Configurational lattice dynamics: The phase diagram of Rh − Pd

Free energies of Rh-Pd alloys as functions of both temperature and composition are calculated using quasiharmonic lattice dynamics. The free energy of the disordered solid is determined from an ensemble of a large number of randomly generated configurations. Both configurational and vibrational contributions to the entropy and enthalpy of mixing are taken into account. We study the convergence with the number of random configurations, and analyze the validity of the zero static internal stress approximation ZSISA, where only external strains are relaxed fully dynamically while internal stresses are relaxed in the static approximation. It is shown that the use of ZSISA allows an accurate calculation of free energies in a fraction of the time needed to carry out fully dynamic optimizations. From the values of free energies as functions of composition and temperature the phase diagram of Rh-Pd alloys is calculated, showing a good agreement with Monte Carlo simulations as well as with experiment. It is also shown that although free energies of mixing appear to be linear functions of temperature to a good approximation, the explicit expressions given by the configurational lattice dynamics method show that both enthalpies and entropies of mixing change appreciably with temperature.Fil: Cienfuegos, Clarisa. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Isoardi, E. P.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; ArgentinaFil: Barrera, Gustavo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentin

Current rectification in a single molecule diode: the role of electrode coupling

We demonstrate large rectification ratios (> 100) in single-molecule junctions based on a metal-oxide cluster (polyoxometalate), using a scanning tunneling microscope (STM) both at ambient conditions and at low temperature. These rectification ratios are the largest ever observed in a single-molecule junction, and in addition these junctions sustain current densities larger than 10^5 A/cm^2. By following the variation of the I-V characteristics with tip-molecule separation we demonstrate unambiguously that rectification is due to asymmetric coupling to the electrodes of a molecule with an asymmetric level structure. This mechanism can be implemented in other type of molecular junctions using both organic and inorganic molecules and provides a simple strategy for the rational design of molecular diodes

Genetic and phenotypic relationships between physiological traits and performance test traits in sheep

International audienc

Variations in Victim Presence in Restorative Youth Conferencing Programs: The Use of Surrogate Victims Increases Reparation Completion

Victim-offender conferencing programs have expanded the type of victims involved in restorative rituals. However, little research has examined how variations in victim presence might impact these interventions. The aim of this study was to examine whether conferences involving actual victims resulted in higher reparation completion and how surrogate characteristics might impact reparation outcomes. Using regression modeling, we estimated how the variables of interest predicted reparation completion. Conferences with surrogates had a higher probability of completion than those with actual victims. Using surrogates may be a promising strategy to expand restorative justice practices when actual victim participation is not possible

Geochemistry of H2- and CH4-enriched hydrothermal fluids of Socorro Island, Revillagigedo Archipelago, Mexico. Evidence for serpentinization and abiogenic methane

Socorro Island is the exposed part of an approx. 4000-m-high volcanic edifice rising from the oceanic floor to approx. 1000 m asl at the northern part of the Mathematician Ridge, Western Pacific. The volcano is active, with the most recent basaltic eruption in 1993. Moderate fumarolic activity and diffuse degassing with a total CO2 flux of approx. 20 total day)1 are concentrated in the summit region of the volcano composed of a group of rhy- olite domes. Low-temperature, boiling point, fumaroles discharge gas with high H2 (up to 20 mol% in dry gas) and CH4 (up to 4 mol%). Both carbon and He isotopic ratios and abundances correspond to those in MORB flu- ids (d13CCO2 )5&; 3He ⁄ 4He = 7.6 Ra, CO2 ⁄ 3He = (2–3) · 109, where Ra is the atmospheric ratio 3He ⁄ 4He of 1.4 · 10)6. Light hydrocarbons (CH4, C2H6, C3H8, and C4H10) are characterized by a high C1 ⁄C2+ ratio of approx. 1000. Methane is enriched in 13C (d13CCH4 from )15 to )20&) and 2H (d2H from )80 to )120&), and hydrocarbons show an inverse isotopic trend in both d13C and d2H (ethane is isotopically lighter than methane). These isotopic and concentration features of light hydrocarbons are similar to those recently discovered in fluids from ultramafic-hosted spreading ridge vents and may be related to the serpentinization processes: H2 generation and reduction of CO2 to CH4 within high-temperature zone of volcano-seawater hydrothermal system hosted in basaltic and ultramafic rocks beneath a volcano edifice. The thermodynamic analysis of this unusual composition of the Socorro fluids and the assessment of endmember compositions are complicated by the near-surface cool- ing, condensation and mixing with meteoric water

Numerical simulation of strongly nonlinear and dispersive waves using a Green-Naghdi model

We investigate here the ability of a Green-Naghdi model to reproduce strongly nonlinear and dispersive wave propagation. We test in particular the behavior of the new hybrid finite-volume and finite-difference splitting approach recently developed by the authors and collaborators on the challenging benchmark of waves propagating over a submerged bar. Such a configuration requires a model with very good dispersive properties, because of the high-order harmonics generated by topography-induced nonlinear interactions. We thus depart from the aforementioned work and choose to use a new Green-Naghdi system with improved frequency dispersion characteristics. The absence of dry areas also allows us to improve the treatment of the hyperbolic part of the equations. This leads to very satisfying results for the demanding benchmarks under consideration

Profilaxis antibiótica en cirugía

Existe una abundantísima documentación en la literatura acerca de la eficacia de los antibióticos utilizados profilácticamente en cirugía (1-10). Probablemente lo más útil para el trabajo diario de un hospital sea la adopción de pautas concretas que permitan ser evaluadas periódicamente a través de la colaboración, entre otros, de anestesistas, cirujanos y microbiólogos (11,12). En esta línea hemos revisado, de una manera intencionadamente esquemática, diversas facetas relativas a la profilaxis antibiótica en cirugía. Para ello comentaremos algunos aspectos generales de profilaxis de la infección postquirúrgica, unas breves normas para la utilización profiláctica de antibióticos y resumiremos determinadas indicaciones en función del tipo de intervención

Hydrochemical characterization of a mine water geothermal energy resource in NW Spain

Abandoned and flooded mine networks provide underground reservoirs of mine water that can be used as a renewable geothermal energy source. A complete hydrochemical characterization of mine water is required to optimally design the geothermal installation, understand the hydraulic behavior of the water in the reservoir and prevent undesired effects such as pipe clogging via mineral precipitation. Water pumped from the Barredo-Figaredo mining reservoir (Asturias, NW Spain), which is currently exploited for geothermal use, has been studied and compared to water from a separate, nearby mountain mine and a river that receives mine water discharge and partially infiltrates into the mine workings. Although the hydrochemistry was altered during the flooding process, the deep mine waters are currently near neutral, net alkaline, high metal waters of Na-HCO3 type. Isotopic values suggest that mine waters are closely related to modern meteoric water, and likely correspond to rapid infiltration. Suspended and dissolved solids, and particularly iron content, of mine water results in some scaling and partial clogging of heat exchangers, but water temperature is stable (22 °C) and increases with depth, so, considering the available flow (> 100 L s− 1), the Barredo-Figaredo mining reservoir represents a sustainable, long-term resource for geothermal use