一类高阶中立型泛函微分方程周期解的存在性

该文利用重合度理论研究了一类具有分布时滞的高阶中立型泛函微分方程的周期解问题,得到了周期解存在的简单判别条件.     

基于光纤光栅的物体表面附近温度场测量

提出一种利用光纤布喇格光栅温度传感器测量物体表面法向局域内温度场分布的新方法.将多个毛细管封装的波分复用光纤光栅温度传感器串接,沿待测位置法线方向平行于表面等间距放置,对法向局域内的温度进行准分布式监测,封装后的传感器响应时间为2.74s.利用ANSYS软件对空气的热稳态层流进行分析,获得温度场分布的等值线图.实验得到温度随高度变化的一阶变化率为-24.262,二阶变化率为10.117 2,而ANSYS仿真结果给出的分别为-22.842和8.613,两者基本相符,验证了此测量方法的可靠性.该技术为了解温度场的局域分布提供了技术支撑,为航空器选材和构型的确定提供新的测试方案.     

Performance of scheduling algorithms for no-wait flowshops with parallel machines

We study the performance of scheduling algorithms for a manufacturing system, called the ‘no-wait flowshop’, which consists of a certain number of machine centers. Each center has one or more identical parallel machines. Each job is processed by at most one machine in each center. The problem of finding the minimum finish time schedule is considered here in a flowshop consisting of two machine centers. Heuristic algorithms are presented and are analyzed in the worst case performance context. For the case of two centers, one with a single machine and the other with m, two heuristics are presented with tight performance guarantees of 3 − (1/m) and 2. When both centers have m machines, a heuristic is presented with an upper bound performance guarantee of . It is also shown that this bound can be reduced to 2(1 + ε). For the flowshop with any number of machines in each center, we provide a heuristic algorithm with an upper bound performance guarantee that depends on the relative number of machines in the centers.     

A genetic approach to the dielectric investigation of the high-temperature phase transition of TEA2MnCl4 crystals

The dielectric function of TEA₂MnCl₄ crystals is studied for a temperature range of 203–263?K in a frequency range of 1 kHz to 10?MHz. The measurement results are processed in the framework of the Cole–Cole model. An influence of the phase transition on the results is widely discussed. A genetic approach is successfully applied to the measured data and it is explained in detail. The method renders it possible to calculate the temperature dependence of dielectric properties in the time domain. The calculation method (the genetic algorithm) proved to be trustworthy and it is recommended to be employed in studying dielectric properties. A structural properties of the high temperature phase (i.e. above the phase transition temperature) will be also discussed and certain presumptions on the low temperature phase will be given.     

面向工程全局优化的混沌优化算法研究进展Research advances of chaos optimization algorithms for engineering global optimization

近年来,基于混沌的初值敏感性、伪随机性、遍历性以及自相似分形等非线性动力学特性所发展的混沌优化方法,是一种有潜力的工程全局优化新工具,已广泛应用于科学与工程技术的各学科领域。根据混沌优化方法的发展历程,以算法基本思想和工程应用研究状况为重点,评述了混沌神经网络优化方法、第一类混合混沌优化算法（基于混沌搜索）、第二类混合混沌优化算法（混沌序列代替随机序列）以及混沌分形优化四种主要混沌优化算法。混沌映射最早被引入神经网络,发展了混沌神经网络优化方法,可解决复杂的组合优化等全局优化问题。遗传算法及粒子群等启发式随机算法虽具全局搜索能力,但易出现早熟并陷入局部最优。然后,出现了混沌搜索的概念,研究者将其嵌入启发式算法建立了第一类混合混沌优化算法,可有效克服原启发式算法早熟收敛的缺点。随后,利用混沌映射产生的混沌序列代替启发式算法中的随机参数形成了第二类混合混沌优化算法。混合混沌优化算法有益于实现快速全局收敛和提高计算精度。最后,利用混沌分形特性,从分形理论出发提出一类新颖的混沌分形优化算法,可搜索到优化问题的所有全局最优解。此外,对混沌优化算法研究的几个发展方向进行了展望,诸如加强混沌优化算法的参数设计、处理大规模优化、多目标优化问题以及使用代理模型等。     

BOTDR分布式检测技术在复杂地层钻孔灌注桩测试中的应用研究

分析了Kagome格栅的等效刚度和屈服面. 其屈服面奇异,由4段直线围成. 利用该屈服面, 估算了Kagome具有I型、II型半无限大裂纹的裂尖塑性区,有限元计算验证了解析预测的 准确性. 与奇异屈服面相比,由Mises光滑屈服面给出的塑性区误差较大. 因此只有弹性情 况,可以将Kagome等效为各向同性;若材料塑性,或应力场奇异性较强,Kagome的强度依 赖于主应力方向,不能用各向同性模型来描述.     

Discrete element simulation of shock wave propagation in polycrystalline copper

The implementation of the characteristic of compressive plasticity into the Discrete Element Code, DM2, while maintaining its quasi-molecular scheme, is described. The code is used to simulate the shock compression of polycrystalline copper at 3.35 and 11.0 GPa. The model polycrystal has a normal distribution of grain sizes, with mean diameter 14 μm, and three distinct grain orientations are permitted with respect to the shock direction; 〈1 0 0〉, 〈1 1 0〉, and 〈1 1 1〉. Particle velocity dispersion (PVD) is present in the shock-induced flow, attaining its maximum magnitude at the plastic wave rise. PVD normalised to the average particle velocity of and are yielded for the 3.35 and 11.0 GPa shocks, respectively, and are of the same order as those seen in the experiment. Non-planar elastic and plastic wave fronts are present, the distribution in shock front position increasing with propagation distance. The rate of increase of the spread in shock front positions is found to be significantly smaller than that seen in probabilistic calculations on nickel polycrystals, and this difference is attributed, in the main, to grain interaction. Reflections at free surfaces yield a region of tension near to the target free surface. Due to the dispersive nature of the shock particle velocity and the non-planarity of the shock front, the tensile pressure is distributed. This may have implications for the spall strength, which are discussed. Simulations reveal a transient shear stress distribution behind the shock front. Such a distribution agrees with that put forward by Lipkin and Asay to explain the quasi-elastic reloading phenomenon. Simulation of reloading shocks show that the shear stress distribution can give rise to quasi-elastic reloading on the grain scale.     

一种基于小波变换的故障诊断改进算法

为提高多传感器组合导航系统对各导航传感器的在线故障检测能力，提出了一种基于调频高斯小波变换的导航传感器故障诊断改进算法。该算法在分析调频高斯小波特性的基础上，采用高斯小波变换计算出观测量的小波系数后，然后利用带遗忘因子的数据平滑算法对小波系数进行平滑，通过判断平滑值来诊断导航工作正常与否。其优点是仅利用传感器的观测量来直接检测导航传感器故障，适当选择小波变换的拉伸因子和数据的衰减因子可以对方差突变等软故障进行有效的在线检测，并解决了误检问题。仿真结果证明了该算法的有效性。     

End-to-end availability-dependent pricing of network services

We discuss how a new pricing scheme can be integrated within a communication network. The pricing scheme is based on the availability of end-to-end communications, and is an alternative to congestion pricing, which is not applicable when communication capacity is higher than demand (as happens in most communication backbone networks). We also investigate how, based on this scheme, an optimization algorithm for updating the network topology can be applied. The network update problem is modeled as a combinatorial optimization problem, which is approximately solved using a Genetic Algorithm. The good results obtained in a case study show that the method is robust and can be applied even when end-to-end availability measures can only be computed approximately (in this case, using a Monte Carlo method). This research is part of the PAIR associated research project, supported by the INRIA, France, and has also received the support of ECOS-Sud, under Action U03E02. The participation of Pablo Rodríguez was supported by the French Embassy in Uruguay as part of the French Ministère des Affaires étrangères scientific cooperation program; and by the “Programa de Jóvenes Investigadores” of CSIC, UDELAR, Uruguay.     

Fast mixing for independent sets,colorings, and other models on trees

We study the mixing time of the Glauber dynamics for general spin systems on the regular tree, including the Ising model, the hard‐core model (independent sets), and the antiferromagnetic Potts model at zero temperature (colorings). We generalize a framework, developed in our recent paper (Martinelli, Sinclair, and Weitz, Tech. Report UCB//CSD‐03‐1256, Dept. of EECS, UC Berkeley, July 2003) in the context of the Ising model, for establishing mixing time O(nlog n), which ties this property closely to phase transitions in the underlying model. We use this framework to obtain rapid mixing results for several models over a significantly wider range of parameter values than previously known, including situations in which the mixing time is strongly dependent on the boundary condition. We also discuss applications of our framework to reconstruction problems on trees. © 2006 Wiley Periodicals, Inc. Random Struct. Alg., 2007