Lead time adjustment through scrap management

In a discrete parts manufacturing environment, it is necessary to compensate for the decreasing planned batch size resulting from production of scrap (defectives) in the production line, by increasing the planned production volume. This calls for a revision in the initially computed manufacturing lead time (MLT). A survey of the literature reveals that although issues related to product quantity regeneration have been studied in detail, little has been done to assess the impact on manufacturing lead times. This paper discusses the impact of scrap on manufacturing lead time in a shop with an intermittent-flow, bath-oriented, discrete-parts manufacturing environment, producing make-to-stock items.     

Shared frailty models based on reversed hazard rate for modified inverse Weibull distribution as baseline distribution

The unknown or unobservable risk factors in the survival analysis cause heterogeneity between individuals. Frailty models are used in the survival analysis to account for the unobserved heterogeneity in individual risks to disease and death. To analyze the bivariate data on related survival times, the shared frailty models were suggested. The most common shared frailty model is a model in which frailty act multiplicatively on the hazard function. In this paper, we introduce the shared gamma frailty model and the inverse Gaussian frailty model with the reversed hazard rate. We introduce the Bayesian estimation procedure using Markov chain Monte Carlo (MCMC) technique to estimate the parameters involved in the model. We present a simulation study to compare the true values of the parameters with the estimated values. We also apply the proposed models to the Australian twin data set and a better model is suggested.     

Estimation of variance of a normal population

In this paper we have suggested two estimators of variance of a normal population developed from the estimators of u² suggested by Govindarajulu and Sahai and Das. These have been shown to be more efficient than the usual estimator s².     

An integrated system for capacity planning and facility layout

In order to achieve efficient facility design for service type activities, operating under dynamic conditions and a large number of constraints, the use of a traditional approach has proved to be tedious and time consuming. Development of an efficient decision support system for such a situation calls for the consideration of the complex nature of interaction between the system parameters and the relationship between the working environment and the resources within the system. Mathematical programming techniques, e.g. linear and integer programming as well as queuing models, though useful in handling combinatorial optimization problems, are incapable of dealing with stochastic utilization problems normally encountered in the design of facilities of a fast changing environment. This paper makes use of a pattern search algorithm for the optimal allocation of service facility resources. The layout of the facilities has then been optimized by the use of the CLASS algorithm. The two separate algorithms have suitably been integrated together into a single simulation-based system. The effectiveness of the proposed methodology has been demonstrated by means of a real case study pertaining to design and layout optimization of a multi-functional gasoline service station in Bangkok.     

Canada Wide Standard for Particulate Matter and Ozone: Cost-Benefit Analysis Using a Life Quality Index

The adverse impacts of particulate air pollution and ground-level ozone on public health and the environment have motivated the development of Canada Wide Standards (CWS) on air quality. In cost-benefit analysis of air-quality options, valuation of reduction in mortality is a critical step as it accounts for almost 80% of the total benefits and any bias in its evaluation can significantly skew the outcome of the analysis. The overestimation of benefits is a source of concern since it has the potential of diverting valuable resources from other needs to support broader health care objectives, education, and social services that contribute to enhanced quality of life. We have developed a framework of reasoning for the assessment of risk-reduction initiatives that would support the public interest and enhance safety and quality of life. This article presents the Life Quality Index (LQI) as a tool to quantify the level of expenditure beyond which it is no longer justifiable to spend resources in the name of safety. It is shown that the LQI is a compound social indicator comprising societal wealth and longevity, and it is also equivalent to a utility function consistent with the basic principles of welfare economics and decision analysis. The LQI approach overcomes several shortcomings of the method used by the CWS Development Committee and provides guidance on the compliance costs that can be justified to meet the Standards.     

Shrinkage estimation of scale in exponential distribution from censored samples

In this paper some shrunken and pretest shrunken estimators are suggested for the scale parameter of an exponential distribution, when observations become available from life test experiments. These estimators are shown to be more efficient than the usual estimator when a guessed value is nearer to the true value.