Raymond A. Patterson

The Design of Reverse Distribution Networks: Models and Solution Procedures

Reverse distribution, or the management of product return flows, induced by various forms of reuse of products and materials, has received growing attention throughout this decade. In this paper we discuss reverse distribution, and propose a mathematical programming model for a version of this problem. Due to the complexity of the proposed model, we introduce a heuristic solution methodology for this problem. The solution methodology complements a heuristic concentration procedure, where sub-problems with reduced sets of decision variables are iteratively solved to optimality. Based on the solutions from the sub-problems, a final concentration set of potential facility sites is constructed, and this problem is solved to optimality. The potential facility sites are then expanded in a greedy fashion to obtain the final solution. This ‘‘heuristic expansion’’ was also performed using the solution found with a greedy heuristic to provide a short-list of potential facility sites. Computational tests demonstrate a great deal of promise for this solution method, as high-quality solutions are obtained while expending modest computational effort. � 2003 Published by Elsevier Science B.V.

A Memory Adaptive Reasoning Technique for Solving the Capacitated Minimum Spanning Tree Problem

In this paper we propose a hybrid memory adaptive heuristic for solving the Capacitated Minimum Spanning Tree (CMST) problem. We augment the problem formulation with additional non-redundant constraints via use of adaptive memory, to improve upon the performance of an elementary heuristic (the Esau-Williams heuristic). Our methodology is tested against many of the previously reported heuristics for the CMST. We conclude that our generalized procedure performs on par with the best of these approaches in terms of solution quality, while expending a very modest amount of computational effort.

The network design problem with relays

The network design problem with relays (NDPR) is defined on an undirected graph G = (V, E, K), where V = {1, … , n} is a vertex set, E = {(i, j) : i, j ∈ V, i

Wisdom of the Crowds: Decentralized Knowledge Construction in Wikipedia

Recently, Nature published an article comparing the quality of Wikipedia articles to those of Encyclopedia Britannica (Giles 2005). The article, which gained much public attention, provides evidence for Wikipedia quality, but does not provide an explanation of the underlying source of that quality. Wikipedia, and wikis in general, aggregate information from a large and diverse author-base, where authors are free to modify any article. Building upon Surowieckis (2005) Wisdom of Crowds, we develop a model of the factors that determine wiki content quality. In an empirical study of Wikipedia, we find strong support for our model. Our results indicate that increasing size and diversity of the author-base improves content quality. We conclude by highlighting implications for system design and suggesting avenues for future research.

Improving outpatient health care quality: understanding the quality dimensions.

Abstract: Based on literature review, we derive a set of dimensions that influence patient-perceived health care quality. Utilizing outpatient survey data from 222 different physicians, we identified six underlying quality factors and classified them according to the derived dimensions. These quality factors explain approximately 51 percent of the variation in overall patient-perceived health care quality.

Research NoteInformation Technology, Contract Completeness, and Buyer-Supplier Relationships

The theory of incomplete contracts has been used to study the relationship between buyers and suppliers following the deployment of modern information technology to facilitate coordination between them. Previous research has sought to explain anecdotal evidence from some industries on the recent reduction in the number of suppliers selected to do business with buyers by appealing to relationship-specific costs that suppliers may incur. In contrast, this paper emphasizes that information technology enables greater completeness of buyer-supplier contracts through more economical monitoring of additional dimensions of supplier performance. The number of terms included in the contract is an imperfect substitute for the number of suppliers. Based on this idea, alternative conditions are identified under which increased use of information technology leads to a reduction in the number of suppliers without invoking relationship-specific costs. We find that a substantial increase in contract completeness due to reduced cost of information technology could increase the cost per supplier even though the cost of coordination and the cost per term monitored decrease. Such an increase in the cost per supplier leads to a reduction in the number of suppliers with whom the buyer chooses to do business. Similarly, we find that if coordination cost is reduced when more information technology is deployed so that the number of suppliers in the buyers pool increases substantially, the buyer might choose to make the supplier contracts less complete, instead relying on a more market-oriented approach to finding a supplier with good fit.

Hybrid Fiber Coaxial Network Design

Much interest exists in broadband network services to deliver a variety of products to consumers, such as Internet access, telephony, interactive TV, and video on demand. Due to its cost efficiency, Hybrid Fiber Coaxial (HFC) technology is currently being considered by most Telcos and cable companies as the technology to deliver these products. The topological HFC network design problem as implemented by several major companies is a form of the capacitated tree-star network design problem. We propose a new formulation for this problem and present a heuristic based on hierarchical decomposition of the problem. The proposed solution methodology exploits an Adaptive Reasoning Technique (ART), embedded as a meta-heuristic over specialized heuristics for the subproblems. In this context, we demonstrate the dynamic use of an exact solution technique within ART. The generalizability of the proposed solution methodology is demonstrated by applying it to a second problem, the Traveling Salesman Problem (TSP). Computational results are presented for both the HFC network design problem and the TSP, indicating high-quality solutions expending a very modest computational effort. The proposed solution method is found to be effective, and is shown to be easily adaptable to new problems without much crafting, and as such, has a broad appeal to the general operations research community.

Market Impact on IT Security Spending

Traditionally, IT security investment decisions are made in isolation. However, as firms that compete for customers in an industry are closely interlinked, a macro perspective is needed in analyzing the IT security spending decisions and this is a key contribution of the paper. We introduce the notions of direct- and cross-risk elasticity to describe the customer response to adverse IT security events in the firm and competitor, respectively, thus allowing us to analyze optimal security investment decisions. Both symmetric and asymmetric cases are examined for a duopoly in a continuous-time Markov chain (CTMC) setting. We demonstrate that optimal IT security spending, expected firm profits and willingness of firms to cooperate with competitors to improve security are highly dependent on the nature of customer response to adverse events, especially whether customer response to adverse security events in the competitor increases or decreases firm demand.

Memory Adaptive Reasoning & Greedy Assignment Techniques for the Capacitated Minimum Spanning Tree Problem

It is the purpose of this paper to investigate effects of adding randomization to a memory-based heuristic. The algorithms we propose are applied to the Capacitated Minimum Spanning Tree problem (CMST), and we study the combined effects of simultaneously applying a memory-based and a randombased heuristic to the CMST. This paper uses the Adaptive Reasoning Technique (ART) and concepts from the greedy randomized adaptive search procedure for solving the CMST. The resulting hybrid procedure is tested against the stand-alone Esau-Williams heuristic procedure, as well as the stand-alone greedy assignment technique. We find that randomization does not constructively add to the memory-based procedure, as ART alone typically outperforms all other approaches in terms of solution quality, while expending a modest amount of computational effort.

The cardinality constrained covering traveling salesman problem

In this paper, we propose a new method for partitioning a graph into an unspecified number of Hamiltonian subgraphs with minimum and maximum size requirements on the subgraphs. We refer to this problem as the cardinality constrained covering traveling salesman problem (CCC-TSP). Special cases of this problem include the assignment problem and the traveling salesman problem (TSP). This paper proposes a heuristic solution methodology to a general class of problems that is important because by setting the parameters, one can obtain different important problems including the traveling salesman problem and the assignment problem. Although these specific problems have been studied extensively in the past, the generalized version proposed here and the solution methodology set forth, are new contributions. The solution methodology presented in this paper produces solutions within known error bounds of the optimal solution value. The computational results indicate an ability to obtain very high-quality solutions by expending a modest computational effort for problems in excess of 200 nodes.