Irreducibility of joint inventory positions in an assemble‐to‐order system under (r,nQ) policies

In a typical assemble‐to‐order system, a customer order may request multiple items, and the order may not be filled if any of the requested items are out of stock. A key customer service measure when unfilled orders are backordered is the order‐based backorder level. To evaluate this crucial performance measure, a fundamental question is whether the stationary joint inventory positions follow an independent and uniform distribution. In this context, this is equivalent to the irreducibility of the Markov chain formed by the joint inventory positions. This article presents a necessary and sufficient condition for the irreducibility of such a Markov chain through a set of simultaneous Diophantine equations. This result also leads to sufficient conditions that are more general than those in the published reports. © 2011 Wiley Periodicals, Inc. Naval Research Logistics, 2011     

舰船航渡过程中的松弛时间与航渡策略问题

针对舰船特点和任务要求,提出了舰船航渡中的松弛时间问题。在对问题分析的基础上,给出了松弛时间的定义并对其进行了建模,讨论了航渡失败的判断准则,给出了松弛时间的上下限以及航渡中实际的松弛时间的计算方法,并采用仿真的方法进行了典型航渡过程的松弛时间和成功概率的计算。在大量计算的基础上,初步探讨了航渡成功概率与各类航渡参数之间的关系,并对舰船最优航渡策略问题进行了初步分析,最后对于优化目标、计算初值、结果的表达方式等提出了一个可行的解决方案。     

The effect of al particle size on thermal decomposition,mechanical strength and sensitivity of Al/ZrH2/PTFE composite

To study the thermal decomposition of Al/ZrH2/PTFE with different Al particle size as well as mechanical strength and impact sensitivity under medium and low strain rates, molding-vacuum sintering was adopted to prepare four groups of power materials and cylindrical specimens with different Al particle size. The active decomposition temperature of ZrH2 was obtained by TG-DSC, and the quasi-static me-chanics/reaction characteristics as well as the impact sensitivity of the specimen were studied respec-tively by quasi-static compression and drop-hammer test. The results show that the yield strength of the material decreased with the increase of the Al particle size, while the compressive strength, failure strain and toughness increased first and then decreased, which reached the maximum values of 116.61 MPa, 191％, and 119.9 MJ/m respectively when the Al particle size is 12—14μm because of particle size grading. The specimens with the highest strength and toughness formed circumferential open cracks and reacted partly when pressed. Those with developmental cracks formed inside did not react. It is considered that fracture of specimens first triggered initial reaction between Al and PTFE to release an amount of heat. Then ZrH2 was activated and decomposed, and participated in subsequent reaction to generate ZrC. The impact sensitivity of the specimens decreased with the increase of Al particle size.     

单一来源同类装备价格形成机制存在的问题及对策

近年来,随着国防和军队全面深化改革的深入推进和装备建设的快速发展,装备价格管理工作的重要性不断提升,但军队目前承担的装备审价任务日趋繁重,存量不减、增量日增等新情况和新问题给装备价格管理工作带来了新挑战。本文以单一来源同类装备为研究对象,借鉴《军品定价议价规则(试行)》中竞争议价和征询议价不审价的原理,从单一来源同类装备价格的形成主体、装备审价任务量、装备价格的测算方法、装备价格的形成过程以及装备价格的影响因素等五个方面分析了价格形成机制存在的问题,并从主观因素和客观因素两方面探讨了存在问题的原因,提出应在明确价格形成主体的职能权限、科学确定价格的测算方法、完善价格法律法规、建设价格数据平台、加强价格人才队伍建设等方向优化单一来源同类装备价格形成机制的对策建议。     

A melt-cast Duan-Zhang-Kim mesoscopic reaction rate model and experiment for shock initiation of melt-cast explosives

A melt-cast Duan-Zhang-Kim (DZK) mesoscopic reaction rate model is developed for the shock initiation of melt-cast explosives based on the pore collapse hot-spot ignition mechanism. A series of shock initiation experiments was performed for the Comp B melt-cast explosive to estimate effects of the loading pressure and the particle size of granular explosive component, and the mesoscopic model is validated against the experimental data. Further numerical simulations indicate that the initial density and formula proportion greatly affect the hot-spot ignition of melt-cast explosives.     

A critical look at the U.S. deceased‐donor organ procurement and utilization system

The U.S. system for procuring and utilizing deceased‐donor organs for transplantation has been studied and written about in many articles. The purpose of this paper is to examine the interactions between the elements that comprise this system, and point out improvement opportunities that may be affected through operations research/management techniques. The authors demonstrate the need for developing data‐driven and analytic tools. In fact, data is used to generate hypotheses and support claims throughout the paper. The paper also points out the need to fully leverage data that is available to researchers, and to seek data that is currently not deposited in a centralized archive.     

Vondrak-Cepek组合滤波在北斗共视和卫星双向时间比对融合中的应用

为减小卫星双向时间比对(Two-Way Satellite Time and Frequency Transfer, TWSTFT)中的周日效应,利用北斗共视链路没有周日效应的特点,通过Vondrak-Cepek组合滤波方法对中国科学院国家授时中心(National Time Service Center, NTSC)、德国物理技术研究院(Physikalisch-Technische Bundesanstalt, PTB)以及中国计量科学研究院(National Institute of Metrology, NIM)间的北斗共视时间比对结果分别与硬件卫星时间和距离测量设备(SAtellite Time and Ranging Equipment, SATRE) TWSTFT和软件接收机(Software-Defined Radio, SDR)TWSTFT结果进行了融合处理。采用时间偏差和幅值频谱两个指标以及GPS精密单点定位(Precise Point Positioning, PPP)时间比对分别对融合结果进行内外符合评估。结果表明,经过Vondrak-Cepek滤波的融合结果中周日效应基本消失,其与GPS PPP链路差值结果的绝对值保持在链路校准的不确定度范围内。对于长基线NTSC-PTB链路,融合结果1 d的时间偏差稳定度对SATRE和SDR TWSTFT的增益因子分别为1.85和1.81;对于短基线NTSC-NIM链路,融合结果对SATRE和SDR TWSTFT的增益因子分别为1.69和1.59。融合结果的短期稳定度显著提高。