Integrating decisions with advance supply information in an assemble-to-order system

We study a periodic-review assemble-to-order (ATO) system with multiple components and multiple products, in which the inventory replenishment for each component follows an independent base-stock policy and stochastic product demands are satisfied according to a First-Come-First-Served rule. We assume that the replenishment for various component suffers from lead time uncertainty. However, the decision maker has the so-called advance supply information (ASI) associated with the lead times and thus can take advantage of the information for system optimization. We propose a multistage stochastic integer program that incorporates ASI to address the joint optimization of inventory replenishment and component allocation. The optimal base-stock policy for the inventory replenishment is determined using the sample average approximation algorithm. Also, we provide a modified order-based component allocation (MOBCA) heuristic for the component allocation. We additionally consider a special case of the variable lead times where the resulting two-stage stochastic programming model can be characterized as a single-scenario case of the proposed multistage model. We carry out extensive computational studies to quantify the benefits of integrating ASI into joint optimization and to explore the possibility of employing the two-stage model as a relatively efficient approximation scheme for the multistage model.     

On efficient algorithms for finding efficient salvo policies

We consider the salvo policy problem, in which there are k moments, called salvos, at which we can fire multiple missiles simultaneously at an incoming object. Each salvo is characterized by a probability p_i: the hit probability of a single missile. After each salvo, we can assess whether the incoming object is still active. If it is, we fire the missiles assigned to the next salvo. In the salvo policy problem, the goal is to assign at most n missiles to salvos in order to minimize the expected number of missiles used. We consider three problem versions. In Gould's version, we have to assign all n missiles to salvos. In the Big Bomb version, a cost of B is incurred when all salvo's are unsuccessful. Finally, we consider the Quota version in which the kill probability should exceed some quota Q. We discuss the computational complexity and the approximability of these problem versions. In particular, we show that Gould's version and the Big Bomb version admit pseudopolynomial time exact algorithms and fully polynomial time approximation schemes. We also present an iterative approximation algorithm for the Quota version, and show that a related problem is NP-complete.     

金属靶体材料动力硬度测试及动态阻力分析

以高速侵彻下45钢靶体侵彻阻力为研究对象,开展了弹体高速侵彻45钢靶体试验,获取了典型弹体对45钢靶体的成坑参数。基于高速侵彻阻力模型对靶体侵彻阻力及影响因素进行分析。结合流体动力学侵彻模型对不同弹体材料侵彻45钢靶体侵彻深度规律进行研究。研究结果表明:随着撞击速度的增大,45钢的靶体阻力从5. 13 GPa减小到3. 7 GPa;基于材料动力硬度测试方法的靶体动态阻力测试结果和理论计算结果吻合较好;随着靶体动态屈服强度的增大,靶体阻力呈线性增大的趋势;侵彻深度及靶体动态阻力理论计算结果和试验数据吻合较好,说明所提动态阻力确定方法可行,可为高速侵彻动力学研究提供参考。     

次级通道估计误差对Fx-Newton算法的影响

Fx-Newton算法在执行过程中需要估计次级通道模型,针对主被动隔振工程应用中次级通道估计存在误差的问题,假设输入信号为正弦信号,建立含次级通道估计误差的Fx-Newton算法结构模型,推导了Fx-Newton算法的稳定性条件,并就相位误差和幅值误差对Fx-Newton算法稳定性和收敛性的影响做了详细阐述。最后对两自由度主被动隔振模型开展仿真研究,验证了理论分析结果。     

面向作战任务的最小风险传感器调度方法

基于风险理论提出一种面向不同目标探测任务的传感器调度方法。将主动传感器辐射被截获风险和目标探测风险结合起来,建立一般目标探测框架下的传感器最小风险调度模型。分目标跟踪、目标识别和目标威胁等级评估三种情况将传感器最小风险调度模型具体化,给出不同情况下目标探测风险值的计算方法。针对模型的求解提出一种基于混沌思想、反向学习和双向轮盘赌的改进人工蜂群算法。通过仿真实验证明了模型的可行性和算法的有效性。     

Application of Markov renewal theory and semi-Markov decision processes in maintenance modeling and optimization of multi-unit systems

In this paper, a condition-based maintenance model for a multi-unit production system is proposed and analyzed using Markov renewal theory. The units of the system are subject to gradual deterioration, and the gradual deterioration process of each unit is described by a three-state continuous time homogeneous Markov chain with two working states and a failure state. The production rate of the system is influenced by the deterioration process and the demand is constant. The states of the units are observable through regular inspections and the decision to perform maintenance depends on the number of units in each state. The objective is to obtain the steady-state characteristics and the formula for the long-run average cost for the controlled system. The optimal policy is obtained using a dynamic programming algorithm. The result is validated using a semi-Markov decision process formulation and the policy iteration algorithm. Moreover, an analytical expression is obtained for the calculation of the mean time to initiate maintenance using the first passage time theory.     

智能时代的军事训练变革

随着智能技术的发展,人类已逐步迈入智能时代,而智能时代催生了军事训练变革。本文从智能技术影响军事训练典型领域的角度,分析了智能时代背景下,以大数据和人工智能为核心的智能技术,如何影响军事训练的理念、内容、方式及管理,并催生了这些领域的变革。研究表明,智能时代发展背景下,军事训练理念将更加先进,训练内容更加融合,训练方式更加有效,训练管理更加精准。     

The Gravity of Arms

The aim of this paper is to investigate the determinants of international arms transfers in a gravity model framework. By distinguishing between the decision to export arms (extensive margin) and the value of the arms exported (intensive margin), while also considering its interdependence, is what differentiates this paper from previous research. A theoretically justified gravity model of trade augmented with political and security motives is estimated using a two-stage panel data approach for 104 exporting countries over the period from 1950 to 2007. In addition to the usual gravity variables related to the economic mass of the trading countries and the trade cost factors, the model is extended with political and security factors. The level of democracy in both trading partners, political differences between trading partners and voting similarity with the United States in the UN General Assembly of the countries engaged in trade are the main political factors, whereas the existence of conflicts, military pacts, and embargoes are taken as security motives. The key result indicates that both political and security motives are an important determinant of an arms trade, but their effects on the extensive margin of exports (the decision to order a transfer) differs from their effect on the intensive margin (average value of exports). Moreover, the relative importance of the factors under study has changed since 1989. In the post-cold war period, countries that are less democratic are more likely to export arms, military pacts are less relevant and embargoes play a role.     

Buy now,pay later: American military intervention and the strategic cost paradox

This paper explores the notion that US efforts to evade the political costs of war paradoxically contribute to the subsequent exacerbation of costs over time. Leaders seek to purchase political capital in the short term by limiting the costs and requirements of military operations, but in doing so cause strategic and political liabilities to mount in the long run. While identification of such behaviour is not new, insufficient attention has been devoted to explaining its causes, dynamics, and manifestations in relation to key decisions on and in war. Evidence derived from studies of recent American discretionary campaigns is analysed to advance an argument with respect to this pattern of self-defeating strategic behaviour.     

On the roles of free play in army exercises and the Russians

The article outlines the essential role of free play elements in various types of exercises for the development of in-depth and practical military professionalism. It thereafter argues why such use of free play contradicts the military science founded Russian Way of War.