Cilt:69 Sayı:01 (2020)

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https://dspace.ankara.edu.tr/handle/20.500.12575/75966

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A comparative study of classifiers for early diagnosis of gestational Diabetes Mellitus
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Muller, Priya Shirley; Nirmala, M.; Other; Other
Gestational Diabetes Mellitus (GDM), usually found deploying a medical test called the Oral Glucose Tolerance Test (OGTT), is a prevalent complication during pregnancy. Early detection of GDM and identifying the most influential risk factors of GDM pose to be a challenging problem and is found to be crucial as GDM has dreadful health indications for both mother and the baby. The performances of computational techniques like Radial Basis Function (RBF) neural network and Multilayer Perceptron Network (MLP) were collated with that of the statistical technique Discriminant Analysis (DA) on real time GDM datasets for diagnosis of GDM in multigravida pregnant women, specifically women who have been pregnant more than once, without even a visit to the hospital. The most influential risk factors were identified using DA while the overall performance of MLP beyond doubt established itself to be the most effective technique for early diagnosis of GDM in women during pregnancy.
A comparison of different methods of estimation for the flexible Weibull distribution
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Ali, Sajid; Dey, Sanku; Tahir, M. H.; Mansoor, Muhammad; Other; Other
This article presents different parameter estimation methods for flexible Weibull distribution introduced by Bebbington et al. (Reliability Engineering and System Safety 92:719-726, 2007), which is a modified version of the Weibull distribution and is suitable to model different shapes of the hazard rate. We consider both frequentist and Bayesian estimation methods and present a comprehensive comparison of them. For frequentist estimation, we consider the maximum likelihood estimators, least squares estimators, weighted least squares estimators, percentile estimators, the maximum product spacing estimators, the minimum spacing absolute distance estimators, the minimum spacing absolute log-distance estimators, Cramér von Mises estimators, Anderson Darling estimators, and right tailed Anderson Darling estimators, and compare them using a comprehensive simulation study. We also consider Bayesian estimation by assuming gamma priors for both shape and scale parameters. We use a Markov Chain Monte Carlo algorithm to compute the posterior summaries. A real data example is also a part of this work.
A generalized nonlinear iterative algorithm for the explicit midpoint rule of nonexpansive semigroup
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Sahebi, Hamid Reza; Azhini, Mahdi; Cheragni, Masume; Other; Other
In this paper, we introduce a new iterative midpoint rule for finding a solution of xed point problem for a nonexpansive semigroup in real Hilbert spaces. We establish a strong convergence theorem for the sequences generated by our proposed iterative scheme. Furthermore, we provide application to Fredholm integral equations. A numerical example is presented to illustrate the convergence result. Our results improve and extend the corresponding results in the literature.
A new family of lifetime distributions in terms of cumulative hazard rate function
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Kharazmi, Omid; Jahangard, Shahla; Other; Other
In the present paper, a new family of lifetime distributions is introduced according to cumulative hazard rate function, the well-known concept in survival analysis and reliability engineering. Some important properties of proposed model including survival function, quantile function, hazard function, order statistic and some results of stochastic ordering are obtained in general setting. An especial case of this new family is introduced by considering Weibull distribution as the parent distribution; in addition estimating unknown parameters of specialized model will be examined from the perspective of Bayesian and classic statistics. Moreover, three examples of real data sets: complete, right-censored and progressively type-I interval-censored data are studied; point and interval estimations of all parameters are obtained. Finally, the superiority of proposed model in terms of parent Weibull distribution over other fundamental statistical distributions is shown via complete real observations.
A note on hyperbolic (p,q)-Fibonacci quaternions
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Yağmur, Tülay; Other; Other
In this paper, we introduce a new quaternion sequence called hyperbolic (p,q)-Fibonacci quaternions. This new quaternion sequence includes hyperbolic Fibonacci, hyperbolic k-Fibonacci, hyperbolic Pell, hyperbolic k-Pell, hyperbolic Jacobsthal, hyperbolic k-Jacobsthal quaternions. We give generating function and Binet formula for these quaternions. We also obtain some identities such as d'Ocagne's, Catalan's and Cassini's identities involving hyperbolic (p,q)-Fibonacci quaternions.
A space-time discontinuous Galerkin method for linear hyperbolic PDE's with high frequencies
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Toprakseven, Şuayip; Other; Other
The main purpose of this paper is to describe a space-time discontinuous Galerin (DG) method based on an extended space-time approximation space for the linear first order hyperbolic equation that contains a high frequency component. We extend the space-time DG spaces of tensor-product of polynomials by adding trigonometric functions in space and time that capture the oscillatory behavior of the solution. We construct the method by combining the basic framework of the space-time DG method with the extended finite element method. The basic principle of the method is integrating the features of the partial differential equation with the standard space-time spaces in the approximation. We present error analysis of the space-time DG method for the linear first order hyperbolic problems. We show that the new space-time DG approximation has an improvement in the convergence compared to the space-time DG schemes with tensor-product polynomials. Numerical examples verify the theoretical findings and demonstrate the effects of the proposed method.
A study on comparisons of Bayesian and classical parameter estimation methods for the two-parameter Weibull distribution
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Yılmaz, Asuman; Kara, Mahmut; Aydoğdu, Halil; İstatistik; Fen Fakültesi
The main objective of this paper is to determine the best estimators of the shape and scale parameters of the two parameter Weibull distribution. Therefore, both classical and Bayesian approximation methods are considered. For parameter estimation of classical approximation methods maximum likelihood estimators (MLEs), modified maximum likelihood estimators-I (MMLEs-I), modified maximum likelihood estimators -II (MMLEs-II), least square estimators (LSEs), weighted least square estimators (WLSEs), percentile estimators (PEs), moment estimators (MEs), L-moment estimators (LMEs) and TL- moment estimators (TLMEs) are used. Since the Bayesian estimators don't have the explicit form. There are Bayes estimators are obtained by using Lindley's and Tierney Kadane's approximation methods in this study. In Bayesian approximation, the choice of loss function and prior distribution is very important. Hence, Bayes estimators are given based on both the non- informative and informative prior distribution. Moreover, these estimators have been calculated under different symmetric and asymmetric loss functions. The performance of classical and Bayesian estimators are compared with respect to their biases and MSEs through a simulation study. Finally, a real data set taken from Turkish State Meteorological Service is analysed for better understanding of methods presented in this paper.
A Tychonoff theorem for graded ditopological texture spaces
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Ekmekçi, Ramazan; Other; Other
In this paper, initial and product graded ditopologies are formulated and accordingly it is shown that d f G D i t o p is topological over d f T e x × d f T e x . By means of spectrum idea, (di)compactness in graded ditological texture spaces is defined as a generalization of (di)compactness in ditopological case and its relation with the ditopological case is investigated. Moreover, using graded difilters, two characterizations of dicompactness of graded ditological texture spaces are obtained.
Alternative partner curves in the Euclidean 3-space
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Yılmaz, Beyhan; Has, Aykut; Other; Other
In the present paper, a new type of special curve couple which are called WC^{∗}-partner curves are introduced according to alternative moving frame {N,C,W}. The distance function between the corresponding points of reference curve and its partner curve is obtained. Besides, the angle function between the vector fields of alternative frame of the curves is expressed by means of alternative curvatures f and g. In addition to these, various characterizations are obtained related to these curves.
An evaluation of some methods used for determination of homogenous structural break point in mean of panel data
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Dağlıoğlu, Selim; Bakır, Mehmet Akif; Other; Other
In this study, performances of correct break point estimation of Simple Mean Shift Model Method, Fluctuation Test, Wald Statistic Test and Kim Test methods used to investigate presence of structural break and determine the date of break in a panel data consisting of N time series, each of T length, belonging to N cross-section have been investigated. In this context 108 Monte Carlo simulations with each 3000 repeats have been carried out for 3, 3, 4 and 3 levels of factors, respectively number of cross-section units, length of series, size of break and proportion of break, to evaluate the performance of these tests used for determination of structural break in panel data. According to the Monte Carlo simulations it is concluded that Simple Mean Shift Model approach has better performance of break point estimation than other methods. Moreover, while Wald Test puts forth its best performance in the case where the breaks in series are at the half of the series, Fluctuation and Kim Tests showed their best performances in the case that the breaks are at the third quarter of series. Generally, correct break point estimation performances of tests decrease as the number of cross-section or length of series increases, even if it is limited. The changes at the levels of the proportion of break factor also lead to high accuracy estimation performance of different methods. Moreover, increases at the size of break usually decreases rates of correct estimation of methods and they approach to zero while means of the series changed 40% and over after break.
Analysis of joint reliability importance in linear m-consecutive-k,l -out-of-n:F system
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Kan, Cihangir; Özkut, Murat; Other; Other
Combinatorial techniques have an important role to compute the joint reliability importance (JRI) of some coherent systems. We obtain combinatorial formula for calculation of the JRI of two components in a generalized version of consecutive type systems consisting of n linearly ordered components such that system fails if and only if (iff) there are at least m l-overlapping runs of k consecutive failed components (n>= m(k-l)+l,l
Analysis of the Rayleigh wave field due to a tangential load applied on the surface of a coated elastic half-space
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Şahin, Onur; Other; Other
The paper deals with 3D dynamic response of a coated elastic half space subject to in-plane surface loading. The problem is formulated by a pair of elliptic equations over the interior and a two dimensional singularly perturbed hyperbolic equation expressed in terms of shear wave potentials along the interface. As an example, a point force acting one of the in-plane axis is considered and the integral solution of the normal displacement along the interface is derived through the use of the relation between the wave potentials.
Approximate test for testing a null variance ratio in the Unbalanced One-Way Random Model
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Güven, Bilgehan; Demircioğlu, Sevgi; Other; Other
The approximate test for testing the signicance of the random effect is presented in the unbalanced one-way random model in which both random effects and errors are from non-normal universes. The test is based on the asymptotic distribution of the F-statistic. Under the condition that the number of groups tends to infinity while the average of powers of the group sizes is bounded, the asymptotic distribution of the F-statistic is obtained. Robustness of the proposed test is given.
Approximation by sampling type discrete operators
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Aslan, İsmail; Other; Other
In this paper, we deal with discrete operators of sampling type. It is known that this type of operators are related to generalized sampling series and they have important applications. In this work, using bounded and uniformly continuous functions we get general estimations under usual supremum norm with the help of summability method. We also study the degree of approximation with respect to suitable Lipschitz class of continuous functions. Finally, we give specific kernels which verify our kernel assumptions.
Asymptotic behaviour of resonance eigenvalues of the Schrödinger operator with a matrix potential
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Akduman, Setenay; Karakılıç, Sedef; Coşkan, Didem; Other; Other
We will discuss the asymptotic behaviour of the eigenvalues of a Schrödinger operator with a matrix potential defined by the Neumann boundary condition in L₂^{m}(F), where F is a d-dimensional rectangle and the potential is an m×m matrix with m≥2, d≥2 , when the eigenvalues belong to the resonance domain, roughly speaking they lie near the planes of diffraction.
Classical and strongly classical 2-absorbing second submodules
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Farshadifar, Faranak; Ansari-Toroghy, Habibollah; Other; Other
‎In this paper‎, ‎we will introduce the concept of classical (resp‎. ‎strongly classical) 2-absorbing second submodules of modules over a commutative ring as a generalization of 2-absorbing (resp‎. ‎strongly 2-absorbing) second submodules and investigate some basic properties of these classes of modules‎.
Compactness and stability in diframes
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Korkmaz, Esra; Ertürk, Rıza; Other; Other
The concept of diframe was introduced as a generalization of ditopological texture spaces. The purpose of this paper is to present the results of a study on the concepts of compactness and stability in the setting of diframes. Further, the bitopological concepts of locally compactness and locally stability are extended to diframes.
Confidence regions for bivariate probability density functions using polygonal areas
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Kesemen, Orhan; Özkul, Eda; Ünsal, Ülkü; Other; Other
In this study, a polygonal approach is suggested to generalize the notion of the condence region of the univariate probability density function for the bivariate probability density function. The equal density approach is used to demonstrate that condence regions can be polygonal shapes. The bisection method is the preferred method in nding the equal density value that reveals the desired condence coecient. Condence regions estimate not only bivariate unimodal probability functions but also bivariate multimodal probability functions. An approach is enhanced to estimate these condence regions for probability density functions which are dened as rectangular, polygonal and innite expanse areas.
Curves and ruled surfaces according to alternative frame in dual space
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Çalışkan, Abdussamet; Şenyurt, Süleyman; Other; Other
In this paper, the vectorial moments of the alternative vectors are expressed in terms of alternative frame. According to the new versions of these vectorial moments, the parametric equations of the closed ruled surfaces corresponding to the (^N); (^C); (^W) dual curves are given. The integral invariants of the these surfaces are computed and illustrated by presenting with examples.
Decomposition of soft continuity via soft locally b-closed set
(Ankara Üniversitesi Fen Fakültesi, 2020-06-30) Demirtaş, Naime; Ergül, Zehra Güzel; Other; Other
In this paper, we introduce soft locally b-closed sets in soft topological spaces which are defined over an initial universe with a fixed set of parameters and study some of their properties. We investigate their relationships with different types of subsets of soft topological spaces with the help of counterexamples. Also, the concept of soft locally b-continuous functions is presented. Finally, a decomposition of soft continuity is obtained.

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