Biomedical subjects

M Ripoll

Publications and source records attributed to M Ripoll.

18 recordsLinked to original sources

PubMed2006

Star polymers in shear flow.

Linear and star polymers in solution are studied in the presence of shear flow. The solvent is described by a particle-based mesoscopic simulation technique, which accounts for hydrodynamic interactions. The scaling properties of the average gyration tensor, the orientation angle, and the rotation frequency are investigated for various arm lengths and arm numbers. With increasing functionality f, star polymers exhibit a crossover in their flow properties from those of linear polymers to a novel behavior, which resembles the tank-treading motion of elastic capsules.

Elasticity↗

PubMed2005

Dynamics of polymers in a particle-based mesoscopic solvent.

We study the dynamics of flexible polymer chains in solution by combining multiparticle-collision dynamics (MPCD), a mesoscale simulation method, and molecular-dynamics simulations. Polymers with and without excluded-volume interactions are considered. With an appropriate choice of the collision time step for the MPCD solvent, hydrodynamic interactions build up properly. For the center-of-mass diffusion coefficient, scaling with respect to polymer length is found to hold already for rather short chains. The center-of-mass velocity autocorrelation function displays a long-time tail which decays algebraically as (Dt)(-3/2) as a function of time t, where D is the diffusion coefficient. The analysis of the intramolecular dynamics in terms of Rouse modes yields excellent agreement between simulation data and results of the Zimm model for the mode-number dependence of the mode-amplitude correlation functions.

Journal Article↗

PubMed2005

Dynamic regimes of fluids simulated by multiparticle-collision dynamics.

We investigate the hydrodynamic properties of a fluid simulated with a mesoscopic solvent model. Two distinct regimes are identified, the "particle regime" in which the dynamics is gaslike and the "collective regime" where the dynamics is fluidlike. This behavior can be characterized by the Schmidt number, which measures the ratio between viscous and diffusive transport. Analytical expressions for the tracer diffusion coefficient, which have been derived on the basis of a molecular-chaos assumption, are found to describe the simulation data very well in the particle regime, but important deviations are found in the collective regime. These deviations are due to hydrodynamic correlations. The model is then extended in order to investigate self-diffusion in colloidal dispersions. We study first the transport properties of heavy pointlike particles in the mesoscopic solvent, as a function of their mass and number density. Second, we introduce excluded-volume interactions among the colloidal particles and determine the dependence of the diffusion coefficient on the colloidal volume fraction for different solvent mean-free paths. In the collective regime, the results are found to be in good agreement with previous theoretical predictions based on Stokes hydrodynamics and the Smoluchowski equation.

Journal Article↗

PubMed2005

Power law tails of time correlations in a mesoscopic fluid model.

In a quenched mesoscopic fluid, modeling transport processes at high densities, we perform computer simulations of the single particle energy autocorrelation function C(e) (t) , which is essentially a return probability. This is done to test the predictions for power law tails, obtained from mode coupling theory. We study both off and on-lattice systems in one- and two-dimensions. The predicted long time tail approximately t(-d/2) is in excellent agreement with the results of computer simulations. We also account for finite size effects, such that smaller systems are fully covered by the present theory as well.

Journal Article↗

PubMed2005

Model system for classical fluids out of equilibrium.

A model system for classical fluids out of equilibrium, referred to as a dissipative particles dynamics (DPD) solid, is studied by analytical and simulation methods. The time evolution of a DPD particle is described by a fluctuating heat equation. This DPD solid with transport based on collisional transfer (high-density mechanism) is complementary to the Lorentz gas with only kinetic transport (low-density mechanism). Combination of both models covers the qualitative behavior of transport properties of classical fluids over the full-density range. The heat diffusivity is calculated using a mean-field theory, leading to a linear-density dependence of this transport coefficient, which is exact at high densities. Subleading density corrections are obtained as well. At lower densities the model has a conductivity threshold below which heat conduction is absent. The observed threshold is explained in terms of percolation diffusion on a random proximity network. The geometrical structure of this network is the same as in continuum percolation of completely overlapping spheres, but the dynamics on this network differs from continuum percolation diffusion. Furthermore, the kinetic theory for DPD is extended to the generalized hydrodynamic regime, where the wave-number-dependent decay rates of the Fourier modes of the energy and temperature fields are calculated.

Journal Article↗

PubMed2003

Does short-course antibiotic therapy better meet patient expectations?

A pan-European market research study of 3254 patients designed to determine patient attitudes, expectations and behaviour to antibiotic management of mild-moderate RTIs, identified three key drivers of perceived antibiotic efficacy: length of antibiotic course, time to onset of symptom relief and time to complete resolution of symptoms. Azithromycin was selected as "drug therapy of shortest dosage schedule" for common outpatient infections. The results demonstrate that once-daily, short-course treatment is perceived to be significantly more effective than longer antibiotic courses and thus, better meets patient expectations of therapy. This perception of efficacy with short-course therapy also correlates with overall satisfaction with management by the physician and compliance with therapy. These findings have important implications for the way physicians manage patients with mild-moderate RTIs.

Adolescent↗

PubMed2002

Attitudinal classification of patients receiving antibiotic treatment for mild respiratory tract infections.

The aim of this study was to determine patients' perceptions of antibiotic therapy and the doctor's skill in the management of ambulatory respiratory tract infections. Standardized face-to-face interviews were used with more than 3000 randomized patients or parents from four European countries. Attitudinal dimensions relating to their doctor identified four patient types: Involved (30%), Deferent (23%), Ignored (13%) and Critical (17%). Involved and Deferent patients were the most satisfied by the information received from their doctor (43%/39% compared with 17%/16% for Ignored/Critical, respectively, P < 0.01). They also scored more highly on the accurate use of antibiotics, with 80%/80% vs. 38%/62%, respectively (P < 0.01), understanding dosing intervals and 77%/77% vs. 36%/60% (P < 0.01), understanding the course length. Involved and Deferent patients showed better compliant behaviour, with 91% of both groups vs. 86% of the Ignored and Critical claiming to have taken every dose (P < 0.001) and 92%/87% vs. 84%/85% claiming to have finished the course (P < 0.001 for Involved only). Involved and Deferent patients were less prone to save part of a course of antibiotics than the Ignored and Critical (46%/41% vs. 20%/31%, P < 0.001), and they perceived the antibiotics prescribed to be more effective (36%/31% vs. 21%/15%, P < 0.001). By analysing patient perceptions, this study identifies an important mirror effect, whereby a more sympathetic attitude from the doctor should increase the patient's involvement in disease management, for a more appropriate use of antibiotics in common infections.

Adolescent↗

PubMed1980