Network design for time‐constrained delivery

To meet customer demand, delivery companies are offering an increasing number of time‐definite services. In this article, we examine the strategic design of delivery networks which can efficiently provide these services. Because of the high cost of direct connections, we focus on tree‐structured networks. As it may not be possible to identify a tree‐structured network that satisfies all of the delivery guarantees, we allow these guarantees to be violated but seek to minimize the sum of the violations. We establish the complexity of the problem and exploit an empirically identified solution structure to create new neighborhoods which improve solution values over more general neighborhood structures. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008     

Scheduling parallel machines with inclusive processing set restrictions

We consider the problem of assigning a set of jobs to different parallel machines of the same processing speed, where each job is compatible to only a subset of those machines. The machines can be linearly ordered such that a higher‐indexed machine can process all those jobs that a lower‐indexed machine can process. The objective is to minimize the makespan of the schedule. This problem is motivated by industrial applications such as cargo handling by cranes with nonidentical weight capacities, computer processor scheduling with memory constraints, and grades of service provision by parallel servers. We develop an efficient algorithm for this problem with a worst‐case performance ratio of + ε, where ε is a positive constant which may be set arbitrarily close to zero. We also present a polynomial time approximation scheme for this problem, which answers an open question in the literature. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008     

Strategic capacity decision‐making in a stochastic manufacturing environment using real‐time approximate dynamic programming

In this study, we illustrate a real‐time approximate dynamic programming (RTADP) method for solving multistage capacity decision problems in a stochastic manufacturing environment, by using an exemplary three‐stage manufacturing system with recycle. The system is a moderate size queuing network, which experiences stochastic variations in demand and product yield. The dynamic capacity decision problem is formulated as a Markov decision process (MDP). The proposed RTADP method starts with a set of heuristics and learns a superior quality solution by interacting with the stochastic system via simulation. The curse‐of‐dimensionality associated with DP methods is alleviated by the adoption of several notions including “evolving set of relevant states,” for which the value function table is built and updated, “adaptive action set” for keeping track of attractive action candidates, and “nonparametric k nearest neighbor averager” for value function approximation. The performance of the learned solution is evaluated against (1) an “ideal” solution derived using a mixed integer programming (MIP) formulation, which assumes full knowledge of future realized values of the stochastic variables (2) a myopic heuristic solution, and (3) a sample path based rolling horizon MIP solution. The policy learned through the RTADP method turned out to be superior to polices of 2 and 3. © 2010 Wiley Periodicals, Inc. Naval Research Logistics 2010     

非线性滤波方法在水下目标跟踪中的应用

在对扩展卡尔曼滤波、不敏卡尔曼滤波和粒子滤波3种非线性滤波方法进行研究的基础上,对粒子滤波算法的重要性密度函数的选取方法进行了研究。结合水下目标的被动跟踪的应用背景,比较了3种滤波算法在水下目标跟踪中的性能差异。结果表明,粒子滤波算法能较好的用于非线性、非高斯条件下的水下目标跟踪。     

卫星差分码偏差对北斗三号双频精密单点定位的影响

为探讨北斗三号系统不同频点组合卫星差分码偏差(differential code bias, DCB)对精密单点定位(precise point positioning, PPP)的影响,推导北斗三号系统不同频点无电离层组合卫星端DCB改正模型,并基于MGEX跟踪站连续7天4站的观测数据按7种不同双频组合进行DCB改正实验。结果表明,DCB改正对PPP精度在最初的历元有明显提升,有助于滤波的收敛及提高单天解的均方根,但对于最终定位精度无明显提升。B2a/B3I及B2b/B3I组合定位精度及收敛速度明显低于其他组合,DCB改正后有所提升。其他5种组合改正后定位精度及收敛时间相当：静态PPP单天解均方根在E、N和U方向约为5.50 cm、2.50 cm和6.25 cm,较未改正前提升20%～65%;平均收敛时间为38 min,提升约6%;动态PPP平均收敛时间为59 min,提升约20%;最终定位精度水平方向优于5 cm,高程方向优于7 cm。     

基于WVD-Radon变换的宽带延展目标回波参数提取

分析了宽带延展目标的时延-时间伸缩效应及其导致的回波信号在时域和频率域的特性;针对LFM信号的时频分布特点,利用WVD和Radon联合变换技术,提取LFM信号在时-频域分布上的特性参数,提出了一种宽带延展目标回波参数提取方法,得到了目标的时延—时间伸缩分布.仿真结果表明,该方法是可行的.     

非平稳数据处理方法与瞬时频率

利用“经验模式分解”(EMD)方法,任何复杂的数集都能够被分解为有限且通常数量较少的“本征模式函数”。“本征模式函数”产生瞬时频率,最终结果表示为H ilbert谱规定的能量-频率-时间分布。应用“经验模式分解”方法表示自然现象中的传统非线性平衡系统及其数据的数值结果,同时给出实例展示了这种新方法的作用和效果。这种方法阐明了能量-频率-时间分布,进一步显示出对非线性非平稳系统的处理效果———精确化、形象化和可视化。     

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     

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。     

基于模糊Petri网的实时系统功能模型构建

Petri网在描述具有模糊行为的系统时是有缺陷的,为了更好地分析、评价和开发实时系统,提出了一种利用模糊Petri网构建实时系统功能模型的方法,阐述了模糊Petri网的基本原理,详细介绍了利用模糊Petri网的特征分析实时系统的功能及绘制实时系统功能模型的步骤。