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Yayın Head-on collision of the solitary waves in fluid-filled elastic tubes(Işık University Press, 2018-04-12) Özden, Ali Erinç; Demiray, HilmiIn the present work, by employing the field equations given in [15] and the extended PLK method derived in [9], we have studied the head-on collision of solitary waves in arteries. Introducing a set of stretched coordinates which include some unknown functions characterizing the higher order dispersive effects and the trajectory functions to be determined from the removal of possible secularities that might occur in the solution. Expanding these unknown functions and the field variables into power series of the smallness parameter epsilon and introducing the resulting expansions into the field equations we obtained the sets of partial differential equations. By solving these differential equations and imposing the requirements for the removal of possible secularities we obtained the speed correction terms and the trajectory functions. The results of our calculation show that both the evolution equations and the phase shifts resulting from the head-on collision of solitary waves are quite different from those of Xue [15], who employed the incorrect formulation of Su and Mirie [4]. As opposed to the result of previous works on the same subject, in the present work the phase shifts depend on the amplitudes of both colliding waves.Yayın On progressive wave solution for non-planar KDV equation in a plasma with q-nonextensive electrons and two oppositely charged ions(Işık University Press, 2020) Demiray, Hilmi; El-Zahar, Essam Roshdy; Shan, Shaukat AliIn this paper, the ion-acoustic wave is investigated in a plasma with q-nonextensive electrons and two oppositely charged ions with varying masses. These parameters are found to modify the linear dispersion relation and nonlinear solitary structures. The reductive perturbation method is employed to derive modified Korteweg-de Vries (KdV) equation. To solve the obtained governing evolution equation, the exact solution in the planar geometry is obtained and used to obtain an analytical approximate progressive wave solution for the nonplanar evolution equation. The analytical approximate solution so obtained is compared with the numerical solution of the same nonplanar evolution equation and the results are presented in 2D and 3D figures. The results revealed that both solutions are in good agreement. A parametric study is carried out to investigate the effect of different physical parameters on the nonlinear evolution solution behavior. The obtained solution allows us to study the impact of various plasma parameters on the behavior of the nonplanar ion-acoustic solitons. The suitable application of the present investigations can be found in laboratory plasmas, where oppositely charged ions and nonthermal electrons dwell.Yayın Book Review: Oktay Veliyev. Multidimensional Periodic Schrödinger Operator (Perturbation Theory and Applications)(Işık University Press, 2015) Hasanoğlu, Elman[No abstract available]Yayın Yayın Modulational instability of three dimensional waves in a plasma with vortex electron distribution(Işık University Press, 2019-02-10) Demiray, HilmiIn the present work, employing the three dimensional equations of a plasma composed of a cold electron fluid, hot electrons obeying a trapped / vortex-like distribution, and stationary ions, we study the amplitude modulation of an electron-acoustic waves by use of the conventional reductive perturbation method. Employing the field equations with fractional power type of nonlinearity, we obtained the three dimensional form of the modified nonlinear Schrodinger equation as the evolution equation of the same order of nonlinearity. The modulational instability of the homogeneous harmonic solution is investigated and the criteria for the instability is discussed as a function of the obliqueness angle. The numerical calculations show that the critical value of the wave number of the envelop wave increases with the wave number k of the carrier wave and the obliqueness angle gamma.Yayın A note on the cylindrical waves with transverse distortion in a plasma with vortex electron distribution(Işık University Press, 2020-01-20) Demiray, HilmiIn the present work, employing the conventional reductive perturbation method and the nonlinear field equations of a plasma consisting of a cold electron uid, hot electrons obeying a non-isothermal (trapped/vortex-like) distribution and station-ary ions with transverse distortion, we studied the propagation of nonlinear waves in such a plasma medium and obtained the modified CKP equation. Seeking a progressive wave solution to this evolution equation we obtained the exact analytical solution. It is observed that the speed of the solitary wave is directional dependent and the wave front is not circularly cylindrical surface any more.Yayın Harmonic mappings related to starlike function of complex order ?(Işık University Press, 2014) Aydoğan, Seher MelikeLet SH be the class of harmonic mappings defined by SH = { f = h(z) + g(z) | h(z) = z + ?? n=2 anz?, g(z) = ?? n=1 bnz?} The purpose of this talk is to present some results about harmonic mappings which was introduced by R. M. Robinson [8].Yayın Higher order perturbation expansion for ion-acoustic solitary waves with q-nonextensive nonthermal velocity distribution(Işık University Press, 2018-09-11) Demiray, HilmiThe basic nonlinear equations describing the dynamics of a two component plasma consisting of cold positive ions and electrons obeying hybrid q-nonextensive nonthermal velocity distribution are examined through the use of modified PLK formalism and the reductive perturbation method and obtained the KdV equation for the lowest order term in the perturbation expansion. The method is further extended to include the contribution of higher order terms in the expansion; the evolution equation for the second order term is found to be the degenerate(linearized) KdV equation with non-homogeneous term. Seekink the localized travelling wave solution (solitons) to these evolution equations we obtained the speed correction terms and the wave profiles. Numerical results for the set of suitable parameters( Williams et. al. [23]) are shown inb the form of some graphs. The combined effect of nonextensive parameter (q) and the nonthermal parameter (alpha) on the soliton dynamics has also been studied.Yayın Some results on a subclass of harmonic mappings of order alpha(Işık University Press, 2014) Varol, Dürdane; Aydoğan, Seher Melike; Owa, ShigeyoshiLet S-H be the class of harmonic mappings defined by S-H - {f - h(z) + <(g(z))over bar> vertical bar h(z) - z + Sigma(infinity)(n=2)a(n)z(n) , g(z) - b(1)z + Sigma(infinity)(n=2) b(n)z(n), b(1) < 1} where h(z) and g(z) are analytic. Additionally f(z) is an element of S-H(alpha) double left right arrow vertical bar zh'(z) - <(zg'(z))over bar>/h(z) + <(g(z))over bar> - 1-(b(1)) over bar /1+(b(1)) over bar vertical bar < vertical bar 1 - <(b(1))over bar>/1 + (b(1)) over bar vertical bar - alpha, z is an element of u, 0 <= alpha < 1 - <(b(1))over bar>/1 + (b(1)) over bar In the present work, by considering the analyticity of the functions defined by R. M. Robinson [7], we discuss the applications to the harmonic mappings.Yayın An application of modified reductive perturbation method to symmetric regularized-long-wave(Işık University Press, 2011-03-24) Demiray, HilmiIn this work, we extended the application of "the modified reductive perturbation method" to symmetrical regularized long waves with quadratic nonlinearity and obtained various form of KdV equations as the governing equations. Seeking a localized travelling wave solutions to these evolution equations we determined the scale parameters g(1) and g(2) so as to remove the possible secularities that might occur. To indicate the power and elegance of the present method, we compared our result with the exact travelling wave solution of the symmetric regularized long-wave equation with quadratic nonlinearity. These results show that for weakly nonlinear case the solutions for both approaches coincide with each other. The present method is seen to be fairly simple as compared to the renormalization method of Kodama and Taniuti [4] and the multiple scale expansion method of Kraenkel et al [6].
