材料力学教学深层互动探索与实践

大学课堂教学中影响教学质量的主要问题是学生的学习态度,如何调动学生学习的积极性,是每位任课教师需要深入思考的问题。本文以材料力学课程教学为载体,结合管理学中的二八定律,以大学生力学竞赛为契机,研讨教师与学生之间的深层互动交流问题。深层互动分为课程授课中的互动和力学兴趣小组的互动两个层次,通过互动一方面为优秀学生打开上升通道,另一方面将优秀学生树为榜样,潜移默化中影响其他学生的学习态度,进而改善整个班级的学习风气。实践表明,深层互动教学模式能有效激发学生学习材料力学的兴趣,取得了良好的教学效果。

     

Focal shift of hollow Gaussian beams through a thin lens

In this paper, the focal shift of hollow Gaussian beams (HGBs) passing through a thin lens is investigated in detail. An analytic expression of the location of the axial maximum intensity for the HGBs is derived. It is found that, both the relative focal shift and the relative location of the axial maximal intensity of the HGBs is strongly affected by the ratio α (where α=s/f, here s is the axial distance from the input plane to the lens plane and f is the focus length of the lens), and it is also greatly affected by the changes of both the effective Fresnel number N_w and the order n of HGBs.     

Gaussian estimates for elliptic operators with unbounded drift

We consider a strictly elliptic operator

     

正螺面的两个特征

通过对曲线主法线面的研究,得到了正螺面的两个特征.     

光斑环围参量阵列测试法的测量不确定度

为评定光斑环围参量（包括环围功率和环围尺寸）阵列测试法的测量不确定度,给出了环围参量一般形式的定义和连续形式的计算表达式,归纳并比较了阵列测试法下光斑环围参量的3种常用计算方法,即近似环围功率法、准确环围功率法和等效环围尺寸法,给出了零阶近似下环围参量离散形式的计算表达式。根据不确定度传递律,推导了基于等效环围尺寸法的环围参量测量不确定度的一般表达式,讨论了常见简化条件下的环围参量测量不确定度表达式。建立了光斑环围参量计算及其不确定度评定的一套较完整的方法。以强度为高斯分布的光斑为例,得到了简化条件下的环围参量测量不确定度的解析表达式,并用数值模拟法验证了其正确性。     

Upper bounds for Gaussian stochastic programs

We present a construction which gives deterministic upper bounds for stochastic programs in which the randomness appears on the right–hand–side and has a multivariate Gaussian distribution. Computation of these bounds requires the solution of only as many linear programs as the problem has variables. Received December 2, 1997 / Revised version received January 5, 1999? Published online May 12, 1999     

高斯－谢尔模型光束的变换特性

在一般情况下推导出高斯－谢尔模型光束经ＡＢＣＤ光学系统变换后的相干模迭加表示式。     

Experimental and numerical investigation of combined isotropic-kinematic hardening behavior of sheet metals

To prevent a sheet specimen from buckling subjected to a tension-compression cyclic loading, a new fixture has been developed to use with a regular tensile-compression machine. The novelty of this device lies in 4-block wedge design with pre-loaded springs. This design allows blocks to freely move in the vertical direction while providing the normal support to the entire length of the specimen during the tension-compression cycle. The entire test is easy to setup, which is another advantage of this design. In order to measure the strain accurately, the transmission type laser extensometer was utilized together with the implementation of double-side fins in the specimen. Experimental results of tension-compression tests are presented followed by a review of existing testing methods. In order to describe the accurate cyclic tension-compression behavior, the combined isotropic-kinematic hardening law based on the modified Chaboche model and the practical two-surface model based on Dafalias-Popov and Krieg models have been modified in this work, considering the permanent softening behavior during reverse loading and the non-symmetric behavior during reloading. Through tension-compression tests, the material characterization has been performed for three base materials, BH180, DP600 steels and AA6111-T4 sheets.