4,122 research outputs found
Equation of state and transport processes in self--similar spheres
We study the effect of transport processes (diffusion and free--streaming) on
a collapsing spherically symmetric distribution of matter in a self--similar
space--time. A very simple solution shows interesting features when it is
matched with the Vaidya exterior solution. In the mixed case (diffusion and
free--streaming), we find a barotropic equation of state in the stationary
regime. In the diffusion approximation the gravitational potential at the
surface is always constant; if we perturb the stationary state, the system is
very stable, recovering the barotropic equation of state as time progresses. In
the free--streaming case the self--similar evolution is stationary but with a
non--barotropic equation of state.Comment: 9 pages, 2 figure
Irrigação por bacias em nível na cultura da bananeira.
Descrição do sistema de irrigação; Vantagens, desvantagens e adaptabilidade; Bases para o dimensionamento; Operação e manejo do sistema de irrigação; Considerações sobre a exploração comercial da bananeira irrigada por bacias em nível.bitstream/item/71927/1/CPAMN-CIR.-TEC.-04-92.pd
Fabry Perot Halpha Observations of the Barred Spiral NGC 3367
We report the gross properties of the velocity field of the barred spiral
galaxy NGC 3367. The following values were found: inclination with respect to
the plane of the sky, i=30 deg; position angle (PA) of receding semi major axis
PA=51 and systemic velocity V(sys)=3032 km/s. Large velocity dispersion are
observed of upt o 120 km/s in the nuclear region, of up to 70 km/s near the
eastern bright sources just beyond the edge of the stellar bar where three
spiral arms seem to start and in the western bright sources at about 10 kpc.
Deviations from normal circular velocities are observed from all the disk but
mainly from the semi circle formed by the string of south western Halpha
sources. An estimate of the dynamical mass is M(dyn)=2x10^11 Msolar.Comment: Accepted to be published in May 2001 issue in the A.J. 19 pages, 7
figure
Nonadiabatic charged spherical evolution in the postquasistatic approximation
We apply the postquasistatic approximation, an iterative method for the
evolution of self-gravitating spheres of matter, to study the evolution of
dissipative and electrically charged distributions in General Relativity. We
evolve nonadiabatic distributions assuming an equation of state that accounts
for the anisotropy induced by the electric charge. Dissipation is described by
streaming out or diffusion approximations. We match the interior solution, in
noncomoving coordinates, with the Vaidya-Reissner-Nordstr\"om exterior
solution. Two models are considered: i) a Schwarzschild-like shell in the
diffusion limit; ii) a Schwarzschild-like interior in the free streaming limit.
These toy models tell us something about the nature of the dissipative and
electrically charged collapse. Diffusion stabilizes the gravitational collapse
producing a spherical shell whose contraction is halted in a short
characteristic hydrodynamic time. The streaming out radiation provides a more
efficient mechanism for emission of energy, redistributing the electric charge
on the whole sphere, while the distribution collapses indefinitely with a
longer hydrodynamic time scale.Comment: 11 pages, 16 Figures. Accepted for publication in Phys Rev
Área de ocorrência do mexilhão dourado (Limnoperna fortunei) na bacia do Alto Paraguai, entre os anos de 1998 e 2004.
O uso de água armazenada nos grandes navios marítimos para obter maior estabilidade, ajudar na propulsão e em manobras, a chamada "água de lastro", é o principal meio de introdução de organismos marinhos em ambientes aquáticos, tanto marinhos como de água doce. Em todo o mundo são transferidas anualmente cerca de 12 bilhões de toneladas de "água de lastro", que transportam aproximadamente 4.500 espécies diferentes. No Brasil, aproximadamente 95% de todo o comércio exterior é feito por via marítima e estima-se que 40.000 navios visitem os portos brasileiros anualmente, deslastrando 40 milhões de toneladas de água por ano (Silva & Souza, 2004). Pela "água de lastro" a espécie de bivale de água doce Limnoperna fortunei (Dunker, 1857) foi introduzida no estuário do rio da Prata, em 1991, provavelmente trazido por navios da Korea e Hong Kong (Pastorino et al., 1993). E a navegação no sistema Paraguai-Paraná foi o principal vetor da introdução desta espécie na Bacia do Alto Paraguai, onde foi observada pela primeira vez em 1998, no rio Paraguai, próximo à cidade de Corumba (MS).bitstream/item/39645/1/DOC64.pd
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