341 research outputs found
Energy non-equipartition in multicomponent granular mixtures
We study non-equipartition of energy in granular fluids composed by an
arbitrarily large number of components. We focus on a simple mean field model,
based upon a Maxwell collision operator kernel, and predict the temperature
ratios for the species. Moreover, we perform Direct Monte Carlo simulations in
order to verify the predictions.Comment: submitted to PR
From particle segregation to the granular clock
Recently several authors studied the segregation of particles for a system
composed of mono-dispersed inelastic spheres contained in a box divided by a
wall in the middle. The system exhibited a symmetry breaking leading to an
overpopulation of particles in one side of the box. Here we study the
segregation of a mixture of particles composed of inelastic hard spheres and
fluidized by a vibrating wall. Our numerical simulations show a rich
phenomenology: horizontal segregation and periodic behavior. We also propose an
empirical system of ODEs representing the proportion of each type of particles
and the segregation flux of particles. These equations reproduce the major
features observed by the simulations.Comment: 10 page
Raman scattering in a Heisenberg {\boldmath } antiferromagnet on the triangular lattice
We investigate two-magnon Raman scattering from the Heisenberg
antiferromagnet on the triangular lattice, considering both the effect of
renormalization of the one-magnon spectrum by 1/S corrections and final-state
magnon-magnon interactions. The bare Raman intensity displays two peaks related
to one-magnon van-Hove singularities. We find that 1/S self-energy corrections
to the one-magnon spectrum strongly modify this intensity profile. The central
Raman-peak is significantly enhanced due to plateaus in the magnon dispersion,
the high frequency peak is suppressed due to magnon damping, and the overall
spectral support narrows considerably. Additionally we investigate final-state
interactions by solving the Bethe-Salpeter equation to . In contrast to
collinear antiferromagnets, the non-collinear nature of the magnetic ground
state leads to an irreducible magnon scattering which is retarded and
non-separable already to lowest order. We show that final-state interactions
lead to a rather broad Raman-continuum centered around approximately twice the
'roton'-energy. We also discuss the dependence on the scattering geometry.Comment: 7 pages, 5 figure
A note on dualities in Einstein's gravity in the presence of a non-minimally coupled scalar field
We show that the action of Einstein's gravity with a scalar field coupled in
a generic way to spacetime curvature is invariant under a particular set of
conformal transformations. These transformations relate dual theories for which
the effective couplings of the theory are scaled uniformly. In the simplest
case, this class of dualities reduce to the S-duality of low-energy effective
action of string theory.Comment: 12 page
High-dimensional quantum dynamics of adsorption and desorption of H at Cu(111)
We performed high-dimensional quantum dynamical calculations of the
dissociative adsorption and associative desorption of hydrogen on Cu(111). The
potential energy surface (PES) is obtained from density functional theory
calculations. Two regimes of dynamics are found, at low energies sticking is
determined by the minimum energy barrier, at high energies by the distribution
of barrier heights. Experimental results are well-reproduced qualitatively, but
some quantitative discrepancies are identified as well.Comment: 4 two column pages, revtex, 4 figures, to appear in Phys. Rev. Let
Bond-impurity induced bound states in disordered spin-1/2 ladders
We discuss the effect of weak bond-disorder in two-leg spin ladders on the
dispersion relation of the elementary triplet excitations with a particular
focus on the appearance of bound states in the spin gap. Both the cases of
modified exchange couplings on the rungs and the legs of the ladder are
analyzed. Based on a projection on the single-triplet subspace, the
single-impurity and small cluster problems are treated analytically in the
strong-coupling limit. Numerically, we study the problem of a single impurity
in a spin ladder by exact diagonalization to obtain the low-lying excitations.
At finite concentrations and to leading order in the inter-rung coupling, we
compare the spectra obtained from numerical diagonalization of large systems
within the single-triplet subspace with the results of diagrammatic techniques,
namely low-concentration and coherent-potential approximations. The
contribution of small impurity clusters to the density of states is also
discussed.Comment: 9 pages REVTeX4 including 7 figures, final version; Fig. 5 modifie
Anomalous frequency and intensity scaling of collective and local modes in a coupled spin tetrahedron system
We report on the magnetic excitation spectrum of the coupled spin tetrahedral
system CuTeOCl using Raman scattering on single
crystals. The transition to an ordered state at T=18.2 K evidenced
from thermodynamic data leads to the evolution of distinct low-energy magnetic
excitations superimposed by a broad maximum. These modes are ascribed to
magnons with different degree of localization and a two-magnon continuum. Two
of the modes develop a substantial energy shift with decreasing temperature
similar to the order parameter of other Neel ordered systems. The other two
modes show only a negligible temperature dependence and dissolve above the
ordering temperature in a continuum of excitations at finite energies. These
observations point to a delicate interplay of magnetic inter- and
intra-tetrahedra degrees of freedom and an importance of singlet fluctuations
in describing a spin dynamics.Comment: 7pages, 6figures, 1tabl
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