Effect of change of sand properties on travel distance of ricocheted debris

The debris from exploded buildings can ricochet after colliding with the ground, thus increasing the debris travel distance and danger from any associated impacts or collisions. To reduce this danger, the travel distance of ricocheted debris must be accurately predicted. This study analyzed the change in the travel distance of ricocheted concrete debris relative to changes in the properties of a sand medium. Direct shear tests were conducted to measure the change in internal friction angle as a function of temperature and water content of the sand. Finite element analysis (FEA) was then applied to these variables to predict the speed and angle of the debris after ricochet. The FEA results were compared with results of low-speed ricochet experiments, which employed variable temperature and water content. The travel distance of the debris was calculated using MATLAB, via trajectory equations considering the drag coefficient. As the internal friction angle decreased, the shear stress decreased, leading to deeper penetration of the debris into the sand. As the loss of kinetic energy increased, the velocity and travel distance of the ricocheted debris decreased. Changes in the ricochet velocity and travel distance of the debris, according to changes in the internal friction angle, indicated that the debris was affected by the environment.     

Numerical investigation on cooling performance of filter in a pyrotechnic gas generator

As a key part of the pyrotechnic gas generator,the filter not only removes the particulate matter but also cools the hot gas to a safe level.This paper aims to improve the understanding of the basic heat and flow phenomenon in the gas generator.The pyrotechnic gas generator is modelling by a simplified filter structure with fiber arrays.A finite-volume model of the heat and fluid flow is proposed to simulate the detailed multi-dimensional flow and energy conversion behaviors.Several verification results are in good agreement with data in different references.Simulation results demonstrate that the filter can not only absorb heat from the gas but also cause the high intensity enhancement of the heat transfer.The per-formance difference between inline and staggered arrays is also discussed.The findings of the study put a further prediction tool for the understanding and design of the filter system with fibers.     

The parallel machine min-max weighted absolute lateness scheduling problem

Given a set of jobs, a processing time and a weight for each job, several parallel and identical machines, and a common due date that is not too early to constrain the scheduling decision, we want to find an optimal job schedule so as to minimize the maximum weighted absolute lateness. We show that this problem is NP-complete even for the single-machine case, and is strongly NP-complete for the general case. We present a polynomial time heuristic for this problem and analyze its worst-case performance. Empirical testing of the heuristic is reported, and the results suggest that the performance is asymptotically optimal as the number of jobs tends to infinity. © 1994 John Wiley & Sons, Inc.     

VRML及其在WEB MIS中的应用

简要介绍了虚拟现实建模语言 ,以及该技术在防险救生这一特殊领域中的应用 ;探讨了基于WEB管理信息系统中VRML的实现以及与数据库的关联 .     

多指数连续相位调制信号的早迟环定时同步

针对多指数连续相位调制信号提出基于序列检测的早迟环定时同步,利用维特比算法的幸存度量构造定时误差估计器。根据误差估计的S曲线和方差,优化定时误差捕获范围和估计精度、消除环路假锁点,同时利用多指数连续相位调制的脉冲幅度调制分解对定时误差估计器进行简化。仿真结果表明,优化后的早迟环定时误差捕获范围最大可达±0.5个符号周期,估计精度在中低信噪比下能够接近修正的克拉美罗界,在高信噪比下也有较好的估计性能;当早迟环定时支路的分支度量简化至最大似然序列检测的1/8时,对多进制、部分响应的多指数连续相位调制信号,造成的解调性能损失小于0.5 d B。     

火灾统计失实问题的现状及对策

以四川省为例介绍火灾统计失实的情况 ,并分析火灾统计失实问题的原因 ,提出纠正火灾统计失实问题的工作意见。     

西部大开发 城市要先行——北疆铁路沿线城镇带发展战略

以北疆铁路沿线城市发展作为先导,带动全疆经济和社会的全面发展,是新疆大开发的重要战略.从区域经济发展的角度,提出了优化区域城镇带的具体方案和完善城镇带空间布局的设想和建议.     

直流电动机推进调速系统的建模仿真研究

针对某消磁船大功率直流电动机推进控制系统存在的问题 ,建立了研究该控制系统的模型 ,进行了仿真研究 ,并根据仿真结果 ,提出改进方案     

基于Web Service的网上超市的设计

近年来形成的Internet技术———WebService技术已被称为下一代电子商务的核心。首先讨论WebSer vice及关键技术,然后阐述了WebService技术的网上超市应用框架及实现。