Quantum Monte Carlo Simulation of the High-Pressure Molecular-Atomic Crossover in Fluid Hydrogen

A first-order liquid-liquid phase transition in high-pressure hydrogen between molecular and atomic fluid phases has been predicted in computer simulations using ab initio molecular dynamics approaches. However, experiments indicate that molecular dissociation may occur through a continuous crossover rather than a first-order transition. Here we study the nature of molecular dissociation in fluid hydrogen using an alternative simulation technique in which electronic correlation is computed within quantum Monte Carlo, the so-called Coupled Electron Ion Monte Carlo (CEIMC) method. We find no evidence for a first-order liquid-liquid phase transition.Comment: 4 pages, 5 figures; content changed; accepted for publication in Phys. Rev. Let

Coupled Electron Ion Monte Carlo Calculations of Dense Metallic Hydrogen

We present a new Monte Carlo method which couples Path Integral for finite temperature protons with Quantum Monte Carlo for ground state electrons, and we apply it to metallic hydrogen for pressures beyond molecular dissociation. We report data for the equation of state for temperatures across the melting of the proton crystal. Our data exhibit more structure and higher melting temperatures of the proton crystal than Car-Parrinello Molecular Dynamics results. This method fills the gap between high temperature electron-proton Path Integral and ground state Diffusion Monte Carlo methods

Desarrollo de una aplicación informática lúdica para estudiantes del primer grado, asignatura de matemática unidad III y IV, Colegio “San José “, Matagalpa año 2011

Las tecnologías de la información y comunicación (TIC´s) evolucionan rápidamente desarrollando la sociedad. En la educación apoyan al proceso enseñanza aprendizaje mejorando los conocimientos iniciales en las escuelas, exceso de población en las aulas de clase es uno de los factores que dificulta dar una atención adecuada a cada estudiante y estas deficiencias se observan en la actualidad cuando los estudiantes realizan exámenes de admisión en las universidades, por esto se considera que mediante la creación de un software que combine estrategias lúdicas y las TIC´s se pueden obtener mayores beneficios en el campo educativo. Esta investigación inició estudiando las dificultades que presentaban los estudiantes de primer grado del colegio “San José” en la asignatura de matemáticas, con el propósito de aportar una herramienta que mejore el proceso enseñanza aprendizaje, se analizaron las ventajas que la lúdica ofrece para superar estas debilidades a través del uso de un software lúdico educativo. Para crear una aplicación informática se tomaron en cuenta las características y ventajas que brindan las herramientas informáticas siguiendo algunos pasos para desarrollar software de calidad; inicialmente se recopiló la información necesaria, conocer cómo trabaja el colegio, se aplicó pruebas a los niños para identificar en qué temas se presentaban debilidades y se seleccionaron herramientas adecuadas para desarrollar la aplicación. La implementación del software lúdico educativo “Matemáticas para niñ@s” ayudará al desarrollo de la clase de forma dinámica, mejorando los conocimientos matemáticos en los alumnos de primer grado del colegio “San José”, obteniendo mayor rendimiento académico en esta asignatura y reforzando conocimientos de computació

Anodic dissolution of metals in oxide-free cryolite melts

The anodic behavior of metals in molten cryolite-alumina melts has been investigated mostly for use as inert anodes for the Hall-Héroult process. In the present work, gold, platinum, palladium, copper, tungsten, nickel, cobalt and iron metal electrodes were anodically polarized in an oxide-free cryolite melt (11%wt. excess AlF3 ; 5%wt. CaF2) at 1273 K. The aim of the experiments was to characterize the oxidation reactions of the metals occurring without the effect of oxygen-containing dissolved species. The anodic dissolution of each metal was demonstrated, and electrochemical reactions were assigned using reversible potential calculation. The relative stability of metals as well as the possibility of generating pure fluorine is discussed

Evidence for strong electron-phonon coupling and polarons in the optical response of La_{2-x}Sr_xCuO_4

The normal state optical response of La_{2-x}Sr_xCuO_4 is found to be consistent with a simple multi-component model, based on free carriers with strong electron-phonon interaction, localized polaronic states near 0.15 eV and a mid-infrared band at 0.5 eV. Normal state reflectance and absorbance of La_{1.83}Sr_{0.17}CuO_4 are investigated and their temperature dependence is explained. Both, the ac and dc response are recovered and the quasi-linear behavior of the optical scattering rate up to 3000- 4000 cm^{-1} is found to be consistent with strong electron-phonon interaction, which also accounts for the value of T_c. Although not strictly applicable in the superconducting state, our simple model accounts for the observed penetration depth and the optical response below T_c can be recovered by introducing a small amount of additional carriers. Our findings suggest that the optical response of La_{2-x}Sr_xCuO_4 could be explained both, in the normal and superconducting state, by a simple multi-fluid model with strong electron-phonon interaction if the gap symmetry and the temperature dependence of the 0.5 eV mid-infrared band are adequately taken into account.Comment: 22 pages, REVTeX, 12 figures in ps-fil

Trial wave functions for High-Pressure Metallic Hydrogen

Many body trial wave functions are the key ingredient for accurate Quantum Monte Carlo estimates of total electronic energies in many electron systems. In the Coupled Electron-Ion Monte Carlo method, the accuracy of the trial function must be conjugated with the efficiency of its evaluation. We report recent progress in trial wave functions for metallic hydrogen implemented in the Coupled Electron-Ion Monte Carlo method. We describe and characterize several types of trial functions of increasing complexity in the range of the coupling parameter $1.0 \leq r_s \leq1.55$. We report wave function comparisons for disordered protonic configurations and preliminary results for thermal averages.Comment: 11 pages, 6 figures, submitted to Computer Physics Communication

AMMECR1: a single point mutation causes developmental delay, midface hypoplasia and elliptocytosis

Background: Deletions in the Xq22.3–Xq23 region, inclusive of COL4A5, have been associated with a contiguous gene deletion syndrome characterised by Alport syndrome with intellectual disability (Mental retardation), Midface hypoplasia and Elliptocytosis (AMME). The extrarenal biological and clinical significance of neighbouring genes to the Alport locus has been largely speculative. We sought to discover a genetic cause for two half-brothers presenting with nephrocalcinosis, early speech and language delay and midface hypoplasia with submucous cleft palate and bifid uvula.Methods: Whole exome sequencing was undertaken on maternal half-siblings. In-house genomic analysis included extraction of all shared variants on the X chromosome in keeping with X-linked inheritance. Patient-specific mutants were transfected into three cell lines and microscopically visualised to assess the nuclear expression pattern of the mutant protein.Results: In the affected half-brothers, we identified a hemizygous novel non-synonymous variant of unknown significance in AMMECR1 (c.G530A; p.G177D), a gene residing in the AMME disease locus. Transfected cell lines with the p.G177D mutation showed aberrant nuclear localisation patterns when compared with the wild type. Blood films revealed the presence of elliptocytes in the older brother.Conclusions: Our study shows that a single missense mutation in AMMECR1 causes a phenotype of midface hypoplasia, mild intellectual disability and the presence of elliptocytes, previously reported as part of a contiguous gene deletion syndrome. Functional analysis confirms mutant-specific protein dysfunction. We conclude that AMMECR1 is a critical gene in the pathogenesis of AMME, causing midface hypoplasia and elliptocytosis and contributing to early speech and language delay, infantile hypotonia and hearing loss, and may play a role in dysmorphism, nephrocalcinosis and submucous cleft palate.<br/