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Öğe Analysis of Polycrystal Acrylamide by Electron Spin Resonance and Thermo-Analytical Methods(WILEY-BLACKWELL, 2011) Usta, Ayhan; Filiz, Ali; Birey, Mehmet; Ozmen, AyhanElectron spin resonance (ESR), thermogravimetry analysis (TGA), and differential thermal analysis (DTA) were performed on acrylamide (C(3)H(5)NO) polycrystal samples. The samples were irradiated at 298 K for 24, 48, 72, and 96 h using (60)Co - gamma source. ESR measurements were carried out between 120 and 450 K. The ESR signals were recorded from the samples exposed to (60)Co - gamma rays for 72 and 96 h. Between 120 and 450 K the spectra changed in a manner roughly. It was detected by means of e.s.r. spectra that unpaired electron took place due to scission of pi bond in the carbon-carbon double bonds in the substance. The produced radiation damage center on the sample was attributed to center dot CH(2)-CH-R Additionally, thermal behavior of the acrylamide samples were investigated by using TGA and DTA methods. It was observed that both irradiated and not irradiated samples decomposed at three steps. (C) 2011 Wiley Periodicals, Inc. Concepts Magn Reson Part A 38A: 102-106, 2011.Öğe Calculation of hyperfine interaction in spherical quantum dot(ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2015) Yakar, Yusuf; Cakir, Bekir; Ozmen, AyhanIn this study, we have calculated the unperturbed wavefunctions and energy eigenvalues of the ground and excited states of a spherical quantum dot, GaAs/AlxGa1-xAs, by using quantum genetic algorithm and Hartree-Fock Roothaan method. Hyperfine coupling constant and hyperfine energy of is, 2p, 3d and 4f levels are carried out as a function of dot radius. The results show that the hyperfine constant and hyperfine energy varies rapidly in the strong and medium confining regions as dot radius decreases. It is worth pointing out that dot radius, impurity charge and angular momentum have a strong influence on the hyperfine energy. It is also found that hyperfine energy and hyperfine splitting vary with aluminium concentration ratio x. (C) 2015 Elsevier Ltd. All rights reserved.Öğe Calculation of oscillator strength. and the effects of electric field on energy states, static and dynamic polarizabilities of the confined hydrogen atom(ELSEVIER, 2014) Cakir, Bekir; Yakar, Yusuf; Ozmen, AyhanIn this study, we investigate the effect of an electric field on energy states of a spherical quantum dot with infinite confining potential using the perturbation method. We also perform the static dipole and dynamic dipole polarizabilities. In addition, the oscillator strengths have been calculated for the dipole transitions between higher unperturbed states. The results show that impurity and dot radius have an important effect on the Stark shift, and the effect of electric field is insensitive in small dot radii. For the excited states the Stark shift from the first-order increases linearly with the increase of electric field strength. On the other hand, the Stark shift from the first-order decreases with increasing of the magnetic quantum number. A very important future is that, for dot radius region 1.8 a(B) <= R <= 7a(B), the static dipole polarizabilities change very quickly. In addition, it is found that as the dot radius increases, the photon energy corresponding to the singularity of dynamic dipole polarizability decreases. (C) 2013 Elsevier B.V. All rights reserved.Öğe Calculation of Zeeman splitting and Zeeman transition energies of spherical quantum dot in uniform magnetic field(ELSEVIER SCIENCE BV, 2016) Cakir, Bekir; Atav, Ufet; Yakar, Yusuf; Ozmen, AyhanIn this study we report a detailed theoretical investigation of the effect of an external magnetic field on the 1s-, 2p-, 3d- and 4f-energy states of a spherical quantum dot. We treat the contribution of the diamagnetic term as a perturbation and discuss the effect of the diamagnetic term on the 1s-, 2p-, 3d- and 4f-energy states. We also have calculated the Zeeman transition energies between 2p -> 1s and 3d -> 2p states with m = 0, +/- 1 and 0, +/- 1, +/- 2 as a function of dot radius and the magnetic field strength. The results show that the magnetic field, impurity charge and dot radius have a strong influence on the energy states and the Zeeman transitions. It is found that the energies of the electronic states with m < 0 addition of the diamagnetic term firstly decrease toward a minimum, and then increase with the increasing magnetic field strength. We have seen that as magnetic field intensity is adjusted, frequency of the emitted light can be changed for Zeeman transitions. (C) 2016 Elsevier B.V. All rights reserved.Öğe Computation of hyperfine energies of hydrogen, deuterium and tritium quantum dots(ELSEVIER SCIENCE BV, 2016) Cakir, Bekir; Ozmen, Ayhan; Yakar, YusufThe hyperfine energies and hyperfine constants of the ground and excited states of hydrogen, deuterium and tritium quantum dots(QDs) are calculated. Quantum genetic algorithm (QGA) and Hartree-Fock-Roothaan (HFR) methods are employed to calculate the unperturbed wave functions and energy eigenvalues. The results show that in the medium and strong confinement regions the hyperfine energy and hyperfine constant are strongly affected by dot radius, impurity charge, electron spin orientation, impurity spin and impurity magnetic moment. Besides, in all dot radii, the hyperfine splitting and hyperfine constant of the confined hydrogen and tritium atoms are approximately equivalent to each other and they are greater than the confined deuterium atom. (C) 2015 Elsevier B.V. All rights reserved.Öğe Computation of Ionization and Various Excited State Energies of Helium and Helium-Like Quantum Dots(WILEY-BLACKWELL, 2011) Yakar, Yusuf; Cakir, Bekir; Ozmen, AyhanIn the effective mass approximation, we calculated the wave functions and some energy states of helium and helium-like quantum dots (QDs) with impurity charges Z = 0, 1, 2, 3, and 4. In addition, we carried out the ionization energies of these QDs as a function of dot radius, and we investigated the influence of impurity on the ionization energy. We utilized the method that is a combination of quantum genetic algorithm (QGA) and Hartree-Fock Roothaan (HFR). The results are in a good agreement with literature results. (C) 2011 Wiley Periodicals, Inc. Int J Quantum Chem 111: 4139-4149, 2011Öğe Computation of relativistic terms in a spherical quantum dot(ELSEVIER, 2013) Yakar, Yusuf; Cakir, Bekir; Ozmen, AyhanWe studied a hydrogenic impurity located at the center of a spherical quantum dot with an infinite spherical confining potential and calculated energy levels and wavefunctions using Quantum Genetic Algorithm(QGA) and Hartree-Fock Roothaan (HFR) method. In addition, we investigated the first-order relativistic terms such as the relativistic correction to the kinetic energy, Darwin and spin-orbit interaction term. These terms were calculated using the first-order perturbation theory. The electronic charge density for the Darwin term was carried out from a global operator defined by Hiller, Sucher and Feinberg. The results revealed that the relativistic corrections are important in small dot radii and they should not be neglected to improve the accuracy of calculations. Crown Copyright (c) 2012 Published by Elsevier B.V. All rights reserved.Öğe Computation of relativistic terms in a spherical quantum dot (vol 134, pg 778, 2013)(ELSEVIER SCIENCE BV, 2013) Yakar, Yusuf; Cakir, Bekir; Ozmen, Ayhan[Abstract not Available]Öğe Computation of the oscillator strength and absorption coefficients for the intersubband transitions of the spherical quantum dot(ELSEVIER SCIENCE BV, 2009) Ozmen, Ayhan; Yakar, Yusuf; Cakir, Bekir; Atav, UelfetThe electronic structure and optical properties of one-electron Quantum Dot (QD) with and without an on-center impurity were investigated by assuming a spherically symmetric confining potential of finite depth. The energy eigenvalues and the state functions of QD were calculated by using a combination of Quantum Genetic Algorithm (QGA) and Hartree-Fock Roothan (HFR) method. We have calculated the binding energy for the states 1s,1p,1d,1f, oscillator strengths, the linear and third-order nonlinear optical absorption coefficients as a function of the incident photon energy and incident optical intensity for the 1s-1p, 1p-1d and id-If transitions. The existence of the impurity has great influence on the optical absorption spectra and the oscillator strengths. Also we found that the magnitudes of the total absorption coefficients of the spherical QD increase for transitions between higher states. (C) 2009 Elsevier B.V. All rights reserved.Öğe Determination of radicals produced by irradiation in cholesteryl octanoate single crystals using esr technique(GAZI UNIV, 2016) Sayin, Ulku; Buyukcelebi, Sami; Ozmen, AyhanIn this study, the radicals produced by gamma irradiation was determined using ESR technique in cholesteryl octanoate (C35H60O2), a cholesterol ester, which has medical importance. The samples that crystallized in ethanol solution were irradiated with 60Co-source. The molecules that have diamagnetic property become paramagnetic after irradiation. ESR spectra were recorded in different microwave powers and different temperatures at 10 degrees intervals in the magnetic field applied along each of the perpendicular axes using JEOL JESFA-300 X-band ESR spectrometer located in Selcuk University Advanced Technology Research and Application Center. By considering the chemical structure and ESR spectra of Cholesteryl octanoate molecule, it was identified that radiation produced stable and long lived radical, R-CH 3 alpha CH beta CH2 gamma in the sample. The hyperfine splitting and spectroscopic splitting values which have anisotropic property due the location of crystal in the magnetic field were obtained. In addition, simulations were made for identified radical and a good agreement was found with the experimental spectra.Öğe Dipole and quadrupole polarizabilities and oscillator strengths of spherical quantum dot(ELSEVIER SCIENCE BV, 2018) Yakar, Yusuf; Cakir, Bekir; Ozmen, AyhanIn this study, the energy eigenvalues and eigenfunctions of the ground and excited states of a spherical quantum dot are calculated by using the Quantum Genetic algorithm (QGA) and Hartree-Eock Roothaan (HFR) method. Based on the calculated energies and wave functions, the static and dynamic dipole polarizabilities, the quadrupole polarizability, dipole and quadrupole oscillator strengths of spherical quantum dot are carried out as a function of dot size and the confining potential as perturbative. The results show that dot size and confining potential have a great influence on the polarizability and oscillator strength. It is found that the polarizability increases due to the spatial confinement effect in the strong confinement region. In the weak confinement region, the polarizability increases again until it reaches the saturation value. In addition, the peak positions of the dipole and quadrupole oscillator strengths shift toward smaller dot radii with the increases of the potential well depth.Öğe Electronic structure and relativistic terms of one-electron spherical quantum dot(ELSEVIER SCIENCE BV, 2013) Ozmen, Ayhan; Cakir, Bekir; Yakar, YusufWe calculated the energy eigenvalues and eigenfunctions of the ground and excited states of a hydrogenic impurity located at the center of a spherical quantum dot using the Quantum Genetic Algorithm (QGA) and Hartree-Fock Roothaan (HFR) method. In addition, we carried out the relativistic effects such as the relativistic correction to the kinetic energy, spin-orbit and Darwin terms by using the perturbation method. The electronic charge density for the Darwin term is computed from the Hiller, Sucher and Feinberg formulation instead of the traditional delta function operator. The results show that impurity, dot radius and confining potential have a great influence on the relativistic effects. In addition, as the absolute value of confining potential increases, the peak values of relativistic corrections increase and move toward lower dot radii. (C) 2013 Elsevier B.V. All rights reserved.Öğe Electronic structure of two-electron quantum dot with parabolic potential(TAYLOR & FRANCIS LTD, 2015) Yakar, Yusuf; Cakir, Bekir; Ozmen, AyhanIn this study, we investigate the parabolic potential effects on the ground and excited energy states of two-electron quantum dot with impurity inside an infinite spherical confining potential well. The wave function and energy eigenvalues were calculated using a modified variational optimization procedure based mainly on quantum genetic algorithm and Hartree-Fock-Roothaan method. The results show that the parabolic potential and impurity charge have a strong effect on the energy states and ionization energies. It is worth pointing out that as impurity charge increases, the ionization energy rises, but the ionization dot radius decreases. On the other hand, as parabolic potential increases, the ionization energy decreases, but the ionization dot radius increases.Öğe EPR investigation of gamma irradiated single crystal guaifenesin: A combined experimental and computational study(PERGAMON-ELSEVIER SCIENCE LTD, 2016) Tasdemir, Halil Ugur; Sayin, Ulku; Turkkan, Ercan; Ozmen, AyhanGamma irradiated single crystal of Guaifenesin (Glyceryl Guaiacolate), an important expectorant drug, were investigated with Electron Paramagnetic Resonance (EPR) spectroscopy between 123 and 333 K temperature at different orientations in the magnetic field. Considering the chemical structure and the experimental spectra of the gamma irradiated single crystal of guaifenesin sample, we assumed that alkoxy or alkyl-type paramagnetic species may be produced by irradiation. Depending on this assumption, eight possible alkoxy and alkyl-type radicals were modeled and EPR parameters of these modeled radicals were calculated using the B3LYP/6-311+ +G(d,p)-level of density functional theory (DFT). Theoretically calculated values of alkyl-type modeled radical(R3) are in good agreement with experimentally determined EPR parameters of single crystal. Furthermore, simulation spectra which are obtained by using the thepretical initial values are well matched with the experimental spectra. It was determined that a stable C alpha H2 alpha C beta H beta C gamma H2 gamma (R3) alkyl radical was produced in the host crystal as a result of gamma irradiation. (C) 2015 Elsevier Ltd. All rights reserved.Öğe EPR study of gamma-irradiated 2-Bromo-4 '-methoxyacetophenone single crystals(TAYLOR & FRANCIS LTD, 2016) Tasdemir, Halil Ugur; Turkkan, Ercan; Sayin, Ulku; Ozmen, AyhanThe gamma-irradiated single crystals of 2-Bromo-4'-methoxyacetophenone (2B4MA) were investigated using electron paramagnetic resonance (EPR) technique. Density-functional theory calculations were employed to investigate and identify the radicals that have been assumed to be formed upon irradiation of 2B4MA single crystals. The EPR spectra of 2B4MA were recorded at different orientations in the magnetic field at room temperature. Taking into account the chemical structure and experimental spectra of irradiated single crystal of 2B4MA, it was assumed that at least two different radicals were produced in the sample. Following this assumption, six possible radicals were modeled and EPR parameters were calculated by using the DFT, B3LYP/6-311+G(d), for the modeled radicals individually. The calculated hyperfine coupling constants and g-tensors were used as initial values for simulation studies. The three crystallographic axes on the simulated spectra were well matched with experimental spectra for the two modeled radicals. Thus, we identified the R1 type radical and R4 type radical as paramagnetic species produced in gamma-irradiated 2B4MA.Öğe An EPR Study On Cytosine Irradiated(WILEY, 2011) Usta, Ayhan; Vural, Hasibe Cingilli; Usta, Keziban; Aras, Erdal; Ceylan, Yusuf; Ozmen, AyhanIn this study, paramagnetic centers over the cytosine were formed by photolysis then these centers were investigated using EPR method. EPR signals were not recorded from non-irradiated the cytosine, but irradiated polycrystalline exhibited complex EPR spectra. For obtaining of cytosine polycrystalline, novel crystallization method was performed on powder cytosine. Effective crystallization conditions were achieved by adjustment of the concentration of the metal ions, chemical solutions, NaCl, KCl, glacial asetic acid, nitric oxide, percloric acid, glutamic acid, and pH of buffer. Cytosine (C4H5N2O) polycrystalline obtained were irradiated with Co-60 - rays at room temperature for 24 and 72 h. At the sample irradiated for 72 h, the paramagnetic centers were determined between 120 and 450 K by X-band EPR spectrometer. The spectra were found to be dependent slightly on temperature. Two cation radicals were determined in the structure and these were called Radicals I and II. The g and hyperfine constants were found to be a(H2a) = 61 G, a(N2) = 9.39 G, a(N1) = 7.15 G, and g(1) = 2.0026 for the Radical I; a(H3) = 10.57 G, a(H1) = 3 G, a(N3) = 6.72 G, a(N1) = 5.36 G for, and g(2) = 2.0034 the Radical II. Copyright (C) 2010 John Wiley & Sons, Ltd.Öğe An EPR study on irradiated 4-(1,3,5-triazin-2-yloxy)cyclohexanecarbaldehyde single crystal(ELSEVIER SCIENCE BV, 2011) Usta, Ayhan; Ozmen, Ayhan; Birey, MehmetThe single crystals of 4-(1,3,5-triazin-2-yloxy)cyclohexanecarbaldehyde [C(10)H(13)N(3)O(2)] were produced by slow evaporation of a concentrated ethyl acetate solutions. These single crystals were exposed to (60)Co gamma rays with dose speed of 0.980 kGy/h at the room temperature for 48 and 72 h. The free radical of the sample was observed using EPR-X band spectrometer.The EPR spectra were recorded between 120 and 450 K. The sample irradiated for 72 h was rotated in steps of 10 degrees and analysed for different orientations of the crystal in the magnetic field. The hyperfine constants of the sample were found to be anisotropic. The average values of these constants were calculated as following: g = 1.9979, a(H1) = 10.75 G, a(H2) = 2.28 G, and a(N) = 3.83 (C) 2010 Elsevier B.V. All rights reserved.Öğe ESR analysis of kumyer location archeological ceramics and determination of suitability for ESR dating(GAZI UNIV, 2017) Bakkal, Gamze; Sayin, Ulku; Isik, Ilker; Ozmen, Ayhan; Kilic, Hamdi SukurIn this study paramagnetic centers in quartz minerals of Kumyer Location archeological samples were identified using Electron Spin Resonance (ESR) technique. ESR spectra were recorded at different microwave powers and various spectrometer temperatures with JEOL JESFa-300 X-band ESR spectrometer located in Selcuk University Advanced Technology Research and Application Center (ILTEK). It was determined that there is Al, Ti-Li, Ti-H and Ge paramagnetic centers which were produced by natural radiation in quartz minerals of ceramic samples and ESR parameters of these centers were measured. In order to determine whereas Kumyer Location archeological ceramics are suitable samples for ESR dating, ESR spectra of artificial irradiated samples recorded at 300K and 81K temperature were analyzed. Thermal stability of Al and Ti centers were determined by isochronal annealing experiment of artificial irradiated samples. As a result of experimental studies, it was determined that quartz minerals of Kumyer location archeological ceramic samples have stable and radiation dependent paramagnetic centers thus, these samples can be used for ESR dating.Öğe Experimental and theoretical research on -irradiated 7-methoxy-4-methylcoumarin powder through EPR and DFT methods(TAYLOR & FRANCIS LTD, 2018) Sarikaya, Ebru Karakas; Ates, Levent; Sayin, Ulku; Ozmen, Ayhan; Dereli, OmerIn this paper, the effects of gamma irradiation on 7-Methoxy-4-methylcoumarin (7M4MC) molecule, an essential coumarin derivative, which has an inherent variety of biological activities, therapeutic properties and industrial usage were examined. For this purpose, the sample was irradiated with Co-60-gamma ray source for about 100kGy total doses. Theoretical calculations were performed using GAUSSIAN03 program for the possible radicals that were modeled from two stable conformations with lowest energies. In order to get well-resolved spectra and to determine the radical identity experimentally, EPR spectra of the irradiated 7M4MC sample were recorded at several spectrometer conditions. By considering the molecular structure and EPR spectra, alkyl-type radical was assumed to be formed by gamma irradiation. To support the estimations, simulations were done using theoretical EPR parameters as an initial value. The experimental spectra were well matched with the sum of simulated spectra obtained from two same type modeled radicals of two different conformations. As a result of experimental estimations and theoretical calculations, radiation-induced radicals were identified as two neutral alkyl radicals, originated from two stable conformations.Öğe Investigation of electronic structure of a Quantum Dot using Slater-Type Orbitals and Quantum Genetic Algorithm(WORLD SCIENTIFIC PUBL CO PTE LTD, 2007) Cakir, Bekir; Ozmen, Ayhan; Atav, Uelfet; Yuksel, Hueseyin; Yakar, YusufIn this study, electronic properties of a low-dimensional quantum mechanical structure have been investigated by using Genetic Algorithm (GA). One-and two-electron Quantum Dot (QD) systems with an on-center impurity are considerable by assuming the confining potential to be infinitely deep and spherically symmetric. Linear combinations of Slater-Type Orbitals (STOs) were used for the description of the single electron wave functions. The parameters of the wave function of the system were used as individuals in a generation, and the corresponding energy expectation values were used for objective functions. The energy expectation values were determined by using the Hartree-FockRoothaan (HFR) method. The orbital exponent zeta(i)'s and the expansion coefficient c(i)'s of the STOs were determined by genetic algorithm. The obtained results were compared with the exact result and found to be in a good agreement with the literature.
