Browsing by Author "Bayrak, Ozlem Turker"

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Citation - WoS: 0
Citation - Scopus: 0
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.
Citation - WoS: 20
Citation - Scopus: 23
Classification Models Based On Tanaka's Fuzzy Linear Regression Approach: the Case of Customer Satisfaction Modeling
(Ios Press, 2010) Sekkeli, Gizem; Koksal, Gulser; Batman, Inci; Bayrak, Ozlem Turker; 56416
Fuzzy linear regression (FLR) approaches are widely used for modeling relations between variables that involve human judgments, qualitative and imprecise data. Tanaka's FLR analysis is the first one developed and widely used for this purpose. However, this method is not appropriate for classification problems, because it can only handle continuous type dependent variables rather than categorical. In this study, we propose three alternative approaches for building classification models, for a customer satisfaction survey data, based on Tanaka's FLR approach. In these models, we aim to reflect both random and fuzzy types of uncertainties in the data in different ways, and compare their performances using several classification performance measures. Thus, this study contributes to the field of fuzzy classification by developing Tanaka based classification models.
Citation - WoS: 0
Citation - Scopus: 0
Coexistence of Urban Nightlife Activities With Residential Areas: a Mixed-Use Neighborhood Case From Denizli, Türkiye
(Asce-amer Soc Civil Engineers, 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.
Citation - WoS: 3
Cyclical Behavior of Stock ExchangeIndex By Sectors: A Case From Turkey
(Elsevier Science Bv, 2012) Yuksel, Ebru; Bayrak, Ozlem Turker; 18500
In 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 Arasli
Citation - WoS: 0
Citation - Scopus: 0
Effect of estimation under nonnormality on the phase II performance of linear profile monitoring approaches
(Wiley, 2019) Aytacoglu, Burcu; Bayrak, Ozlem Turker; 56416
The 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.
Citation - WoS: 9
Electricity Price Modelling for Turkey
(Springer-verlag Berlin, 2012) Yildirim, Miray Hanim; Yıldırım, Miray Hanım; Ozmen, Ayse; Bayrak, Ozlem Turker; Weber, Gerhard Wilhelm; 56416; Endüstri Mühendisliği
This paper presents customized models to predict next-day's electricity price in short-term periods for Turkey's electricity market. Turkey's electricity market is evolving from a centralized approach to a competitive market. Fluctuations in the electricity consumption show that there are three periods; day, peak, and night. The approach proposed here is based on robust and continuous optimization techniques, which ensures achieving the optimum electricity price to minimize error in periodic price prediction. Commonly, next-day's electricity prices are forecasted by using time series models, specifically dynamic regression model. Therefore electricity price prediction performance was compared with dynamic regression. Numerical results show that CMARS and RCMARS predicts the prices with 30% less error compared to dynamic regression.
Citation - WoS: 2
Citation - Scopus: 2
Evaluation 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
The 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.
Citation - WoS: 0
Citation - Scopus: 0
Impact 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
This 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.
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; 56416
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.
Citation - WoS: 0
Citation - Scopus: 1
Linear contrasts in one-way classification AR(1) model with gamma innovations
(Hacettepe Univ, Fac Sci, 2016) Senoglu, Birdal; Bayrak, Ozlem Turker; 56416
In 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.