Browsing by Subject "Production"
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Item Restricted 1970'ten itibarenTürkiye'nin fındık üretimi ve ihracatı(Bilkent University, 2018) Kurucu, Mehmet Bora; Akçakuş, Didem; Akgün, Ela Nur; Elmas, İbrahim; Özkan, SelenBu araştırma, Türkiye’deki 1970 yılından 2000 yılına kadar gerçekleşen fındık ihracatını ve üretimini konu almaktadır. Araştırmada fındık ihracatı ve üretimi ile ilgili istatistikler sunuldu, aynı zamanda birçok farklı açıdan ele alınıp yorumlandı. örneğin Türkiye 1980 öncesi dönemde ihracat konusunda içe dönük bir politika izlerken, 1980 sonrasında ise fındık ihracatına verdiği önemi büyük oranda arttırmış ve yabancı ülkelere mal satımını arttırmıştır. Bu ve bunu gibi bunun gibi değişimlerin sebepleri ve analizleri araştırmanın temeli olmuştur.Item Open Access Analyses of serial production line systems for interdeparture time variability and WIP inventory systems(International Journal of Operations and Quantitative Management, 2004) Erel, E.; Sabuncuoglu, I.; Kok, G. A.This paper investigates the well-known and extensively studied unpaced production line problem for the interdeparture time variability and work-in-process (WIP) inventory. The primary objective is to examine the relationships between the interdeparture time variability and some system design factors such as the number of stations, buffer capacity, and location of a bottleneck station. The performance of the system is also evaluated for average and variance of WIP inventory. Simulation is used as a modeling and analysis tool with the results being tested by appropriate statistical procedures. The analysis of the results reveals several important findings on the interdeparture time variability and WIP inventory. We confirm and strengthen some of the previous findings on throughput. In this paper, we also discuss managerial implications and suggest further research areas.Item Restricted Antalya İplik ve Pamuklu Dokuma Fabrikası'nın tarihi(Bilkent University, 2021) Köse, Beyza Simay; Şimşek, Melike; Altınışık, Mustafa Asım; Koç, Mustafa Kaan; Torusdağ, Ömer Bahadır1950’lerden itibaren çeşitli teşvik ve yatırımlarla birlikte, işsizliği azaltmak ve ovalardaki pamuk üretiminin artışından faydalanmak amacıyla Antalya İplik ve Pamuklu Dokuma Fabrikası’nın kurulması planlandı. 1955’te bir devlet/özel sektör ortak girişimi olarak kuruldu ve 1961 yılında üretime başladı. 2004’te Sümer Holding Yönetim Kurulu fabrikayı resmen kapatma kararı aldı. Bu kararın ardından çeşitli el değiştirmeler sonucunda fabrika Antalya Belediyesi’ne devredildi ve fabrika için müzeye dönüştürme kararı alındı. Tesis son devirden sonra müze olarak faaliyet göstermeye başladı.Item Restricted Arçelik Ankara Bulaşık Makinesi Fabrikası(Bilkent University, 2020) Özaltan, Ömer; Sancak, Ahmet Batuhan; Kantik, Efser Efe; Çetin, Şule; Özçifçi, EmreBu araştırmada, 1993'te kurulan Ankara Arçelik Bulaşık Makinesi Fabrikası'nın kuruluş aşamasından günümüze kadarki gelişimi araştırıldı. Araştırma kapsamında ilk olarak Türkiye'nin 90'lar öncesindeki beyaz eşya imalatı ve fabrikanın açılışına değin piyasadaki talep değişimleri hakkında bilgiler edinildi. Fabrikanın kuruluş aşaması incelendi. Fabrikanın açılışının ülke ve bölgeye etkileri ele alındı. İlerleyen yıllarda fabrikada yaşanan değişiklikler ve üretim hacmindeki büyümeyle iyileşmeler araştırıldı. Fabrikanın kuruluş döneminde ve ilk yıllarında görev alan çalışanlarla yapılan görüşmeler başta olmak üzere sözlü ve yazılı kaynaklardan faydalanılarak araştırma tamamlandı.Item Open Access Batch scheduling to minimize maximum lateness(Elsevier, 1997) Ghosh, J. B.; Gupta, J. N. D.We address the single-machine batch scheduling problem which arises when there are job families and setup requirements exist between these families; our objective is to minimize the maximum lateness. As our main result, we give an improved dynamic program for the solution of the problem.Item Restricted Bir kentin ekonomik ve kültürel devrimi: İskenderun Demir-Çelik Fabrikası(Bilkent University, 2020) Çiçek, Berk; Mutlu, Mehmet Ali; Cangül, Merve; Aydın, Berk Can; Alp, MuratThis guide is aiming to inform people about the effects of ISDEMIR on both Iskenderun and Turkey. It consists of six parts after the introduction that is included to answer the question about the establishment of ISDEMIR and the effects of ISDEMIR on people and Turkey. The first part that is named "Establishment of ISDEMIR" informs people about the conditions in İskenderun before the ISDEMIR and construction process of ISDEMIR. In the second part, the differences between ISDEMIR and other companies are explained and also the co-partners of Iskenderun are mentioned. In the third part, the effects of ISDEMIR port on Iskenderun and Turkey are explained. In the fourth part, there are commentaries given by the people who witnessed to effects of ISDEMIR on people. In the fifth part, the effects of the military coup that happened in 1980 are given. In the sixth part, the reasons why there was a strike in 1989 and consequences are given. This paper will help people to understand the cultural and economic revolution which is caused by ISDEMIR.Item Open Access Capacitated strategic assortment planning under explicit demand substitution(Elsevier BV, 2021-11-01) Dolgan, N. G.; Ünver, N. F.; Cephe, E.; Alper, ŞenBuyers have easier access to a variety of products with the rise of multi-channel distribution strategies and the increase in new product introductions. On the other hand, firms experience greater pressure in offering the correct product variety given that the manufacturing infrastructure often imposes physical and financial constraints in attaining variety. This study examines a firm’s optimal assortment planning problem under an exogenous demand model, where each customer has a predetermined preference for each product from a potential set. Proportional demand substitutions are allowed from out-of-assortment products to those available. We show that the problem is NP-complete. We also show that an optimal assortment is composed of some number of the highest margin products, if one product having a higher margin than another implies that the former product has a lower demand rate than the latter. The firm’s assortment capacity is fully utilized at the optimum if the customers’ substitution ratio does not exceed a particular threshold. We also introduce several approximate assortment policies that can be easily implemented, and test these policies through extensive numerical analyses. The results reveal that some of the policies can provide less than a 1% profit gap with an optimal solution for a 20-product set. The policy’s performance highly depends on the firm’s assortment capacity-to-product set size ratio. Moreover, we provide performance bounds for two of these well-performing approximate policies.Item Open Access Chalcogenide microresonators tailored to distinct morphologies by the shaping of glasses on silica tapers(OSA - The Optical Society, 2017) Aktaş, O.Production of chalcogenide (As2Se3) microresonators in sphere, loop, and bottle morphologies by the shaping of glasses at appropriate temperatures between cleaved silica tapers is reported. The quality factors exceed QS = 6.2×105, QB = 6.7 × 105, and QL = 1.6 × 104 for the sphere, bottle, and loop microresonators, respectively. All-optical thermally assisted tuning with a rate of 0.61 nm/mW is demonstrated for a bottle microcavity pumped via a silica taper at a wavelength of 670 nm. This technique enables practical and robust in situ production of chalcogenide microresonators thermally spliced to silica fibers in several morphologies with a wide tuning range of size.Item Open Access Continuous time control of make-to-stock production systems(Bilkent University, 2010) Bulut, ÖnderWe consider the problem of production control and stock rationing in a make-tostock production system with multiple servers –parallel production channels--, and several customer classes that generate independent Poisson demands. At decision epochs, in conjunction with the stock allocation decision, the control specifies whether to increase the number of operational servers or not. Previously placed production orders cannot be cancelled. We both study the cases of exponential and Erlangian processing times and model the respective systems as M /M /s and M /Ek /s make-to-stock queues. We characterize properties of the optimal cost function, and of the optimal production and rationing policies. We show that the optimal production policy is a state-dependent base-stock policy, and the optimal rationing policy is of state-dependent threshold type. For the M /M /s model, we also prove that the optimal ordering policy transforms into a bang-bang type policy when we relax the model by allowing order cancellations. Another model with partial ordercancellation flexibility is provided to fill the gap between the no-flexibility and the full-flexibility models. Furthermore, we propose a dynamic rationing policy for the systems with uncapacitated replenishment channels, i.e., exogenous supply systems. Such systems can be modeled by letting s --the number of replenishment channels-- go to infinity. The proposed policy utilizes the information on the status of the outstanding replenishment orders. This work constitutes a significant extension of the literature in the area of control of make-to-stock queues, which considers only a single server. We consider an arbitrary number of servers that makes it possible to cover the spectrum of the cases from the single server to the infinite servers. Hence, our work achieves to analyze both the exogenous and endogenous supply leadtimes.Item Open Access The effectiveness of audiobooks on pronunciation skills of EFL learners at different proficiency levels(Bilkent University, 2015) Saka, ZeynepThis study mainly explored the effectiveness of audiobooks on pronunciation skills of university level EFL students at different proficiency levels. This study also aimed to find out whether a difference in students’ pronunciation skills as a result of exposure to audiobooks occurs based on their proficiency levels. Lastly, students’ perceptions about audiobooks and their effectiveness on pronunciation learning and teaching were also investigated in the study. This study was conducted with the participation of 65 students from elementary, pre-intermediate, and intermediate levels at Uludağ University School of Foreign Languages. Among the most problematic phonemes for Turkish EFL learners to pronounce correctly, six phonemes were selected to be explored in the study. Three audiobooks from three different proficiency levels were chosen for the study and participants listened to each of the audiobooks. In order to investigate the effectiveness of audiobooks on pronunciation skills both on sound recognition and production levels of university EFL students, sound recognition and production tests, which were prepared by including the selected problematic phonemes, were administered to the students before and after audiobook listening period. Before and after the audiobook listening session, the students were administered a questionnaire with the intent to find out their perceptions about the effectiveness of audiobooks on their pronunciation. In order to address the second research question which is about the effects of audiobooks on pronunciation skills, the mean values and standard deviations were calculated and compared between the first and second test performances of the students. In order to answer the second research question which is about the effects of audiobooks on pronunciation skills of EFL learners at different level, the test results of the elementary, pre-intermediate and intermediate level students were compared to investigate any difference in the effectiveness of audiobooks on pronunciation skills according to proficiency levels. Analysis of the data revealed that audiobook listening is effective on both recognition and production aspects of pronunciation skills of university EFL students, and it appeared to have a greater effect on pre-intermediate level students than it did on elementary and intermediate level students. The results from the questionnaire showed that students had positive perspectives about audiobooks and their effects on pronunciation. Finally, the study emphasizes the importance of audiobooks, suggesting that teachers can incorporate them as an alternative approach to traditional pronunciation teaching practices.Item Open Access An equipment replacement problem with dynamic production planning and capacity considerations(Taylor & Francis, 1996) Gill, A.; Adil, G. K.; Bector, C. R.In this paper, we propose a 0-1 integer programming formulation for an equipment replacement problem in which the demand of a product varies from period to period and different types of equipment with different production capacities are available. Since all the variables involved in the model are restricted to have binary values, the model is fairly efficient and hence can be used for large-sized problems. The use of the model is demonstrated with the help of some numerical examples.Item Open Access The general behavior of pull production systems: the allocation problems(Elsevier, 1999) Kırkavak, N.; Dinçer, C.The design of tandem production systems has been well studied in the literature with the primary focus being on how to improve their e ciency. Considering the large costs associated, a slight improvement in e ciency can lead to very signi®cant savings over its life. Division of work and allocation of bu er capacities between workstations are two critical design problems that have attracted the attention of many researchers. In this study, ®rst an understanding into how the system works is to be provided. Except for the integration of two allocation problems, the basic model utilized here is essentially the same as the previous studies. Theoretical results that characterize the dynamics of these systems may also provide some heuristic support in the analysis of large-scale pull production systems. Ó 1999 Elsevier Science B.V. All rights reserved.Item Open Access An integrated approach to inventory and flexible capacity management subject to fixed costs and non-stationary stochastic demand(Springer, 2009) Tan, T.; Alp O.In a manufacturing system with flexible capacity, inventory management can be coupled with capacity management in order to handle fluctuations in demand more effectively. Typical examples include the effective use of temporary workforce and overtime production. In this paper, we discuss an integrated model for inventory and flexible capacity management under non-stationary stochastic demand with the possibility of positive fixed costs, both for initiating production and for using contingent capacity. We analyze the characteristics of the optimal policies for the integrated problem. We also evaluate the value of utilizing flexible capacity under different settings, which enable us to develop managerial insights. © 2008 The Author(s).Item Open Access Integrated capacity and inventory management with capacity acquisition lead times(Elsevier, 2009-08-01) Mincsovicz, G.; Tan, T.; Alp, O.We model a make-to-stock production system that utilizes permanent and contingent capacity to meet non-stationary stochastic demand, where a constant lead time is associated with the acquisition of contingent capacity. We determine the structure of the optimal solution concerning both the operational decisions of integrated inventory and flexible capacity management, and the tactical decision of determining the optimal permanent capacity level. Furthermore, we show that the inventory (either before or after production), the pipeline contingent capacity, the contingent capacity to be ordered, and the permanent capacity are economic substitutes. We also show that the stochastic demand variable and the optimal contingent capacity acquisition decisions are economic complements. Finally, we perform numerical experiments to evaluate the value of utilizing contingent capacity and to study the effects of capacity acquisition lead time, providing useful managerial insights.Item Restricted Kuşkonmaz bitkisinin Türkiye’ye gelişi ve ekonomik katkıları(Bilkent University, 2024) Gürsoy, Ali Can; Yıldız, Dilan; Duru, Eda; Topan, İlayda; Altan, Mualla NurgülBu makale kuşkonmaz bitkisini, bu bitkinin Türkiye’ye geliş hikayesini, üretim bölgelerini ve gelişi itibariyle ekonomiye olan katkılarını istatistiksel açıdan inceleyen bir çalışma olacaktır. Bu makale sözlü tarih çalışmaları çerçevesinde kuşkonmaz bitkisinin ekonomik katkılarının araştırılmasını hedeflemektedir. Bu çalışma sırasında Kemal Arman Badur ile görüşülerek kuşkonmaza dair Türkiye’deki genel durumun anlatılması hedeflenmektedir. Bu çalışma Türkiye’de bilinirliği kısıtlı olan kuşkonmazı tanıtmak ve katkılarını belirtmek için önemlidir.Item Open Access A load-based and due-date-oriented approach to order review release in job shops(Wiley-Blackwell Publishing, 2000) Sabuncuoğlu, I.; Karapınar, H. Y.In this paper, a new order review/release (ORR) method is proposed for shop floor control systems. The proposed method utilizes both job due date and shop load information to improve the effectiveness of the ORR function in production systems. The performance of the new method is compared to those of a few well-known ORR methods under four experimental conditions. The results of extensive simulation experiments indicate that the proposed method is superior with respect to the mean absolute deviation measure. In general, it is also better than existing methods for the other performance measures. Furthermore, we show that the proposed method is more robust to variations in system load and processing times than the other ORR methods examined.Item Open Access A neural network model for scheduling problems(Elsevier, 1996) Sabuncuoğlu, İ.; Gurgun, B.Artificial neural networks (ANNs) have been successfully applied to solve a variety of problems. This paper proposes a new neural network approach to solve the single machine mean tardiness scheduling problem and the minimum makespan job shop scheduling problem. The proposed network combines the characteristics of neural networks and algorithmic approaches. The performance of the network is compared with the existing scheduling algorithms under various experimental conditions. A comprehensive bibliography is also provided in the paper.Item Open Access On the newsvendor problem with multiple inputs under a carbon emission constraint(Bilkent University, 2012) Sözüer, SibelIn this thesis, we consider two problems in the newsvendor setting with multiple inputs, under a carbon emission constraint and non-linear production functions. In the first problem, we assume a strict carbon cap and find the optimal production quantity and input allocation that will maximize the expected profit under this constraint. In the second problem, we consider an emission trading scheme where an advance purchase of carbon emission permits is made at an initial price before the random demand is realized. When the demand is realized and new carbon trade prices are revealed, it is possible to buy additional permits or to sell an excess amount. The aim is to decide on the optimal allocation of the inputs as well as the carbon trading policy so as to maximize the expected profit. In both problems, the production quantity is linked to multiple inputs via the Cobb-Douglas and Leontief production functions. Optimal policy structures are derived and numerical examples are provided.Item Open Access Optimal streaming of a single job in a two-stage flow shop(Elsevier, 1998-10-01) Şen, A.; Topaloğlu, E.; Benli, Ö.Lot streaming is moving some portion of a process batch ahead to begin a downstream operation. The problem to be considered in this paper is the following: a single job consisting of U units is to be processed on two machines in the given order. Given a fixed number of possible transfer batches between the two machines, the problem is to find the timing and the size of the transfer batches (or, sublots) so as to optimize a given criterion. The schedules can be evaluated based on job completion, sublot completion, or item completion times. In the single job lot streaming problem, minimizing job completion time corresponds to minimizing the makespan, for which formulas for optimal sublot sizes are available. In this paper, the results for the sublot and item completion time models are presented. 0 1998 Elsevier Science B.V. All rights reserved.Item Restricted Prefabrikasyonun Türkiye'deki tarihi ve gelişim süreci(Bilkent University, 2018) Çetin, İsmail Sümer; Borucu, Ümran; Turan, Fatma Zehra; Orak, Elif İpek; Kayaçağlayan, AtakanBu araştırmada prefabrikasyonun Türkiye’de ortaya çıkması ve bunda etkili olan nedenler, ilk örnekleri, kullanımının ve üretiminin yaygınlaşması incelenmiştir. Bu süreç içerisindeki zorluklar, sosyal ve ekonomik katkıları ve prefabrik kullanımının yaygınlaşması amacıyla yürütülen etkinlikler üzerinde durulmuştur. Araştırma sürecinde yazılı ve sözlü bazı kaynaklara başvurulmuştur.