5,031 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
The Post-Quasistatic Approximation as a test bed for Numerical Relativity
It is shown that observers in the standard ADM 3+1 treatment of matter are
the same as the observers used in the matter treatment of Bondi: they are
comoving and local Minkowskian. Bondi's observers are the basis of the
post--quasitatic approximation (PQSA) to study a contracting distribution of
matter. This correspondence suggests the possibility of using the PQSA as a
test bed for Numerical Relativity. The treatment of matter by the PQSA and its
connection with the ADM 3+1 treatment are presented, for its practical use as a
calibration tool and as a test bed for numerical relativistic hydrodynamic
codes.Comment: 4 pages; to appear as a Brief Report in Physical Review
Avaliação das condições de salinidade, drenagem e fertilidade e alterações químicas ocorridas em areia quartzozas apos cinco anos sob irrigação localizada.
Este trabalho foi conduzido em uma área de areia quartzoza da Fazenda Boa Esperança, em Petrolina-Pe, cultivada c om videira e mangueira. Avaliou-se o efeito d a irrigação e da adubação, aplicadas durante cinco anos, sobre algumas características químicas do solo e aparecimento de lençol freático. O sistema de irrigação utilizado foi micro-aspersão. Amostragem do solo foi feita em 34 pontos da área cultivada, onde estão localizados os poços, para observação do nível do lençol freático. Os resultados analíticos mostraram que houve um aumento da CE das bases trocáveis e do fósforo "disponível" e o aparecimento do lençol freático, na área da videira
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
The Weibull-Geometric distribution
In this paper we introduce, for the first time, the Weibull-Geometric
distribution which generalizes the exponential-geometric distribution proposed
by Adamidis and Loukas (1998). The hazard function of the last distribution is
monotone decreasing but the hazard function of the new distribution can take
more general forms. Unlike the Weibull distribution, the proposed distribution
is useful for modeling unimodal failure rates. We derive the cumulative
distribution and hazard functions, the density of the order statistics and
calculate expressions for its moments and for the moments of the order
statistics. We give expressions for the R\'enyi and Shannon entropies. The
maximum likelihood estimation procedure is discussed and an algorithm EM
(Dempster et al., 1977; McLachlan and Krishnan, 1997) is provided for
estimating the parameters. We obtain the information matrix and discuss
inference. Applications to real data sets are given to show the flexibility and
potentiality of the proposed distribution
Is disclosing an autism spectrum disorder in school associated with reduced stigmatization?
This is the final version. Available on open access from SAGE Publications via the DOI in this recordDisclosing an autism diagnosis is associated with reduced stigmatization for autistic
adults. However, it is unknown whether this is true for autistic adolescents. We used a
vignette-and-questionnaire design to study stigmatizing attitudes with adolescents (aged 11-
12 and 14-16 years, total N=250) in a UK school. We investigated the effect of disclosing
that a fictional adolescent was autistic on stigmatizing attitudes of peers by testing the effect
of disclosure on the social and emotional distance pupils wanted to maintain from the autistic
adolescent and their assessment of the adolescent’s responsibility for their own behaviour.
Moderation of effects by gender and age-group were analysed. Disclosing autism made no
improvement to the social and emotional distance peers wanted to maintain from the autistic
adolescent, but was associated with significant reduction in personal responsibility attributed
to the adolescent’s behaviour. Boys attributed more personal responsibility to the autistic
adolescent than girls, but this gender effect was reduced when autism was disclosed. These
findings suggest that disclosing autism to other pupils may be of limited use in reducing
stigmatization by peers in UK schools.Wellcome Trus
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