摘要:

AbstractThis paper presents an address given‘in praise of Steve Cook’at the 1989 Cambridge Conference onOR and the Social Sciences. The preamble explains why it takes the form it does and offers a few general views on how Steve's work might be re-examined in the light of current interest in furthering a closer rapport between OR and other specializations.

ISSN:0160-5682    

DOI:10.1057/jors.1989.187

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractExpert system technology can fairly be described as high profile at present. Yet its track record as a useful method for tackling problems is subject to widely differing views. This paper considers the domain of production planning and control, which has been described as a good application area for expert systems a domain where OR has had little success. The authors argue that mainstream expert system methodology is exploratory rather than problem-driven and thus is not suited to the domain. A problem-driven approach to expert system development is presented, an approach which makes use of soft systems methodology. The reasons for such an approach within production planning and control are discussed, and the use of soft systems methodology within the approach is reflected on.

ISSN:0160-5682    

DOI:10.1057/jors.1989.188

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThis paper presents a model to assist in setting the daily production rates for an offshore oilfield to achieve a quarterly production target. The produced crude oil is frequently accompanied by the production of gas, which has much lower value. Since there are environmental limits to the amount of gas that can be flared to waste, problems on gas-processing can very quickly limit oil output. With the commencement of natural decline in many oilfields in the North Sea, the loss of crude output as a result of gas constraints cannot be compensated in the same planning period. This makes the ultimate output, and hence the reward, more sensitive to the problems associated with gas-processing. The model uses a stochastic dynamic programming algorithm to maximize the financial reward. Gas-related limiting factors and the oil and gas plant downtime are considered. The user is allowed to interrogate the model and interact with it when major unforeseen restrictions are imposed on gas capacities. The output includes the optimal production rate and probability and cost of not achieving the target.

ISSN:0160-5682    

DOI:10.1057/jors.1989.189

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractNHS hospitals contribute to medical education, training nurses and research, as well as to the care of patients. In the past they have been funded largely on the basis of resources employed, with additional funding for medical education and training nurses. The intellectual basis for the funding of medical education is a single econometric study of English hospitals in the financial year 1969-70. The methodology used has since been criticized, and it has been suggested that actual expenditure has been very much less than that earmarked by the health departments. New estimates are obtained using Scottish data for the financial year 1985-86. The method used is to proceed in a two-stage fashion, identifying via regression techniques variables measuring hospital activity and resources which contribute significantly to hospital costs. We then assess the significance of medical education, nurse training and hospitals' teaching status against this background. Our conclusions include: (1) actual expenditure on medical education was probably less than the funding formula allowed, but the error of margin is too large to suggest overfunding; (2) training nurses incurs significant financial costs, even after the explicit allowances made; and (3), major teaching hospitals tended to cost more, but not significantly more than their non-teaching counterparts. These financial implications for NHS hospitals should be borne in mind given the current NHS review.

ISSN:0160-5682    

DOI:10.1057/jors.1989.190

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe standard vehicle-scheduling problem is deterministic, assuming all factors are known with certainty in advance of scheduling. In practice there are several areas which might contain uncertainty. This paper suggests ways of tackling these, but concentrates on problems where some customers do not need deliveries during a scheduling period. If the number of such customers is small, semi-fixed routes may be acceptable. As the number of customers omitted rises, there comes a point when rescheduling becomes preferable. The potential savings made by semi-fixed or variable routes over fixed routes are estimated for standard problems. The implications of these savings are then evaluated for a wholesale distributor.

ISSN:0160-5682    

DOI:10.1057/jors.1989.191

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractA multiperiod linear programming model of the production planning problem is used to argue for a different costing, profit and resource-evaluation procedure in manufacturing. This procedure is based on the concept of‘pseudo shadow prices’, and it avoids many of the pitfalls associated with the more traditional accounting methodologies. Conclusions are drawn which question the profit objectives used by many firms, as well as by those in academia.

ISSN:0160-5682    

DOI:10.1057/jors.1989.192

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThis paper presents an alternative to the beta continuous probability distribution for risk analysis. Particular attention has been given to two major applications of distributions, namely project management risk and critical path analysis (PERT). In conjunction with the beta, the triangular and normal distributions are frequently employed in order to give sufficient robustness to risk analysis. The beta distribution, as used in PERT, has a major theoretical implementation flaw. The new distribution was developed to give a possible alternative method of assessing risk. It is shown that the requirement to estimate the most pessimistic variate may be replaced by the probability to exceed the mode. Proposals for other simplifications in risk analysis are discussed. Practical means to validate the most appropriate distributions for risk analysis are outlined, and a cost-data case study is included.

ISSN:0160-5682    

DOI:10.1057/jors.1989.193

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractIn this paper we consider the problem of scheduling a set of simultaneously available jobs on several parallel and identical machines. The problem is to find the optimal due-date, assuming this to be the same for all jobs. We also seek to sequence the jobs such that some are early and some are late so as to minimize a penalty function. For the single-machine problem, we present a simple proof of the well-known optimality result that the optimal due-date coincides with one of the job completion times. We show that the optimal job sequence for the single-machine problem can be easily determined. We prove that the same optimal due-date result can be generalized to the parallel-machine problem. However, determination of the optimal job sequence for such a problem is much more complex, and we present a simple heuristic to find an approximate solution. On the basis of a limited experiment, we observe that the heuristic is very effective in obtaining near-optimal solutions.

ISSN:0160-5682    

DOI:10.1057/jors.1989.194

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractIn this paper we deal with the location of one facility on the surface of the sphere (globe) that minimizes the weighted sum of distances to a given set of demand points on the surface of the sphere. We assume that demand points are randomly generated on the sphere, and so are the weights. We prove that when the number of demand points increases to infinity, then the ratio between the maximum possible value of the objective function and the minimum possible value of the objective function converges to one. We also show that the expected number of demand points that are a local minimum is approximately one when there are a large number of demand points. Some computational experiments are presented.

ISSN:0160-5682    

DOI:10.1057/jors.1989.195

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe problem considered in this study is that of non-pre-emptive scheduling of the activities in a project network to minimize project duration under limited resource availabilities. Various heuristic rules and optimization techniques have been applied to this problem, and comparisons of their effectiveness have been made in the literature. However, no thorough investigation of the types of network and resource characteristics which play an underlying role in determining heuristic performance and which account for the variability of results has been made previously. In this study, a new heuristic rule which compares favourably with the widely-used heuristic rules is developed, and the influence of network/resource characteristics on the performance of different heuristic rules is investigated.

ISSN:0160-5682    

DOI:10.1057/jors.1989.196

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor