We study the evolution of a perfect--fluid sphere coupled to a scalar
radiation field. By ensuring a Ricci invariant regularity as a conformally flat
spacetime at the central world line we find that the fluid coupled to the
scalar field satisfies the equation of state $\rho_c+3p_c=$ constant at the
center of the sphere, where the energy $\rho_c$ density and the pressure $p_c$
do not necessarily contain the scalar field contribution. The fluid can be
interpreted as anisotropic and radiant because of the scalar field, but it
becomes perfect and non radiative at the center of the sphere. These results
are being currently considered to build up a numerical relativistic
hydrodynamic solver.Comment: 4 pages; to appear in Physical Review
Two salts of the biopolymer chitosan were prepared in aqueous medium by employing an excess of HCl or HNO3 in order to ensure neutralization of all NH2-chitosan groups. Chitosan salts were extensively dialyzed in dionised water and dried at 40 ºC until film formation. The films were characterized by thermogravimetry, FTIR and conductimetric tritration. QH+Cl− and QH+NO3− salts were viscosimetrically evaluated in free acid aqueous solutions in the presence of NaCl to control ionic strength of the medium. Unexpected high intrinsic viscosity values were obtained at low ionic strength when QH+NO3− salt were evaluated. Smidsrod´s approach was employed to estimate the stiffness parameter of both salts and B = 0.084 and 0.120 for QH+Cl− and QH+NO3−, respectively, were obtained.
A study is presented for the non linear evolution of a self gravitating distribution of matter coupled to a massless scalar field. The characteristic formulation for numerical relativity is used to follow the evolution by a sequence of light cones open to the future. Bondian frames are used to endow physical meaning to the matter variables and to the massless scalar field. Asymptotic approaches to the origin and to infinity are achieved; at the boundary surface interior and exterior solutions are matched guaranteeing the Darmois-Lichnerowicz conditions. To show how the scheme works some numerical models are discussed. We exemplify evolving scalar waves on the following fixed backgrounds: A) an atmosphere between the boundary surface of an incompressible mixtured fluid and infinity; B) a polytropic distribution matched to a Schwarzschild exterior; C) a Schwarzschild-Schwarzschild spacetime. The conservation of energy, the Newman-Penrose constant preservation and other expected features are observed.
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