106,817 research outputs found
Entropy Production in Relativistic Binary Mixtures
In this paper we calculate the entropy production of a relativistic binary
mixture of inert dilute gases using kinetic theory. For this purpose we use the
covariant form of Boltzmann's equation which, when suitably transformed, yields
a formal expression for such quantity. Its physical meaning is extracted when
the distribution function is expanded in the gradients using the well-known
Chapman-Enskog method. Retaining the terms to first order, consistently with
Linear Irreversible Thermodynamics we show that indeed, the entropy production
can be expressed as a bilinear form of products between the fluxes and their
corresponding forces. The implications of this result are thoroughly discussed
Characterizing the propagation of gravity waves in 3D nonlinear simulations of solar-like stars
The revolution of helio- and asteroseismology provides access to the detailed
properties of stellar interiors by studying the star's oscillation modes. Among
them, gravity (g) modes are formed by constructive interferences between
progressive internal gravity waves (IGWs), propagating in stellar radiative
zones. Our new 3D nonlinear simulations of the interior of a solar-like star
allows us to study the excitation, propagation, and dissipation of these waves.
The aim of this article is to clarify our understanding of the behavior of IGWs
in a 3D radiative zone and to provide a clear overview of their properties. We
use a method of frequency filtering that reveals the path of {individual}
gravity waves of different frequencies in the radiative zone. We are able to
identify the region of propagation of different waves in 2D and 3D, to compare
them to the linear raytracing theory and to distinguish between propagative and
standing waves (g modes). We also show that the energy carried by waves is
distributed in different planes in the sphere, depending on their azimuthal
wave number. We are able to isolate individual IGWs from a complex spectrum and
to study their propagation in space and time. In particular, we highlight in
this paper the necessity of studying the propagation of waves in 3D spherical
geometry, since the distribution of their energy is not equipartitioned in the
sphere.Comment: 14 pages, 12 figues, accepted by Astronomy & Astrophysic
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