2,979 research outputs found
Critical behavior of the Widom-Rowlinson mixture: coexistence diameter and order parameter
The critical behavior of the Widom-Rowlinson mixture [J. Chem. Phys. 52, 1670
(1970)] is studied in d=3 dimensions by means of grand canonical Monte Carlo
simulations. The finite size scaling approach of Kim, Fisher, and Luijten
[Phys. Rev. Lett. 91, 065701 (2003)] is used to extract the order parameter and
the coexistence diameter. It is demonstrated that the critical behavior of the
diameter is dominated by a singular term proportional to t^(1-alpha), with t
the relative distance from the critical point, and alpha the critical exponent
of the specific heat. No sign of a term proportional to t^(2beta) could be
detected, with beta the critical exponent of the order parameter, indicating
that pressure-mixing in this model is small. The critical density is measured
to be rho*sigma^3 = 0.7486 +/- 0.0002, with sigma the particle diameter. The
critical exponents alpha and beta, as well as the correlation length exponent
nu, are also measured and shown to comply with d=3 Ising criticality
Domain formation in membranes with quenched protein obstacles: Lateral heterogeneity and the connection to universality classes
We show that lateral fluidity in membranes containing quenched protein
obstacles belongs to the universality class of the two-dimensional random-field
Ising model. The main feature of this class is the absence of a phase
transition: there is no critical point, and macroscopic domain formation does
not occur. Instead, there is only one phase. This phase is highly
heterogeneous, with a structure consisting of micro-domains. The presence of
quenched protein obstacles thus provides a mechanism to stabilize lipid rafts
in equilibrium. Crucial for two-dimensional random-field Ising universality is
that the obstacles are randomly distributed, and have a preferred affinity to
one of the lipid species. When these conditions are not met, standard Ising or
diluted Ising universality apply. In these cases, a critical point does exist,
marking the onset toward macroscopic demixing.Comment: 10 pages, 10 figure
Simulation and theory of fluid demixing and interfacial tension of mixtures of colloids and non-ideal polymers
An extension of the Asakura-Oosawa-Vrij model of hard sphere colloids and
non-adsorbing polymers, that takes polymer non-ideality into account through a
repulsive stepfunction pair potential between polymers, is studied with grand
canonical Monte Carlo simulations and density functional theory. Simulation
results validate previous theoretical findings for the shift of the bulk fluid
demixing binodal upon increasing strength of polymer-polymer repulsion,
promoting the tendency to mix. For increasing strength of the polymer-polymer
repulsion, simulation and theory consistently predict the interfacial tension
of the free colloidal liquid-gas interface to decrease significantly for fixed
colloid density difference in the coexisting phases, and to increase for fixed
polymer reservoir packing fraction.Comment: 10 pages, 4 figure
Fluids with quenched disorder: Scaling of the free energy barrier near critical points
In the context of Monte Carlo simulations, the analysis of the probability
distribution of the order parameter , as obtained in simulation
boxes of finite linear extension , allows for an easy estimation of the
location of the critical point and the critical exponents. For Ising-like
systems without quenched disorder, becomes scale invariant at the
critical point, where it assumes a characteristic bimodal shape featuring two
overlapping peaks. In particular, the ratio between the value of at
the peaks () and the value at the minimum in-between ()
becomes -independent at criticality. However, for Ising-like systems with
quenched random fields, we argue that instead should be observed, where is the
"violation of hyperscaling" exponent. Since is substantially non-zero,
the scaling of with system size should be easily detectable in
simulations. For two fluid models with quenched disorder, versus
was measured, and the expected scaling was confirmed. This provides further
evidence that fluids with quenched disorder belong to the universality class of
the random-field Ising model.Comment: sent to J. Phys. Cond. Mat
- …