545 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
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
UK utility data integration: overcoming schematic heterogeneity
In this paper we discuss syntactic, semantic and schematic issues which inhibit the integration of utility data in the UK. We then focus on the techniques employed within the VISTA project to overcome schematic heterogeneity. A Global
Schema based architecture is employed. Although automated approaches to Global Schema definition were attempted
the heterogeneities of the sector were too great. A manual approach to Global Schema definition was employed. The
techniques used to define and subsequently map source utility data models to this schema are discussed in detail. In order to ensure a coherent integrated model, sub and cross domain validation issues are then highlighted. Finally the proposed framework and data flow for schematic integration is introduced
SCOZA for Monolayer Films
We show the way in which the self-consistent Ornstein-Zernike approach
(SCOZA) to obtaining structure factors and thermodynamics for Hamiltonian
models can best be applied to two-dimensional systems such as thin films. We
use the nearest-neighbor lattice gas on a square lattice as an illustrative
example.Comment: 10 pages, 5 figure
Systematic evaluation of radiological findings in the assessment of resectability of peri-ampullary cancer by CT using different contrast phase protocols
Aims: To determine the relative significance of radiological signs in determining the resectability of peri-ampullary cancer (PC) and to assess the value of multi-phase imaging in detecting these findings.
Materials and Methods: Blinded, double re-reporting of pre-operative imaging from five hospitals was undertaken of 411 patients undergoing surgery for PC over an eight year period, of whom 119 patients were found to be inoperable at the time of surgery.
Results: The median tumour size was 26.7 mm and the proportion of patients reported to have regional lymphadenopathy (RL), venous (VI) and arterial involvement (AI) was 24.7%, 11.5% and 3.9% respectively and was similar regardless of the number of contrast phases undertaken. Significant associations were however noted between individual risk factors: VI was closely associated with tumour size (p=0.002) and AI (p< 0.0001). In multi-variable analysis AI, VI and RL were independently associated with resectability (relative risk of resection =0.05, 0.31 and 0.51 respectively). Tumour size however was not associated with resectability when VI was included in the multivariate model
The density functional theory of classical fluids revisited
We reconsider the density functional theory of nonuniform classical fluids
from the point of view of convex analysis. From the observation that the
logarithm of the grand-partition function is a convex
functional of the external potential it is shown that the Kohn-Sham free
energy is a convex functional of the density . and constitute a pair of Legendre transforms and each
of these functionals can therefore be obtained as the solution of a variational
principle. The convexity ensures the unicity of the solution in both cases. The
variational principle which gives as the maximum of a
functional of is precisely that considered in the density functional
theory while the dual principle, which gives as the maximum of
a functional of seems to be a new result.Comment: 10 page
Prevalence and risk factors for mast cell tumours in dogs in England
BACKGROUND: Mast cell tumour (MCT) appears to be a frequent tumour type in dogs, though there is little published in relation to its frequency in dogs in the UK. The current study aimed to investigate prevalence and risk factors for MCTs in dogs attending English primary-care veterinary practices. METHODS: Electronic patient records from practices participating in the VetCompass animal surveillance project between July 2007 and June 2013 were searched for MCT diagnosis. Various search terms and standard diagnostic terms (VeNom codes) identified records containing MCT diagnoses, which were evaluated against clinical criteria for inclusion to the study. MCT prevalence for the entire dataset and specific breed types were calculated. Descriptive statistics characterised MCT cases and multivariable logistic regression methods evaluated risk factors for association with MCT (P < 0.05). RESULTS: Within a population of 168,636 dogs, 453 had MCT, yielding a prevalence of 0.27% (95% confidence interval (CI) 0.24% - 0.29%). The highest breed type specific prevalences were for the Boxer at 1.95% (95% CI 1.40% - 2.51%), Golden Retriever at 1.39% (0.98% - 1.81%) and Weimaraner at 0.85% (95% CI 0.17% to 1.53%). Age, insurance status, neuter status, weight and breed type were associated with MCT diagnosis. Of dogs of specific breed type, the Boxer, Pug and Staffordshire Bull Terrier showed greater odds of MCT diagnosis compared with crossbred dogs. Conversely, the German Shepherd Dog, Border Collie, West Highland White Terrier, Springer Spaniel and Cocker Spaniel had reduced odds of MCT diagnosis compared with crossbred dogs. No association was found between MCT diagnosis and sex. CLINICAL SIGNIFICANCE: This study highlights a clinically significant prevalence of MCT and identifies specific breed types with predisposition to MCT, potentially aiding veterinarian awareness and facilitating diagnosis
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