Person:
Alexopoulos, Christos

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Agent-based simulations using human performance models for national airspace system risk assessment

2009-07-14 , Goldsman, David , Alexopoulos, Christos , Fujimoto, Richard M. , Loper, Margaret L. , Pritchett, Amy R.

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Class of methods for analyzing stochastic systems

1995-10 , Alexopoulos, Christos

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Single Stage Heuristic for Perishable Inventory Control in Two-Echelon Supply Chains

2006-09-16 , Ferguson, Mark E. , Lystad, Erik D. , Alexopoulos, Christos

We study the problem of determining stocking levels for fixed-life perishable products in a two-echelon supply chain. We consider both serial chains and distribution networks consisting of a warehouse and n non-identical retail locations. Inventory retains constant utility throughout its lifetime, lead-times are deterministic, there are no fixed ordering costs, and unmet demand is backlogged. Although an extensive literature exists for the nonperishable product case, the consideration of perishability significantly complicates the problem. For instance, a major complication is the need to track the age of inventory as well as its position in the supply chain, adding a dimension to the already burdensome state space of dynamic programming formulations. We provide accurate single-stage heuristics for determining the stocking levels for two-echelon supply chains. We use these heuristics to develop insight and intuition into the proper management of perishable inventory. Our heuristics are robust, easy-to-use, and simple enough to be implemented using spreadsheet applications.

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Evaluation of proposals for emission inspection stations in the state of Georgia

1995-05 , Alexopoulos, Christos

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A Simple and Robust Batch-Ordering Inventory Policy Under Incomplete Demand Knowledge

2005-12-16 , Ferguson, Mark E. , Bai, Liwei , Alexopoulos, Christos , Tsui, Kwok-Leung

Generally, the derivation of an inventory policy requires the knowledge of the underlying demand distribution. Unfortunately, in many settings such as retail, demand is not completely observable in a direct way or inventory records may be inaccurate. A variety of factors, including the potential inaccuracy of inventory records, motivate retailers to seek replenishment policies with a fixed order quantity. We derive estimators of the first two moments of the (periodic) demand by means of renewal theoretical concepts. We then propose a regression-based approximation to improve the quality of the estimators. These estimators are used in conjunction with the Power Approximation (PA) method of Ehrhardt and Mosier (1984) to obtain an (r, Q) replenishment policy. The proposed methodology is robust and easy to code into a spreadsheet application. A series of numerical studies are carried out to evaluate the accuracy and precision of the estimators, and to investigate the impact of the estimation on the optimality of the inventory policies. Our experiments indicate that the proposed (r, Q) policy is very close, with regard to the mean total cost per period, to the (s, S) policy obtained via the PA method when the demand process is fully observable.

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