2,029 research outputs found
Bose-Hubbard Models in Confining Potentials: An Inhomogeneous Mean-Field Theory
We present an extensive study of Mott insulator (MI) and superfluid (SF)
shells in Bose-Hubbard (BH) models for bosons in optical lattices with harmonic
traps. For this we develop an inhomogeneous mean-field theory. Our results for
the BH model with one type of spinless bosons agrees quantitatively with
quantum Monte Carlo (QMC) simulations. Our approach is numerically less
intensive than such simulations, so we are able to perform calculation on
experimentally realistic, large 3D systems, explore a wide range of parameter
values, and make direct contact with a variety of experimental measurements. We
also generalize our inhomogeneous mean-field theory to study BH models with
harmonic traps and (a) two species of bosons or (b) spin-1 bosons. With two
species of bosons we obtain rich phase diagrams with a variety of SF and MI
phases and associated shells, when we include a quadratic confining potential.
For the spin-1 BH model we show, in a representative case, that the system can
display alternating shells of polar SF and MI phases; and we make interesting
predictions for experiments in such systems.Comment: 17 pages, 18 figure
Hepatitis B virus genotypes in Iran
[No abstract available
Multi-kink collisions in the model
We study simultaneous collisions of two, three, and four kinks and antikinks
of the model at the same spatial point. Unlike the kinks, the
kinks are asymmetric and this enriches the variety of the collision
scenarios. In our numerical simulations we observe both reflection and bound
state formation depending on the number of kinks and on their spatial ordering
in the initial configuration. We also analyze the extreme values of the energy
densities and the field gradient observed during the collisions. Our results
suggest that very high energy densities can be produced in multi-kink
collisions in a controllable manner. Appearance of high energy density spots in
multi-kink collisions can be important in various physical applications of the
Klein-Gordon model.Comment: 21 pages, 8 figures; v2: minor changes to match version published in
JHE
The role of phase dynamics in a stochastic model of a passively advected scalar
Collective synchronous motion of the phases is introduced in a model for the
stochastic passive advection-diffusion of a scalar with external forcing. The
model for the phase coupling dynamics follows the well known Kuramoto model
paradigm of limit-cycle oscillators. The natural frequencies in the Kuramoto
model are assumed to obey a given scale dependence through a dispersion
relation of the drift-wave form , where is a
constant representing the typical strength of the gradient. The present aim is
to study the importance of collective phase dynamics on the characteristic time
evolution of the fluctuation energy and the formation of coherent structures.
Our results show that the assumption of a fully stochastic phase state of
turbulence is more relevant for high values of , where we find that the
energy spectrum follows a scaling. Whereas for lower there
is a significant difference between a-synchronised and synchronised phase
states, and one could expect the formation of coherent modulations in the
latter case.Comment: Accepted for publication in Physics of Plasma
Acoustic wave propagation in the solar sub-photosphere with localised magnetic field concentration: effect of magnetic tension
Aims: We analyse numerically the propagation and dispersion of acoustic waves in the solar-like sub-photosphere with localised non-uniform magnetic field concentrations, mimicking sunspots with various representative magnetic field configurations.
Methods: Numerical simulations of wave propagation through the solar sub-photosphere with a localised magnetic field concentration are carried out using SAC, which solves the MHD equations for gravitationally stratified plasma. The initial equilibrium density and pressure stratifications are derived from a standard solar model. Acoustic waves are generated by a source located at the height corresponding approximately to the visible surface of the Sun. By means of local helioseismology we analyse the response of vertical velocity at the level corresponding to the visible solar surface to changes induced by magnetic field in the interior.
Results: The results of numerical simulations of acoustic wave propagation and dispersion in the solar sub-photosphere with localised magnetic field concentrations of various types are presented. Time-distance diagrams of the vertical velocity perturbation at the level corresponding to the visible solar surface show that the magnetic field perturbs and scatters acoustic waves and absorbs the acoustic power of the wave packet. For the weakly magnetised case, the effect of magnetic field is mainly thermodynamic, since the magnetic field changes the temperature stratification. However, we observe the signature of slow magnetoacoustic mode, propagating downwards, for the strong magnetic field cases
- …