Piezoelectric properties of (Na0.5K0.5)(Nb1‐xSbx)O3‐SrTiO3 ceramics with tetragonal‐pseudocubic PPB structure

CuO‐added 0.96(Na_0.5K_0.5)(Nb_1‐xSb_x)O₃‐0.04SrTiO₃ ceramics sintered at the low temperature of 960°C for 10 hours showed dense microstructures and high relative densities. The specimens with 0.0 ≤  x ≤ 0.04 had orthorhombic‐tetragonal polymorphic phase boundary (PPB) structure. Tetragonal‐pseudocubic PPB structure was observed in specimens with 0.05 ≤  x ≤ 0.07, while the specimen with x = 0.08 has a pseudocubic structure. The structural variation in the specimens is explained by the decreases in the orthorhombic‐tetragonal transition temperature and Curie temperature with the addition of Sb⁵⁺ ions. The specimens with 0.05 ≤  x ≤ 0.07, which have tetragonal‐pseudocubic PPB structure, had large electric field‐induced strains of 0.14%‐0.016%. Moreover, these specimens also showed increased d₃₃ values between 280 pC/N and 358 pC/N. In particular, the specimen with x = 0.055 showed particularly enhanced piezoelectric properties: d₃₃ of 358 pC/N, k_p of 0.45, and the electric field‐induced strain of 0.16% at 4.5 kV/mm.     

翡翠的光谱特征及致色机理

翡翠是一种珍贵的宝石,有玉石之王的美誉。翡翠的颜色艳丽和丰富,成因较为复杂。综述了通过对不同颜色翡翠进行X-射线荧光(XRF)光谱、X射线光电子能谱(XPS)、红外光谱(IR)和紫外-可见光(UV-VIS)吸收光谱等的测试分析,对翡翠颜色的成因进行探讨,从而提高了人们对翡翠颜色成因的认识。     

基于多层Ｃ／Ｓ结构的标准网上虚拟学校的研究和设计

由于开发课件工程的不同,以及网上教学系统实现的差异,所以不同系统之间的课件很难通用。该文结合ＸＭＬ技术和ＩＥＥＥ ＬＴＳＣ（Ｌearning Technolgy Stendards Committee)标准,介绍了能在不同网上教学系统间通用的标准课件的设计,以及基于Ｗeb的多层Ｃ／Ｓ结构的能应用标准课件进行智能教学的ＣＭＩ系统的研究和设计。并且对于ＩＥＥＥ ＬＴＳＣ中对ＣＭＩ系统只准对Ｂ／Ｓ两层结构的设计拓广到Ｃ／Ｓ多层结构的设计。     

Cost-optimal parallel algorithms for the tree bisector and relatedproblems

An edge is a bisector of a simple path if it contains the middle point of the path. Let T=(V,E) be a tree. Given a source vertex s ∈ V, the single-source tree bisector problem is to find, for every vertex υ ∈ V, a bisector of the simple path from s to υ. The all-pairs tree bisector problem is to find for, every pair of vertices u, υ ∈ V, a bisector of the simple path from u to υ. In this paper, it is first shown that solving the single-source tree bisector problem of a weighted tree has a time lower bound Ω(n log n) in the sequential case. Then, efficient parallel algorithms are proposed on the EREW PRAM for the single-source and all-pairs tree bisector problems. Two O(log n) time single-source algorithms are proposed. One uses O(n) work and is for unweighted trees. The other uses O(n log n) work and is for weighted trees. Previous algorithms for the single-source problem could achieve the same time O(log n) and the same optimal work, O(n) for unweighted trees and O(n log n) for weighted trees, on the CRCW PRAM. The contribution of our single-source algorithms is the improvement from CRCW to EREW. One all-pairs parallel algorithm is proposed. It requires O(log n) time using O(n²) work. All the proposed algorithms are cost-optimal. Efficient tree bisector algorithms have practical applications to several location problems on trees. Using the proposed algorithms, efficient parallel solutions for those problems are also presented