试论PBL教学法在少数民族预科汉语教学中的作用

PBL教学法是以问题为基础的教学模式。PBL教学法改变了传统的教学模式,把先进的教学理念引入了预科汉语教学课堂,不但能改变民族学生学习长期被动的处境,而且可以增强民族学生学习汉语的积极性与问题意识,与此同时也将会对目前预科汉语教学的环境、教师、学生提出挑战。     

Comparison of rank aggregation methods based on inherent ability

Ranking is a common task for selecting and evaluating alternatives. In the past few decades, combining rankings results from various sources into a consensus ranking has become an increasingly active research topic. In this study, we focus on the evaluation of rank aggregation methods. We first develop an experimental data generation method, which can provide ground truth ranking for alternatives based on their “inherent ability.” This experimental data generation method can generate the required individual synthetic rankings with adjustable accuracy and length. We propose characterizing the effectiveness of rank aggregation methods by calculating the Kendall tau distance between the aggregated ranking and the ground truth ranking. We then compare four classical rank aggregation methods and present some useful findings on the relative performances of the four methods. The results reveal that both the accuracy and length of individual rankings have a remarkable effect on the comparison results between rank aggregation methods. Our methods and results may be helpful to both researchers and decision‐makers.     

An efficient SPH methodology for modelling mechanical characteristics of particulate composites

Particulate composites are one of the widely used materials in producing numerous state-of-the-art components in biomedical, automobile, aerospace including defence technology. Variety of modelling techniques have been adopted in the past to model mechanical behaviour of particulate composites. Due to their favourable properties, particle-based methods provide a convenient platform to model failure or fracture of these composites. Smooth particle hydrodynamics (SPH) is one of such methods which demonstrate excellent potential for modelling failure or fracture of particulate composites in a Lagrangian setting. One of the major challenges in using SPH method for modelling composite materials depends on accurate and efficient way to treat interface and boundary conditions. In this paper, a master-slave method based multi-freedom constraints is proposed to impose essential boundary conditions and interfacial displacement constraints in modelling mechanical behaviour of composite materials using SPH method. The proposed methodology enforces the above constraints more accurately and requires only smaller condition number for system stiffness matrix than the procedures based on typical penalty function approach. A minimum cut-off value-based error criteria is employed to improve the compu-tational efficiency of the proposed methodology. In addition, the proposed method is further enhanced by adopting a modified numerical interpolation scheme along the boundary to increase the accuracy and computational efficiency. The numerical examples demonstrate that the proposed master-slave approach yields better accuracy in enforcing displacement constraints and requires approximately the same computational time as that of penalty method.     

Adaptive phasefield modelling of crack propagation in orthotropic functionally graded materials

In this work, we extend the recently proposed adaptive phase field method to model fracture in orthotropic functionally graded materials (FGMs). A recovery type error indicator combined with quadtree decomposition is employed for adaptive mesh refinement. The proposed approach is capable of capturing the fracture process with a localized mesh refinement that provides notable gains in computational efficiency. The implementation is validated against experimental data and other nu-merical experiments on orthotropic materials with different material orientations. The results reveal an increase in the stiffness and the maximum force with increasing material orientation angle. The study is then extended to the analysis of orthotropic FGMs. It is observed that, if the gradation in fracture properties is neglected, the material gradient plays a secondary role, with the fracture behaviour being dominated by the orthotropy of the material. However, when the toughness increases along the crack propagation path, a substantial gain in fracture resistance is observed.     

Survivability assessment of spacecraft impacted by orbit debris

To help optimize the spacecraft design and reduce the risk of spacecraft mission failure, a new approach to assess the survivability of spacecraft in orbit is presented here, including the following three steps:1) Sensitivity Analysis of spacecraft. A new sensitivity analysis method, a ray method based on virtual outer wall, is presented here. Using rays to simulate the debris cloud can effectively address the component shadowing issues. 2) Component Vulnerability analysis of spacecraft. A function"Component functional reduction degree — Component physical damage degree"is provided here to clearly describe the component functional reduction. 3) System-level Survivability Assessment of spacecraft. A new method based on expert knowledge reasoning, instead of traditional artificial failure tree method, is presented here to greatly improve the efficiency and accuracy of calculation.     

Exact analysis of (R,s, S) inventory control systems with lost sales and zero lead time

We study an (R, s, S) inventory control policy with stochastic demand, lost sales, zero lead‐time and a target service level to be satisfied. The system is modeled as a discrete time Markov chain for which we present a novel approach to derive exact closed‐form solutions for the limiting distribution of the on‐hand inventory level at the end of a review period, given the reorder level (s) and order‐up‐to level (S). We then establish a relationship between the limiting distributions for adjacent values of the reorder point that is used in an efficient recursive algorithm to determine the optimal parameter values of the (R, s, S) replenishment policy. The algorithm is easy to implement and entails less effort than solving the steady‐state equations for the corresponding Markov model. Point‐of‐use hospital inventory systems share the essential characteristics of the inventory system we model, and a case study using real data from such a system shows that with our approach, optimal policies with significant savings in inventory management effort are easily obtained for a large family of items.     

飞行控制系统的重构技术研究

飞行控制系统的重构技术可以有效地提高飞行器的生存能力和任务效能,已成为现代飞行器综合设计领域的热门研究专题之一.介绍了飞控系统重构技术的发展历史及现状,对目前几种重要的飞行控制系统重构方法进行了概述和分析,总结了飞控系统重构技术领域里的一些热点问题,最后展望了未来飞控系统重构技术的发展趋势.     

证据推理法在C4ISR系统可靠性评价中的应用

首先参考外军NATO COBP阐述了不确定性处理在C4ISR系统评价中的重要性,鉴于ER方法的先进思想,介绍了ER(Evidential Reasoning)方法在不确定条件下的基本评价框架,并对ER方法和AHP方法,D-S证据理论以及模糊综合评价方法进行了比较综合,针对我军C4ISR系统可靠性评价中的数据不完备等实际问题,初步应用此方法进行评价,对决策人员有一定的参考意义.     

基于SNF的一种检测和跟踪性能优化方法

对于一个监视系统,跟踪性能的优化要求检测系统和跟踪系统通过引入反馈进行联合设计,针对最大量测幅值邻域滤波器(SNF),提出了先验和后验检测跟踪优化准则,通过分析得出先验优化准则不可行这一结论,而利用后验优化准则同时对检测阈值和门值的联合优化,仿真结果表明,用后验优化准则进行检测和跟踪性能优化,不仅具有比恒虚警率更好的跟踪精度,而且其计算代价也大为降低.     

消防模拟训练操作规程设置探究

近年来,随着各地培训基地的建立和发展,全国建成的模拟训练设施逐年增多,模拟实战训练被逐渐提到议事日程。但是,各地开展模拟设施训练相对较少,训练的操作规程还不完善,大都处于摸索探究阶段。针对广东总队培训基地开展模拟训练情况进行分析,对模拟训练科目的设置原则,操作规程编写内容及要求、考核标准的确定进行了探究,并对今后模拟训练的科学有效开展提出参考建议。