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Bayrak, Özlem

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https://hdl.handle.net/20.500.12416/8909
Name Variants
Bayrak, Ö.T.
Türker, Özlem
Bayrak, Ozlem Tuker
Bayrak, Özlem Türker
Türker Bayrak, Özlem
Bayrak, Ozlem Turker
Bayrak, Oezlem Tuerker
Bayrak, O.T.
Bayrak, O. Turker
Job Title
Doç. Dr.
Email Address
ozlemt@cankaya.edu.tr
Main Affiliation
Ortak Dersler Bölümü
Status
Current Staff
Website
ORCID ID
0000-0003-0821-150X
Scopus Author ID
Turkish CoHE Profile ID
Google Scholar ID
WoS Researcher ID
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Sustainable Development Goals

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CLIMATE ACTION
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8

DECENT WORK AND ECONOMIC GROWTH
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3

GOOD HEALTH AND WELL-BEING
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15

LIFE ON LAND
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17

PARTNERSHIPS FOR THE GOALS
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14

LIFE BELOW WATER
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4

QUALITY EDUCATION
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11

SUSTAINABLE CITIES AND COMMUNITIES
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CLEAN WATER AND SANITATION
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REDUCED INEQUALITIES
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9

INDUSTRY, INNOVATION AND INFRASTRUCTURE
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RESPONSIBLE CONSUMPTION AND PRODUCTION
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ZERO HUNGER
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NO POVERTY
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AFFORDABLE AND CLEAN ENERGY
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GENDER EQUALITY
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PEACE, JUSTICE AND STRONG INSTITUTIONS
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Scholarly Output

28

Articles

13

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2699/207

Supervised MSc Theses

1

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WoS Citation Count

67

Scopus Citation Count

70

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4

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WoS Citations per Publication

2.39

Scopus Citations per Publication

2.50

Open Access Source

7

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JournalCount
Applied Acoustics2
1st International Symposium on Fuzzy Systems -- OCT 01-02, 2009 -- Ankara, TURKEY1
35th International Conference on Computers and Industrial Engineering1
35. Ulusal Yöneylem Araştırması ve Endüstri Mühendisliği Kongresi1
58th World Statistical Congress1
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Now showing 1 - 10 of 28
  • Thumbnail Image
    Conference Object
    Estimation of AR(1) Model Having Generalized Logistic Disturbances
    (2020) Akkaya, Ayşen; Türker Bayrak, Özlem
    Non-normality is becoming a common feature in real life applications. Using non-normal disturbances in autoregressive models induces non-linearity in the likelihood equations so that maximum likelihood estimators cannot be derived analytically. Thus, modified maximum likelihood estimation (MMLE) technique is introduced in literature to overcome this difficulty. However, this method assumes the shape parameter to be known which is not realistic in real life. Recently, for unknown shape parameter case, adaptive modified maximum likelihood estimation (AMMLE) method that combines MMLE with Huber estimation method is suggested in literature. In this study, we adopt AMMLE method to AR(1) model where the disturbances are Generalized Logistic distributed. Although Huber M-estimation is not applicable to skew distributions, the AMMLE method extends Huber type work to skew distributions. We derive the estimators and evaluate their performance in terms of effici
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    Article
    Adaptive Estimation of Autoregression Models Under Long-Tailed Symmetric Distribution
    (Taylor & Francis inc, 2024) Yentur, Begum; Akkaya, Aysen D.; Bayrak, Ozlem Turker
    Non-normal innovations in autoregression models frequently occur in practice. In this situation, least squares (LS) estimators are known to be inefficient and non-robust, and maximum likelihood (ML) estimators need to be solved numerically, which becomes a daunting task. In the literature, the modified maximum likelihood (MML) estimation technique has been proposed to obtain the estimators of model parameters. While an explicit solution can be found via this method, the requirement of knowing the shape parameter becomes a drawback, especially in machine learning. In this study, we use the adaptive modified maximum likelihood (AMML) methodology, which combines the MML with Huber's M-estimation so that this assumption is relaxed. The performance of the method in terms of efficiency and robustness is analyzed via simulation and compared to LS, MML and ML estimates that are obtained numerically via the Expectation Conditional Maximization (ECM) algorithm. Test statistics are proposed for the crucial parameters of the model. The results show that the AMML estimators are preferable in most of the settings according to the mean squared error (MSE) criterion and the test statistics based on AMML method are more robust than the others. Furthermore, both real life and synthetic data examples are given.
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    Article
    Citation - WoS: 1
    Citation - Scopus: 1
    Coexistence of Urban Nightlife Activities With Residential Areas: a Mixed-Use Neighborhood Case From Denizli, Türkiye
    (American Society of Civil Engineers (ASCE), 2025) Orhan, Ezgi; Yilmaz, Gokce; Bayrak, Ozlem Turker
    Since the relationship between work and leisure has been reorganized as an outcome of postmodern everyday life, the nighttime has been a brightened subject for the local development agenda and revitalization policies of decayed urban centers. Even though the night activities accompanied by the leisure and entertainment industry have been prioritized to meet the increasing demand, their amalgamation with residential uses tends to lead to contradictory consequences, and the preservation of residents' quality of life needs tailored policies. Departing from the conflictive demands on urban nightscape, this study aims to reveal the satisfaction of entrepreneurs and residents coexisting in a neighborhood. To show the social, spatial, and temporal impacts of the extension of nocturnal activities, empirical research was conducted at the neighborhood level in Denizli, T & uuml;rkiye, data from 50 firms through snowball sampling were gathered through in-depth interviews and questionnaires, and a sample of 140 households were selected through stratified random sampling. For the analytical procedure, in addition to the descriptive statistics indicating business and household profiles, satisfaction levels with doing night business and residing in the neighborhood were inquired. Findings suggested that entertainment enterprises tended to cluster in newly developed areas to benefit from the proximity advantages to customers and support the expansion of central districts, and residents showed high satisfaction levels from the vitality ignited by night activities. Also, residents' overall satisfaction was found to be associated with the economic effects of nightlife and their attachment to the neighborhood. A policy frame is presented for socially sustainable nighttime activities targeting potential investors and decision makers and for preventing the old core's decay.
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    Conference Object
    Citation - Scopus: 3
    Autoregressive Models With Stochastic Design Variables and Nonnormal Innovations
    (2011) Bayrak, O.T.; Akkaya, A.D.
    In autoregression models the design variable has traditionally been assumed to be non-stochastic and innovations are normal. In most real life situations, however, the design variable is stochastic having a non-normal distribution as the innovations. Modified maximum likelihood method is utilized to estimate unknown parameters in such situations. Closed form estimators are obtained and shown to be efficient and robust.
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    Conference Object
    Citation - WoS: 2
    Citation - Scopus: 1
    Inter-Laboratory Comparison Scheme for Fuel Sector, Labkar in Turkey
    (Springer, 2009) Bayrak, Ozlem Turker; Okandan, Ender; Uckardes, Hale
    Fuel sector is one of the powerful sectors in Turkish industry. The implementation of a new law for regulating the fuel sector had enforced the quality control of fuels sold to public. This resulted in several accredited fuel-testing laboratories to emerge. Thus, a scheme to evaluate their proficiency in measurements became an important requirement. The inter-laboratory comparison scheme LABKAR for gasoline, diesel oil, LPG, lubricating oil and biodiesel samples have evolved to fulfill this need. In this paper, LABKAR is introduced; the results obtained from the program are analyzed and discussed. The kernel densities of the participants' results show that the use of robust mean as a consensus value is appropriate for fuel samples. Although the number of rounds is not enough to derive strict conclusions, it is seen that the performance of the scheme based on the standard deviations and coefficient of variations is improving in each round. It has been observed that the number of laboratories receiving "action" or "warning" is decreasing, which indicates that they are benefiting from the scheme.
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    Article
    Citation - WoS: 8
    Citation - Scopus: 12
    Estimating Parameters of a Multiple Autoregressive Model by the Modified Maximum Likelihood Method
    (Elsevier, 2010) Bayrak, Oezlem Tuerker; Akkaya, Aysen D.
    We consider a multiple autoregressive model with non-normal error distributions, the latter being more prevalent in practice than the usually assumed normal distribution. Since the maximum likelihood equations have convergence problems (Puthenpura and Sinha, 1986) [11], we work Out modified maximum likelihood equations by expressing the maximum likelihood equations in terms of ordered residuals and linearizing intractable nonlinear functions (Tiku and Suresh, 1992) [8]. The solutions, called modified maximum estimators, are explicit functions of sample observations and therefore easy to compute. They are under some very general regularity conditions asymptotically unbiased and efficient (Vaughan and Tiku, 2000) [4]. We show that for small sample sizes, they have negligible bias and are considerably more efficient than the traditional least Squares estimators. We show that Our estimators are robust to plausible deviations from an assumed distribution and are therefore enormously advantageous as compared to the least squares estimation. We give a real life example. (C) 2009 Elsevier B.V. All rights reserved.
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    Conference Object
    Forecasting The Natural Gas Demand At New Locations A Case Study For Turkey
    (2005) Türker Bayrak, Özlem; Köksal, Gülser; Okandan, Ender
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    Master Thesis
    The Relationship Between Academic Success of Architecture Students and Their Levels of Motivation and Cognitive Flexibility: the Case of Çankaya University
    (2024) Koç, Burcu; Akan, Aslı Er; Bayrak, Özlem Türker
    Bu araştırma Çankaya Üniversitesi Mimarlık Fakültesi öğrencilerinin akademik başarılarının motivasyon düzeyleri ve bilişsel esneklik arasındaki ilişkiyi araştırmayı amaçlamaktadır. Bu amaç doğrultusunda 156 üniversite lisans öğrencisine ulaşılmış ve araştırmaya dâhil edilen öğrencilere Sosyodemografik bilgi formu, Akademik Motivasyon ve Bilişsel Kontrol Esneklik Ölçeği uygulanmıştır. Veriler toplandıktan sonra verilerin analizi TURCOSA istatistik yazılımında gerçekleştirilmiştir. Bu çalışmadaki bulgular, katılımcıların demografik özellikleri ve çeşitli psikolojik ölçekler üzerindeki performansları hakkında önemli bilgiler sunmaktadır. Elde edilen bulgular cinsiyetin akademik motivasyon ve bilişsel esneklik düzeyi üzerinde anlamlı olduğunu tespit etmiştir. Buna karşın, bilişsel kontrol ve esneklik ölçeği ile içsel ve dışsal motivasyon arasında babanın eğitim düzeyleri açısından anlamlı bir farklılık gözlenmemiştir (p>,05).Ancak motivasyonsuzluk ölçeği puanlarının babanın eğitim düzeyi açısından istatistiksel olarak anlamlı farklılıklar göstermiştir (p<,05).Yine elde edilen bulgulara göre çalışan ve çalışmayan öğrenciler arasında bilişsel kontrol, bilişsel esneklik ve motivasyon düzeyleri açısından anlamlı farklılıklar bulunmamaktadır(p>,05).Bilişsel kontrol ve esneklik ölçeğinin değerlendirme ve başa çıkma esnekliği alt boyutu ile içsel motivasyon arasında pozitif yönde zayıf bir ilişki (r=0.316) tespit edilmiştir. Bilişsel kontrol ve esneklik ile motivasyon ve motivasyonsuzluk arasındaki ilişkilerin zayıf düzeyde de olsa var olduğu görülmüştür. Bu bulgular, bireylerin bilişsel becerilerinin, motivasyonel durumlarını etkileyebileceğini ve bunun da akademik başarıyı etkileyebileceğini düşündürdüğünden konunun daha derinlemesine incelenmesi gerektiğini ortaya koymaktadır. Bu alandaki araştırmalar, akademik başarı için yapılacak müdahale ve destek programlarının önemini vurgulamakta ve bireylerin motivasyonlarını ve bilişsel esneklik düzeylerini artırmaya yönelik stratejilerin geliştirilmesi gerektiğini önermektedir. Bu sonuçlar literatürde daha önce yapılan araştırmalarla karşılaştırılmış ve tartışılmıştır. Araştırma sonuçlarına dayalı olarak, öğrencilerin akademik başarılarını artırmak için eğitim stratejileri önerilmiştir.
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    Article
    Normal Olmayan Dağılımlar Altında Tahminin Basit Doğrusal Profil İzleme Üzerine Etkisi
    (2019) Bayrak, Özlem Türker; Aytaçoğlu, Burcu
    Son yıllarda, bir ürün veya sürecin kalitesinin tepki ve açıklayıcı değişken(ler) arasındaki ilişkinin fonksiyonu ile ifade edildiği profillerin izlenmesi için pek çok kalite şeması önerilmiştir. Bu yöntemlerin çoğu Faz II analizlerinde kontrol parametre değerlerinin bilindiğini ve artıkların normal dağıldığını varsaymaktadır. Oysaki uygulamada parametreler Faz I analizlerinde tahmin edilir ve artıklar normal olmayabilir. Bu çalışmada simülasyon ile artıkların t dağıldığı ve parametrelerin tahmin edildiği durumlarda basit doğrusal profillerin izlenmesi için önerilen T2, EWMA-R ve EWMA-3 yöntemlerinin performansları değerlendirilmiştir. Performans ölçüsü olarak hem ortalama koşu uzunluğu hem de koşu uzunluğu standart sapması dikkate alınmıştır. En sonunda uygulayıcılar için bazı öneriler tablo halinde özetlenmiştir.
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    Conference Object
    Citation - Scopus: 1
    Survey and Evaluation on Modelling of Next-Day Electricity Prices
    (Springer New York LLC, 2014) Bayrak, Ö.T.; Weber, G.-W.; Yıldırım, M.H.