Phase behavior of hard-core lattice gases: A Fundamental Measure approach

We use an extension of fundamental measure theory to lattice hard-core fluids to study the phase diagram of two different systems. First, two-dimensional parallel hard squares with edge-length $\sigma=2$ in a simple square lattice. This system is equivalent to the lattice gas with first and second neighbor exclusion in the same lattice, and has the peculiarity that its close packing is degenerated (the system orders in sliding columns). A comparison with other theories is discussed. Second, a three-dimensional binary mixture of parallel hard cubes with $\sigma_{\rm{L}}=6$ and $\sigma_{\rm{S}}=2$. Previous simulations of this model only focused on fluid phases. Thanks to the simplicity introduced by the discrete nature of the lattice we have been able to map out the complete phase diagram (both uniform and nonuniform phases) through a free minimization of the free energy functional, so the structure of the ordered phases is obtained as a result. A zoo of entropy-driven phase transitions is found: one-, two- and three-dimensional positional ordering, as well as fluid-ordered phase and solid-solid demixings.Comment: 14 pages, 16 figure

First-principles derivation of density functional formalism for quenched-annealed systems

We derive from first principles (without resorting to the replica trick) a density functional theory for fluids in quenched disordered matrices (QA-DFT). We show that the disorder-averaged free energy of the fluid is a functional of the average density profile of the fluid as well as the pair correlation of the fluid and matrix particles. For practical reasons it is preferable to use another functional: the disorder-averaged free energy plus the fluid-matrix interaction energy, which, for fixed fluid-matrix interaction potential, is a functional only of the average density profile of the fluid. When the matrix is created as a quenched configuration of another fluid, the functional can be regarded as depending on the density profile of the matrix fluid as well. In this situation, the replica-Ornstein-Zernike equations which do not contain the blocking parts of the correlations can be obtained as functional identities in this formalism, provided the second derivative of this functional is interpreted as the connected part of the direct correlation function. The blocking correlations are totally absent from QA-DFT, but nevertheless the thermodynamics can be entirely obtained from the functional. We apply the formalism to obtain the exact functional for an ideal fluid in an arbitrary matrix, and discuss possible approximations for non-ideal fluids.Comment: 19 pages, uses RevTeX

La lucha contra el terrorismo en el marco de la seguridad y defensa de España

En este ARI se expone la forma de combatir el terrorismo en el marco de la seguridad y defensa de España. El contexto geoestratégico actual ha hecho necesario adaptar el concepto tradicional de “defensa” a uno más amplio de “seguridad y defensa”, en el que la lucha contra el terrorismo se concibe desde una óptica multilateral, multinacional y multifuncional. La Ley Orgánica de la Defensa Nacional, la nueva Directiva de Defensa Nacional y el proyecto de Directiva de Política de Defensa reconocen la existencia de la amenaza terrorista, de ahí la necesidad de que las Fuerzas Armadas colaboren en apoyo de otras instituciones del Estado en la lucha contra terrorista. La actuación del Ministerio de Defensa en este campo se extiende también a los ámbitos de la prevención e inteligencia y cobra un significado especial en el escenario internacional, con la participación de las Fuerzas Armadas españolas en la misión de ISAF en Afganistán

- FIRM-SPECIFIC TEMPORAL VARIATION IN TECHNICAL EFFICENCY RESULTS OF: A STOCHASTIC OUTPUT DISTANCE FUNCTION

The aim of this paper is to test the temporal variation of technical efficiency of the Spanish Savings Banks during the period 1985-1994. Furthermore, a stochastic output distance function (Shephard, 1970) is employed to accommodate multiple output technology. The distance function provides the advantage that it does not need information about prices, so it can accommodate the multiproduct nature of the financial sector only using the quantitiesas data. The temporal variation of efficiency is modeled using an extension of Battese and Coelli (1992), allowing for firm-specific patterns of temporal change. El objetivo de este trabajo es contrastar la variación temporal de la eficiencia técnica de las Cajas de Ahorros españolas durante el periodo 1985-1994. Para ello la tecnología se modeliza a través de la función de distancia (Shephard, 1970) y el término de ineficiencia se especifica mediante una generalización del modelo propuesto por Battese y Coelli (1992). La función de distancia tiene la ventaja de que puede recoger tecnologías multiproducto sin precisar de información acerca de precios. Esta ventaja es mayor en un sector como el bancario en el que, generalmente, los precios se construyen a partir de gastos, lo cual podría suponer un problema. Por último, el modelo propuesto permite que el término de ineficiencia varíe con el tiempo de forma particular para cada empresa.Eficiencia técnica variante en el tiempo, Funciones de distancia estocásticas Time-varying Technical Efficiency, Stochastic Distance Functions, Panel Data.

Human oocytes and zygotes are ready for ultra-fast vitrification after 2 minutes of exposure to standard CPA solutions

Vitrification of human oocytes and embryos in different stages of development is a key element of daily clinical practice of in vitro fertilization treatments. Despite the cooling and warming of the cells is ultra-fast, the procedure as a whole is time consuming. Most of the duration is employed in a long (8–15 minutes), gradual or direct exposure to a non-vitrifying cryoprotectant solution, which is followed by a short exposure to a more concentrated vitrifying solution. A reduction in the duration of the protocols is desirable to improve the workflow in the IVF setting and reduce the time of exposure to suboptimal temperature and osmolarity, as well as potentially toxic cryoprotectants. In this work it is shown that this reduction is feasible. In silico (MatLab program using two-parameter permeability model) and in vitro observations of the oocytes’ osmotic behaviour indicate that the dehydration upon exposure to standard cryoprotectant solutions occurs very fast: the point of minimum volume of the shrink-swell curve is reached within 60 seconds. At that point, intracellular water ejection is complete, which coupled with the permeation of low molecular weight cryoprotectants results in similar intracellular and extracellular solute concentrations. This shows that prolonging the exposure to the cryoprotectant solutions does not improve the cytosolic glass forming tendency and could be avoided. To test this finding, human oocytes and zygotes that were donated for research were subjected to a shortened, dehydration-based protocol, consisting of two consecutive exposures of one-minute to two standard cryoprotectant solutions, containing ethylene glycol, dimethyl sulfoxide and sucrose. At the end of this two-minute dehydration protocol, the critical intracellular solute concentration necessary for successful vitrification was attained, confirmed by the post-warming survival and ability to resume cytokinesis of the cells. Further studies of the developmental competency of oocytes and embryos would be necessary to determine the suitability of this specific dehydration protocol for clinical practice, but based on our results, short times of exposure to increasingly hypertonic solutions could be a more time-efficient strategy to prepare human oocytes and embryos for vitrification

Environmental Efficiency Measurement with Translog Distance Functions: A Parametric Approach

We use a flexible parametric hyperbolic distance function to estimate environmental efficiency when some outputs are undesirable. Cuesta and Zofio (J. Prod. Analysis (2005), 31-48) introduced this distance function specification in conventional input-output space to estimate technical efficiency within a stochastic frontier context. We extend their approach to accommodate undesirable outputs and to estimate environmental efficiency within a stochastic frontier context. This provides a parametric counterpart to Färe et al.’s popular nonparametric environmental efficiency measures (Rev. Econ. Stat. 75 (1989), 90-98). The distance function model is applied to a panel of U.S. electricity generating units that produce marketed electricity and non-marketed SO2 emissions.Undesirable outputs; parametric distance functions; stochastic frontier analysis; environmental efficiency

A density functional theory for general hard-core lattice gases

We put forward a general procedure to obtain an approximate free energy density functional for any hard-core lattice gas, regardless of the shape of the particles, the underlying lattice or the dimension of the system. The procedure is conceptually very simple and recovers effortlessly previous results for some particular systems. Also, the obtained density functionals belong to the class of fundamental measure functionals and, therefore, are always consistent through dimensional reduction. We discuss possible extensions of this method to account for attractive lattice models.Comment: 4 pages, 1 eps figure, uses RevTeX