Excess Thermodynamics of Mixtures Involving Xenon and Light Linear Alkanes by Computer Simulation

Excess molar enthalpies and excess molar volumes as a function of composition for liquid mixtures of xenon + ethane (at 161.40 K), xenon + propane (at 161.40 K) and xenon + n-butane (at 182.34 K) have been obtained by Monte Carlo computer simulations and compared with available experimental data. Simulation conditions were chosen to closely match those of the corresponding experimental results. The TraPPE-UA force field was selected among other force fields to model all the alkanes studied, whereas the one-center Lennard−Jones potential from Bohn et al. was used for xenon. The calculated and for all systems are negative, increasing in magnitude as the alkane chain length increases. The results for these systems were compared with experimental data and with other theoretical calculations using the SAFT approach. An excellent agreement between simulation and experimental results was found for xenon + ethane system, whereas for the remaining two systems, some deviations that become progressively more significant as the alkane chain length increases were observed

Reação de linhagens de feijoeiro ao oídio.

O objetivo do trabalho foi avaliar 55 linhagens de feijoeiro do banco de germoplasma da Universidade Federal de Lavras quanto à reação ao Oídio em casa de vegetação. Foram utilizadas duas testemunhas com reação conhecida, a linhagem ESAL 686 (resistente) e a cultivar Eriparsa (suscetível). A inoculação do patógeno foi feita com a disposição de vasos contendo plantas severamente infectadas alternadamente entre as parcelas. As notas foram atribuídas por três avaliadores que utilizaram um escala de notas de nove graus proposta por Rezende et al. (1999). A ocorrência da doença foi intensa e permitiu discriminar as linhagens. Verificou-se grande variabilidade para reação ao oídio. Não houve relação entre tipo de grão e reação à doença. Os resultados indicam que é possível selecionar linhagens com bom nível de resistência e diferentes tipos de grãos

Solubilities of oxygen and carbon dioxide in PDMS oils by computer simulation

Bioconversion reactions involving whole cells are usually characterized by low volumetric productivities in aqueous media, due to the low solubility of both the substrates and the reaction products in water. In order to overcome this problem, organic solvents have been used as substrate/product pools, including some environmentally friendly substances in view of their low volatility and toxicity [1]. Silicone oils have successfully been used as production medium in conversion of sterols to steroids with whole cells in monophasic and biphasic systems [1]. For the process scale-up, a number of physical properties of the system are needed, such as viscosity of the production medium and solubility of metabolic gases (oxygen and carbon dioxide) in the organic solvent. Polydimethylsiloxane (PDMS) and polymethylphenylsiloxane have been the most used silicone oils in production media for bioconversion reactions. In the case of polydimethylsiloxane, oils with kinematic viscosities of around 20 cSt are common (molecular weight of 2000). Solubilities of oxygen and carbon dioxide in such silicone oils are very scarce as well as their prediction by molecular simulation. Makrodimitri et al [2] have developed a united atom force field for the calculation of structural and thermodynamic properties of pure PDMS. Using this force field, they have obtained, by simulation, solubilities of oxygen in PDMS (with an average molecular weight of around 6000), as well as solubilities and diffusion coefficients of other penetrant gases, such as n-alkanes, n-perfluoroalkanes and noble gases [3]. This work focused on prediction of the properties of silicone oils of short to moderate chain length (8 to 25 monomers, which corresponds to a molecular weight between around 750 and 2000) by computer simulation, in particular the solubility of oxygen and carbon dioxide in these liquids. Two different force fields were tested against experimental measurements of density for the shortest dimethylsiloxanes methyl terminated: Gromos-43 A1 and the force field developed by Makrodimitri et al specifically for PDMS. Henry’s constants for the dissolution of oxygen and carbon dioxide in PDMS oils were obtained as a function of temperature by computer simulation using both the force fields tested. The calculations were done for PDMS with three different chain lengths: 8, 16 and 25 monomers [(CH3)2SiO units] with methyl termination in all cases. The force field developed by Makrodimitri et al provides the best description of the PDMS oils studied both in terms of density and gas solubility. Liquid structure and interaction between gas solute and solvent were also investigated by simulation

Implicações da severidade de mancha angular em experimentos de avaliação de linhagens elite de feijoeiro.

Para verificar se a avaliação por meio de uma escala de notas de severidade da mancha angular (Pseudocercospora griseola) contribui para explicar a variação entre linhagens de feijão com relação à produtividade de grãos, foi realizado o presente trabalho

Melhoramento do feijoeiro de grãos tipo carioca para produtividade, arquitetura ereta da planta e resistência a patógenos.

Esse trabalho teve por objetivos obter linhagens de feijoeiro com boa produtividade, grãos tipo carioca, de porte ereto e resistentes aos fungos Colletotrichum lindemuthianum e Pseudocercospora griseola.CONAFE

Acumulação de metais pesados pelo uso de insumos agrícolas na microbacia de Caetés, Paty do Alferes, RJ.

O município de Paty do Alferes, localizado na região serrana do Estado do Rio de Janeiro, inserido no bioma Mata Atlântica e com declividade de até 50%, tem exclusivamente a horticultura, com uso intensivo de insumos, como atividade econômica (40% de todo o tomate do estado e um grande percentual de outras hortaliças - repolho, pepino, vagem, pimentão), mas, em função do declínio rápido da produtividade, as áreas estão sendo abandonadas, dando lugar a pastagem com pouco manejo. Diante do diagnóstico do uso excessivo de agroquímicos, este trabalho teve o objetivo de avaliar o seu impacto na contaminação do solo, água, sedimentos e plantas hortícolas por metais pesados na microbacia de Caetés (Paty do Alferes, RJ) e a influência da topografia e do uso agrícola na acumulação de metais pesados. Para tanto selecionaram-se duas toposseqüências de solos representativas da microbacia de Caetés: (a) toposseqüência 1 (T1) apresenta menor declividade e pendente longa, com três formas distintas de uso: capoeira, pasto (antiga área de horticultura) e horticultura atual; (b) na outra (T2), observa-se declividade mais acentuada (45%) e pendente curta, sendo os tipos de uso do solo os mesmos de T1. Notou-se que a contaminação por metais pesados nos solos da microbacia de Caetés concentrou-se onde ocorria a aplicação intensiva de agroquímicos (áreas de horticultura), mas não atingiu os níveis críticos estabelecidos para solos e estava distribuída em formas químicas pouco biodisponíveis (tomate, pimentão, repolho e pepino). A acumulação de metais pesados só não foi maior devido ao terreno ser muito declivoso, o que promoveu um arraste excessivo e contínuo da camada arável, sendo depositado nos córregos pelo uso agrícola inadequado à topografia. Em virtude do processo erosivo, constataram-se nos sedimentos da microbacia de Caetés incrementos nos teores totais de metais pesados de acordo com a posição de coleta na área, todavia esses metais não estavam presentes em formas químicas biodisponíveis. Entretanto, houve contaminação da água do córrego e do açude, que apresentou teor total de Mn e Cd acima dos padrões máximos estabelecidos para água potável.bitstream/item/159432/1/bp05-1998.pdfConvênio Financiadora de Estudos e Projetos (FINEP), Comunidade Econômica Européia (CEE) e Fundo Nacional de Meio Ambiente (FNMA)

Diffusion coefficients of 2,2,2-trifluoroethanol/water mixtures

Aqueous mixtures of 2,2,2-trifluoroethanol have received significant attention in the last years because their applications, such as working fluid in Rankine cycle thermal engines or as solvent in studies of protein stability (protein folding). From the fundamental point of view, fluoroalcohols have an amphyphile character, due to the simultaneous presence of a hydrophobic (and alkane-phobic) fluorinated surface and a hydroxyl group. Mixtures of 2,2,2-trifluoroethanol with hydrogenated alcohols were studied recently in our research group (experimental determination of pVT surfaces as well as thermal, volumetric and structural properties by computer simulation) [1]. In the case of 2,2,2-trifluoroethanol/water this study suggested a preference of cross hydrogen bond. Hydrogen bonds play a determinant role in the structure of aqueous mixtures of alcohols, and should influence the dynamic properties of binary systems of fluorinated alcohols with water. The goal of this work is to study a dynamic property (diffusion coefficient) of binary mixtures 2,2,2-trifluoroethanol/water, comparing the results with equilibrium and structural properties already known for this and related systems

Comportamento de linhagens de feijão em relação à competição das plantas invasoras.

O objetivo desse trabalho foi o de estimar o dano provocado pela planta invasora e se a competição varia em função da linhagem de feijão utilizada

Nitrous oxide emission factor for cattle urine and dung in subtropical Brazilian pastureland.

Resumo

Estimation of genetic progress after eight cycles of recurrent selection for common bean grain yield.

The objective of this study was to estimate the genetic progress of eight cycles of recurrent selection for common bean lines with high yield. The base population was obtained from 10 parents differing in several characters. To date, eight selection cycles have been performed. In each cycle the selection process continues after recombination, until lines are established, which are then evaluated more extensively in the experiment of evaluation of elite lines together with lines of other programs. The genetic progress was estimated based on the data of evaluations of these lines in each cycle over the years. The estimated genetic progress of 3.3 % per cycle allows the conclusion that recurrent selection for grain yield is efficient