5,748 research outputs found
Full capacitance-matrix effects in driven Josephson-junction arrays
We study the dynamic response to external currents of periodic arrays of
Josephson junctions, in a resistively capacitively shunted junction (RCSJ)
model, including full capacitance-matrix effects}. We define and study three
different models of the capacitance matrix : Model A
includes only mutual capacitances; Model B includes mutual and self
capacitances, leading to exponential screening of the electrostatic fields;
Model C includes a dense matrix that is constructed
approximately from superposition of an exact analytic solution for the
capacitance between two disks of finite radius and thickness. In the latter
case the electrostatic fields decay algebraically. For comparison, we have also
evaluated the full capacitance matrix using the MIT fastcap algorithm, good for
small lattices, as well as a corresponding continuum effective-medium analytic
evaluation of a finite voltage disk inside a zero-potential plane. In all cases
the effective decays algebraically with distance, with
different powers. We have then calculated current voltage characteristics for
DC+AC currents for all models. We find that there are novel giant capacitive
fractional steps in the I-V's for Models B and C, strongly dependent on the
amount of screening involved. We find that these fractional steps are quantized
in units inversely proportional to the lattice sizes and depend on the
properties of . We also show that the capacitive steps
are not related to vortex oscillations but to localized screened phase-locking
of a few rows in the lattice. The possible experimental relevance of these
results is also discussed.Comment: 12 pages 18 Postscript figures, REVTEX style. Paper to appear in July
1, Vol. 58, Phys. Rev. B 1998 All PS figures include
Nonlinear AC resistivity in s-wave and d-wave disordered granular superconductors
We model s-wave and d-wave disordered granular superconductors with a
three-dimensional lattice of randomly distributed Josephson junctions with
finite self-inductance. The nonlinear ac resistivity of these systems was
calculated using Langevin dynamical equations. The current amplitude dependence
of the nonlinear resistivity at the peak position is found to be a power law
characterized by exponent . The later is not universal but depends on
the self-inductance and current regimes. In the weak current regime is
independent of the self-inductance and equal to 0.5 or both of s- and d-wave
materials. In the strong current regime this exponent depends on the screening.
We find for some interval of inductance which agrees with
the experimental finding for d-wave ceramic superconductors.Comment: 4 pages, 5 figures, to appear in Phys. Rev. Let
Transverse depinning and melting of a moving vortex lattice in driven periodic Josephson junction arrays
We study the effect of thermal fluctuations in a vortex lattice driven in the
periodic pinning of a Josephson junction array. The phase diagram current ()
vs. temperature () is studied. Above the critical current we find a
moving vortex lattice (MVL) with anisotropic Bragg peaks. For large currents
, there is a melting transition of the MVL at . When
applying a small transverse current to the MVL, there is no dissipation at low
. We find an onset of transverse vortex motion at a transverse depinning
temperature .Comment: 4 pages, 4 figures, Figure 2 changed, added new reference
Reply to the comment on ''On the problem of initial conditions in cosmological N-body simulations''
We reply to some comments in astro-ph/0309381 concerning the problem of
setting-up initial conditions in cosmological N-body simulationsComment: 2 pages, 1 postscript figure, style epl.cl
Hydrodynamic approach to the evolution of cosmological structures
A hydrodynamic formulation of the evolution of large-scale structure in the
Universe is presented. It relies on the spatially coarse-grained description of
the dynamical evolution of a many-body gravitating system. Because of the
assumed irrelevance of short-range (``collisional'') interactions, the way to
tackle the hydrodynamic equations is essentially different from the usual case.
The main assumption is that the influence of the small scales over the
large-scale evolution is weak: this idea is implemented in the form of a
large-scale expansion for the coarse-grained equations. This expansion builds a
framework in which to derive in a controlled manner the popular ``dust'' model
(as the lowest-order term) and the ``adhesion'' model (as the first-order
correction). It provides a clear physical interpretation of the assumptions
involved in these models and also the possibility to improve over them.Comment: 14 pages, 3 figures. Version to appear in Phys. Rev.
Competing for the disability tourism market - A comparative exploration of the factors of accessible tourism competitiveness in Spain and Australia
© 2014 Elsevier Ltd. This paper seeks to address the research question of what factors make a destination competitive for the accessible tourism market. The research design is based on destination competitiveness theories. The objective is to formulate a ranking that can compare the competitiveness factors between two countries, with historical and appropriate data sets, in order to examine destination competitiveness for accessible tourism across the tourist regions of both countries. The current research examines the background of destination competitiveness theories, both generally and specifically, as they relate to the research contexts. The research design was developed to examine the underlying elements that facilitate accessible tourism experiences through factorial and cluster analyses, adapting the Crouch's model of competitiveness destination. The findings suggest that the competitiveness factors are different in determinance and importance, and are country-dependent. The climate, locale and tourist structure are the most important for Spain, whereas quality of services, brand and infrastructure are of great importance for Australia. The cluster analysis of the different tourist regions suggests the existence of three main stages. These stages where related to their accessibility level of offered tourism product and their policies
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