Optimizing usage and maintenance decisions for k‐out‐of‐n systems of moving assets

We consider an integrated usage and maintenance optimization problem for a k‐out‐of‐n system pertaining to a moving asset. The k‐out‐of‐n systems are commonly utilized in practice to increase availability, where n denotes the total number of parallel and identical units and k the number of units required to be active for a functional system. Moving assets such as aircraft, ships, and submarines are subject to different operating modes. Operating modes can dictate not only the number of system units that are needed to be active, but also where the moving asset physically is, and under which environmental conditions it operates. We use the intrinsic age concept to model the degradation process. The intrinsic age is analogous to an intrinsic clock which ticks on a different pace in different operating modes. In our problem setting, the number of active units, degradation rates of active and standby units, maintenance costs, and type of economic dependencies are functions of operating modes. In each operating mode, the decision maker should decide on the set of units to activate (usage decision) and the set of units to maintain (maintenance decision). Since the degradation rate differs for active and standby units, the units to be maintained depend on the units that have been activated, and vice versa. In order to minimize maintenance costs, usage and maintenance decisions should be jointly optimized. We formulate this problem as a Markov decision process and provide some structural properties of the optimal policy. Moreover, we assess the performance of usage policies that are commonly implemented for maritime systems. We show that the cost increase resulting from these policies is up to 27% for realistic settings. Our numerical experiments demonstrate the cases in which joint usage and maintenance optimization is more valuable. © 2017 Wiley Periodicals, Inc. Naval Research Logistics 64: 418–434, 2017     

Progress payments and cost overruns in defence contracts

In recent years military procurement agencies have used “progress payments” in contracting. Although, overall, the adoption of such a policy may well have contributed to a decrease in total costs of procurement, we identify a class of inefficiencies that are likely to have been generated by it.     

The impact of defense and non‐defense public spending on growth in Asia and Latin America∗

For a three‐sector Feder‐Ram framework, we present time‐series, cross‐sectional estimates for two cohorts, consisting of Asian and Latin American countries. The estimates indicate that private investment, and defense and non‐defense public spending are growth promoting for alternative error components representations. For the best error components representation, greater growth enhancement is associated with the two forms of public spending in Asia than in Latin America, while the opposite comparison characterizes private investment. Although defense is growth promoting, an opportunity cost exists insofar as non‐defense spending, financed by defense spending, appears to give a small net boost to growth in Latin America.     

Statistical equivalency and optimality of simple step‐stress accelerated test plans for the exponential distribution

Accelerated life testing (ALT) is commonly used to obtain reliability information about a product in a timely manner. Several stress loading designs have been proposed and recent research interests have emerged concerning the development of equivalent ALT plans. Step‐stress ALT (SSALT) is one of the most commonly used stress loadings because it usually shortens the test duration and reduces the number of required test units. This article considers two fundamental questions when designing a SSALT and provides formal proofs in answer to each. Namely: (1) can a simple SSALT be designed so that it is equivalent to other stress loading designs? (2) when optimizing a multilevel SSALT, does it degenerate to a simple SSALT plan? The answers to both queries, under certain reasonable model assumptions, are shown to be a qualified YES. In addition, we provide an argument to support the rationale of a common practice in designing a SSALT, that is, setting the higher stress level as high as possible in a SSALT plan. © 2012 Wiley Periodicals, Inc. Naval Research Logistics, 2013     

The Skybolt Crisis of 1962: Muddle or Mischief?

This paper revisits the controversy over the cancellation of the US Skybolt air-launched ballistic missile in 1962. Cancellation provoked an acute crisis in Anglo-US relations, which historians and political scientists on both sides of the Atlantic have generally sought to explain in terms of mis-communication. This approach may be termed the 'muddle' thesis. Other analysts have been more suspicious of British intentions and tactics in the run-up to cancellation - the 'mischief' thesis. In order to assess these interpretations, the paper poses three questions. First, were the British fully informed about what was likely to happen, or just selective listeners to Washington opinion? Second, had the British government really staked its hopes unequivocally on Skybolt, or was it from the outset hedging its bets? And third, how were alternatives to Skybolt evaluated? The flows of information between Washington and London are examined to establish what was known, when, and what other choices were open to the British government.     

The Wilson government and the demise of TSR‐2, October 1964 – April 1965

Domestic factors play an important role in the formulation and evolution of a country's foreign and security policy. This is clearly seen in the case study of a Soviet successor state, Ukraine. The article brings together in seven sections theory with the key domestic factors that influence Ukrainian security policy, such as economics, energy, national identity, elites and political parties. The article provides an insight into how these domestic factors influence the course of Ukrainian security policy which is striking a balance between the twin extremes of Soviet re‐integration, which would be tantamount to the loss of independence, and nationalist maximalism which seeks to place as much distance as possible between Ukraine and Russia.