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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6
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Publication Open Access An investigation of time-inconsistency(Informs, 2009) Öncüler, Ayşe; Department of Business Administration; Department of Business Administration; Sayman, Serdar; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; 112222Preference between two future outcomes may change over time-a phenomenon labeled as time inconsistency. The term "time inconsistency" is usually used to refer to cases in which a larger-later outcome is preferred over a smaller-sooner one when both are delayed by some time, but then with the passage of time a preference switches to the smaller-sooner outcome. The current paper presents four empirical studies showing that time inconsistency in the other direction is also possible: A person may prefer the smaller-sooner outcome when both options are in the future, but decide to wait for the larger-later one when the smaller option becomes immediately available. We. find that such "reverse time inconsistency" is more likely to be observed when the delays to and between the two outcomes are short (up to a week). We propose that reverse time inconsistency may be associated with a reversed-S shape discount function, and provide evidence that such a discount function captures part of the variation in intertemporal preferences.Publication Open Access An empirical investigation of four well-known polynomial-size VRP formulations(NA, 2018) Öncan, Temel; Department of Business Administration; N/A; Aksen, Deniz; Sadatizamanabad, Mirehsan Hesam; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; Graduate School of Sciences and Engineering; 40308; N/AThis study presents an in-depth computational analysis of four well-known Capacitated Vehicle Routing Problem (CVRP) formulations with polynomial number of subtour elimination constraints: a node-based formulation and three arc-based (single, two- and multi-commodity flow) formulations. For each formulation, several valid inequalities (VIs) are added for the purpose of tightening the formulation. Moreover, a simple topology-driven granulation scheme is proposed to reduce the number of a certain type of VIs. The lower and upper bounding performance and the solution efficiency of the formulations and respective VI configurations are benchmarked with state-of-the-art commercial optimization software. The extensive computational analysis embraces 121 instances with up to 100 customer nodes. We believe that our findings could be useful for practitioners as well as researchers developing algorithms for the CVRP.Publication Open Access How does self-concept clarity influence happiness in social settings? The role of strangers versus friends(Taylor _ Francis, 2018) Merdin-Uygur, Ezgi; Sarıal-Abi, Gülen; Hesapçı, Özlem; Department of Business Administration; Canlı, Zeynep Gürhan; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; 16135Self-concept clarity (SCC), defined as the extent to which the content of an individual’s self-beliefs is clearly and confidently defined and internally consistent, influences experiences in social relationships. This paper extends the previous literature on SCC by proposing and demonstrating that high-SCC individuals anticipate and experience more happiness than low-SCC individuals when they share a social setting with friends and anticipate and experience less happiness than low-SCC individuals when they share a social setting with strangers and that this is because of perceived interpersonal distance. A series of four studies, including both online studies and a field study, support these predictions. Alternative explanations of self-esteem and self-efficacy are also ruled out. The findings yield both theoretical contributions and practical implications.Publication Open Access Purchasing, production, and sales strategies for a production system with limited capacity, fluctuating sales and purchasing prices(Taylor _ Francis, 2019) N/A; Department of Business Administration; Karabağ, Oktay; Tan, Barış; Resercher; Faculty Member; Department of Business Administration; Graduate School of Sciences and Engineering; College of Administrative Sciences and Economics; N/A; 28600In many industries, the revenue and cost structures of manufacturers are directly affected by the volatility of purchasing and sales prices in the markets. We analyze the purchasing, production, and sales policies for a continuous-review discrete material flow production/inventory system with fluctuating and correlated purchasing and sales prices, exponentially distributed raw material and demand inter-arrival times, and processing time. The sales and purchasing prices are driven by the random environmental changes that evolve according to a discrete state space continuous-time Markov process. We model the system as an infinite-horizon Markov decision process under the average reward criterion and prove that the optimal purchasing, production, and sales strategies are state-dependent threshold policies. We propose a linear programming formulation to compute the optimal threshold levels. We examine the effects of the sales price variation, purchasing price variation, correlation between sales and purchasing prices, customer arrival rate and limited inventory capacities on the system performance measures, through a range of numerical experiments. We also examine under which circumstances the use of the optimal policy notably improves the system profit compared to the use of the buy low and sell high naive policy. We show that using the optimal purchasing, production, and sales policies allow manufacturers to improve their profits when the purchasing and sales prices fluctuate.Publication Open Access United we stand: the impact of buying groups on retailer productivity(American Marketing Association (AMA), 2015) Geyskens, Inge; Gielens, Katrijn; Department of Business Administration; Wuyts, Stefan; Faculty Member; Department of Business Administration; College of Administrative Sciences and EconomicsIn diverse industries, from grocery retailing to health care, retailers join buying groups to achieve better terms with suppliers. The authors track the buying group membership of Europe's largest grocery retailers over a 15-year period and evaluate why some buying groups are better than others in increasing retailer performance and why different members belonging to the same group do not always benefit equally from their membership. They find that, on average, buying groups indeed generate scale advantages for their members: group scale increases group members' productivity and sales and decreases their cost of goods sold. Still, bigger is not always better. Retailers benefit less from buying group scale when the group is more heterogeneous in terms of member size and when it extends its scope across too many markets. Moreover, the smaller a member is within the group and the more it overlaps with fellow members, the less it benefits.Publication Open Access Base-rate information in consumer attributions of product-harm crises(American Marketing Association (AMA), 2012) Lei, Jing; Dawar, Niraj; Department of Business Administration; Department of Business Administration; Canlı, Zeynep Gürhan; Researcher; Department of Business Administration; College of Administrative Sciences and Economics; 16135Consumers spontaneously construct attributions for negative events such as product-harm crises. Base-rate information influences these attributions. The research findings suggest that for brands with positive prior beliefs, a high (vs. low) base rate of product-harm crises leads to less blame if the crisis is said to be similar to others in the industry (referred to as the "discounting effect"). However, in the absence of similarity information, a low (vs. high) base rate of crises leads to less blame toward the brand (referred to as the "subtyping effect"). For brands with negative prior beliefs, the extent of blame attributed to the brand is unaffected by the base-rate and similarity information. Importantly, the same base-rate information may have a different effect on the attribution of a subsequent crisis depending on whether discounting or subtyping occurred in the attribution of the first crisis. Consumers who discount a first crisis also tend to discount a second crisis for the same brand, whereas consumers who subtype a first crisis are unlikely to subtype again.Publication Open Access Production control of a pull system with production and demand uncertainty(Institute of Electrical and Electronics Engineers (IEEE), 2002) Department of Business Administration; Tan, Barış; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; 28600We consider a continuous material-flow manufacturing system with an unreliable production system and a variable demand source which switches randomly between zero and a maximum level. The failure and repair times of the production system and the switching times of the demand source are assumed to be exponentially distributed random variables. The optimal production flow control policy that minimizes the expected average inventory carrying and backlog costs is characterized as a double-hedging policy. The optimal hedging levels are determined analytically by minimizing the closed-form expression of the cost function. We investigate two approximate single hedging policies. It is empirically shown that an approximate policy that uses a single hedging level which is the sum of a production uncertainty term and a demand uncertainty term gives accurate results for the expected average cost.Publication Open Access Capacity planning for effective cohorting of hemodialysis patients during the coronavirus pandemic: a case study(Elsevier, 2023) Bozkır, C.D.C.; Özmemiş, C.; Kurbanzade, A.K.; Balçık, B.; Tuğlular, S.; Department of Business Administration; Güneş, Evrim Didem; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; 51391Planning treatments of different types of patients have become challenging in hemodialysis clinics during the COVID-19 pandemic due to increased demands and uncertainties. In this study, we address capacity planning decisions of a hemodialysis clinic, located within a major public hospital in Istanbul, which serves both infected and uninfected patients during the COVID-19 pandemic with limited resources (i.e., dialysis machines). The clinic currently applies a 3-unit cohorting strategy to treat different types of patients (i.e., uninfected, infected, suspected) in separate units and at different times to mitigate the risk of infection spread risk. Accordingly, at the beginning of each week, the clinic needs to allocate the available dialysis machines to each unit that serves different patient cohorts. However, given the uncertainties in the number of different types of patients that will need dialysis each day, it is a challenge to determine which capacity configuration would minimize the overlapping treatment sessions of different cohorts over a week. We represent the uncertainties in the number of patients by a set of scenarios and present a stochastic programming approach to support capacity allocation decisions of the clinic. We present a case study based on the real-world patient data obtained from the hemodialysis clinic to illustrate the effectiveness of the proposed model. We also compare the performance of different cohorting strategies with three and two patient cohorts.Publication Open Access Modeling and analysis of an auction-based logistics market(Elsevier, 2008) Ağralı, Semra; Department of Business Administration; Department of Industrial Engineering; Tan, Barış; Karaesmen, Fikri; Faculty Member; Faculty Member; Department of Business Administration; Department of Industrial Engineering; College of Administrative Sciences and Economics; College of Engineering; 28600; 3579We consider a logistics spot market where the transportation orders from a number of firms are matched with two types of carriers through a reverse auction. In the spot market, local carriers compete with in-transit carriers that have lower costs. In order to analyze the effects of implementing a logistics spot market on these three parties: firms, local carriers, and in-transit carriers and also the effects of various system parameters, we develop a two-stage stochastic model. We first model the auction in a static setting and determine the expected auction price based on the number of carriers engaging in the auction and their cost distributions. We then develop a continuous-time Markov chain model to evaluate the performance of the system in a dynamic setting with random arrivals and possible abandonment of orders and carriers. By combining these two models, we evaluate the performance measures such as the expected auction price, price paid to the carriers, distribution of orders between local and in-transit carriers, and expected number of carriers and orders waiting at the logistics center in the long run. We present analytical and computational results related to the performance of the system and discuss operation of such a logistics spot market in Turkey.Publication Open Access Partisan and apportionment bias in creating a predominant party system(Elsevier, 2019) Department of International Relations; Department of Business Administration; Çarkoğlu, Ali; Aksen, Deniz; Faculty Member; Faculty Member; Department of International Relations; Department of Business Administration; College of Administrative Sciences and Economics; 125588; 40308Moving beyond the analytical characteristics of apportionment methods or election systems, this article focuses on their outcomes in practice. We illustrate how apportionment and partisan biases working with a high threshold created an electoral environment conducive to the establishment of a predominant party system. We use the historical example of the Turkish experience. We trace the historical development of disproportionality for the entire multi-party elections for the 1950-2015 period. Focusing on the five most recent elections of this period since 2002, we demonstrate how the biases introduced by the apportionment method in use and the 10% threshold have advantaged the leading Justice and Development Party (Adalet ye Kalkinma Partisi, AKP). Our study suggests that a partisan bias favoring AKP still continues to exist at a lower level even after correcting the apportionment and the threshold biases. We underline how these biases form the foundation for a conservative over-representation and emphasize the path-dependent dynamics that keep challengers to the AKP away from the electoral scene, effectively helping to continue its hegemonic position in the system.