18,843 research outputs found
Massive stars and globular cluster formation
We first present chemodynamical simulations to investigate how stellar winds
of massive stars influence early dynamical and chemical evolution of forming
globular clusters (GCs). In our numerical models, GCs form in
turbulent,high-density giant molecular clouds (GMCs), which are embedded in a
massive dark matter halo at high redshifts. We show how high-density, compact
stellar systems are formed from GMCs influenced both by physical processes
associated with star formation and by tidal fields of their host halos. We also
show that chemical pollution of GC-forming GMCs by stellar winds from massive
stars can result in star-to-star abundance inhomogeneities among light elements
(e.g., C, N, and O) of stars in GCs. The present model with a canonical initial
mass function (IMF) also shows a C-N anticorrelation that stars with smaller
[C/Fe] have larger [N/Fe] in a GC. Although these results imply that
``self-pollution'' of GC-forming GMCs by stellar winds from massive stars can
cause abundance inhomogeneities of GCs, the present models with different
parameters and canonical IMFs can not show N-rich stars with [N/Fe] ~ 0.8
observed in some GCs (e.g., NGC 6752). We discuss this apparent failure in the
context of massive star formation preceding low-mass one within GC-forming GMCs
(``bimodal star formation scenario''). We also show that although almost all
stars (~97%) show normal He abundances (Y) of ~0.24 some stars later formed in
GMCs can have Y as high as ~0.3 in some models. The number fraction of He-rich
stars with Y >0.26 is however found to be small (~10^-3) for most models.Comment: 10 pages, 8 figures, accepted by Ap
FISH DIVERSITY ALONG THE LONGITUDINAL GRADIENT IN A MAN–MADE LAKE OF WEST AFRICA, TAABO HYDROELECTRIC RESERVOIR, IVORY COAST
Fish assemblage patterns in Taabo Reservoir, a hydroelectric lake of Ivory Coast, were studied and related to the longitudinal gradient (river–dam gradient) composed of riverine, transitional, and lacustrine zones. Data were collected at 5 stations and each one was sampled during 5 surveys. Fish community structure was analysed using alpha and beta diversity indices. In total, 53 fish species were obtained in the whole ecosystem. Total species richness recorded at each ecological zone was 42, 43 and 45 species respectively in the riverine, transitional and lacustrine zones. Alpha diversity did not differed significantly along the longitudinal gradient but reached the highest value (33 species) in the transitional zone and the lowest (18 species) occurred in both the riverine and lacustrine zones. Temporal variability of Alpha diversity according to the hydrological regime of the lake differed with the zone. Beta diversity showed that fish assemblages similarity was higher between the transitional and the riverine zones (βw = 0.43) and lower between the riverine and the lacustrine zones (βw = 0.79)
Avoided crossings in mesoscopic systems: electron propagation on a non-uniform magnetic cylinder
We consider an electron constrained to move on a surface with revolution
symmetry in the presence of a constant magnetic field parallel to the
surface axis. Depending on and the surface geometry the transverse part of
the spectrum typically exhibits many crossings which change to avoided
crossings if a weak symmetry breaking interaction is introduced. We study the
effect of such perturbations on the quantum propagation. This problem admits a
natural reformulation to which tools from molecular dynamics can be applied. In
turn, this leads to the study of a perturbation theory for the time dependent
Born-Oppenheimer approximation
The Spectroscopic Age of 47 Tuc
High signal-to-noise integrated spectra of the metal-rich globular cluster 47
Tuc, spanning the H-gamma(HR) and Fe4668 line indices, have been obtained. The
combination of these indices has been suggested (Jones & Worthey 1995, ApJ,
446, L31) as the best available mechanism for cleanly separating the
age-metallicity degeneracy which hampers the dating of distant, unresolved,
elliptical galaxies. For the first time, we apply this technique to a nearby
spheroidal system, 47 Tuc, for which independent ages, based upon more
established methods, exist. Such an independent test of the technique's
suitability has not been attempted before, but is an essential one before its
application to more distant, unresolved, stellar populations can be considered
valid. Because of its weak series of Balmer lines, relative to model spectra,
our results imply a spectroscopic ``age'' for 47 Tuc well in excess of 20 Gyr,
at odds with the colour-magnitude diagram age of 14+/-1 Gyr. The derived metal
abundance, however, is consistent with the known value. Emission ``fill-in'' of
the H-gamma line as the source of the discrepancy cannot be entirely excluded
by existing data, although the observational constraints are restrictive.Comment: 17 pages, 4 figures, LaTeX, accepted for publication in The
Astronomical Journal, also available at
http://casa.colorado.edu/~bgibson/publications.htm
First-order transitions and triple point on a random p-spin interaction model
The effects of competing quadrupolar- and spin-glass orderings are
investigated on a spin-1 Ising model with infinite-range random -spin
interactions. The model is studied through the replica approach and a phase
diagram is obtained in the limit . The phase diagram, obtained
within replica-symmetry breaking, exhibits a very unusual feature in magnetic
models: three first-order transition lines meeting at a commom triple point,
where all phases of the model coexist.Comment: 9 pages, 2 ps figures include
Seca do frutos do açaizeiro no estado do Pará.
Objetivou-se relatar a seca dos frutos do açaizeiro, em três diferentes municípios do estado do Pará, safra 2014. Amostras de frutos secos dos municípios de Abaetetuba e Belém foram analisadas no Laboratório de Fitopatologia da Embrapa Amazônia Oriental e do município de Igarapé Mirim no Laboratório de Microbiologia de Alimentos do IFPA - Campus Castanhal, respectivamente. Os frutos foram incubados em caixas do tipo 'gerbox' à temperatura de 25±2 ºC e fotoperíodo de 12h, durante até 72h. Procederam-se isolamentos diretos em placas de Petri com meio de cultura ágar-água a 20%. Frutos com esporulação do patógeno foram utilizados para o isolamento direto, sem incubação prévia, e analisados em microscópios estereoscópio e de luz. Após três dias de incubação, discos de micélios foram repicados para o meio de cultura batata dextrose ágar (BDA). Observaram-se crescimento micelial branco e, após 10 dias de incubação, verificou-se a formação de colônias de coloração acinzentada nas placas de Petri. Foram confeccionadas lâminas para microscopia de luz. Verificaram-se a presença de hifas septadas e ramificadas e intensa produção de conídios unicelulares hialinos, em ambas as amostras. A doença seca dos frutos foi confirmada em amostras oriundas dos municípios de Abaetetuba, Belém e Igarapé Mirim, com associação do fungo Colletotrichum spp
Zoneamento socioeconômico da população ribeirinha do Pantanal: Comunidade do Castelo, Corumbá, MS.
Este trabalho descreve brevemente informações socioeconômicas da população moradora da Baía do Castelo. Foram realizadas entrevistas e vistas locais para levantamento de dados. Observamos que a maior parte da população é idosa, existem poucas crianças no local devido a ausência de escolas. População predominantemente masculina e com atividade econômica divida entre a pesca (50%) e pecuária em pequena escala (50%). Apesar dasdificuldades existentes a maior parte da população prefere morar e trabalhar no local. Afirmandoque o pantanal, apesar de possuir características inóspitas não é só um espaço natural cênico, ele é todo um modo de vida que alimenta e determina uma cultura própria, ímpar de sua populaçãolocal
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