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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3

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    Imported intermediate goods and product innovation
    (Elsevier B.V., 2024) Şeker, Murat; Rodriguez-Delgado, Jose Daniel; Department of Business Administration; Ulu, Mehmet Fatih; Department of Business Administration; College of Administrative Sciences and Economics
    We build a structural model of multi-product firms to illustrate how access to foreign intermediate goods contributes to product innovation. We establish a stochastic dynamic model of firm evolution and allow firms to be heterogeneous in their efficiency levels. The model's mechanism to capture the effects of importing intermediate goods is twofold: (i) importing these goods increases the revenue per each product introduced, and (ii) increases the likelihood of introducing new varieties using newly available inputs. We calibrate the model to firm-level data from India. The model successfully explains the heterogeneous innovation dynamics and statistical moments related to importing and product distribution. Counterfactual exercises further illustrate and quantify the mechanism between trade, innovation performance, and product growth. We find that the critical contribution of trade to growth and product innovation is mainly through access to new imported varieties rather than just the direct import cost. © 2024 Elsevier B.V.
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    Production and energy mode control of a production-inventory system
    (Elsevier, 2023) Karabag, Oktay; Khayyati, Siamak; Department of Business Administration; Tan, Barış; Department of Business Administration; College of Administrative Sciences and Economics
    Energy efficiency in manufacturing can be improved by controlling energy modes and production dy-namically. We examine a production-inventory system that can operate in Working, Idle, and Off energy modes with mode-dependent energy costs. There can be a warm-up delay to switch between one mode to another. With random inter-arrival, production and warm-up times, we formulate the problem of de-termining in which mode the production resource should operate at a given time depending on the state of the system as a stochastic control problem under the long-run average profit criterion considering the sales revenue together with energy, inventory holding and backlog costs. The optimal solution of the problem for the exponential inter-arrival, production and warm-up times is determined by solving the Markov Decision Process with a linear programming approach. The structure of the optimal policy for the exponential case uses two thresholds to switch between the Working and Idle or Working and Off modes. We use the two-threshold policy as an approximate policy to control a system with correlated inter-event times with general distributions. This system is modelled as a Quasi Birth and Death Process and analyzed by using a matrix-geometric method. Our numerical experiments show that the joint pro-duction and energy control policy performs better compared to the pure production and energy control policies depending on the system parameters. In summary, we propose a joint energy and production control policy that improves energy efficiency by controlling the energy modes depending on the state of the system.
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    Energy-efficient production control of a make-to-stock system with buffer- and time-based policies
    (Taylor and Francis Ltd., 2023) Karabağ, Oktay; Khayyati, Siamak; Department of Business Administration; Tan, Barış; Department of Business Administration; College of Administrative Sciences and Economics
    Increasing energy efficiency in manufacturing has significant environmental and cost benefits. Turning on or off a machine dynamically while considering the production rate requirements can offer substantial energy savings. In this work, we examine the optimal policies to control production and turn on and off a machine that operates in working, idle, off, and warmup modes for the case where demand inter-arrival, production, and warmup times have phase-type distributions. The optimal control problem that minimises the expected costs associated with the energy usage in different energy modes and the inventory and backlog costs is solved using a linear program associated with the underlying Markov Decision Process. We also present a matrix-geometric method to evaluate the steady-state performance of the system under a given threshold control policy. We show that when the inter-arrival time distribution is not exponential, the optimal control policy depends on both the current phase of the inter-arrival time and inventory position. The phase-dependent policy implemented by estimating the current phase based on the time elapsed since the last arrival yields a buffer- and time-based policy to control the energy mode and production. We show that policies that only use the inventory position information can be effective if the control parameters are chosen appropriately. However, the control policies that use both the inventory and time information further improve the performance.
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    Continuous-flow simulation of manufacturing systems with assembly/disassembly machines, multiple loops and general layout
    (Elsevier Sci Ltd, 2023) Scrivano, Salvatore; Tolio, Tullio; Department of Business Administration; Tan, Barış; Department of Business Administration; College of Administrative Sciences and Economics
    Performance evaluation methods are important to design and control manufacturing systems. Approximate analytical methods are fast, but they may be limited by the restrictive assumptions on the system. On the contrary, simulation has not specific limitations in its applicability, but the time to model and analyse a manufacturing system can increase as the level of detail addressed by the model increases. The main contribution of this study is presenting a computationally efficient methodology to simulate single-part continuous-flow manufacturing systems with assembly/disassembly machines, multiple loops, general layout and general inter-event time distributions. By using graph theory, a new method is presented to identify the machines causing slowdown, blocking and starvation in a general layout and determine the time before the occurrence of a state transition for each machine and the time before the fulfilment or depletion of each buffer. By advancing the time clock to the next event-time accordingly, the number of discrete events needed to be simulated is decreased compared to a discrete-event simulation with discrete flow of parts. As a result, the proposed method is on average 15 times faster than DES methods in the analysis of discrete-flow systems, and 110 times faster on average in the analysis of continuous-flow systems. The low computational time of the proposed method allows to simulate systems under general assumptions and in a very short time.
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    Enabling older employees' well-being through HR attributions: the moderating role of management context
    (Wiley, 2024) Department of Business Administration; Aksoy, Eda; Marcus, Justin; Department of Business Administration; College of Administrative Sciences and Economics
    Fusing the extant literature on successful aging at work (SAW) and HR attributions, we examined the confluence of employee-oriented internal HR attributions and unit-level employee management context on burnout for employees across the age spectrum. Time-lagged, multi-level survey data were collected from a sample of 1762 blue-collar employees from 178 work units at the manufacturing plants of a large firm operating in the Turkish energy industry, which is characterized as a high-risk safety environment. A cross-level moderated mediation model was tested using multi-level structural equation modeling (MSEM). Results supported study hypotheses such that the negative association between age and burnout was mediated by employee-oriented positive HR attributions, and this indirect association was moderated by unit-level perceptions of the employee management context. Development-oriented contexts that emphasized personal development/growth-indicated by the degree of emphasis on innovation strategy, safety training, and active unit safety leadership-weakened the negative indirect (i.e., buffering) effect of age on burnout via less positive HR attributions. Conversely, a maintenance-oriented context that emphasized maintaining the status quo-indicated by passive unit safety leadership-strengthened said effect through more positive HR attributions. The theoretical and practical implications of these findings for fostering employee well-being across the age spectrum are discussed.
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    Patient adherence in healthcare operations: a narrative review
    (Elsevier Ltd, 2024) Department of Business Administration; Kılıç, Hakan; Güneş, Evrim Didem; Department of Business Administration; Graduate School of Sciences and Engineering; College of Administrative Sciences and Economics
    Patient nonadherence to healthcare providers’ recommendations is a major obstacle to desired health outcomes. It results in health deterioration and hospitalization, which might have been avoided with a high level of patient adherence. This paper reviews the literature addressing the issue of adherence in healthcare operations. A total of 73 published articles from operations research and management science journals are included in the review as a result of the systematic search that covered studies from inception until October 26, 2022. This paper is the first comprehensive review of adherence-related research in the operations research field. We summarize how adherence is measured, the research contexts, interactions between adherence and the healthcare system, and how adherence is modeled mathematically. Furthermore, we review adherence-related research at clinical, hospital, and healthcare system levels of planning and control, in addition to medical decision-making. We identify the opportunities in adherence research under the following themes: Supporting proactive management of adherence for healthcare providers, designing a healthcare system that enables adherence, developing personalized treatments, and addressing the global health issues of antimicrobial resistance and vaccine hesitancy. © 2023
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    Technical efciency in banks: a review of methods, recent innovations and future research agenda
    (Springer Heidelberg, 2024) Abdou, Hussein A.; Hayek, Ali I.; Nwachukwu, Jacinta C.; Elamer, Ahmed A.; Pyke, Chris; Department of Business Administration; Akdeniz, Özlem Olgu; Department of Business Administration; College of Administrative Sciences and Economics
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    Firm complexity and post-earnings announcement drift
    (Springer, 2024) Barinov, Alexander; Park, Shawn Saeyeul; Department of Business Administration; Yıldızhan, Çelim; Department of Business Administration; College of Administrative Sciences and Economics
    We show that the post-earnings announcement drift (PEAD) is stronger for conglomerates than single-segment firms. Conglomerates, on average, are larger than single segment firms, so it is unlikely that limits-to-arbitrage drive the difference in PEAD. Rather, we hypothesize that market participants find it more costly and difficult to understand firm-specific earnings information regarding conglomerates, as they have more complicated business models than single-segment firms. This in turn slows information processing about them. In support of our hypothesis, we find that, compared to single-segment firms with similar firm characteristics, conglomerates have relatively low institutional ownership and short interest, are covered by fewer analysts, and these analysts have less industry expertise and make larger forecast errors. Finally, we find that an increase in organizational complexity leads to larger PEAD and document that more complicated conglomerates have even greater PEAD. Our results are robust to an extensive list of alternative explanations of PEAD as well as alternative measures of firm complexity. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2022. Springer Nature or its licensor holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s);author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
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    New product introductions with selection of unique and common features in monopoly markets
    (Pergamon-Elsevier Science Ltd, 2024) Schwarz, Justus Arne; Department of Business Administration; Çelik, Burak; Tan, Barış; Department of Business Administration;  ; College of Administrative Sciences and Economics; Graduate School of Sciences and Engineering
    Firms have to determine the right features and prices for their new products as they introduce new product generations to the market. We consider the problem of determining the features of a new product that a monopolist will introduce into a market that contains an existing product as well as setting the prices of the existing and the new products. The firm also decides on offering only the new product or both the existing and the new products. We explicitly capture the effects of unique features, which are specific to one of the two products, and common features which are shared between the new and the existing product on these decisions. The problem is formulated as a nonlinear-mixed-integer program with general cost, demand, and price functions. For the case of linear cost, demand, and price, the nonlinear-mixed-integer program is converted to a nonlinear program and solved analytically. Based on this solution, the optimal prices for both products and the optimal unique features for the new product are derived in closed form, a linear-time algorithm is presented to determine the optimal common features, and the optimality conditions of keeping the existing product in the market are characterized. We show that the selection of the unique features, but not the common ones, is based on the difference between a feature's contribution to the product's demand and its cost adjusted by the price sensitivity in the linear case. Moreover, we find that the firm, if it wants to avoid demand cannibalization, should remove the existing product from the market rather than offer two products with mainly unique features. Capturing the effects of unique and common features directly allows firms to decide on the best rollover strategy and determine the right features and prices
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    Brands and branding around the World
    (Sage Publications Inc, 2024) Batra, Rajeev; Steenkamp, Jan-Benedict E. M.; Department of Business Administration; Tunalı, Ayşegül Özsomer; Department of Business Administration; College of Administrative Sciences and Economics
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