Optimal control policies for an inventory system with commitment lead time

We consider a firm which faces a Poisson customer demand and uses a base‐stock policy to replenish its inventories from an outside supplier with a fixed lead time. The firm can use a preorder strategy which allows the customers to place their orders before their actual need. The time from a customer's order until the date a product is actually needed is called commitment lead time. The firm pays a commitment cost which is strictly increasing and convex in the length of the commitment lead time. For such a system, we prove the optimality of bang‐bang and all‐or‐nothing policies for the commitment lead time and the base‐stock policy, respectively. We study the case where the commitment cost is linear in the length of the commitment lead time in detail. We show that there exists a unit commitment cost threshold which dictates the optimality of either a buy‐to‐order (BTO) or a buy‐to‐stock strategy. The unit commitment cost threshold is increasing in the unit holding and backordering costs and decreasing in the mean lead time demand. We determine the conditions on the unit commitment cost for profitability of the BTO strategy and study the case with a compound Poisson customer demand.     

Inventory management with advance capacity information

An important aspect of supply chain management is dealing with demand and supply uncertainty. The uncertainty of future supply can be reduced if a company is able to obtain advance capacity information (ACI) about future supply/production capacity availability from its supplier. We address a periodic‐review inventory system under stochastic demand and stochastic limited supply, for which ACI is available. We show that the optimal ordering policy is a state‐dependent base‐stock policy characterized by a base‐stock level that is a function of ACI. We establish a link with inventory models that use advance demand information (ADI) by developing a capacitated inventory system with ADI, and we show that equivalence can only be set under a very specific and restrictive assumption, implying that ADI insights will not necessarily hold in the ACI environment. Our numerical results reveal several managerial insights. In particular, we show that ACI is most beneficial when there is sufficient flexibility to react to anticipated demand and supply capacity mismatches. Further, most of the benefits can be achieved with only limited future visibility. We also show that the system parameters affecting the value of ACI interact in a complex way and therefore need to be considered in an integrated manner. © 2011 Wiley Periodicals, Inc. Naval Research Logistics, 2011     

指挥控制参考模型研究进展

介绍指挥控制参考模型领域取得的最新进展。在理论上分析了该模型体系结构的不足,引入了逻辑端口的概念。在应用上讨论了建模过程中层次的分拆、组合的原则,并将使用实例图引入该模型的理论研究和对实际系统的建模,取得了若干重要结论。     

Peace enforcement in Africa: Doctrinal distinctions between the African Union and United Nations

When the United Nations (UN) Security Council needs to authorize a peace enforcement operation in Africa, its partner of choice is the African Union (AU). Africa has developed significant peace operations capacity over the past decade. In addition to deploying eight AU operations, Africa now contributes 50% of all UN peacekeepers. African stability operations, like its mission in Somalia, are often described as peace enforcement operations. In this article, I question whether it is accurate to categorize African stability operations as peace enforcement? I answer the question by considering what the criteria are that are used to differentiate between peace enforcement and peacekeeping operations in the UN context. I then use the peace enforcement criteria to assess whether AU stabilization operations would qualify as peace enforcement operations. In conclusion, I consider the implications of the findings for the strategic partnership between the AU and the UN.     

图像融合的客观质量评估

随着图像融合技术在武器自动化系统中的广泛应用,图像融合的质量评估问题,即图像融合的性能评估问题,在融合方案的选择中具有重要地位。由于人工主观的图像融合评估具有很大的工程化和自动化难度,国际上研究人员都将研究目标投向了客观图像融合质量评估的研究中。从历史发展的角度系统地回顾了客观图像融合质量评估的发展历程和研究现状,对近十年来的客观图像融合质量评估方法进行了分类和分析。同时,对于国际上几种流行的图像融合质量评估方法的性能测定思路进行了介绍。对于图像融合质量评估现状的分析和讨论有助于我们对图像融合的质量评估方法进行更深入的研究。     

具有终端约束的制导炸弹模糊变结构制导律设计

针对INS/GPS制导炸弹对地面目标的精确打击问题,提出带落角约束的模糊变结构制导律。在变结构制导律的基础上,引入终端落角约束项,应用模糊规则对所设计制导律中的变结构开关项系数增益进行在线调节。仿真结果表明,在对地面目标进行攻击时,该制导律降低变结构控制系统的抖振,同时满足制导精度和期望落角的要求,具有有效性和鲁棒性。     

星载三频GNSS接收机的整周模糊度解算

TCAR算法是GNSS中常用的快速确定三频模糊度的方法。虽然原理简单,计算方便,但是模糊度解算正确的概率很小,需要验证求解数值的正确性。而星载GNSS接收机存在着可见星数目低于3颗的情况,无法进行验证,文章通过结合递推加权最小二乘,对算法进行了改进,给出了适合于任何情况下求解模糊度的改进的TCAR加权算法,克服了TCAR算法在可见星不足情况下,无法获取正确的模糊度数值的缺点。同时在GNSS可见星不低于3颗的情况下,对改进的TCAR加权算法添加了模糊度搜索环节,使得算法在确保模糊度解算成功率的前提下,进一步提高解算效率。最后通过对比仿真表明,在可视卫星数目小于3时,只能采用改进的TCAR加权算法进行模糊度的确定;在可视卫星数目不低于3时,采用改进的TCAR搜索算法求解模糊度,拥有高成功率和高效率的特点。     

基于云模型的无人机作战系统效能评估

对无人机作战系统进行效能评估有利于了解无人机的能力和不足,为无人机的后继研发提供有效依据。针对作战系统指标的相对性、模糊性与不确定性,通过层次分析法建立无人机作战系统效能评估的指标体系,采用云模型实现作战系统指标的定性属性与定量属性的相互结合与转换,结合专家打分法给出作战系统指标的定性权重和评价,并利用正态云拟合算法得出无人机作战系统的综合效能。通过实例分析,表明该方法具有可行性。     

ARUAV前沿判别法抗多点源诱偏性能研究

基于反辐射无人机的时域鉴别技术,提出了一种以小波分析为手段的前沿判别法。将被动雷达导引头使用固定波门对脉冲前沿进行采样所得的信号作小波分析,对分析结果进行判定,当判定采样信号内为单辐射源信号时对其进行测向、测频、跟踪和打击。针对两点源诱偏系统分析表明,在大部分空域中,反辐射无人机总是能首先跟踪诱饵信号。通过建模与仿真,验证了前沿判别法能够有效对抗两点源诱偏系统,并由固定波门得到了有效的判别空域。     

Worst‐case performance of approximation algorithms for tool management problems

Since the introduction of flexible manufacturing systems, researchers have investigated various planning and scheduling problems faced by the users of such systems. Several of these problems are not encountered in more classical production settings, and so‐called tool management problems appear to be among the more fundamental ones of these problems. Most tool management problems are hard to solve, so that numerous approximate solution techniques have been proposed to tackle them. In this paper, we investigate the quality of such algorithms by means of worst‐case analysis. We consider several polynomial‐time approximation algorithms described in the literature, and we show that all these algorithms exhibit rather poor worst‐case behavior. We also study the complexity of solving tool management problems approximately. In this respect, we investigate the interrelationships among tool management problems, as well as their relationships with other well‐known combinatorial problems such as the maximum clique problem or the set covering problem, and we prove several negative results on the approximability of various tool management problems. © 1999 John Wiley & Sons, Inc. Naval Research Logistics 46: 445–462, 1999