基于TCP协议的远程控制系统网络时延仿真研究

为了能够在同一网络环境下对远程控制系统进行研究,使用结构数组对网络时延进行了仿真。将数据报的信息存放在与其网络时延相对应的结构数组元素中,在每个采样点系统只使用结构数组相应元素中的信息,实现对网络时延的仿真。在基于时间驱动工作方式的控制系统中,可以采用这样的方法进行网络时延仿真。     

纯时滞三种群捕食系统持续生存与全局吸引性

研究了具有HollingⅡ功能性反应的纯时滞的两捕食者、一食饵生物系统,通过构造合理的Lyapunov函数讨论了系统的全局吸引性,并得到系统持续生存的充分条件。     

论闲暇教育

随着社会的发展,个人所掌握的闲暇时间越来越多,闲暇教育也越来越为人重视。其实追溯历史,闲暇教育思想源远流长,梳理前人对闲暇教育的认识能使我们更好地理解闲暇教育。     

变论域模糊自适应滑模有限时间收敛制导律

针对拦截高速机动目标的需求,研究了一种变论域模糊自适应滑模有限时间收敛制导律。推导了导弹-目标空间拦截模型,设计了三维滑模制导律;根据有限时间收敛制导律专家的经验,采用模糊自适应控制方法对滑模制导律的非切换项进行逼近,并设计了有限时间收敛模糊控制规则;提出了一种新型变论域伸缩因子,设计了基于新型伸缩因子的变论域模糊自适应滑模有限时间收敛制导律。仿真结果表明,所设计的制导律能够使导弹准确命中目标,并能够达到视线角速率有限时间收敛,且与比例制导律相比,具有更高的制导精度和更短的飞行时间。     

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.     

Cooperative interception with fast multiple model adaptive estimation

For the case that two pursuers intercept an evasive target, the cooperative strategies and state estimation methods taken by pursuers can seriously affect the guidance accuracy for the target, which performs a bang For the case that two pursuers intercept an evasive target, the cooperative strategies and state estimation methods taken by pursuers can seriously affect the guidance accuracy for the target, which performs a bang-bang evasive maneuver with a random switching time. Combined Fast multiple model adaptive estimation (Fast MMAE) algorithm, the cooperative guidance law takes detection configuration affecting the accuracy of interception into consideration. Introduced the detection error model related to the line-of-sight (LOS) separation angle of two interceptors, an optimal cooperative guidance law solving the optimization problem is designed to modulate the LOS separation angle to reduce the estimation error and improve the interception performance. Due to the uncertainty of the target bang-bang maneuver switching time and the effective fitting of its multi-modal motion, Fast MMAE is introduced to identify its maneuver switching time and estimate the acceleration of the target to track and intercept the target accurately. The designed cooperative optimal guidance law with Fast MMAE has better estimation ability and interception performance than the traditional guidance law and estimation method via Monte Carlo simulation.     

基于时间反转声学理论的超声相控阵超分辨率成像方法

在超声相控阵检测领域,常规成像方法遵守瑞利准则,其成像分辨率受到波长限制。研究时间反转多信号分类(Time Reversal-MUltiple SIgnal Classification, TR-MUSIC)方法,在保持超声波工作频率不变且不影响系统探测深度的前提下,可提高成像分辨率,实现超分辨率成像。通过全矩阵采集方法获取被测对象的超声阵列数据;利用平面B扫描和TR-MUSIC方法处理数据,得到二维和三维超声图像;依据图像特征评估被测对象内部状况。实验选取加工不锈钢试块作为被测对象,搭建超声相控阵检测系统,在试块内部加工6个直径为1 mm、可视为点散射体的相邻贯通孔作为缺陷。实验表明,TR-MUSIC方法能够区分并定位这6个相邻点散射体,而平面B扫描方法则不能。因此,基于时间反转声学理论的TR-MUSIC方法可以提高成像分辨率,改善超声图像质量。     

一类具有时滞的捕食系统的稳定性与Hopf分支

研究一类具有时滞的两种群捕食系统,通过分析特征方程讨论了正平衡点的局部稳定性问题。通过构造适当的Lyapunov泛函,得到了保证系统正平衡点全局渐近稳定的充分条件,并讨论了在正平衡点附近Hopf分支的存在性问题。     

What you should know about queueing models to set staffing requirements in service systems

One traditional application of queueing models is to help set staffing requirements in service systems, but the way to do so is not entirely straightforward, largely because demand in service systems typically varies greatly by the time of day. This article discusses ways—old and new—to cope with that time‐varying demand. © 2007 Wiley Periodicals, Inc. Naval Research Logistics, 2007     

辉煌与式微：《今古奇观》的历史沉浮

《今古奇观》是中国话本小说史上重要的小说选集,成书于崇祯五年至十七年之间。热情歌颂了明代中叶以来趋于活跃的市民精神和个性解放。世界范围内,有关《今古奇观》的研究日渐式微,但是从历史时段和选本观念来看,仍有难以掩盖的辉煌。