Equipment replacement under technological change

For infinite-horizon replacement economy problems it is common practice to truncate the problem at some finite horizon. We develop bounds on the error due to such a truncation. These bounds differ from previous results in that they include both revenues and costs. Bounds are illustrated through a numerical example from a real case in vehicle replacement. © 1994 John Wiley & Sons, Inc.     

Multi-item service constrained (s,S) policies for spare parts logistics systems

Many organizations providing service support for products or families of products must allocate inventory investment among the parts (or, identically, items) that make up those products or families. The allocation decision is crucial in today's competitive environment in which rapid response and low levels of inventory are both required for providing competitive levels of customer service in marketing a firm's products. This is particularly important in high-tech industries, such as computers, military equipment, and consumer appliances. Such rapid response typically implies regional and local distribution points for final products and for spare parts for repairs. In this article we fix attention on a given product or product family at a single location. This single-location problem is the basic building block of multi-echelon inventory systems based on level-by-level decomposition, and our modeling approach is developed with this application in mind. The product consists of field-replaceable units (i.e., parts), which are to be stocked as spares for field service repair. We assume that each part will be stocked at each location according to an (s, S) stocking policy. Moreover, we distinguish two classes of demand at each location: customer (or emergency) demand and normal replenishment demand from lower levels in the multiechelon system. The basic problem of interest is to determine the appropriate policies (s_i S_i) for each part i in the product under consideration. We formulate an approximate cost function and service level constraint, and we present a greedy heuristic algorithm for solving the resulting approximate constrained optimization problem. We present experimental results showing that the heuristics developed have good cost performance relative to optimal. We also discuss extensions to the multiproduct component commonality problem.     

A set-processing algorithm for scheduling staff on 4-day or 3-day work weeks

This paper presents an efficient algorithm for scheduling a single-category work force on 4-day or 3-day work weeks. Employees work 4 or 3 days each week, have A out of every B weekends off, and work no more than 5 consecutive days in a work stretch on 4-day work weeks and no more than 4 days in a work stretch on 3-day work weeks. Such conditions often prevail in 7-day-a-week organizations such as hospitals, manufacturing plants, and retail stores. We determine the minimum number of workers required to satisfy the scheduling constraints under any pattern of daily requirements. Then we present the algorithm for assigning days off for each worker, thereby determining the work schedules. We show that the algorithm, by construction, will necessarily satisfy the scheduling constraints. © 1998 John Wiley & Sons, Inc. Naval Research Logistics 45: 839–853, 1998     

基于神经网络信息融合技术的卫星定姿算法

姿态确定系统是卫星姿态控制系统中的重要组成部分,卫星姿态确定的精度直接影响卫星控制精度.为得到高姿态精度,针对由惯性测量单元(Inertial Measurement Unit),红外地平仪和太阳敏感器组成的卫星姿态确定系统,分别采用BP网络算法和径向基(RBF)网络算法对不同的姿态敏感器的输出数据进行融合,并用STK(Satellite Tool Kit)数据进行了仿真.仿真分析结果表明这两种学习算法均可以提高卫星定姿精度,相对而言,RBF网络无论是精度上还是收敛速度上均优于BP网络.     

A continuous-review inventory model with constant resupply time and defective items

As a result of imperfect production and inspection by suppliers, pilferage, and/or damage in transit, it is common that procurement orders may contain defective items. This article deals with a continuous-review inventory system with Poisson demand arrivals and constant resupply time. Items in resupply lots may not be of perfect quality. The operating characteristics of such a system are analyzed. For purposes of computational savings, an approximation scheme for the operating characteristics is presented. As a result of the approximation, the determination of the optimal ordering policy becomes much simpler. Extensive numerical tests suggest that the approximation scheme is very effective in giving the optimal or near-optimal ordering policies for such a system.     

Bounds and properties of the expected value of sample information for a project-selection problem

In this article we extend the work of Mehrez and Stulman [5] on the expected value of perfect information (EVPI) to the expected value of sample information (EVSI) for a class of economic problems dealing with the decision to reject or accept an investment project. It is shown that shifting the mean of the underlying a priori distribution of X, the project's monetary value from zero in either direction will decrease the associated EVSI of Y, the random sampled information. A theorem is then presented which gives an upper bound on the EVSI over all distributions of Y, as well as the structure of the posterior mean E[X|Y] for which this upper bound is achieved. Finally, the case where E[X|Y] is linear in Y is discussed and its performance compared with that of the optimal case.     

高功率电磁环境下C4ISR系统接口电路的阈值实验

采用非接触式电流脉冲注入法,设计了一种通用的接口电路实验模型和测试软件,进行了高功率电磁脉冲对指控系统接口电路的注入损伤实验,测量接口电路耦合电压和耦合电流,并对实验结果进行了分析.实验表明,强电磁能量耦合到电子装备和电气设备内部,可在其接口电路上产生过电压或过电流,从而使设备受到干扰和损伤.     

一种Mini-SAR的极坐标成像算法

Mini-SAR技术是目前SAR领域一个新兴的重要研究方向,但目前投入实用的成像算法很少。针对Mini-SAR的成像原理,给出了一种新的投入实用的极坐标成像算法,通过对该算法优缺点的研究,分析了Mini-SAR成像场景、分辨率及作用距离三者之间的关系,讨论了该算法对成像场景尺寸的限制要求,明确了算法的适用条件;最后利用某型Mini-SAR实际复数图像数据验证了该算法的正确性。研究结论对国内小型SAR的研制具有一定参考价值。