Yazar "Gülveren, Berna" seçeneğine göre listele

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    Efficiency of Genetic Algorithm and Determination of Ground State Energy of Impurity in a Spherical Quantum Dot
    (World Scientific Publ Co Pte Ltd, 2003) Şafak, Haluk; Şahin, Mehmet; Gülveren, Berna; Tomak, Mehmet
    In the present work, genetic algorithm method (CA) is applied to the problem of impurity at the center of a spherical quantum dot for infinite confining potential case. For this purpose, any trial variational wave function is considered for the ground state and energy values are calculated. In applying the GA to the problem under investigation, two different approaches were followed. Furthermore, a standard variational procedure is also performed to determine the energy eigenvalues. The results obtained by all methods are found in satisfactory agreement with each other and also with the exact values in literature. But, it is found that the values obtained by genetic algorithm based upon wavefunction optimization are closer to the exact values than standard variational and also than gene-tic algorithm based on parameter optimization methods.
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    An insight into titania nanopowders modifying with manganese ions: A promising route for highly efficient and stable photoelectrochemical solar cells
    (PERGAMON-ELSEVIER SCIENCE LTD, 2017) Öztürk, Teoman; Gülveren, Berna; Gülen, Mahir; Akman, Erdi; Sönmezoğlu, Savaş
    In this study, we firstly report the synthesis of pure and manganese (Mn) doped titania nanopowders by solution-based chemical process followed by ball-milling and ultra-sonication processes and their usage as photoanode material in dye-sensitized solar cells (DSSCs). Besides examining the properties of physical and charge transfer dynamics, we also made a detailed cost analysis to compare with commercial P25 nanopowders. By incorporating Mn4+ ions into titania matrix, we have also succeeded not only in lower price but also in significantly enhancing the dye loading capability by increasing specific surface area and the retarding the recombination of electron-hole pairs by forming the discrete interstitial states within the band gap as well as accelerating electron transfer by tailoring in energy gap, leading to better photovoltaic performance. Such that, the cell assembled with 0.4 mol% Mn doped TiO2 yields an efficiency of 7.33%, which is similar to 47% and similar to 65% higher than the value obtained for P25 and pure titania-based photoanode, respectively, and shows a fast, stable, and completely reversible photocurrent response accompanying each switch-on/off event. Furthermore, the photoinduced electron transfer (PET) measurements indicate an efficient interfacial charge transfer for 0.4 mol%Mn doped titania (k(ET) = 0.99 x 10(8) s(-1)) compared to the both synthesized pure TiO2 (0.74 x 10(8) s(-1)) and commercial P25 (0.94 x 10(8) s(-1)) photoanodes. This work renders the possibility of synthesizing low-cost and easy-preparation Mn-doped titania nanopowders and describes an innovative approach to further boost the efficiency of green technologies such as solar-driven water splitting, photoelectrochemical and perovskite solar cells applications. (C) 2017 Elsevier Ltd. All rights reserved.
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    Thermal Properties of Interacting Electron Gas in A Harmonic Potential
    (WORLD SCIENTIFIC PUBL CO PTE LTD, 2012) Gülveren, Berna
    In this work, the thermal properties, such as total energy, pressure and free energy of an interacting electron gas system have been investigated. The Thomas-Fermi equation was numerically solved for a harmonically confined, two-dimensional gas system at finite temperatures. Numerical results were compared with analytical ones provided by the literature for a non-interacting case at finite temperatures and for a interacting case at T = 0 K. Excellent agreement was achieved for both cases. The results indicate that interactions affect the density of particles and hence, the density-dependent thermal functions significantly.
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    Thermodynamic Properties of an Electron Gas System Trapped Within Various Shapes of Potentials
    (WORLD SCIENTIFIC PUBL CO PTE LTD, 2012) Gülveren, Berna
    The Thomas-Fermi (TF) equation is solved numerically for an electron gas system that interacts via the Coulomb potential. An emphasis is placed on how certain physical properties, such as the chemical potential and the total energy, change with the shape of the confinement at finite temperatures. By comparing these results with the results calculated for the noninteracting case, we are able to analyze how the inter-particle forces affect the thermodynamic properties of electrons. It is shown that the total energy and other properties of an electron gas is very sensitive to the particle interactions and the shape of the confining potential, even at high temperatures. The results are also applicable to nanostructures like two-dimensional quantum dot systems, wires.