Solid-to-solid isostructural transition in the hard sphere/attractive Yukawa system

A thermodynamically consistent density functional-perturbation theory is used to study the isostructural solid-to-solid transition which takes place in the hard sphere/attractive Yukawa system when the Yukawa tail is sufficiently short-ranged. A comparison with results for the square well potential allows us to study the effect of the attractive potential form on the solid-solid transition. Reasonable agreement with simulations is found for the main transition properties as well as for the phase diagram evolution with the the range of the attractive potential.Comment: 14 pages, latex, 5 figures available upon request: ([email protected]

Los ejemplos y contraejemplos como herramientas para facilitar el proceso de generalización conceptual

La generalización es una de las operaciones conceptuales que más se utiliza en la matemática. En el trabajo se presenta una organización del conocimiento escolar de siete de las veintitrés generalizaciones del concepto de derivada puntual de una función f, que no exceden la extensión del concepto de función real de una variable real; tomando como criterio de generalización el debilitamiento sucesivo de las exigencias sobre la existencia del límite de la función Fc(h)=[f(c+h)-f(c)]/h, h≠0, cuando h tiende a cero, o de las características topológicas de c con respecto al dominio de f. En el trabajo se hace, además, un análisis de la utilidad de la construcción de ejemplos y contraejemplos para facilitar la realización de los procesos de generalización; y se presenta un conjunto de tareas que también facilitan y dan orden a estos procesos

Modelación de parámetros estáticos de vigas

Se presenta una organización del conocimiento escolar para la modelación de cinco conceptos relativos a vigas y sus relaciones: intensidad de carga, elástica, ángulo de giro, momento flector y fuerza cortante. Se construyó un modelo mediante funciones para cada uno de los cinco conceptos y por medio de operadores diferenciales o integrales para cada una de las relaciones entre ellos, de tal forma que dado un modelo de uno de los conceptos se puede determinar el modelo de otro cualquiera de los cuatro conceptos restantes. En el trabajo se muestra la modelación de las relaciones entre la intensidad de carga y la fuerza cortante y se comentan algunos de los resultados de la aplicación de 10 hojas de trabajo, con el objetivo que los estudiantes de un grupo de una carrera de matemáticas aplicadas participen en los distintos procesos de modelación antes descritos

Equation of State of the Hard-Sphere Crystal

A new approach to the averaged two-particle distribution function of a crystalline phase is presented. It includes an indirect check of the merit of the Gaussian approximation for the local density and a new way to inferring values of the thermodynamic variables from simulation data. The equation of state and the compressibility of the hard-sphere FCC crystal is computed from Tarazona free energy density functional [Phys. Rev. A {\bf 31}, 2672 (1985)]. They are in excellent agreement with simulation results over the physical range of densities up to almost close packing. We also include the comparison with the results obtained by two other functional approaches which are also excellent.Comment: 6 pages, latex, 5 figures available upon request: ([email protected]) To be appeared in Phys.Rev.E, Jun

Demixing behavior in two-dimensional mixtures of anisotropic hard bodies

Scaled particle theory for a binary mixture of hard discorectangles and for a binary mixture of hard rectangles is used to predict possible liquid-crystal demixing scenarios in two dimensions. Through a bifurcation analysis from the isotropic phase, it is shown that isotropic-nematic demixing is possible in two-dimensional liquid-crystal mixtures composed of hard convex bodies. This bifurcation analysis is tested against exact calculations of the phase diagrams in the framework of the restricted-orientation two-dimensional model (Zwanzig model). Phase diagrams of a binary mixture of hard discorectangles are calculated through the parametrization of the orientational distribution functions. The results show not only isotropic-nematic, but also nematic-nematic demixing ending in a critical point, as well as an isotropic-nematic-nematic triple point for a mixture of hard disks and hard discorectangles.Comment: 13 pages, 14 figures. To appear in PR

Depletion effects in smectic phases of hard rod--hard sphere mixtures

It is known that when hard spheres are added to a pure system of hard rods the stability of the smectic phase may be greatly enhanced, and that this effect can be rationalised in terms of depletion forces. In the present paper we first study the effect of orientational order on depletion forces in this particular binary system, comparing our results with those obtained adopting the usual approximation of considering the rods parallel and their orientations frozen. We consider mixtures with rods of different aspect ratios and spheres of different diameters, and we treat them within Onsager theory. Our results indicate that depletion effects, and consequently smectic stability, decrease significantly as a result of orientational disorder in the smectic phase when compared with corresponding data based on the frozen--orientation approximation. These results are discussed in terms of the $\tau$ parameter, which has been proposed as a convenient measure of depletion strength. We present closed expressions for $\tau$, and show that it is intimately connected with the depletion potential. We then analyse the effect of particle geometry by comparing results pertaining to systems of parallel rods of different shapes (spherocylinders, cylinders and parallelepipeds). We finally provide results based on the Zwanzig approximation of a Fundamental--Measure density--functional theory applied to mixtures of parallelepipeds and cubes of different sizes. In this case, we show that the $\tau$ parameter exhibits a linear asymptotic behaviour in the limit of large values of the hard--rod aspect ratio, in conformity with Onsager theory, as well as in the limit of large values of the ratio of rod breadth to cube side length, $d$, in contrast to Onsager approximation, which predicts $\tau\sim d^3$.Comment: 15 pages, 11 figure

La cronología absoluta de la prehistoria reciente del sureste de la Península Ibérica

El objetivo de este trabajo es presentar la cronología calibrada absoluta de la prehistoria reciente del Sureste de la Península Ibérica, que incluye las provincias de Almería, Granada, Jaén, Murcia y sur de Alicante, con una discusión de sus contextos arqueológicos, aportando la secuencia cronológica provisional entre el Neolítico Inicial al Bronce Final I.The aim of this paper is to display the absolute calendar chronology of the Late Prehistory in the Southeast Iberian Peninsula, Almería, Granada, Jaen, Murcia and south Alicante, with a discussion ofthe archaeological evidence in each archaeological site, and to attemps to establish a provisional chronological secuence between the Early Neolithic to the Late Bronze I