724 research outputs found
A liquid state theory that remains successful in the critical region
A thermodynamically self-consistent Ornstein-Zernike approximation (SCOZA) is
applied to a fluid of spherical particles with a pair potential given by a
hard-core repulsion and a Yukawa attractive tail . This
potential allows one to take advantage of the known analytical properties of
the solution to the Ornstein-Zernike equation for the case in which the direct
correlation function outside the repulsive core is given by a linear
combination of two Yukawa tails and the radial distribution function
satisfies the exact core condition for . The predictions for the
thermodynamics, the critical point, and the coexistence curve are compared here
to other theories and to simulation results. In order to unambiguously assess
the ability of the SCOZA to locate the critical point and the phase boundary of
the system, a new set of simulations has also been performed. The method
adopted combines Monte Carlo and finite-size scaling techniques and is
especially adapted to deal with critical fluctuations and phase separation. It
is found that the version of the SCOZA considered here provides very good
overall thermodynamics and a remarkably accurate critical point and coexistence
curve. For the interaction range considered here, given by , the
critical density and temperature predicted by the theory agree with the
simulation results to about 0.6%.Comment: Prepared for the John Barker festschrift issue of Molecular Physics.
22 pages Latex, 6 ps figure
Liquid-gas phase behaviour of an argon-like fluid modelled by the hard-core two-Yukawa potential
We study a model for an argon-like fluid parameterised in terms of a
hard-core repulsion and a two-Yukawa potential. The liquid-gas phase behaviour
of the model is obtained from the thermodynamically self-consistent
Ornstein-Zernike approximation (SCOZA) of Hoye and Stell, the solution of which
lends itself particularly well to a pair potential of this form. The
predictions for the critical point and the coexistence curve are compared to
new high resolution simulation data and to other liquid-state theories,
including the hierarchical reference theory (HRT) of Parola and Reatto. Both
SCOZA and HRT deliver results that are considerably more accurate than standard
integral-equation approaches. Among the versions of SCOZA considered, the one
yielding the best agreement with simulation successfully predicts the critical
point parameters to within 1%.Comment: 10 pages 6 figure
A framework for utility data integration in the UK
In this paper we investigate various factors which prevent utility knowledge from being
fully exploited and suggest that integration techniques can be applied to improve the
quality of utility records. The paper suggests a framework which supports knowledge
and data integration. The framework supports utility integration at two levels: the
schema and data level. Schema level integration ensures that a single, integrated geospatial
data set is available for utility enquiries. Data level integration improves utility data
quality by reducing inconsistency, duplication and conflicts. Moreover, the framework
is designed to preserve autonomy and distribution of utility data. The ultimate aim of
the research is to produce an integrated representation of underground utility infrastructure
in order to gain more accurate knowledge of the buried services. It is hoped that
this approach will enable us to understand various problems associated with utility data,
and to suggest some potential techniques for resolving them
The Logic of Discrete Qualitative Relations
We consider a modal logic based on mathematical morphology which allows the expression of mereotopological relations between subgraphs. A specific form of topological closure between graphs is expressible in this logic, both as a combination of the negation ¬ and its dual , and as modality, using the stable relation Q, which describes the incidence structure of the graph. This allows to define qualitative spatial relations between discrete regions, and to compare them with earlier works in mereotopology, both in the discrete and in the continuous space
The Logic of Discrete Qualitative Relations
We consider a modal logic based on mathematical morphology which allows the expression of mereotopological relations between subgraphs. A specific form of topological closure between graphs is expressible in this logic, both as a combination of the negation ¬ and its dual , and as modality, using the stable relation Q, which describes the incidence structure of the graph. This allows to define qualitative spatial relations between discrete regions, and to compare them with earlier works in mereotopology, both in the discrete and in the continuous space
Structural precursor to freezing: An integral equation study
Recent simulation studies have drawn attention to the shoulder which forms in
the second peak of the radial distribution function of hard-spheres at
densities close to freezing and which is associated with local crystalline
ordering in the dense fluid. We address this structural precursor to freezing
using an inhomogeneous integral equation theory capable of describing local
packing constraints to a high level of accuracy. The addition of a short-range
attractive interaction leads to a well known broadening of the fluid-solid
coexistence region as a function of attraction strength. The appearence of a
shoulder in our calculated radial distribution functions is found to be
consistent with the broadened coexistence region for a simple model potential,
thus demonstrating that the shoulder is not exclusively a high density packing
effect
A globally accurate theory for a class of binary mixture models
Using the self-consistent Ornstein-Zernike approximation (SCOZA) results for
the 3D Ising model, we obtain phase diagrams for binary mixtures described by
decorated models. We obtain the plait point, binodals, and closed-loop
coexistence curves for the models proposed by Widom, Clark, Neece, and Wheeler.
The results are in good agreement with series expansions and experiments.Comment: 16 pages, 10 figure
Mesoscopic theory for size- and charge- asymmetric ionic systems. I. Case of extreme asymmetry
A mesoscopic theory for the primitive model of ionic systems is developed for
arbitrary size, , and charge, ,
asymmetry. Our theory is an extension of the theory we developed earlier for
the restricted primitive model. The case of extreme asymmetries
and is studied in some detail in a mean-field
approximation. The phase diagram and correlation functions are obtained in the
asymptotic regime and , and for infinite
dilution of the larger ions (volume fraction or less). We find a
coexistence between a very dilute 'gas' phase and a crystalline phase in which
the macroions form a bcc structure with the lattice constant . Such coexistence was observed experimentally in deionized aqueous
solutions of highly charged colloidal particles
The interaction between diabetes, body mass index, hepatic steatosis, and risk of liver resection: insulin dependent diabetes is the greatest risk for major complications
Background. This study aimed to assess the relationship between diabetes, obesity, and hepatic steatosis in patients undergoing liver resection and to determine if these factors are independent predictors of major complications. Materials and Methods. Analysis of a prospectively maintained database of patients undergoing liver resection between 2005 and 2012 was undertaken. Background liver was assessed for steatosis and classified as <33% and ≥33%. Major complications were defined as Grade III–V complications using theindo-Clavien classification. Results. 504 patients underwent liver resection, of whom 56 had diabetes and 61 had steatosis ≥33%. Median BMI was 26kg/m2 (16–54kg/m 2). 94 patients developed a major complication (18.7%). BMI ≥ 25kg/m2
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