131 research outputs found
Liquid crystal hyperbolic metamaterial for wide-angle negative-positive refraction and reflection
We show that nanosphere dispersed liquid crystal (NDLC) metamaterial can be
characterized in near IR spectral region as an indefinite medium whose real
parts of effective ordinary and extraordinary permittivities are opposite in
signs. Based on this fact we design a novel electrooptic effect: external
electric field driven switch between normal refraction, negative refraction and
reflection of TM incident electromagnetic wave from the boundary vacuum/NDLC. A
detailed analysis of its functionality is given based on effective medium
theory combined with a study of negative refraction in anisotropic
metamaterials, and Finite Elements simulations
Short-time dynamics of the positional order of the two-dimensional hard disk system
We investigate the positional order of the two-dimensional hard disk model
with short-time dynamics and equilibrium simulations. The melting density and
the critical exponents z and eta are determined. Our results rule out a phase
transition as predicted by the Kosterlitz-Thouless-Halperin-Nelson-Young theory
as well as a first-order transition.Comment: 8 pages, 4 figures, minor change
The hexatic phase of the two-dimensional hard disks system
We report Monte Carlo results for the two-dimensional hard disk system in the
transition region. Simulations were performed in the NVT ensemble with up to
1024^2 disks. The scaling behaviour of the positional and bond-orientational
order parameter as well as the positional correlation length prove the
existence of a hexatic phase as predicted by the
Kosterlitz-Thouless-Halperin-Nelson-Young theory. The analysis of the pressure
shows that this phase is outside a possible first-order transition.Comment: 6 pages, 4 figures (minor changes
Van der Waals loops and the melting transition in two dimensions
Evidence for the existence of van der Waals loops in pressure p versus volume
v plots has for some time supported the belief that melting in two dimensions
is a first order phase transition. We report rather accurate equilibrium p(v)
curves for systems of hard disks obtained from long Monte Carlo simulations.
These curves, obtained in the constant volume ensemble, using periodic boundary
conditions, exhibit well defined van der Waals loops. We illustrate their
existence for finite systems that are known to undergo a continuous transition
in the thermodynamic limit. To this end, we obtain magnetization m versus
applied field curves from Monte Carlo simulations of the 2D Ising model, in the
constant m ensemble, at the critical point. Whether van der Waals loops for
disk systems behave in the thermodynamic limit as they do for the 2D Ising
model at the critical point cannot be ruled out. Thus, the often made claim
that melting in 2D is a first order phase transition, based on the evidence
that van der Waals loops exist, is not sound.Comment: 10 pages, 6 Postscript figures (submitted to Phys.Rev.E). For related
work, see http://pipe.unizar.es/~jf
Phase Behavior of Columnar DNA Assemblies
The pair interaction between two stiff parallel linear DNA molecules depends
not only on the distance between their axes but on their azimuthal orientation.
The positional and orientational order in columnar B-DNA assemblies in solution
is investigated, based on the DNA-DNA electrostatic pair potential that takes
into account DNA helical symmetry and the amount and distribution of adsorbed
counterions. A phase diagram obtained by lattice sum calculations predicts a
variety of positionally and azimuthally ordered phases and bundling transitions
strongly depending on the counterion adsorption patterns.Comment: 4 pages, 3 figures, submitted to PR
Phases in Strongly Coupled Electronic Bilayer Liquids
The strongly correlated liquid state of a bilayer of charged particles has
been studied via the HNC calculation of the two-body functions. We report the
first time emergence of a series of structural phases, identified through the
behavior of the two-body functions.Comment: 5 pages, RevTEX 3.0, 4 ps figures; Submitted to Phys. Rev. Let
A Simple Model of Liquid-liquid Phase Transitions
In recent years, a second fluid-fluid phase transition has been reported in
several materials at pressures far above the usual liquid-gas phase transition.
In this paper, we introduce a new model of this behavior based on the
Lennard-Jones interaction with a modification to mimic the different kinds of
short-range orientational order in complex materials. We have done Monte Carlo
studies of this model that clearly demonstrate the existence of a second
first-order fluid-fluid phase transition between high- and low-density liquid
phases
Elastic moduli, dislocation core energy and melting of hard disks in two dimensions
Elastic moduli and dislocation core energy of the triangular solid of hard
disks of diameter are obtained in the limit of vanishing dislocation-
antidislocation pair density, from Monte Carlo simulations which incorporates a
constraint, namely that all moves altering the local connectivity away from
that of the ideal triangular lattice are rejected. In this limit, we show that
the solid is stable against all other fluctuations at least upto densities as
low as . Our system does not show any phase transition so
diverging correlation lengths leading to finite size effects and slow
relaxations do not exist. The dislocation pair formation probability is
estimated from the fraction of moves rejected due to the constraint which
yields, in turn, the core energy E_c and the (bare) dislocation fugacity y.
Using these quantities, we check the relative validity of first order and
Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) melting scenarios and obtain
numerical estimates of the typical expected transition densities and pressures.
We conclude that a KTHNY transition from the solid to a hexatic phase preempts
the solid to liquid first order transition in this system albeit by a very
small margin, easily masked by crossover effects in unconstrained
``brute-force'' simulations with small number of particles.Comment: 17 pages, 8 figure
Determining level of care appropriateness in the patient journey from acute care to rehabilitation
Background: The selection of patients for rehabilitation, and the timing of transfer from acute care, are important clinical decisions that impact on care quality and patient flow. This paper reports utilization review data on inpatients in acute care with stroke, hip fracture or elective joint replacement, and other inpatients referred for rehabilitation. It examines reasons why acute level of care criteria are not met and explores differences in decision making between acute care and rehabilitation teams around patient appropriateness and readiness for transfer. Methods: Cohort study of patients in a large acute referral hospital in Australia followed with the InterQual utilization review tool, modified to also include reasons why utilization criteria are not met. Additional data on team decision making about appropriateness for rehabilitation, and readiness for transfer, were collected on a subset of patients. Results: There were 696 episodes of care (7189 bed days). Days meeting acute level of care criteria were 56% (stroke, hip fracture and joint replacement patients) and 33% (other patients, from the time of referral). Most inappropriate days in acute care were due to delays in processes/scheduling (45%) or being more appropriate for rehabilitation or lower level of care (30%). On the subset of patients, the acute care team and the utilization review tool deemed patients ready for rehabilitation transfer earlier than the rehabilitation team (means of 1.4, 1.3 and 4.0 days from the date of referral, respectively). From when deemed medically stable for transfer by the acute care team, 28% of patients became unstable. From when deemed stable by the rehabilitation team or utilization review, 9% and 11%, respectively, became unstable. Conclusions: A high proportion of patient days did not meet acute level of care criteria, due predominantly to inefficiencies in care processes, or to patients being more appropriate for an alternative level of care, including rehabilitation. The rehabilitation team was the most accurate in determining ongoing medical stability, but at the cost of a longer acute stay. To avoid inpatients remaining in acute care in a state of \u27terra nullius\u27, clinical models which provide rehabilitation within acute care, and more efficient movement to a rehabilitation setting, is required. Utilization review could have a decision support role in the determination of medical stability
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