381 research outputs found
Influence of polydispersity on the critical parameters of an effective potential model for asymmetric hard sphere mixtures
We report a Monte Carlo simulation study of the properties of highly
asymmetric binary hard sphere mixtures. This system is treated within an
effective fluid approximation in which the large particles interact through a
depletion potential (R. Roth {\em et al}, Phys. Rev. E{\bf 62} 5360 (2000))
designed to capture the effects of a virtual sea of small particles. We
generalize this depletion potential to include the effects of explicit size
dispersity in the large particles and consider the case in which the particle
diameters are distributed according to a Schulz form having degree of
polydispersity 14%. The resulting alteration (with respect to the monodisperse
limit) of the metastable fluid-fluid critical point parameters is determined
for two values of the ratio of the diameters of the small and large particles:
and . We find that inclusion of
polydispersity moves the critical point to lower reservoir volume fractions of
the small particles and high volume fractions of the large ones. The estimated
critical point parameters are found to be in good agreement with those
predicted by a generalized corresponding states argument which provides a link
to the known critical adhesion parameter of the adhesive hard sphere model.
Finite-size scaling estimates of the cluster percolation line in the one phase
fluid region indicate that inclusion of polydispersity moves the critical point
deeper into the percolating regime. This suggests that phase separation is more
likely to be preempted by dynamical arrest in polydisperse systems.Comment: 11 pages, 10 figure
Self-trapping at the liquid vapor critical point
Experiments suggest that localization via self-trapping plays a central role
in the behavior of equilibrated low mass particles in both liquids and in
supercritical fluids. In the latter case, the behavior is dominated by the
liquid-vapor critical point which is difficult to probe, both experimentally
and theoretically. Here, for the first time, we present the results of
path-integral computations of the characteristics of a self-trapped particle at
the critical point of a Lennard-Jones fluid for a positive particle-atom
scattering length. We investigate the influence of the range of the
particle-atom interaction on trapping properties, and the pick-off decay rate
for the case where the particle is ortho-positronium.Comment: 12 pages, 3 figures, revtex4 preprin
Critical phenomena in colloid-polymer mixtures: interfacial tension, order parameter, susceptibility and coexistence diameter
The critical behavior of a model colloid-polymer mixture, the so-called AO
model, is studied using computer simulations and finite size scaling
techniques. Investigated are the interfacial tension, the order parameter, the
susceptibility and the coexistence diameter. Our results clearly show that the
interfacial tension vanishes at the critical point with exponent 2\nu ~ 1.26.
This is in good agreement with the 3D Ising exponent. Also calculated are
critical amplitude ratios, which are shown to be compatible with the
corresponding 3D Ising values. We additionally identify a number of subtleties
that are encountered when finite size scaling is applied to the AO model. In
particular, we find that the finite size extrapolation of the interfacial
tension is most consistent when logarithmic size dependences are ignored. This
finding is in agreement with the work of Berg et al.[Phys. Rev. B, V47 P497
(1993)]Comment: 13 pages, 16 figure
Are critical finite-size scaling functions calculable from knowledge of an appropriate critical exponent?
Critical finite-size scaling functions for the order parameter distribution
of the two and three dimensional Ising model are investigated. Within a
recently introduced classification theory of phase transitions, the universal
part of the critical finite-size scaling functions has been derived by
employing a scaling limit that differs from the traditional finite-size scaling
limit. In this paper the analytical predictions are compared with Monte Carlo
simulations. We find good agreement between the analytical expression and the
simulation results. The agreement is consistent with the possibility that the
functional form of the critical finite-size scaling function for the order
parameter distribution is determined uniquely by only a few universal
parameters, most notably the equation of state exponent.Comment: 11 pages postscript, plus 2 separate postscript figures, all as
uuencoded gzipped tar file. To appear in J. Phys. A
Development and randomized controlled trial of an animated film aimed at reducing behaviours for acquiring antibiotics
Background
Antimicrobial resistance (AMR) is a global health crisis but reducing antibiotic use can help. Some antibiotic use is driven by patient demand.
Objectives
To develop an intervention to discourage antibiotic-seeking behaviour in adults.
Methods
Literature reviewed to identify behaviours for acquiring antibiotics among adults in the community. Behaviour change wheel approach was used to select the target behaviour and behaviour change techniques. An intervention in the form of a short animated film was developed and its potential impact evaluated in a randomized, controlled, online questionnaire study.
Results
Asking a general medical/dental practitioner for antibiotics was identified as the target behaviour. A short stop-motion animated film was chosen to deliver several behaviour-change techniques. Education and persuasion were delivered around information about the normal microbial flora, its importance for health, the negative effect of antibiotics, and about AMR. 417 UK-based individuals completed the questionnaire; median age 34.5 years, 71% female, 91% white ethnicity. 3.8% of participants viewing the test film intended to ask for antibiotics compared with 7.9% viewing the control film. Test film viewers had significantly higher knowledge scores. At 6 week follow up, knowledge scores remained significantly different, while most attitude and intention scores were not different.
Conclusions
Some patients continue to ask for antibiotics. The film increased knowledge and reduced intentions to ask for antibiotics. At 6 weeks, knowledge gains remained but intentions not to ask for antibiotics had waned. Evaluation in the clinical environment, probably at the point of care, is needed to see if antibiotic prescribing can be impacted
The Ultimate Fate of Supercooled Liquids
In recent years it has become widely accepted that a dynamical length scale
{\xi}_{\alpha} plays an important role in supercooled liquids near the glass
transition. We examine the implications of the interplay between the growing
{\xi}_{\alpha} and the size of the crystal nucleus, {\xi}_M, which shrinks on
cooling. We argue that at low temperatures where {\xi}_{\alpha} > {\xi}_M a new
crystallization mechanism emerges enabling rapid development of a large scale
web of sparsely connected crystallinity. Though we predict this web percolates
the system at too low a temperature to be easily seen in the laboratory, there
are noticeable residual effects near the glass transition that can account for
several previously observed unexplained phenomena of deeply supercooled liquids
including Fischer clusters, and anomalous crystal growth near T_g
Temperature and density extrapolations in canonical ensemble Monte Carlo simulations
We show how to use the multiple histogram method to combine canonical
ensemble Monte Carlo simulations made at different temperatures and densities.
The method can be applied to study systems of particles with arbitrary
interaction potential and to compute the thermodynamic properties over a range
of temperatures and densities. The calculation of the Helmholtz free energy
relative to some thermodynamic reference state enables us to study phase
coexistence properties. We test the method on the Lennard-Jones fluids for
which many results are available.Comment: 5 pages, 3 figure
Interface localisation-delocalisation transition in a symmetric polymer blend: a finite-size scaling Monte Carlo study
Using extensive Monte Carlo simulations we study the phase diagram of a
symmetric binary (AB) polymer blend confined into a thin film as a function of
the film thickness D. The monomer-wall interactions are short ranged and
antisymmetric, i.e, the left wall attracts the A-component of the mixture with
the same strength as the right wall the B-component, and give rise to a first
order wetting transition in a semi-infinite geometry. The phase diagram and the
crossover between different critical behaviors is explored. For large film
thicknesses we find a first order interface localisation/delocalisation
transition and the phase diagram comprises two critical points, which are the
finite film width analogies of the prewetting critical point. Using finite size
scaling techniques we locate these critical points and present evidence of 2D
Ising critical behavior. When we reduce the film width the two critical points
approach the symmetry axis of the phase diagram and for we encounter a tricritical point. For even smaller film thickness the
interface localisation/delocalisation transition is second order and we find a
single critical point at .
Measuring the probability distribution of the interface position we determine
the effective interaction between the wall and the interface. This effective
interface potential depends on the lateral system size even away from the
critical points. Its system size dependence stems from the large but finite
correlation length of capillary waves. This finding gives direct evidence for a
renormalization of the interface potential by capillary waves in the framework
of a microscopic model.Comment: Phys.Rev.
The Critical Behaviour of the Spin-3/2 Blume-Capel Model in Two Dimensions
The phase diagram of the spin-3/2 Blume-Capel model in two dimensions is
explored by conventional finite-size scaling, conformal invariance and Monte
Carlo simulations. The model in its -continuum Hamiltonian version is
also considered and compared with others spin-3/2 quantum chains. Our results
indicate that differently from the standard spin-1 Blume-Capel model there is
no multicritical point along the order-disorder transition line. This is in
qualitative agreement with mean field prediction but in disagreement with
previous approximate renormalization group calculations. We also presented new
results for the spin-1 Blume-Capel model.Comment: latex 18 pages, 4 figure
Asymmetric Fluid Criticality I: Scaling with Pressure Mixing
The thermodynamic behavior of a fluid near a vapor-liquid and, hence,
asymmetric critical point is discussed within a general ``complete'' scaling
theory incorporating pressure mixing in the nonlinear scaling fields as well as
corrections to scaling. This theory allows for a Yang-Yang anomaly in which
\mu_{\sigma}^{\prime\prime}(T), the second temperature derivative of the
chemical potential along the phase boundary, diverges like the specific heat
when T\to T_{\scriptsize c}; it also generates a leading singular term,
|t|^{2\beta}, in the coexistence curve diameter, where t\equiv
(T-T_{\scriptsize c}) /T_{\scriptsize c}. The behavior of various special loci,
such as the critical isochore, the critical isotherm, the k-inflection loci, on
which \chi^{(k)}\equiv \chi(\rho,T)/\rho^{k} (with \chi = \rho^{2}
k_{\scriptsize B}TK_{T}) and C_{V}^{(k)}\equiv C_{V}(\rho,T)/\rho^{k} are
maximal at fixed T, is carefully elucidated. These results are useful for
analyzing simulations and experiments, since particular, nonuniversal values of
k specify loci that approach the critical density most rapidly and reflect the
pressure-mixing coefficient. Concrete illustrations are presented for the
hard-core square-well fluid and for the restricted primitive model electrolyte.
For comparison, a discussion of the classical (or Landau) theory is presented
briefly and various interesting loci are determined explicitly and illustrated
quantitatively for a van der Waals fluid.Comment: 21 pages in two-column format including 8 figure
- …