Ostrovska, Sofiya
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Name Variants
Ostrovska, Sofıya
Ostrovska,S.
Ostrovska, Sofia
S., Ostrovska
S.,Ostrovska
O., Sofiya
Ostrovska, S
Sofiya, Ostrovska
Ostrovska, S.
Ostrovska, Sofiya
Ostrovska S.
O.,Sofiya
Ostrovska,S.
Ostrovska, Sofia
S., Ostrovska
S.,Ostrovska
O., Sofiya
Ostrovska, S
Sofiya, Ostrovska
Ostrovska, S.
Ostrovska, Sofiya
Ostrovska S.
O.,Sofiya
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Profesor Doktor
Email Address
sofia.ostrovska@atilim.edu.tr
ORCID ID
Scopus Author ID
Turkish CoHE Profile ID
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WoS Researcher ID
Scholarly Output
92
Articles
86
Citation Count
765
Supervised Theses
1
92 results
Scholarly Output Search Results
Now showing 1 - 10 of 92
Article Citation Count: 2A new proof that the product of three or more exponential random variables is moment-indeterminate(Elsevier Science Bv, 2010) Ostrovska, Sofiya; Stoyanov, Jordan; MathematicsWe present a direct, short and transparent proof of the following result: The product X-1 ... X-n of independent exponential random variables X-1,...,X-n is moment-indeterminate if and only if n >= 3. This and other complex analytic results concerning Stieltjes moment sequences and properties of the corresponding distributions appeared recently in Berg (2005). (C) 2010 Elsevier B.V. All rights reserved.Article Citation Count: 1On the powers of polynomial logistic distributions(Brazilian Statistical Association, 2016) Ostrovska, Sofiya; MathematicsLet P(x) be a polynomial monotone increasing on (-infinity, +infinity). The probability distribution possessing the distribution function F(x) = 1/1 + exp{-P(x)} is called the polynomial logistic distribution associated with polynomial P and denoted by PL(P). It has recently been introduced, as a generalization of the logistic distribution, by V. M. Koutras, K. Drakos, and M. V. Koutras who have also demonstrated the importance of this distribution in modeling financial data. In the present paper, for a random variable X similar to PL(P), the analytical properties of its characteristic function are examined, the moment-(in)determinacy for the powers X-m, m is an element of N and vertical bar X vertical bar(p), p is an element of (0, +infinity) depending on the values of m and p is investigated, and exemplary Stieltjes classes for the moment-indeterminate powers of X are constructed.Book Part Citation Count: 0Approximation of Discontinuous Functions by q-Bernstein Polynomials(Springer international Publishing Ag, 2016) Ostrovska, Sofiya; Ozban, Ahmet Yasar; Özban, Ahmet Yaşar; MathematicsThis chapter presents an overview of the results related to the q-Bernstein polynomials with q > 1 attached to discontinuous functions on [0, 1]. It is emphasized that the singularities of such functions located on the set Jq : = {0} boolean OR {q-l}(l=0, infinity), q > 1 are definitive for the investigation of the convergence properties of their q-Bernstein polynomials.Article Citation Count: 2On the analyticity of functions approximated by their q-Bernstein polynomials when q > 1(Elsevier Science inc, 2010) Ostrovska, Sofiya; Ostrovska, Sofiya; MathematicsSince in the case q > 1 the q-Bernstein polynomials B-n,B-q are not positive linear operators on C[0, 1], the investigation of their convergence properties for q > 1 turns out to be much harder than the one for 0 < q < 1. What is more, the fast increase of the norms parallel to B-n,B-q parallel to as n -> infinity, along with the sign oscillations of the q-Bernstein basic polynomials when q > 1, create a serious obstacle for the numerical experiments with the q-Bernstein polynomials. Despite the intensive research conducted in the area lately, the class of functions which are uniformly approximated by their q-Bernstein polynomials on [0, 1] is yet to be described. In this paper, we prove that if f : [0, 1] -> C is analytic at 0 and can be uniformly approximated by its q-Bernstein polynomials (q > 1) on [0, 1], then f admits an analytic continuation from [0, 1] into {z: vertical bar z vertical bar < 1}. (C) 2010 Elsevier Inc. All rights reserved.Article Citation Count: 2DISTORTION OF EMBEDDINGS OF BINARY TREES INTO DIAMOND GRAPHS(Amer Mathematical Soc, 2018) Ostrovska, Sofiya; Nelson, Sarah; Ostrovska, Sofiya; Ostrovskii, Mikhail; MathematicsDiamond graphs and binary trees are important examples in the theory of metric embeddings and also in the theory of metric characterizations of Banach spaces. Some results for these families of graphs are parallel to each other; for example superreflexivity of Banach spaces can be characterized both in terms of binary trees (Bourgain, 1986) and diamond graphs (Johnson-Schechtman, 2009). In this connection, it is natural to ask whether one of these families admits uniformly bilipschitz embeddings into the other. This question was answered in the negative by Ostrovskii (2014), who left it open to determine the order of growth of the distortions. The main purpose of this paper is to get a sharp up-to-a-logarithmic-factor estimate for the distortions of embeddings of binary trees into diamond graphs and, more generally, into diamond graphs of any finite branching k >= 2. Estimates for distortions of embeddings of diamonds into infinitely branching diamonds are also obtained.Article Citation Count: 7On the q-Bernstein polynomials of rational functions with real poles(Academic Press inc Elsevier Science, 2014) Ostrovska, Sofiya; Ozban, Ahmet Yasar; Özban, Ahmet Yaşar; MathematicsThe paper aims to investigate the convergence of the q-Bernstein polynomials B-n,B-q(f; x) attached to rational functions in the case q > 1. The problem reduces to that for the partial fractions (x - alpha)(-J), j is an element of N. The already available results deal with cases, where either the pole a is simple or alpha not equal q(-m), m is an element of N-0. Consequently, the present work is focused on the polynomials Bn,q(f; x) for the functions of the form f (x) = (x - q(-m))(-j) with j >= 2. For such functions, it is proved that the interval of convergence of {B-n,B-q(f; x)} depends not only on the location, but also on the multiplicity of the pole - a phenomenon which has not been considered previously. (C) 2013 Elsevier Inc. All rights reserved.Article Citation Count: 3On the Metric Space of the Limit q-Bernstein Operators(Taylor & Francis inc, 2019) Turan, Mehmet; Turan, Mehmet; Ostrovska, Sofiya; MathematicsIn this paper, some properties of uniformly discrete metric space are established. The metric rho comes out naturally in the evaluation of the distance between two limit q-Bernstein operators with respect to the operator norm on The exact value of this distance is found for all Furthermore, a number of properties of metric bases in M are presented alongside all possible isometries on M.Article Citation Count: 6The norm estimates of the q-Bernstein operators for varying q > 1(Pergamon-elsevier Science Ltd, 2011) Ostrovska, Sofiya; Ozban, Ahmet Yasar; Özban, Ahmet Yaşar; MathematicsThe aim of this paper is to present norm estimates in C [0, 1] for the q-Bernstein basic polynomials and the q-Bernstein operators B-n,B-q in the case q > 1. While for 0 < q <= 1, vertical bar vertical bar B-n,B-q vertical bar vertical bar = 1 for all n is an element of N. in the case q > 1, the norm vertical bar vertical bar B-n,B-q vertical bar vertical bar increases rather rapidly as q -> +infinity. In this study, it is proved that vertical bar vertical bar B-n,B-q vertical bar vertical bar similar to C(n)q(n(n-1)/2), q -> +infinity with C-n = 2/n (1- 1/n)(n-1). Moreover, it is shown that vertical bar vertical bar B-n,B-q vertical bar vertical bar similar to 2q(n(n-1)/2) /ne as n -> infinity, q -> +infinity. The results of the paper are illustrated by numerical examples. (C) 2011 Elsevier Ltd. All rights reserved.Article Citation Count: 1THE CONVERGENCE OF q-BERNSTEIN POLYNOMIALS (0 < q < 1) AND LIMIT q-BERNSTEIN OPERATORS IN COMPLEX DOMAINS(Rocky Mt Math Consortium, 2009) Ostrovska, Sofiya; Wang, Heping; MathematicsDue to the fact that the convergence properties of q-Bernstein polynomials are not similar to those in the classical case q = 1, their study has become an area of intensive research with a wide scope of open problems and unexpected results. The present paper is focused on the convergence of q-Bernstein polynomials, 0 < q < 1, and related linear operators in complex domains. An analogue of the classical result on the simultaneous approximation is presented. The approximation of analytic functions With the help of the limit q-Bernstein operator is studied.Article Citation Count: 0Moment Determinacy Versus q-moment Determinacy of Probability Distributions(Springer Basel Ag, 2021) Turan, Mehmet; Turan, Mehmet; Ostrovska, Sofiya; MathematicsSince the classical moment problem is an important issue deeply connected to various mathematical disciplines, its q-analogue based on the notion of q-moments has emerged in the study of q-distributions. For a wide class of probability distributions, both of these problems can be considered. The aim of this work is to establish a connection between the two moment problems. In this paper, the class A of probability distributions possessing finite moments of all orders and support on (0, infinity) is examined. For each q is an element of(0,1), a distribution P is an element of A can be characterized with respect to moment-determinacy as well as q-moment determinacy. It is proved that the properties of P regarding these characterizations may differ, and that the q-moment determinacy of P may depend on the value of q.
