薄壁曲线箱梁剪力滞计算的有限段方法

采用能量变分法导出的控制微分方程的齐次解作为梁段的有限元位移模式,建立了考虑初曲率的弯曲、扭转、剪力滞耦合和畸变的半解析有限段模型.由直接刚度法导出了梁段单元的刚度矩阵;由功能原理获得单元荷载列阵,提出了一种能对工程中常用的多跨连续曲线箱梁剪力滞计算的有限段法.制作了一两跨连续曲线箱梁有机玻璃实验模型,分别进行了在集中荷载和均布荷载作用下的剪力滞效应实验研究.其结果与有限段法计算结果以及有限元法的计算值均符合良好,从而验证了有限段方法的正确性. 关键词： 薄壁箱梁 剪力滞 有限段法 模型实验     

服务业集聚和经济增长对我国城镇化影响的实证研究——基于半参数空间滞后模型

针对已有文献研究城镇化时忽视的服务业的空间集聚效应以及经济增长对人口城镇化的非线性关系的问题,文章根据第六次全国人口普查数据,利用半参数空间滞后模型实证研究了我国人口城镇化的影响因素。结果表明:(1)服务业的发展大力推动了我国区域人口城镇化发展,且它的影响强度明显高于工业化发展所带来的影响。服务业集聚效应对该省的人口城镇化具有促进作用,第二产业集聚对该省的人口城镇化的作用不显著。(2)经济欠发达地区(云贵川等)的经济增长对人口城镇化的促进作用较小。而多数位于中部和沿海经济较发达地区(福建、广州等)的经济增长显著促进了人口城镇化的发展。然而,在经济发达地区(如上海、北京、浙江)的经济增长对人口城镇化的促进效果明显开始减弱,甚至是负向的关系。(3)半参数空间滞后模型比普通参数模型具有更高的拟合优度和更丰富的结论,它能够有效刻画城镇化过程中空间相关性与非线性特征。     

Isogeometric analysis for the dynamic problem of curved structures including warping effects

Curved beam structures have been used in many civil, mechanical, aircraft, and aerospace constructions. The analysis is mainly based on solid and plate models due to the fact that traditional curved beam elements do not include nonuniform warping effects, especially in the dynamic analysis. In this article, independent warping parameters have been taken into account and the initial curvature effect is considered. Curved beam’s behavior becomes more complex, even for dead loading, due to the coupling between axial force, bending moments, and torque that curvature produces. In addition to these, the Isogeometric tools (b-splines or NURBS), either integrated in the Finite Element Method or in a Boundary Element–based Method called Analog Equation Method, have been employed in this contribution for the dynamic analysis of horizontally curved beams of open or closed (box-shaped) cross sections. Free vibration characteristics and responses of the stress resultants and displacements to moving loading have been studied.     

钱塘江二桥变截面连续箱形梁剪滞效应的分析

本文结合钱塘江二桥应用变分法推导了变截面箱形梁剪滞效应的微分方程并利用有限差分法求得解答。所得结果与大桥工程局桥梁科学研究所模型试验数据比较吻合。最后通过有限元法,验证了理论分析并对钱塘江二桥的剪滞效应进行分析。     

辅以时滞的pH-敏感介孔膦酸锆对双氯芬酸钠的可控结肠靶向释放

以pH-敏感介孔膦酸锆作为药物载体, 选用治疗时辰节律性疾病(风湿性关节炎)的药物双氯芬酸钠作为药物模型, 利用蘸涂的方法对载药的pH-敏感介孔膦酸锆进行时滞膜的包覆, 建立起一个时滞型和pH-敏感型相结合的口服结肠靶向给药系统. 在系统研究pH-敏感介孔膦酸锆对双氯芬酸钠吸附和释放的基础之上, 通过调控时滞膜的厚度控制释放双氯芬酸钠的时滞时间约为6 h. 该给药系统在人工模拟胃液中3 h内完全不释放双氯芬酸钠, 而在人工模拟肠液中最初的3 h(可以看成发生在小肠)所释放的双氯芬酸钠仅为全部释放量的9%, 在之后的46 h内(可以看成发生在结肠)缓慢释放的双氯芬酸钠则占全部释放量的90%以上. 这样, pH-敏感介孔膦酸锆作为新型药物载体与时滞效应相结合, 通过时滞和pH-敏感双重控制实现了治疗时辰节律性疾病药物在结肠的定位释放.     

Lag synchronization between discrete chaotic systems with diverse structure

A lag synchronization controller is designed in studying discrete chaotic systems with diverse structures to realize synchronization between Henon and Ikeda sys- terns. The structure of the lag synchronization controller and the error equations of state variables between discrete chaotic systems are presented based on the stability theory. The designed controller has unique structures for different chaotic systems. Lag synchro- nization between any discrete chaotic systems with diverse structures can be achieved. Simulation results show that this control method is effective and feasible.     

A delayed biophysical system for the Earth's climate

Summary We consider further the Differential Daisyworld model of Watson and Lovelock that we have analyzed in a previous paper (De Gregorio et al., 1992). In this work we introduce a delay in the birthrate of the species. We consider three different models: the constant time lag model and the strong and the weak delay models. In the weak delay case no value of the delay changes the asymptotic stability of the stationary solutions. In the constant time lag and in the strong delay models, however, there exists a critical value of the delay, above which periodic solutions appear. These periodic solutions are numerically found to be globally attracting even for large delay when the linear approximation analysis is no longer valid. For both models, very regular behavior is obtained if the percentage coverage of the fertile ground of the Earth is much less than 1. As the percentage of the fertile ground increases, however, chaotic behavior is possible.     

加强篮球传球准确性的教学和训练

本文按照篮球运动的规律和教学训练的特点,就传球准确性问题作比较全面、深入的阐述;对球行路线,移动中传球的特点,传球者和防守者之间的相对位置关系,传球的时机、速度、方向、位置、落点以及如何培养学生传球意识等方面问题进行了一定的分析;着重指出学生练习中易犯错误和纠正方法,并提供一些加强传球准确性的教学训练手段。     

中国股市一期价格行为研究

本文运用 CJ统计量与一步 Markov转移概率矩阵研究了中国沪、深两市的一期价格行为 .实证结果表明 :大约自 1997年以来 ,一期价格行为表现出很强的随机性 .     

基于长余辉材料的激光书写和显示

本文给出了长余辉材料一个新的用途,研制了一台以长余辉材料为屏幕的激光书写显示装置,可以人为控制激光笔在余辉材料上随意书写文字、画图并显示.该装置利用单片机和步进电机控制两组轴镜在不同方向的转动,从自己建立的开源矢量图库中调用相关图片,使激光光束在长余辉材料上进行二维矢量的扫描,完成文字书写和绘图显示.用VASP(Vienna abinitio simulation package)软件计算出长余辉材料Mn(H_2PO_4)_2的能级结构,测试了SrAl_2O_4:Eu~(2+),Dy~(3+)和Mn(H_2PO_4)_2的余辉强度衰减曲线,便于调整样机电机的书写速度,测试了Mn(H_2PO_4)_2的反射谱和拉曼谱,其拉曼峰值在625,769和1049 nm及远红外.通过理论和实验研究,掌握了与相应长余辉材料匹配的激发最佳激光波段.制作样机后得到英文、中文、图像的实时书写和显示结果.本装置犹如一只无形的"笔"在纸上挥舞,流畅书写绘画,书写过程配上音乐颇具观赏性,该装置可应用于商业广告显示、动态标语书写、教学投影辅助设备、舞台效果、新型艺术表现形式等领域.