Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/260

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Citation - WoS: 12
Citation - Scopus: 17
Abstraction-Based Verification of Codiagnosability for Discrete Event Systems
(Pergamon-elsevier Science Ltd, 2010) Schmidt, K.
In this paper, we investigate the verification of codiagnosability for discrete event systems (DES). That is, it is desired to ascertain if the occurrence of system faults can be detected based on the information of multiple local sites that partially observe the overall DES. As an improvement of existing codiagnosability tests that resort to the original DES with a potentially computationally infeasible state space, we propose a method that employs an abstracted system model on a smaller state space for the codiagnosability verification. Furthermore, we show that this abstraction can be computed without explicitly evaluating the state space of the original model in the practical case where the DES is composed of multiple subsystems. (c) 2010 Elsevier Ltd. All rights reserved.
Citation - WoS: 4
Citation - Scopus: 5
Application of the Complex Point Source Method To the Schrodinger Equation
(Elsevier Sci Ltd, 2010) Umul, Yusuf Z.
The paraxial wave equation is a reduced form of the Helmholtz equation. Its solutions can be directly obtained from the solutions of the Helmholtz equation by using the method of complex point source. We applied the same logic to quantum mechanics, because the Schrodinger equation is parabolic in nature as the paraxial wave equation. We defined a differential equation, which is analogous to the Helmholtz equation for quantum mechanics and derived the solutions of the Schrodinger equation by taking into account the solutions of this equation with the method of complex point source. The method is applied to the problem of diffraction of matter waves by a shutter. (C) 2010 Elsevier Ltd. All rights reserved.
Citation - WoS: 73
Citation - Scopus: 80
Average Intensity and Spreading of Partially Coherent Standard and Elegant Laguerre-Gaussian Beams in Turbulent Atmosphere
(Emw Publishing, 2010) Wang, F.; Cai, Y.; Eyyuboglu, H. T.; Baykal, Y.
Analytical expressions for the average intensity, mean-squared beam width and angular spread of partially coherent standard and elegant Laguerre-Gaussian (LG) beams propagating in turbulent atmosphere are derived. The properties of the average intensity, spreading and directionality of partially coherent standard and elegant LG beams in turbulent atmosphere are studied numerically and comparatively. It is found that the beam parameters and structure constant of turbulence together determine the properties of the beams in turbulent atmosphere. Partially coherent standard and elegant LG beams with smaller coherence length, larger beam orders and longer wavelength are less affected by the turbulence. A partially coherent elegant LG beam is less affected by turbulence than a partially coherent standard LG beam under the same condition. Furthermore, it is found that there exist equivalent partially coherent standard and elegant LG beams, equivalent fully coherent standard and elegant LG beams, equivalent Gaussian Schell-model beams that may have the same directionality as a fully coherent Gaussian beam both in free space and in turbulent atmosphere. Our results will be useful in long distance free-space optical communications.
Citation - WoS: 12
Citation - Scopus: 12
Averaging of Receiver Aperture for Flat-Topped Incidence
(Elsevier Sci Ltd, 2013) Kamacioglu, Canan; Baykal, Yahya; Yazgan, Erdem
Using a flat-topped profile for the incident beam, the power scintillation index for weak atmospheric turbulence is formulated and analytically evaluated. Through the use of the aperture averaging factor, the averaging effect of the finite receiver aperture on the intensity fluctuations for a flat-topped incident beam is examined. The influence of the order of flatness on the averaging is investigated. At large propagation lengths, increasing the flatness parameter decreases the power scintillations and it is possible to further reduce the scintillation by increasing the receiver aperture. Increasing the structure constant increases this effect. (C) 2013 Elsevier Ltd. All rights reserved.
Citation - WoS: 4
Citation - Scopus: 4
Boundary Diffraction Wave Theory Approach To Corner Diffraction
(Springer, 2019) Umul, Yusuf Ziya
The scattering process of plane waves by a discontinuous edge contour is studied with the three dimensional boundary diffraction wave theory. The edge and corner diffracted fields are obtained from the stationary phase and edge point evaluations of the line integral. A new corner diffraction coefficient is derived. The behaviors of the uniform edge and corner diffracted waves are investigated numerically.
Citation - WoS: 5
Citation - Scopus: 5
Boundary Diffraction Wave Theory of Junctions Between Two Surfaces With Different Face Impedances
(Elsevier Sci Ltd, 2012) Umul, Yusuf Ziya
The line integral of the boundary diffraction wave theory is derived for the diffraction process of waves by a junction between two surfaces with different face impedances. The exact solution of Maliuzhinets is used with this aim. The resultant integral is applied to the diffraction of waves by a circular junction between two impedance surfaces. The results are examined numerically. (C) 2011 Elsevier Ltd. All rights reserved.
Citation - WoS: 11
Citation - Scopus: 12
Changes of the Centroid Position of Laser Beams Propagating Through an Optical System in Turbulent Atmosphere
(Elsevier Sci Ltd, 2013) Ji, Xiaoling; Baykal, Yahya; Jia, Xinhong
In this paper, the effects of atmospheric turbulence, initial field amplitude, optical system and thermal blooming on the centroid position of laser beams propagating through the atmosphere are studied in detail. With the average over the ensemble of the turbulent medium, the centroid position is independent of turbulence. However, the centroid position depends on the centroid positions at the source plane and in the far-field, and the elements of ray-transfer-matrix. The physical reason why the centroid position changes on propagation is that the far-field centroid position is not located on the propagation z-axis due to the field phase distortion and the decentred intensity. The centroid position of laser beams with the spherical aberration and the decentred intensity is examined analytically. When laser beams with the decentred intensity propagate through the atmosphere, the effect of thermal blooming on the centroid position is investigated by using the four-dimensional (4D) computer code of the time-dependent propagation of high power laser beams through the atmosphere. (C) 2013 Elsevier Ltd. All rights reserved.
Citation - WoS: 5
Citation - Scopus: 5
Comments on "on the Modified Theory of Physical Optics
(Ieee-inst Electrical Electronics Engineers inc, 2014) Umul, Yusuf Z.
Citation - WoS: 45
Citation - Scopus: 47
Density Functional Study of Albn Clusters for N=1-14
(Elsevier Science Sa, 2011) Boyukata, Mustafa; Guvenc, Ziya B.
Density functional theory (DFT) B3LYP at 6-311++G(d,p) level is employed to optimize the structures of AlBn (n = 1-14) microclusters. Analysis of the energetic and structural stability of these clusters and their various isomers are presented. Total and binding energies of the clusters have been calculated. Their harmonic frequencies, point symmetries, and the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gaps have been determined. Results are evaluated by comparing to the previous similar works. (C) 2011 Elsevier B.V. All rights reserved.
Citation - WoS: 15
Citation - Scopus: 15
A Density Functional Study of Small Li-B and Li-B Clusters
(Pergamon-elsevier Science Ltd, 2009) Yildirim, E. K.; Guvenc, Z. B.
In this work we present the results of a detailed theoretical research for the small LinBm clusters and their hydrogen storage properties by means of density functional theory. All calculations were performed by using Gaussian03 program. For the optimization of the clusters 6-311++G(d,p) basis set was employed. We have chosen global minimum of B-6 cluster as the starting point and replaced the boron atoms one at a time, in a stepwise manner, with Li atoms. For these new structures we have searched for the stable configurations, and calculated their energies, HOMO-LUMO energy gaps, Raman and infrared data, average boron, and lithium charge distribution, and vibrational frequencies. Our results show that as the number of Li atoms increases, stability of the clusters decreases and they become more reactive. In addition to that, there are significant charge transfers from boron atoms to lithium atoms on average. The hydrogen storage capabilities of the most stable isomers of LinBm and B-6 clusters have also been investigated by the same methods, and the results are compared. The Li3B3 has the highest hydrogen storage capacity among the clusters investigated in this study. Furthermore, formation of hydrogen molecules is observed in the vicinity of the clusters, some of which are attached to the Li atoms. In addition, as the number of hydrogen atoms increases, the boron atoms are separated from the other boron atoms, and they form satellite BHx (x = 3,4) clusters around the center. These are attached to the system by a bridging bond of a hydrogen or a Li atom. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Citation - WoS: 4
Citation - Scopus: 3
Developing Interaction Potential for H (2h) → Cu(111) Interaction System: a Numerical Study
(Elsevier Science Bv, 2010) Vurdu, Can D.; Guevenc, Ziya B.
In this study, we have used London-Eyring-Polanyi-Sato (LEPS) functional form as an interaction potential energy function to simulate H (2H) -> Cu(1 1 1) interaction system The parameters of the LEPS function are determined in order to analyze reaction dynamics via molecular dynamics computer simulations of the Cu(1 1 1) surface and H/(2H) system. Nonlinear least-squares method is used to find the LEPS parameters. For this purpose, we use the energy points which were calculated by a density-functional theory method with the generalized gradient approximation including exchange-correlation energy for various configurations of one and two hydrogen atoms on the Cu(1 1 1) surface. After the fitting procedures, two different parameters sets are obtained that the calculated root-mean-square values are close to each other. Using these sets, contour plots of the potential energy surfaces are analyzed for H -> Cu(1 1 1) and 2H -> Cu(1 1 1) interactions systems. In addition. sticking, penetration, and scattering sites on the surface are analyzed by using these sets. (C) 2009 Elsevier B.V. All rights reserved.
Citation - WoS: 13
Dft Study of Al Doped Cage B12hn Clusters
(Pergamon-elsevier Science Ltd, 2011) Boyukata, Mustafa; Guvenc, Ziya B.
Density Functional Theory (DFT) with B3LYP/6-311++g** level has been performed to investigate the electronic structures of cage B12Hn for up to n <= 12 and AlB12Hn for up to n <= 13. Moreover, the computations has been extended to the charged clusters of [B12H12](q), [AlB12H12](q) and [AlB12H13](q) where (q = +/- 1 and +/- 2). Their energetics are calculated and structural analysis have been carried out. Cage form of the B-12 remains stable against to hydrogen adsorptions. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Citation - WoS: 15
Citation - Scopus: 13
Diffraction of Line Source Field by a Resistive Half-Plane Between Isorefractive Media
(Springer, 2017) Umul, Yusuf Ziya
The scattering process of cylindrical waves by a resistive half-plane, residing at the interface of isorefractive media, is investigated. The uniform expression of the diffracted cylindrical waves by a resistive half-screen is obtained for a single medium. Then the initial fields are found for an interface between isorefractive media. The scattered geometrical optics waves are derived by subtracting the initial fields from the total geometrical optics waves when the resistive half-plane exists at the interface. The diffracted fields are determined by using the scattered geometrical optics waves. The behavior of the resultant waves is analyzed numerically.
Citation - WoS: 3
Citation - Scopus: 4
Diffraction of Plane Waves by a Black Wedge
(Elsevier Sci Ltd, 2010) Umul, Yusuf Z.
The scattering of plane waves by a black wedge is examined. Two methods are considered for the solution of the problem. A closed-form series solution is derived by performing the technique of the separation of variables using boundary conditions of Macdonald. The second approach is the method of the modified theory of physical optics. The results are compared numerically. (C) 2009 Elsevier Ltd. All rights reserved.
Citation - WoS: 6
Citation - Scopus: 8
Diffraction of Waves by a Perfect Electromagnetic Conductor Half-Plane Between Isorefractive Media
(Springer, 2019) Basdemir, Husnu Deniz
In this study, diffraction of waves by a perfectly electromagnetic conductor half-plane which is lying at the boundary of isorefractive media is investigated. The diffracted field expressions are constructed by using the relation between scattered geometrical optics fields and the transition boundaries. The high frequency asymptotic expressions of diffracted fields reach infinite magnitude values at the transition boundaries. The uniform expressions of fields are obtained by using the uniform theory of diffraction method in order to obtain the finite magnitude values at the transition boundaries and the results are analyzed numerically for different set of parameters.
Citation - WoS: 3
Citation - Scopus: 3
Dissociative Chemisorption of an H2 (V,j) Molecule on Rigid Ni (100) Surface: Dependence on Surface Topologies and Initial Rovibrational States of the Molecules
(Iop Publishing Ltd, 2005) Evecen, M; Böyükata, M; Çivi, M; Güvenç, ZB
The H-2(v,j)+Ni(100) collision system has been studied to understand the effects of the surface sites and initial rovibrational states of the molecule on molecule-surface interactions, by a quasiclassical molecular dynamic simulation method. Dissociative adsorption of an H-2 molecule on the rigid Ni(100) surface is investigated at topologically different three sites of the surface. Interaction between the molecule and Ni surface was described by a London-Eyring Polani-Sato (LEPS) potential. Dissociative chemisorption probabilities of the H-2(v, j) molecule on various sites of the surface are presented as a function of the translation energies between 0.001-1.0eV. The probabilities obtained at each collision site have unique behaviour. At lower collision energies, indirect processes enhance the reactivity, effects of the rotational excitations and impact sites on the reactivity are more pronounced. The results are compared with the available studies, The physical mechanisms underlying the results and quantum effects are discussed.
Citation - WoS: 2
Citation - Scopus: 3
Dynamical Analysis of Sputtering at Threshold Energy Range: Modelling of Ar+ni(100) Collision System
(Iop Publishing Ltd, 2008) Hundur, Yakup; Guvenc, Ziya B.; Hippler, Rainer
The sputtering process of Ar+Ni(100) collision systems is investigated by means of constant energy molecular dynamics simulations. The Ni(100) slab is mimicked by an embedded-atom potential, and the interaction between the projectile and the surface is modelled by using the reparametrized ZBL potential. Ni atom emission from the lattice is analysed over the range of 20-50 eV collision energy. Sputtering yield, angular and energy distributions of the scattered Ar and of the sputtered Ni atoms are calculated, and compared to the available theoretical and experimental data.
Citation - WoS: 3
Citation - Scopus: 4
Edge Diffraction in an Anomalously Reflecting Half-Plane
(Springer, 2018) Umul, Yusuf Ziya
A half-plane, formed of anomalously reflecting metasurface, is taken into account. The layer is modeled by an impedance half-screen. In order to obtain the diffracted fields, the geometrical optics waves are evaluated as a sum of equivalent soft, hard and impedance surfaces. The diffracted waves are derived by the superposition of the diffracted fields from the equivalent surfaces. The uniform field expressions are obtained by the method of uniform theory of diffraction. The behaviors of the fields are studied numerically.
Citation - WoS: 72
Citation - Scopus: 85
Entropy-Functional Online Adaptive Decision Fusion Framework With Application To Wildfire Detection in Video
(Ieee-inst Electrical Electronics Engineers inc, 2012) Toreyin, Behcet Ugur; Kose, Kivanc; Cetin, A. Enis; Gunay, Osman
In this paper, an entropy-functional-based online adaptive decision fusion (EADF) framework is developed for image analysis and computer vision applications. In this framework, it is assumed that the compound algorithm consists of several subalgorithms, each of which yields its own decision as a real number centered around zero, representing the confidence level of that particular subalgorithm. Decision values are linearly combined with weights that are updated online according to an active fusion method based on performing entropic projections onto convex sets describing subalgorithms. It is assumed that there is an oracle, who is usually a human operator, providing feedback to the decision fusion method. A video-based wildfire detection system was developed to evaluate the performance of the decision fusion algorithm. In this case, image data arrive sequentially, and the oracle is the security guard of the forest lookout tower, verifying the decision of the combined algorithm. The simulation results are presented.
Citation - WoS: 30
Citation - Scopus: 31
Estimation of Aperture Averaged Scintillations in Weak Turbulence Regime for Annular, Sinusoidal and Hyperbolic Gaussian Beams Using Random Phase Screen
(Elsevier Sci Ltd, 2013) Eyyuboglu, Halil T.
Using the random phase screen method, aperture averaged scintillations for annular, sinusoidal and hyperbolic Gaussian beams are estimated. Prior to this estimation, the designed random phase screen setup is tested against the known results of the existing literature from the aspects of receiver intensity distribution, point-like scintillation index and aperture averaged scintillation of spherical and Gaussian beam waves. Having obtained satisfactory results, we then proceed to estimate aperture averaged scintillations for annular, sinusoidal and hyperbolic Gaussian beams. Our findings indicate that at a fixed aperture radius of 5 cm, sine Gaussian beam exhibits the highest scintillation, annular Gaussian beam has on the other hand has the lowest scintillations. When examined against varying aperture sizes, the scintillation ordering of beams does not change. Furthermore, although larger aperture sizes achieve substantial scintillation reductions, the rate of reductions gradually become smaller. (C) 2013 Elsevier Ltd. All rights reserved.

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