摘要:

AbstractSatellite communications, like batches of work in a job shop, need to be scheduled in order to use their resources as efficiently as possible. The most common satellite communications system in use today is known as Time Division Multiple Access (TDMA), in which data from earth stations is buffered before being transmitted to the appropriate receiver on a satellite. Cycles of transmission are fixed for all stations. Since the same satellite will be used for routeing data in several different ways, a schedule must be devised to use the receivers, repeaters and transmitters on board to minimize the time needed for completion of a batch of work. This paper is a survey of current scheduling algorithms used for optimizing satellite communications resources. Apart from telecommunications, the methods presented here could be applied to more general scheduling problems with renewable resources but without precedence constraints.

ISSN:0160-5682    

DOI:10.1057/jors.1994.99

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractLog bucking is an industrial problem of subdividing longer logs into smaller logs such that potential revenue is maximized. The model has been solved using dynamic programming predominately, and branch-and-bound to a lesser extent. This research considers the effect of modelling assumptions that have been used to accommodate the solution techniques. Three levels of increasing model detail are considered. An examination of the nature and amount of error is made by using a model of lesser detail instead of a more precise model. The main experiment is used to show the differences in solution accuracy for the three dynamic programming strategies when compared with the accuracy of solutions generated by using branch-and-bound. The final analysis considers the cost in terms of time to solution for each solution technique to produce highly comparable solution accuracy.

ISSN:0160-5682    

DOI:10.1057/jors.1994.100

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractAlthough network modelling techniques have been available for a number of years now, in the transport sector they have largely been confined to the planning function, and the analysis of schemes with long lead-times. However, recent analysis by London Underground Ltd has used a Network Model to estimate changes in revenue and passenger time resulting from the possible failure of key parts of their infrastructure. Future engineering strategy will attempt to repair first those sites where the disbenefits of failure are greatest. This paper also introduces a number of algorithmic developments (in terms of a group of choice models) which have underpinned this analysis and have significantly improved the accuracy of the modelling tools available.

ISSN:0160-5682    

DOI:10.1057/jors.1994.101

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractFor many years Loughborough University Business School has been operating a system for the allocation of responsibilities carried out by academic staff under the broad headings of supervision, teaching, administration and research. The aim is to have a balanced total load for each staff member, allowing for the strengths and weaknesses of individuals. The system has a large measure of credibility with staff. Four models are derived and discussed, illustrating various options available in dealing with the allocation of one of these components—lecture loads.

ISSN:0160-5682    

DOI:10.1057/jors.1994.102

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractStochastic inventory models, such as continuous review models and periodic review models, require information on the lead time demand. However, information about the form of the probability distribution of the lead time demand is often limited in practice. We relax the assumption that the cumulative distribution function, sayF, of the lead time demand is completely known and merely assume that the first two moments ofFare known and finte. The minmax distribution free approach for the inventory model consists of finding the most unfavourable distribution for each decision variable and then minimizing over the decision variable. We solve both the continuous review model and the periodic review model with a mixture of backorders and lost sales using the minmax distribution free approach.

ISSN:0160-5682    

DOI:10.1057/jors.1994.103

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe traditional Delphi method has been used for many years as an approach for knowledge capture and consensus building in a variety of social and managerial areas, including model building. This paper describes research into the development and initial application of a computerized version of the Delphi method to assist model building in situations where the domain experts to be consulted are large in number and geographically dispersed. Specifically, it has been developed to assist System Dynamics model building, where the purpose of the modelling was to help with the design and assessment of computer-based information systems. The features of a Hypermedia-based Delphi system, which was developed for the Apple Macintosh are described and the results of its application to a modelling exercise are discussed, with particular emphasis on its ability to create consensus influence diagrams and graphical relationships.

ISSN:0160-5682    

DOI:10.1057/jors.1994.104

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThis paper describes a greedy heuristic for a class of combinatorial optimization problems; a central feature of the method being a look-ahead capability. The power of the heuristic is demonstrated through experimentation using a large, real-life vehicle scheduling problem with tight time-window constraints. Incorporation of the look-ahead feature gave an improvement in performance that was at least as great as, and in addition to, that which had been obtained through use of the well-known‘savings’method. Based upon the experimental results, some guidelines are proposed for the application of the heuristic to other problems. One of the conclusions is that designers of heuristics should give greater consideration to the inclusion of a look-ahead element in their algorithms.

ISSN:0160-5682    

DOI:10.1057/jors.1994.105

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractWe consider the problem of assigning a common due-date and sequencing a set of simultaneously available jobs on several identical parallel-machines. The objective is to minimize some penalty function of earliness, tardiness and due-date values. We show that the problem is NP-hard with either a total or a maximal penalty function. For the problem with a total penalty function, we show that the special case in which all jobs have an equal processing time is polynomially-solvable.

ISSN:0160-5682    

DOI:10.1057/jors.1994.106

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThis paper considers the problem of long-term manpower planning on the number of teaching staff for the case of a tertiary institution—the City Polytechnic of Hong Kong (CPHK). Due to the high turnover experienced in recent years, it is found necessary to study the wastage pattern of staff, defined as the number of new appointees who have left CPHK employment, rather than simply addressing just the issue of strength (namely number in post). A cohort analysis technique is therefore applied to characterize statistically the wastage rate as related to the length of service of individual cohorts of staff, being groups of newcomers joining CPHK in the same periods of time. This results in a log-normal model, showing a significant cohort specific effect on the wastage behaviour. Extending this cohort analysis technique, together with double exponential smoothing forecasts, to future retention rates (1—cumulative wastage rates), a long-term planning model is constructed to study the relation between expected yearly recruitment levels and the target manpower requirements for the future five-year planning horizon. While the idea and model developed here are generally applicable, the present computational results provide valuable decision supports for an actual case study, for CPHK in particular.

ISSN:0160-5682    

DOI:10.1057/jors.1994.107

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe existence of uncertainty is a feature of the business world. Forecasting does not remove this uncertainty, but sets out to measure and minimize it. This paper suggests decomposing the forecast error into three components, namely the residual unexplained error, the error resulting from the estimation procedures of the model, and the errors due to the approximate nature of the model. The quantification of this division for a steady-state model, or exponentially weighted moving average (EWMA) process, is used as an illustration. The results obtained indicate the maximum safe limits for extrapolating this model into the future.

ISSN:0160-5682    

DOI:10.1057/jors.1994.108

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor