摘要:

In this paper the approximation of general distributions, with known squared coefficient of variation, by phase-type distributions using the first three moments is studied. The phase-type distributions presented in this paper can be fitted to observed data sets and also can be used to approximate general distributions to be used in analytical models as well as in simulation. Formulas for the approximating distributions are presented and examples are given to show the approximations.

ISSN:0740-817X    

DOI:10.1080/07408178508975280

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The relationship between profitability and efficiency in a production line is discussed at length for the continuous production model. We prove that a solution which maximizes efficiency will not necessarily maximize profit. Several useful relationships between profitability and efficiency are developed which can greatly enhance computational efficiency. A solution procedure is developed which will determine the optimal number of work stations by maximizing an assumed profit function. An example is provided to illustrate these relationships and the entire solution procedure.

ISSN:0740-817X    

DOI:10.1080/07408178508975281

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Six factors that affect either the transient or the long-term growth rate of equity capital are identified. The use of the net present value method of financial accounting to compute the equity value of hypothetical firms is described. Simulation of sequences of capital budgeting decisions in hypothetical firms was used to illustrate the effects of the six factors on the growth rate of equity capital. The upper limit of a firm's steady-state capital growth rate was affected by (1) the maximum yield attainable from its long-term investments, (2) its debt policy, (3) its budget allocation policy, and (4) the (average) life of its long-term investments. Unless the selection procedure was random, the transient values of a firm's annual growth rate of equity were affected appreciably by (1) the growth rate of its long-term investment opportunities, (2) its debt policies, and (3) its past decisions. Random variation in the growth rate of investment opportunities had little affect on the average growth rate of the firm, but it had appreciable affect on the year to year values. The factors that had the greatest influence on the long-term growth of equity capital were generation of high yielding investment opportunities and estimating expected values of cash flows accurately.

ISSN:0740-817X    

DOI:10.1080/07408178508975282

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Classical statistical estimation techniques have limited usage in predicting system availability when a system, e.g., a computer or telecommunications system, is highly reliable. A Bayesian solution is suggested in this paper. Gamma priors, which are rich in shapes, are assigned to the scale parameters of a gamma distributed component on-time and off-time. Estimation of the gamma priors follows engineer's past experiences for reliability modeling. Both steady-state and instantaneous availabilities are derived using Bayes Theorem. An illustration highlights the assessment and evaluation of the proposed availability measure.

ISSN:0740-817X    

DOI:10.1080/07408178508975283

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Priority rules are widely used in jobshop scheduling to determine the sequence in which jobs are to be processed. The research in this area has been directed at developing generally applicable priority rules. This paper presents a method for determining an effective priority rule specific to the jobshop scheduling problem to be solved. First, a generalized objective function is formulated which is the sum of costs of tardiness, carrying in-process inventory and machine idleness. Second, a multifactor priority rule is developed which is a weighted average of four factors used in simple priority rules. Third, a method is presented for using a computer search technique to determine the best weights to use in the priority rule. Finally, a computer simulation for testing this approach versus using other priority rules is described and the experimental results are reported.

ISSN:0740-817X    

DOI:10.1080/07408178508975284

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

In this paper, it is assumed that the purchase of automation has the effect of reducing the per unit production and in-process inventory costs. The optimal dynamic mix of automation and manual output is derived to minimize the cost incurred over the planning horizon due to (1) deviating from the future goal levels of output, (2) production, (3) inventory, (4) changing the level of manual output, and (5) acquiring automation. The cost of purchasing automation and the effectiveness of automation on reducing the per unit. production and in-process inventory costs are expressed as functions of time to include the impact of learning or anticipated technological advancement. Furthermore, the effectiveness of automation on reducing the per unit production and in-process inventory costs is assumed to decrease as the level of automation held by the organization increases due to diminishing returns. We show that it is rarely optimal to increase automation without simultaneously modifying the level of manual output. In addition, a numerical solution algorithm is presented to compute the optimal times and levels of changes in automation and manual output.

ISSN:0740-817X    

DOI:10.1080/07408178508975285

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

In this paper we extend the classical economic batch size model of Camp to situations where a range of products is made to stock and where the products are manufactured in a production shop consisting of a number of work centers of functionally grouped machines. Assuming that the flow times of the batches along the work centers can be modelled as a queueing process, it is shown that the batch sizes influence the batch waiting times in the shop, and the amount of work in process. The cost function to be minimized consists of ordering costs, final inventory holding costs, and work-in-process carrying costs. We show that the cost function is strictly convex and that the optimal batch sizes can be found by means of well-known numerical methods. We present an outline of an iterative procedure in which the batch size optimization procedure is combined with a shop load optimization procedure to achieve a good overall performance. Using a simplified model that assumes that the products are homogeneous in all respects, we also show that there exists an upper limit for the optimal batch size, which is determined by the ordering costs and the work-in-process carrying costs. Finally, we show that not taking into account work-in-process carrying costs may result in substantial errors in both batch size and cost.

ISSN:0740-817X    

DOI:10.1080/07408178508975286

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Optimal project duration for situations where project duration can be shortened by “crashing” activities is analyzed. The cost components considered are; regular direct costs, crashing costs and overhead costs. The regular direct costs are those associated with carrying out the various activities of the project. The crashing costs are those associated with shortening the project duration and represent the time-cost tradeoff. The overhead costs are assumed to be constant throughout the project's life. To facilitate the analysis, the costs are approximated by mathematical expressions. Calculating the cumulative future value of all costs leads to determining the optimal project duration.

ISSN:0740-817X    

DOI:10.1080/07408178508975287

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

This paper presents an algorithm for grouping the values of qualitative predictor variables while minimizing the loss of information about a dichotomous dependent variable. The algorithm is based on Shannon's measure of uncertainty. Subpopulations corresponding to the predictor values are ranked by their conditional Bernoulli parameter. At each iteration the increase in uncertainty resulting from grouping each pair of adjacent subpopulations is computed, and the pair with the least increase is grouped. Stopping rules based on the number of values remaining, the cumulative loss of information and the Maximum Likelihood Chi-Square Statistic are proposed, A numerical example is included.

ISSN:0740-817X    

DOI:10.1080/07408178508975288

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

This paper treats a problem of optimal conversion from an old to a new production technique, where the new technique is governed by learning curve behavior. Using optimal control theory, a simple optimal operating policy form is developed. The impact of the analysis on the problem of deciding when to invest in the new form of production is also discussed.

ISSN:0740-817X    

DOI:10.1080/07408178508975289

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor