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Yayın Design of optimum nyquist signals based on generalized sampling theory for data communications(IEEE, Piscataway, NJ, United States, 1999-06) Panayırcı, Erdal; Özuğur, Timuçin; Çağlar, HakanA new method is given for the optimal design of bandlimited Nyquist-type signal shapes for data communications, which maximizes its energy in a given time interval. The method is based on the periodically nonuniform sampling (PNS) theory making use of the linear splines. The computation is straightforward, and the constraint for intersymbol interferrence is shown to be easy to include in the problem. A numerical example is given, and performance of the optimal signal shapes is compared with that resulting from the use of previously obtained signal shapes in the literature. It is also concluded that the optimal signal shapes thus obtained are almost immune to small offsets at the sampling instants.Yayın A travelling wave solution to the KdV-Burgers equation(Elsevier Inc, 2004-07-15) Demiray, HilmiIn the present work, by introducing a new potential function and by using the hyperbolic tangent method and an exponential rational function approach, a travelling wave solution to the KdV-Burgers (KdVB) equation is presented. It is observed that both methods lead to the same type of solution. The solution method we introduced here is less restrictive and comprises some solutions existing in the current literature [Wave Motion 11 (1989) 559; Wave Motion 14 (1991) 559].Yayın A factorized high dimensional model representation on the nodes of a finite hyperprismatic regular grid(Elsevier Science inc, 2005-05-25) Tunga, Mehmet Alper; Demiralp, MetinWhen the values of a multivariate function f(x(1),...,x(N)), having N independent variables like x(1),...,x(N) are given at the nodes of a cartesian, product set in the space of the independent variables and ail interpolation problem is defined to find out the analytical structure of this function some difficulties arise in the standard methods due to the multidimensionality of the problem. Here, the main purpose is to partition this multivariate data into low-variate data and to obtain the analytical structure of the multivariate function by using this partitioned data. High dimensional model representation (HDMR) is used for these types of problems. However, if HDMR requires all components, which means 2(N) number of components, to get a desired accuracy then factorized high dimensional model representation (FHDMR) can be used. This method uses the components of HDMR. This representation is needed when the sought multivariate function has a multiplicative nature. In this work we introduce how to utilize FHDMR for these problems and present illustrative examples.Yayın Hybrid high dimensional model representation (HHDMR) on the partitioned data(Elsevier B.V., 2006-01-01) Tunga, Mehmet Alper; Demiralp, MetinA multivariate interpolation problem is generally constructed for appropriate determination of a multivariate function whose values are given at a finite number of nodes of a multivariate grid. One way to construct the solution of this problem is to partition the given multivariate data into low-variate data. High dimensional model representation (HDMR) and generalized high dimensional model representation (GHDMR) methods are used to make this partitioning. Using the components of the HDMR or the GHDMR expansions the multivariate data can be partitioned. When a cartesian product set in the space of the independent variables is given, the HDMR expansion is used. On the other band, if the nodes are the elements of a random discrete data the GHDMR expansion is used instead of HDMR. These two expansions work well for the multivariate data that have the additive nature. If the data have multiplicative nature then factorized high dimensional model representation (FHDMR) is used. But in most cases the nature of the given multivariate data and the sought multivariate function have neither additive nor multiplicative nature. They have a hybrid nature. So, a new method is developed to obtain better results and it is called hybrid high dimensional model representation (HHDMR). This new expansion includes both the HDMR (or GHDMR) and the FHDMR expansions through a hybridity parameter. In this work, the general structure of this hybrid expansion is given. It has tried to obtain the best value for the hybridity parameter. According to this value the analytical structure of the sought multivariate function can be determined via HHDMR.Yayın Harmonic mappings related to Janowski starlike functions(Elsevier Science BV, 2014-11) Kahramaner, Yasemin; Polatoğlu, Yaşar; Aydoğan, Seher MelikeThe main purpose of the present paper is to give the extent idea which was introduced by Robinson(1947) [6]. One of the interesting application of this extent idea is an investigation of the class of harmonic mappings related to Janowski starlike functions.Yayın Subclass of m-quasiconformal harmonic functions in association with Janowski starlike functions(Elsevier Science Inc, 2018-02-15) Sakar, Fethiye Müge; Aydoğan, Seher MelikeLet's take f(z) = h (z) + <(g(z))over bar> which is an univalent sense-preserving harmonic functions in open unit disc D = {z : vertical bar z vertical bar < 1}. If f (z) fulfills vertical bar w(z)vertical bar = |g'(z)/h'(z)vertical bar < m, where 0 <= m < 1, then f(z) is known m-quasiconformal harmonic function in the unit disc (Kalaj, 2010) [8]. This class is represented by S-H(m).The goal of this study is to introduce certain features of the solution for non- linear partial differential equation <(f)over bar>((z) over bar) = w(z)f(z) when vertical bar w(z)vertical bar < m, w(z) (sic) m(2)(b(1)-z)/m(2)-b(1)z, h(z) is an element of S*(A, B). In such case S*(A, B) is known to be the class for Janowski starlike functions. We will investigate growth theorems, distortion theorems, jacobian bounds and coefficient ineqaulities, convex combination and convolution properties for this subclass.Yayın Confluent tip singularity of the electromagnetic field at the apex of a material cone(Elsevier Science, 2003-09) İdemen, Mehmet MithatThe tip singularity of the electromagnetic field at the apex of a cone (conical sheet) is investigated in its most general framework. To this end one considers, without loss of generality, a circularly symmetric cone which separates two simple media having different constitutive parameters, and tries to reveal the asymptotic behaviour of the electromagnetic field created near the apex of the cone by any rotationally symmetric source distribution. To cover various boundary conditions which are extensively used in actual investigations, the cone is supposed to be formed by an infinitely thin material sheet having its own constitutive parameters. The results show that the type and order of the singularity depend, in general, on various parameters such as (i) the apex angle of the cone, (ii) the constitutive parameters of the mediums separated by the cone, (iii) the constitutive parameters of the material cone itself and (iv) the topology of the conical surface. The problem of determining the order in question gives rise to a transcendental algebraic equation involving the Legendre functions of the first kind with complex orders. If the order is a simple root of this equation, then the singularity is always of the algebraic typed whereas a multiple root gives rise also to logarithmic singularities. A numerical method suitable to find a good approximate solution to this equation is also established. Since the general expressions of the boundary conditions on the material cone, which, are compatible with both the Maxwell equations and the topology of the cone, are not known, an attempt has also been made to derive these expressions. Some examples concerning the boundary conditions which are extensively considered in actual investigations are given.Yayın Complex travelling wave solutions to the KdV and Burgers equations(Elsevier Science Inc, 2005-03) Demiray, HilmiIn the present work, making use of the hyperbolic tangent method, some complex travelling wave solutions to the Korteweg-deVries and Burgers equations are obtained. It is observed that the real part of the Solution for the Burgers equation is of shock type whereas the imaginary part is the localized travelling wave. However, for the solution of the Korteweg-deVries equation the real part is a solitary wave while the imaginary part is the product of a solitary wave with a shock.Yayın Influence of the velocity on the energy patterns of moving scatterers(Taylor & Francis, 2004) İdemen, Mehmet Mithat; Alkumru, AliParallel to the developments in the communication through space vehicles achieved during the last two decades, the scattering problems connected with moving objects became more and more important from both theoretical and practical points of view. Same problems are also arisen in point of space science, radio astronomy, radar techniques and particle physics. The earlier investigations available in the open literature concern the analysis of the scattered field pattern and, hence, treat the polarization, frequency shift (Doppler effect), aberration, etc, which are all important from both pure scientific and technological points of view. But, another issue which is also important in regard to the communication, antennas and particle physics is the influence of the motion on the scattered energy patterns which involves the radar cross-section and scattering coefficient. This paper is devoted to this purpose and aims to study the influence of the velocity on the received and scattered energies. Notice that the scattered wave is not time-harmonic even though the incident wave is so because the Lorentz transformation formulas interrelate the space coordinates and time, which makes impossible to extend the notion of radar cross-section to moving bodies. For the sake of simplicity of the mathematical manipulations, only two-dimensional case is taken into account but the method can be adapted by straightforward extensions to other types of scatterer.Yayın Derivation of the Lorentz transformation from the Maxwell equations(VSP BV, Brill Academic Publishers, 2005) İdemen, Mehmet MithatThe Special Theory of Relativity had been established nearly one century ago to conciliate some seemingly contradictory concepts and experimental results such as the Ether, universal time, contraction of dimensions of moving bodies, absolute motion of the Earth, speed of the light, etc. Hence the fundamental revolutionary formulas of the Theory, i.e., the Lorentz Formulas, had been derived first by Einstein by dwelling on a postulate which stipulated the constancy of the speed of the light. To this end he had first postulated that every reference system has a time proper to itself and then redefined the notions of simultaneity, synchronous clocks, time interval, the length of a rod in a system at rest, the length in a moving system, etc. A second postulate of Einstein, which stated that every physical theory is invariant under the Lorentz transformation, enabled him to claim that the Theory of Electromagnetism is correct but the Newtonian Mechanics has to be re-established. Since then the Theory was almost always presented in this way by both Einstein and others except only a few. The aim of this paper is to show that the Lorentz formulas can be derived from the Maxwell equations if one pstulates that the total electric charge of an isolated body does not change if it is in motion. To this end one dwells only on the permanence principle of functional equations, which is not a physical but purely mathematical concept. Thus, from one side the Special Relativity becomes a natural issue (or a part) of the Maxwell Theory and, from the other side, the derivation of the transformation rules pertinent to the electromagnetic field becomes straightforward and easy.
