Yazar "Tarhan, I." seçeneğine göre listele

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    Energy distributions of the Szekeres universes in teleparallel gravity
    (Springer/Plenum Publishers, 2008) Aygun, S.; Tarhan, I.; Baysal, H.
    In order to evaluate the energy distribution (due to matter and fields including gravitation) associated with a space-time model of Szekeres class I and II metrics, we consider the Einstein, Bergmann-Thomson and Landau-Lifshitz energy definitions in the teleparallel gravity (the tetrad theory of gravitation (TG)). We have found that Einstein and Bergmann-Thomson energy distributions give the same results, Landau-Lifshitz distribution is disagree in TG with these definitions. These results are the same as a previous works of Aygun et al., they investigated the same problem by using Einstein, Bergmann-Thomson, Landau-Lifshitz (LL) and Moller energy-momentum complexes in GR. However, both GR and TG are equivalent theories that is the energy densities are the same using different energy-momentum complexes in both theories. Also, our results are support the Cooperstock's hypothesis.
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    Energy-momentum localization in Marder space-time
    (Indian Acad Sciences, 2007) Aygun, S.; Aygun, M.; Tarhan, I.
    Considering the Einstein, Moller, Bergmann-Thomson, Landau-Lifshitz (LL), Papapetrou, Qadir-Sharif and Weinberg's definitions in general relativity, we find the momentum four-vector of the closed Universe based on Marder space-time. The momentum four-vector (due to matter plus field) is found to be zero. These results support the viewpoints of Banerjee-Sen, Xulu and Aydogdu-Salti. Another point is that our study agrees with the previous works of Cooperstock-Israelit, Rosen, Johri et al.
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    Moller energy-momentum complex in general relativity for higher dimensional universes
    (Iop Publishing Ltd, 2007) Ayguen, M.; Ayguen, S.; Yilmaz, I.; Baysal, H.; Tarhan, I.
    Using the Moller energy momentum definition in general relativity (GR) we calculate the total energy momentum distribution associated with (n + 2)-dimensional homogeneous and isotropic model of the universe. It is found that total energy of Moller is vanishing in (n + 2) dimensions everywhere but n-momentum components of Moller in (n + 2) dimensions are different from zero. Also, we evaluate the static Einstein Universe, FRW universe and de Sitter universe in four dimensions by using (n + 2)-type -metric, then calculate the Moller energy momentum distribution of these spacetimes. However, our results are consistent with the results of Banerjee and Sen, Xulu, Radinschi, Vargas, Cooperstock-Israelit, Aygun et at., Rosen, and Johri et al. in four dimensions.
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    On the energy-momentum problem in static Einstein universe
    (Iop Publishing Ltd, 2007) Aygun, S.; Tarhan, I.; Baysal, H.
    The energy-momentum distributions of Einstein's simplest static geometrical model for an isotropic and homogeneous universe are evaluated. For this purpose, Einstein, Bergmann-Thomson, Landau-Lifshitz (LL), Moller and Papapetrou energy-momentum complexes are used in general relativity. While Einstein and Bergmann-Thomson complexes give exactly the same results, LL and Papapetrou energy-momentum complexes do not provide the same energy densities. The Moller energy-momentum density is found to be zero everywhere in Einstein's universe. Also, several spacetimes are the limiting cases considered here.
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    The Decay of Massive Scalar Field in Non-Static Godel Type Universe with Viscous Fluid and Heat Flow
    (Springer/Plenum Publishers, 2008) Ayguen, S.; Tarhan, I.
    In this study, we have investigated the dynamics of non-static Godel type rotating universe with massive scalar field, viscous fluid and heat flow in the presence of cosmological constant. For various cosmic matter forms, the behavior of the cosmological constant (Sigma), shear (eta) and bulk (xi) viscosity coefficients and other kinematic quantities have studied in the early universe. We have showed the decay of massive scalar field in the non-static rotating Godel type universe and we have obtained constant scalar field with and without source density. Also, we have investigated the effects of massive scalar field on the matter density and pressure. From solutions of the field equations, we have a cosmological model with non-zero expansion, shear, heat flux and rotation. Also some physical and geometrical aspects of the model discussed.