Optimal burn‐in procedure for periodically inspected systems

Burn‐in is a widely used method to improve the quality of products or systems after they have been produced. In this paper, we study burn‐in procedure for a system that is maintained under periodic inspection and perfect repair policy. Assuming that the underlying lifetime distribution of a system has an initially decreasing and/or eventually increasing failure rate function, we derive upper and lower bounds for the optimal burn‐in time, which maximizes the system availability. Furthermore, adopting an age replacement policy, we derive upper and lower bounds for the optimal age parameter of the replacement policy for each fixed burn‐in time and a uniform upper bound for the optimal burn‐in time given the age replacement policy. These results can be used to reduce the numerical work for determining both optimal burn‐in time and optimal replacement policy. © 2007 Wiley Periodicals, Inc. Naval Research Logistics, 2007     

中美采办政策的若干差异和对策建议

通过对中美两国武器装备采办政策的对比分析,提出当前我国武器装备研制与管理政策方面的若干建议。     

Epidemics,national security,and US immigration policy

What are relationships between epidemics, national security, and US immigration policy? This question is important because it sheds light on transnational or nontraditional security areas, American immigration policy, and a pressing issue for US leaders who have recently faced epidemics such as the West Africa Ebola outbreak that began in 2013. This article answers it and lays ground in the area by reviewing epidemics in world history, using International Relations and Security Studies works to specify dangers of contagions for states, and identifying three general immigration measures that American leaders have utilized from the seventeenth century to the present day to protect against contagions, which are (1) policies restricting entrance of foreigners thought to carry specified diseases, (2) the isolation or quarantining of immigrants with contagious disease, and (3) delegating the President with authority to stop immigration in the event of an epidemic abroad. This study has implications for research and contemporary US immigration policy.     

The limits of robotic solutions to human challenges in the land domain

In the face of rapid technological change and the creation of ambitious military modernisation programmes, this paper argues that land forces, in managing the relationship between force levels and the adoption of military robotics, must recognise that there are inherent limits to techno-centric force reduction efforts and realise the inefficacy of substituting skilled soldiers with robots. It begins with an overview of how the proper integration of robotics into a military’s force structure can improve capability, save lives and potentially reduce costs, but suggests that common accounts of robot utility are exaggerated and endanger the risk assessment processes governing the adoption of said technologies and relevant personnel settings. The paper explores the limits of robotic solutions to military problems, discussing their technical limitations, redundancy and related issues that, when combined with a technico-moral skills degradation problem also detailed within, point to the need to reshape force structures to suit the adoption of robotics while preserving existing levels of human staffing.     

A survey of performance issues in defence innovation

This article reviews innovation processes in defence. It analyses the way and the context under which these processes are carried out. The article covers the features of defence goods with impact on innovation, the development of a new good, the institutional arrangements that support these processes and the effect of innovation on industrial market. The analysis helps to identify the causes of facts observed in practice, such as poor performance in terms of product quality, cost or delivery time, as well as to assess potential remedies. Some policy implications, which can be derived from this analysis, are finally outlined.     

Assessing the value of demand sharing in supply chains

We consider the problem of assessing the value of demand sharing in a multistage supply chain in which the retailer observes stationary autoregressive moving average demand with Gaussian white noise (shocks). Similar to previous research, we assume each supply chain player constructs its best linear forecast of the leadtime demand and uses it to determine the order quantity via a periodic review myopic order‐up‐to policy. We demonstrate how a typical supply chain player can determine the extent of its available information in the presence of demand sharing by studying the properties of the moving average polynomials of adjacent supply chain players. The retailer's demand is driven by the random shocks appearing in the autoregressive moving average representation for its demand. Under the assumptions we will make in this article, to the retailer, knowing the shock information is equivalent to knowing the demand process (assuming that the model parameters are also known). Thus (in the event of sharing) the retailer's demand sequence and shock sequence would contain the same information to the retailer's supplier. We will show that, once we consider the dynamics of demand propagation further up the chain, it may be that a player's demand and shock sequences will contain different levels of information for an upstream player. Hence, we study how a player can determine its available information under demand sharing, and use this information to forecast leadtime demand. We characterize the value of demand sharing for a typical supply chain player. Furthermore, we show conditions under which (i) it is equivalent to no sharing, (ii) it is equivalent to full information shock sharing, and (iii) it is intermediate in value to the two previously described arrangements. Although it follows from existing literature that demand sharing is equivalent to full information shock sharing between a retailer and supplier, we demonstrate and characterize when this result does not generalize to upstream supply chain players. We then show that demand propagates through a supply chain where any player may share nothing, its demand, or its full information shocks (FIS) with an adjacent upstream player as quasi‐ARMA in—quasi‐ARMA out. We also provide a convenient form for the propagation of demand in a supply chain that will lend itself to future research applications. © 2014 Wiley Periodicals, Inc. Naval Research Logistics 61: 515–531, 2014     

Demobilisation,disarmament and reintegration in the Democratic Republic of Congo: The numbers game

Abstract

The creation of the Africa Command (AFRICOM) has reflected the growth in the strategic importance of Africa in US foreign policy since the end of the 1990s. One of the objectives of this new geographical military command is to forge closer links between foreign, security and development policies. However, this approach met with a number of difficulties associated with the challenge of ‘inter-agency cooperation’ among rather disparate actors from foreign affairs, defence and development. In addition, the establishment of AFRICOM has met with fierce criticism in the US and elsewhere – especially in Africa – culminating in the charge that the US foreign and development policies in Africa are being militarised. Although AFRICOM has a number of interesting features, this paper shows that it has reacted to these criticisms by realigning itself more closely with the traditional model of a military command, at the expense of the innovative interagency elements.     

Japan's plutonium policy: Consequences for nonproliferation

ABSTRACT

What do we mean by nuclear proliferation? What does it mean to proliferate? This article investigates both the literal and figurative meaning of the term “proliferation.” It argues that many of the definitions and conceptualizations of nuclear proliferation often used by scholars are either limited in their utility or logically inconsistent. It then reconceptualizes and redefines the term, incorporating an understanding of both its etymological origins and the geopolitical context in which the phenomenon occurs. It concludes by exploring the potential impact that the politicization of the phenomenon may have on the identification of occurrences of proliferation, from both an academic and a policy-making perspective.     

Limiting behavior of the stochastic sequential assignment problem

The stochastic sequential assignment problem (SSAP) considers how to allocate available distinct workers to sequentially arriving tasks with stochastic parameters such that the expected total reward obtained from the sequential assignments is maximized. Implementing the optimal assignment policy for the SSAP involves calculating a new set of breakpoints upon the arrival of each task (i.e., for every time period), which is impractical for large‐scale problems. This article studies two problems that are concerned with obtaining stationary policies, which achieve the optimal expected reward per task as the number of tasks approaches infinity. The first problem considers independent and identically distributed (IID) tasks with a known distribution function, whereas in the second problem tasks are derived from r different unobservable distributions governed by an ergodic Markov chain. The convergence rate of the expected reward per task to the optimal value is also obtained for both problems. © 2013 Wiley Periodicals, Inc. Naval Research Logistics, 2013     

特定m维修策略更新过程系统可用度模型

将武器装备系统的组成部分分为3类,通过分析得出适合装备系统的特定m维修策略,能够在保证装备较高使用可用度的同时,最大程度地缩减维修保障成本.利用更新过程某些特性,建立特定m维修策略下的使用可用度模型,简化了使用可用度的计算.