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We describe a periodic review inventory system where emergency orders, which have a shorter supply lead time but are subject to higher ordering cost compared to regular orders, can be placed on a continuous basis. We consider the periodic review system in which the order cycles are relatively long so that they are possibly larger than the supply lead times. Study of such systems is important since they are often found in practice. We assume that the difference between the regular and emergency supply lead times is less than the order-cycle length. We develop a dynamic programming model and derive a stopping rule to end the computation and obtain optimal operation parameters. Computational results are included that support the contention that easily implemented policies can be computed with reasonable effort. © 1998 John Wiley & Sons, Inc. Naval Research Logistics 45: 187–204, 1998 相似文献
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提出了电偶极子源在时域有限差分(FDTD)网格中设置的一种新方法,它是以电偶极子源周围若干个FDTD网格组成的立方体来对其进行替代,并对立方体表面上的网格节点施加切向解析电场来模拟电偶极子源。文中把由此方法计算的电偶极子辐射场数值结果分别与电流密度添加形式的设置方法和解析法所得结果进行了对比,空间中各点的电磁场值都一致,验证了此设置方法的正确性。 相似文献
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In order‐quantity reorder‐point formulations for inventory items where backordering is allowed, some of the more common ways to prevent excessive stockouts in an optimal solution are to impose either a cost per unit short, a cost per stockout occasion, or a target fill rate. We show that these popular formulations, both exact and approximate, can become “degenerate” even with quite plausible parameters. By degeneracy we mean any situation in which the formulation either cannot be solved, leads to nonsensical “optimal” solutions, or becomes equivalent to something substantially simpler. We explain the reasons for the degeneracies, yielding new insight into these models, and we provide practical advice for inventory managers. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 686–705, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/nav.10037 相似文献
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Statistical analysis of exponential lifetimes under an adaptive Type‐II progressive censoring scheme
In this article, a mixture of Type‐I censoring and Type‐II progressive censoring schemes, called an adaptive Type‐II progressive censoring scheme, is introduced for life testing or reliability experiments. For this censoring scheme, the effective sample size m is fixed in advance, and the progressive censoring scheme is provided but the number of items progressively removed from the experiment upon failure may change during the experiment. If the experimental time exceeds a prefixed time T but the number of observed failures does not reach m, we terminate the experiment as soon as possible by adjusting the number of items progressively removed from the experiment upon failure. Computational formulae for the expected total test time are provided. Point and interval estimation of the failure rate for exponentially distributed failure times are discussed for this censoring scheme. The various methods are compared using Monte Carlo simulation. © 2009 Wiley Periodicals, Inc. Naval Research Logistics, 2009 相似文献
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针对现有短波频率优选方法中数据处理过程复杂、输入参数条件苛刻、工程实现难度较大等不足,结合电离层变化特性,提出了一种基于球状模型的泛克里金法,应用于短波频率的重构。利用短波频率管理系统中大量的实测频率数据,构建了符合频率数据变化特征的基于球状模型的变异函数,建立了反映沿经度、纬度及水平方向通信频率变化剧烈程度的漂移表达式。随机选取多个样本数据,通过交叉重构法对短波频率数据进行重构。实验结果表明,基于球状模型的泛克里金法具有较高的频率重构精度,能够应用于短波通信频率的重构,特别是满足军事通信方面对短波频率优选手段的需求。 相似文献
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Flexible capacity strategy in an asymmetric oligopoly market with competition and demand uncertainty 下载免费PDF全文
This article studies flexible capacity strategy (FCS) under oligopoly competition with uncertain demand. Each firm utilizes either the FCS or inflexible capacity strategy (IFCS). Flexible firms can postpone their productions until observing the actual demand, whereas inflexible firms cannot. We formulate a new asymmetrical oligopoly model for the problem, and obtain capacity and production decisions of the firms at Nash equilibrium. It is interesting to verify that cross‐group competition determines the capacity allocation between the two groups of firms, while intergroup competition determines the market share within each group. Moreover, we show that the two strategies coexist among firms only when cost differentiation is medium. Counterintuitively, flexible firms benefit from increasing production cost when the inflexible competition intensity is sufficiently high. This is because of retreat of inflexible firms, flexibility effect, and the corresponding high price. We identify conditions under which FCS is superior than IFCS. We also demonstrate that flexible firms benefit from increasing demand uncertainty. However, when demand variance is not very large, flexible firms may be disadvantaged. We further investigate the effects of cross‐group and intergroup competition on individual performance of the firms. We show that as flexible competition intensity increases, inflexible firms are mainly affected by the cross‐group competition first and then by the intergroup competition, whereas flexible firms are mainly affected by the intergroup competition. Finally, we examine endogenous flexibility and identify its three drivers: cost parameters, cross‐group competition, and intergroup competition. © 2017 Wiley Periodicals, Inc. Naval Research Logistics 64: 117–138, 2017 相似文献
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In a series of articles published in the Fall 1990 issue of Defence Economics Alexander (1990), Atesoglu and Mueller (1990) and Huang and Mintz (1990) have all specified and empirically estimated defence‐growth models based on a neoclassical production function. We now isolate the externality component in our model, re‐estimate its coefficients using data on the U.S. economy 1952–88 and compare specifications and results with Atesoglu and Mueller (1990) and Alexander (1990). 相似文献
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The allocation of redundancies in a system to optimize the reliability of system performance is an interesting problem in reliability engineering and system security. In this article, we focus on the optimal allocation of two exponentially distributed active (standby) redundancies in a two‐component series system using the tool of stochastic ordering. For the case of active redundancy, stochastic comparisons are carried out in terms of the likelihood ratio and reversed hazard rate orders. For the case of standby redundancy, a likelihood ratio ordering result is developed. The results established here generalize and strengthen corresponding results in the recent literature. In addition, several numerical examples are used to explicate the results. © 2013 Wiley Periodicals, Inc. Naval Research Logistics, 2013 相似文献