Yazar "Yesil, Ali" seçeneğine göre listele

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    An approach for unipolar corona discharge in N2/O2 gas mixture by considering townsend conditions
    (Elsevier Science Bv, 2011) Alisoy, Hafiz Z.; Yesil, Ali; Koseoglu, Murat; Unal, Ibrahim
    In this study (alpha/p)=f(E/p) functional relation is derived for the gas mixture of N-2/O-2 by considering Townsend approach, and formation mechanism of corona discharge is investigated for the coaxial electrode system located in this gas medium. The electron energy distribution function (EEDF) which is required for estimation of ionization coefficient, is determined by considering probability distribution function of inelastic electron collisions versus energy. An algorithm for determining ionization coefficient for binary gas mixture is presented. The development and motion of the electron avalanche in inter-electrode gap are studied by considering the effect of positive space charges. It is determined by considering the derived mathematical expressions that the formation of corona discharge is related with the variation of the current characteristics in inter-electrode gaps depending on the change of potential of central electrode. (C) 2011 Elsevier B.V. All rights reserved.
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    The characterization of diffusion tensor for mid-latitude ionospheric plasma
    (Ist Nazionale Di Geofisica E Vulcanologia, 2014) Sagir, Selcuk; Yesil, Ali; Sanac, Gulay; Unal, Ibrahim
    In this study, the relationship between diffusion and the electrical conductivity tensor is investigated by using the real geometry of the Earth's magnetic field in the Northern Hemisphere for mid-latitudes. This relationship is derived from equation. Only in the elements of the diagonal of the tensor is an equal relationship found between the electrical conductivity called the longitudinal conductivity and the diffusion coefficient. The diagonal elements are equal to each other and do not depend on the Earth's magnetic field; however, the other elements of the tensor strongly depend on the Earth's magnetic field and they have characteristic of Bohm diffusion became a semi-empirical model (D-B= (1/16)kT/eB) but they do not depend on the electrical conductivity or the classical diffusion coefficient.
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    The effect of the geomagnetic activity to the hourly variations of ionospheric foF2 values at low latitudes
    (Springer Heidelberg, 2014) Timocin, Erdinc; Yesil, Ali; Unal, Ibrahim
    In this study, the relationship between the hourly changes of the ionospheric critic frequency values of F2 layers in low latitudes and geomagnetic activity is examined by using statistical methods. The ionospheric critical frequency data has been taken from the Manila (121.1A degrees A E, 14.7A degrees A N) ionosonde station. In order to investigate the effect of sun activity on ionospheric critical frequency, the data of 1981 when the sun was active and of 1985 when the sun was less active has been used. According to the Granger causality test results, on 5 % significance level, a causality relationship from disturbance storm time (Dst) index values to ionospheric critical frequency values direction has been observed. However, a causality relationship from ionospheric critical frequency values to Dst values has not been observed. From the results of cause-and-effect analysis, it is evaluated that the effect of a shockwave occurring in geomagnetic activity on ionospheric critical frequency continues along 72 h, that is, geomagnetic activity has a long-term effect on ionospheric critical frequency. The response of ionospheric critical frequency to geomagnetic activity substantially depends on seasons. This response is more observed especially in equinox period when the sun is active and in winter months. The increase in geomagnetic activity causes ionospheric critical frequency to decrease in night hours and increase in day hours. The same relationship has not been observed exactly, though observed very little in winter months, for 1985 when the sun was less active.
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    The Effect of the Midlatitude Electron Density Trough on the Ionospheric Conductivities
    (Springer International Publishing Ag, 2019) Timocin, Erdinc; Unal, Ibrahim; Yesil, Ali
    In this study, we have investigated the effect of midlatitude electron density trough on ionospheric conductivities for different altitudes. For this purpose, parallel conductivity (sigma (0)), Pedersen conductivity (sigma (1)) and Hall conductivity (sigma (2)) data were calculated by using the International Reference Ionosphere (IRI) model for seven different geographic coordinates in the midlatitude region of the northern hemisphere during the June and December solstices of 1972. Planetary geomagnetic activity index () data are used as a geomagnetic activity indicator. These conductivity values computed for each position were classified according to geomagnetic active () and geomagnetic quiet () conditions; and these values were examined according to invariant magnetic latitudes (I >) for different heights, seasonal, geomagnetic activity and local times. From the analysis results, it is found that the midlatitude electron density trough does not have any effects on sigma (0) for all situations, but the trough is influential on sigma (1) and sigma (2) during night hours of the December solstices. In addition, it was observed that the trough increased its effect on sigma (1) and sigma (2) with the increasing geomagnetic activity level and altitude for December solstices.
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    Performance of IRI-based ionospheric critical frequency calculations with reference to forecasting
    (Amer Geophysical Union, 2011) Unal, Ibrahim; Senalp, Erdem Turker; Yesil, Ali; Tulunay, Ersin; Tulunay, Yurdanur
    Ionospheric critical frequency (foF2) is an important ionospheric parameter in telecommunication. Ionospheric processes are highly nonlinear and time varying. Thus, mathematical modeling based on physical principles is extremely difficult if not impossible. The authors forecast foF2 values by using neural networks and, in parallel, they calculate foF2 values based on the IRI model. The foF2 values were forecast 1 h in advance by using the Middle East Technical University Neural Network model (METU-NN) and the work was reported previously. Since then, the METU-NN has been improved. In this paper, 1 h in advance forecast foF2 values and the calculated foF2 values have been compared with the observed values considering the Slough (51.5 degrees N, 0.6 degrees W), Uppsala (59.8 degrees N, 17.6 degrees E), and Rome (41.8 degrees N, 12.5 degrees E) station foF2 data. The authors have considered the models alternative to each other. The performance results of the models are promising. The METU-NN foF2 forecast errors are smaller than the calculated foF2 errors. The models may be used in parallel employing the METU-NN as the primary source for the foF2 forecasting.
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    The Responses of Ionospheric Conductivities on the Mid-Latitudes to Changes in the BZ Component of Interplanetary Magnetic Field
    (Springer, 2020) Timocin, Erdinc; Yesil, Ali; Unal, Ibrahim
    In this study, we investigate the response of the ionospheric conductivities on the middle latitudes to the southward and northward turnings of the B-Z component of the interplanetary magnetic field (IMF). For this purpose, parallel conductivity (sigma(0)), Pedersen conductivity (sigma(1)), Hall conductivity (sigma(2)) data calculated for Rome (41.8 degrees N, 12.5 degrees E); Juliusruh (54.6 degrees N, 13.4 degrees E); Uppsala (59.8 degrees N, 17.6 degrees E); Lycksele (64.7 degrees N, 18.8 degrees E) during the 22nd solar cycle are examined. The superposed epoch analysis method is used to investigate the response of the conductivities to the southward and northward turnings of the B-Z component. From the analysis results it is observed that the turnings in the B-Z component of the IMF have significant effect on all conductivities. At the event moment (zero time), the southward turnings of the B-Z component increases all conductivities while the northward turnings of the B-Z component decreases all conductivities. The effect on the conductivities of the changes in the B-Z component occurs before about 18 h from the event moment, and this effect disappears after about 24 h from the event moment. Furthermore, all of ionospheric conductivities shows or does less reaction to changes in the B-Z component as latitude increase.
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    Seasonal Variations of Impedance in the Ionospheric Plasma
    (Gazi Univ, 2020) Unal, Ibrahim; Karatay, Secil; Yesil, Ali; Hancerliogullari, Aybaba
    The ionosphere is an ionized layer that extends between 50 km and 1000 km altitudes in the atmosphere. It plays an important role in atmospheric electricity. The ionosphere has the number of electrically charged particles and thus, it affects the propagation of the radio waves. In this study, magnitudes of impedance for different seasons and different geomagnetic activity periods in the ionospheric plasma are calculated using the real geometry of Earth. It is observed that the impedance of the ionospheric plasma in all directions generally has high values for all seasons. The diagonal components of the tensor of the impedance are greater than the other components. It is also observed that the ionospheric plasma, generally, has weak conductivity in all directions and seasons. Impedance varies inversely with electron density. Hence, geomagnetic activity periods which lead to an increase in electron density decreases the impedance. It is observed that the ionospheric plasma has a reactive character in the geographic coordinates where the study was performed. The ionosphere displays a dielectric structure.