Yavuz Gunalay - Academia.edu (original) (raw)

Papers by Yavuz Gunalay

As the urbanization rate increases every day, city logistics become more and more important. Elec... more As the urbanization rate increases every day, city logistics become more and more important. Electric vehicles are both environmentally friendly and also less costly alternative to internal combustion engine vehicles. However, decision methods employed by businesses are not useful to evaluate these systems. We propose a new model that helps businesses to evaluate the contribution of electric vehicles in city logistics.

Performance Evaluation, Dec 1, 2013

Optical buffering based on fiber delay lines (FDLs) has been proposed as a means for contention r... more Optical buffering based on fiber delay lines (FDLs) has been proposed as a means for contention resolution in an optical packet switch. In this article, we propose a queuing model for feedback-type shared-per-node recirculating FDL optical buffers in asynchronous optical switching nodes. In this model, optical packets are allowed to recirculate over FDLs as long as the total number of recirculations is less than a predetermined limit to meet signal loss requirements. Markov Modulated Poisson Process (MMPP)-based overflow traffic models and fixed-point iterations are employed to provide an approximate analysis procedure to obtain blocking probabilities as a function of various buffer parameters in the system when the packet arrival process at the optical switch is Poisson. The proposed algorithm is numerically efficient and accurate especially in a certain regime identified with relatively long and variably-sized FDLs, making it possible to dimension optical buffers in next-generation optical packet switching systems.

European Journal of Operational Research, Jul 1, 2001

A common lament of the preventive maintenance (PM) crusaders is that production supervisors are o... more A common lament of the preventive maintenance (PM) crusaders is that production supervisors are often unwilling to lose valuable machine time when there are job waiting to be processed and do not assign high enough priority to PM. Maintenance activities that depend dynamically on system state are too complicated to implement and their overall impact on system performance, measured in terms of average tardiness or work-in-process (WIP) inventory, is dicult to predict. In this article, we present some easy to implement state-dependent PM policies that are consistent with the realities of production environment. We also develop polling models based analyses that could be used to obtain system performance metrics when such policies are implemented. We show that there are situations in which increased PM activity can lower total expected WIP (and overall tardiness) on its own, i.e., without accounting for the lower unplanned downtime. We also include examples that explain the interaction between duration of PM activity and switchover times. We identify cases in which a simple state-independent PM policy outperforms the more sophisticated state-dependent policies.

Sixth International Conference on Advances in Applied Science and Environmental Engineering - ASEE 2016, 2016

Asian Journal of Information Technology, 2006

The fashion industry is often criticised for lack of traceability. This paper explores the implem... more The fashion industry is often criticised for lack of traceability. This paper explores the implementation of traceability in the fashion supply chain using blockchain technology (BT). Using a demon ...

Several recent studies have shown that significant quantities of leaded wastes recovered from the... more Several recent studies have shown that significant quantities of leaded wastes recovered from the disposal of television cathode ray tubes (CRTs) will be entering the waste stream over the next 50 years in a form that is ideal for post-consumer remanufacturing. Furthermore, numerous countries have recently enacted legislation requiring industrial systems to engage in the practice of industrial ecology by having all discarded, returned, or otherwise spent products from manufacturing processes become raw material inputs in subsequent manufacturing operations. Therefore legislation banning CRT disposal together with mandated remanufacturing requirements could lead to numerous potentially attractive business ventures for reprocessing and recycling the high lead content found in this waste. This paper examines inventory issues related to the effective management of these leaded CRT wastes and the nature of the waste flows is considered from the perspective of different management options for inventory control through the use of supply contracts. An effective inventory management policy is extremely important when there is great uncertainty and variability in the year-to-year or within-year quantity of product available - as is the case with the supply of CRT wastes. If it is anticipated that a high percentage of the waste stream will be utilized, then an effective inventory policy proves absolutely essential - but also proves to be an extremely complex process. Consequently, the supply contract approach can be employed to reconcile different pricing preferences with the varying delivery time horizons of different customers. © 2005 ISEIS - International Society for Environmental Information Sciences

International Journal of Smart Vehicles and Smart Transportation, 2020

As a consequence of urban intensification, logistics planning becomes more important than ever. E... more As a consequence of urban intensification, logistics planning becomes more important than ever. Electric vehicles have proved to be both environmentally friendly and a lower-cost alternative to internal combustion engine vehicles. However, existing decision methods employed by businesses and municipalities are not universally conducive to the optimization and evaluation of urban transportation systems. An innovative model and planning approach is proposed to enable urban planners to more readily evaluate the contribution of electric vehicles in city logistics and to support the decision-making process. When faced with decision-making situations that involve multiple and inconsistent performance objectives, it is often preferable to consider several quantifiably good alternatives that provide various, very different perspectives. This paper provides a modeling-to-generate-alternatives (MGA) decision-support procedure that uses the firefly algorithm (FA) metaheuristic for generating s...

WSEAS TRANSACTIONS ON COMPUTERS, 2020

Increasing urban intensification has caused civic planners to devote additional resources to more... more Increasing urban intensification has caused civic planners to devote additional resources to more appropriate logistics planning. Electric vehicles have proved to be both a lower cost alternative and more environmentally friendly than the more ubiquitous internal combustion engine vehicles. However, prevailing decision-making formulations employed by municipalities and businesses are not necessarily computationally conducive for the evaluation and optimization of urban transportation systems using electric vehicles. An innovative computational approach, the range limited routing problem, is introduced that enables urban planners to more readily evaluate the contributions of electric vehicles to the city logistics decision-making process. While there is no generalized solution technique for solving this new formulation, this paper employs the Firefly Algorithm (FA) metaheuristic to solve the range limited routing problem using electric trucks.

Electric vehicles still lack the flexibility and thus the prevalence of internal combustion engin... more Electric vehicles still lack the flexibility and thus the prevalence of internal combustion engines mostly due to inadequacy of battery technologies. Electric vehicles designed for general use, mostly result in economic, operational and sometimes technical infeasibilities. Eliminating these feasibility issues is necessary in taking advantage of electric vehicles. Many of those infeasibilities can be eliminated through individual customization and configuration of vehicles according to their intended use and areas. Our study tries to answer according to what criteria electrification of city buses should be made in order to maintain economic feasibility. These criteria are applied on selected city bus lines and the configuration parameters are determined.

International Journal of Operations Research and Information Systems, 2013

Public sector decision-making typically involves complex problems that are riddled with incompati... more Public sector decision-making typically involves complex problems that are riddled with incompatible performance objectives and possess competing design requirements which are very difficult – if not impossible – to quantify and capture when supporting decision models need to be constructed. There are invariably unmodelled design issues, not apparent at the time of model creation, which can greatly impact the acceptability of the solutions proposed by the model. Consequently, it is generally preferable to create several quantifiably good alternatives that provide multiple, disparate perspectives and very different approaches to the particular problem. These alternatives should possess near-optimal objective measures with respect to the known modelled objective(s), but be fundamentally different from each other in terms of the system structures characterized by their decision variables. By generating a set of very different solutions, it is hoped that some of the dissimilar alternati...

Open Environmental Sciences, 2009

New waste management legislation provides a driver for materials recovery, industrial ecology, an... more New waste management legislation provides a driver for materials recovery, industrial ecology, and remanufacturing practices throughout the global electronics industry. Paradoxically, the resulting regulations are incongruent and unsustainable because the targeted practitioners can neither legally re-use the resultant reclaimed materials nor legally store or dispose of the ensuing wastes.

Advances in Combinatorial Methods and Applications to Probability and Statistics, 1997

This article summarizes some recent advances in the analysis of polling models in which the serve... more This article summarizes some recent advances in the analysis of polling models in which the server uses system-state information to affect its behavior. Literature dealing with a special class of such models in which the server lies dormant upon finding the system empty, and reactivates only when the system is populated by a critical number of customers, is closely examined. Rather than provide a broad review of literature, the focus of this article is on providing insights, on building bridges with earlier literature, and on identifying common underlying principles.

Queueing Systems - Theory and Applications, 1998

A threshold start-up policy is appealing for manufacturing (service) facilities that incur a cost... more A threshold start-up policy is appealing for manufacturing (service) facilities that incur a cost for keeping the machine (server) on, as well as for each restart of the server from its dormant state. Analysis of single product (customer) systems operating under such a policy, also known as the N-policy, has been available for some time. This article develops mathematical analysis

Resources Policy, 2012

Determining the optimum cutting age for timber resources has proved to be a very challenging prob... more Determining the optimum cutting age for timber resources has proved to be a very challenging problem for both economists and silviculturists. Based upon Samuelson&#x27;s seminal work on this issue, the majority of economists have concluded that the optimum felling age occurs at a time when the net marginal benefits fall below the current rate of interest. Recently, concern about climate change has increased the importance of forestry projects, since trees act as natural biological scrubbers by removing CO2 from the ...

International Journal of Production Economics, 2011

Developing models and algorithms to generate robust project schedules that are less sensitive to ... more Developing models and algorithms to generate robust project schedules that are less sensitive to disturbances are essential in today's highly competitive uncertain project environments. This paper addresses robust scheduling in project environments; specifically, we address the discrete time/cost trade-off problem (DTCTP). We formulate the robust DTCTP with three alternative optimization models in which interval uncertainty is assumed for the unknown cost parameters. We develop exact and heuristic algorithms to solve these robust optimization models. Furthermore, we compare the schedules that have been generated with these models on the basis of schedule robustness.

The International Journal of Advanced Manufacturing Technology, 2010

Suppliers produce a variety of products to serve both large and small customer orders with unreli... more Suppliers produce a variety of products to serve both large and small customer orders with unreliable demand information. Furthermore, suppliers also face customer pressure to improve quality, lower cost, and reduce delivery delay. These conflicting objectives lead firms to use both make-to-stock and make-toorder production strategies together. These manufacturing strategies were known to be competing policies and in some cases the choice depends on characteristics of the product. In this study, the firms that manufactured multiple-item types are considered to be free to choose either production policy for each product type (no product-specific requirements are present). Then, using the order-arrival characteristics and cost parameters for each product type, the firm wants to decide which production/scheduling policy to use for each product type. Two production policy (MTS vs MTO) and two scheduling strategy (FIFO vs cyclic) are considered in this study. The analysis and numerical study show that there is no dominant strategy neither for production policy, nor product scheduling policy.

The International Journal of Advanced Manufacturing Technology, 2007

The customer order scheduling problem (COSP) is defined as to determine the sequence of tasks to ... more The customer order scheduling problem (COSP) is defined as to determine the sequence of tasks to satisfy the demand of customers who order several types of products produced on a single machine. A setup is required whenever a product type is launched. The objective of the scheduling problem is to minimize the average customer order flow time. Since the customer order scheduling problem is known to be strongly NP-hard, we solve it using four major metaheuristics and compare the performance of these heuristics, namely, simulated annealing, genetic algorithms, tabu search, and ant colony optimization. These are selected to represent various characteristics of metaheuristics: nature-inspired vs. artificially created, population-based vs. local search, etc. A set of problems is generated to compare the solution quality and computational efforts of these heuristics. Results of the experimentation show that tabu search and ant colony perform better for large problems whereas simulated annealing performs best in small-size problems. Some conclusions are also drawn on the interactions between various problem parameters and the performance of the heuristics.

IIE Transactions, 1997

Abstract We analyze a class of cyclic service (polling) systems with multiple customer classes (s... more Abstract We analyze a class of cyclic service (polling) systems with multiple customer classes (stations) in which the server stops cycling upon finding the entire system empty and initiates a setup only when the polled station has at least one customer in the queue. Interest in such systems is fueled by applications in design and performance analysis of manufacturing as well as telecommunication systems, We develop a discrete Fourier transform (DFT)-based near-exact numerical technique and an approximate method for ...