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 $w(r)=-\exp [-z(r-1)]/r$. 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 $g(r)$ satisfies the exact core condition $g(r)=0$ for $r<1$. 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 $z=1.8$, 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

Federated authentication and authorisation for e-science

The Grid and Web service community are defining a range of standards for a complete solution for security. The National e-Science Centre (NeSC) at the University of Glasgow is investigating how the various pre-integration components work together in a variety of e-Science projects. The EPSRC-funded nanoCMOS project aims to allow electronics designers and manufacturers to use e-Science technologies and expertise to solve problems of device variability and its impact on system design. To support the security requirements of nanoCMOS, two NeSC projects (VPMan and OMII-SP) are providing tools to allow easy configuration of security infrastructures, exploiting previous successful projects using Shibboleth and PERMIS. This paper presents the model in which these tools interoperate to provide secure and simple access to Grid resources for non-technical users

Model Energy Landscapes of Low-Temperature Fluids: Dipolar Hard Spheres

An analytical model of non-Gaussian energy landscape of low-temperature fluids is developed based on the thermodynamics of the fluid of dipolar hard spheres. The entire excitation profile of the liquid, from the high temperatures to the point of ideal-glass transition, has been obtained from the Monte Carlo simulations. The fluid of dipolar hard spheres loses stability when reaching the point of ideal-glass transition transforming via a first-order transition into a columnar liquid phase of dipolar chains locally arranged in a body-centered tetragonal order.Comment: 4 pages, 3 figure

Long wavelength structural anomalies in jammed systems

The structural properties of static, jammed packings of monodisperse spheres in the vicinity of the jamming transition are investigated using large-scale computer simulations. At small wavenumber $k$, we argue that the anomalous behavior in the static structure factor, $S(k) \sim k$, is consequential of an excess of low-frequency, collective excitations seen in the vibrational spectrum. This anomalous feature becomes more pronounced closest to the jamming transition, such that $S(0) \to 0$ at the transition point. We introduce an appropriate dispersion relation that accounts for these phenomena that leads us to relate these structural features to characteristic length scales associated with the low-frequency vibrational modes of these systems. When the particles are frictional, this anomalous behavior is suppressed providing yet more evidence that jamming transitions of frictional spheres lie at lower packing fractions that that for frictionless spheres. These results suggest that the mechanical properties of jammed and glassy media may therefore be inferred from measurements of both the static and dynamical structure factors.Comment: 8 pages, 6 figure captions. Completely revised version to appear in Phys. Rev.

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

Gas-liquid critical point in ionic fluids

Based on the method of collective variables we develop the statistical field theory for the study of a simple charge-asymmetric $1:z$ primitive model (SPM). It is shown that the well-known approximations for the free energy, in particular DHLL and ORPA, can be obtained within the framework of this theory. In order to study the gas-liquid critical point of SPM we propose the method for the calculation of chemical potential conjugate to the total number density which allows us to take into account the higher order fluctuation effects. As a result, the gas-liquid phase diagrams are calculated for $z=2-4$. The results demonstrate the qualitative agreement with MC simulation data: critical temperature decreases when $z$ increases and critical density increases rapidly with $z$.Comment: 18 pages, 1 figur

Critical behavior of a fluid in a disordered porous matrix: An Ornstein-Zernike approach

Using a liquid-state approach based on Ornstein-Zernike equations, we study the behavior of a fluid inside a porous disordered matrix near the liquid-gas critical point.The results obtained within various standard approximation schemes such as lowest-order $\gamma$-ordering and the mean-spherical approximation suggest that the critical behavior is closely related to that of the random-field Ising model (RFIM).Comment: 10 pages, revtex, to appear in Physical Review Letter

Differentiating Simple Hepatic Cysts from Mucinous Cystic Neoplasms: Radiological Features, Cyst Fluid Tumour Marker Analysis and Multidisciplinary Team Outcomes

Background: Differentiating hepatic mucinous cystic neoplasms (MCNs) from simple hepatic cysts (SCs) preoperatively is a challenging task. Our aim was to determine whether radiological features on ultrasound scan (USS), CT or MRI, cyst fluid tumour markers, or multidisciplinary team (MDT) outcomes could differentiate MCN from SC. Methods: A retrospective review of radiological features, cyst fluid tumour marker levels and MDT outcomes in 52 patients was performed. Results: There were 13 patients with MCN, 38 with SC and one ciliated foregut cyst. MCNs were more often solitary (p = 0.006). Although no other individual radiological characteristic on USS, CT or MRI was predictive of MCN, MDT outcomes stating that a cyst was complex in nature were highly predictive (p = 0.0007). Cyst fluid carbohydrate antigen 19-9, carcino-embryonic antigen and cancer antigen 125 were unable to differentiate MCN from SC (p = 0.45, p = 0.49, and p = 0.73, respectively). Conclusions: MDT outcomes are of greatest value when trying to differentiate MCN from SC, as well as having a solitary cyst on imaging. Conventional cyst fluid tumour markers are unhelpful. All suspicious cystic liver lesions should be discussed pre-operatively by a hepatobiliary MDT to determine the most appropriate surgical approach

Implementation of the Hierarchical Reference Theory for simple one-component fluids

Combining renormalization group theoretical ideas with the integral equation approach to fluid structure and thermodynamics, the Hierarchical Reference Theory is known to be successful even in the vicinity of the critical point and for sub-critical temperatures. We here present a software package independent of earlier programs for the application of this theory to simple fluids composed of particles interacting via spherically symmetrical pair potentials, restricting ourselves to hard sphere reference systems. Using the hard-core Yukawa potential with z=1.8/sigma for illustration, we discuss our implementation and the results it yields, paying special attention to the core condition and emphasizing the decoupling assumption's role.Comment: RevTeX, 16 pages, 2 figures. Minor changes, published versio