A Numerical Model for Brownian Particles Fluctuating in Incompressible Fluids

We present a numerical method that consistently implements thermal fluctuations and hydrodynamic interactions to the motion of Brownian particles dispersed in incompressible host fluids. In this method, the thermal fluctuations are introduced as random forces acting on the Brownian particles. The hydrodynamic interactions are introduced by directly resolving the fluid motions with the particle motion as a boundary condition to be satisfied. The validity of the method has been examined carefully by comparing the present numerical results with the fluctuation-dissipation theorem whose analytical form is known for dispersions of a single spherical particle. Simulations are then performed for more complicated systems, such as a dispersion composed of many spherical particles and a single polymeric chain in a solvent.Comment: 6 pages, 8 figure

La salud bucal en los niños a través de la tercera edad. Una experiencia intergeneracional

En las situaciones en que los ancianos logran superar los estigmas sociales y culturales relacionados con la edad, estos han demostrado su productividad, aunque si bien, ya no corresponde a la productividad económica, sus actuaciones tienen relación con actividades intelectuales, culturales y recreativas. En el trabajo comunitario con adultos mayores resulta interesante buscar las formas de promocionar la salud, abordando el envejecimiento desde la concepción del desarrollo humano tanto individual como colectivo. El contexto social que dio origen a este proyecto fue la tercera edad y la niñez, si bien en ambas etapas de la vida se presentan problemáticas diferentes en relación a lo social, una etapa es el inicio de la vida y la otra etapa es el camino al final. Biológicamente ambas son muy diferentes; las respuestas orgánicas son también heterogéneos, sin embargo ambos estratos sociales son afectados en la cavidad bucal por dos enfermedades comunes: la Caries y la Enfermedad Periodontal. La iniciativa se desarrolló en el marco de los saberes populares conjugado con los saberes científicos apuntados por los universitarios en relación a las dos generaciones los adultos mayores y los niños. Uno de los ejes centrales fue propiciar la vinculación entre el conocimiento científico-tecnológico existente en la Universidad Nacional Córdoba con las problemáticas sociales y, en esa línea, promover la articulación entre la investigación científica y las necesidades de la sociedad. Al generarse un dialogo entre los diferentes actores, los abuelos y los niños se esperó que basados en el encuentro generacional provoque mayor interés en la Salud Bucal, tanto en las personas mayores como en los niños para mejorar el nivel de las conductas preventivas en lo que se refiere al cuidado de la Boca. Y re-orientar los conocimientos para que los alumnos y docentes universitarios participantes del proyecto, prioricen las acciones en prevención en sus futuros pacientes y planes de estudio de la Carrera de Odontología. El proyecto comenzó, en una primera etapa, con reuniones de coordinación del grupo. En la segunda etapa, se trabajó conjuntamente con los abuelos. En la tercera etapa se llevó a cabo las estrategias planificadas entre abuelos y los nietos; cuarta etapa, presentación de los resultados a la comunidad educativa. La experiencia se evaluó mediante un instrumento ad- doc el cual fue creado por los actores universitarios para los participantes. En el que se solcita información como cuantos dientes tiene en boca, si usa o no prótesis dental, con qué frecuencia y como los higieniza a ambospublishedVersio

Scheduling M2M traffic over LTE uplink of a dense small cell network

We present an approach to schedule Long Term Evolution (LTE) uplink (UL) Machine-to-Machine (M2M) traffic in a densely deployed heterogeneous network, over the street lights of a big boulevard for smart city applications. The small cells operate with frequency reuse 1, and inter-cell interference (ICI) is a critical issue to manage. We consider a 3rd Generation Partnership Project (3GPP) compliant scenario, where single-carrier frequency-division multiple access (SC-FDMA) is selected as the multiple access scheme, which requires that all resource blocks (RBs) allocated to a single user have to be contiguous in the frequency within each time slot. This adjacency constraint limits the flexibility of the frequency-domain packet scheduling (FDPS) and inter-cell interference coordination (ICIC), when trying to maximize the scheduling objectives, and this makes the problem NP-hard. We aim to solve a multi-objective optimization problem, to maximize the overall throughput, maximize the radio resource usage and minimize the ICI. This can be modelled through a mixed-integer linear programming (MILP) and solved through a heuristic implementable in the standards. We propose two models. The first one allocates resources based on the three optimization criteria, while the second model is more compact and is demonstrated through numerical evaluation in CPLEX, to be equivalent in the complexity, while it performs better and executes faster. We present simulation results in a 3GPP compliant network simulator, implementing the overall protocol stack, which support the effectiveness of our algorithm, for different M2M applications, with respect to the state-of-the-art approaches

Lattice Boltzmann simulations of soft matter systems

This article concerns numerical simulations of the dynamics of particles immersed in a continuum solvent. As prototypical systems, we consider colloidal dispersions of spherical particles and solutions of uncharged polymers. After a brief explanation of the concept of hydrodynamic interactions, we give a general overview over the various simulation methods that have been developed to cope with the resulting computational problems. We then focus on the approach we have developed, which couples a system of particles to a lattice Boltzmann model representing the solvent degrees of freedom. The standard D3Q19 lattice Boltzmann model is derived and explained in depth, followed by a detailed discussion of complementary methods for the coupling of solvent and solute. Colloidal dispersions are best described in terms of extended particles with appropriate boundary conditions at the surfaces, while particles with internal degrees of freedom are easier to simulate as an arrangement of mass points with frictional coupling to the solvent. In both cases, particular care has been taken to simulate thermal fluctuations in a consistent way. The usefulness of this methodology is illustrated by studies from our own research, where the dynamics of colloidal and polymeric systems has been investigated in both equilibrium and nonequilibrium situations.Comment: Review article, submitted to Advances in Polymer Science. 16 figures, 76 page

Optimization of chaotic micromixers using finite time Lyapunov exponents

In microfluidics mixing of different fluids is a highly non-trivial task due to the absence of turbulence. The dominant process allowing mixing at low Reynolds number is therefore diffusion, thus rendering mixing in plain channels very inefficient. Recently, passive chaotic micromixers such as the staggered herringbone mixer were developed, allowing efficient mixing of fluids by repeated stretching and folding of the fluid interfaces. The optimization of the geometrical parameters of such mixer devices is often performed by time consuming and expensive trial and error experiments. We demonstrate that the application of the lattice Boltzmann method to fluid flow in highly complex mixer geometries together with standard techniques from statistical physics and dynamical systems theory can lead to a highly efficient way to optimize micromixer geometries. The strategy applies massively parallel fluid flow simulations inside a mixer, where massless and noninteracting tracer particles are introduced. By following their trajectories we can calculate finite time Lyapunov exponents in order to quantify the degree of chaotic advection inside the mixer. The current report provides a review of our results published in [1] together with additional details on the simulation methodology

Numerical simulations of complex fluid-fluid interface dynamics

Interfaces between two fluids are ubiquitous and of special importance for industrial applications, e.g., stabilisation of emulsions. The dynamics of fluid-fluid interfaces is difficult to study because these interfaces are usually deformable and their shapes are not known a priori. Since experiments do not provide access to all observables of interest, computer simulations pose attractive alternatives to gain insight into the physics of interfaces. In the present article, we restrict ourselves to systems with dimensions comparable to the lateral interface extensions. We provide a critical discussion of three numerical schemes coupled to the lattice Boltzmann method as a solver for the hydrodynamics of the problem: (a) the immersed boundary method for the simulation of vesicles and capsules, the Shan-Chen pseudopotential approach for multi-component fluids in combination with (b) an additional advection-diffusion component for surfactant modelling and (c) a molecular dynamics algorithm for the simulation of nanoparticles acting as emulsifiers.Comment: 24 pages, 12 figure