The effects of information on a queue with balking and phase‐type service times

This article generalizes the models in Guo and Zipkin, who focus on exponential service times, to systems with phase‐type service times. Each arriving customer decides whether to stay or balk based on his expected waiting cost, conditional on the information provided. We show how to compute the throughput and customers' average utility in each case. We then obtain some analytical and numerical results to assess the effect of more or less information. We also show that service‐time variability degrades the system's performance. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008     

多约束下的高超声速飞行器三维非线性自适应末制导律

面向多约束下高超声速飞行器末制导过程中的通道耦合、参数扰动、模型失配等突出问题,设计一种适于高超声速飞行器的三维非线性自适应末制导律。为了模型描述的完整性和简洁性,引入视线旋量和旋量速度的概念,并基于此建立三维制导参考模型和实际系统的表达式;为了保证制导律的鲁棒性和自适应性,基于自适应控制理论,设计一种三维非线性自适应制导律;通过数学推导证明了该制导律的稳定性。该制导律能够从理论上克服高超声速飞行器末制导面临的通道耦合、参数扰动、模型失配等突出问题,满足多约束制导要求。仿真结果验证了所设计制导律的有效性。     

含轴间距误差的消隙齿轮刚柔耦合动力学仿真

轴间距误差对消隙齿轮精度和性能有重要影响,但其机理和规律并不清楚。基于接触碰撞力约束关系建立齿轮接触动力学模型,进一步利用ADAMS/Flex建立单级消隙齿轮传动系统的刚柔耦合模型,通过刚柔耦合动力学仿真研究消隙齿轮传动在不同轴间距制造误差条件下的振动及频率特性。研究发现:随着轴间距的减小,扭簧的平均力矩增大,齿轮齿面间的啮合力矩以及摩擦力矩也将增大,从而阻碍扭矩的正常传递,并导致固定齿轮转速幅值降低;随着轴间距的增大,固定齿轮主谐振频率整体上降低,而且在轴间距稍大于标准中心距时降低很快。这一发现可指导消隙齿轮传动的设计和装配。     

金属泡沫断裂韧性的试验研究

金属泡沫在其实际应用中,断裂性能和断裂韧性对于承载的多孔金属泡沫有着重要的意义。基于美国试验材料学会相关标准,采用三点弯曲试样测定了铝泡沫的I型断裂韧性。研究表明,金属泡沫的断裂为脆性断裂,在裂纹尖端附近,孔壁最薄弱的区域最容易发生变形;随着进一步加载,一些孔壁发生断裂,微裂纹在断裂尖端附近出现。随着载荷的增加,主裂纹在缺口根部形成或由微裂纹合并而成,并开始在多孔结构内传播。裂纹沿着结构最薄弱处传播,并产生次生裂纹和裂纹桥。裂纹总的扩展方式还是I型断裂。根据试验P-V曲线特点,取最大载荷点对应的力与位移求解出铝泡沫的裂纹尖端临界张开位移的平均值为0.051 mm。     

Convolutions and generalization of logconcavity: Implications and applications

Additive convolution of unimodal and α‐unimodal random variables are known as an old classic problem which has attracted the attention of many authors in theory and applied fields. Another type of convolution, called multiplicative convolution, is rather younger. In this article, we first focus on this newer concept and obtain several useful results in which the most important ones is that if is logconcave then so are and for some suitable increasing functions ?. This result contains and as two more important special cases. Furthermore, one table including more applied distributions comparing logconcavity of f(x) and and two comprehensive implications charts are provided. Then, these fundamental results are applied to aging properties, existence of moments and several kinds of ordered random variables. Multiplicative strong unimodality in the discrete case is also introduced and its properties are investigated. In the second part of the article, some refinements are made for additive convolutions. A remaining open problem is completed and a conjecture concerning convolution of discrete α‐unimodal distributions is settled. Then, we shall show that an existing result regarding convolution of symmetric discrete unimodal distributions is not correct and an easy alternative proof is presented. © 2016 Wiley Periodicals, Inc. Naval Research Logistics 63: 109–123, 2016     

A bivariate optimal replacement policy for a cold standby repairable system with repair priority

In this article, an optimal replacement policy for a cold standby repairable system consisting of two dissimilar components with repair priority is studied. Assume that both Components 1 and 2, after repair, are not as good as new, and the main component (Component 1) has repair priority. Both the sequence of working times and that of the components'repair times are generated by geometric processes. We consider a bivariate replacement policy (T,N) in which the system is replaced when either cumulative working time of Component 1 reaches T, or the number of failures of Component 1 reaches N, whichever occurs first. The problem is to determine the optimal replacement policy (T,N)* such that the long run average loss per unit time (or simply the average loss rate) of the system is minimized. An explicit expression of this rate is derived, and then optimal policy (T,N)* can be numerically determined through a two‐dimensional‐search procedure. A numerical example is given to illustrate the model's applicability and procedure, and to illustrate some properties of the optimal solution. We also show that if replacements are made solely on the basis of the number of failures N, or solely on the basis of the cumulative working time T, the former class of policies performs better than the latter, albeit only under some mild conditions. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010     

关于半鞅的可料表示性

利用鞅空间H1的泛函表示定理、泛函分析中的Hahn-Banach定理、半鞅向量随机积分的Girsanov定理,获得了半鞅可料表示性的特征。由于使用的是半鞅的向量随机积分,它推广了经典的结论。     

子空间预测控制在固体氧化物燃料电池中的应用

为使固体氧化物燃料电池(SOFC)输出满足一定约束的稳定电压、提高其输出功率跟踪性能,采用文献中给出的SOFC动态模型,设计了基于子空间矩阵的预测控制器。将子空间辨识和预测控制算法结合起来,直接从开环输入输出数据获得预测控制器的控制矩阵,而不须经过中间参数模型辨识的步骤。仿真结果验证了所提子空间预测控制算法(SPC)的实用性。     

俄罗斯军事人才生成机制对武警视级指挥院校任职教育的启示

俄罗斯军事教育注重培养学员的国家意识,强调教员必须具有很强的综合能力,教学方法灵活、实用,考试方法突出能力素质的考核。俄罗斯军事人才培养形成了注重实战演练、坚持岗位轮换、引进竞争机制、重视鉴定考核的良性机制,保证了人才培养的质量。武警部队初级指挥院校提高任职教育质量应借鉴俄罗斯军事人才培养方法,在培训内容、教员选拔、授课方法、考试形式等方面进行改革。     

灰色预测模型在非致命武器经济寿命预测中的应用

针对目前非致命武器经济寿命方面的研究相当缺乏的现状,结合非致命武器的自身特点,在全面分析装备全寿命周期费用的基础上,引入灰色理论,运用GM（1,1）模型对非致命武器的经济寿命周期费用进行估算和预测。通过分析,灰色预测模型具有较高的建模精度,预测方法和结果对非致命武器的经济寿命预测具有很强的实用性。