920 research outputs found
Anisotropic Energy Distribution in Three-Dimensional Vibrofluidized Granular Systems
We examine the energy distribution in a three-dimensional model granular
system contained in an open cylinder under the influence of gravity. Energy is
supplied to the system by a vibrating base. We introduce spatially resolved,
partial particle-particle ``dissipations'' for directions parallel and
perpendicular to the energy input, respectively. Energy balances show that the
total (integrated) ``dissipation'' is less than zero in the parallel direction
while greater than zero in the perpendicular directions. The energy supplied to
the perpendicular directions is dissipated by particle-wall collisions. We
further define a fractional energy transfer, which in the steady state
represents the fraction of the power supplied by the vibrating base that is
dissipated at the wall. We examine the dependence of the fractional energy
transfer on the number of particles, the velocity of the vibrating base, the
particle-particle restitution coefficient, and the particle-wall restitution
coefficient. We also explore the influence of the system parameters on the
spatially dependent partial dissipations.Comment: 10 pages, 10 figures, RevTeX forma
Energy exchanges in a damped Langevin-like system with two thermal baths and an athermal reservoir
We study the properties of energy transfers in a Langevin-like model which
describes an inertial particle in a one-dimensional harmonic potential and
subjected to two heat baths and one athermal environment. The thermal noises
are white and Gaussian, and the temperatures of heat reservoirs are different.
The athermal medium act through an external non-Gaussian noise of Poisson type.
We discuss the long-time behavior of first cumulants of time-integrated power
due to the athermal reservoir. The averages and covariances of heat exchanged
with thermal baths are also evaluated for stationary states. The properties of
these cumulants are investigated in terms of the characteristics of external
noise.Comment: 23 pages, 7 figure
The Ferromagnetic Potts model under an external magnetic field: an exact renormalization group approach
The q-state ferromagnetic Potts model under a non-zero magnetic field coupled
with the 0^th Potts state was investigated by an exact real-space
renormalization group approach. The model was defined on a family of diamond
hierarchical lattices of several fractal dimensions d_F. On these lattices, the
renormalization group transformations became exact for such a model when a
correlation coupling that singles out the 0^th Potts state was included in the
Hamiltonian. The rich criticality presented by the model with q=3 and d_F=2 was
fully analyzed. Apart from the Potts criticality for the zero field, an
Ising-like phase transition was found whenever the system was submitted to a
strong reverse magnetic field. Unusual characteristics such as cusps and
dimensional reduction were observed on the critical surface.Comment: 8 pages, 6 figures. Accepted to be published in Phys. Rev B (2006
Lamellae Stability in Confined Systems with Gravity
The microphase separation of a diblock copolymer melt confined by hard walls
and in the presence of a gravitational field is simulated by means of a cell
dynamical system model. It is found that the presence of hard walls normal to
the gravitational field are key ingredients to the formation of well ordered
lamellae in BCP melts. To this effect the currents in the directions normal and
parallel to the field are calculated along the interface of a lamellar domain,
showing that the formation of lamellae parallel to the hard boundaries and
normal to the field correspond to the stable configuration. Also, it is found
thet the field increases the interface width.Comment: 4 pages, 2 figures, submitted to Physical Review
The impact of two-dimensional elastic disk
The impact of a two-dimensional elastic disk with a wall is numerically
studied. It is clarified that the coefficient of restitution (COR) decreases
with the impact velocity. The result is not consistent with the recent
quasi-static theory of inelastic collisions even for very slow impact. The
abrupt drop of COR is found due to the plastic deformation of the disk, which
is assisted by the initial internal motion.(to be published in J. Phys. Soc.
Jpn.)Comment: 6 Pages,2 figure
Scaling properties of granular materials
Given an assembly of viscoelastic spheres with certain material properties,
we raise the question how the macroscopic properties of the assembly will
change if all lengths of the system, i.e. radii, container size etc., are
scaled by a constant. The result leads to a method to scale down experiments to
lab-size.Comment: 4 pages, 2 figure
Exact Nonequilibrium Work Generating Function for a Small Classical System
We obtain the exact nonequilibrium work generating function (NEWGF), for a
small system consisting of a massive Brownian particle connected to internal
and external springs. The external work is provided to the system for a finite
time interval. The Jarzynski equality (JE), obtained in this case directly from
the NEWGF, is shown to be valid for the present model, in an exact way
regardless of the rate of external work
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