中学生如何建立自己合理的物理知识结构?

 在积累知识的过程中,除如何猎取知识外,还有一个如何储存知识的问题.深刻的理解加上合理的储存,就能运用自如地掌握知识,而靠死记硬背储存知识,遇到灵活性强、比较隐蔽的问题就束手无策了.合理的知识结构应当具有以下特征:一、系统性.处于游离状态的知识,完全失去了其应有价值,成了大脑的负担;而系统化的知识,各个知识点前后呼应,表现出1+1>2的价值,减少了记忆量和记忆难度.因此,学习中不仅要善于获得知识,更要善于整理自己的知识系统.     

利用SLR技术实测当今全球板块运动参数

本文利用最近5年(1983—1988)的全球SLR资料实测了位于北美、南美、澳大利亚、太平洋和欧亚板块上一些激光站的站间基线长度的现时变化速度,测定的精度好于1cm/a,所测的结果从广义上与由长期地质资料平均确定的板块运动模型(Minster-Jordan,1978)一致,这表明在离板块边界足够远地区的运动在过去百万年间似乎是稳定的,不符的情况主要出现在板块边界地区,沿着著名的圣·安德列斯转换断层两侧的基线测量,这次测得的基线变化速度为2.9cm/a(M/J:5.3cm/a),可能与板块边缘周期性形变的假设和突发性的板块运动局限于板块边界的概念有关,本文还简要叙述了利用SLR技术测定板块运动的原理和“多级复弧”的解算方法,对实测中的各误差源进行了一定的分析。     

Hamiltonian parametric element and semi-analytical solution for smart laminated plates

Based on the Hellinger-Reissner (H-R) mixed variational principle for piezoelectric material, a unified 4-node Hamiltonian isoparametric element of anisotropy piezoelectric material is established. A new semi-analytical solution for the natural vibration of smart laminated plates and the transient response of the laminated cantilever with piezoelectric patch is presented. The major steps of mathematical model are as follows: the piezoelectric layer and host layer of laminated plate are considered as unattached three-dimensional bodies and discretized by the Hamiltonian isoparametric elements. The control equation of whole structure is derived by considering the compatibility of generalized displacements and generalized stresses on the interface between layers. There is no restriction for the side-face geometrical boundaries, the thickness and the number of layers of plate by the use of the present isoparametric element. Present method has wide application area.