ic mechanism it is not known whether the 9. D. L. Novikov, V A. Gubanov. A J. Freeman, Physica C 191, 399 (1 992). in the matrix 10. S. Chakravarty, M. P. Gelfand, S. Kivelson, Scisponding to hopping on (13C, ,12C, , ) , , ence 254, 970 (1 991) v.2 --Versus I t 6 , a n d -' i~6 i clusters wa give rise 11. G. Baskaran and E ' Tossatti. Curr. Sci. 61, 33 (1991). to significant variations in Tc' Or whether 12. J. Bardeen, L N. Cooper, J. R. Schrieffer, Phys. these differences are averaged in the mean-Rev. 108. 1175 (1957). field model used to estimate T,. Calcula-13. P. Morel and P. W. Anderson, rbid. 125. 1263tions for the electronic model are needed to address this essential issue. Our experimental isotope effect data ohtained on a series of specifically substituted Rb3C6, superconductors provide an unambiguous value for the isotope shift in completely substituted fullerene superconductors and elucidate a unique difference between intermolecular and intramolecular isotopic substitution. A theoretical understanding of these experimental results may lead to a single viable mechanism for superconductivity in the fullerenes.
Growth of epitaxial films of the L1 0 phase of FePt, with the tetragonal c axis along either the film normal or in-plane, is described. Films were grown by coevaporation of Fe and Pt, under ultrahigh vacuum conditions, onto a seed film of Pt grown on MgO or SrTiO 3 substrates. The perpendicular or in-plane orientation of the c axis was controlled by selecting the ͑001͒ or ͑110͒ substrate plane, respectively. Nearly complete chemical ordering was achieved for growth at 500°C for both orientations. Magnetic and magneto-optical characterization of these films confirmed the huge magnetic anisotropy expected for this phase. In the most highly ordered films, anisotropy fields in excess of 120 kOe were measured.
The first 42 elements of the Allen Telescope Array (ATA-42) are beginning to deliver data at the Hat Creek Radio Observatory in Northern California. Scientists and engineers are actively exploiting all of the flexibility designed into this innovative instrument for simultaneously conducting surveys of the astrophysical sky and conducting searches for distant technological civilizations. This paper summarizes the design elements of the ATA, the cost savings made possible by the use of COTS components, and the cost/performance trades that eventually enabled this first snapshot radio camera. The fundamental scientific program of this new telescope is varied and exciting; some of the first astronomical results will be discussed.
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