Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8651
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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 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.Article Citation - Scopus: 1Pyrrolizine-3 Synthesis and Evaluation of Photophysical Properties(Taylor & Francis inc, 2024) Tasgin, Dilek Isik; Bayraktar, Irem; Isik Tasgin, DilekWe describe a synthetic approach for pyrrolizine-3-one derivatives and their photophysical properties. These compounds are prepared by a series of reactions employing the substituted pyrroles in one-pot, two-step oxidation, and intramolecular cyclization processes. The photophysical properties of the synthesized compounds were studied by using UV-Vis and fluorescence spectroscopy in different solvents. Maximum absorbance peaks were observed around 306-416 nm and maximum fluorescence emission around 603-614 nm and 465-498 nm for pyrrolyl and N-methyl pyrrolyl substituents, respectively. The introduction of a pyrrolyl substituent had a significant impact on the Stokes shifts (192-206 nm) and quantum yield values ranged from 0.002 to 0.046.Article Citation - WoS: 4Citation - Scopus: 4Critical Decision Making for Rehabilitation of Hydroelectric Power Plants(Taylor & Francis inc, 2023) Westerman, Jerry; Celebioglu, Kutay; Ayli, Ece; Ulucak, Oguzhan; Aradag, SelinDue to their diminishing performance, reliability, and maintenance requirements, there has been a rise in the demand for the restoration and renovation of old hydroelectric power facilities in recent decades. Prior to initiating a rehabilitation program, it is crucial to establish a comprehensive understanding of the power plant's current state. Failure to do so may result in unnecessary expenses with minimal or no improvements. This article presents a systematic rehabilitation methodology specifically tailored for Francis turbines, encompassing a methodological approach for condition assessment, performance testing, and evaluation of rehabilitation potential using site measurements and CFD analysis, and a comprehensive decision-making process. To evaluate the off-design performance of the turbines, a series of simulations are conducted for 40 different flow rate and head combinations, generating a hill chart for comprehensive evaluation. Various parameters that significantly impact the critical decision-making process are thoroughly investigated. The validity of the reverse engineering-based CFD methodology is verified, demonstrating a minor difference of 0.41% and 0.40% in efficiency and power, respectively, between the RE runner and actual runner CFD results. The optimal efficiency point is determined at a flow rate of 35.035 m(3)/s, achieving an efficiency of 94.07%, while the design point exhibits an efficiency of 93.27% with a flow rate of 38.6 m(3)/s. Cavitation is observed in the turbine runner, occupying 27% of the blade suction area at 110% loading. The developed rehabilitation methodology equips decision-makers with essential information to prioritize key issues and determine whether a full-scale or component-based rehabilitation program is necessary. By following this systematic approach, hydroelectric power plants can efficiently address the challenges associated with aging Francis turbines and optimize their rehabilitation efforts.Article Citation - WoS: 62Citation - Scopus: 64Multiple Linear Regression Model Under Nonnormality(Taylor & Francis inc, 2004) Islam, MQ; Tiku, MLWe consider multiple linear regression models under nonnormality. We derive modified maximum likelihood estimators (MMLEs) of the parameters and show that they are efficient and robust. We show that the least squares esimators are considerably less efficient. We compare the efficiencies of the MMLEs and the M estimators for symmetric distributions and show that, for plausible alternatives to an assumed distribution, the former are more efficient. We provide real-life examples.Article Citation - WoS: 5Citation - Scopus: 6Exploring the Belief Systems of Software Development Professionals(Taylor & Francis inc, 2015) O'Connor, Rory V.; Yilmaz, MuratIt is commonly accepted that an individual's beliefs and actions are based on his or her assessment and perceptions of the world. In order to determine what practices an individual is likely to follow at any given time, it is necessary to understand the individual's behavioral intention in a given circumstance. From an Information Technology perspective, a software development professional's belief systems are potentially the basis for the adoption and implementation of new and innovative work practices and processes. In this article, we explore the belief systems of software development professionals in order to understand the beliefs underlying intention and practice, and we seek answers about how they adopt or reject new and innovative software development processes and practices. The results point out a strong influence of past experiences, personality types, and repeated behavior on current software development processes and practices in industrial settings.Article Citation - WoS: 20Citation - Scopus: 22Simultaneous Spectrophotometric Analysis of Codeine Phosphate, Acetylsalicylic Acid, and Caffeine in Tablets by Inverse Least-Squares and Principal Component Regression Techniques(Taylor & Francis inc, 2002) Baleanu, D; Onur, F; Dinç, EInverse least-squares (ILS) and principal component regression (PCR) techniques were proposed for the spectrophotometric simultaneous analysis of ternary mixture containing codeine phosphate, acetylsalicylic acid and caffeine without any pretreatment. A training set of the title drugs was randomly prepared for both techniques. The absorbance values were measured at the 15 points in the wavelength range 220-290 nm for the absorption spectra. The ILS and PCR calibrations were constructed by using their algorithms and they were tested for the synthetic mixtures of three drugs. Means recoveries and relative standard deviations for ILS and PCR were found as 100.2 and 1.23%, 99.5 and 2.10% for codeine phosphate, 100.5 and 1.30%, 100.3 and 1.18% for acetylsalicylic acid and 99.4 and 1.33%, 99.3 and 1.31% for caffeine, respectively. We realised the numerical computations by using the 'Maple V' software. The results were successfully observed by applying the chemometric techniques to the tablets, and a good agreement was found between the obtained values and the indicated quantities of the pharmaceutical formulation marketed in Turkey.Article Citation - WoS: 54Citation - Scopus: 59An Approach To Quantitative Two-Component Analysis of a Mixture Containing Hydrochlorothiazide and Spironolactone in Tablets by One-Dimensional Continuous Daubechies and Biorthogonal Wavelet Analysis of Uv-Spectra(Taylor & Francis inc, 2003) Baleanu, D; Üstündag, Ö; Dinç, EIn this study a new method of quantitative two-component analysis of a mixture of hydrochlorothiazide (HCT) and spironolactone (SP) in the presence of strongly overlapping signals was achieved by using one-dimensional continuous wavelet analysis. This new method was built on the simultaneous use of both continuous wavelet transform and the zero crossing technique for the quantitative resolution of this binary mixture. A series of solutions, in the concentration range of 2-22 mg/ml for both compounds, in methanol and 0.2 M sodium acetate buffer, pH = 5 (20:80), were considered. The absorption spectra of the standard solutions were recorded in the wavelength range of 215-330 nm. To apply our methods we selected 400 points from the absorption spectra and we subjected the corresponding signal to Daubechies2 (DAUB2) and Biorthogonal1.5 (BIOR1.5) one-dimensional wavelet transform. In the transformed signals, the amplitude of HCT was measured at the position of a zero crossing point of SP and vice versa. Thus simple linear regression analysis can be applied to establish calibrations for both components. These calibrations were validated with synthetic mixtures of HCT and SP. MATLAB 6.5 software was used for one-dimensional wavelet analysis, and the basic concepts about wavelet method are briefly explained. The method developed in this paper is rapid, easy to apply, inexpensive and it is suitable for analysis of the overlapping signals of compounds in their mixtures without any chemical pre-treatment.Article Citation - WoS: 27Citation - Scopus: 29Nonnormal Regression. I. Skew Distributions(Taylor & Francis inc, 2001) Islam, MQ; Tiku, ML; Yildirim, FIn a linear regression model of the type y = thetaX + e, it is often assumed that the random error e is normally distributed. In numerous situations, e.g., when y measures life times or reaction times, e typically has a skew distribution. We consider two important families of skew distributions, (a) Weibull with support IR: (0, infinity) on the real line, and (b) generalised logistic with support IR: (-infinity, infinity). Since the maximum likelihood estimators are intractable in these situations, we derive modified likelihood estimators which have explicit algebraic forms and are, therefore, easy to compute. We show that these estimators are remarkably efficient, and robust. We develop hypothesis testing procedures and give a real life example.Article Citation - WoS: 42Citation - Scopus: 47Nonnormal Regression.: Ii.: Symmetric Distributions(Taylor & Francis inc, 2001) Tiku, ML; Islam, MQ; Selçuk, ASSalient features of a family of short-tailed symmetric distributions, introduced recently by Tiku and Vaughan [1], are enunciated. Assuming the error distribution to be one of this family, the methodology of modified likelihood is used to derive MML estimators of parameters in a linear regression model. The estimators are shown to be efficient, and robust to inliers. This paper is essentially the first to achieve robustness to infers. The methodology is extended to long-tailed symmetric distributions and the resulting estimators are shown to be efficient, and robust to outliers. This paper should be read in conjunction with Islam et al. [2] who develop modified likelihood methodology for skew distributions in the context of linear regression.Conference Object Citation - WoS: 8Citation - Scopus: 9Fractional Wavelet Transform-Continous Wavelet Transform for the Quantification of Melatonin and Its Photodegradation Product(Taylor & Francis inc, 2012) Ragno, Gaetano; Baleanu, Dumitru; De Luca, Michele; Ioele, Giuseppina; Dinc, ErdalIn this study a new signal processing approach based on the simultaneous use of fractional and continuous wavelet transforms was suggested for the quantitative estimation of melatonin and its photodegradation products in their samples. The UV spectra of melatonin and its degradation product were recorded between 200.0 and 455.0 nm and processed by the fractional wavelet algorithm. The obtained fractional wavelet coefficients were treated by biorthogonal and symplets wavelet families in order to quantify melatonic and its photodegradation product, respectively. The calibration graphs for the related main compound and its degradation product were obtained by measuring the fractional-continuous wavelet amplitudes at 432.0 nm for melatonin and 435.0 nm for its degradation product. The validity and applicability of the double transforms based on fractional and continuous wavelets were confirmed by analyzing various synthetic mixtures of melatonin and its degradation product. Successful results were reported in the application of the improved fractional-continuous wavelet transform to the sample analysis.