Person: DENİZEL, Meltem
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Meltem
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DENİZEL
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ArticlePublication Metadata only The one-warehouse multiretailer problem with an order-up-to level inventory policy(Wiley, 2010-10) Solyalı, O.; Süral, H.; Denizel, Meltem; Industrial Engineering; DENİZEL, MeltemWe consider a two-level system in which a warehouse manages the inventories of multiple retailers. Each retailer employs an order-up-to level inventory policy over T periods and faces an external demand which is dynamic and known. A retailer's inventory should be raised to its maximum limit when replenished. The problem is to jointly decide on replenishment times and quantities of warehouse and retailers so as to minimize the total costs in the system. Unlike the case in the single level lot-sizing problem, we cannot assume that the initial inventory will be zero without loss of generality. We propose a strong mixed integer program formulation for the problem with zero and nonzero initial inventories at the warehouse. The strong formulation for the zero initial inventory case has only T binary variables and represents the convex hull of the feasible region of the problem when there is only one retailer. Computational results with a state-of-the art solver reveal that our formulations are very effective in solving large-size instances to optimality.ArticlePublication Metadata only Effective network formulations for lot sizing with backlogging in two-level serial supply chains(Informa Group, 2016) Solyali, O.; Denizel, Meltem; Süral, H.; Industrial Engineering; DENİZEL, MeltemThis study considers the serial lot sizing problem with backlogging in two-level supply chains to determine when and how much to order at a warehouse and ship to a retailer over a T-period planning horizon so that the external known demand occurring at the retailer is satisfied and the total cost at all levels is minimized. In particular, the uncapacitated two-level serial lot sizing problem with backlogging and the two-level serial lot sizing problem with cargo capacity and backlogging are formulated using effective shortest-path network representations, which define the convex hull of their feasible solutions. These representations lead to efficient algorithms with O(T3) time for the uncapacitated problem and O(T6) time for the capacitated problem. Furthermore, a tight reformulation with O(T3) variables and O(T2) constraints (resp. O(T6) variables and O(T5) constraints) is proposed for the uncapacitated (resp. capacitated) problem.ArticlePublication Metadata only Testing for convergence in bank efficiency: a cross-country analysis(Taylor & Francis, 2011) Kösedağ, A.; Denizel, Meltem; Özdemir, Ö.; Industrial Engineering; DENİZEL, MeltemThis paper empirically investigates a possible convergence among the operational efficiency of financial institutions across countries. We explore (i) the relative performance of banking industries in two samples (European and global) over time, and (ii) whether banking industries are likely to attain the same level of efficiency in the long run as implied by international financial integration. We find that convergence in bank efficiency is incomplete and limited to European banking industries. Differing level of bank efficiencies across the globe may offer opportunities for international investors who would like to capitalize on such market imperfections. Our findings also have implications for policy makers who are concerned with the full integration and the stability of the global financial system.ArticlePublication Metadata only Recovery decisions of a producer in a legislative disposal fee environment(Elsevier, 2012-01-16) Özdemir, Ö.; Denizel, Meltem; Guide Jr., V. D. R.; Industrial Engineering; DENİZEL, MeltemThe main objectives of the environmental legislation originating from extended producer responsibility (EPR) principle are to lead producers to undertake recovery initiatives for their end-of-use products and to promote environmentally desirable product design. It is still controversial whether current implementations of EPR principle are effective in attaining these objectives. This study seeks to answer the following questions: (1) What is the impact of EPR legislation on the product recovery decisions of producers? (2) How do the redesign opportunities (i.e., design for disassembly) affect the willingness of producers for product recovery? (3) How do the investment needs to start recovery practices and the reluctance of producers to allocate sufficient funds for this purpose affect the optimal recovery decisions? We use stylized economic models to represent the implementation in practice and solving our models we obtain closed form and numerical solutions that help us to see the impact of various parameters on the optimal decisions of a producer. Our findings indicate that redesign opportunities encourage producers for more recovery, however the reluctance of producers to cover the initial investments may substantially reduce the effectiveness of the legislation and the recovery amounts.