Fizik Bölümü / Department of Physics
Permanent URI for this collectionhttps://hdl.handle.net/11413/6785
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Browsing Fizik Bölümü / Department of Physics by Publisher "Amer Inst Physics, 2 Huntington Quadrangle, Ste 1No1, Melville, Ny 11747-4501 USA"
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Publication A Natural Limit on the Observable Periods of Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters(Amer Inst Physics, 2 Huntington Quadrangle, Ste 1No1, Melville, Ny 11747-4501 USA, 2011) Ertan, Ünal; Çalışkan, Şirin; Ekşi, Kazım Yavuz; Erkut, M. Hakan; Alpar, M. Ali; 179806; 273308; 26028We investigate the dependence of the evolution of neutron stars with fallback disks on the strength of the magnetic dipole field of the star. Using the same model as employed by Ertan et al. (2009), we obtain model curves for different dipole fields showing that the neutron stars with magnetic dipole fields greater than similar to 10(13) G on the surface of the star are not likely to become anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs). Other sources with conventional dipole fields evolve into the AXP phase if their disk can penetrate the light cylinder. The upper limits to the observed periods of AXP and SGRs could be understood if the disk becomes inactive below a low temperature around 100 K. We summarize our present and earlier results indicated by the evolutionary model curves of these sources with an emphasis on the importance of the minimum disk temperature and the X-ray irradiation in the long-term evolution of AXPs and SGRs with fallback disks.Publication High-Frequency QPOs as a Product of Inner Disk Dynamics around Neutron Stars(Amer Inst Physics, 2 Huntington Quadrangle, Ste 1No1, Melville, Ny 11747-4501 USA, 2011) Erkut, M. HakanThe kHz QPOs observed in a neutron star low mass X-ray binary are likely to be produced in the innermost regions of accretion disk around the neutron star. The rotational dynamics of the inner disk can be characterized by the presence of either sub-Keplerian or super-Keplerian accretion flow depending on the relative fastness of the neutron spin as compared to the Keplerian frequency at the inner disk radius. Within the magnetosphere-disk interaction model, the frequency difference between the two kHz QPOs observed in a given source can be estimated to be slightly higher than or nearly around the neutron star spin frequency if the neutron star is a slow rotator and less than the stellar spin frequency if the neutron star is a fast rotator.Publication Matrix Isolation Infrared Spectra and Photochemistry of Hydantoin(Amer Inst Physics, 2 Huntington Quadrangle, Ste 1No1, Melville, Ny 11747-4501 USA, 2013-01-31) Nunes, Claudio M.; Fausto, Rui; ILDIZ, GÜLCE ÖĞRÜÇ; 107326Hydantoin (C3H4N2O2, 2,4-imidazolidinedione) was isolated in argon matrix at 10 K and its infrared spectrum and unimolecular photochemistry were investigated. The molecular structure of the compound was studied both at the DFT(B3LYP) and MP2 levels of approximation with valence triple- and quadruple-zeta basis sets (6-311++G(d,p); cc-pVQZ). It was concluded that the minima in the potential energy surfaces of the molecule correspond to C-1 symmetry structures. However, the energy barrier separating the two-equivalent-by-symmetry minima stays below their zero-point energy, which makes the C-s symmetry structure, which separates the two minima, the experimentally relevant one. The electronic structure of the molecule was studied in detail by performing the Natural Bond Orbital analysis of its electronic configuration within the DFT(B3LYP)/cc-pVQZ space. The infrared spectrum of the matrix isolated compound was fully assigned also with help of the theoretically predicted spectrum. Upon irradiation at lambda = 230 nm, matrix-isolated hydantoin was found to photofragment into isocyanic acid, CO, and methylenimine.Publication Position Observations of NEAs at the RTT150(Amer Inst Physics, 2 Huntington Quadrangle, Ste 1No1, Melville, Ny 11747-4501 USA, 2008) Aslan, Zeki; Ivantsov, Anatoliy V.; Gumerov, Rustem I.; Hudkova, Lyudmila A.; Khamitov, Irek; Pinigin, Gennadiy I.; 142225In 2004-2007, 560 observations of 17 Near-Earth Asteroids of 15-21 magnitudes were made at the Russian-Turkish telescope (RTT150). The reduction was made using reference stars from the UCAC2 and USNO-B1 catalogues. The comparison of the observed and calculated positions of the asteroids using the HORIZONS system gave standard errors of a single position in the range 0.05 divided by 0.50 ''. Analysis of the (O - C) is given in this paper.