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    Design of Broadband RF-DC Converter
    (IEEE, 2016) Dursun, Bekir; Uzun, Yunus
    Almost all of the wireless devices are supplied by chemical batteries. These batteries have a number of disadvantages. In this study, a broadband RF energy harvester was designed to providing the use of wireless devices without batteries or increasing battery life. The system is designed to work between 500 MHz and 900 MHz. Thus, the proposed system can be obtained electrical energy from both DTV and GSM signals at the same time. The system efficiency which is mentioned above frequencies ranges is close to 80% for 0 dBm input power level.
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    The Effects of Overvoltage Aging on 20 kV XLPE Power Cable
    (IEEE, 2019) Uydur, Cihat Cagdas; Arikan, Oktay; Kucukaydin, Baris; Dursun, Bekir; Kumru, Celal Fadil
    XLPE power cables have been widely used with the development of city power grid because of their obvious advantages. To improve the reliability of power supplies and meet the requirements of urban landscaping, however, faults in the electricity distribution grid and load/demand imbalance cause degradation in underground cables. This degradation leads the cable to be aged and reduce its lifetime. Therefore, it is important to examine the behavior of the XLPE insulated cable dielectric parameters. In this study, a 12/20 kV XLPE cable was aged using 60 kV overvoltage and this voltage was applied to the test samples for 15 minutes intervals. 80 cycles of aging were carried out and dissipation factor (tan delta), dielectric losses (P-k) and partial discharge (PD) measurements were performed after each aging cycle. OMICRON CPC100/CPTD1 was used to measure dissipation factor (tans), dielectric losses (Pk) and OMICRON MPD600 was used to measure partial discharge.
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    Energy distributions and radiation emissions in an inertial electrostatic confinement (IEC) device under low and moderate magnetic fields
    (Pergamon-Elsevier Science Ltd, 2017) Dursun, Bekir; Kurt, Erol; Kurt, Hilal
    The energy distributions and electromagnetic emissions of deuterium ions and electrons in an inertial electrostatic confinement (IEC) unit are reported for low and moderate magnetic field cases. The IEC device has a central wire system inside the grid system of the chamber for the production of the azimuthal magnetic field. The real-time simulations are performed by time integration method by using a finite difference method (FDM) for the physical geometry of device. It is observed that the field induces helical trajectories on the particles especially at the central region where the magnetic force is maximized in a fully ionized Deuterium media. The results prove that the particles have rich dynamics in terms of their trajectories. The effect of negative potential and particle particle interaction play important roles to determine the trajectories even for low number of ions and electrons. Ion temperatures are calculated as T-i = 6.9 keV after 6 mu s for low field case and T-i = 1.517 MeV after 22 mu s for medium field case. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    Enhancing Predictive Capabilities: Machine Learning Approaches for Predicting Mechanical Behavior in Friction Stir Welded Aluminum Alloys
    (Springer, 2024) Dorbane, Abdelhakim; Harrou, Fouzi; Dursun, Bekir; Sun, Ying
    Accurate prediction of friction stir welding (FSW) joint behavior is crucial for optimizing welding processes and ensuring structural integrity. This study exploits machine learning to predict the mechanical behavior of aluminum alloy FSW joints under varying temperatures. It involves a comparison of predictive performance across 18 models, including support vector regression (SVR), Gaussian process regression (GPR), ensemble models, and five distinct types of neural networks (NN). The assessment used Al6061-T6 aluminum alloy with the FSW joining method at temperatures of 25, 100, 200, and 300 degrees C. To ensure robustness, the machine learning models were developed using a fivefold cross-validation approach, with Bayesian optimization applied for fine-tuning during training. Results revealed the ability of machine learning to precisely predict the mechanical behavior of FSW joints. Specifically, GPR and the triple NN model outperformed other models, achieving average R2 values of 0.9879 and 0.9703, respectively.
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    Many-body solution to the D2 gas filled inertial electrostatic confinement device
    (Pergamon-Elsevier Science Ltd, 2016) Dursun, Bekir; Kurt, Erol
    The simulations of the electrostatic confinement fusion unit have been presented in low magnetic field case, which is produced by a central wire system inside the grid system of the chamber. The time-dependent simulations have been realized by the time integration together with the finite difference elements (FDE). Especially, FDEs have been used to compute the chamber potential and magnetic field interaction of the particles, namely electrons and ions with the chamber structures. The central wires exert a magnetic field in the azimuthal direction inside the central grid. It is found that this field induces helical trajectories on the particles. The model unit has six cathodes around the center. The system is simulated in a Deuterium media which is fully ionized. Considering the boundaries of the unit, the electrical and magnetic forces are determined by using the many-body technique with the particle-chamber and particle particle interactions. According to the results, many of the electrons can be repelled by the negative potential; however the ions have changeable trajectories with slower attitudes. The ion temperature has been found as T-i = 6.9 keV at the end of 6 mu s. The ion distribution proves that 45% of ions exist inside the grid however the increasing trend of ion temperature proves that this value is to be increased further. The velocity distribution shows a maximum around 5 x 10(5) m/s, however there are also highly energetic particles. (C) 2015 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    Particle Trajectories and Energy Distribution from a New IEC Fusion Device: A Many-Body Approach
    (Springer, 2016) Kurt, Erol; Dursun, Bekir
    This paper reports the explorations on the particle dynamics, ion distribution, energy spectra and temperature in a new-designed inertial electrostatic confinement fusion device in case of low azimuthal magnetic field. The proposed design has six bar-sized cathodes at the vicinity of the central region and a central DC current-carrying bar injects a homogeneous azimuthal magnetic flux on the particles. The cylindrical device is simulated in the fully ionized Deuterium media. Following the 3D design of the chamber, the real-time simulations have been performed by the time integration of the electrical and magnetic forces. The model uses the many-body approach with the particle-particle and particle-chamber interactions. To implement the particle-chamber interaction, the finite difference method has been applied. Besides, the model includes reflection effects of particles from the electrically grounded chamber wall. According to the simulations, the particle trajectories exhibit complex fluctuations in the central region and nearby the chamber walls. The ion temperature has been calculated around T (i) = 35 keV for the source potential V = -150 kV. In addition, the ion distribution indicates that 68 % of ions can be collected in the central region. According to the velocity distribution, there exists a double Gaussian distribution with a low velocity peak. In addition, nearly 61 % of ions stay in the energy scale between 2 keV a parts per thousand currency sign E a parts per thousand currency sign 39 keV. The averaged neutron rate is estimated as 5.96 x 10(5) n/s.