Analysis of a two-component series system with a geometric process model

In this article, a geometric process model is introduced for the analysis of a two-component series system with one repairman. For each component, the successive operating times form a decreasing geometric process with exponential distribution, whereas the consecutive repair times constitute an increasing geometric process with exponential distribution, but the replacement times form a renewal process with exponential distribution. By introducing two supplementary variables, a set of partial differential equations is derived. These equations can be solved analytically or numerically. Further, the availability and the rate of occurrence of failure of the system are also determined. © 1996 John Wiley & Sons, Inc.     

基于Monte Carlo仿真的武器装备贡献度评估法

为了更加科学、准确地对武器装备贡献度进行评估,从装备体系的角度出发,立足于作战任务实际,充分体现信息化条件下空战过程的随机性,提出了一种基于Monte Carlo仿真的武器装备贡献度评估法。对典型空中作战场景进行了任务阶段划分。提出了能够准确描述作战能力的指标项,建立了能够反映能力指标项的随机矩阵。并以拦截空中目标为作战背景,运用Monte Carlo仿真进行了验证,得出了与实际结果一致的结论。为武器装备的装备贡献度评估提供了理论支撑和方法模型。     

Inventory policies with quantized ordering

This article studies (nQ, r) inventory policies, under which the order quantity is restricted to be an integer multiple of a base lot size Q. Both Q and r are decision variables. Assuming the one-period expected holding and backorder cost function is unimodal, we develop an efficient algorithm to compute the optimal Q and r. The algorithm is facilitated by simple observations about the cost function and by tight upper bounds on the optimal Q. The total number of elementary operations required by the algorithm is linear in these upper bounds. By using the algorithm, we compare the performance of the optimal (nQ, r) policy with that of the optimal (s, S) policy through a numerical study, and our results show that the difference between them is small. Further analysis of the model shows that the cost performance of an (nQ, r) policy is insensitive to the choice of Q. These results establish that (nQ, r) models are potentially useful in many settings where quantized ordering is beneficial.     

Interdiction models for delaying adversarial attacks against critical information technology infrastructure

Information technology (IT) infrastructure relies on a globalized supply chain that is vulnerable to numerous risks from adversarial attacks. It is important to protect IT infrastructure from these dynamic, persistent risks by delaying adversarial exploits. In this paper, we propose max‐min interdiction models for critical infrastructure protection that prioritizes cost‐effective security mitigations to maximally delay adversarial attacks. We consider attacks originating from multiple adversaries, each of which aims to find a “critical path” through the attack surface to complete the corresponding attack as soon as possible. Decision‐makers can deploy mitigations to delay attack exploits, however, mitigation effectiveness is sometimes uncertain. We propose a stochastic model variant to address this uncertainty by incorporating random delay times. The proposed models can be reformulated as a nested max‐max problem using dualization. We propose a Lagrangian heuristic approach that decomposes the max‐max problem into a number of smaller subproblems, and updates upper and lower bounds to the original problem via subgradient optimization. We evaluate the perfect information solution value as an alternative method for updating the upper bound. Computational results demonstrate that the Lagrangian heuristic identifies near‐optimal solutions efficiently, which outperforms a general purpose mixed‐integer programming solver on medium and large instances.     

Single‐machine scheduling with deadlines to minimize the total weighted late work

We consider scheduling a set of jobs with deadlines to minimize the total weighted late work on a single machine, where the late work of a job is the amount of processing of the job that is scheduled after its due date and before its deadline. This is the first study on scheduling with the late work criterion under the deadline restriction. In this paper, we show that (i) the problem is unary NP‐hard even if all the jobs have a unit weight, (ii) the problem is binary NP‐hard and admits a pseudo‐polynomial‐time algorithm and a fully polynomial‐time approximation scheme if all the jobs have a common due date, and (iii) some special cases of the problem are polynomially solvable.     

在求“变”中推进西南边防部队转型发展

西南边防部队驻防于我国西南边境地区,西起西藏自治区的日土县,东至广西壮族自治区的防城港市,担负着边防管控和边境防御作战等重要职能,在捍卫国家主权和安全中地位作用十分特殊。随着军队调整改革的深入落实,西南边防部队正处于转型重塑的关键时期,必须紧紧围绕新形势、新体制、新职能,着眼应急指挥、军事训练、边境管控、内外环境等关键要素和现实问题,在求"变"中推进创新发展,不断提升履职能力,切实为捍卫国家领土主权完整和维护边境稳定提供坚强保证。     

商务印书馆函授学校英文科学员来源地考察——基于《英语周刊》(1921-1922)记载的分析

商务印书馆函授学校英文科在中国近现代成人教育史、职业教育史上都占据着非常重要的位置.1921年至1922年期间的《英语周刊》对英文科学员来源地等信息均有着较为详细的记载,弥补了已发现的相关史料的不足,从而可以对其办学效果做出一个客观、精确的评价.通过《英语周刊》的相关记载,可以发现英文科学员来源地范围覆盖区域非常广泛,其学员来源地构成状况呈现出了多元化、多样化的特点.仅仅从学员来源地状况的角度去审视、考察,商务函授学校英文科取得了显著的办学效果,它在一定程度上弥补了普通学校教育资源的不足,有力促进了中国教育近代化事业的发展.     

动态滑翔运动建模、机理分析与航迹优化

信天翁凭借动态滑翔的飞行技巧从梯度风中获取能量,从而在几乎不拍翅膀的情况下进行长时间、长距离飞行,这种技巧应用于小型无人机上可拓展其完成任务的能力。基于飞行器动力学对梯度风场中的无人机运动方程进行推导和简化处理;利用简化的运动方程,分别从非惯性参考系中的动能定理和机械能变化的角度,对动态滑翔获取能量的机理进行分析;利用微分平坦法,以最小平均控制输入变化率为目标函数,对徘徊模式和平移模式的动态滑翔航迹进行优化计算。分析结果表明:逆风爬升、顺风下滑是动态滑翔基本获能方式。优化结果表明:控制输入变得更加平滑,甚至出现阶段性的常值,使得控制更加简化;徘徊模式下,当风梯度作为决策变量时,优化过程可在[0,0.5 s-1]的区间上找到使得目标函数值最小的风梯度;平移模式下,目标函数值在该区间上单调递减。