A significant enhancement of J , in a magnetic fieid for Ag-sheathed Bi-Pb-Sr-Ca-Cu-0 (BPSCCO) tapes has been achieved by post-annealing at reduced temperature after processing. This post-annealing at reduced temperature introduced extra oxygen into the oxide superconductor. Weak links were eliminated and J, has been increased in the post-annealed tapes by a factor of 1.5 to 3 at 0 T over the normally processed tapes without post-annealing. The optimized J , values for the post-annealed tapes ranged from 30000 to 57 000 A cm-2 at 77.3 K and 0 T. The irreversibility lines measured by a DC SQUID exhibited an improvement in flux pinning in the post-annealed tapes compared with that in normally processed tapes. The introduced oxygen ions are responsible for the enhanced J. and may affect two dimensionality in superconductivity for the BPSCCO system.

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D b r i e m e n t d'ktrophysique Relativiste et d e Cosmologie O b m t o i r e , 92190 Meudon, France AbsImacL Slatting from the equations of motion obeyed by fields, as they result from general approximations [they are m!ia to be of the following form [k2n(k)]+ = 0, for quasi bosons, and a similar equation for quasifermions] a lagmgian formalism is derived and, accordingly, consewed quantities are obtained. Next these fields are quantized and general expressions for the main observables are derived. Statistical mechanics of quasiparlicles then follow via the use of covariant Wigner functions.

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