Phase diagrams of classical spin fluids: the influence of an external magnetic field on the liquid-gas transition

The influence of an external magnetic field on the liquid-gas phase transition in Ising, XY, and Heisenberg spin fluid models is studied using a modified mean field theory and Gibbs ensemble Monte Carlo simulations. It is demonstrated that the theory is able to reproduce quantitatively all characteristic features of the field dependence of the critical temperature T_c(H) for all the three models. These features include a monotonic decrease of T_c with rising H in the case of the Ising fluid as well as a more complicated nonmonotonic behavior for the XY and Heisenberg models. The nonmonotonicity consists in a decrease of T_c with increasing H at weak external fields, an increase of T_c with rising H in the strong field regime, and the existence of a minimum in T_c(H) at intermediate values of H. Analytical expressions for T_c(H) in the large field limit are presented as well. The magnetic para-ferro phase transition is also considered in simulations and described within the mean field theory.Comment: 14 pages, 12 figures (to be submitted to Phys. Rev. E

Modified Gravity and Cosmology

In this review we present a thoroughly comprehensive survey of recent work on modified theories of gravity and their cosmological consequences. Amongst other things, we cover General Relativity, Scalar-Tensor, Einstein-Aether, and Bimetric theories, as well as TeVeS, f(R), general higher-order theories, Horava-Lifschitz gravity, Galileons, Ghost Condensates, and models of extra dimensions including Kaluza-Klein, Randall-Sundrum, DGP, and higher co-dimension braneworlds. We also review attempts to construct a Parameterised Post-Friedmannian formalism, that can be used to constrain deviations from General Relativity in cosmology, and that is suitable for comparison with data on the largest scales. These subjects have been intensively studied over the past decade, largely motivated by rapid progress in the field of observational cosmology that now allows, for the first time, precision tests of fundamental physics on the scale of the observable Universe. The purpose of this review is to provide a reference tool for researchers and students in cosmology and gravitational physics, as well as a self-contained, comprehensive and up-to-date introduction to the subject as a whole.Comment: 312 pages, 15 figure

Exact and asymptotic solutions to tensor-scalar cosmologies

In the tensor-scalar theory of gravity, we give a number of explicit solutions and examine analytically their asymptotic behavior. We consider homogeneous cosmologies with perfect fluid matter distribution satisfying the equation of state p = λ ρ where λ is a constant -1 ≤ λ ≥ 1. The convergence of our theory to general relativity is considered to be "good" if the scalar field φ = const. is an attractor of the equations of motion. When p = -ρ new varieties of inflation arise in which the scale factor a(t) ∞ tα exp (K · tβ).SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Phase transitions in ferromagnetic fluids

Doctorat en Sciencesinfo:eu-repo/semantics/nonPublishe

Phase diagrams of the classical Heisenberg fluid within the extended van der Waals approximation

info:eu-repo/semantics/publishe

Thermodynamic stability of ferromagnetic liquids in the presence of nematic interactions

info:eu-repo/semantics/publishe

Interfaces of polydisperse fluids: Surface tension and adsorption properties

We consider a system of spherical colloidal particles with a size polydispersity and use a simple van der Waals description in order to study the combined effect of both the polydispersity and the spatial nonuniformity induced by a planar interface between a low-density fluid phase (enriched in small particles) and a high-density fluid phase (enriched in large particles). We find a strong adsorption of small particles at the interface, the latter being broadened with respect to the monodisperse case. We also find that the surface tension of the polydisperse system results from a competition between the tendency of the polydispersity to lower the surface tension and its tendency to raise the critical-point temperature (i.e. its tendency to favor phase separation) with the former tendency winning at low temperatures and the latter at the higher temperatures.Journal Articleinfo:eu-repo/semantics/publishe