Palatini formulation of f(R,T)f(R,T) gravity theory, and its cosmological implications

We consider the Palatini formulation of $f(R,T)$ gravity theory, in which a nonminimal coupling between the Ricci scalar and the trace of the energy-momentum tensor is introduced, by considering the metric and the affine connection as independent field variables. The field equations and the equations of motion for massive test particles are derived, and we show that the independent connection can be expressed as the Levi-Civita connection of an auxiliary, energy-momentum trace dependent metric, related to the physical metric by a conformal transformation. Similarly to the metric case, the field equations impose the non-conservation of the energy-momentum tensor. We obtain the explicit form of the equations of motion for massive test particles in the case of a perfect fluid, and the expression of the extra-force, which is identical to the one obtained in the metric case. The thermodynamic interpretation of the theory is also briefly discussed. We investigate in detail the cosmological implications of the theory, and we obtain the generalized Friedmann equations of the $f(R,T)$ gravity in the Palatini formulation. Cosmological models with Lagrangians of the type $f=R-\alpha ^2/R+g(T)$ and $f=R+\alpha ^2R^2+g(T)$ are investigated. These models lead to evolution equations whose solutions describe accelerating Universes at late times.Comment: 22 pages, no figures, accepted for publication in EPJC; references adde

Phase equilibria of CO2 hydrate in NaCl-MgCl2 aqueous solutions

Phase equilibrium data for CO2 hydrate in presence of binary NaCl-MgCl2 aqueous solutions were obtained at four different concentrations (2 wt%NaCl-8 wt%MgCl2, 8 wt%NaCl-2wt%MgCl2, 5 wt% NaCl-15 wt%MgCl2, 15 wt% NaCl-5 wt%MgCl2) in the temperature range of (258.63 to 276.45) K and in the pressure range of (1.34 to 3.41) MPa, respectively. The measurements were carried out by employing isochoric pressure search method with uncertainties of +/- 0.1 K for temperature and +/- 0.02 MPa for pressure. The hydrate equilibrium data for the (CO2 + water) system were compared with some experimental data from the literature, and the acceptable agreement demonstrated the reliability of the experimental method used in this work. The van der Waals and Platteeuw (vdW-P) solid solution theory was used to model the hydrate phase, and the equation of Weiss combined with Pitzer-based model was applied to characterize the activity of water. The predicted results were in good consistency with the experimental data, and the average pressure deviation was 5.13%. (C) 2012 Elsevier Ltd. All rights reserved.</p

Soliton solution of continuum magnetization-equation in conducting ferromagnet with a spin-polarized current

Exact soliton solutions of a modified Landau-Lifshitz equation for the magnetization of conducting ferromagnet in the presence of a spin-polarized current are obtained by means of inverse scattering transformation. From the analytical solution effects of spin-current on the frequency, wave number, and dispersion law of spin wave are investigated. The one-soliton solution indicates obviously current-driven precession and periodic shape-variation as well. The inelastic collision of solitons by which we mean the shape change before and after collision appears due to the spin current. We, moreover, show that complete inelastic collisions can be achieved by adjusting spectrum and current parameters. This may lead to a potential technique for shape control of spin wave.Comment: 8 pages, 2 figure