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Öğe Computation of Clebsch-Gordan and Gaunt Coefficients Using Binomial Coefficients(ACADEMIC PRESS INC JNL-COMP SUBSCRIPTIONS, 1995) Guseinov, I.I.; Özmen, A.; Atav, U.; Yüksel, H.Using binomial coefficients the Clebsch-Gordan and Gaunt coefficients were calculated for extremely large quantum numbers. The main advantage of this approach is directly calculating these coefficients, instead of using recursion relations. Accuracy of the results is quite high for quantum numbers l(1) and l(2) up to 100. Despite direct calculation, the CPU times are found comparable with those given in the related literature.Öğe Computation of Overlap Integrals Over Slater-Type Orbitals Using Auxiliary Functions(JOHN WILEY & SONS INC, 1998) Guseinov, I. I.; Özmen, A.; Atav, U.; Yüksel, H.Analytical expressions through the binomial coefficients and recursive relations are derived for the expansion coefficients of overlap integrals in terms of a product of well-known auxiliary functions A(k) and B-k. These formulas are especially useful for the calculation of overlap integrals for large quantum numbers. Accuracy of the computer results is satisfactory for the values of quantum numbers up to 50 and for the arbitrary values of screening constants of atomic orbitals and internuclear distances.Öğe Edge state distribution in an Aharonov-Bohm electron interferometer in the integer quantum Hall regime(IOP PUBLISHING LTD, 2011) Ozturk, T.; Kavruk, A. E.; Ozturk, A.; Atav, U.; Yuksel, H.In this study we analyze the density distributions of the two dimensional electron system for an experimental geometry which is topologically equivalent of an Aharonov-Bohm interferometer in three dimensions in the quantum Hall regime and obtain the spatial distribution of the edge states. We employ the Thomas-Fermi approximation in our analysis and solve the Poisson equation in three dimensional using a multi grid technique. Also we obtain the distribution of incompressible strips for a wide range of magnetic fields strengths and comment on their relation with experimental results in literature.Öğe Isospin-dependent multifragmentation of relativistic projectiles(AMER PHYSICAL SOC, 2011) Ogul, R.; Botvina, A. S.; Atav, U.; Buyukcizmeci, N.; Mishustin, I. N.; Adrich, P.; Aumann, T.The N/Z dependence of projectile fragmentation at relativistic energies has been studied with the ALADIN forward spectrometer at the GSI Schwerionen Synchrotron (SIS). Stable and radioactive Sn and La beams with an incident energy of 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. For the interpretation of the data, calculations with the statistical multifragmentation model for a properly chosen ensemble of excited sources were performed. The parameters of the ensemble, representing the variety of excited spectator nuclei expected in a participant-spectator scenario, are determined empirically by searching for an optimum reproduction of the measured fragment-charge distributions and correlations. An overall very good agreement is obtained. The possible modification of the liquid-drop parameters of the fragment description in the hot freeze-out environment is studied, and a significant reduction of the symmetry-term coefficient is found necessary to reproduce the mean neutron-to-proton ratios < N >/Z and the isoscaling parameters of Z <= 10 fragments. The calculations are, furthermore, used to address open questions regarding the modification of the surface-term coefficient at freeze-out, the N/Z dependence of the nuclear caloric curve, and the isotopic evolution of the spectator system between its formation during the initial cascade stage of the reaction and its subsequent breakup.Öğe Linear and nonlinear intersubband optical absorptions in an asymmetric rectangular quantum well(SPRINGER, 2007) Karabulut, I.; Atav, U.; Safak, H.; Tomak, M.The linear and nonlinear intersubband optical absorptions in AlxlGa1-xlAs/GaAs/AlxrGa1-xrAs asymmetric rectangular quantum well are studied within the framework of the density matrix formalism. We have calculated the electron energy levels and the envelope wave functions using the effective mass approach. In addition, we have obtained an expression for saturation intensity. It is shown that the parameters such as asymmetry and width of potential well not only shift the peak positions in absorption spectrum but also considerably modify their height. These results suggest that the absorption process can be easily controlled by the structure parameters of an asymmetric rectangular quantum well. Also, the incident optical intensity has a great effect on the total absorption spectrum. We have seen that the absorption peak is reduced by half when the optical intensity is approximately 0.8 MW/cm(2) for well width L = 90 angstrom and beta = 0.5. Moreover, it is seen that the saturation intensity is quite sensitive to the structure parameters of an asymmetric rectangular quantum well. Thus, the results presented here can be useful for electro-optical modulators and photodetectors in the infrared region.Öğe Phase Instabilities in Nuclear Matter and Droplet Formation(WORLD SCIENTIFIC PUBL CO PTE LTD, 2001) Oğul, R.; Atav, U.We have investigated droplet formation which may occur during the expansion of an excited blob of nuclear matter in the metastable region at subnuclear densitites. The free energy change accompanying the formation of a drop is calculated as a function of droplet radius for various saturation ratios.Öğe The self-consistent calculation of the edge states in bilayer quantum Hall bar(IOP PUBLISHING LTD, 2011) Kavruk, A. E.; Ozturk, T.; Ozturk, A.; Atav, U.; Yuksel, H.In this study, we present the spatial distributions of the edge channels for each layer in bilayer quantum Hall bar geometry for a wide range of applied magnetic fields. For this purpose, we employ a self-consistent Thomas-Fermi-Poisson approach to obtain the electron density distributions and related screened potential distributions. In order to have a more realistic description of the system we solve three dimensional Poisson equation numerically in each iteration step to obtain self consistency in the Thomas-Fermi-Poisson approach instead of employing a "frozen gate" approximation.Öğe Surface and symmetry energies in isoscaling for multifragmentation reactions(IOP PUBLISHING LTD, 2009) Ogul, R.; Atav, U.; Bulut, F.; Buyukcizmeci, N.; Erdogan, M.; Imal, H.; Botvina, A. S.The possibilities of modifications for symmetry and surface energy coefficients of nuclear matter at freeze-out density are investigated theoretically by means of isoscaling (isotopic scaling) on the basis of a statistical multifragmentation model. It is seen that while the isoscaling parameters as predicted by Markov chain calculations for the single sources (124)Sn and (112)Sn are very sensitive to the symmetry term, the surface energy variation slightly affects the isoscaling parameters in the multifragmentation region. The influence of these changes on the mean neutron to proton ratios of light fragments for 2 <= Z <= 10 is also shown. Comparing our results with MSU experimental data, it is confirmed that a significant reduction of the symmetry-term coefficient is found necessary to reproduce the isoscaling parameters of Z <= 8 fragments.Öğe Surface and Symmetry Energy Effects in Nuclear Multifragmentation(AMER INST PHYSICS, 2009) Ogul, R.; Atav, U.; Bianchin, S.; Botvina, A. S.; Buyukcizmeci, N.; de Napoli, M.; Le Fevre, A.It has been shown that the symmetry energy and the surface energy of hot fragments at the low-density freeze-out can be considerably modified. The influence of these changes on fragment yields and isotope distributions is discussed by analyzing recent ALADIN experimental data on spectator fragmentation at incident energy 600 A MeV.
