Design and control of agile automated CONWIP production lines

In this article, we study the design and control of manufacturing cells with a mix of manual and automated equipment, operating under a CONWIP pull protocol, and staffed by a single agile (cross‐trained) worker. For a three‐station line with one automated station, we fully characterize the structure of the optimal control policy for the worker and show that it is a static priority policy. Using analytical models and extensive simulation experiments, we also evaluate the effectiveness of practical heuristic control policies and provide managerial insights on automation configuration design of the line. This characterization of the worker control policy enables us to develop managerial insights into the design issues of how best to locate and concentrate automation in the line. Finally, we show that, in addition to ease of control and greater design flexibility, the CONWIP protocol also offers higher efficiency and robustness than does the push protocol. © 2008 Wiley Periodicals, Inc. Naval Research Logistics 2009     

The determination of optimal base-stock inventory policy when the costs of under- and oversupply are uncertain

This article considers the determination of the optimal base-stock inventory policy for the newsboy inventory model when there is uncertainty about either or both of its basic cost inputs: either C_u, the marginal cost of an undersupply mistake, or C_o, the marginal cost of an oversupply mistake. Such uncertainties often arise in implementing the newsboy model, especially with respect to C_u, whose value depends mostly on the often-imponderable economic consequences of a lost sale or backorder. Given this uncertainty, we use decision theory to propose and analyze two measures of policy “goodness” and two base-stock selection criteria, which in combination provide four alternative “optimal” base-stock policies. Formulas and/or conditions defining each alternative policy are provided. Our empirical study indicates that the recommended policy can be quite sensitive to the measure/criterion chosen, and that the consequences of the wrong choice can be quite considerable.     

Warranty reserving

This paper considers a problem of warranty reserving, namely, the current practice of setting aside part of a product revenue to meet future claims arising from the warranty. We define a Compound Poisson stochastic model for warranty claims and reserve and obtain, using a sample paths technique, the long-run probability distribution of a warranty reserves, managed under alternative warranties and reserve policies.     

Transient solution of a finite-capacity M/Ga,b/1 queueing system

In this article we consider a single-server, bulk-service queueing system in which the waiting room is of finite capacity. Arrival process is Poisson and all the arrivals taking place when the waiting room is full are lost. The service times are generally distributed independent random variables and the distribution is depending on the batch size being served. Using renewal theory, we derive the time-dependent solution for the system-size probabilities at arbitrary time points. Also we give expressions for the distribution of virtual waiting time in the queue at any time t.     

A theoretical justification for an increasing average failure rate strength distribution in fibrous composites

A general model for the failure of fibrous composite materials is described. It is shown to contain some of the well-known models in the literature. The composite material is viewed as a coherent system of independent identically distributed component strengths. Under the assumption that the applied load is redistributed “homotonically” to the unfailed components upon the failure of a component (an individual fiber segment) and that the distributions of component strengths are IFRA, it is shown that the system (composite) strength distribution is also IFRA. Examples are given using carbon reinforced composite data to illustrate the IFRA property.     

Level crossing analysis of priority queues and a conservation identity for vacation models

The two purposes of this article are to illustrate the power and simplicity of level crossing analysis and to present a conservation identity for M/G/1 priority queues with server vacations. To illustrate the use of level crossing analysis we apply it to preemptive (resume) priority M/G/1 queues with single- and multiple-server vacations considered by Kella and Yechiali (1986) and to non-preemptive priority M/M/c queues considered by Kella and Yechiali (1985). The conservation identity presented here states that the ratios of mean waiting times in an M/G/1 queue with and without server vacation policies are independent of the service discipline for first come first served, shortest processing time, shortest processing time within generations and non-preemptive priority service disciplines.     

A usable past: a contemporary approach to history for the Western profession of arms

The most effective way for the Western profession of arms to use history is to disavow the purism and narrow specialisation of today’s academia in favour of developing a contemporary approach to the subject. The latter aims to foster a range of applied diagnostic skills that transcend the temporal dimensions of past, present, and future. A contemporary approach to history for military professionals emphasises the use of inter-disciplinary war studies to enhance policy relevance. In any defense and security organisation, history must be usable in the sense of providing cognitive and interpretative skills for probing relationships between possibility and actuality, between experience and expectation, and between singularity and repetition. Using history to examine such dialectical interconnections is particularly valuable when military establishments confront their essential task of analyzing emerging trends in the future of war.     

Integrating the Services and Harnessing the Military Area Commands

ABSTRACT

The Chinese People’s Liberation Army (PLA) is halfway through a multi-decade modernization process. It has begun a major restructuring effort as it shifts its focus from a traditional continental defensive posture to a more maritime-oriented emphasis. In order to create more balanced joint force, it has adjusted the structure of its highest command organization, the Central Military Commission; abolished the former four General Departments and seven Military Regions; created five new joint Theater Commands and service-level commands for the Army and Rocket Force; and is reducing the size of its active duty force by 300,000 personnel. While seeking to overcome numerous internal obstacles, the PLA continues to develop and improve its capabilities to conduct integrated joint operations to deter a variety of threats to China’s sovereignty and territory and, if deterrence fails, to win informationized local war.     

China’s Search for a ‘Strategic Air Force’

Once dismissed by many outside observers, the Chinese People’s Liberation Army Air Force (PLAAF) has undergone an impressive transformation over the past two decades, emerging as one of the world’s premier air forces. As it continues to modernize, it is focused on becoming a ‘strategic air force.’ PLAAF strategists suggest this means it should play a decisive role in protecting Chinese national interests, field modern capabilities commensurate with China’s standing as a major power, and enjoy the institutional status befitting its role as a ‘strategic service,’ an important consideration given the historical dominance of the ground force in China’s military.     

The ‘first’ surge: the repulse of the Easter Invasion in South Vietnam, 1972 – implications for Iraq and Afghanistan

In a military intervention, do surges work? I compare the failed ‘surge’ in Vietnam, the repulse of the Easter Invasion in 1972, as a means of assessing the more ambiguous surges in Iraq and Afghanistan. I identify four features of a surge for this analysis: the military dimensions and strategy of the surging forces, the military capabilities of the host forces, the political vitality and will of the host country, and the political commitment in the domestic politics of the intervener. I find that the last feature is the most critical; and, in all three surges, the American political commitment was lacking.