Catastrophic rupture of heterogeneous brittle materials under impact loading

The catastrophic failure of heterogeneous brittle materials under impact loading is not fully understood. To describe the catastrophic failure behavior of heterogeneous brittle materials under impact loading, an elasto-statistical-brittle (ESB) model is proposed in this paper. The ESB model characterizes the disordered inhomogeneity of material at mesoscopic scale with the statistical description of the shear strength of mesoscopic units. If the applied shear stress reaches the strength, the mesoscopic unit fails, which causes degradation in the shear modulus of the material. With a simplified ESB model, the failure wave in brittle material under uni-axial compression is analyzed. It is shown that the failure wave is a wave of strain or particle velocity resulted from the catastrophic fracture in an elastically stressed brittle media when the impact velocity reaches a critical value. In addition, the failure wave causes an increase in the rear surface velocity, which agrees well with experimental observations. The critical condition to generate failure wave and the speed of failure wave are also obtained.

基于考生比例的考场编排问题的分治算法

根据高考考场编排的一般要求和约束条件,建立了相应的数学模型,提出了基于考生比例的考场编排问题的分治算法,给出了算法的具体步骤,分析了算法的复杂度,验证了算法的合理性和有效性。实验结果表明,该算法能有效控制考生的分布,编排过程完全可以控制,最大程度地避免了前后左右相邻考生属同一中学,编排结果达到了比较理想的均衡状态。该算法速度快、效率高、易于实现、继承性强,很容易推广到其它类似问题的求解。

Combination of amperometric detector & UV detector for capillary electrophoresis

A new electrochemical cell assembly with the combination of UV and amperometric detector (AD) based on their complementarity was described. A Nafion tubing junction was used to decouple the high voltage from the separation capillary in the rear of on-column UV detector. In this mode, the electroactive and inert compounds could be detected by UV and AD at the same time. Aromatic amines were determined with the UV and the end-column AD detection to evaluate the performances of the cell assembly. Such an improved electrochemical detector could match the capillary with different diameters. By simple adjustment of the screws, the positioning of the working electrode and the detection capillary was easily gained without microscope. It is also very easy to assemble and disassemble the working electrode when needed. (C) 1999 Elsevier Science B.V. All rights reserved.

两轮驱动自动引导车辆定位停车研究

建立了两轮独立驱动自动引导车辆的运动学模型，计算了两轮以不同速度行驶时的运动轨迹。基于所建的运动学模型，提出了两轮驱动自动引导车的定位控制策略。通过试验证实，这种定位控制策略具有很快的停车速度和较高的定位精度。