Bayrak, Özlem
Loading...
Profile URL
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
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
15
LIFE ON LAND
0
Research Products
14
LIFE BELOW WATER
1
Research Products
4
QUALITY EDUCATION
1
Research Products
16
PEACE, JUSTICE AND STRONG INSTITUTIONS
0
Research Products
7
AFFORDABLE AND CLEAN ENERGY
1
Research Products
10
REDUCED INEQUALITIES
0
Research Products
2
ZERO HUNGER
0
Research Products
11
SUSTAINABLE CITIES AND COMMUNITIES
0
Research Products
9
INDUSTRY, INNOVATION AND INFRASTRUCTURE
0
Research Products
6
CLEAN WATER AND SANITATION
0
Research Products
5
GENDER EQUALITY
0
Research Products
17
PARTNERSHIPS FOR THE GOALS
0
Research Products
12
RESPONSIBLE CONSUMPTION AND PRODUCTION
0
Research Products
8
DECENT WORK AND ECONOMIC GROWTH
0
Research Products
3
GOOD HEALTH AND WELL-BEING
0
Research Products
13
CLIMATE ACTION
0
Research Products
1
NO POVERTY
0
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
3/0
Supervised MSc Theses
1
Supervised PhD Theses
0
WoS Citation Count
69
Scopus Citation Count
70
WoS h-index
4
Scopus h-index
3
Patents
0
Projects
0
WoS Citations per Publication
2.46
Scopus Citations per Publication
2.50
Open Access Source
7
Supervised Theses
1
| Journal | Count |
|---|---|
| Applied Acoustics | 2 |
| 1st International Symposium on Fuzzy Systems -- OCT 01-02, 2009 -- Ankara, TURKEY | 1 |
| 35th International Conference on Computers and Industrial Engineering | 1 |
| 35. Ulusal Yöneylem Araştırması ve Endüstri Mühendisliği Kongresi | 1 |
| 58th World Statistical Congress | 1 |
Current Page: 1 / 6
Scopus Quartile Distribution
Competency Cloud
28 results
Scholarly Output Search Results
Now showing 1 - 10 of 28
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 - 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 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.Article Citation - Scopus: 1Inference of Autoregressive Model With Stochastic Exogenous Variable Under Short-Tailed Symmetric Distributions(Springer international Publishing Ag, 2018) Bayrak, Ozlem Tuker; Akkaya, Aysen DenerIn classical autoregressive models, it is assumed that the disturbances are normally distributed and the exogenous variable is non-stochastic. However, in practice, short-tailed symmetric disturbances occur frequently and exogenous variable is actually stochastic. In this paper, estimation of the parameters in autoregressive models with stochastic exogenous variable and non-normal disturbances both having short-tailed symmetric distribution is considered. This is the first study in this area as known to the authors. In this situation, maximum likelihood estimation technique is problematic and requires numerical solution which may have convergence problems and can cause bias. Besides, statistical properties of the estimators can not be obtained due to non-explicit functions. It is also known that least squares estimation technique yields neither efficient nor robust estimators. Therefore, modified maximum likelihood estimation technique is utilized in this study. It is shown that the estimators are highly efficient, robust to plausible alternatives having different forms of symmetric short-tailedness in the sample and explicit functions of data overcoming the necessity of numerical solution. A real life application is also given.Article Forecasting the Methane Yield of a Commercial-Scale Anaerobic Digestor Based on the Biomethane Potential of Feedstocks(Multidisciplinary Digital Publishing Institute (MDPI), 2025) Türker Bayrak, Ö.T.; Uludaǧ-Demirer, S.; Xu, M.; Liao, W.; Bayrak, Ozlem TurkerWith rising energy demand and the need for sustainable waste treatment, anaerobic digestion (AD) has emerged as a key technology for converting organic residues into renewable energy. However, predicting methane yield in full-scale facilities remains challenging due to the complexity of AD processes, the variability of feedstocks, and the impracticality of frequent biochemical methane potential (BMP) testing. In this study, we developed a simple, data-driven approach to forecast methane production in a commercial-scale digester co-digesting manure and food waste. The model employs weekly cumulative BMP of feedstock mixtures, calculated from literature values, as the explanatory variable. The model achieved an R2 of 0.70 and a forecast mean absolute percentage error (MAPE) of 7.4, indicating its potential for full-scale AD prediction. Importantly, the analysis revealed a long-run equilibrium between BMP and methane yield, with deviations corrected within roughly one month—closely matching the system’s hydraulic retention time. These findings demonstrate that literature-based BMP values can be used to reliably predict methane yield in operating AD systems, offering a low-cost and scalable tool to support decision-making in waste management and biogas plant operations. © 2025 by the authors.Conference Object Global Krizler için Doğrusal Profillere Dayalı Kontrol Şemaları ile Oluşturulan Erken Uyarı Sistemi(2015) Türker Bayrak, Özlem; Aytaçoğlu, Burcu; Yüksel Haliloğlu, EbruArticle Citation - WoS: 2Citation - Scopus: 2Evaluation of the Turkish Soundscape Circumplex Model, and the Effects of Sound Source Dominance, Sequence, and Gender on the Perceived Affective Quality(Elsevier Sci Ltd, 2024) Yorukoglu, Papatya Nur Dokmeci; Bayrak, Ozlem Turker; Coban, Nilguen Akbulut; Osma, Ugur Beyza Ercakmak; Nur Dökmeci Yörükoğlu, Papatya; Beyza Erçakmak Osma, Uğur; Türker Bayrak, Özlem; Akbulut Çoban, NilgünThe International Standard Organization (ISO) standards series on soundscape for the identification, data collection and data analysis present a general framework for the soundscape studies that are conducted globally. Perceived Affective Qualities (PAQs) including 8 soundscape perceptual attributes in ISO/TS 12913-2:2018 and ISO/TS 12913-3:2019 are published in English language. Therefore, the 'Soundscape Attributes Translation Project' focuses on the reliable standardized translations of the PAQs in other languages. In the previously published Turkish translation and validation study, the PAQs were presented as; 'hareketli' (eventful), 'coskulu' (vibrant), 'keyifli' (pleasant), 'sakin' (calm), 'dura.gan' (uneventful), 'tekduze' (monotonous), 'rahatsiz edici' (annoying), and 'karmas ik' (chaotic). Within the scope of this follow-up study, firstly, sound sources in each audio stimulus are identified according to their dominance to explore their relation with the Soundscape Circumplex Model (SCM) quadrants and found that the human dominant audio stimuli are evaluated as 'vibrant' in SCM. Other noise dominating audio stimuli are categorized as 'monotonous' while traffic combined with other noise audio stimuli are evaluated as 'chaotic'. When the audio stimuli evaluated as 'calm' are investigated, they are either purely dominated by natural sounds or mixture of each category dominated by natural sounds. Secondly, a comparison between the Turkish and the English participants' evaluation of audio stimuli according to the SCM is done and found that they are similar except two audio stimuli. Furthermore, the effect of audio stimulus sequence and gender on 8 PAQs are statistically analysed through Kruskall-Wallis and Mann-Whitney tests; respectively and found that both are significant. The sequences shifting from 'chaotic' to 'calm' or vice versa frequently are seen to be evaluated with higher scores whereas more homogenous ones in sequence, i.e. audio stimuli having the same dominating sound source are sequenced together mostly are graded with lower scores of 8 PAQs except 'chaotic' compared to drastic changes in the sound source and found that men grade 'cos kulu' (vibrant), 'dura.gan' (uneventful), 'tekduze' (monotonous), 'rahatsiz edici' (annoying) and 'karmasik' (chaotic) more than women by 5, 11, 24, 8 and 10 points, respectively according to the median values. Finally, conformance to the SCM is evaluated by the principal component analysis (PCA) and found that it can be reduced to two dimensions named as "pleasantness" and "eventfulness" in expected order but the main PAQs pleasant-annoying and eventful-uneventful are not aligned indicating the lack of achieving the ideal circumplexity. It is believed that the results of this study could contribute to both national and international future soundscape research with a focus on listening tests applying PAQs.Article Citation - WoS: 2Citation - Scopus: 2Impact of Indoor Soundscape Workshop on Sound Awareness of Interior Architecture Studentsa)(Acoustical Soc Amer Amer inst Physics, 2025) Al-Bayyar, Zinah; Yorukoglu, Papatya Nur Dokmeci; Kitapci, Kivanc; Bayrak, Ozlem Turker; Dökmeci Yörükoğlu, Papatya Nur; Türker Bayrak, ÖzlemThis study aims to investigate the effects of attending a soundscape workshop on the awareness of sound as a design element for interior architects. The workshop is structured in three phases: theoretical lectures, practical applications, and discussions. In the first phase, fundamentals of architectural acoustics, the sense of place, and soundscape theory were delivered through theoretical lectures. In the second phase, participants were asked to design a sound environment for a restaurant and an office. In the third and final phase, participants discussed their sound designs from the perspectives of the lectures and sound-related topics. Additionally, participants completed an open-ended questionnaire to evaluate their workshop experience and provided suggestions for improvement. The effectiveness of the workshop in raising awareness was tested using a pre-test/post-test analysis method, with data collected through structured questionnaires completed by participants before and after the workshop. The results of the statistical analysis show that attending the workshop changed participants' evaluations of sound expectations and preferences, as well as their sensitivity to sound. The findings indicate that participating in an indoor soundscape workshop can positively influence interior architects' understanding of sound as a design element to be considered in their future work. (C) 2025 Acoustical Society of America.
- «
- 1 (current)
- 2
- 3
- »