周期黎卡提微分方程正定解的存在性

讨论了标准的周期黎卡提微分方程,给出了其存在埃尔米特周期正定（HPPD）解的一个完整的充分必要条件。准确地说,在经过一个适当的状态空间基底变换后该条件通过能稳性和能检测性概念表述。结果表明,当HP－PD解存在时,它或者是唯一的,或者有无限多个。这一结果可以看作是Richardson和Kwong的结果对周期时变情况的扩展。     

钴基非晶丝应力电阻抗效应

研究了钴基非晶丝材料显示的应力电阻抗 (SI)效应。结果表明 ,淬态钴基非晶丝在其两端受到外加轴向压力作用下可呈现显著的应力电阻抗效应 ,它与驱动电流频率及幅值均有关     

The periodic nature of the positive solutions of a nonlinear fuzzy max-difference equation

We investigate the periodic nature of the positive solutions of the fuzzy difference equation , where k, m are positive integers, A₀, A₁, are positive fuzzy numbers and the initial values x_i, i = −d, −d + 1, … , −1, d = max{k, m}, are positive fuzzy numbers. In addition, we give conditions so that the solutions of this equation are unbounded.     

Responses of the autonomic nervous system during periods of perceived high and low work stress in younger and older female teachers

The aim of this study was to examine the response of the autonomic nervous system in younger (mean age 31 yrs, n=14) and older (mean age 54 yrs, n=14) healthy female teachers during work periods of perceived high and low stress. In the younger participants, heart rate, cortisol excretion rate and psychosomatic symptoms were significantly higher during the high work stress period. The older participants experienced no decrease in their heart rate and cortisol excretion during the low stress period and they exhibited no significant decrease in blood pressure after the work in the evening during both periods. It may be concluded that the recovery from the stress in the older teachers was insufficient particularly in view of their elevated diastolic blood pressure during the low work stress period. Ergonomic and individually tailored measures in terms of work time control, specific relaxation techniques, and a part-time retirement may improve the stress management of older teachers.     

Limitations of nonlinear discrete periodic control for disturbance attenuation and robust stabilization

This paper presents a performance analysis of nonlinear periodically time-varying discrete controllers acting upon a linear time-invariant discrete plant. Time-invariant controllers are distinguished from strictly periodically time-varying controllers. For a given nonlinear periodic controller, a time-invariant controller is constructed. Necessary and sufficient conditions are given under which the time-invariant controller gives strictly better control performance than the time-invariant controller from which it was obtained, for the attenuation of l_p exogenous disturbances and the robust stabilization of l_p unstructured perturbations, for all p[1,∞].     

超混沌系统自周期轨道链接式控制

基于混沌同步和周期轨道理论提出一种超混沌系统自周期轨道链接式控制法。从超混沌系统状态变量的时间序列中提取周期轨道并用于对系统的实时控制,可使混沌系统稳定运行于某一周期轨道。将提周期轨道经链接组合后用于系统控制,可得到大量的大周期轨道。对4阶蔡氏电路进行数字仿真实验,获得了满意的结果。     

碾压混凝土坝的温度规律初探

本文综合了“七五”国家科技攻关项目《碾压混凝土筑坝技术在大型水电主体工程中的应用》专题中有关碾压混凝土坝在温度控制方面的研究成果,对碾压混凝土块以及坝体的温度和温度应力的规律性进行了初步探讨。     

低压大型化工贮罐优化设计浅谈

大型贮罐的设计与一般压力容器有较大区别,力求归纳一下这方面的经验并结合工程实例,供广大设计和工程部门的同行借鉴。     

加固用复合材料力学性能的影响因素

在土木工程中，混凝土结构的加固补强要求连续纤维增强树脂基复合材料应具有较高的抗拉强度、弹性模量和一定的断裂延伸率，本文探讨了在一定成型工艺和环氧树脂基体的条件下，影响这些性能的因素．试验表明，纤维品种、纤维表面处理方法、片材厚度对这些性能有显著的影响；纤维束或纤维布与树脂基体复合固化后，由于固化应力的作用，其增强效率将大大下降。对此，在加固设计时应予以重视。     

江垭碾压混凝土坝无应力变形统计模型分析

无应力变形分析是大坝安全监测资料分析中应力应变分析的基础。文章以江垭大坝无应力变形实际监测资料为依据,通过温度因子、时效因子的选择建立无应力变形的统计模型,进而对模型的各个分量进行分析,得出江垭大坝目前无应力变形的状态。