摘要:

AbstractHollander, Park, and Proschan define a survival functionSof a positive random variableXto be new better than used at aget0(NBU‐{t0}) ifSsatisfies\documentclass{article}\pagestyle{empty}\begin{document}$ \begin{array}{*{20}c} {\frac{{S(x + t_0)}}{{S\left({t_0} \right)}} \le S\left(x \right),}&{{\rm for}\,{\rm all}\,x\, \ge \,0,} \\ \end{array}$ \end{document}whereS(x) =P(X>x). The NBU‐{t0} class is a special case of the NBU‐Afamily of survival distributions, whereAis a subset of [0, ∞). These families introduce a variety of modeling possibilities for use in reliability studies. We treat problems of nonparametric estimation of survival functions from these classes by estimators which are themselves members of the classes of interest. For a number of such classes, a recursive estimation technique is shown to produce closed‐form estimators which are strongly consistent and converge to the true survival distribution at optimal rates. For other classes, additional assumptions are required to guarantee the consistency of recursive estimators. As an example of the latter case, we demonstrate the consistency of a recursive estimator forS∈ NBU‐[t0, ∞) based on lifetime data from items surviving a preliminary “burn‐in” test. The relative precision of the empirical survival curve and several recursive estimators ofSare investigated via simulation; the results provide support for the claim that recursive estimators are superior to the empirical survival curve in restricted nonparametric estimation problems of

ISSN:0894-069X    

DOI:10.1002/1520-6750(199104)38:2<123::AID-NAV3220380202>3.0.CO;2-O

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractIn 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

ISSN:0894-069X    

DOI:10.1002/1520-6750(199104)38:2<145::AID-NAV3220380203>3.0.CO;2-D

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractVisual search is an important aspect of human tasks in industrial and military applications. Physically, a visual search process consists of a sequence of eye fixations. It has been hypothesized, based on search patterns found in early studies, that it is possible for fixations to follow both random and systematic patterns. Some early research works have been done in visual search. Analysis of human visual search involves examining experimental data and fitting the search time distribution. Some investigations have found that search times are described well by exponential distribution. This article discusses a visual search performance model based on derived search time distributions. The investigation of such a model is helpful in computing the probability of detecting a target, given a specified duration of search.

ISSN:0894-069X    

DOI:10.1002/1520-6750(199104)38:2<157::AID-NAV3220380204>3.0.CO;2-5

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe paper addresses the problem of a patrol trying to stop smugglers who are attempting to ship a cargo of perishable contraband across a strait in one ofMtime units. The situation was modeled as a two‐person zero‐sum game of exhaustion by Thomas and Nisgav and this article extends their results. The game has many characteristics in common with the Inspection Game in Owen's book on Game Theory; this Inspection Game is generalized and the relations between the two games are discus

ISSN:0894-069X    

DOI:10.1002/1520-6750(199104)38:2<171::AID-NAV3220380205>3.0.CO;2-2

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThis article details several procedures for using path control variates to improve the accuracy of simulation‐based point and confidence‐interval estimators of the mean completion time of a stochastic activity network (SAN). Because each path control variate is the duration of the corresponding directed path in the network from the source to the sink, the vector of selected path controls has both a known mean and a known covariance matrix. This information is incorporated into estimation procedures for both normal and nonnormal responses. To evaluate the performance of these procedures experimentally, we examine the bias, variance, and mean square error of the controlled point estimators as well as the average half‐length and coverage probability of the corresponding confidence‐interval estimators for a set of SANs in which the following characteristics are systematically varied: (a) the size of the network (number of nodes and arcs); (b) the topology of the network; (c) the percentage of activities with exponentially distributed durations; and (d) the relative dominance of the critical path. The experimental results show that although large improvements in accuracy can be achieved with some of these procedures, the confidence‐interval estimators for normal responses may suffer serious loss of coverage probability in some app

ISSN:0894-069X    

DOI:10.1002/1520-6750(199104)38:2<183::AID-NAV3220380206>3.0.CO;2-V

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractWe consider the problem of deciding whether to keep a piece of equipment or replace it with a more advanced technology in an environment of technological change. Our model assumes that the costs associated with the presently available technology and future technologies are known, but that the appearance times of future technologies are uncertain. We develop a procedure for computing the optimal keep‐or‐replace decision that iteratively incorporates a technological forecast. For a certain class of situations, we show that our approach requires the minimum possible amount of forecasted d

ISSN:0894-069X    

DOI:10.1002/1520-6750(199104)38:2<203::AID-NAV3220380207>3.0.CO;2-E

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractIn this article we consider a stochastic model for two products which have a single‐period inventory structure and which can be used as substitutes for each other should the need arise. Substitution will occur with probability one, but at perhaps a different revenue level. We prove that the expected profit function is concave, allowing us to find optimal stocking levels for the two products. We compare optimum inventory levels for the case of single substitution with that where there is no substitution. It is demonstrated for the case of single substitution that total optimum order quantities can actually increase or decrease with the substitution revenu

ISSN:0894-069X    

DOI:10.1002/1520-6750(199104)38:2<221::AID-NAV3220380208>3.0.CO;2-7

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractEmpirical distance functions are used to estimate actual travel distances in a transportation network, to verify the accuracy of road mileage data, and to formulate continuous location models. In this article we consider the problem of fitting the weightedlpnorm to a given network. Mathematical properties are derived for two fitting criteria found in the literature. These properties are used to develop an accurate and efficient methodology to solve for the best‐fitting parameter values. The directional bias of thelpnorm is analyzed for its effect on the range of search for the optimal p value. Concepts and methodology are applied to a case study of the road system in Southern Ontario. In conclusion, a general framework for other types of distance functions is briefly discusse

ISSN:0894-069X    

DOI:10.1002/1520-6750(199104)38:2<241::AID-NAV3220380209>3.0.CO;2-Z

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractJobs with known processing times and due dates have to be processed on a machine which is subject to a single breakdown. The moment of breakdown and the repair time are independent random variables. Two cases are distinguished with reference to the processing time preempted by the breakdown (no other preemptions are allowed): (i) resumption without time losses and (ii) restart from the beginning. Under certain compatible conditions, we find the policies which minimize stochastically the number of tardy jobs.

ISSN:0894-069X    

DOI:10.1002/1520-6750(199104)38:2<261::AID-NAV3220380210>3.0.CO;2-I

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThis article considers the problem of scheduling parallel processors to minimize the makespan. The article makes two key contributions: (1) It develops a new lower bound on the makespan for an optimal schedule, and (2) it proposes an efficient two‐step algorithm to find schedules of any desired accuracy, or percent above optimal. In addition, a posterior bound on LPT (longest processing time) sequencing is developed in the article. It is proved that this bound dominates the previously reported bounds on LPT sequencin

ISSN:0894-069X    

DOI:10.1002/1520-6750(199104)38:2<273::AID-NAV3220380211>3.0.CO;2-A

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY