294 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
Thermal conductivity in large- two-dimensional antiferromagnets: Role of phonon scattering
Motivated by the recent heat transport experiments in 2D antiferromagnets,
such as LaCuO, where the exchange coupling is larger than the Debye
energy , we discuss different types of relaxation processes for
magnon heat current with a particular focus on coupling to 3D phonons. We study
thermal conductivity by these in-plane magnetic excitations using two distinct
techniques, Boltzmann formalism within the relaxation-time approximation and
memory-function approach. Within these approaches, a close consideration is
given to the scattering of magnons by both acoustic and optical branches of
phonons. A remarkable accord between the two methods with regards to the
asymptotic behavior of the effective relaxation rates is demonstrated.
Additional scattering mechanisms, due to grain boundaries, impurities, and
finite correlation length in the paramagnetic phase, are discussed and included
in the calculations of the thermal conductivity . Again, we
demonstrate a close similarity of the results from the two techniques of
calculating . Our complementary approach strongly suggests that
scattering from optical or zone-boundary phonons is important for magnon heat
current relaxation in a high temperature window of .Comment: 21+ pages, 16 figure
Highly Dispersive Scattering From Defects In Non-Collinear Magnets
We demonstrate that point-like defects in non-collinear magnets give rise to
a highly dispersive structure in the magnon scattering, violating a standard
paradigm of its momentum independence. For a single impurity spin coupled to a
prototypical non-collinear antiferromagnet we find that the resolvent is
dominated by a distinct dispersive structure with its momentum-dependence set
by the magnon dispersion and shifted by the ordering vector. This feature is a
consequence of umklapp scattering off the impurity-induced spin texture, which
arises due to the non-collinear ground state of the host system. Detailed
results for the staggered and uniform magnetization of this texture as well as
the T-matrix from numerical linear spin-wave theory are presented.Comment: 5+5 pages, 4+5 fig
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
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
Spin-Dynamics of the antiferromagnetic S=1/2-Chain at finite magnetic Fields and intermediate Temperatures
We present a study of the dynamic structure factor of the antiferromagnetic
spin-1/2 Heisenberg chain at finite temperatures and finite magnetic fields.
Using Quantum-Monte-Carlo based on the stochastic series expansion and
Maximum-Entropy methods we evaluate the longitudinal and the transverse dynamic
structure factor from vanishing magnetic fields up to and above the threshold
for ferromagnetic saturation, as well as for high and for intermediate
temperatures. We study the field-induced redistribution of spectral weight
contrasting longitudinal versus transverse excitations. At finite fields below
saturation incommensurate low-energy modes are found consistent with zero
temperature Bethe-Ansatz. The crossover between the field induced ferromagnet
above and the Luttinger liquid below is analyzed in terms of the
transverse spin-dynamics. Evaluating sum-rules we assess the quality of the
analytic continuation and demonstrate excellent consistency of the
Maximum-Entropy results.Comment: 10 pages, 6 figure
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