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Yayın Tractable supply chain production planning, modeling nonlinear lead time and quality of service constraints(Elsevier Ltd, 2007) Anlı, Osman Murat; Caramanis, Michael C.; Paschalidis, Ioannis Ch.This paper addresses the task of coordinated planning of a supply chain (SC). Work in process (WIP) in each facility participating in the SC, finished goods inventory, and backlogged demand costs are minimized over the planning horizon. In addition to the usual modeling of linear material flow balance equations, variable lead time (LT) requirements, resulting from the increasing incremental WIP as a facility's utilization increases, are also modeled. In recognition of the emerging significance of quality of service (QoS), that is control of stockout probability to meet demand on time, maximum stockout probability constraints are also modeled explicitly. Lead time and QoS modeling require incorporation of nonlinear constraints in the production planning optimization process. The quantification of these nonlinear constraints must capture statistics of the stochastic behaviour of production facilities revealed during a time scale for shorter than the customary weekly time scale of the planning process. The apparent computational complexity of planning production against variable LT and QoS constraints has long resulted in MRP-based scheduling practices that ignore the LT and QoS constraints has long resulted in MRP-based scheduling practices that ignore the LT and QoS impact to the plan's detriment. The computational complexity challenge was overcome by proposing and adopting a time-scale decomposition approach to production planning where short-time-scale stochastic dynamics are modeled in multiple facility-specific subproblems that receive tentative targets from a deterministic master problem and return statistics to it. A converging and scalable iterative methodology is implemented, providing evidence that significantly lower cost production plans are achievable in a computationally tractable manner.Yayın Investment in improved inventory accuracy in a decentralized supply chain(Elsevier Science BV, 2008-06) Uçkun, Canan; Karaesmen, Ahmet Fikri; Savaş, SelçukIt is known that inaccurate inventory records can lead to profit losses in a supply chain. Inventory records may not be correct due to various reasons such as transaction errors, misplacement, shrinkage, etc. In order to eliminate inventory inaccuracy, companies may invest in new information technologies such as radio frequency identification (RFID). In this paper, we consider a supply chain consisting of a retailer (distributor) and a supplier. We assume a single-period newsvendor-type setting where the retailer purchases the items from the supplier and distributes them to the regional warehouses. The paper focuses on the problem of finding the optimal investment levels that maximize profit by decreasing inventory inaccuracy. The optimal level of investment is examined both for the centralized and the decentralized systems under two scenarios: inventory sharing between the warehouses is allowed and not allowed. The coordination problem is also considered for both scenarios. Finally, several extensions of the model are considered: asymmetric warehouse parameters, demand and inventory inaccuracy correlation and imperfect RFID implementation.
