Informs Annual Meeting 2017

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INFORMS Houston – 2017

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3 - Fast Replacement or Low Purchase Prices: An Optimal Definition of Line Replaceable Units Joachim Jacob Arts, Associate Professor, Luxembourg University, P.O. Box 513, Luxembourg, j.j.arts@tue.nl, Joni Driessen, Geert-Jan Van Houtum When an asset fails, the broken Line Replaceable Unit (LRU) needs to be replaced. A LRU is a collection of parts that is replaced when a part in the LRU fails. A LRU can decrease the costs for replacements, as faster replacements may be possible. On the other hand, the company purchases new LRUs and typically large LRUs are more expensive to purchase. Thus, the objective is to determine an optimal definition of LRUs such that the total costs of purchasing and replacement downtime are minimized. We prove this problem non-linear integer program is NP-hard and provide an efficient column generation algorithm. 351B Procurement and Purchasing Management Contributed Session Chair: Hyunhong Choi, Seoul National University, Seoul, 010greenday@gmail.com 1 - Planning Accumulated Employee Vacations under Varying Workload and Contractual Restrictions Ayyuce Aydemir-Karadag, Asst. Prof., Cankaya University, Eskisehir Yolu 29. km, Mimar Sinan Cd. No. 4, Yukariyurtcu Mh., Etimesgut, Ankara, 06790, Turkey, aykaradag@cankaya.edu.tr, Gonca Yildirim Accumulation of past years’ contractual vacation days is one of the common problems observed in workplaces such as hospitals and banks, where some employees may not be able to use their vacation periods completely due to recurring busy periods, followups required, contractual restrictions on vacation periods, or simply because of the insufficient workforce. We develop an integer programming formulation that will maximize the total usage of contractual vacation days over a year, taking into account realistic vacation restriction policies for associated classes of employees who are eligible to do some tasks grouped according some predetermined criteria. 2 - Affordability Analysis using a Capability Roadmap Optimization Approach Michael Lehocky, Operations Research Analyst, U.S. Coast Guard Research and Development Center, 1 Chelsea St, New London, CT, 06320, United States, mlehocky@cathward.com In organizations with acquisition projects supporting the recapitalization of assets that are near or beyond the end of their economic life, extending, deferring or canceling construction could force disproportionate impacts on capabilities, either through reduction in operating capacity or diversion of operating funds from direct support to emergency maintenance or service-life extension. Affordability analysis in these cases should consider total capability roadmap cost rather than just procurement outlays. This study examines an example affordability analysis approach using a capability roadmap optimization of the U. S. Coast Guard’s offshore cutter fleet recapitalization. 3 - Modeling for Efficient Assignment of Multiple Demand Zones to Distribution Centers for the Equitable and Effective Distribution of Donated Food Md Hafizul Islam, North Carolina State University, 111 Lampe Drive, Daniels Hall 373, Raleigh, NC, 27695, United States, mislam5@ncsu.edu, Julie Simmons Ivy Satisfying hunger of food unsecured people with limited supply is a challenge for the local food bank. Food bank seeks to distribute donated foods equitably so that each county receives food proportional to its demand while minimizing the undistributed food donations. The food bank also wants to identify appropriate distribution branches to maximize the accessibility of the counties to donated food. An assignment and distribution model is developed to minimize the cost of maintaining a user specified cap on the maximum inequity in food distribution. 4 - Designing Sustainable Transportation Policy: Considering Substitution Pattern for Different Vehicle Types Hyunhong Choi, Seoul National University, 1 Gwanak-ro Gwanak-gu, Seoul, 08826, Korea, Republic of, 010greenday@gmail.com, Yoonmo Koo Transport sector is being pointed out as one of the main contributors of air pollution problems. To cope with such problems, many countries are employing various type of incentive programs to promote environmentally friendly vehicles such as electric vehicles. However, to design an effective policy, we need to analyze how consumers choose and substitute their vehicles. In this study, we present a model which can capture the substitution patterns of consumers considering which type of vehicle they currently own. Using the model, we can analyze how each type of car owners react to different type of promotion policies. With the results of simulation analysis, we provide some policy implications. WC32

351D Networks and Graphs Contributed Session Chair: Mingxian Zhong, Columbia University, New York, NY, United States, mz2325@columbia.edu 1 - Modeling of the Growing Processes of Connectivity of the Components for Networks Based on Analysis of Coupling Coefficients Changes Jianjun Lu, Professor, China Agricultural University, Haidian District, 17 Qinghuadong Road, Beijing, 100083, China, ljjun@cau.edu.cn This paper describes connectivity analysis by using a model of the coupling coefficient change between the components by edge snapping in the network and its applications. When the coupling is formed between the network components, we formulate the synchronization by using edge snapping. As a method of synchronizing analysis in this modeling, we propose the optimization of the connections’ relation between the fluctuant constituent units, by optimizing the connection and non-connection of the branches that connect the constituent units. The model is a mechanism of smoothly changing the coupling coefficient according to the second-order fluctuation system with respect to the time delay. 2 - The K-cardinality Assignment Problem Applied for the Analysis of Split Networks Ivan Belik, Norwegian School of Economics, Helleveien 30, Bergen, 5045, Norway, ivan.belik@nhh.no In terms of social networks, split graphs correspond to the variety of interpersonal and intergroup relations. We analyze the interaction between cliques (socially strong and trusty groups) and independent sets (fragmented and non-connected groups) as the basic components of any split graph. Based on the semi- Lagrangean relaxation for the k-cardinality assignment problem, we show the way of minimizing socially risky interactions between cliques and independent sets within social networks. 3 - The Influence of Structural Properties of Social Networks on Information Diffusion Xu Dong, Research Assistant, University of Miami, 1251 Memorial Drive, Coral Gables, FL, 33146, United States, x.dong3@umiami.edu, Nazrul I.Shaikh The scale and scope of the information diffusion are strongly impacted by the topological properties of the social network on which it takes place. However, the effects of these properties are usually nested and mutually correlated. Using principle component analysis (PCA), we decompose the effect of network topology into several independent structural characteristics, i.e. clustering, cohesiveness, density, etc., and identify the pattern of how they collectively affect certain information diffusion. 4 - Obstructions for Three-coloring and List Three-coloring H-free Graphs Mingxian Zhong, Columbia University, New York, NY, 10027, United States, mz2325@columbia.edu A graph G is called H-free (k +1)-vertex-critical if G does not contain H as an induced subgraph and the chromatic number of G is k +1, but every induced proper subgraph of G is k-colorable. We characterize all graphs H for which there are only finitely many H-free 4-vertex-critical graphs. This solves a problem posed by Golovach et al. As a second result, we characterize all graphs H for which there are only finitely many H-free minimal obstructions for list 3-colorbility. This is joint work with M. Chudnovsky, J. Goedgebeur and O. Schaudt. 351E Supply Chain, Closed Loop Contributed Session Chair: Thomas Nowak, Vienna University of Economics and Business, Vienna, Austria, thomas.nowak@wu.ac.at 1 - Managing Closed Loop Supply Chain under Returns and Demand Uncertainty Ravi Shankar, Indian Institute of Technology Delhi, Vishwakarma Bhawan, Shaheed Jeet Singh Marg, Hauz Khas, New Delhi, 110016, India, ravi1@dms.iitd.ac.in, Sushil Punia A multi-echelon supply chain comprising a manufacturer producing new products as well as re-manufactured products, and a retailer dealing with multi- products is considered. Using interval programming, a comprehensive decision model under uncertain returns and uncertain demand environment is developed for the optimal acquisitions of products and components. Simple and easy-to-use solution techniques are used instead of complex meta-heuristics. WC35

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