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Full-Text Articles in Operations Research, Systems Engineering and Industrial Engineering

On-Line Job-Shop Scheduling Of A Manufacturing System Based On A Virtual Supervisor Concept, Jesús Trujillo, Zbigniew Pasek, Enrique Baeyens Jan 2005

On-Line Job-Shop Scheduling Of A Manufacturing System Based On A Virtual Supervisor Concept, Jesús Trujillo, Zbigniew Pasek, Enrique Baeyens

Industrial and Manufacturing Systems Engineering Publications

The controls for reconfigurable manufacturing systems have to be capable not only of identifying exceptions on-line, but also simultaneously developing on-line strategies for unpredictable customer orders or inaccurate estimates of processing times. This paper presents an approach for job-shop scheduling with uncertain arrival times. The approach exploits Virtual Supervisor (VS) concept, which provides access to all system information during program execution and thus can readily monitor the overall system performance. The goal is to minimize expected part tardiness and earliness cost. A solution methodology based on a combined Lagrangian relaxation, VS-Patterns, Maxwell equations and temporal difference is developed to obtain ...


Allocating Work In Process In A Multiple-Product Conwip System With Lost Sales, Sarah M. Ryan, Jumpol Vorasayan Jan 2005

Allocating Work In Process In A Multiple-Product Conwip System With Lost Sales, Sarah M. Ryan, Jumpol Vorasayan

Industrial and Manufacturing Systems Engineering Publications

To operate a multiple-product manufacturing system under a CONWIP control policy, one must decide how to assign kanbans to products. With a fixed total number of kanbans in a competitive environment, the goal is to determine their allocation to product types in order to minimize lost sales equitably. In particular, we consider systems in which the products may make multiple visits to the same station with a different processing time distribution on each repeat visit. With a fixed number of kanbans dedicated to each product, the system is modeled as a multiple-chain multiple-class closed queuing network. A nonlinear program simultaneously ...


On The Validity Of The Geometric Brownian Motion Assumption, Rahul Ratnakar Marathe, Sarah M. Ryan Jan 2005

On The Validity Of The Geometric Brownian Motion Assumption, Rahul Ratnakar Marathe, Sarah M. Ryan

Industrial and Manufacturing Systems Engineering Publications

The geometric Brownian motion (GBM) process is frequently invoked as a model for such diverse quantities as stock prices, natural resource prices and the growth in demand for products or services. We discuss a process for checking whether a given time series follows the GBM process. Methods to remove seasonal variation from such a time series are also analyzed. Of four industries studied, the historical time series for usage of established services meet the criteria for a GBM; however, the data for growth of emergent services do not.


Likelihood-Based Statistical Estimation From Quantized Data, Stephen B. Vardeman, Chiang-Sheng Lee Jan 2005

Likelihood-Based Statistical Estimation From Quantized Data, Stephen B. Vardeman, Chiang-Sheng Lee

Industrial and Manufacturing Systems Engineering Publications

Most standard statistical methods treat numerical data as if they were real (infinite-number-of-decimal-places) observations. The issue of quantization or digital resolution can render such methods inappropriate and misleading. This article discusses some of the difficulties of interpretation and corresponding difficulties of inference arising in even very simple measurement contexts, once the presence of quantization is admitted. It then argues (using the simple case of confidence interval estimation based on a quantized random sample from a normal distribution as a vehicle) for the use of statistical methods based on "rounded data likelihood functions" as an effective way of handling the matter.


Sheppard's Correction For Variances And The "Quantization Noise Model", Stephen B. Vardeman Jan 2005

Sheppard's Correction For Variances And The "Quantization Noise Model", Stephen B. Vardeman

Industrial and Manufacturing Systems Engineering Publications

In this paper, we examine the relevance of Sheppard's correction for variances and (both the original and a valid weak form of) the so-called "quantization noise model" to understanding the effects of integer rounding on continuous random variables. We further consider whether there is any real relationship between the two. We observe that the strong form of the model is not really relevant to describing rounding effects. We demonstrate using simple cases the substantial limitations of the Sheppard correction, and use simple versions of a weak form of the model to establish that there is no real connection between ...


Likelihood And Bayesian Methods For Accurate Identification Of Measurement Biases In Pseudo Steady-State Processes, Sriram Devanathan, Stephen B. Vardeman, Derrick K. Rollins Sr. Jan 2005

Likelihood And Bayesian Methods For Accurate Identification Of Measurement Biases In Pseudo Steady-State Processes, Sriram Devanathan, Stephen B. Vardeman, Derrick K. Rollins Sr.

Industrial and Manufacturing Systems Engineering Publications

Two new approaches are presented for improved identification of measurement biases in linear pseudo steady-state processes. Both are designed to detect a change in the mean of a measured variable leading to an inference regarding the presence of a biased measurement. The first method is based on a likelihood ratio test for the presence of a mean shift. The second is based on a Bayesian decision rule (relying on prior distributions for unknown parameters) for the detection of a mean shift. The performance of these two methods is compared with that of a method given by Devanathan et al. (2000 ...


Characterization Of Reverse Logistics Networks For Outsourcing Decisions, Marco Serrato, Sarah M. Ryan, Juan Gaytan Jan 2005

Characterization Of Reverse Logistics Networks For Outsourcing Decisions, Marco Serrato, Sarah M. Ryan, Juan Gaytan

Industrial and Manufacturing Systems Engineering Publications

Strategic decisions about reverse logistics (RL) are complicated by the uncertainty of product returns. To aid firms in deciding whether to outsource RL activities, a characterization of RL networks according to two critical factors is proposed. These factors are the length of the product life cycle, which affects variability of expected returns over time, and the uncertainty of the rate of returns in each time period. Even if changes in the average return rate according to the life cycle are well understood, the variability in returns relative to the known average differs significantly depending on the product characteristics, as well ...