H∞ filtering for discrete-time systems subject to stochastic missing measurements: a decomposition approach

This paper deals with the problem of H_∞ filtering for discrete-time systems with stochastic missing measurements. A new missing measurement model is developed by decomposing the interval of the missing rate into several segments. The probability of the missing rate in each subsegment is governed by its corresponding random variables. We aim to design a linear full-order filter such that the estimation error converges to zero exponentially in the mean square with a less conservatism while the disturbance rejection attenuation is constrained to a given level by means of an H_∞ performance index. Based on Lyapunov theory, the reliable filter parameters are characterised in terms of the feasibility of a set of linear matrix inequalities. Finally, a numerical example is provided to demonstrate the effectiveness and applicability of the proposed design approach.     

高速钢复合轧辊液固结合过程数值模拟

在试验的基础上,建立了高速钢复合轧辊铸造过程中外层高速钢钢液充型湍流流动及辊芯和外层高速钢液固结合时的三维速度场和温度场的计算模型,模拟了辊芯预热温度对凝固及界面结合情况的影响。结果表明,高速钢钢液在铸型中是从下到上、从两侧的交界面向中间顺序凝固的,但随着辊芯表面预热温度的不同,呈现出不同的特点。在同一截面上,当预热温度较低时,其最后凝固的位置位于工作层金属中间的某一位置,当预热温度较高时,最后凝固的位置位于工作层金属和辊芯之间的界面上。预热温度较低时,两者之间将难以形成冶金结合,预热温度适宜时,两者之间可以形成良好的冶金结合,适宜的辊芯预热温度为1100~1200℃。     

A piecewise analysis method to stability analysis of linear continuous/discrete systems with time‐varying delay

The delay‐dependent stability problem of linear continuous/discrete systems with time‐varying delay is investigated based on a piecewise analysis method (PAM). In the method, the variation interval of the time delay is firstly divided into several subintervals. By checking the variation of the Lyapunov functional in every subinterval, some new delay‐dependent stability criteria are derived. Several numerical examples show that our method can lead to much less conservative results than those in the existing references. Moreover, when the number of the divided subintervals increases, the corresponding criteria can provide an improvement on the results. Copyright © 2008 John Wiley & Sons, Ltd.     

Medical image contrast enhancement based on improved sparrow search algorithm

The collection or transmission of medical images is often disturbed by various factors, such as insufficient brightness and noise pollution, which will result in the deterioration of image quality and significantly affect the clinical diagnosis. To improve the quality of medical images, a contrast enhancement method based on improved sparrow search algorithm is proposed in this paper. The method is divided into two steps to enhance the medical images. First, a new transform function is introduced to improve the brightness or contrast of medical images, and two parameters in the transform function are optimized by the improved sparrow search algorithm. Second, adaptive histogram equalization method with contrast limited is used to equalize the result image of the previous step to make the pixel distribution of the image more uniform. Finally, a large number of experiments and qualitative and quantitative analyses were conducted on the common data sets. The analysis results demonstrate that the presented approach outperforms some existing medical image processing approaches.     

电加热实现过盈配合的工艺改进

介绍一种投资少、简单实用、低耗清洁、适合多部位和不同部件使用的小型加热盘——电加热工艺法。解决了形状特异、大而重的金属件加热处理后,在热胀冷缩状态下,满足过盈配合的需要。通过工艺改进与传统方法对比、分析,阐述了在机械制造领域中的应用效果。     

Strength of Cu-28 wt%Ag composite solidified under high magnetic field followed by cold drawing

Cu-Ag composite is one of the best conductors for high-field magnets. Increasing its strength is crucial for designing newer high-field magnets. Cu-28 wt%Ag samples were solidified with and without a 12-T high magnetic field (HMF), and then cold-drawn. We investigated the influence of HMF on microstructure, hardness and strength of Cu-Ag samples both before and after cold-drawing. The introduction of external HMF during solidification increased both the dendrite arm spacing and the dissolved Ag in Cu, and it reduced the spacing between both the Ag precipitates in proeutectic Cu and the eutectic lamellae. The transversal microstructure after cold-drawing inherited the network solidification structure, but at a refined scale. The Cu dendrite spacing in the 12-T HMF samples at all deformation strain was larger than that without HMF. HMF slightly increased the intensity of <111> fiber texture of Cu, which strengthened proeutectic Cu at the level of 3.5 deformation strain. In samples deformed to strain of 3.5, refined Ag precipitation spacing, increased Ag solubility in Cu matrix, and refined eutectic lamellar spacing by 12-T HMF increased the strength by 5% in the sample compared with that without HMF.     

Effect of Diffusion Length in Modeling of Equiaxed Dendritic Solidification under Buoyancy Flow in a Configuration of Hebditch–Hunt Experiment

Metallurgical and Materials Transactions B - Modeling of equiaxed solidification is vital for understanding the solidification process of metallic alloys. In this work, an extended literature...     

方坯连铸过程中钢液流动、凝固及溶质分布的耦合数值模拟

采用Fe-C二元合金的连续介质模型，对方坯连铸过程进行紊流动，凝固及溶质传输的三维耦合数值模拟，计算表明，注流在结晶器上部形成的回,大部分返回主入流股，其余部分随凝固坯壳向下流动，凝固坯壳在截面上由于注流冲刷造成不均匀分布，与实际情况相符，随凝固进行，液相中的溶质不断富集，最终在铸坯中心区域形成宏观偏析。     

Sojourn-probability-dependent H∞ control for networked switched systems under asynchronous switching

This paper considers H_∞ controller design for a class of networked switched discrete systems under asynchronous switching. The sojourn probability information – the probability of the switched systems staying in each subsystem – is first used to rebuild the networked switched systems. Also, a time-varying lag, depending on both the network-induced delays and switching signals, is taken into consideration between the switching instants of the controllers and systems model. By considering both sojourn probability information and asynchronous switching, a new kind of networked switched system model is proposed, wherein a set of random variables are proposed to describe the sojourn probabilities of the subsystems. Then, stability analysis and H_∞ performance analysis under asynchronous switching are derived. It should be noted that the system performance depends not only on the time-varying lag, but also on the sojourn probabilities. Finally, an example is given to illustrate the effectiveness of the proposed approach.     

原位形变铜基复合材料研究现状

原位形变铜基复合材料是一类具有广阔应用前景的高性能功能材料.由于其具有良好的高强度、高导电率匹配关系,受到国内外的广泛研究.从不同最终形变工艺、热稳定性、强化机理及导电机理等方面对凝固/形变法制备原位形变铜基复合材料的国内外研究现状进行综述,并指出这类材料的发展趋势.