Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/260
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Article Prunable collision free random interleaver design(Springer, 2012) Gazi, OrhanIn this article we introduce a new collision free prunable random interleaver. The suggested interleaver is a joint structure involving rectangular and S-random interleaver. It comprises a general model for all kind of collision free prunable random interleavers. In addition, it can be designed for any number of parallel processors and any length of information sequence vector and can be considered also as a template for collision free prunable interleavers. The proposed interleaver can be used with all kind of turbo-like codes. The performance of the proposed interleaver is measured with parallel decodable serially concatenated convolutional codes (PDSCCCs) and compared to the PDSCCCs' performance with collision full S-random interleaver.Article Citation - WoS: 1Citation - Scopus: 2Physical Optics Approach To Wave Diffraction by a Perfect Electromagnetic Conductor Half-Plane(Springer, 2021) Umul, Yusuf ZiyaThe scattering of electromagnetic plane waves by a perfect electromagnetic conductor is investigated. The method of physical optics is used for the analysis of the problem. The reflected fields by a whole-plane are taken into account. The surface electric and magnetic current densities are constructed with the aid of the incident wave and the reflected field from the whole-surface. The scattering integrals are obtained for the electric and magnetic vector potentials. The scattered electric and magnetic fields are expressed in terms of the vector potentials. The scattering integrals are evaluated asymptotically for large values of the wave-number. Some numerical results are given.Article Citation - WoS: 15Citation - Scopus: 16Binary Phase Shift Keying-Subcarrier Intensity Modulation Performance in Weak Oceanic Turbulence(Elsevier, 2019) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin CanerThe performance analysis of underwater wireless optical communication (UWOC) system that employs binary phase shift keying-subcarrier intensity modulation (BPSK-SIM) is investigated in weak oceanic turbulence. BPSK-SIM Gaussian beam and finite sized positive-intrinsic-negative (PIN) photodetector are employed at the transmitter and at the receiver, respectively. Bit error rate (BER) is taken as the performance indicator and in the evaluation of the BER, the required signal power and the aperture averaged scintillation index are obtained respectively by the use of the extended Huygens-Fresnel principle and the Rytov theory. Considering various noise types in underwater turbulence, BER variations are examined versus the oceanic turbulence parameters and the photodetector parameters, namely receiver aperture diameter, PIN-responsivity, noise factor, load resistor, and the electronic bandwidth. (c) 2019 Elsevier B.V. All rights reserved.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: 7Citation - Scopus: 7Structure and Dynamical Properties of Aun, N=12-14 Clusters: Molecular Dynamics Simulation(World Scientific Publ Co Pte Ltd, 2005) Yildirim, EK; Atis, M; Güvenç, ZBUsing molecular dynamics and thermal quenching methods on the basis of Voter-Chen version of the embedded-atom method, we have studied the melting behavior of Au-N (N = 12, 13, 14) clusters. This behavior is described in terms of overall and atom resolved root-mean-square bond-length fluctuations, specific-heat, short- and long-time average coordination numbers of each atom and short-time average temperatures of the clusters. The isomer sampling probabilities are obtained from the thermal quenching of the molten clusters, and their energy-spectrum widths are investigated. Phase change of a cluster takes place with the collective and simultaneous motion of all the atoms.Article Citation - WoS: 34Citation - Scopus: 35Average Transmittance in Turbulence for Partially Coherent Sources(Elsevier, 2004) Baykal, YAverage intensity and power-transmittance in turbulence are formulated for a source with arbitrary degree of coherence (both spatial and temporal). Average power-transmittance is shown to reduce to the average intensity-transmittance if the receiver dimension is much less than the beam size. The average transmittance is found to attain its minimum value when the source is on the order of the Fresnel zone, irrespective of the degree of coherence of the source. We obtain the correct average intensity when the source is coherent, partially coherent and incoherent. Average transmittances due to turbulence are found for practical FSO (Free Space Optics) communication links. (C) 2003 Elsevier B.V. All rights reserved.Article Citation - WoS: 27Citation - Scopus: 28Beam Wander of J 0- and I 0-Bessel Gaussian Beams Propagating in Turbulent Atmosphere(Springer, 2010) Eyyuboglu, H. T.; Baykal, Y.; Korotkova, O.; Cai, Y.; Cil, C. Z.Root mean square (rms) beam wander of J (0)-Bessel Gaussian and I (0)-Bessel Gaussian beams, normalized by the rms beam wander of the fundamental Gaussian beam, is evaluated in atmospheric turbulence. Our formulation is based on the first and the second statistical moments obtained from the Rytov series. It is found that after propagating in atmospheric turbulence, the collimated J (0)-Bessel Gaussian and the I (0)-Bessel Gaussian beams have smaller rms beam wander than that of the Gaussian beam, regardless of the choice of Bessel width parameter. However, the extent of such an advantage depends on the chosen width parameter, Gaussian source size, propagation distance and the wavelength. Focusing at finite distances of the considered beams causes the rms beam wander to decrease sharply at the propagation distances equal to the focusing parameter.Article Citation - WoS: 18Citation - Scopus: 19Reaction Dynamics of Nin (N=19 and 20) With D2: Dependence on Cluster Size, Temperature and Initial Rovibrational States of the Molecule(World Scientific Publ Co Pte Ltd, 2005) Böyükata, M; Güvenç, ZB; Özçelik, S; Durmus, P; Jellinek, JThe Ni(n)(n = 19, 20) + D2(v, j) collision systems have been studied to investigate the dependence of cluster reactivity on the cluster temperature and the initial rovibrational states of the molecule using quasiclassical molecular dynamics simulations. The clusters are described by an embedded atom potential, whereas the interaction between the molecule and the cluster is modeled by a LEPS (London-Eyring-Polani-Sato) potential energy function. Reaction (dissociative adsorption) cross-sections are computed as functions of the collision energy for different initial rovibrational states of the molecule and for different temperatures of the clusters. Rovibrational, temperature and size-dependent rate constants are also presented, and the results are compared with earlier studies. Initial vibrational excitation of the molecule increases the reaction cross-section more efficiently than the initial rotational excitation. The reaction cross-sections strongly depend on the collision energies below 0.1 eV.Article Citation - WoS: 6Citation - Scopus: 7Bombardment of Ni(100) Surface With Low-Energy Argons: Molecular Dynamics Simulations(Elsevier Science Sa, 2005) Güvenç, ZB; Hippler, R; Jackson, BResults of molecular dynamics simulations of the sputtering of Ni(100) by Ar atoms are reported. The solid is described by an embedded atom potential, and the interaction between the projectile and the metal atoms is modelled by a Morse-like function. Processes leading to Ni atom emissions from the lattice are analysed over the energy range of 70-80 eV In this energy range cluster (larger than three atoms) emission is not observed. The maximum penetration depth of Ar, the kinetic energy and angular distributions of the reflected Ar, and the sputtered Ni atoms are evaluated as functions of the impact energy and sputtering time. The computed sputtering yield is compared with the available theoretical and experimental data. (C) 2004 Elsevier B.V. All rights reserved.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.