Disk evolution in the Ori OB1 association

We analyze multi-band photometry of a subsample of low mass stars in the associations Ori OB1a and 1b discovered during the CIDA Orion Variability Survey, which have ages of 7 - 10 Myr and 3 - 5 Myr, respectively. We obtained UBVRcIc photometry at Mt. Hopkins for 6 Classical T Tauri stars (CTTS) and 26 Weak T Tauri stars (WTTS) in Ori OB1a, and for 21 CTTS and 2 WTTS in Ori OB1b. We also obtained L band photometry for 14 CTTS at Mt. Hopkins, and 10um and 18um photometry with OSCIR at Gemini for 6 CTTS; of these, all 6 were detected at 10um while only one was detected at 18um. We estimate mass accretion rates from the excess luminosity at U, and find that they are consistent with determinations for a number of other associations, with or without high mass star formation. The observed decrease of mass accretion rate with age is qualitatively consistent with predictions of viscous evolution of accretion disks. We find an overall decrease of disk emission from Taurus to Ori OB1b to Ori OB1a. This decrease implies that significant grain growth and settling towards the midplane has taken place in the inner disks of Ori OB1. We compare the SED of the star detected at both 10um and 18um with disk models for similar stellar and accretion parameters. We find that the low <= 18 um fluxes of this Ori OB1b star cannot be due to the smaller disk radius expected from viscous evolution in the presence of the FUV radiation fields from the OB stars in the association. Instead, we find that the disk of this star is essentially a flat disk, with little if any flaring, indicating a a significant degree of dust settling towards the midplane, as expected from dust evolution in protoplanetary disks.Comment: 35 pages, 11 figures, to appear in the Astronomical Journal. Full resolution figures in http://www.cida.ve/~briceno/publications

Carbon stock change due to land use in argisols on pernambucano-brazillan semiarid

Carbon stored in soils depends on the type of vegetation and management applied. Native vegetation removed for the installation of pastures and grassland affects carbon stocks in the soil.Argisols are one the most used type of soils in agriculture, due its excellent physical and chemical characteristics. Asses carbon stored in these soils under different land uses and understand the dynamics of the C element in ecosystems is important. In this study we examined four types of vegetation cover in three sites on interior of Pernambuco state in Brazil. Trenches of 0.7 x 0.7 m with 0.4 m deep were open and soil samples were collected at 0-10, 10-20, 20-30 and 30-40 cm layers to determine carbon content and soil density. Carbon concentrations were determined by dry combustion using a CHN elemental analyzer (CN TruSpec LECO® 2006, St. Joseph, USA). Land use change altered carbon stocks in soil, dense caatinga presented higher stocks than open caatinga, grassland and agriculture. In the 0-10 cm layer expressed biggest difference in C stocks in different vegetation cover

Spectra and Symmetry in Nuclear Pairing

We apply the algebraic Bethe ansatz technique to the nuclear pairing problem with orbit dependent coupling constants and degenerate single particle energy levels. We find the exact energies and eigenstates. We show that for a given shell, there are degeneracies between the states corresponding to less and more than half full shell. We also provide a technique to solve the equations of Bethe ansatz.Comment: 15 pages of REVTEX with 2 eps figure

Porosidade e densidade de solos sob uso agrícola no município de Sobradinho-BA.

Considerando que o manejo do solo altera suas propriedades físicas, imprescindíveis ao oferecimento de condições favoráveis ao desenvolvimento produtivo, objetivou-se com este estudo avaliar a porosidade e a densidade de quatro solos sob uso agrícola, localizados as margens do Lago de Sobradinho, no município de Sobradinho-BA. Foram selecionadas quatro propriedades rurais onde foram coletadas amostras de solos nas profundidades de 0,00?0,10; 0,10-0,20 e 0,20-0,40 m tanto na área agrícola como na área sob caatinga, utilizada como referência. Em laboratório avaliou-se granulometria, argila dispersa em água e densidade do solo. Além disso, foram calculados: índice de floculação, macroporosidade e microporosidade. O intenso processo de mecanização adotado no uso agrícola proporcionou comportamentos distintos aos solos, em relação aos índices analisados, sendo que houve aumento na sua densidade e redução da macroporosidade

Cover crop cocktails as N and P source in the Brazilian Semiarid.

The objective was to evaluate the availability of N and P by plant cocktails used as cover crop and green manure in the semiarid

Fertilização in vivo, modo de reprodução e viabilidade polínica em passifloras com potencial ornamental.

O objetivo deste trabalho foi avaliar a biologia floral de dez espécies de Passiflora (P. capsularis L., P. racemosa Brot., P. morifolia L., P. edmundoi Sacco, P. suberosa Mast. P. gibertii N.E.Br, P. edulis f. flavicarpa, P. galbana L., P. tenuifila Killip e P. muchronata Sessé & Moc.) por meio da polinização in vivo e viabilidade polínica. O sistema reprodutivo foi determinado por três tipos de polinizações controladas in vivo (autogamia, xenogamia e interespecífica), sendo 4 botões florais para cada tipo de cruzamento