This paper examines the stability of the transition from the early decelerating stage of the Universe to the recent accelerating stage for the perfect fluid cosmological locally rotationally symmetric(LRS) Bianchi-I m...This paper examines the stability of the transition from the early decelerating stage of the Universe to the recent accelerating stage for the perfect fluid cosmological locally rotationally symmetric(LRS) Bianchi-I model in f(R, T) theory. To determine the solution of field equations, the idea of a timevarying deceleration parameter(DP) which yields a scale factor, for which the Universe attains a phase transition scenario and is consistent with recent cosmological observations, is used. The time-dependent DP yields a scale factor a=exp■, where β and k are respectively arbitrary and integration constants. By using the recent cons_traints(H_0 _= 73.8, and q_0 =-0.54) from Type Ia Supernova(SN Ia) data in combination with Baryonic Acoustic Oscillations(BAO) and Cosmic Microwave Background(CMB) observations(Giostri et al.), we obtain the values of β = 0.0062 and k = 0.000016 for which we have derived a cosmological model from the early decelerated phase to the present accelerating phase. By applying_ other r_ecent constraints(H_0 = 73.8, q_0 =-0.73) from SNe Ia Union data(Cunha), we obtain the values of β = 0.0036 and k = 0.000084 for which we have derived a cosmological model in the accelerating phase only. We have compared both models with experimental data. The stability of the background solution has been examined also for the metric perturbations alongside the properties of future singularities in a Universe ruled by dark energy with phantom type fluid. We demonstrate the presence of a stable fixed point with a condition of state ω <-1 and numerically affirm this is really a late-time attractor in the ghost overwhelmed Universe. Some physical and geometric properties of the model are found and examined.展开更多
We present the interior solutions of distributions of magnetized fluid inside a sphere in f（R, T） gravity. Tile magnetized sphere is embedded in an exterior Reissner NordstrOm metric. We assume that all physical qua...We present the interior solutions of distributions of magnetized fluid inside a sphere in f（R, T） gravity. Tile magnetized sphere is embedded in an exterior Reissner NordstrOm metric. We assume that all physical quantities are in static equilibrium. The perfect fluid matter is studied under a particular form of the Lagrangian density f（R, T）. The magnetic field profile in modified gravity is calculated. Observational data of neutron stars are used to plot suitable models of magnetized compact objects. We reveal the effect of f（R, T） gravity on the magnetic field profile, with application to neutron stars, especially highly magnetized neutron stars found in x-ray pulsar systems. Finally, the effective potential Veff and innermost stable circular orbits, arising out of the motion of a test particle of negligible mass influenced by attraction or repulsion from the massive center, are discussed.展开更多
In this paper, the dynamical behavior of an anisotropic universe in an extended gravity e.g. the f (R,T ) theory of gravity is studied. We use f (R,T ) = R + 2μT , where R is the Ricci scalar, T is the trace of energ...In this paper, the dynamical behavior of an anisotropic universe in an extended gravity e.g. the f (R,T ) theory of gravity is studied. We use f (R,T ) = R + 2μT , where R is the Ricci scalar, T is the trace of energy-momentum tensor and μ is a constant. Two cosmological models are constructed using the power law expansion and hybrid law cosmology in Bianchi type I universe, where the matter field is considered to be a perfect fluid. It is found that in both the cases the anisotropic behavior is in agreement with the observational results. The state finder diagnostic pair and energy conditions are also calculated and analyzed.展开更多
In this paper, the cosmological models of the universe are constructed in gravity with choice of the functional in the form ?and . The space-time considered here is Bianchi Type I and the energy momentum tensor is in ...In this paper, the cosmological models of the universe are constructed in gravity with choice of the functional in the form ?and . The space-time considered here is Bianchi Type I and the energy momentum tensor is in the form of perfect fluid. Two cosmological models are presented using a power form of exponential function and a hyperbolic form. The energy conditions along with the state finder diagnostic pair have been obtained and analyzed.展开更多
We report a viable exponential gravity model for the accelerated expansion of the universe in Bianchi VI<sub>h</sub> space-time. By considering the estimated physical parameters, the cosmological models ar...We report a viable exponential gravity model for the accelerated expansion of the universe in Bianchi VI<sub>h</sub> space-time. By considering the estimated physical parameters, the cosmological models are constructed and analyzed in detail. We found that the state parameter in both the models increases to a higher negative range in an early epoch of the phantom domain and it goes to the positive domain at a late phase of the evolution. The effective cosmological constant remains in a positive domain for both models, which is a good sign of accelerating expansion of the universe.展开更多
Based on the potential-hybrid/mixed finite element scheme, 4-node quadrilateral plate-bending elements MP4, MP4a and cylindrical shell element MCS4 are derived with, the inclusion of splitting rotations. All these ele...Based on the potential-hybrid/mixed finite element scheme, 4-node quadrilateral plate-bending elements MP4, MP4a and cylindrical shell element MCS4 are derived with, the inclusion of splitting rotations. All these elements demonstrate favorable convergence behavior over the existing counterparts, free from spurious kinematic mode's and do not exhibit locking phenomenon in thin platef shell limit. Inter-connections between the existing modified variational functionals for the use of formulating C0-and C1-continuous elements are also indicated. Important particularizations of the present scheme include Prathop's consistent field formulation, the RIT/SRIT-compatible displacement model and so on.展开更多
In the present study, a homogeneous and anisotropic LRS Bianchi type I universe model is considered in <i>f</i>(<i>R</i>, <i>T</i>) theory of gravity. In order to find an exact solu...In the present study, a homogeneous and anisotropic LRS Bianchi type I universe model is considered in <i>f</i>(<i>R</i>, <i>T</i>) theory of gravity. In order to find an exact solution of the field equations of the model, the model presented is based on a unique condition of periodically time varying deceleration parameter. The physical and geometrical characteristics of the universe model have been studied. It has been shown that the model has point-type singularity and all the cosmological parameters possess periodic time behavior. The model has a cyclic expansion history, for example, the model starts with the decelerating expansion, and later it transits to an accelerating phase of expansion and then goes to super-exponential phase of expansion in a period.展开更多
文摘This paper examines the stability of the transition from the early decelerating stage of the Universe to the recent accelerating stage for the perfect fluid cosmological locally rotationally symmetric(LRS) Bianchi-I model in f(R, T) theory. To determine the solution of field equations, the idea of a timevarying deceleration parameter(DP) which yields a scale factor, for which the Universe attains a phase transition scenario and is consistent with recent cosmological observations, is used. The time-dependent DP yields a scale factor a=exp■, where β and k are respectively arbitrary and integration constants. By using the recent cons_traints(H_0 _= 73.8, and q_0 =-0.54) from Type Ia Supernova(SN Ia) data in combination with Baryonic Acoustic Oscillations(BAO) and Cosmic Microwave Background(CMB) observations(Giostri et al.), we obtain the values of β = 0.0062 and k = 0.000016 for which we have derived a cosmological model from the early decelerated phase to the present accelerating phase. By applying_ other r_ecent constraints(H_0 = 73.8, q_0 =-0.73) from SNe Ia Union data(Cunha), we obtain the values of β = 0.0036 and k = 0.000084 for which we have derived a cosmological model in the accelerating phase only. We have compared both models with experimental data. The stability of the background solution has been examined also for the metric perturbations alongside the properties of future singularities in a Universe ruled by dark energy with phantom type fluid. We demonstrate the presence of a stable fixed point with a condition of state ω <-1 and numerically affirm this is really a late-time attractor in the ghost overwhelmed Universe. Some physical and geometric properties of the model are found and examined.
文摘We present the interior solutions of distributions of magnetized fluid inside a sphere in f（R, T） gravity. Tile magnetized sphere is embedded in an exterior Reissner NordstrOm metric. We assume that all physical quantities are in static equilibrium. The perfect fluid matter is studied under a particular form of the Lagrangian density f（R, T）. The magnetic field profile in modified gravity is calculated. Observational data of neutron stars are used to plot suitable models of magnetized compact objects. We reveal the effect of f（R, T） gravity on the magnetic field profile, with application to neutron stars, especially highly magnetized neutron stars found in x-ray pulsar systems. Finally, the effective potential Veff and innermost stable circular orbits, arising out of the motion of a test particle of negligible mass influenced by attraction or repulsion from the massive center, are discussed.
文摘In this paper, the dynamical behavior of an anisotropic universe in an extended gravity e.g. the f (R,T ) theory of gravity is studied. We use f (R,T ) = R + 2μT , where R is the Ricci scalar, T is the trace of energy-momentum tensor and μ is a constant. Two cosmological models are constructed using the power law expansion and hybrid law cosmology in Bianchi type I universe, where the matter field is considered to be a perfect fluid. It is found that in both the cases the anisotropic behavior is in agreement with the observational results. The state finder diagnostic pair and energy conditions are also calculated and analyzed.
文摘In this paper, the cosmological models of the universe are constructed in gravity with choice of the functional in the form ?and . The space-time considered here is Bianchi Type I and the energy momentum tensor is in the form of perfect fluid. Two cosmological models are presented using a power form of exponential function and a hyperbolic form. The energy conditions along with the state finder diagnostic pair have been obtained and analyzed.
文摘We report a viable exponential gravity model for the accelerated expansion of the universe in Bianchi VI<sub>h</sub> space-time. By considering the estimated physical parameters, the cosmological models are constructed and analyzed in detail. We found that the state parameter in both the models increases to a higher negative range in an early epoch of the phantom domain and it goes to the positive domain at a late phase of the evolution. The effective cosmological constant remains in a positive domain for both models, which is a good sign of accelerating expansion of the universe.
文摘Based on the potential-hybrid/mixed finite element scheme, 4-node quadrilateral plate-bending elements MP4, MP4a and cylindrical shell element MCS4 are derived with, the inclusion of splitting rotations. All these elements demonstrate favorable convergence behavior over the existing counterparts, free from spurious kinematic mode's and do not exhibit locking phenomenon in thin platef shell limit. Inter-connections between the existing modified variational functionals for the use of formulating C0-and C1-continuous elements are also indicated. Important particularizations of the present scheme include Prathop's consistent field formulation, the RIT/SRIT-compatible displacement model and so on.
文摘In the present study, a homogeneous and anisotropic LRS Bianchi type I universe model is considered in <i>f</i>(<i>R</i>, <i>T</i>) theory of gravity. In order to find an exact solution of the field equations of the model, the model presented is based on a unique condition of periodically time varying deceleration parameter. The physical and geometrical characteristics of the universe model have been studied. It has been shown that the model has point-type singularity and all the cosmological parameters possess periodic time behavior. The model has a cyclic expansion history, for example, the model starts with the decelerating expansion, and later it transits to an accelerating phase of expansion and then goes to super-exponential phase of expansion in a period.
