616 research outputs found
Hydrodynamics of domain growth in nematic liquid crystals
We study the growth of aligned domains in nematic liquid crystals. Results
are obtained solving the Beris-Edwards equations of motion using the lattice
Boltzmann approach. Spatial anisotropy in the domain growth is shown to be a
consequence of the flow induced by the changing order parameter field
(backflow). The generalization of the results to the growth of a cylindrical
domain, which involves the dynamics of a defect ring, is discussed.Comment: 12 revtex-style pages, including 12 figures; small changes before
publicatio
Numerical calculations of the phase diagram of cubic blue phases in cholesteric liquid crystals
We study the static properties of cubic blue phases by numerically minimising
the three-dimensional, Landau-de Gennes free energy for a cholesteric liquid
crystal close to the isotropic-cholesteric phase transition. Thus we are able
to refine the powerful but approximate, semi-analytic frameworks that have been
used previously. We obtain the equilibrium phase diagram and discuss it in
relation to previous results. We find that the value of the chirality above
which blue phases appear is shifted by 20% (towards experimentally more
accessible regions) with respect to previous estimates. We also find that the
region of stability of the O5 structure -- which has not been observed
experimentally -- shrinks, while that of BP I (O8-) increases thus giving the
correct order of appearance of blue phases at small chirality. We also study
the approach to equilibrium starting from the infinite chirality solutions and
we find that in some cases the disclination network has to assemble during the
equilibration. In these situations disclinations are formed via the merging of
isolated aligned defects.Comment: 16 pages, 5 figures. Accepted for publication in Phys. Rev.
The empirical analysis of cigarette tax avoidance and illicit trade in Vietnam, 1998-2010.
Illicit trade carries the potential to magnify existing tobacco-related health care costs through increased availability of untaxed and inexpensive cigarettes. What is known with respect to the magnitude of illicit trade for Vietnam is produced primarily by the industry, and methodologies are typically opaque. Independent assessment of the illicit cigarette trade in Vietnam is vital to tobacco control policy. This paper measures the magnitude of illicit cigarette trade for Vietnam between 1998 and 2010 using two methods, discrepancies between legitimate domestic cigarette sales and domestic tobacco consumption estimated from surveys, and trade discrepancies as recorded by Vietnam and trade partners. The results indicate that Vietnam likely experienced net smuggling in during the period studied. With the inclusion of adjustments for survey respondent under-reporting, inward illicit trade likely occurred in three of the four years for which surveys were available. Discrepancies in trade records indicate that the value of smuggled cigarettes into Vietnam ranges from 300 million between 2000 and 2010 and that these cigarettes primarily originate in Singapore, Hong Kong, Macao, Malaysia, and Australia. Notable differences in trends over time exist between the two methods, but by comparison, the industry estimates consistently place the magnitude of illicit trade at the upper bounds of what this study shows. The unavailability of annual, survey-based estimates of consumption may obscure the true, annual trend over time. Second, as surveys changed over time, estimates relying on them may be inconsistent with one another. Finally, these two methods measure different components of illicit trade, specifically consumption of illicit cigarettes regardless of origin and smuggling of cigarettes into a particular market. However, absent a gold standard, comparisons of different approaches to illicit trade measurement serve efforts to refine and improve measurement approaches and estimates
Dynamics of a Driven Single Flux Line in Superconductors
We study the low temperature dynamics of a single flux line in a bulk type-II
superconductor, driven by a surface current, both near and above the onset of
an instability which sets in at a critical driving. We found that above the
critical driving, the velocity profile of the flux line develops a
discontinuity.Comment: 10 pages with 4 figures, REVTE
Domain Walls and Phase Transitions in the Frustrated Two-Dimensional XY Model
We study and compare the critical properties of the two-dimensional (2D) XY
model in a transverse magnetic field with magnetic filling factors f=1/3 and
f=2/5. In addition to the spin waves, the low energy excitations of the system
consist of various domain walls between degenerate ground states. The lowest
energy domain wall has a similar structure for both f=1/3 and f=2/5 and its
properties dictate the nature of the phase transition. For f=2/5 these lowest
energy walls have a negative energy for binding to each other, giving rise to a
branching domain-wall structure and leading to a first order phase transition.
For f=1/3 this binding energy is positive, resulting in a linear critical
interface. In order to make a comparison to recent experiments, we investigate
the effect of small quenched bond disorder for f=2/5. A finite-size scaling
analysis of extensive Monte Carlo simulations strongly suggests that the
critical exponents of the phase transition for f=1/3, and for f=2/5 with
disorder, fall into the universality class of the two-dimensional Ising model.Comment: 5 pages, 3 eps figures, REVTEX, revised version with new figure
Biological significance as a determinant of cue competition.
ABSTRACT Many researchers have noted the similarities between causal judgment in humans an
Critical Behavior of Frustrated Josephson Junction Arrays with Bond Disorder
The scaling behavior of the current-voltage () characteristics of a
two-dimensional proximity-coupled Josephson junction array (JJA) with quenched
bond disorder was investigated for frustrations , 1/3, 2/5, and 1/2. For
all these frustrations including 1/5 and 2/5 where a strongly first-order phase
transition is expected in the absence of disorder, the characteristics
exhibited a good scaling behavior. The critical exponent indicates that
bond disorder may drive the phase transitions of frustrated JJA's to be
continuous but not into the Ising universality class, contrary to what was
observed in Monte Carlo simulations. The dynamic critical exponent for
JJA's was found to be only 0.60 - 0.77.Comment: RevTeX4, 4 pages, 4 figures, the manuscript is replaced with the
published versio
Equilibrium properties of a Josephson junction ladder with screening effects
In this paper we calculate the ground state phase diagram of a Josephson
Junction ladder when screening field effects are taken into account. We study
the ground state configuration as a function of the external field, the
penetration depth and the anisotropy of the ladder, using different
approximations to the calculation of the induced fields. A series of tongues,
characterized by the vortex density , is obtained. The vortex density
of the ground state, as a function of the external field, is a Devil's
staircase, with a plateau for every rational value of . The width of
each of these steps depends strongly on the approximation made when calculating
the inductance effect: if the self-inductance matrix is considered, the
phase tends to occupy all the diagram as the penetration depth
decreases. If, instead, the whole inductance matrix is considered, the width of
any step tends to a non-zero value in the limit of very low penetration depth.
We have also analyzed the stability of some simple metastable phases: screening
fields are shown to enlarge their stability range.Comment: 16 pp, RevTex. Figures available upon request at
[email protected] To be published in Physical Review B (01-Dec-96
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