Number 95, September 22, 1992 by Phillip F. Schewe and Ben Stein|
STUDIES OF THE COSMIC MICROWAVE BACKGROUND (CMB) can provide information about the inflationary expansion of the early universe. A few months ago Lawrence Krauss and Martin White of Yale asserted (Phys. Rev. Lett., 10 Aug.) that variations in the CMB may be due in part to gravitational waves (tensor perturbations) and not just to matter-density fluctuations (scalar perturbations). A new paper by theorists and experimenters, including George Smoot of LBL, Paul Steinhardt of the University of Pennsylvania, and Michael Turner of the University of Chicago, examines the likely contributions of tensor and scalar perturbations to the CMB variations for the case of several different inflationary models. They conclude that a combination of large-angular-scale data from the Cosmic Microwave Explorer (COBE) and small-angular-scale data from other CMB detectors might be able to distinguish scalar from tensor effects. (R.L. Davis et al., Phys. Rev. Lett., 28 Sept. 1992.)
ULYSSES' JUPITER ENCOUNTER has engendered 13 articles in the 11 Sept. issue of Science. Ulysses, the first spacecraft to visit Jupiter (Feb. 1992) since the Voyager missions in the 1970s, is destined to pass beneath the Sun's south pole in the summer of 1994. In the meantime its side trip to Jupiter has supplied plentiful information about the Jovian environment: the magnetosphere was found to be inflated to a size much larger than at the time of the Voyagers; the presence in the magnetosphere of sulphur and oxygen ions, produced mostly at the volcanic moon Io (at a rate of about one ton per second) was confirmed; very little dust was found near Jupiter; Io's principal volcano, Loki, was quiet.
TIME-RESOLVED REFLECTION HIGH ENERGY ELECTRON DIFFRACTION (RHEED) permits the detailed study of melting. Hani Elasayed-Ali and John Herman, scientists at the University of Rochester, use laser light to simultaneously heat a crystalline sample and also unleash an electron gun which shoots probing electrons at the crystal. The distinctive pattern of electrons diffracting from the crystal surface changes when the top layers begin to melt. Elasayed-Ali and Herman used RHEED to study the melting of lead crystals with a time resolution of 190 psec. They got different results for different angles of attack: looking at the so-called (110) crystal surface, their laser beam produced a sort of premelting---the formation of a liquid-like film---at a temperature some 40 K below the normal melting point (660.7 K). For the more densely packed (111) surface, the Rochester scientists found evidence for superheating; heated at that angle, the lead atoms resisted melting up to a point 120 K above the normal melting point. (Science News, 12 Sept. 1992.)
BUCKYBALL BEAMS at energies up to 50 MeV per bucky have been created by Yvon Le Beyec at the Nuclear Physics Institute at Orsay, France. Cesium ions are used to strike and ionize C-60 molecules residing in a solid pellet. Accelerated buckyballs are potentially useful projectiles since they possess relatively large energy but small velocity, insuring that they won't penetrate a target to any great depth. (Science, 11 Sept.)