Yazar "Tomak, Mehmet" seçeneğine göre listele

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    Applications of Genetic Algorithm to Quantum Mechanical Systems
    (2006) Şahin, Mehmet; Atav, Ülfet; Tomak, Mehmet
    Genetic algorithm (GA) inspired by the biological world is a general search and optimization method. It was first proposed by Holland in 1975. GA has been applied to many scientific areas especially in engineering optimization problems. It is also used in solving of quantum mechanical problems. In this study, we have applied this method to different realistic quantum mechanical problems of both self-consistent and non-self-consistent type. The results obtained are compared with the results of other methods and it is seen that the GA can be a very powerful alternative to some other traditional techniques such as variational method. © TÜBİTAK.
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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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    Intersubband resonant enhancement of the nonlinear optical properties in compositionally asymmetric and interdiffused quantum wells
    (AMER INST PHYSICS, 2008) Karabulut, Ibrahim; Safak, Haluk; Tomak, Mehmet
    We report the resonant enhancement of the second- and third-order optical nonlinearities in compositionally asymmetric quantum wells with finite confining potential and interdiffused quantum wells. The energy levels and the envelope wave functions in quantum wells are obtained by solving numerically the Schrodinger equation. The optical rectification, second and third harmonic generation coefficients are calculated within the framework of the density matrix formalism. The effect of the structure parameters such as the well width and the barrier height on the nonlinear optical properties is investigated in detail. The resulting nonlinear susceptibilities obtained in both quantum wells are considerably larger than those of bulk GaAs. (C) 2008 American Institute of Physics.
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    Second harmonic generation in an asymmetric rectangular quantum well under hydrostatic pressure
    (ELSEVIER SCIENCE BV, 2007) Karabulut, Ibrahim; Atav, Ulfet; Safak, Haluk; Tomak, Mehmet
    The effects of structure parameters and hydrostatic pressure oil the electronic states and the second harmonic generation (SHG) susceptibility of asymmetric rectangular quantum Well (ARQW) are studied. The asymmetry of the potential can be controlled by changing the structural parameters and this adjustable asymmetry is important for optimizing the SHG susceptibility. We have calculated analytically the electronic states in ARQW within the framework of the envelope function approach. Numerical results for Al-x/Ga1-x/As/GaAs/AlxrGa1-xr. As quantum well are presented. The results obtained show that the hydrostatic pressure and the structure parameters of ARQW significantly influence the SHG susceptibility. This behavior in the SHG susceptibility gives a new degree of freedom in regions of interest for device applications. (c) 2007 Elsevier B.V. All rights reserved.
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    Self-Consistent Calculation of Semiconductor Heterojunctions Using Quantum Genetic Algorithm
    (World Scientific Publ Co Pte Ltd, 2002) Şahin, Mehmet; Tomak, Mehmet
    In this study, we have investigated the ground state energy level of electrons in modulation doped GaAs/AlxGa1-xAs heterojunctions. For this purpose, Schrodinger and Poisson equations are solved self consistently using quantum genetic algorithm (QGA). In this way, we have found the potential profile, the ground state subband energy and their corresponding envelope functions, Fermi level, and the amount of tunneling charge from barrier to channel region. Their dependence on various device parameters are also examined.
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    Theoretical investigation of intersubband nonlinear optical rectification in AlxlGa1-xlAs/GaAs/AlxrGa1-xrAs asymmetric rectangular quantum wells
    (WILEY-V C H VERLAG GMBH, 2007) Karabulut, Ibrahim; Atav, Uelfet; Safak, Haluk; Tomak, Mehmet
    In this study, a theoretical investigation of intersubband nonlinear optical rectification in Alx1Ga1-x1As/ GaAs/AlxrGa1-xrAs asymmetric rectangular quantum wells is presented. The electronic states in the asymmetric rectangular quantum well are described within the framework of the envelope function approach including the effects of band nonparabolicity and the effective mass mismatch. The nonlinear optical rectification is calculated using the density matrix formalism. It is found that the nonlinear optical rectification in the asymmetric rectangular quantum well depends sensitively on the parameters such as the width and the asymmetry of the potential well. The adjustable parameters allow for tuning of the asymmetric rectangular quantum well system to the desired wavelength while retaining a large optical rectification coefficient. This gives a new degree of freedom in various device applications based on nonlinear optical properties. Band nonparabolicity is found to significantly influence both electronic states and nonlinear optical rectification. Moreover the resulting optical rectification coefficient is much larger than the ones for bulk GaAs and some other theoretical studies in literature. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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    Thermodynamics of a two-dimensional interacting Bose gas trapped in a quartic potential
    (ELSEVIER SCIENCE BV, 2011) Karabulut, Elife O.; Koyuncu, Mustafa; Atav, Ulfet; Tomak, Mehmet
    We have studied the Bose-Einstein condensation (BEC) of an interacting Bose gas confined in a two-dimensional (2D) quartic potential by using a mean-field, semiclassical two-fluid model. A thermodynamic analysis including the chemical potential, condensate fraction, total energy, and specific heat has been carried out by considering different values of the interaction strength. Finally, we have found that the behaviour of the condensate fraction and specific heat of quartically trapped bosons differs from those of bosons trapped in a harmonic potential. (C) 2010 Elsevier B.V. All rights reserved.
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    Thermodynamics of Bose-Einstein gas trapped in D-dimensional quartic potentials
    (ELSEVIER SCIENCE BV, 2010) Karabulut, Elife Oe; Koyuncu, Mustafa; Tomak, Mehmet
    Quartic potentials play air important role in a broad range of fields in the Bose-Einstein Condensation (BEC) literature, from optical lattices to vortices and even to the quantum phase transitions. This also makes the study of thermodynamic properties of systems confined by these potentials interesting. For this purpose, the BEC of an ideal Bose system with a finite number of particles is considered in three and lower dimensions. A comprehensive thermodynamic analysis including the condensation temperature, chemical potential, condensate fraction, hear capacity, total energy, and entropy has been carried Out with a special emphasis oil low-dimensional case for which the standard semi-classical method is not applicable. As a result of our Calculations based Oil a quantum mechanical treatment we have shown that BEC is possible in a one-dimensional quartic potential, in contrast with the predictions of the standard method. Moreover it is also possible to corroborate Our results by using a modified semi-classical approximation that enables LIS to estimate the condensation temperatures for one-dimensional traps for all powers of the confining potential. We have found higher condensation temperatures than for the harmonic traps for all the three spatial configurations of the quartic trap. (C) 2009 Elsevier B.V. All rights reserved.