A unified model for demand prediction in the context of provisining and replenishment

An improved demand prediction model is presented which incorporates features of two earlier models. The unified model pools usage data classified by repair part class and by component class. The performance of the model is evaluated in a provisioning and replenishment context and compared with that for the current procedure which employs technicians' usage estimates.     

A methodology for estimating expected usage of repair parts with application to parts with no usage history

In this paper a model is presented which focuses on the difficult problem of predicting demands for items with extremely low usage rates. These form the bulk of repair parts in military systems. The basic notion underlying the model is the pooling of usage data for common design items with movement for the purpose of estimating usage rates for similar items which have shown no movement. A unique feature of the model is that it also makes possible the estimation of usage rates for items newly introduced into a system for which no previous usage history is available.     

A comparison of usage data among types of aircraft

It has long been an accepted proposition that base level usage df technical repair items for aircraft is related to program elements. The program element most often cited in this connection is flying hours. Evidence of this relationship on a line item basis, however, has been sparse. This study suggests that although the supposed relation is intuitively plausible, for most line items it cannot be effectively utilized in projecting base level requirements. The basis of this conclusion is an analysis of demand characteristics for technical repair items for a variety of naval aircraft.     

A note on first passage times in birth and death and nonnegative diffusion processes

Consider a birth and death process starting in state 0. Keilson has shown by analytical arguments that the time of first passage into state n has an increasing failure rate (IFR) distribution. We present a probabilistic proof for this. In addition, our proof shows that for a nonnegative diffusion process, the first passage time from state 0 to any state x is IFR.     

A replacement schedule for multicomponent life-limited parts

In previous papers [1], [2] the authors developed a maintenance policy for a single life-limited part. Using an opportunistic replacement approach a scheme was devised which utilized early replacement of equipment to offset more costly future expenditures. This paper will extend the results to the multicomponent case. Examples are given illustrating the benefits of this new technique.     

A modified block replacement policy

A well known preventive replacement policy is the block replacement policy (BRP). In such a policy the item undergoes a planned replacement at a sequence of equally spaced time points independent of failure history. The main advantage of a BRP is its simplicity, because under this policy it is unnecessary to keep detailed records about times of failures or ages of items. The main drawback of a BRP is that at planned replacement times we may be replacing practically new items. In this paper we study a modified BRP which is free of this drawback. We calculate the expected cost of following a modified BRP for lifetime distributions possessing a special structure and illustrate it for the case of an Erlang distribution. A numerical comparison is made between a modified BRP and a standard BRP for the special case of a two stage Erlang distribution.     

Swords,sandals, and insurgencies: Ancient history goes to the movies

This article explores the question of why so few insurgencies from the ancient world have ever made it onto the big screen. Many of these stories have been made into documentaries, but have been ignored by Hollywood. Even those events that have been made into Hollywood films, like the uprising of Spartacus, do not show any of the successful uprisings, only the defeats. Among the possible reasons may be Hollywood's fascination with big wars and big battles rather than small wars because they are more cinematic. Another reason is that American movies are reluctant to show successful slave uprisings or insurgencies against great powers. In the end, all movies are about the present, not the past, and thus Western bias will side with the imperial power, not the terrorist.     

A sequential scheduling problem with impatient jobs

There are n customers that need to be served. Customer i will only wait in queue for an exponentially distributed time with rate λ_i before departing the system. The service time of customer i has distribution F_i, and on completion of service of customer i a positive reward r_i is earned. There is a single server and the problem is to choose, after each service completion, which currently in queue customer to serve next so as to maximize the expected total return. © 2015 Wiley Periodicals, Inc. Naval Research Logistics 62: 659–663, 2015     

WHO IS THE ENEMY?

We examine who benefits when there is a strong leader in place, and who benefits when a situation lacks a proper leader. There are fractious terrorist groups who seek to serve the same people in common cause against a common enemy. The groups compete for rents obtained from the public by engaging in actions against the common enemy. We determine the leadership structure under which each group is better off, as well as the circumstance that the common enemy prefers. We are able to state simple and general conditions for each group and the common enemy to benefit.