Browsing by Subject "Purchasing"
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Item Open Access Age-based vs. stock level control policies for a perishable inventory system(2001) Tekin, E.; Gürler Ü.; Berk, E.In this study, we investigate the impact of modified lotsize-reorder control policy for perishables which bases replenishment decisions on both the inventory level and the remaining lifetimes of items in stock. We derive the expressions for the key operating characteristics of a lost sales perishable inventory model, operating under the proposed age-based policy, and examine the sensitivity of the optimal policy parameters with respect to various system parameters. We compare the performance of the suggested policy to that of the classical (Q,r) type policy through a numerical study over a wide range of system parameters. Our findings indicate that the age-based policy is superior to the stock level policy for slow moving perishable inventory systems with high service levels.Item Restricted Dünyamızı batılılaştıran semboller(1995) Ay, TanerItem Restricted Dünyamızı batılılaştıran semboller(1995) Ay, TanerItem Restricted Dünyamızı batılılaştıran semboller; Citroen(1995) Ay, TanerItem Restricted Fenomenoloji; Dünyamızı batılılaştıran semboller; Peugeot(1996) Ay, TanerItem Open Access Match-up scheduling under a machine breakdown(Elsevier, 1999) Aktürk, M. S.; Görgülü, E.When a machine breakdown forces a modified flow shop (MFS) out of the prescribed state, the proposed strategy reschedules part of the initial schedule to match up with the preschedule at some point. The objective is to create a new schedule that is consistent with the other production planning decisions like material flow, tooling and purchasing by utilizing the time critical decision making concept. We propose a new rescheduling strategy and a match-up point determination procedure through a feedback mechanism to increase both the schedule quality and stability. The proposed approach is compared with alternative reactive scheduling methods under different experimental settings. © 1999 Elsevier Science B.V. All rights reserved.Item Open Access An Online Causal Inference Framework for Modeling and Designing Systems Involving User Preferences: A State-Space Approach(Hindawi Limited, 2017) Delibalta, I.; Baruh, L.; Kozat, S. S.We provide a causal inference framework to model the effects of machine learning algorithms on user preferences. We then use this mathematical model to prove that the overall system can be tuned to alter those preferences in a desired manner. A user can be an online shopper or a social media user, exposed to digital interventions produced by machine learning algorithms. A user preference can be anything from inclination towards a product to a political party affiliation. Our framework uses a state-space model to represent user preferences as latent system parameters which can only be observed indirectly via online user actions such as a purchase activity or social media status updates, shares, blogs, or tweets. Based on these observations, machine learning algorithms produce digital interventions such as targeted advertisements or tweets. We model the effects of these interventions through a causal feedback loop, which alters the corresponding preferences of the user. We then introduce algorithms in order to estimate and later tune the user preferences to a particular desired form. We demonstrate the effectiveness of our algorithms through experiments in different scenarios. © 2017 Ibrahim Delibalta et al.Item Open Access Purchase order finance: a conceptual model with economic insights(Now Publishers Inc, 2017) Tanrisever, Fehmi; Van Bergen, M.; Reindorp, M.Purchase Order (PO) finance is a form of financial intermediation which can alleviate capital constraints in certain supply chains. PO finance is typically utilized by small and medium-sized enterprises (SMEs) that operate as importers, exporters, wholesalers, or distributors and have high sales growth. When applicable, PO finance creates value for the supply chain by providing capital that is not available through regular lending channels, due to informational problems. We provide a conceptual model that clarifies the value proposition of PO finance and describe how the transactions are carried out in practice. The conceptual model allows us to highlight the settings where economic conditions will favor the application of PO finance.