Percolation and electrical resistivity in the YBa2Cu3O7−Ag composite system

We have measured the resistivity of the YBa₂Cu₃O₇–Ag composite system with Ag volume fraction,p _Ag ranging from 0–100%. The percolation behavior and the normal-state resistivity are studied. We find a three-dimensional threshold for the Ag matrix occurring atp _Ag 20% and a threshold for the superconducting matrix occurring at 1–p _Ag30%. The electrical resistivity is interpreted in terms of a resistivity model for granular YBa₂Cu₃O₇ proposed by Halbritter et al. [Z. Phys. B —Condensed Matter71, 411 (1988)]. Based on this model, we show that the resistivities between the YBa₂Cu₃O₇ grains and flaws in the grains are greatly diminished in the samples, indicating significantly improved grain growth behavior of the YBa₂Cu₃O₇ phase resulting from the addition of Ag. With the diminishing of the grain boundary resistivities, an intrinsic value for the temperature coefficient of resistivity, (1/gr)(d/dT), can be inferred, which is 3.3×10^–3/K at 300 K. This value is very close to that observed in the Cu–O₂ planes in single crystals and epitaxial films of YBa₂Cu₃O₇.     

非相干光源用于“核-环比”法测量表面粗糙度

本文将文献[1-5]的用激光测量表面粗糙度的“核-环比”法推广到采用其他非相干光源,给出测量原理的定量公式及测量装置的结构框图。     

The increments of partial sums of a dependent sequence when the moment generating functions do not exist

In the paper, we give the almost sure limiting behaviour of the increments of partial sums of a-mixing sequence when the moment generating functions do not exist. The results obtained are close to those for an independent sequence provided that the mixing coefficients tend to zero rapidly enough.The Project Supported by National Natural Science Foundation of China.     

Optimality for set functions with values in ordered vector spaces

Let (X, , ) be a finite atomless measure space,L a convex subfamily of , andY andZ locally convex Hausdorff topological vector spaces which are ordered by the conesC andD, respectively. LetF:LY beC-convex andG:LZ beD-convex set functions. Consider the following optimization problem (P): minimizeF(), subject to L andG() _D . The paper generalizes the Moreau-Rockafellar theorem with set functions. By applying this theorem, a Kuhn-Tucker type optimality condition and a Fritz John type optimality condition for problem (P) are established. The duality theorem for problem (P) is also studied.This work was partially supported by National Science Council, Taipei, Taiwan. This paper was written while the first author was visiting at the University of Iowa, 1987-88.The authors would like to express their gratitude to the two anonymous referees for their valuable comments. Also, they would like to thank Professor P. L. Yu for his encouragement and suggestions which improved the material presented here considerably.