8,713 research outputs found
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
Fitomassa e nitrogênio acumulado em coquetéis vegetais utilizados no cultivo de melão no Semiárido pernambucano.
Fitomassa seca e teor de nitrogênio total em coqueteis vegetais utilizados no cultivo de melão no Semiárido pernambucano.
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
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