Elektrik Elektronik Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/411
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Article Citation - WoS: 3Citation - Scopus: 2Correlations of Multimode Optical Incidences in a Turbulent Biological Tissue(Optica Publishing Group, 2023) Gokce, Muhsin Caner; Gerekcioglu, Hamza; Ata, Yalin; Baykal, Yahya; Gerçekcioğlu, HamzaIn a turbulent biological tissue, field correlations at the observation plane are found when a multimode optical incidence is used. For different multimode structures, variations of the multimode field correlations are evaluated against the biological tissue turbulence parameters, i.e., the strength coefficient of the refractive-index fluctuations, fractal dimension, characteristic length of heterogeneity, and the small length-scale factor. Using a chosen multimode content, for specific biological tissue types of liver parenchyma (mouse), intestinal epithelium (mouse), upper dermis (human), and deep dermis (mouse), field correlations are evaluated versus the strength coefficient of the refractive-index fluctuations and small length-scale factor. Again, with a chosen multimode content, behavior of the field correlations is studied against the strength coefficient of the refractive-index fluctuations for various diagonal lengths and the transverse coordinate at the observation plane. Finally, the field correlation versus the strength coefficient of the refractive-index fluctuations is reported for different single modes, which are special cases of multimode excitation. This topic is being reported in the literature for the first time, to our knowledge, and the presented results can be employed in many important biological tissue applications. (c) 2023 Optica PublishingArticle Citation - WoS: 1Citation - Scopus: 3Performance of a Free-Space Optical Communication System Employing Receive Diversity Techniques in Anisotropic Atmospheric Non-Kolmogorov Turbulence(Optica Publishing Group, 2022) Gokce, Muhsin Caner; Ata, Yalcin; Baykal, YahyaIn this paper, bit error rate (BER) performance of a free-space optical communication (FSOC) system operating in anisotropic non-Kolmogorov weak turbulence is investigated together with the spatial diversity techniques. The spatial diversity techniques are implemented as maximum ratio combining (MRC), equal gain combining (EGC), and selection combining (SC) and applied to the receiver. The propagating beam is the Gaussian beam wave, and the modulation scheme is binary phase-shift keying (BPSK). Results are obtained for various parameters such as the anisotropy factor, non-Kolmogorov power law exponent, photodetector responsivity, equivalent load resistor, electronic bandwidth, Gaussian beam radius, wavelength, propagation distance, and turbulence structure constant. It is found that the spatial diversity technique used at the receiver causes significant improvement in the performance of an FSOC system under the conditions of anisotropic non-Kolmogorov atmospheric turbulence. It is also observed that BER performance improves as the atmospheric turbulence becomes more anisotropic. Among the spatial diversity techniques, SC is inferior to EGC and EGC is inferior toMRC in terms of BER performance. (C) 2022 Optica Publishing GroupArticle Citation - WoS: 1Citation - Scopus: 1Sustainable Management of a Renewable Fishery Resource With Depensation Dynamics From a Control Systems Perspective(Gazi Univ, 2022) Cıfdaloz, OguzhanHuman societies are exploiting natural renewable sources such as fisheries, forests, groundwater basins, rivers, and soil at an increasing intensity. Around the world, these resources are being managed by various institutions or governments. One of the challenges faced by institutions is to develop strategies and policies to effectively manage these renewable resources under social and ecological uncertainties, disturbances, policy implementation difficulties, and measurement errors. In this paper, a fishery is considered as an example and the problem of managing a fishery is approached from a control systems perspective. The justification behind this approach is due to the observation that the problem of managing a renewable resource can be posed as a control systems problem and that the discipline of control systems possesses tools and methods to deal with model uncertainties, external disturbances, measurement errors and implementation issues. For the fishery, a depensation type population dynamics model is considered. Depensatory models are used in social/ecological systems in order to model dynamics of certain species of fish populations. An optimal control strategy based on Pontryagin’s Maximum Principle is derived and its sustainability and robustness properties with respect to parametric uncertainties, measurement errors and disturbances are examined. Finally, a sub-optimal but more robust control strategy is proposed and its robustness properties are provided. The main objective of the paper is to show that a control systems engineering approach can be applied to a social-ecological problem and it can provide easy to implement management strategies, insight, and guidance into the management of renewable resources.Article Citation - WoS: 7Citation - Scopus: 8Field Correlations of Partially Coherent Optical Beams in Underwater Turbulence(Optica Publishing Group, 2022) Baykal, Yahya; Gercekcioglu, HamzaField correlations of partially coherent optical beams at the receiver plane are formulated and evaluated in underwater turbulence. Variations of the field correlations are examined against changes in the degree of source coherence, diagonal length from the receiver point, receiver point, propagation distance, source size, ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of mean-squared temperature, and rate of dissipation of kinetic energy per unit mass of fluid. Under any underwater turbulence and link conditions, it is found that field correlations at the receiver plane reduce when the optical source becomes less coherent. (c) 2022 Optica Publishing GroupArticle Citation - WoS: 3Citation - Scopus: 3Field Correlations of a Partially Coherent Optical Gaussian Wave in Tissue Turbulence(Optica Publishing Group, 2022) Baykal, YahyaFor a partially coherent Gaussian optical wave, field correlations in turbulent tissues are examined. Changes in the field correlations are evaluated when the degree of source coherence, diagonal length from the receiver point, transverse receiver coordinate, tissue type, tissue length, source size, characteristic length of heterogeneity, strength coefficient of the refractive-index fluctuations, fractal dimension, and the small length-scale factor of the turbulent tissue vary. Investigated turbulent tissue types are liver parenchyma (mouse), upper dermis (human), intestinal epithelium (mouse), and deep dermis (mouse). For all the examined tissue types, field correlations are found to increase as the degree of source coherence, fractal dimension, and small length-scale factor increase and as the diagonal length from the receiver point, transverse receiver coordinate, tissue length, characteristic length of heterogeneity, and strength coefficient of the refractive-index fluctuations decrease. For the coherent source, an increase in the source size will increase the field correlations; however, for the partially coherent source, this trend is reversed. (c) 2022 Optica Publishing GroupArticle Citation - WoS: 1Citation - Scopus: 1Design Studies of Vsc Hvdc Converter According To Ac Voltage Tests(Mdpi, 2022) Iskender, Ires; Haliloglu, Ali BurhanSince high-voltage direct current (HVDC) systems are very expensive and operationally critical, these systems must be tested before they are put into service. Insulation and performance tests are the two main subjects of these tests. AC voltage tests, as part of the insulation tests, should be performed after system installation is complete and before commissioning. However, in this study, the objective was to perform these tests during the prototype phase of VSC HVDC. Unlike other studies, this study attempted to use COMSOL Multiphysics to determine in advance the problems that may occur in the real system. In this regard, the busbars connecting the submodules of the VSC HVDC system were first modeled in 3D, and the tests to be performed were simulated using COMSOL Multiphysics software. During the simulation, the finite element method (FEM) was used to identify critical points that could cause partial discharge. To validate the simulation results, partial discharge tests on a real system were conducted, and the design changes made in response to each test result were explained. After the improvement actions, the targeted partial discharge values were achieved.Article Citation - WoS: 5Citation - Scopus: 7Analysis of Wander and Spreading of an Optical Beam by Using the Oceanic Turbulence Optical Power Spectrum(Optica Publishing Group, 2022) Baykal, Yahya; Gokce, Muhsin Caner; Ata, YalcInVariance of beam displacement and short-term and long-term spreading of a Gaussian beam propagating in the presence of underwater turbulence are examined by using the oceanic turbulence optical power spectrum (OTOPS). Analytical expressions for both beam wander displacement variance and beam spreading are presented. Results show that the underwater turbulent channel causes deflection from the on-axis mean irradiance and brings significant wander and spreading effects to the propagating Gaussian beam wave. The variations of beam wander and short- and long-term spreading are obtained depending on the underwater medium parameters such as the average temperature, average salinity concentration, temperature-salinity gradient ratio, and temperature and energy dissipation rates. In particular, the real values of the average temperature and salinity concentration of turbulent water are used to obtain the results. In addition, the effects of propagation distance, Gaussian beam source size, and wavelength are shown. The results demonstrate that the underwater turbulent channel brings displacements in the centroid and spreading of the optical beam. (C) 2022 Optica Publishing GroupArticle Citation - WoS: 4Citation - Scopus: 5Accurate Method To Calculate Noise Figure in a Low Noise Amplifier: Quantum Theory Analysis(Elsevier Sci Ltd, 2022) Salmanogli, Ahmad; Gecim, H. SelcukIn this study, a low-noise amplifier is quantum-mechanically analyzed to study the behavior of the noise figure. The analysis view has been changed from classic to quantum, because using quantum theory produces some degrees of freedom, which may be ignored when a circuit is analyzed using classical theory. For this purpose, the Lagrangian is initially derived by considering the related nonlinearity of the transistor, and then using the Legendre transformation and canonical quantization procedure, the quantum Hamiltonian is derived. As an interesting point of this study, the low-noise amplifier is deliberately considered as two oscillators connecting to each other to share the photonic modes between them; accordingly, the voltage and current as measurable observations and the noise figure as a critical quantity in a low-noise amplifier are theoretically expressed in terms of the oscillator's mean photon number. The main goal of this work is to study quantities such as the noise figure in a sufficient detail using quantum theory. In addition, as an advantage of this theory, one can control and manipulate the noise figure only by manipulation of the oscillator's mean photon number and coupling it between two oscillators. Finally, the circuit is classically designed and simulated to verify the derived results using quantum theory. The comparison results show that there is a partial consistency between the two approaches; as the frequency increases, the noise figure becomes minimized at a particular frequency.Article Beam wander of J 0- and i 0-Bessel Gaussian beams propagating in turbulent atmosphere(2010) Çil, C.Z.; Eyyuboğlu, H.T.; Baykal, Y.; Korotkova, O.; Cai, Y.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: 3Citation - Scopus: 2Modulation Transfer Function Variation Through Anisotropic Turbulence in Biological Tissue(Optica Publishing Group, 2023) Gokce, Muhsin Caner; Baykal, Yahya; Ata, YalcinAnalysis of the long-exposure modulation transfer function (MTF) is performed for optical imaging using plane and spherical waves through anisotropic turbulence in biological tissues. To obtain the MTF, the wave structure functions of plane and spherical waves are obtained in closed-form expressions. Results are presented depending on various parameters of the turbulent medium and optical beam. The positive effect of anisotropy on optical imaging is remarkable in turbulent biological tissues. Besides scattering and absorption, taking anisotropy into account as well as turbulence will lead to a more accurate description of the performance of the medical imaging systems that use optical spectrums in biological tissues. (c) 2023 Optica Publishing Group