on radio waves returning to Earth from NEAR owing to the (very slight) gravitational tug between asteroid and spacecraft, Mathilde's mass could be estimated. Surprisingly, its density turns out to be not much greater than that of water, suggesting that it is not a solid object but rather a compacted pile of debris. NEAR's next assignment is to meet and orbit the asteroid Eros in 1999 (Science, 4 July 1997.)

CANCER-FIGHTING RADIOACTIVITY can be made safer and more efficient by using antibodies to carry tailored isotopes directly to cancer cells, thus zapping bad cells with targeted doses of ionizing radiation while sparing healthy cells. Isotopes emitting short-ranged alpha particles (helium-4 nuclei) would be especially appropriate for combating cancers---such as leukemia--- involving small clumps of cells or for spreading (metastasizing) cancers, while more-penetrating beta (electron) emitting isotopes would be preferable for larger cancer masses. The trick has been to get the radioactive atom to hitch a ride with an antibody. One example: at the Arlington Cancer Center in Texas yttrium-90, a beta emitter, can be teamed with an antibody called IGM and injected directly into tumors. Promising clinical trials of internally delivered radiopharmaceuticals, alone or in tandem with whole-body irradiation, have been underway for several years. (Science News, 19 July 1997.)

THE CHAOTIC MOTION OF DISKS sinking in a fluid can be mapped onto a diagram whose parameters reflect the density and viscosity of the fluid and the size and density of the disk. A Colorado State/Michigan collaboration has discovered that the disk trajectories (videotaped and anatomized into numerical coordinates) are of four types: steady falling, tumbling, periodic oscillating, and an unpredictable chaotic mode. (Stuart Field et al., Nature, 17 July 1997; more details at University of Michigan website)

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