A RIS treatment of the mean-square dipole moment of PMMA chains in consideration of the pendant ester group orientations

According to the six-state scheme proposed by Vacatello and Flory, the mean-square dipole moments 〈M²〉/x (x: number of monomeric units) of poly(methyl methacrylate) (PMMA) chains and their temperature dependence were calculated by the matrix algebra method of rotational isomeric state theory. To take account of the orientation effect of polar ester groups, the statistical weight matrices, U′ and U″, were recast into an expanded form. A Bernoullian probability λ introduced to measure the preference between the two alternative orientations (χ=0 and χ=π) of the side ester groups was found to give rise to a large effect on the mean-square dipole moment of polymers. When the skeletal bonds of a meso dyad are both in trans, an exceptionally strong dipole-dipole interaction may take place. If the two adjacent ester groups adopt the same orientation, the dipoles must be situated nearly parallel to each other in a close proximity. Such repulsive interactions may be alleviated by taking a staggered conformation, i.e. (χ,χ′)=(0,π) or (π,0). Such neighbor-dependent correlation inherent to the meso dyad is considered by assigning a parameter λ′ to the proper element of the U_m″ matrix. The values of 〈M²〉/x observed at 30 °C were satisfactorily reproduced by adopting λ=0.270 and λ′=0.865. The thermal coefficients were found to be reconciled with the available experimental data by allowing the orientation parameters λ and λ′ to be slightly temperature dependent. The stereochemical characteristics of the chain terminals were examined in order to extend the treatment to include the dipole moment of PMMA oligomers.     

基于功率控制技术的智能天线信号四阶矩空间定向法

部分可扩展线阵是智能天线中一种有效扩展孔径的线性阵列,但由于此类阵列结构的特殊性,需要对其输出采用预处理后才能应用通用的信号空间定向方法.基于移动通信系统中业已成熟应用的功率控制技术,结合阵列输出的高阶统计量,提出了一种新的预处理方法,该法简单、快捷,虽然性能稍逊一些,但仍然能有效地实现信号空间定向,具有较强的实用价值.     

Reliability evaluation of electrical power systems including multi-state considerations

A new approach is introduced for calculating the electrical network reliability indices, such as multi-state stationary availability, expected multi-state capacity, expected unsupplied demand, loss of load probability and total failed system probability. The universal moment generating function approach (UMGF) is used to evaluate the different reliability indices of the power system. In this paper we present a survey of recent work which treats the more sophisticated and realistic models in which components and systems may comprise many states ranging from perfect-working to complete failure. Such systems are multi-state (MSS) as they can have different levels of output performance. The objective is to determine the power structure which minimizes costs and satisfies reliability levels. A computer program has been developed to implement the UMGF technique, and an illustrative example is presented.     

硫酸盐长期侵蚀下混凝土受弯构件受力性能试验

通过硫酸盐介质环境中长期工作混凝土构件受弯试验和混凝土材料性能试验,指出在某些情况下受硫酸盐侵蚀混凝土受弯构件可会有更好的抗裂性能。     

正交设计在钢框架梁柱连接性能分析中的应用

在钢结构框架中,梁柱腹板连接同翼缘连接一样普遍,而且设计和施工更为困难,因此对梁柱腹板连接的性能分析具有重要意义.在钢结构工程设计中,梁柱连接的承载力是反映连接性能的一项重要指标.本文通过在钢框架梁柱腹板连接承载力影响因素分析中引入正交设计方法,找出了主要因素和次要因素.结果表明:在梁柱腹板连接中,梁的高度对连接的承载力影响最大,柱翼缘宽度和柱翼缘厚度次之,而梁翼缘厚度的影响并不显著,对今后钢框架的设计有着一定的指导意义.     

中板厂加热炉钢坯托出机的研制与应用

介绍自主创新研制的钢坯托出机，整个系统采用机械升降和行走以及摆轮结构，速度采用PLC控制，简易，可靠，易于维护，满足加热炉、辊道、厂房空间布置的要求，并保证出炉钢板的表面质量。     

Ф280×4轧机四联箱振动原因分析及措施

对四联箱振动异常机理进行了分析。连接轴结构中虚约束多,造成倾角过大,转动时不平衡附加负荷引起四联箱振动超常。通过改变连接轴花键结构、简化连接轴设计,改变了连接轴传统使用方法,减振效果显著,四联箱轴承寿命提高3倍以上。     

用MATLAB实现弯矩图的自动绘制

介绍用MATLAB实现有限元位移法结构计算的全过程，并直接绘出弯矩图。     

110 kV内桥接线变电站主变压器差动保护装置的选型

详细分析了内桥接线变电站中采用主变压器绕组数差动保护装置造成误操作的弊端，并提出了相应的补救措施；介绍了目前福建省110kV主变压器差动保护使用主要产品的应用特点和选型要求；最后建议采用主变压器绕组数 1的差动保护装置。     

Smith联接的单相自励感应发电机

针对需要单相电源的场合时有采用三相异步电机自动单相运行这种工况，对自励发电运行方式进行了分析。利用对称分量法导出了Smith联接的单相自励感应发电机对称运行条件及性能计算公式。计算表明：Smith联接的三相感应电机单相自励发电运行时，电压变化率较大，且离开平衡点负序电流迅速增加；利用最优化方法确定三相自励感应发电机不对称运行时的稳态工作点简单有效。实验结果与理论计算基本一致。