George Vairaktarakis | Case Western Reserve University (original) (raw)
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Papers by George Vairaktarakis
Procedia - Social and Behavioral Sciences, 2015
The purpose of this study is to investigate the relation between organizational culture and job s... more The purpose of this study is to investigate the relation between organizational culture and job satisfaction. In particular, the research hypothesis is that the type of organization culture in a specific institution
Proceedings of the Sixth IEEE Computer Society Workshop on Future Trends of Distributed Computing Systems, 1997
International Series in Operations Research & Management Science, 2010
Lecture Notes in Computer Science, 2007
First this paper considers a Common Due Window (CDW) scheduling problem of n jobs on a single mac... more First this paper considers a Common Due Window (CDW) scheduling problem of n jobs on a single machine to minimize the sum of common weighted earliness and weighted number of tardy jobs when only one manufacturer processes these jobs. Two dynamic algorithms are designed for two cases respectively and each case is proved to be ordinary NP-hard. Successively the scenario,
Journal of Systems Science and Systems Engineering, 2014
We consider dynamic capacity booking problems faced by multiple manufacturers each outsourcing ce... more We consider dynamic capacity booking problems faced by multiple manufacturers each outsourcing certain operations to a common third-party firm. Each manufacturer, upon observing the current state of the third-party schedule, books capacity with the objective to jointly minimize holding costs that result from early deliveries, tardiness penalties due to late deliveries, and third-party capacity booking costs. When making a reservation, each manufacturer evaluates two alternative courses of action: (i) reserving capacity not yet utilized by other manufactures who booked earlier; or (ii) forming a coalition with a subset or all of other manufacturers to achieve a schedule minimizing coalition costs, i.e., a centralized schedule for that coalition. The latter practice surely benefits the coalition as a whole; however, some manufacturers may incur higher costs if their operations are either pushed back too much, or delivered too early. For this reason, a cost allocation scheme making each manufacturer no worse than they would be when acting differently (i.e., participating in a smaller coalition or acting on their own behalf,) must accompany centralized scheduling for the coalition. We model this relationship among the manufacturers as a cooperative game with transferable utility, and present optimal and/or heuristic algorithms to attain individually and coalitionally optimal schedules as well as a linear program formulation to find a core allocation of the manufacturers' costs.
Complexity in Numerical Optimization, 1993
SSRN Electronic Journal, 2000
Subcontracting has become a prominent business practice across many industries. Subcontracting of... more Subcontracting has become a prominent business practice across many industries. Subcontracting of in- dustrial production is generally based on short-term need for additional processing capacity, and is oftentimes employed by manufacturers to process customer orders more quickly than using only in-house production. In this paper we study a popular business model where multiple manufacturers, each capable of processing his entire workload in-house, have the option to subcontract some of their operations to a single third-party with a flexible resource. Each manufacturer can deliver customer orders only after his entire batch of jobs, processed in-house and at the third-party, is completed. Every time unit at the third-party represents scarce capacity, resulting in competition due to sequencing of the subcontracted workloads. Current business prac- tice of First-Come-First-Served (FCFS) processing of the subcontracted workloads as well as the competitive Nash equilibrium schedules developed in earlier studies both result in two types of inefficiencies; the third- party capacity is not maximally utilized, and the manufacturers incur decentralization cost. In this paper we develop models to assess the value created by coordinating the manufacturers' subcontracting decisions by comparing two types of centralized control against FCFS and Nash equilibrium schedules. We present optimal and/or approximate algorithms to quantify the third-party under-utilization and the manufactur- ers' decentralization cost. We find that both inefficiencies are more severe with competition than they are when the third-party allocates capacity in a FCFS manner. However, without centralized control, a larger percentage of the players prefer Nash equilibrium schedules to FCFS schedules. We extend our analysis to in- complete information scenarios where manufacturers reveal limited demand information, and find that more information dramatically benefits the third-party and the manufacturers, however, the marginal benefits are decreasing.
Flexible manufacturing systems (FMSs) for two stage production may possess a variety of operating... more Flexible manufacturing systems (FMSs) for two stage production may possess a variety of operating flexibilities in the form of tooling capabilities for the machines, and alternative routings for each operation. In the paper we compare the throughput performance of several flexible flowshop and job shop designs. We consider 2-stage assembly flowshops with m parallel machines in stage 1, and a single assembly facility in stage 2. Every upstream operation can be processed by any one of the machines in stage 1 prior to the assembly stage. We also study a similar design where every stage 1 operation is processed by a predetermined machine. For both designs, we present heuristic algorithms with good worst case error bounds, and show that the average performance of these algorithms is near optimal. The algorithms presented are used to compare the performance of the two designs between themselves and other related flexible flowshop designs. It is shown, both analytically and experimentally, that the mode of flexibility possessed by a design has implications on the throughput performance of the production system.
Procedia - Social and Behavioral Sciences, 2015
The purpose of this study is to investigate the relation between organizational culture and job s... more The purpose of this study is to investigate the relation between organizational culture and job satisfaction. In particular, the research hypothesis is that the type of organization culture in a specific institution
Proceedings of the Sixth IEEE Computer Society Workshop on Future Trends of Distributed Computing Systems, 1997
International Series in Operations Research & Management Science, 2010
Lecture Notes in Computer Science, 2007
First this paper considers a Common Due Window (CDW) scheduling problem of n jobs on a single mac... more First this paper considers a Common Due Window (CDW) scheduling problem of n jobs on a single machine to minimize the sum of common weighted earliness and weighted number of tardy jobs when only one manufacturer processes these jobs. Two dynamic algorithms are designed for two cases respectively and each case is proved to be ordinary NP-hard. Successively the scenario,
Journal of Systems Science and Systems Engineering, 2014
We consider dynamic capacity booking problems faced by multiple manufacturers each outsourcing ce... more We consider dynamic capacity booking problems faced by multiple manufacturers each outsourcing certain operations to a common third-party firm. Each manufacturer, upon observing the current state of the third-party schedule, books capacity with the objective to jointly minimize holding costs that result from early deliveries, tardiness penalties due to late deliveries, and third-party capacity booking costs. When making a reservation, each manufacturer evaluates two alternative courses of action: (i) reserving capacity not yet utilized by other manufactures who booked earlier; or (ii) forming a coalition with a subset or all of other manufacturers to achieve a schedule minimizing coalition costs, i.e., a centralized schedule for that coalition. The latter practice surely benefits the coalition as a whole; however, some manufacturers may incur higher costs if their operations are either pushed back too much, or delivered too early. For this reason, a cost allocation scheme making each manufacturer no worse than they would be when acting differently (i.e., participating in a smaller coalition or acting on their own behalf,) must accompany centralized scheduling for the coalition. We model this relationship among the manufacturers as a cooperative game with transferable utility, and present optimal and/or heuristic algorithms to attain individually and coalitionally optimal schedules as well as a linear program formulation to find a core allocation of the manufacturers' costs.
Complexity in Numerical Optimization, 1993
SSRN Electronic Journal, 2000
Subcontracting has become a prominent business practice across many industries. Subcontracting of... more Subcontracting has become a prominent business practice across many industries. Subcontracting of in- dustrial production is generally based on short-term need for additional processing capacity, and is oftentimes employed by manufacturers to process customer orders more quickly than using only in-house production. In this paper we study a popular business model where multiple manufacturers, each capable of processing his entire workload in-house, have the option to subcontract some of their operations to a single third-party with a flexible resource. Each manufacturer can deliver customer orders only after his entire batch of jobs, processed in-house and at the third-party, is completed. Every time unit at the third-party represents scarce capacity, resulting in competition due to sequencing of the subcontracted workloads. Current business prac- tice of First-Come-First-Served (FCFS) processing of the subcontracted workloads as well as the competitive Nash equilibrium schedules developed in earlier studies both result in two types of inefficiencies; the third- party capacity is not maximally utilized, and the manufacturers incur decentralization cost. In this paper we develop models to assess the value created by coordinating the manufacturers' subcontracting decisions by comparing two types of centralized control against FCFS and Nash equilibrium schedules. We present optimal and/or approximate algorithms to quantify the third-party under-utilization and the manufactur- ers' decentralization cost. We find that both inefficiencies are more severe with competition than they are when the third-party allocates capacity in a FCFS manner. However, without centralized control, a larger percentage of the players prefer Nash equilibrium schedules to FCFS schedules. We extend our analysis to in- complete information scenarios where manufacturers reveal limited demand information, and find that more information dramatically benefits the third-party and the manufacturers, however, the marginal benefits are decreasing.
Flexible manufacturing systems (FMSs) for two stage production may possess a variety of operating... more Flexible manufacturing systems (FMSs) for two stage production may possess a variety of operating flexibilities in the form of tooling capabilities for the machines, and alternative routings for each operation. In the paper we compare the throughput performance of several flexible flowshop and job shop designs. We consider 2-stage assembly flowshops with m parallel machines in stage 1, and a single assembly facility in stage 2. Every upstream operation can be processed by any one of the machines in stage 1 prior to the assembly stage. We also study a similar design where every stage 1 operation is processed by a predetermined machine. For both designs, we present heuristic algorithms with good worst case error bounds, and show that the average performance of these algorithms is near optimal. The algorithms presented are used to compare the performance of the two designs between themselves and other related flexible flowshop designs. It is shown, both analytically and experimentally, that the mode of flexibility possessed by a design has implications on the throughput performance of the production system.