Diffusion of hydrogen in crystalline silicon

The coefficient of diffusion of hydrogen in crystalline silicon is calculated using tight-binding molecular dynamics. Our results are in good quantitative agreement with an earlier study by Panzarini and Colombo [Phys. Rev. Lett. 73, 1636 (1994)]. However, while our calculations indicate that long jumps dominate over single hops at high temperatures, no abrupt change in the diffusion coefficient can be observed with decreasing temperature. The (classical) Arrhenius diffusion parameters, as a consequence, should extrapolate to low temperatures.Comment: 4 pages, including 5 postscript figures; submitted to Phys. Rev. B Brief Repor

Consumo energético de vehículos pesados en México

The objective of this work was to determine the fuel consumption of heavy-duty vehicles under real operating conditions in Mexico. Using telemetry systems, a sample of 6.955 vehicles was monitored during the last 3 years of operation. The sample included different manufacturers, engines, and vehicle model-year. It was found that currently, 99 % of heavy vehicles in Mexico operate with diesel. T3 tractors used for freight transport consume 44.25 L/100 km and B2 buses used for passenger transport in urban centers consume 22.4 L/100 km. The few vehicles (< 1 %) that operate with natural gas have a higher consumption (> 23 % in trucks y 147 % in buses) than diesel vehicles. However, the small fraction (< 0.01 %) of electric vehicles used for passenger transport have consumptions ~ 52 % lower than diesel vehicles. The results obtained can be used by local authorities and companies to establish strategies to reduce energy consumption and greenhouse gas emissions.El objetivo del presente trabajo fue determinar el consumo de combustible de los vehículos pesados bajo condiciones reales de operación en México. Usando sistemas de telemetría, se monitoreó una muestra de 6.955 vehículos durante los últimos 3 años de operación. La muestra incluyó diferentes marcas, motores, y año-modelo. Se encontró que actualmente, el 99 % de vehículos pesados en México operan con diésel. Los tractocamiones T3 usados para el transporte de carga consumen 44,25 L/100 km y los autobuses B2 usados para el transporte de pasajeros en centros urbanos consumen 22,72 L/100 km. Los pocos vehículos (< 1 %) que operan a gas natural presentan consumos superiores (> 23 % en tractocamiones y 147 % en buses) a los vehículos diésel. Sin embargo, la pequeña fracción (< 0,01 %) de vehículos eléctricos usados para el transporte de pasajeros presentan consumos ~ 52 % inferiores a los vehículos diésel. Los resultados obtenidos pueden ser usados por las autoridades locales y empresas para establecer estrategias de reducción de consumo energético y emisiones de gases de efecto invernadero

Energy Efficiency of Heavy-Duty Vehicles in Mexico

The energy consumption of a large sample of vehicles (6955) operating during the last 3 years under everyday conditions across Mexico was monitored via OBD-based telematics systems. A life cycle statistical analysis of the obtained data showed that, on average, 54 t diesel vehicles used for long-distance freight transport consume 44.25 L/100 km and emit 1513 g CO2e/km. When these vehicles are powered by natural gas, the energy consumption and the emissions of greenhouse gases (GHG) are increased by 23% and reduced by 0.8%, respectively. Using manufacturers’ data, these values reduce energy consumption by 16% and GHG emissions by 52% when they are electric. Similar observations were made for other vehicles sizes used for transporting goods and people

Global transcriptome analysis of Rhizobium favelukesii LPU83 in response to acid stress

Nilsson JF, Castellani LG, Draghi WO, et al. Global transcriptome analysis of Rhizobium favelukesii LPU83 in response to acid stress. FEMS Microbiology Ecology. 2021;97(1): fiaa235.Acidic environments naturally occur worldwide and inappropriate agricultural management may also cause acidification of soils. Low soil pH values are an important barrier in the plant–rhizobia interaction. Acidic conditions disturb the establishment of the efficient rhizobia usually used as biofertilizer. This negative effect on the rhizobia–legume symbiosis is mainly due to the low acid tolerance of the bacteria. Here, we describe the identification of relevant factors in the acid tolerance of Rhizobium favelukesii using transcriptome sequencing. A total of 1924 genes were differentially expressed under acidic conditions, with ∼60% underexpressed. Rhizobium favelukesii acid response mainly includes changes in the energy metabolism and protein turnover, as well as a combination of mechanisms that may contribute to this phenotype, including GABA and histidine metabolism, cell envelope modifications and reverse proton efflux. We confirmed the acid-sensitive phenotype of a mutant in the braD gene, which showed higher expression under acid stress. Remarkably, 60% of the coding sequences encoded in the symbiotic plasmid were underexpressed and we evidenced that a strain cured for this plasmid featured an improved performance under acidic conditions. Hence, this work provides relevant information in the characterization of genes associated with tolerance or adaptation to acidic stress of R. favelukesii