Periodic inspection policy with preventive maintenance

This article considers a modified inspection policy with periodic check intervals, where the unit after check has the same age as before with probability p and is as good as new with probability q. The mean time to failure and the expected number of checks before failure are derived, forming renewal-type equations. The total expected cost and the expected cost per unit of time until detection of failure are obtained. Optimum inspection policies which minimize the expected costs are given as a numerical example.     

Modified discrete preventive maintenance policies

This article proposes a modified preventive maintenance (PM) policy which may be done only at scheduled times nT (n = 1,2, …): The PM is done at the next such time if and only if the total number of failures exceeds a specified number k. The optimal number k^* to minimize the expected cost rate is discussed. Further, four alternative similar PM models are considered, when the system fails due to a certain number of faults, uses, shocks, and unit failures.     

A cumulative damage shock model with imperfect preventive maintenance

In this article we consider a cumulative damage shock model under a periodic preventive maintenance (PM) policy. The PM is imperfect in the sense that each PM reduces the damage level by 100(1 – b)%, 0 < b < 1. A system suffers damage due to shocks and fails when the damage level exceeds some threshold. We derive a sufficient condition for the time to failure to have an IFR distribution. We also discuss the associated problem of finding the number of PM's that minimizes the expected cost rate.     

International Security,Multiple Public Good Provisions,and The Exploitation Hypothesis

Since the 1960s Olson-Zeckhauser’s (1966) analysis, its ‘exploitation of the great by the small’ has provided economists’ core model of alliance’s provision of security/defense. But with the end of the Cold War, countries’ allocative behavior has diverged markedly from OZ’s predictions for defense as a homogeneous pure public good voluntarily provided. This paper suggests a replacement for OZ, with the essential difference that ‘defense’ rather than being aggregated into their single public good is disaggregated into more realistic categories of self-insurance and self-protection. Because allocative behavior in public good groups is essentially driven by income effects, we concentrate on these, which become complex and conflicted, giving much greater scope for goods-inferiority. The analysis is followed by numerical simulations, which conform to actual experienced allocations in NATO much better than the conventional ‘exploitation’ model.     

Optimal policy of continuous and discrete replacement with minimal repair at failure

This article considers combined continuous and discrete replacement with minimal repair at failure, in which a unit is replaced at time T or at number N of uses. Both optimal time T* and number N* to minimize the expected cost rate are discussed. They are found by unique solutions of equations when the hazard rates are monotonously increasing. A numerical example is given.