8,315 research outputs found
Earth models consistent with geophysical data
Earth models consistent with geophysical data using Monte Carlo metho
Low temperature properties of the infinite-dimensional attractive Hubbard model
We investigate the attractive Hubbard model in infinite spatial dimensions by
combining dynamical mean-field theory with a strong-coupling continuous-time
quantum Monte Carlo method. By calculating the superfluid order parameter and
the density of states, we discuss the stability of the superfluid state. In the
intermediate coupling region above the critical temperature, the density of
states exhibits a heavy fermion behavior with a quasi-particle peak in the
dense system, while a dip structure appears in the dilute system. The formation
of the superfluid gap is also addressed.Comment: 8 pages, 9 figure
Phase diagram of Landau-Zener phenomena in coupled one-dimensional Bose quantum fluids
We study stationary and dynamical properties of the many-body Landau-Zener
dynamics of a Bose quantum fluid confined in two coupled one-dimensional
chains, using a many-body generalization recently reported [Y.-A. Chen et al.],
within the decoupling approximation and the one-level band scheme. The energy
spectrum evidences the structure of the avoided level crossings as a function
of the on-site inter particle interaction strength. On the dynamical side, a
phase diagram of the transfer efficiency across ground-state and inverse sweeps
is presented. A totally different scenario with respect to the original
single-particle Landau-Zener scheme is found for ground-state sweeps, in which
a breakdown of the adiabatic region emerges as the sweep rate decreases. On the
contrary, the transfer efficiency across inverse sweeps reveals consistent
results with the single-particle Landau-Zener predictions. In the strong
coupling regime, we find that there is a critical value of the on-site
interaction for which the transfer of particles starts to vanish independently
of the sweep rate. Our results are in qualitative agreement with those of the
experimental counterpart.Comment: 15 pages, submitted to Phys. Rev. A (new version
Gutzwiller study of extended Hubbard models with fixed boson densities
We studied all possible ground states, including supersolid (SS) phases and
phase separations of hard-core- and soft-core-extended Bose--Hubbard models
with fixed boson densities by using the Gutzwiller variational wave function
and the linear programming method. We found that the phase diagram of the
soft-core model depends strongly on its transfer integral. Furthermore, for a
large transfer integral, we showed that an SS phase can be the ground state
even below or at half filling against the phase separation. We also found that
the density difference between nearest-neighbor sites, which indicates the
density order of the SS phase, depends strongly on the boson density and
transfer integral.Comment: 14 pages, 14 figures, to be published in Phys. Rev.
A level-set method for the evolution of cells and tissue during curvature-controlled growth
Most biological tissues grow by the synthesis of new material close to the
tissue's interface, where spatial interactions can exert strong geometric
influences on the local rate of growth. These geometric influences may be
mechanistic, or cell behavioural in nature. The control of geometry on tissue
growth has been evidenced in many in-vivo and in-vitro experiments, including
bone remodelling, wound healing, and tissue engineering scaffolds. In this
paper, we propose a generalisation of a mathematical model that captures the
mechanistic influence of curvature on the joint evolution of cell density and
tissue shape during tissue growth. This generalisation allows us to simulate
abrupt topological changes such as tissue fragmentation and tissue fusion, as
well as three dimensional cases, through a level-set-based method. The
level-set method developed introduces another Eulerian field than the level-set
function. This additional field represents the surface density of tissue
synthesising cells, anticipated at future locations of the interface. Numerical
tests performed with this level-set-based method show that numerical
conservation of cells is a good indicator of simulation accuracy, particularly
when cusps develop in the tissue's interface. We apply this new model to
several situations of curvature-controlled tissue evolutions that include
fragmentation and fusion.Comment: 15 pages, 10 figures, 3 supplementary figure
Viscous Hydrodynamics and Relativistic Heavy Ion Collisions
The matter created in relativistic heavy ion collisions is fairly well
described by ideal hydrodynamics, and somewhat better described by viscous
hydrodynamics. To this point, most viscous calculations have been
two-dimensional, based on an assumption of Bjorken boost invariance along the
beam axis. Here, first results are presented for a fully three-dimensional
viscous model. The model is described and tests of the numerical accuracy of
the code are presented. Two- and three-dimensional runs are compared, and
modest changes are observed for mid-rapidity observables at the highest RHIC
(Relativistic Heavy Ion Collider) energies.Comment: 23 pages, 7 figure
Asymmetric Properties of Heat Conduction in a One-Dimensional Frenkel-Kontorova Model
In this Letter, we show numerically that the rectifying effect of heat flux
in a one-dimensional two-segment Frenkel-Kontorova chain demonstrated in recent
literature is merely available under the limit of the weak coupling between the
two constituent segments. Surprisingly, the rectifying effect will be reversed
when the properties of the interface and the system size change. The two types
of asymmetric heat conduction are dominated by different mechanisms, which are
all induced by the nonlinearity. We further discuss the possibility of the
experimental realization of thermal diode or rectifier devices.Comment: 4 Pages, 4 figure
A quantum evaporation effect
A small momentum transfer to a particle interacting with a steep potential
barrier gives rise to a quantum evaporation effect which increases the
transmission appreciably. This effect results from the unexpectedly large
population of quantum states with energies above the height of the barrier. Its
characteristic properties are studied and an example of physical system in
which it may be observed is given.Comment: 7 pages + 3 figure
Neutral and ionic dopants in helium clusters: interaction forces for the and
The potential energy surface (PES) describing the interactions between
and and an extensive
study of the energies and structures of a set of small clusters,
, have been presented by us in a previous series of
publications [1-3]. In the present work we want to extend the same analysis to
the case of the excited and of the
ionized Li moiety. We thus show here calculated
interaction potentials for the two title systems and the corresponding fitting
of the computed points. For both surfaces the MP4 method with cc-pV5Z basis
sets has been used to generate an extensive range of radial/angular coordinates
of the two dimensional PES's which describe rigid rotor molecular dopants
interacting with one He partner
Numerical study of the localization length critical index in a network model of plateau-plateau transitions in the quantum Hall effect
We calculate numerically the localization length critical index within the
Chalker-Coddington (CC) model for plateau-plateau transitions in the quantum
Hall effect. Lyapunov exponents have been calculated with relative errors on
the order . Such high precision was obtained by considering the
distribution of Lyapunov exponents for large ensembles of relatively short
chains and calculating the ensemble average values. We analyze thoroughly
finite size effects and find the localization length critical index .Comment: 4 pages, 4 figure
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