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141.
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. 相似文献
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143.
Lin Zhengyan 《数学学报(英文版)》1989,5(4):289-296
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. 相似文献
144.
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. 相似文献
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149.
用结晶紫选择性电极(自制)以催化电位法对测定微量锰进行了研究。该方法测定标的线性范围为7~74μg/L,对标准钢样中的锰含量测定结果满意,且操作方便。 相似文献
150.
双甲基丙烯酰氧苯基丙烷与苯乙烯共聚物的光学性能 总被引:2,自引:0,他引:2
标题共聚物的耐冲击性与丙烯酸酯均聚物相比有明显改善,但随着双烯单体含量的降低,共聚物的耐热性和表面硬度有所下降。丙烯酸酯含量为70%的共聚物的吸收紫外光能力最强(<370nm全吸收),含量为5%~10%的共聚物耐吸水性、耐酸耐碱性及耐冲击性最好。 相似文献