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.     

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.     

金属表面在反射方向产生光学二次谐波的研究(Ⅰ)

用Rudnick和Stern引入的唯象参数“a”和“b”来描述表面电流,本文推导了金属表面在反射方向产生的光学二次谐波的表达式.由此证明了:从谐波信号随入射光偏振态的变化可以直接得到关于参数“a”的信息.和过去的实验相比,这种方法能更加精确、可靠地测定“a”的数值.     

同位素择尤溅射角分布研究

本文从理论和实验两个方面探讨了同位素溅射角分布问题。从实验上得到的同位素溅射角分布曲线表明,在垂直靶面方向轻同位素择尤溅射,而在倾斜方向,则重同位素择尤溅射。在理论上考虑了原子级联碰撞过程中的能量和动量传输的不对称性,给出了一个与实验结果相符的同位素溅射角分布表达式。 关键词：     

L-半胱氨酸自组装膜电极上锌离子的电化学行为及分析应用

锌是人体必需的微量元素 ,也是金属酶的组成部分和酶的激活剂 ,目前已知有 80多种酶的活性与锌的存在有关 ,因此研究锌在生物分子 (如Ｌ 半胱胺酸 )自组装膜结构中的电化学行为 ,对于研究和了解生物体内生命物质的电子转移及生命现象的本质具有重要意义。本文研究Ｚｎ2 +在Ｌ 半胱氨酸自组装修饰金电极[1～3] ,Ｃｙｓ/ＳＡＭ/Ａｕ上的电化学行为 ,建立了测定Ｚｎ2 +浓度的新方法 ,用于人体发样中痕量Ｚｎ2 +的测定 ,与目前所报道的锌的测定方法[4] 相比 ,具有快速、准确、灵敏度高等特点。1　实验部分1 1　仪器与试剂ＣＨＩ660型电化学工作…