Transient behavior of large Markovian multiechelon repairable item inventory systems using a truncated state space approach

Calculations for large Markovian finite source, finite repair capacity two-echelon repairable item inventory models are shown to be feasible using the randomization technique and a truncated state space approach. More complex models (involving transportation pipelines, multiple-item types and additional echelon levels) are also considered.     

Suppression of enemy air defenses (SEAD) as an information duel

Blue strike aircraft enter region ? to attack Red targets. In Case 1, Blue conducts (preplanned) SEAD to establish air superiority. In the (reactive) SEAD scenario, which is Case 2, such superiority is already in place, but is jeopardized by prohibitive interference from Red, which threatens Blue's ability to conduct missions. We utilize both deterministic and stochastic models to explore optimal tactics for Red in such engagements. Policies are developed which will guide both Red's determination of the modes of operation of his engagement radar, and his choice of Blue opponent to target next. An index in the form of a simple transaction kill ratio plays a major role throughout. Published 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 723–742, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/nav.10046     

Sensitivity of queueing models to the assumption of exponentiality

This study deals with determining the effects on queuing models of assuming that interarrival and service times are exponentially distributed. Steady-state expected value measures of congestion are compared for a variety of GI/G models when assuming an M/M model as an approximation. The majority of this effort involves single-channel queues; however, some multichannel situations are also considered. In addition, effects of the exponential approximation are observed in certain cost-optimization models.     

Inference from accelerated life tests using eyring type re-parameterizations

Least squares estimators of the parameters of the generalized Eyring Model are obtained by using data from censored life tests conducted at several accelerated environments. These estimators are obtained after establishing that the Gauss-Markov conditions for least squares estimation are satisfied. Confidence intervals for the hazard rate at use conditions are obtained after empirically showing that the logarithm of the estimate of the hazard rate at use conditions is approximately normally distributed. The coverage probabilities of the confidence intervals are also verified by a Monte Carlo experiment. The techniques are illustrated by an application to some real data.     

Multiechelon repairable-item provisioning in a time-varying environment using the randomization technique

Multiechelon repairable-item provisioning systems are considered under a time-varying environment. Such conditions could arise, for example, in a military context where a shift from peacetime operation to wartime operation takes place; or, in a civilian setting where a public transit system decides to increase its hours of operation or frequency of service. Exact Markovian models, incorporating a finite population of repairable components and limited repair capacity (nonample service), are treated, with transient solutions obtained using the randomization technique. The exact models are compared with the approximate Dyna-METRIC model which assumes an infinite population of components and ample repair capacity.     

An indicator of combat success

Assessing the effects of changes in weapons systems or battle tactics is difficult because of the variations in battles and the resulting instability of measures of combat effectiveness. Even under the relatively stable conditions of designed combat exercises, traditional measures may fail to reflect important battle events and dynamics. This variation in results makes the design, conduct, and evaluation of combat experiments, combat simulations, and combat training exercises a challenging endeavor, indeed. We develop and examine a combat measure of effectiveness, based on Lanchester models, which we call the battle trace. The battle trace is a measure of ongoing battle results, measured as a function of time into the battle. We describe how such measures might contribute to assessing effects of changing certain battle parameters. We suggest applications of these ideas to developing combat simulations and to enhancing combat training exercises.