Models for the frequency dependence of coercive field and the size dependence of remanent polarization in ferroelectric thin films

Abstract

We have confirmed the theory of Ishibashi and Orihara for the frequency dependence of coercive fields in ferroelectric thin films.SrBi₂NbTaO₉, SrBi₂Ta₂O₉, and PbZr_1-x Ti _x O₃ (PZT) data from DeVilbis et al. reveal a power-law dependence of form E_c (f) = Bf^d/α , where d is the dimensionality of domains (ca. unity in uniaxial ferroelectrics such as SBT and SBNT) and α is approximately 6, in agreement with theoretical predictions. Models are also presented for the polarization and fatigue data from NEC of micron-sized thin-film strontium bismuth tantalate capacitors, emphasizing behaviour at unsaturated voltages.     

CMS实验中关系数据库的精确关键词查询

在大型强子对撞机(LHC)上紧凑型缪子螺线管探测器(CMS)实验的复杂数据环境下,有多个关系型数据源记录了关于数据组织和分布的信息。为实现数据查询系统的精确关键词查询功能,通过分析数据库模式图的方法,将关键词查询语言动态翻译成SQL语言,设计并实现一个跨数据库平台的关键词查询系统。针对动态翻译过程中存在的二义性问题,提出基于查询实体的模式图分析算法,以及基于最小权重树查找的动态连接算法。实验结果表明,该动态连接算法能为关键词查询正确生成所需数据库表的连接方式,使关键词查询系统具有较高的查询效率,以满足用户实时、精确查询的需求。     

ISAR成像的并机并行实时实现

从ＩＳＡＲ实时成像的要求出发，分析了目标横向成像的原理，在实验的基础上对决定横向成像的散射点分布做了研究，提出了自动选取回波抽取间隔的方法，并利用快速算法在由多片数字信号处理器组成的高速并行处理机上对实测数据进行了成像实验，完成了对平稳飞行目标的实时成像。     

紧支波波基的非对称性及改进

文中给出了紧支正交小波基的非对称性的一种简捷且容易理解的证明方法，在讨论了紧支 交小波基的这种非对称性在实际应用中的不便后，系统地总结了两大类的改进方法，提出了一种用多尺度函数来改进其对称必的思路，并对重要的改进法给出了具体的算例。     

微电网技术研究综述

介绍了微网的概念,组成结构、特征及其优点,讨论了微网的运行与控制以及我国对这一领域的研究发展现状,指出不足之处,进行优化,将其中关键技术加强应用,保证电网的安全稳定运行,与大电网一起在负荷出现变化时发挥最大效应。     

科技项目申请书关键词提取方法

关键词提取在文本相似度计算得到应用。传统的关键词提取方法忽略文本中的未登录词以及缺乏对词语语义的理解。针对科技项目申请书,研究提出一种基于未登录词识别与语义的关键词提取方法。应用Lucene和统计相融合的方法进行分词,并识别未登录词作为申请书关键词的一部分;依据社会网络理论构建词语语义相似度网络,并计算词语关联度提取申请书其他关键词。实验结果表明,与传统的关键词提取方法相比,新方法能提取更准确的关键词,有更好的科技项目相似性检查效果。     

基于点过程模型连续语音关键词检测

提出了基于点过程模型（PPM）的连续语音关键词检测方法。该方法首先利用时态模式（TRAP）特征和多层感知器（MLP）计算每个音素的帧级后验概率,在此基础上,将语音可看作多个相互独立的事件（音素）,利用泊松过程对事件建立点过程模型,最后通过计算似然比达到关键词检测目的。实验结果表明,对8kHz采样语音,关键词平均召回率和准确率分别可达69．5％和82％以上。     

(111)-Oriented BaTiO3 thin films hydrothermally formed on TiO2/Si substrate

Abstract

Barium titanate (BaTiO₃) thin films with high (111)-orientation were successfully grown on TiO₂-covered Si(111) substrate using hydrothermal method, where the TiO₂ layer was previously fabricated at room temperature by means of ion-beam-assisted deposition. This processing method provides a simple mild-chemical route for directly producing the analogous crystalline films on different substrates. The BaTiO₃ films did not reach the TiO₂/Si interface even if the hydrothermal treatment was prolonged to 24 hours. Both Rutherford backscattering and spread-resistance profiling characterizations confirmed the diffusion nature of the formed Ba-TiO₃/TiO₂/Si system.     

Electrical properties of paraelectric PLT(28) thin films deposited by dc magnetron sputtering

Abstract

Paraelectric [Pb, La]TiO₃ (PLT, La = 28 mol%) thin films were prepared by dc magnetron sputtering using a multi-element metal target. In order to crystallize the as-deposited PLT thin films into the cubic perovskite structure, a heat treatment was applied at annealing temperatures ranging between 450 and 750°C. The electrical measurements such as dielectric properties, polarization-electric field (P-E), and current-voltage (I–V) were investigated with the change of annealing temperature. The dielectric constant and dissipation factor of paraelectric PLT film annealed at 750°C were 1216 and 0.018, respectively. The charge storage density was approximately 12.5 μC/cm². The leakage current density in PLT film annealed at 650°C was around 0.1 μA/cm² at the electric field of 0.25 MV/cm.