Bayrak, Özlem
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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
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
Scopus Author ID
Turkish CoHE Profile ID
Google Scholar ID
WoS Researcher ID
Files
Sustainable Development Goals
4
QUALITY EDUCATION
1
Research Products
7
AFFORDABLE AND CLEAN ENERGY
1
Research Products
14
LIFE BELOW WATER
1
Research Products
This researcher does not have a Scopus ID.
This researcher does not have a WoS ID.
Scholarly Output
28
Articles
13
Views / Downloads
2670/162
Supervised MSc Theses
1
Supervised PhD Theses
0
WoS Citation Count
65
Scopus Citation Count
68
WoS h-index
4
Scopus h-index
3
Patents
0
Projects
0
WoS Citations per Publication
2.32
Scopus Citations per Publication
2.43
Open Access Source
7
Supervised Theses
1
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Now showing 1 - 10 of 28
Article Citation - WoS: 1Citation - Scopus: 1Effect of Estimation Under Nonnormality on the Phase Ii Performance of Linear Profile Monitoring Approaches(Wiley, 2019) Aytacoglu, Burcu; Bayrak, Ozlem TurkerThe number of studies about control charts proposed to monitor profiles, where the quality of a process/product is expressed as function of response and explanatory variable(s), has been increasing in recent years. However, most authors assume that the in-control parameter values are known in phase II analysis and the error terms are normally distributed. These assumptions are rarely satisfied in practice. In this study, the performance of EWMA-R, EWMA-3, and EWMA-3(d(2)) methods for monitoring simple linear profiles is examined via simulation where the in-control parameters are estimated and innovations have a Student's t distribution or gamma distribution. Instead of the average run length (ARL) and the standard deviation of run length, we used average and standard deviation of the ARL as performance measures in order to capture the sampling variation among different practitioners. It is seen that the estimation effect becomes more severe when the number of phase I profiles used in estimation decreases, as expected, and as the distribution deviates from normality to a greater extent. Besides, although the average ARL values get closer to the desired values as the amount of phase I data increases, their standard deviations remain far away from the acceptable level indicating a high practitioner-to-practitioner variability.Conference Object Estimation of AR(1) Model Having Generalized Logistic Disturbances(2020) Akkaya, Ayşen; Türker Bayrak, ÖzlemNon-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 efficiArticle Adaptive Estimation of Autoregression Models Under Long-Tailed Symmetric Distribution(Taylor & Francis inc, 2024) Yentur, Begum; Akkaya, Aysen D.; Bayrak, Ozlem TurkerNon-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.Conference Object Citation - WoS: 2Citation - Scopus: 1Inter-Laboratory Comparison Scheme for Fuel Sector, Labkar in Turkey(Springer, 2009) Bayrak, Ozlem Turker; Okandan, Ender; Uckardes, HaleFuel 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.Article Citation - Scopus: 1Coexistence 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 TurkerSince 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.Conference Object Citation - Scopus: 3Autoregressive 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.Conference Object Citation - WoS: 3Cyclical Behavior of Stock Exchange Index by Sectors: a Case From Turkey(Elsevier Science Bv, 2012) Yuksel, Ebru; Bayrak, Ozlem TurkerIn this study, the relation between the cyclical behaviors of stock market indices of industry, service, finance and technology sectors at Istanbul Stock Exchange and gross domestic product of Turkey between the 1998 January and 2011 September, is analyzed. The results suggest that stock exchange indices move in the same direction with economic activity and stock market leads the economy by about one quarter. However, when the sectoral differences are considered, movements in technology sector index are transmitted to economy in two months whereas it is three months for the industrial and service sector. The slowest sector is the financial sector for which pass-through speed is four months. (C) 2012 Published by Elsevier Ltd. Selection and/or peer review under responsibility of Prof. Dr. Huseyin ArasliConference Object Global Krizler için Doğrusal Profillere Dayalı Kontrol Şemaları ile Oluşturulan Erken Uyarı Sistemi(2015) Türker Bayrak, Özlem; Aytaçoğlu, Burcu; Yüksel Haliloğlu, EbruArticle Citation - Scopus: 1Linear Contrasts in One-Way Classification Ar(1) Model With Gamma Innovations(Hacettepe Univ, Fac Sci, 2016) Senoglu, Birdal; Bayrak, Ozlem TurkerIn this study, the explicit estimators of the model parameters in oneway classification AR(1) model with gamma innovations are derived by using modified maximum likelihood (MML) methodology. We also propose a new test statistic for testing linear contrasts. Monte Carlo simulation results show that the MML estimators have higher efficiencies than the traditional least squares (LS) estimators and the proposed test has much better power and robustness properties than the normal theory test.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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