850 research outputs found
Energy Dissipation and Trapping of Particles Moving on a Rough Surface
We report an experimental, numerical and theoretical study of the motion of a
ball on a rough inclined surface. The control parameters are , the diameter
of the ball, , the inclination angle of the rough surface and ,
the initial kinetic energy. When the angle of inclination is larger than some
critical value, , the ball moves at a constant average
velocity which is independent of the initial conditions. For an angle , the balls are trapped after moving a certain distance. The
dependence of the travelled distances on , and . is
analysed. The existence of two kinds of mechanisms of dissipation is thus
brought to light. We find that for high initial velocities the friction force
is constant. As the velocity decreases below a certain threshold the friction
becomes viscous.Comment: 8 pages RevTeX, 12 Postscript figure
Equations to predict weaned lamb's empty body weight from slaughter weight of different genetic groups.
Effect of feed levels over empty body weight and their components of lambs from seven genetic groups.
Effect of boundary conditions on diffusion in two-dimensional granular gases
We analyze the influence of boundary conditions on numerical simulations of
the diffusive properties of a two dimensional granular gas. We show in
particular that periodic boundary conditions introduce unphysical correlations
in time which cause the coefficient of diffusion to be strongly dependent on
the system size. On the other hand, in large enough systems with hard walls at
the boundaries, diffusion is found to be independent of the system size. We
compare the results obtained in this case with Langevin theory for an elastic
gas. Good agreement is found. We then calculate the relaxation time and the
influence of the mass for a particle of radius in a sea of particles of
radius . As granular gases are dissipative, we also study the influence of
an external random force on the diffusion process in a forced dissipative
system. In particular, we analyze differences in the mean square velocity and
displacement between the elastic and inelastic cases.Comment: 15 figures eps figures, include
On the velocity distributions of the one-dimensional inelastic gas
We consider the single-particle velocity distribution of a one-dimensional
fluid of inelastic particles. Both the freely evolving (cooling) system and the
non-equilibrium stationary state obtained in the presence of random forcing are
investigated, and special emphasis is paid to the small inelasticity limit. The
results are obtained from analytical arguments applied to the Boltzmann
equation along with three complementary numerical techniques (Molecular
Dynamics, Direct Monte Carlo Simulation Methods and iterative solutions of
integro-differential kinetic equations). For the freely cooling fluid, we
investigate in detail the scaling properties of the bimodal velocity
distribution emerging close to elasticity and calculate the scaling function
associated with the distribution function. In the heated steady state, we find
that, depending on the inelasticity, the distribution function may display two
different stretched exponential tails at large velocities. The inelasticity
dependence of the crossover velocity is determined and it is found that the
extremely high velocity tail may not be observable at ``experimentally
relevant'' inelasticities.Comment: Latex, 14 pages, 12 eps figure
The difference between the narrow line region of Seyfert 1 and Seyfert 2 galaxies
This paper presents a comparative study of emission line ratios of the Narrow
Line Region (NLR) of Seyfert 1 and Seyfert 2 galaxies. It includes a literature
compilation of the emission line fluxes [OII]3727A, [NeIII]3869A, [OIII]5007A
and [NeV]3426A, as well as 60mum continuum flux, for a sample of 52 Seyfert 1's
and 68 Seyfert 2's. The distribution of the emission line ratios [OII]/[NeIII]
and [OII]/[NeV] shows that Seyfert 1's and Seyfert 2's are statistically
different, in the sense that Seyfert 1's have values smaller than those of
Seyfert 2's, indicating a higher excitation spectrum. These and other emission
line ratios are compared with sequences of models which combine different
proportions of matter and ionization bounded clouds and also sequences of
models which vary only the ionization parameter. This comparison shows that the
former models reproduce better the overall distribution of emission line
ratios, indicating that Seyfert 1's have a smaller number of ionization bounded
clouds than Seyfert 2's. This difference, together with other results available
in the literature, are interpreted from the point of view of four different
scenarios. The most likely scenario assumes that Seyfert 1's have NLR's smaller
than those of Seyfert 2's, possibly due to a preferential alignment of the
torus axis close to the host galaxy plane axis in Seyfert 1's.Comment: 13 pages, 9 postscript figures, 3 tables, accepted for publication in
the Astrophysical Journa
The dynamics of apparent horizons in Robinson-Trautman spacetimes
We present an alternative scheme of finding apparent horizons based on
spectral methods applied to Robinson-Trautman spacetimes. We have considered
distinct initial data such as representing the spheroids of matter and the
head-on collision of two non-rotating black holes. The evolution of the
apparent horizon is presented. We have obtained in some cases a mass gap
between the final Bondi and apparent horizon masses, whose implications were
briefly commented in the light of the thermodynamics of black holes.Comment: 9 pages, 7 figure
Service provision and barriers to care for homeless people with mental health problems across 14 European capital cities
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited
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