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Publication Metadata only A bicriteria approach to the two-machine flow shop scheduling problem(Elsevier Science Bv, 1999) N/A; Department of Business Administration; Department of Business Administration; Sayın, Serpil; Karabatı, Selçuk; Faculty Member; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; College of Administrative Sciences and Economics; 6755; 38819In this paper we address the problem of minimizing makespan and sum of completion times simultaneously in a two-machine flow shop environment. We formulate the problem as a bicriteria scheduling problem, and develop a branch-and-bound procedure that iteratively solves restricted single objective scheduling problems until the set of efficient solutions is completely enumerated. We report computational results, and explore certain properties of the set of efficient solutions. We then discuss their implications for the Decision Maker.Publication Metadata only A decomposition model for continuous materials flow production systems(Taylor & Francis, 1997) Yeralan, Sencer; Department of Business Administration; N/A; Tan, Barış; Faculty Member; N/A; Department of Business Administration; College of Administrative Sciences and Economics; N/A; 28600; N/AThis study presents a general and flexible decomposition method for continuous materials flow production systems. The decomposition method uses the station model developed in the first part of this study (Yeralan and Tan 1997). The decomposition method is an iterative method. At each iteration the input and output processes of the station model are matched to the most recent solutions of the adjacent stations. The procedure terminates when the solutions converge and the conservation of materials flow is satisfied. The decomposition method does not alter the station parameters such as the breakdown, repair, and service rates. This method can be used to analyse a wide variety of production systems built from heterogeneous stations. The properties of the decomposition method are studied for the series arrangement of workstations. The convergence and uniqueness of the decomposition method are discussed. The method is compared to other approximation methods. The complexity of the decomposition method is empirically investigated and is shown to be in the order of N-2 where N is the number of stations in the line, irrespective of the buffer capacities.Publication Metadata only A dynamic analysis of market entry rates in a global industry: a community ecology perspective(Emerald, 1999) Çavuşgil, S. Tamer; Department of Business Administration; Tunalı, Ayşegül Özsomer; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; 108158States that it is critical that incumbent firms understand the processes that enhance or inhibit entry of new firms into their industry. A new entrant into an industry may create additional demand by legitimizing the technology/products, and/or may share the existing market by drawing buyers away from incumbents. An analysis of market entry rates is especially important in new, high technology industries where sub‐groups of firms pursue different technology and global market diversification strategies because such sub‐groups may have asymmetrical cross‐effects on entry rates of new firms. Suggests a community ecology approach to assessing the impact of industry density on new firm entry rates. The framework is demonstrated by applying it to the global personal computer industry during the period of 1977‐1992. Results suggest that density has a nonmonotonic positive effect, while the firm‐level variables of technological strategy and market expansion strategies have a monotonic positive effect on new firm entry rates.Publication Metadata only A fuzzy decomposition method for multistation production systems subject to blocking(Elsevier Science Bv, 1996) Yeralan, Sencer; Department of Business Administration; Tan, Barış; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; 28600This study presents a new methodology to adjust the value of the proportionality constant (step length parameter) used in the general decomposition method for multistation heterogeneous production systems proposed in an earlier study for specially unbalanced production systems by using fuzzy logic control. The decomposition method is based on successive approximations. Namely, input rate to each subsystem is adjusted proportional to the difference in production rates of adjacent stations. This process continues until all the subsystems have the same production rate, Fuzzy logic control uses basic observations described in linguistic variables of how production rate changes as a function of input rate, Consequently, the proportionality constant in the successive approximation method is adjusted. These observations are not model specific, Thus, the fuzzy decomposition method can be applied to a wide variety of production systems. The same methodology can also be used in other applications where adjusting the step length parameter to attain the highest convergence rate is not trivial. For example, step length parameter used in subgradient optimization and other search methodologies can also be adjusted by using the fuzzy logic control methodology presented in this study. Numerical experience shows that this method yields a substantial improvement in the convergence rate of the decomposition method for highly unbalanced production system.Publication Metadata only A station model for continuous materials flow production systems(Taylor & Francis, 1997) Yeralan, S; Department of Business Administration; Tan, Barış; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; 28600This study develops a station model for continuous flow production systems. The most prominent use of the model is as a building block for a general and flexible decomposition method to analyse and design continuous materials flow production systems. Station breakdown and a finite capacity buffer are considered. Station inference caused by the blocking and starving phenomena is included in the station model. We assume that the time to station breakdown and station repair are exponentially distributed while the buffer is neither empty nor full. No restrictive assumptions are made about the distributions of the station breakdown and repair times when the station is blocked or starved, that is, while the buffer remains empty or remains full. The production rate and the expected level of the buffer are given in closed form. Numerical results that show the effects of the input parameters on the production rate along with an overview of the decomposition methods are presented.Publication Metadata only A stochastic model of vessel casualties resulting from oil tanker traffic through narrow waterways(Soc Computer Simulation, 1998) Otay, Emre; Department of Business Administration; Tan, Barış; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; 28600In this paper, we present our preliminary results of a stochastic model to investigate vessel casualties resulting from tanker traffic through a waterway. A state-space model of the waterway is developed by dividing it into a number of grids. The model incorporates the effects of physical forcing mechanisms, i.e., currents and waves, winds, visibility, geometry of the waterway and the routes of individual vessels in the drift probabilities of the vessels. Then these probabilities are used as state-transition probabilities of a Markov chain. The transient analysis of the resulting time-varying Markov chain yields risk charts that show the casualty probabilities across the geometry of the waterway at a given time. Furthermore the steady-state analysis allows us to analyze the relationship between the vessel traffic intensity and a global measure of casualty risk.Publication Metadata only Agile manufacturing and management of variability(Wiley-Blackwell, 1998) Department of Business Administration; Tan, Barış; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; 28600In this study, the relationship between agile manufacturing and management of variability is discussed. First, the key concepts of agility and agile manufacturing are introduced. These key concepts are then related to the management of variability. Previous studies on the modeling of variability of manufacturing systems are reviewed. Then the effects of variability of the structure of the production system, and also the processing time variability on the performance of a manufacturing system are studied by utilizing a simple model of a synchronous production line with identical stations and random processing times. Numerical results that examine the effects of the coefficient of variation of service time and the number of stations on the variability of the cycle time are also given.Publication Metadata only An analytical formula for variance of output from a series-parallel production system with no interstation buffers and time-dependent failures(Pergamon-Elsevier Science Ltd, 1998) Department of Business Administration; Tan, Barış; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; 28600This paper presents a method to determine the mean and the variance of the amount of materials produced in a fixed time interval by a continuous materials flow production system with N stations in series and M stations in parallel and no interstation buffers. Unreliable stations with exponential failure and repair times, time dependent failures, and deterministic processing times are considered. Closed-form expressions for the asymptotic mean and variance of the amount of materials produced per unit time are given for series, parallel, and series-parallel production systems with identical stations. It is shown that the distribution of the amount of materials produced in a fixed time is asymptotically normal. By using this property, effects of variability on the due-date performance are investigated by considering the probability of meeting a customer order on time. Numerical experiments that explore some relationships among performance measures and production system parameters are also presented.Publication Metadata only Analysis of multistation production systems with limited buffer capacity part:1 the subsystem model(Pergamon-Elsevier Science Ltd, 1997) Yeralan, S; Department of Business Administration; Tan, Barış; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; 28600We seek efficient techniques to evaluate the performance of multistation production systems with limited interstation buffers and station breakdown. Our ultimate objective is to develop a practical computer implementation that can be used for analysis and design. Practically implies two design considerations: flexibility and computational efficiency. The approach must be flexible enough to be applicable to production systems with various topologies and station characteristics. These include series arrangements of production systems, as well as network topologies and rework (feedback) systems. Similarly the technique must be computationally expedient. Our approach is based on a framework to model single-buffer subsystems to be used within a decomposition technique to evaluate the performance of the entire system. The first part presents a quasi-birth-death process model for the subsystems. Exploiting the spectral characteristics of the associated matrix polynomial, we develop a novel solution procedure for the steady-state probabilities where the computational effort is independent of the buffer size. The solution procedure is applicable to quasi birth-death processes. The efficient solution procedure developed in this part is used as a building block in decomposing and analyzing multistation production systems with various topologies in the second part of the study.Publication Metadata only Analysis of multistation production systems with limited buffer capacity part:2 the decomposition method(Pergamon-Elsevier Science Ltd, 1997) Yeralan, S.; Department of Business Administration; Tan, Barış; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; 28600We seek efficient techniques to evaluate the performance of multistation production systems with limited interstation buffers and station breakdown. Our ultimate objective is to develop a practical computer implementation that can be used for analysis and design. A flexible decomposition framework is developed. This approach allows the analysis of multistation production systems with various structures including series arrangements, network topologies, and rework (feedback) systems. The efficient solution techniques for the subsystems developed in Part 1 are used at each iteration of the decomposition method. It is the generality and efficiency of the subsystem model as well as the flexibility and robustness of the decomposition approach that distinguish our study from earlier work.