Elektronik ve Haberleşme Mühendisliği Bölümü

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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.; 06.08. Mekatronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
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.; 42699; 06.02. Elektronik ve Haberleşme Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
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.; 7688; 7812; 06.02. Elektronik ve Haberleşme Mühendisliği; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
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; 7812; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
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: 5
Citation - Scopus: 5
Boundary Diffraction Wave Theory of Junctions Between Two Surfaces With Different Face Impedances
(Elsevier Sci Ltd, 2012) Umul, Yusuf Ziya; 42699; 06.02. Elektronik ve Haberleşme Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
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: 10
Citation - Scopus: 11
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; 7812; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
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.; 42699; 06.02. Elektronik ve Haberleşme Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
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.; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
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.; 1155; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
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.; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
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.; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
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: 3
Citation - Scopus: 4
Diffraction of Plane Waves by a Black Wedge
(Elsevier Sci Ltd, 2010) Umul, Yusuf Z.; 42699; 06.02. Elektronik ve Haberleşme Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
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: 41
Citation - Scopus: 42
Eley-Rideal and Hot Atom Reactions Between Hydrogen Atoms on Ni(100): Electronic Structure and Quasiclassical Studies
(Amer inst Physics, 2001) Guvenc, ZB; Sha, XW; Jackson, B; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The reactions of gas-phase H (or D) atoms with D (or H) atoms adsorbed onto a Ni(100) surface are studied. Electronic structure calculations based on density functional theory are used to examine the interaction of H atoms with the Ni(100) surface, as well as the interactions between two H atoms near the metal surface. A model potential-energy surface based on ideas from effective medium theory is fit to the results of these electronic structure calculations. Quasiclassical trajectory methods are used to simulate the interaction of low energy H and D atom beams with H and D-covered Ni(100) surfaces. It is found that hot-atom processes dominate the formation of molecular hydrogen. The distribution of energy in the product molecules is examined with regard to the various pathways available for reaction. The initial adsorbate coverage is varied and is shown to control the relative amounts of reflection, reaction, sticking, and subsurface penetration. Our results are compared with those from similar studies on Cu(111) and available experimental data for Ni(100). (C) 2001 American Institute of Physics.
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; 19325; 01. Çankaya Üniversitesi; 06. Mühendislik Fakültesi; 06.03. Elektrik-Elektronik Mühendisliği
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: 29
Citation - Scopus: 30
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.; 7688; 06.02. Elektronik ve Haberleşme Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
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.
Citation - WoS: 17
Citation - Scopus: 18
Field Correlations of Flat-Topped Gaussian and Annular Beams in Turbulence
(Elsevier Sci Ltd, 2011) Baykal, Yahya; 7812; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Starting from the second order moment formulation for multi-beam incidence, field correlations at the receiver plane of flat-topped Gaussian and annular beams are found in turbulence. Reflecting the information on both the randomness due to turbulence and the field profile of the incident field, field correlations of the fiat-topped Gaussian beams are found to become larger at larger source size, smaller flatness parameters and smaller turbulence strengths. For the annular beam structures, field correlations are larger for thicker beams. Field correlations of larger primary beam sized annular incidences are smaller at smaller diagonal distances and larger at larger diagonal distances. As expected, annular beam field correlations are found to be larger at smaller structure constants and at smaller wavelengths. However, at large link lengths, field correlations could be larger than at smaller link lengths due to fact that for annular beams, the field at the centre of the receiver attains very small value at smaller link lengths, however, on propagation in turbulence, receiver field distribution changes to a Gaussian profile. (C) 2011 Elsevier Ltd. All rights reserved.
Citation - WoS: 5
Citation - Scopus: 5
Fringe Waves in an Impedance Half-Plane
(Emw Publishing, 2013) Basdemir, Husnu D.; 20399; 01. Çankaya Üniversitesi; 06.02. Elektronik ve Haberleşme Mühendisliği; 06. Mühendislik Fakültesi
The uniform expressions of scalar fringe waves which are based on the physical theory of diffraction (PTD) were obtained for the impedance half plane in terms of the Fresnel integrals. Asymptotic and uniform forms of the fringe fields were compared. The radiated fields of the fringe expressions were analyzed numerically.
Citation - WoS: 3
Citation - Scopus: 4
General Formulation of the Edge-Diffracted Paraxial Waves
(Elsevier Sci Ltd, 2009) Umul, Yusuf Z.; 42699; 06.02. Elektronik ve Haberleşme Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
A general formula for edge-diffracted paraxial waves is derived in terms of the Fourier integral transform. It is observed that the scattered paraxial wave can be divided into components of the geometrical optics and diffracted fields in the spectral domain. An edge-diffracted Gaussian beam is examined numerically as an application of the formula. (C) 2008 Elsevier Ltd. All rights reserved.
Citation - WoS: 11
Citation - Scopus: 11
Generalized Expression for Optical Source Fields
(Elsevier Sci Ltd, 2012) Kamacioglu, Canan; Baykal, Yahya; 7812; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
A generalized optical beam expression is developed that presents the majority of the existing optical source fields such as Bessel, Laguerre-Gaussian, dark hollow, bottle, super Gaussian, Lorentz, super-Lorentz, flat-topped, Hermite-sinusoidal-Gaussian, sinusoidal-Gaussian, annular, Gauss-Legendre, vortex, also their higher order modes with their truncated, elegant and elliptical versions. Source intensity profiles derived from the generalized optical source beam fields are checked to match the intensity profiles of many individual known beam types. Source intensities for several interesting beam combinations are presented. Our generalized optical source beam field expression can be used to examine both the source characteristics and the propagation properties of many different optical beams in a single formulation. (C) 2012 Elsevier Ltd. All rights reserved.
Citation - WoS: 11
Citation - Scopus: 10
H(D) → D(H)+cu Collision System: Molecular Dynamics Study of Surface Temperature Effects
(Amer inst Physics, 2011) Vurdu, Can D.; Guvenc, Ziya B.; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
All the channels of the reaction dynamics of gas-phase H (or D) atoms with D (or H) atoms adsorbed onto a Cu(111) surface have been studied by quasiclassical constant energy molecular dynamics simulations. The surface is flexible and is prepared at different temperature values, such as 30 K, 94 K, and 160 K. The adsorbates were distributed randomly on the surface to create 0.18 ML, 0.28 ML, and 0.50 ML of coverages. The multi-layer slab is mimicked by a many-body embedded-atom potential energy function. The slab atoms can move according to the exerted external forces. Treating the slab atoms non-rigid has an important effect on the dynamics of the projectile atom and adsorbates. Significant energy transfer from the projectile atom to the surface lattice atoms takes place especially during the first impact that modifies significantly the details of the dynamics of the collisions. Effects of the different temperatures of the slab are investigated in this study. Interaction between the surface atoms and the adsorbates is modeled by a modified London-Eyring-Polanyi-Sato (LEPS) function. The LEPS parameters are determined by using the total energy values which were calculated by a density functional theory and a generalized gradient approximation for an exchange-correlation energy for many different orientations, and locations of one-and two-hydrogen atoms on the Cu(111) surface. The rms value of the fitting procedure is about 0.16 eV. Many different channels of the processes on the surface have been examined, such as inelastic reflection of the incident hydrogen, subsurface penetration of the incident projectile and adsorbates, sticking of the incident atom on the surface. In addition, hot-atom and Eley-Rideal direct processes are investigated. The hot-atom process is found to be more significant than the Eley-Rideal process. Furthermore, the rate of subsurface penetration is larger than the sticking rate on the surface. In addition, these results are compared and analyzed as a function of the surface temperatures. (c) 2011 American Institute of Physics. [doi:10.1063/1.3583811]

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