Cilt:68 Sayı:02 (2019)

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https://dspace.ankara.edu.tr/handle/20.500.12575/75722

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On some problems regarding set valued (α,ψ)-F-contractions
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Nazam, Muhammad; Aydi, Hassen; Arshad, Muhammad; Other; Other
In this paper, we introduce set valued (α,ψ) F-contraction mappings in the setting of a partial metric space. We obtain some common fixed point theorems for a pair of these mappings. These results generalize several recent results existing in the current literature.
The dimension of products of n homogeneous components in free lie algebras
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Masuroğlu, Nil; Other; Other
Let L be a free Lie algebra of finite rank r≥2 over a field F and we let L_{m_{i}} denote the degree m_{i} homogeneous component of L. Ralph Stöhr and Micheal Vaughan-Lee derived formulae for the dimension of the subspaces [L_{m₁},L_{m₂}] for all m₁ and m₂. Then, the author and R. Stöhr obtained formulae for the dimension of the products [L_{m₁},L_{m₂},L_{m₃}] under certain conditions on m₁,m₂,m₃. In this paper, we study on products of n homogeneous components in free Lie algebra and we derive formulae for the dimension of such products.
Weighted standard deviation method for X and S control charts
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Karagöz, Derya; Other; Other
A Shewhart chart based on normality assumption is not appropriate for skewed distributions since its Type-I error rate is inflated. This study presents X and S control charts for monitoring the process variability for skewed distributions. We propose Weighted Standard Deviation (WSD) X and S control charts. Standard deviation estimator is applied to monitor the process variability for estimating the process standard deviation, in the case of the WSD X and S control charts as this estimator is simple and easy to compute. Unlike the Shewhart control chart, the proposed charts provide asymmetric limits in accordance with the direction and degree of skewness to construct the upper and lower limits. The performances of the proposed charts are compared with other heuristic charts for skewed distributions by using Simulation study. The Simulation studies show that the proposed control charts have good properties for skewed distributions and large sample sizes.
Approximation properties of Bernstein-Kantorovich type operators of two variables
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Karahan, Döne; İzgi, Aydın; Other; Other
In this study, the generalized Bernstein-Kantorovich type operators are introduced and some approximation properties of these operators are studied in the space of continuous functions of two variables on a compact set . The convergence rate of these operators are obtained by means of the modulus of continuity. The Voronovskaya type theorem is given and some differential properties of these operators are proved.
Remarks on almost η-Ricci solitons in (ε)-para Sasakian manifolds
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Blaga, Adara M.; Perktaş, Selcen Yüksel; Other; Other
We consider almost η-Ricci solitons in (ε)-para Sasakian manifolds satisfying certain curvature conditions. In the gradient case we give an estimation for the norm of the Ricci curvature tensor and express the scalar curvature of the manifold in terms of the two functions that define the soliton. We also prove that if the Ricci operator is of Codazzi type, then the gradient η-Ricci soliton is expanding if M is spacelike or shrinking if M is timelike.
On irregular coloring of wheel related graphs
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Rohini, A.; Venkatachalam, M.; Other; Other
An irregular coloring is a proper coloring in which distinct vertices have different color codes. In this paper, we obtain the irregular chromatic number for middle graph, total graph, central graph and line graph of wheel graph, helm graph, gear graph and closed helm graph.
Portfolio selection based on a nonlinear neural network: An application on the Istanbul Stock Exchange (ISE30)
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Dalkılıç, Türkan Erbay; Yaman, İlgım; Other; Other
Heuristic techniques have used frequently in portfolio optimization problem. However, almost none of these techniques used a neural network to allocate the proportion of stocks. The main goal of portfolio optimization problem is minimizing the risk of portfolio while maximizing the expected return of the portfolio. This study tackles a neural network in order to solve the portfolio optimization problem. The data set is the daily price of Istanbul Stock Exchange-30 (ISE-30) from May 2015 to May 2017. This study uses Markowitz’s Mean-Variance model. Indeed, the portfolio optimization model is quadratic programming (QP) problem. Therefore, many heuristic methods were used to solve portfolio optimization method such as particle swarm optimization, ant colony optimization etc. In fact, these methods do not satisfy stock markets demands in the financial world. This study proposed a nonlinear neural network to solve the portfolio optimization problem.
On generic submanifold of Sasakian manifold with concurrent vector field
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Yoldaş, Halil İbrahim; Meriç, Şemsi Eken; Yaşar, Erol; Other; Other
In the present paper, we deal with the generic submanifold admitting a Ricci soliton in Sasakian manifold endowed with concurrent vector field. Here, we find that there exists never any concurrent vector field on the invariant distribution D of generic submanifold M. Also, we provide a necessary and sufficient condition for which the invariant distribution D and anti-invariant distribution D^{⊥} of M are Einstein. Finally, we give a characterization for a generic submanifold of Sasakian manifold to be a gradient Ricci soliton.
Loxodromes on helicoidal surfaces and tubes with variable radius in E⁴
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Babaarslan, Murat; Other; Other
In this paper, we generalize the equations of loxodromes on helicoidal surfaces and canal surfaces in E^3 to the case of 4-dimension (E^4). Also we give some examples via Mathematica.
The mean remaining strength of parallel systems in a stress-strength model based on exponential distribution
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Kızılarslan, Fatih; Other; Other
The mean remaining strength of any coherent system is one of the important characteristics in stress-strength reliability. It shows that the system on the average how long can be safe under the stress. In this paper, we consider the mean remaining strength of the parallel systems in the stress-strength model. We assume that the strength and stress components constitute parallel systems separately. The mean remaining strength and its estimations are obtained when the all components follow the exponential distribution. The likelihood ratio order between the remaining strength of the parallel systems is presented for two-component case. The simulation study is performed to compare the derived estimates and their results are presented.
Some characterizations for spacelike inclined curves
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Akgün, M. Aykut; Sivridağ, A. İhsan; Other; Other
In this paper by establishing the Frenet frame {T,N,B₁,B₂} for a spacelike curve we give some characterizations for the spacelike inclined curves and B₂-slant helices in R₂⁴.
Approximation by Nörlund and Riesz means in weighted Lebesgue space with variable exponent
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Testici, Ahmet; Other; Other
We investigate the approximation properties of Nörlund and Riesz means of trigonometric Fourier series are investigated in the subset of weighted Lebesgue space with variable exponent.
A simulation study of the Bayes estimator for parameters in Weibull distribution
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Babacan, Esin Köksal; Kaya, Samet; İstatistik; Fen Fakültesi
The Weibull distribution is one of the most popular distributions in analyzing the lifetime data. In this study, we consider the Bayes estimators of the scale and shape parameters of Weibull distribution under the assumptions of gamma priors and squared error loss function. While computing the Bayes estimates for a Weibull distribution, the continuous conjugate joint prior distribution of the shape and scale parameters does not exist and the closed form expressions of the Bayes estimators cannot be obtained. In this study first we will consider the Bayesian inference of the scale parameter under the assumption that the shape parameter is known. We will assume that the scale parameter has a gamma prior. Under these assumptions Bayes estimate can be obtained in explicit form. When both the parameters are unknown, the Bayes estimates cannot be obtained in closed form. In this case, we will assume that the scale parameter has the gamma prior, and the shape parameter also has the gamma prior and they are independently distributed. We will use the Lindley approximation to obtain the approximate Bayes estimators. Under these assumptions, we will compute approximate Bayes estimators and compare with the maximum likelihood estimators by Monte Carlo simulations.
On some approximation properties of the Gauss-Weierstrass operators
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Yılmaz, Başar; Other; Other
In this paper, we present some approximation properties of the Gauss-Weierstrass operators in exponential weighted spaces including norm convergence of them and Voronovskaya and quantitative Voronovskaya-type theorems.
Equitable edge chromatic number of P_{m}⊗S_{n}⁰ and S_{m}⁰⊗S_{n}⁰
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Vivik, J. Veninstine; Other; Other
The equitable edge chromatic number is the minimum number of colors required to color the edges of a graph G and satisfies the criterion, if for each vertex v∈V(G), the number of edges of any one color incident with v differs from the number of edges of any other color incident with v by atmost one. In this paper, the equitable edge chromatic number of tensor product of Path P_{m} coupled with Crown S_{n}⁰ and also two Crown graphs S_{m}⁰ along with S_{n}⁰ are obtained.
On (λ,A)-statistical convergence of order α
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Şengül, Hacer; Koyun, Özlem; Other; Other
In the paper [B. de Malafosse and V. Rakočević, Linear Algebra Appl. 420, no. 2-3, (2007), 377--387], authors defined the concept of (λ,A)-statistical convergence. In this paper, the concept of (λ,A)-statistical convergence is generalized to (λ,A)-statistical convergence of order α. Also, we introduce the concept of strong (V,λ,A)-convergence of order α and give some inclusion relations between the concepts of (λ,A)-statistical convergence of order α and strong (V,λ,A)-convergence of order α.
(θ,μ,τ)-neighborhood for analytic functions involving modified sigmoid function
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Çağlar, Murat; Orhan, Halit; Other; Other
In the present investigation we discuss the neighborhoods of analytic functions defined by using modified sigmoid function. Further, we also give some applications of Jack's lemma.
Texture spaces with ideal
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Kule, Mehmet; Dost, Şenol; Other; Other
In this paper, the authors define the notion of ideal on texture spaces. The concept of di-local function is also introduced here by utilizing the families of neighborhood structure for a ditopological texture space. These concepts are discussed with a view to finding new ditopological texture spaces from the original one. Finally, we introduce and give some properties of weakly bicontinuous difunction, a subclass of bicontinuous difunction.
Principal functions of impulsive difference operators on semi axis
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Erdal, İbrahim; Yardımcı, Şeyhmus; Matematik; Fen Fakültesi
In this paper, we investigate the continuous spectrum and resolvent operator of a second-order difference operator with an impulsive condition. Then, under certain conditions, we prove finiteness of eigenvalues, spectral singularities. At last, we present principal functions of corresponding impulsive operator.
Spherical indicatrices of a Bertrand curve in three dimensional Lie groups
(Ankara Üniversitesi Fen Fakültesi, 2019-08-01) Çakmak, Ali; Kızıltuğ, Sezai; Other; Other
In this paper, new representations of a Bertrand curve pair in three dimensional Lie groups with bi-invariant metric are given. Besides, the spherical indicatrices of a Bertrand curve pair are obtained and the relations between the spherical indicatrices and new representations of Bertrand curve pair are shown.

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