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101.
We consider a two‐level system in which a warehouse manages the inventories of multiple retailers. Each retailer employs an order‐up‐to level inventory policy over T periods and faces an external demand which is dynamic and known. A retailer's inventory should be raised to its maximum limit when replenished. The problem is to jointly decide on replenishment times and quantities of warehouse and retailers so as to minimize the total costs in the system. Unlike the case in the single level lot‐sizing problem, we cannot assume that the initial inventory will be zero without loss of generality. We propose a strong mixed integer program formulation for the problem with zero and nonzero initial inventories at the warehouse. The strong formulation for the zero initial inventory case has only T binary variables and represents the convex hull of the feasible region of the problem when there is only one retailer. Computational results with a state‐of‐the art solver reveal that our formulations are very effective in solving large‐size instances to optimality. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 相似文献
102.
Traditional inventory systems treat all demands of a given item equally. This approach is optimal if the penalty costs of all customers are the same, but it is not optimal if the penalty costs are different for different customer classes. Then, demands of customers with high penalty costs must be filled before demands of customers with low penalty costs. A commonly used inventory policy for dealing with demands with different penalty costs is the critical level inventory policy. Under this policy demands with low penalty costs are filled as long as inventory is above a certain critical level. If the inventory reaches the critical level, only demands with high penalty costs are filled and demands with low penalty costs are backordered. In this article, we consider a critical level policy for a periodic review inventory system with two demand classes. Because traditional approaches cannot be used to find the optimal parameters of the policy, we use a multidimensional Markov chain to model the inventory system. We use a sample path approach to prove several properties of this inventory system. Although the cost function is not convex, we can build on these properties to develop an optimization approach that finds the optimal solution. We also present some numerical results. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008 相似文献
103.
Previous work has documented a negative correlation between internal conflict and state capacity. We attempt to shed light on mechanisms that underlie this relationship, using data for Colombian municipalities. We rely on identifying heterogeneous effects of different types of violent events on state capacity, taking advantage of variability across municipalities in the prevalence of specific manifestations of conflict and their intensity. Our findings suggest that events making civilians feel targeted affect the state’s capacity to collect taxes, while those reflecting a stronger military capacity of illegal armies, in particular their large-scale attacks, affect the state’s capacity to provide public goods. 相似文献
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获取对应笔画级连通区的最大稳定极值区域,实施形态学闭操作融合相距较近的最大稳定极值区域,融合后最大稳定极值区域对应的单个汉字区域;利用灰度共生矩阵描述最大稳定极值矩形区域的纹理信息,将其作为卷积神经网络的输入,卷积神经网络对最大稳定极值区域进行分类,过滤非汉字部分;利用最大稳定极值区域颜色直方图的Bhattacharyya距离等特征对最大稳定极值区域进行聚类,同一类最大稳定极值区域组合得到汉字文本候选区域;再次利用卷积神经网络对候选文本区域进行分类,过滤非文本部分,剩余的就是定位到的汉字文本区域。实验结果表明,该算法对于汉字区域定位具有良好的效果。 相似文献
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TDMA(时分多址)和CSMA(载波侦听)是两种常见的Ad Hoc网络多址接入方式,两种方法各有利弊。TDMA避免了节点之间的冲突,但是平均时延随着网络规模的扩大而急剧增长,当某节点在给定的时隙内没有发送请求时,会产生空时隙,造成资源浪费;CSMA采用竞争的方式,当网络规模扩大时,节点的碰撞概率很大,信道利用率降低。根据两者的特点,提出了TDMA/CSMA混合多址接入协议,采用固定分配和动态分配相结合的方式,进一步提高网络吞吐量、降低平均时延,并通过MATLAB软件对协议进行仿真建模,验证其性能。 相似文献
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研究以色列区域导弹防御系统的发展动因、进展、影响与趋势,重点分析了以色列近程、中程、远程导弹防御系统的技术和能力,探讨了以色列区域导弹防御系统的影响及发展趋势。 相似文献
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为研究掺砂率对高庙子膨润土一砂混合型缓冲/回填材料液塑限的影响,利用液塑限联合测定仪进行了试验研究,并运用最小二乘法对混合物液塑限试验数据进行了分析。试验结果表明膨润土一砂混合物的可塑性、液塑限值和塑性指数均随掺砂率的增大而降低。对试验结果进行分析,得到了考虑掺砂率影响的混合物液塑限经验公式。混合物的液塑限并不是随掺砂率增大成比例降低,而是液限的实测值小于理论值,塑限的实测值大于理论值。得到的不同掺砂率的膨润土一砂混合型缓冲/回填材料液塑限试验数据可为高放废物深地质处置库建设提供科学依据。 相似文献
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