Enhanced dielectric properties of lead barium zirconate thin films by manganese doping

(Pb_0.5Ba_0.5)ZrO₃ (PBZ) and 1 mol% Mn-doped (Pb_0.5Ba_0.5)ZrO₃ (Mn-PBZ) sol were successfully fabricated, and corresponding thin films were deposited on Pt(1 1 1)/TiO₂/SiO₂/Si(1 0 0) substrates by spin-coating method. Effects of Mn doping on the microstructure and electrical properties of PBZ thin films were investigated systemically. X-ray diffraction patterns showed that both films had a polycrystalline perovskite structure, and that the degree of (1 1 1) orientation were increased by Mn doping. Dielectric measurements illustrated that Mn-doped PBZ thin films not only had a larger dielectric constant, but also possessed a smaller dielectric loss. Accordingly, the tunability and the figure of merit of PBZ films were improved by Mn doping.     

Origin of the 330 nm absorption band and effect of doping Yb in LiYF4 crystals

The electronic structures of LiYF₄ (YLF) crystals containing F color center (YLF-F) and Yb doped YLF crystals (Yb³⁺:YLF, Yb²⁺:YLF) are systematically studied within the framework of the density functional theory. The calculated results indicate that the 330 nm absorption band originates from the F center in YLF crystals. Thus the doping of Yb³⁺ can weaken the 330 nm absorption band by competing with F vacancies in capturing free electrons arising after γ-irradiation and change to Yb². By analyzing the lattice relaxation and the electronic structure of YLF containing Yb²⁺, we can reasonably believe that once Yb²⁺ is formed in YLF crystal, its compensating hole will turn out to be shared by two F⁻ nearest to Yb²⁺ forming a diatomic fluoride molecular ion () perturbed by Yb²⁺, or to say V_F color center. According to the molecular-orbital linear combination of atomic orbital (MO-LCAOs) theory, compared to the alkali halides, e.g. LiF, the in V_F center in LiYF₄ peaks at about 340 nm, which is in agreement with the experimental results.     

Algebraic Properties of the Path Ideal of a Tree

The path ideal (of length t ≥ 2) of a directed graph Γ is the monomial ideal, denoted I _t (Γ), whose generators correspond to the directed paths of length t in Γ. We study some of the algebraic properties of I _t (Γ) when Γ is a tree. We first show that I _t (Γ) is the facet ideal of a simplicial tree. As a consequence, the quotient ring R/I _t (Γ) is always sequentially Cohen–Macaulay, and the Betti numbers of R/I _t (Γ) do not depend upon the characteristic of the field. We study the case of the line graph in greater detail at the end of the article. We give an exact formula for the projective dimension of these ideals, and in some cases, we compute their arithmetical rank.     

高温高压金刚石单晶生长界面的研究

 利用扫描电镜及Auger电子谱技术研究了高温高压下金刚石单晶生长界面的特性，观察到了金刚石单晶表面及金属膜表面的沟槽结构及金刚石-金属、金属-石墨两个主界面间的过渡层结构及界面间C原子电子组态的变化。     

贝叶斯公式的几个应用

介绍了贝叶斯公式的一些应用实例及分析,以使在教学中能帮助学生更深入地理解该公式.     

由Lévy过程驱动的BSDE定义的一般非线性期望

本文研究了平凡可积随机变量的一类非线性期望f-期望.利用陈增敬推广g-期望的方法,扩张了f-期望的定义空间.     

Coordinating a decentralized supply chain with customer returns and price-dependent stochastic demand using a buyback policy

We investigate a decentralized supply chain that consists of a manufacturer and a retailer where the retailer simultaneously determines the retail price and order quantity while experiencing customer returns and price dependent stochastic demand. We propose an agreement between the manufacturer and the retailer that includes two buyback prices, one for unsold inventory and a second for customer returns, and show that this type of easy-to-implement agreement can achieve perfect supply chain coordination and be a win-win for both manufacturer and retailer when a complementary profit-sharing agreement is included.     

一个海洋噬菌体感染模型的分析

对一个海洋病毒感染模型进行研究,分析其动力学行为,研究系统平衡点的存在性,稳定性及分支的产生.这对海洋生态研究具有一定意义.     

半环上的粗糙集

利用同余关系把粗糙集理论引入到半环里,给出了半环中的一个子集的上,下近似的概念,并研究了其一系列性质;另外我们还讨论了半环中的粗糙理想及性质.     

非负交换整半环上矩阵的正/负行列式保持问题

设R为非负交换整半环,用M_n(R)表示R上所有n×n矩阵构成的矩阵半环.令T是M_n(R)到其自身的线性变换,若T满足|T(X)|~+=|X|~+,■X∈M_n(R)(或|T(X)|~-=|X|~-,(?)X∈Mn(R)),称T为M_n(R)上保持正行列式(负行列式)的线性变换.刻画了n≥4时,M_n(R)上保持正行列式/负行列式的线性满射形式.