Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/260
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Article Citation - WoS: 2Citation - Scopus: 3Diffraction in Time of an Entangled Non-Relativistic Quantum Particle(Iop Publishing Ltd, 2021) Umul, Yusuf ZiyaThe diffraction process of an entangled non-relativistic quantum particle in time domain is investigated. The scenario consists of two entangled spin-0 particles and a quantum shutter, which is opened at an initial time. The particles are traveling in two opposite sides and expressed with a single wave function. The integral solution of the Schrodinger equation is considered for two particles case. The initial condition is expressed in terms of an entangled wave function. The time-diffracted matter wave is obtained in terms of the Fresnel integral. The effect of the phenomenon of diffraction in time is examined numerically for the entangled system of two particles.Article Citation - WoS: 24Citation - Scopus: 24Molecular Dynamics Simulation of the Melting Behaviour of 12-, 13-, 14-Atom Icosahedral Platinum Clusters(Iop Publishing Ltd, 2004) Sebetci, A; Guvenc, ZBUsing the molecular dynamics simulation technique, we have studied the melting behaviour of free, icosahedral Pt-N clusters in the size range of N = 12-14. The Voter and Chen version of an embedded-atom model, derived by fitting to experimental data of both the diatomic molecule and bulk platinum simultaneously, has been employed in this study. We present an atom-resolved analysis method that includes physical quantities such as the root mean square bond-length fluctuation and coordination number for individual atoms as functions of temperature. The results show that while the 13-atom icosahedron and the 12-atom cluster with a vacancy on the icosahedral surface exhibit one-stage melting, the 14-atom cluster with an adatom on the icosahedral surface undergoes two-stage melting, as the temperature increases.Article Citation - WoS: 8Citation - Scopus: 8Comparative Analysis on Wavelet-Based Detection of Finite Duration Low-Amplitude Signals Related To Ventricular Late Potentials(Iop Publishing Ltd, 2004) Mousa, A; Yilmaz, AVentricular late potentials (VLPs) are considered as a noninvasive marker of patients with myocardial infarction, who are prone to the development of ventricular tachycardia. This paper investigates the effects of variations in physical properties of myocardial infarcts in terms of their effects on the parametric variations in VLP analysis. A sufficiently large set of signals underlining the behavior of physical parameters was employed to represent the effect of physical size, position, orientation and type of infarct. The approximated signals are variations from real electrocardiography signals by adding potentials representing late potentials based on duration, frequency, amplitude and position. The aim is not to exactly model VLP but rather to generate an approximate set of signals to examine the performance of the standard methods for different possibilities in infarct dynamics. We investigate some of the detection approaches together with their related assumptions, and try to pinpoint the drawbacks and inaccuracies of these methods and also their assumptions. The three widely accepted criteria-QRS duration, root-mean-square and duration of the signal at the end of QRS for VLP detection-were used in the investigation. Results from the application of these parameters to the set of signals are presented. In addition we investigate the physical nature of an infarct and list a number of possible reasons that might be the cause of a low success rate for the detection of additive potentials. To improve the performance of the common methods, two more wavelet transform parameters are added to those of the standard methods. The method derived from this analysis is presented as an alternative means for the detection of late signals named as delayed potentials, a more general class that includes VLP as a subset.Article Citation - WoS: 3Citation - Scopus: 3Dissociative 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, ZBThe 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.Article Citation - WoS: 3Citation - Scopus: 3Collisionless Fragmentation of Non-Rotating Nin (n=4-14) Clusters: a Molecular Dynamics Study(Iop Publishing Ltd, 2003) Avci, H; Çivi, M; Güvenç, ZB; Jellinek, JCollisionless fragmentation of non-rotating Ni-n (n = 4-14) clusters is studied using micro-canonical molecular dynamics (MD) computer simulations. The clusters are modelled by an embedded-atom potential energy surface. The distributions of the channel-specific fragmentation probabilities, and the global and channel-specific fragmentation rate constants are computed and analysed as functions of the internal energy and size of the clusters. The trends derived from the dynamical calculations are compared to the fragmentation energy patterns, those of the Rice-Ramsperger-Kassel (RRK) and statistical approaches. The rate constants are an order of magnitude smaller for the RRK model than with both the MD and transition-state theory approaches. The results are also compared with the other multi-channel fragmentation works.Article Citation - WoS: 4Citation - Scopus: 4Transmission of a Bessel Beam Through a Circular Aperture in an Impedance Screen(Iop Publishing Ltd, 2014) Umul, Yusuf ZiyaThe scattering effect of a circular aperture, located in an impedance plane, on a Bessel beam is investigated by decomposing the scattered wave into two subcomponents, namely the geometrical optics and diffracted fields. The diffracted waves are investigated with the aid of the geometrical theory of diffraction. The detour parameter is evaluated and the existence zones of the geometrical optics fields are determined. The various aspects of the reflected and transmitted scattered waves, including the self healing of the beam, are studied numerically.Article Citation - WoS: 16Citation - Scopus: 17Sinusoidal Gaussian Beam Field Correlations(Iop Publishing Ltd, 2012) Baykal, YahyaField correlations of sinusoidal Gaussian beams are formulated in turbulence, and specifically cos Gaussian (cG) and cosh Gaussian (chG) beam field correlations are evaluated versus the diagonal length at the receiver plane. The effects of the displacement parameters, the coordinates of the first receiver point and the source sizes on the field correlations of monochromatic light sources having cG and chG field distributions are investigated when such beams traverse turbulent media. Such parameters affect spatial heterodyne measurement. Field correlations found at the receiver plane reflect the combined variations of diffraction patterns and turbulence effects. To differentiate the diffraction patterns and the turbulence effects, field correlations of cG and chG beams in turbulence and in the absence of turbulence are compared. For cG beams, the oscillatory behaviour of the field correlations versus the diagonal length at the receiver plane in the absence of turbulence becomes smoother in the presence of turbulence. The received fields of cG and chG beams become decorrelated at shorter diagonal distances in turbulence.Article Citation - WoS: 8Citation - Scopus: 8Intensity Fluctuations of Partially Coherent Cos Gaussian and Cosh Gaussian Beams in Atmospheric Turbulence(Iop Publishing Ltd, 2011) Eyyuboglu, Halil T.; Cil, Celal Z.; Cai, Yangjian; Korotkova, Olga; Baykal, YahyaOn-axis and off-axis scintillation indices of partially coherent collimated cos Gaussian and cosh Gaussian beams are evaluated on their propagation in a weakly turbulent atmosphere. In the coherent limits, our results are in quite good agreement with those for the existing Rytov scintillation index of coherent cos Gaussian and cosh Gaussian beams, especially for very small and very large sized beams and at weaker turbulence levels. The on-axis scintillation index becomes lower as the degree of source coherence decreases for both cos Gaussian and cosh Gaussian beams. Comparing to the partially coherent Gaussian beam on-axis scintillations, partially coherent cos Gaussian beam scintillations are generally lower and partially coherent cosh Gaussian beam scintillations are higher. Scintillations of Gaussian beams are very close to the scintillations of equal-power cos Gaussian and are quite similar to the scintillations of equal-power cosh Gaussian beams. Off-axis evaluations yield that the scintillations of both cos Gaussian and cosh Gaussian beams increase as the diagonal distance from the origin increases, being valid for all degrees of partial coherence.Article Citation - WoS: 5Minimization Effects on Scintillations of Sinusoidal Gaussian Beams in Strong Turbulence(Iop Publishing Ltd, 2011) Gercekcioglu, Hamza; Baykal, YahyaMinimization effects on the on-axis scintillation index of cos Gaussian (cG) and cosh Gaussian (chG) beams are studied in strong turbulence. In our formulation, the unified solution of the Rytov method, which imposes spatial filtering to extend the solution to the strong turbulence regime, is applied. Our solution correctly reduces to the weak turbulence sinusoidal beam scintillations and the strong turbulence Gaussian beam scintillations. The conditions to minimize the scintillations are found to be focused chG beams. Small scale scintillations mainly determine the overall scintillations of cG and chG beams in strong turbulence. In strong turbulence, increase in the source size decreases the scintillations of collimated cG beams but does not change the scintillations of focused cG beams. Collimated cG beams having larger displacement parameters and large focal lengths show smaller scintillations in the strong regime. Change in the displacement parameters for collimated and focused chG beams and the focal length of focused chG beams do not considerably vary their scintillations in strong turbulence.Article Citation - WoS: 14Citation - Scopus: 15Closed Form Series Solution of the Diffraction Problem of Plane Waves by an Impedance Half-Plane(Iop Publishing Ltd, 2009) Umul, Yusuf Z.The scattering problem of plane waves by an impedance half-plane is solved by using the method of separation of variables, and a closed form series expression, which separately reduces to the cases of soft and hard half-planes, is obtained. The results are investigated numerically and compared with the solutions in the literature.