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

Teaching the Modal Auxiliary Verbs Focusing on Those Used for Suggestion and Advice

Modal auxiliary verbs are a neglected group in the lexicon, especially in the EFL classroom. Due to the nature of the nuances they are used to convey, their misuse can cause not just misinformation but also subtle tones that create unpleasant discord in the flow of communication. Modals are easy sources of errors for students of EFL because they follow no readily discernible patterns. Structurally there are six points explained here which can confuse students and cause modals to change their function. There are two main categories of functions: social interaction, which includes advice, suggestion, obligation, social expectation; and logical probability, which includes inference and probability. I maintain that presenting modals within the function is best for students. Introducing only two modals at a time, in contrast, and function-by-function in a real situation, is a more viable way to help students learn to use modals appropriately in conversation. After giving a brief analysis of all modals, both structurally and functionally, I have chosen to focus on two functions: advice and suggestion. The development of my lesson plans is reviewed and my final plan is presented as a model for the effective teaching of modals in the ESL/EFL classroom