1,386 research outputs found
Accurate simulation estimates of phase behaviour in ternary mixtures with prescribed composition
This paper describes an isobaric semi-grand canonical ensemble Monte Carlo
scheme for the accurate study of phase behaviour in ternary fluid mixtures
under the experimentally relevant conditions of prescribed pressure,
temperature and overall composition. It is shown how to tune the relative
chemical potentials of the individual components to target some requisite
overall composition and how, in regions of phase coexistence, to extract
accurate estimates for the compositions and phase fractions of individual
coexisting phases. The method is illustrated by tracking a path through the
composition space of a model ternary Lennard-Jones mixture.Comment: 6 pages, 3 figure
Identifying policy frames through semantic network analysis : an examination of nuclear energy policy across six countries
This study uses semantic network analysis to investigate nuclear energy policy frames in six countries: USA, UK, Germany, France, Japan, and South Korea. It is suggested that semantic network analysis represents a useful tool to investigate policy frames in complex policy environments. The discourse of top-level decision-makers is analyzed to highlight similarities and differences in policy frames and to identify the key policy arguments in the integrated network of all six countries. In total, 14 major policy arguments are identified, which relate to the three major frames of energy security, clean energy, and nuclear safety, along with the meta-issue of economic growth. There are differences in the degree of emphasis on each of the frames in the six countries, and Germany can be seen to have diverged the most following the Fukushima accident, as the emphasis is on clean energy, to the exclusion of the other frames. In contrast, both the USA and Japan have framed the issues primarily in terms of nuclear safety and energy security, while the UK and France have stressed the economic growth frame, and Korea has prioritized nuclear safety
Coexistence Curve Singularities at Critical End Points
We report an extensive Monte Carlo study of critical end point behaviour in a
symmetrical binary fluid mixture. On the basis of general scaling arguments,
singular behaviour is predicted in the diameter of the liquid-gas coexistence
curve as the critical end point is approached. The simulation results show
clear evidence for this singularity, as well as confirming a previously
predicted singularity in the coexistence chemical potential. Both singularities
should be detectable experimentally.Comment: 9 pages Revtex, 3 figures. To appear in Phys. Rev. Let
Freezing line of the Lennard-Jones fluid: a Phase Switch Monte Carlo study
We report a Phase Switch Monte Carlo (PSMC) method study of the freezing line
of the Lennard-Jones (LJ) fluid. Our work generalizes to soft potentials the
original application of the method to hard sphere freezing, and builds on a
previous PSMC study of the LJ system by Errington (J. Chem. Phys. {\bf 120},
3130 (2004)). The latter work is extended by tracing a large section of the
Lennard-Jones freezing curve, the results for which we compare to a previous
Gibbs-Duhem integration study. Additionally we provide new background regarding
the statistical mechanical basis of the PSMC method and extensive
implementation details.Comment: 18 pages, 6 figure
Enthalpies of formation of lanthanide oxyapatite phases
A family of lanthanide silicates adopts an oxyapatite-like structure with structural formula Ln9.33∎0.67(SiO4)6O2 (Ln 4 La, Sm, Nd, Gd, ∎ = vacancy). The enthalpies of solution, DHS, for these materials and their corresponding binary oxides were determined by high-temperature oxide melt solution calorimetry using molten 2PbO·B2O3 at 1078 K. These data were used to complete thermodynamic cycles to calculate
enthalpies of formation from the oxides, ΔHs f-oxides (kJ/mol): La9.33∎0.67(SiO4)6O2 = −776.3 ± 17.9, Nd9.33∎0.67(SiO4)6O2 = −760.4 ± 31.9, Sm9.33∎0.67(SiO4)6O2 = −590.3 ± 18.6, and Gd9.33∎0.67(SiO4)6O2 = −446.9 ± 21.9. Reference data were used to calculate the standard enthalpies of formation from the elements, ΔH0 f (kJ/mol): La9.33∎0.67(SiO4)6O2 = −14611.0 ± 19.4, Nd9.33∎0.67(SiO4)6O2 = −14661.5 ± 32.2, Sm9.33∎0.67(SiO4)6O2 = −14561.7 ± 20.8, and Gd9.33∎0.67(SiO4)6O2 = −14402.7 ± 28.2. The formation enthalpies become more endothermic as the ionic radius of the lanthanide ion decreases
Wetting of a symmetrical binary fluid mixture on a wall
We study the wetting behaviour of a symmetrical binary fluid below the
demixing temperature at a non-selective attractive wall. Although it demixes in
the bulk, a sufficiently thin liquid film remains mixed. On approaching
liquid/vapour coexistence, however, the thickness of the liquid film increases
and it may demix and then wet the substrate. We show that the wetting
properties are determined by an interplay of the two length scales related to
the density and the composition fluctuations. The problem is analysed within
the framework of a generic two component Ginzburg-Landau functional
(appropriate for systems with short-ranged interactions). This functional is
minimized both numerically and analytically within a piecewise parabolic
potential approximation. A number of novel surface transitions are found,
including first order demixing and prewetting, continuous demixing, a
tricritical point connecting the two regimes, or a critical end point beyond
which the prewetting line separates a strongly and a weakly demixed film. Our
results are supported by detailed Monte Carlo simulations of a symmetrical
binary Lennard-Jones fluid at an attractive wall.Comment: submitted to Phys. Rev.
Modelling colloids with Baxter's adhesive hard sphere model
The structure of the Baxter adhesive hard sphere fluid is examined using
computer simulation. The radial distribution function (which exhibits unusual
discontinuities due to the particle adhesion) and static structure factor are
calculated with high accuracy over a range of conditions and compared with the
predictions of Percus--Yevick theory. We comment on rigidity in percolating
clusters and discuss the role of the model in the context of experiments on
colloidal systems with short-range attractive forces.Comment: 14 pages, 7 figures. (For proceedings of "Structural arrest in
colloidal systems with short-range attractive forces", Messina, December
2003
Interfacial tension of the isotropic--nematic interface in suspensions of soft spherocylinders
The isotropic to nematic transition in a system of soft spherocylinders is
studied by means of grand canonical Monte Carlo simulations. The probability
distribution of the particle density is used to determine the coexistence
density of the isotropic and the nematic phases. The distributions are also
used to compute the interfacial tension of the isotropic--nematic interface,
including an analysis of finite size effects. Our results confirm that the
Onsager limit is not recovered until for very large elongation, exceeding at
least L/D=40, with L the spherocylinder length and D the diameter. For smaller
elongation, we find that the interfacial tension increases with increasing L/D,
in agreement with theoretical predictions.Comment: 8 pages, 7 figures, and also 1 tabl
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
Temperature-dependent structural heterogeneity in calcium silicate liquids
X-ray diffraction measurements performed on aerodynamically levitated CaSiO3 droplets have been interpreted using a structurally heterogeneous liquid-state model. When cooled, the high-temperature liquid shows evidence of the polymerization of edge shared Ca octahedra. Diffraction isosbestic points are used to characterize the polymerization process in the pair-distribution function. This behavior is linear in the high-temperature melt but exhibits rapid growth just above the glass transition temperature around 1.2Tg. The heterogeneous liquid interpretation is supported by molecular-dynamics simulations which show the CaSiO3
glass has more edge-shared polyhedra and fewer corner shared polyhedra than the liquid model
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