The age of the Galactic thin disk from Th/Eu nucleocosmochronology II. Chronological analysis

The purpose of this work is to resume investigation of Galactic thin disk dating using nucleocosmochronology with Th/Eu stellar abundance ratios, a theme absent from the literature since 1990. [Th/Eu] abundance ratios for a sample of 20 disk dwarfs/subgiants of F5 to G8 spectral type with -0.8 <= [Fe/H] <= +0.3, determined in the first paper of this series, were adopted for this analysis. We developed a Galactic chemical evolution model that includes the effect of refuses, which are composed of stellar remnants (white dwarfs, neutron stars and black holes) and low-mass stellar formation residues (terrestrial planets, comets, etc.), contributing to a better fit to observational constraints. Two Galactic disk ages were estimated, by comparing literature data on Th/Eu production and solar abundance ratios to the model ((8.7 +5.8-4.1) Gyr), and by comparing [Th/Eu] vs. [Fe/H] curves from the model to our stellar abundance ratio data ((8.2 +/- 1.9) Gyr), yielding the final, average value (8.3 +/- 1.8) Gyr. This is the first Galactic disk age determined via Th/Eu nucleocosmochronology, and corroborates the most recent white dwarf ages determined via cooling sequence calculations, which indicate a low age (<~ 10 Gyr) for the disk.Comment: 9 pages, 7 Postscript figures, accepted for publication in Astronomy & Astrophysics, final versio

Desempenho socioeconômico e ambiental da cultivar BRS Valente.

Embrapa Arroz e Feijão tem dado prioridade à busca de meios de se avaliar os reais benefícios que a atividade feijoeira oferece para o Brasil e, para tanto, foi analisada sua sustentabilidade tomando-se como modelo a cultivar BRS Valente. Os impactos da adoção dessa tecnologia, nas regiões de abrangência Sul, Sudeste e Centro-Oeste, foram avaliados nas dimensões econômica, social e ambiental, considerando as três safras de cultivo, dos anos agrícolas 02/03, 03/04, 04/05, 05/06, 06/07 e 07/08.bitstream/item/58177/1/comunicadotecnico-167.pd

Desempenho socioeconômico e ambiental de cultivares de feijoeiro comum: impacto da BRS Valente.

Neste estudo, tomou-se como exemplo a cultivar BRS Valente para analisar os impactos resultantes de sua adoção nas regiões Sul, Sudeste e Centro-Oeste, considerando as três safras de cultivo

Recomendações técnicas para o cultivo do feijoeiro-comum (Phaseolus vulgaris L.) nas regiões Norte e Nordeste do Brasil.

O feijoeiro-comum (Phaseolus vulgaris L.) ocupa posição de destaque nos estados do Norte e do Nordeste. A maioria da área de produção de feijão é encontrada em pequenas propriedades, em monocultivo e/ou consorciado, nos mais variados arranjos de plantas, o que favorece a diversificação na produção. Os avanços obtidos pela pesquisa disponibilizaram tecnologias limpas e acessíveis à agricultura familiar, que contribuem para a melhoria da sustentabilidade dos agroecossistemas e, ao mesmo tempo, asseguram a produção respeitando os diferentes sistemas culturais. Atentos a essa nova postura, e com o intuito de reunir e disponibilizar as informações existentes sobre a cultura do feijão, a Embrapa reuniu representantes da pesquisa, das organizações de assistência técnica e extensão rural, agentes de desenvolvimento e produtores, para a elaboração desta Circular Técnica. Espera-se, com isso, contribuir para a construção de sistemas de produção inovadores para o feijoeiro, a fim de elevar a produtividade e a renda familiar, incrementar a produção de alimentos saudáveis e promover a diversificação da produção nas regiões Norte e Nordeste.bitstream/item/54551/1/CIRC-TECNICA-89.pd

Seleção simultânea para três caracteres em progênies de feijoeiro de grãos tipo carioca.

Esse trabalho foi conduzido com o objetivo de obter linhagens de feijoeiro com grãos tipo carioca, de porte ereto e resistentes ao fungo causador da mancha angular

Seleção de linhagens de feijoeiro de grãos tipo carioca, de porte ereto e resistentes a mancha angular.

Esse trabalho foi conduzido com o objetivo de obter linhagens de feijoeiro com grãos tipo carioca, de porte ereto e resistentes ao fungo causador da mancha angular

The age of the Galactic thin disk from Th/Eu nucleocosmochronology III. Extended sample

The first determination of the age of the Galactic thin disk from Th/Eu nucleocosmochronology was accomplished by us in Papers I and II. The present work aimed at reducing the age uncertainty by expanding the stellar sample with the inclusion of seven new objects - an increase by 37%. A set of [Th/Eu] abundance ratios was determined from spectral synthesis and merged with the results from Paper I. Abundances for the new, extended sample were analyzed with the aid of a Galactic disk chemical evolution (GDCE) model developed by us is Paper II. The result was averaged with an estimate obtained in Paper II from a conjunction of literature data and our GDCE model, providing our final, adopted disk age T_G = (8.8 +/- 1.7) Gyr with a reduction of 0.1 Gyr (6%) in the uncertainty. This value is compatible with the most up-to-date white dwarf age determinations (<~ 10 Gyr). Considering that the halo is currently presumed to be (13.5 +/- 0.7) Gyr old, our result prompts groups developing Galactic formation models to include an hiatus of (4.7 +/- 1.8) Gyr between the formation of halo and disk.Comment: 7 pages, 5 Postscript figures, accepted for publication in Astronomy & Astrophysic

Abundances of Mn, Co and Eu in a sample of 20 F-G disk stars: the influence of hyperfine structure splitting

We present Mn, Co and Eu abundances for a sample of 20 disk F and G dwarfs and subgiants with metallicities in the range -0.8 <= [Fe/H] <= +0.3. We investigate the influence of hyperfine structure (HFS) on the derived abundances of Mn and Co by using HFS data from different sources in the literature, as well as calculated HFS from interaction factors A and B. Eu abundances were obtained from spectral synthesis of one Eu II line that takes into account HFS from a series of recent laboratory measurements. For the lines analyzed in this study, we find that for manganese, the differences between abundances obtained with different HFSs are no larger than 0.10 dex. Our cobalt abundances are even less sensitive to the choice of HFS than Mn, presenting a 0.07 dex maximum difference between determinations with different HFSs. However, the cobalt HFS data from different sources are significantly different. Our abundance results for Mn offer an independent confirmation of the results from Prochaska & McWilliam (2000), who favour type Ia supernovae as the main nucleosynthesis site of Mn production, in contrast to trends of Mn versus metallicity previously reported in the literature. For Co, we obtain [Co/Fe] ~ 0.0 in the range -0.3 < [Fe/H] < +0.3 and [Co/Fe] rising to a level of +0.2 when [Fe/H] decreases from -0.3 to -0.8, in disagreement with recent results in the literature. The observed discrepancies may be attributed to the lack of HFS in the works we used for comparison. Our results for Eu are in accordance with low-mass type II supernovae being the main site of the r-process nucleosynthesis.Comment: 8 pages, 6 Postscript figures, accepted for publication in Astronomy & Astrophysic

Efficiency of methods for conducting segregating populations in the breeding of common beans for protein quality.

Common bean (Phaseolus vulgaris L.) is part of the daily diet of over 300 million people in the world and is a staple food of low-income populations, due to its high protein content. Many authors have proposed a further improvement by breeding methods that exploit the existing genetic variability. The objective of this research was to evaluate the genetic potential of segregating bean populations with variability for several traits and conducted by different breeding methods. The F2 segregating population was developed from a cross of the parental genotypes CNFC 7812 and CNFC 8056.One hundred and fifty randomly taken F2 plants originated the segregating populations, which were conducted until the fifth generation by the following breeding procedures: Single Seed Descent (SSD), Bulk and Bulk within F2. The total grain protein content of the F5 families was then analyzed. It was concluded that there was enough genetic variability in the cross under study. The Bulk method proved to be the most efficient since it generated families with superior averages for the trait protein content in comparison with the other breeding methods

A New Association of Post-T Tauri Stars Near The Sun

Observing ROSAT sources in 20 x 25 deg centered at the high latitude active star ER Eri, we found evidences for a new young nearby association (~30Myr at~60pc), the Horologium Association (HorA), formed by at least 10 probable and 6 possible members, some being Post-T Tauri stars. We examine several requirements that characterize a young association and they, together, create a strong evidence for the reality of the HorA. In fact, the Li line intensities are between those of the oldest classical T Tauri stars and the ones of the Local Association stars. The space velocities of the HorA relative to the Sun, U= -9.5+/-1.0, V = -20.9 +/- 1.1, W = -2.1 +/- 1.9, are not far from those of the Local Association. We suggest that some hotter and non-X-ray active stars, with similar space velocities, could be massive members of the HorA, among them, the nearby Be star Achernar. The maximum of the mass distribution function of the HorA is around 0.8 solar masses. At its distance, the projected size of the HorA, ~50 pc, would be larger than our surveyed area and many other members could have been missed. We also observed 3 control regions, two at northern and southern galactic latitudes and a third one in the known TW Hya Association (TWA), and the properties and distribution of their young stars strengthen the reality of the HorA. Contrary to the TWA, the only known binaries in the HorA are 2 very wide systems. The HorA is much more isolated from clouds and older than the TWA and could give some clues about the lifetime of the disks around T Tauri stars. Actually, none of the proposed members is an IRAS source indicating an advanced stage of the evolution of their accreting disks. ER Eri itself was found to be a RS CVn-like system.Comment: 25 pages, 5 eps figures, to appear in Astron.