Modeling the structure and thermodynamics of multicomponent and polydisperse hard-sphere dispersions with continuous potentials.

A model system of identical particles interacting via a hard-sphere potential is essential in condensed matter physics; it helps to understand in and out of equilibrium phenomena in complex fluids, such as colloidal dispersions. Yet, most of the fixed time-step algorithms to study the transport properties of those systems have drawbacks due to the mathematical nature of the interparticle potential. Because of this, mapping a hard-sphere potential onto a soft potential has been recently proposed [Báez et al., J. Chem. Phys. 149, 164907 (2018)]. More specifically, using the second virial coefficient criterion, one can set a route to estimate the parameters of the soft potential that accurately reproduces the thermodynamic properties of a monocomponent hard-sphere system. However, real colloidal dispersions are multicomponent or polydisperse, making it important to find an efficient way to extend the potential model for dealing with such kind of many-body systems. In this paper, we report on the extension and applicability of the second virial coefficient criterion to build a description that correctly captures the phenomenology of both multicomponent and polydisperse hard-sphere dispersions. To assess the accuracy of the continuous potentials, we compare the structure of soft polydisperse systems with their hard-core counterpart. We also contrast the structural and thermodynamic properties of soft binary mixtures with those obtained through mean-field approximations and the Ornstein-Zernike equation for the two-component hard-sphere dispersion.

Impact of asymptomatic acute cellular rejection on left ventricle myocardial function evaluated by means of two-dimensional speckle tracking echocardiography in heart transplant recipients.

BACKGROUND: Our objective was to evaluate the impact of asymptomatic acute cellular rejection (ACR) in left ventricular myocardial strain in heart transplant (HT) recipients by means of two-dimensional speckle tracking echocardiography (2DSTE). METHODS: From September 1, 2009 to December 15, 2010 a conventional echocardiography and 2DSTE exam was performed on all consecutive HT recipients in their first year posttransplantation within 3 hours of the surveillance endomyocardial biopsies, as well as on 14 healthy controls. The association of strain echocardiographic variables with different grades of ACR was investigated. RESULTS: Of the 78 studies performed 4 ± 3 months after HT in 20 patients, 32 studies were coincident with grade 0R rejection, 41 with grade 1R, and 5 with grade 2R. Significantly lower values of average radial strain were found with higher grades of ACR (29.1 ± 7.7%, 23.2 ± 8.5%, and 14.3 ± 8.8% for grades 0R, 1R, and 2R of ACR, P = 0.001). Average deformation was similar for controls versus transplanted patients, in the absence of acute rejection: radial 29.1 ± 10.0% versus 29.1 ± 7.7%, P = 0.98; circumferential -19.3 ± 3.2% versus -20.2 ± 5.9%, P = 0.62; and longitudinal -20.7 ± 4.1% versus -18.5 ± 5.4%, P = 0.19. An average radial strain <25% presented 100% sensitivity, 48% specificity, 6% positive predictive value, and 100% negative predictive value for the presence of 2R rejection (area under the curve 0.80, IC 95% 0.60-0.99, P = 0.048). CONCLUSION: In this study, HT recipients showed significantly lower values of average radial left ventricle strain, evaluated by means of 2DSTE, with the presence of ACR.

Soft representation of the square-well and square-shoulder potentials to be used in Brownian and molecular dynamics simulations.

The discrete hard-sphere (HS), square-well (SW), and square-shoulder (SS) potentials have become the battle horse of molecular and complex fluids because they contain the basic elements to describe the thermodynamic, structural, and transport properties of both types of fluids. The mathematical simplicity of these discrete potentials allows us to obtain some analytical results despite the nature and complexity of the modeled systems. However, the divergent forces arising at the potential discontinuities may lead to severe issues when discrete potentials are used in computer simulations with uniform time steps. One of the few routes to avoid these technical problems is to replace the discrete potentials with continuous and differentiable forms built under strict physical criteria to capture the correct phenomenology. The match of the second virial coefficient between the discrete and the soft potentials has recently been successfully used to construct a continuous representation that mimics some physical properties of HSs (Báezet al2018J. Chem. Phys.149164907). In this paper, we report an extension of this idea to construct soft representations of the discrete SW and SS potentials. We assess the accuracy of the resulting soft potential by studying structural and thermodynamic properties of the modeled systems by using extensive Brownian and molecular dynamics computer simulations. Besides, Monte Carlo results for the original discrete potentials are used as benchmark. We have also implemented the discrete interaction models and their soft counterparts within the integral equations theory of liquids, finding that the most widely used approximations predict almost identical results for both potentials.

Thermodynamics, static properties and transport behaviour of fluids with competing interactions.

Competing interaction fluids have become ideal model systems to study a large number of phenomena, for example, the formation of intermediate range order structures, condensed phases not seen in fluids driven by purely attractive or repulsive forces, the onset of particle aggregation under in- and out-of-equilibrium conditions, which results in the birth of reversible and irreversible aggregates or clusters whose topology and morphology depend additionally on the thermodynamic constrictions, and a particle dynamics that has a strong influence on the transport behaviour and rheological properties of the fluid. In this contribution, we study a system of particles interacting through a potential composed by a continuous succession of a short-ranged square-well (SW), an intermediate-ranged square-shoulder and a long-ranged SW. This potential model is chosen to systematically analyse the contribution of every component of the interaction potential on the phase behaviour, the microstructure, the morphology of the resulting aggregates and the transport phenomena of fluids described by competing interactions. Our results indicate that the inclusion of a barrier and a second well leads to new and interesting effects, which in addition result in variations of the physical properties associated to the competition among interactions.

[Changing epidemiology of native valve infective endocarditis]. / Cambios epidemiológicos de la endocarditis infecciosa sobre válvula nativa.

INTRODUCTION AND OBJECTIVES: The aim of our study is to assess changes in the epidemiologic features of patients with native valve infective endocarditis. METHODS: We analyzed a prospective series of 228 cases of native valve infective endocarditis in non-intravenous drug users attending our center between 1987 and 2009. We compared three subperiods: 1987-1994 (67 cases), 1995-2002 (74 cases) and 2003-2009 (87 cases). RESULTS: The mean age of patients has progressively increased (38±22 years in the first subperiod vs 60±16 years in the third; P<.001), as has the proportion of cases without predisposing heart disease (25%, 46% and 67%; P<.001). Incidence of mitral valve prolapse remained stable (12%, 18% and 11%). Percentages of patients with predisposing heart disease and who were aware of their condition have fallen in recent years (45%, 27% and 21%; P<.001). A portal of entry for the infection could not be identified in 64%. Overall, Staphylococcus aureus is the most frequent causative organism (26%) whereas the percentage of cases caused by Streptococcus viridans remains unaltered (22%, 20% and 24%). CONCLUSIONS: We found significant changes in the epidemiology of native valve infective endocarditis. The incidence of patients without predisposing heart disease has increased significantly and staphylococci are the most frequent causative organisms. Full English text available from: www.revespcardiol.org.

Evolución de la función sistólica ventricular derecha tras implante de válvula aórtica percutánea con ecocardiografía speckle tracking bidimensional / Changes in right ventricular systolic function after transcatheter aortic valve implantation assessed by two-dimensional speckle tracking echocardiography

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Cambios epidemiológicos de la endocarditis infecciosa sobre válvula nativa / Changing epidemiology of native valve infective endocarditis

Introducción y objetivos. El objetivo de nuestro estudio es evaluar los cambios producidos en los aspectos epidemiológicos de la endocarditis sobre válvula nativa. Métodos. Estudiamos una serie prospectiva de 228 casos con endocarditis sobre válvula nativa en pacientes no usuarios de drogas por vía parenteral atendidos en nuestra institución desde 1987 hasta 2009, y comparamos tres periodos de estudio: 1987-1994 (67 casos), 1995-2002 (74 casos) y 2003-2009 (87 casos). Resultados. La media de edad de los pacientes ha aumentado progresivamente (38±22 años en el primer periodo frente a 60±16 años en el tercero; p<0,001), así como la proporción de casos sin cardiopatía predisponente (el 25, el 46 y el 67%; p<0,001). La incidencia de prolapso valvular mitral ha permanecido estable (el 12, el 18 y el 11%). La tasa de pacientes portadores de una cardiopatía predisponente y conocedores de ella se redujo significativamente en los últimos años (el 45, el 27 y el 21%; p<0,001). No se pudo identificar una puerta de entrada a la infección en el 64% de los casos. En general, Staphylococcus aureus es el germen causal más frecuente (26%), mientras que la proporción de casos por Streptococcus viridans no se ha modificado (el 22, el 20 y el 24%). Conclusiones. Se han producido cambios significativos en la epidemiología de la endocarditis infecciosa sobre válvula nativa. La incidencia de casos de endocarditis sin cardiopatía predisponente está aumentando significativamente y en ella los estafilococos siguen siendo los más frecuentes (AU)

Introduction and objectives. The aim of our study is to assess changes in the epidemiologic features of patients with native valve infective endocarditis. Methods. We analyzed a prospective series of 228 cases of native valve infective endocarditis in non-intravenous drug users attending our center between 1987 and 2009. We compared three subperiods: 1987-1994 (67 cases), 1995-2002 (74 cases) and 2003-2009 (87 cases). Results. The mean age of patients has progressively increased (38±22 years in the first subperiod vs 60±16 years in the third; P<.001), as has the proportion of cases without predisposing heart disease (25%, 46% and 67%; P<.001). Incidence of mitral valve prolapse remained stable (12%, 18% and 11%). Percentages of patients with predisposing heart disease and who were aware of their condition have fallen in recent years (45%, 27% and 21%; P<.001). A portal of entry for the infection could not be identified in 64%. Overall, Staphylococcus aureus is the most frequent causative organism (26%) whereas the percentage of cases caused by Streptococcus viridans remains unaltered (22%, 20% and 24%). Conclusions. We found significant changes in the epidemiology of native valve infective endocarditis. The incidence of patients without predisposing heart disease has increased significantly and staphylococci are the most frequent causative organisms (AU)