4,794 research outputs found
Phase Transitions in the Two-Dimensional XY Model with Random Phases: a Monte Carlo Study
We study the two-dimensional XY model with quenched random phases by Monte
Carlo simulation and finite-size scaling analysis. We determine the phase
diagram of the model and study its critical behavior as a function of disorder
and temperature. If the strength of the randomness is less than a critical
value, , the system has a Kosterlitz-Thouless (KT) phase transition
from the paramagnetic phase to a state with quasi-long-range order. Our data
suggest that the latter exists down to T=0 in contradiction with theories that
predict the appearance of a low-temperature reentrant phase. At the critical
disorder and for there is no
quasi-ordered phase. At zero temperature there is a phase transition between
two different glassy states at . The functional dependence of the
correlation length on suggests that this transition corresponds to the
disorder-driven unbinding of vortex pairs.Comment: LaTex file and 18 figure
Domain regime in two-dimensional disordered vortex matter
A detailed numerical study of the real space configuration of vortices in
disordered superconductors using 2D London-Langevin model is presented. The
magnetic field is varied between 0 and for various pinning
strengths . For weak pinning, an inhomogeneous disordered vortex matter
is observed, in which the topologically ordered vortex lattice survives in
large domains. The majority of the dislocations in this state are confined to
the grain boundaries/domain walls. Such quasi-ordered configurations are
observed in the intermediate fields, and we refer it as the domain regime (DR).
The DR is distinct from the low-field and the high-fields amorphous regimes
which are characterized by a homogeneous distribution of defects over the
entire system. Analysis of the real space configuration suggests domain wall
roughening as a possible mechanism for the crossover from the DR to the
high-field amorphous regime. The DR also shows a sharp crossover to the high
temperature vortex liquid phase. The domain size distribution and the roughness
exponent of the lattice in the DR are also calculated. The results are compared
with some of the recent Bitter decoration experiments.Comment: 9 pages, 9 figure
Constellations of identity: place-ma(r)king beyond heritage
This paper will critically consider the different ways in which history and belonging have been treated in artworks situated in the Citadel development in Ayr on the West coast of Scotland. It will focus upon one artwork, Constellation by Stephen Hurrel, as an alternative to the more conventional landscapes of heritage which are adjacent, to examine the relationship between personal history and place history and argue the primacy of participatory process in the creation of place and any artwork therein. Through his artwork, Hurrel has attempted to adopt a material process through which place can be created performatively but, in part due to its non-representational form, proves problematic, aesthetically and longitudinally, in wholly engaging the community. The paper will suggest that through variants of ‘new genre public art’ such as this, personal and place histories can be actively re-created through the redevelopment of contemporary urban landscapes but also highlight the complexities and indeterminacies involved in the relationship between artwork, people and place
Site-specific immobilization of microbes using carbon nanotubes and dielectrophoretic force for microfluidic applications
We developed a microbial immobilization method for successful applications in microfluidic devices. Single-walled nanotubes and Escherichia coli were aligned between two cantilever electrodes by a positive dielectrophoretic force resulting in a film of single-walled nanotubes with attached Escherichia coli. Because this film has a suspended and porous structure, it has a larger reaction area and higher reactant transfer efficiency than film attached to the substrate surface. The cell density of film was easily controlled by varying the cell concentration of the suspension and varying the electric field. The film showed excellent stability of enzyme activity, as demonstrated by measuring continuous reaction and long-term storage times using recombinant Escherichia coli that expressed organophosphorus hydrolase.X1133sciescopu
Omnivorousness in sport: The importance of social capital and networks
There has been for some time a significant and growing body of research around the relationship between sport and social capital. Similarly, within sociology there has been a corpus of work that has acknowledged the emergence of the omnivore–univore relationship. Surprisingly, relatively few studies examining sport and social capital have taken the omnivore–univore framework as a basis for understanding the relationship between sport and social capital. This gap in the sociology of sport literature and knowledge is rectified by this study that takes not Putnam, Coleman or Bourdieu, but Lin’s social network approach to social capital. The implications of this article are that researchers investigating sport and social capital need to understand more about how social networks and places for sport work to create social capital and, in particular, influence participating in sporting activities. The results indicate that social networks both facilitate and constrain sports participation; whilst family and friendship networks are central in active lifestyles, those who are less active have limited networks
Simultaneous Diagonal and Off Diagonal Order in the Bose--Hubbard Hamiltonian
The Bose-Hubbard model exhibits a rich phase diagram consisting both of
insulating regimes where diagonal long range (solid) order dominates as well as
conducting regimes where off diagonal long range order (superfluidity) is
present. In this paper we describe the results of Quantum Monte Carlo
calculations of the phase diagram, both for the hard and soft core cases, with
a particular focus on the possibility of simultaneous superfluid and solid
order. We also discuss the appearance of phase separation in the model. The
simulations are compared with analytic calculations of the phase diagram and
spin wave dispersion.Comment: 28 pages plus 24 figures, uuencoded Revtex+postscript file
Critical Behaviour of Superfluid He in Aerogel
We report on Monte Carlo studies of the critical behaviour of superfluid
He in the presence of quenched disorder with long-range fractal
correlations. According to the heuristic argument by Harris, uncorrelated
disorder is irrelevant when the specific heat critical exponent is
negative, which is the case for the pure He. However, experiments on helium
in aerogel
have shown that the superfluid density critical exponent changes. We
hypothesize that this is a cross-over effect due to the fractal nature of
aerogel. Modelling the aerogel as an incipient percolating cluster in 3D and
weakening the bonds at the fractal sites, we perform XY-model simulations,
which demonstrate an increase in from
for the pure case to an apparent value of in the presence of
the fractal disorder, provided that the helium correlation length does not
exceed the fractal correlation length.Comment: 4 pages, RevTex, 3 postscript figures, LaTeX file and figures have
been uuencoded
Universal Conductivity in the Two dimensional Boson Hubbard Model
We use Quantum Monte Carlo to evaluate the conductivity of the
2--dimensional disordered boson Hubbard model at the superfluid-bose glass
phase boundary. At the critical point for particle density , we find
, where from
a finite size scaling analysis of the superfluid density. We obtain
from a direct calculation of the
current--current correlation function. Simulations at the critical points for
other particle densities, and , give similar values for
. We discuss possible origins of the difference in this value from that
recently obtained by other numerical approaches.Comment: 20 pages, figures available upon request. Tex with jnl3.tex and
reforder.tex macros. cond-mat/yymmnn
Dual superfluid-Bose glass critical point in two dimensions and the universal conductivity
We study the continuum version of the dual theory for a system of
two-dimensional, zero temperature, disordered bosons, interacting with short
range repulsion and at a commensurate density. The dual theory, which describes
vortices in the bosonic ground state, and has a form of 3D classical scalar
electrodynamics in random, correlated magnetic field, admits a new disordered
critical point within RG calculation at fixed dimension. The universal
conductivity and the critical exponents at the superfluid-Bose glass critical
point are calculated as series in fixed-point values of the dual coupling
constants, to the lowest non-trivial order: ,
and . The comparison with numerical results and experiments
is discussed.Comment: 8 pages, LaTex, some clarifications and references adde
Three-dimensional Josephson-junction arrays in the quantum regime
We study the quantum phase transition properties of a three-dimensional
periodic array of Josephson junctions with charging energy that includes both
the self and mutual junction capacitances. We use the phase fluctuation algebra
between number and phase operators, given by the Euclidean group E_2, and we
effectively map the problem onto a solvable quantum generalization of the
spherical model. We obtain a phase diagram as a function of temperature,
Josephson coupling and charging energy. We also analyze the corresponding
fluctuation conductivity and its universal scaling form in the vicinity of the
zero-temperature quantum critical point.Comment: 9 pages, LATEX, three PostScript figures. Submitted to Phys. Rev.
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