The inventory control of the products which have intermittent demand is essential for many organi... more The inventory control of the products which have intermittent demand is essential for many organizations since these items have a low lead time demand but a high price. Since the intermittent demand pattern is irregular, the estimation of the lead time demand is challenging. A modified Markov chain model (MMCM) has been proposed for modeling and estimating intermittent demand data, motivated by a case study. The performance of MMCM and the traditional methods have been compared by accuracy measures. The results reveal that the proposed method is a good competitor or even better than other methods.
Stochastic Processes and Models in Operations Research, 2000
A single-server queuing system with impatient customers and Coxian service is examined. It is ass... more A single-server queuing system with impatient customers and Coxian service is examined. It is assumed that arrivals are Poisson with a constant rate. When the server is busy upon an arrival, customer joins the queue and there is an infinite capacity of the queue. Since the variance of the service time is relatively high, the service time distribution is characterized by k-phase Cox distribution. Due to the high variability of service times and since some of the services take extremely long time, customers not only in the queue, but also in the service may become impatient. Each customer, upon arrival, activates an individual timer and starts his patience time. The patience time for each customer is a random variable which has exponential distribution. If the service does not completed before the customer's time expires, the customer abandons the queue never to return. The model is expressed as birth-and-death process and the balance equations are provided.
Scheduling is a crucial phase of operations control in both manufacturing and service industries.... more Scheduling is a crucial phase of operations control in both manufacturing and service industries. With increased emphasis on time-to-market as well as superior customer satisfaction, efficient scheduling has gained considerable interest by operations researchers. The main challenge in tackling real life problems is to develop the mathematical model that reflects the system as close as possible.
This study is mainly concerned with the finitecapacity queuing system with recurrent input, n het... more This study is mainly concerned with the finitecapacity queuing system with recurrent input, n heterogeneous servers, and no waiting line. In the system customers choose only one server from the empty servers with equal probability. When all servers are busy, customers depart from the system without taking any service. These customers are called "lost customers". In this study, the transition probabilities ) ( ij p of the embedded Markov chain are calculated using the generalization of the Takacs' formula. The steady-state probabilities can be obtained from
Dokuz Eylül Üniversitesi Sosyal Bilimler Enstitüsü Dergisi, 2014
In growing competition environment, the importance of game theory, which is a vital instrument in... more In growing competition environment, the importance of game theory, which is a vital instrument in strategic planning of companies, has been increasing day by day. Depending upon the improvements on information technologies, the large proportion of the DEÜ SBE Dergisi, Cilt: 16, Sayı: 1 160 laptop users is the university students. Then the laptop computer companies should care about the likings and the preferences of the university students. In this study, two laptop computer companies, which are the most preferred by the students of the Faculty of Arts and Faculty of Sciences in Dokuz Eylül University, are determined through a designed survey. When a student oriented sales campaign is prepared by the companies, which features should be taken into account by the companies are determined by the game theory approach. The aim of this study is to examine how the student preferences affect on the advertising strategies of the laptop computer firms. To this end, two different game problems have been proposed. The first one is a zero-sum game which expresses the status of the two companies according to each other; and the second one is a nonzero-sum game which analyzes the question that to what extend the both companies meet the students' expectations. As a result of the study, some suggestions have been made with respect to which features of the companies should become prominent for the student oriented sales campaign.
ABSTRACT This paper deals with a multi-server, finite-capacity queuing system with recurrent inpu... more ABSTRACT This paper deals with a multi-server, finite-capacity queuing system with recurrent input and no waiting line. The interarrival times are arbitrarily distributed whereas service times are exponentially distributed. Moreover, the servers are heterogeneous and independent of each other. Arriving customers choose the server with the lowest index number among the empty servers. When all servers are busy at a time of an arrival, that arrival must leave the system without being served. The semi-Markov process method is used to describe this model and embedded Markov chain of the process is obtained. Furthermore, the Laplace–Stieltjes transform of the distribution of interoverflow times is derived which is the main objective of the paper. Finally, it is offered a new formulation for the loss probability which provides more efficient and rapid calculation is proposed.
The inventory control of the products which have intermittent demand is essential for many organi... more The inventory control of the products which have intermittent demand is essential for many organizations since these items have a low lead time demand but a high price. Since the intermittent demand pattern is irregular, the estimation of the lead time demand is challenging. A modified Markov chain model (MMCM) has been proposed for modeling and estimating intermittent demand data, motivated by a case study. The performance of MMCM and the traditional methods have been compared by accuracy measures. The results reveal that the proposed method is a good competitor or even better than other methods.
Stochastic Processes and Models in Operations Research, 2000
A single-server queuing system with impatient customers and Coxian service is examined. It is ass... more A single-server queuing system with impatient customers and Coxian service is examined. It is assumed that arrivals are Poisson with a constant rate. When the server is busy upon an arrival, customer joins the queue and there is an infinite capacity of the queue. Since the variance of the service time is relatively high, the service time distribution is characterized by k-phase Cox distribution. Due to the high variability of service times and since some of the services take extremely long time, customers not only in the queue, but also in the service may become impatient. Each customer, upon arrival, activates an individual timer and starts his patience time. The patience time for each customer is a random variable which has exponential distribution. If the service does not completed before the customer's time expires, the customer abandons the queue never to return. The model is expressed as birth-and-death process and the balance equations are provided.
Scheduling is a crucial phase of operations control in both manufacturing and service industries.... more Scheduling is a crucial phase of operations control in both manufacturing and service industries. With increased emphasis on time-to-market as well as superior customer satisfaction, efficient scheduling has gained considerable interest by operations researchers. The main challenge in tackling real life problems is to develop the mathematical model that reflects the system as close as possible.
This study is mainly concerned with the finitecapacity queuing system with recurrent input, n het... more This study is mainly concerned with the finitecapacity queuing system with recurrent input, n heterogeneous servers, and no waiting line. In the system customers choose only one server from the empty servers with equal probability. When all servers are busy, customers depart from the system without taking any service. These customers are called "lost customers". In this study, the transition probabilities ) ( ij p of the embedded Markov chain are calculated using the generalization of the Takacs' formula. The steady-state probabilities can be obtained from
Dokuz Eylül Üniversitesi Sosyal Bilimler Enstitüsü Dergisi, 2014
In growing competition environment, the importance of game theory, which is a vital instrument in... more In growing competition environment, the importance of game theory, which is a vital instrument in strategic planning of companies, has been increasing day by day. Depending upon the improvements on information technologies, the large proportion of the DEÜ SBE Dergisi, Cilt: 16, Sayı: 1 160 laptop users is the university students. Then the laptop computer companies should care about the likings and the preferences of the university students. In this study, two laptop computer companies, which are the most preferred by the students of the Faculty of Arts and Faculty of Sciences in Dokuz Eylül University, are determined through a designed survey. When a student oriented sales campaign is prepared by the companies, which features should be taken into account by the companies are determined by the game theory approach. The aim of this study is to examine how the student preferences affect on the advertising strategies of the laptop computer firms. To this end, two different game problems have been proposed. The first one is a zero-sum game which expresses the status of the two companies according to each other; and the second one is a nonzero-sum game which analyzes the question that to what extend the both companies meet the students' expectations. As a result of the study, some suggestions have been made with respect to which features of the companies should become prominent for the student oriented sales campaign.
ABSTRACT This paper deals with a multi-server, finite-capacity queuing system with recurrent inpu... more ABSTRACT This paper deals with a multi-server, finite-capacity queuing system with recurrent input and no waiting line. The interarrival times are arbitrarily distributed whereas service times are exponentially distributed. Moreover, the servers are heterogeneous and independent of each other. Arriving customers choose the server with the lowest index number among the empty servers. When all servers are busy at a time of an arrival, that arrival must leave the system without being served. The semi-Markov process method is used to describe this model and embedded Markov chain of the process is obtained. Furthermore, the Laplace–Stieltjes transform of the distribution of interoverflow times is derived which is the main objective of the paper. Finally, it is offered a new formulation for the loss probability which provides more efficient and rapid calculation is proposed.
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