Number 67, February 12, 1992 by Phillip F. Schewe and Ben Stein
BUCKYBALL SUPERCONDUCTIVITY IS MEDIATED BY PHONONS . This is the interpretation scientists at AT&T Bell Labs give to their studies of superconducting compounds of rubidium and carbon-60. They observed that when 13C atoms were substituted for 12C atoms in buckyball molecules, the critical temperature of the Rb3C60 sample decreased by an amount one would expect from BCS theory, which describes superconductivity in terms of electron pairs mediated by phonons (lattice vibrations). An "isotope shift" of this type has been observed in many low-temperature metal superconductors. (A.P. Ramirez et al., 17 Feb. 1992 issue of Physical Review Letters; contact Arthur P. Ramirez, 908-582-2494.)
COPERNICAN CRYSTALLOGRAPHY , a new classification scheme for crystallography formulated by N. David Mermin of Cornell (607-255-9689), puts quasi-periodic materials such as quasicrystals (which form dodecahedral grains) on an equal footing with periodic crystals. Mermin does this by emphasizing the concept of indistinguishable---rather than identical---densities to denote crystallographic taxonomy. The kind of translation that defines microscopic periodicity in perfect crystals would then be just one among several possible translations that map one subregion into a nearby identical subregion. In Mermin's generalized scheme there would be no need to describe quasiperiodic materials as being three-dimensional sections of materials periodic in some higher-dimensional space. Mermin believes that resorting to such a "superspace" is analogous to the use of epicycles in pre-Copernican times to help explain the apparently odd movements of planets in an earth-centered astronomy. He suggests that "Ptolemaic" crystallography (centered on periodic crystals) should be abandoned. (Physical Review Letters, 24 Feb. 1992.)
INFRARED IMAGES OF THE GALACTIC CORE reveal more than two dozen compact sources of near-infrared radiation. The measurements, recorded by the New Technology Telescope (NTT) at the European Southern Observatory (ESO) at La Sill, Chile, also show an expanding bubble of gas centered about 3 arcseconds from Sgr A* (the galactic core). Like evidence at other wavelengths (e.g., radio and gamma), the infrared pictures are consistent with the existence of a massive black hole at the center of the Milky Way. (Nature, 6 Feb. 1992.)
A CRAY 3 COMPUTER , performing 16 billion operations per second, accomplishes in one second a calculation that would have taken the Eniac (an early computer, c1946) 67 years. The technological revolution which made the Cray and other wonder machines possible is summarized in "Materials & Technology: The Role of Physics in Materials Research," a booklet prepared by the American Physical Society Division of Condensed Matter Physics and the Division of Materials Physics. Other items mentioned in the text include the following: in 1991 a million bits of memory were produced for every person on Earth; the highest density of transistors on chips doubles every 18 months; a mile-thick slab of optical fiber is more transparent than a 0.1-inch-thick pane of ordinary window glass. (Copies of the booklet can be obtained from the AIP Public Information Division; phone-212-661-9404.)
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