19,260 research outputs found
The Mass-to-Light Ratio of Binary Galaxies
We report on the mass-to-light ratio determination based on a newly selected
binary galaxy sample, which includes a large number of pairs whose separations
exceed a few hundred kpc. The probability distributions of the projected
separation and the velocity difference have been calculated considering the
contamination of optical pairs, and the mass-to-light ratio has been determined
based on the maximum likelihood method. The best estimate of in the B
band for 57 pairs is found to be 28 36 depending on the orbital
parameters and the distribution of optical pairs (solar unit, km
s Mpc). The best estimate of for 30 pure spiral pairs is
found to be 12 16. These results are relatively smaller than those
obtained in previous studies, but consistent with each other within the errors.
Although the number of pairs with large separation is significantly increased
compared to previous samples, does not show any tendency of increase, but
found to be almost independent of the separation of pairs beyond 100 kpc. The
constancy of beyond 100 kpc may indicate that the typical halo size of
spiral galaxies is less than kpc.Comment: 18 pages + 8 figures, to appear in ApJ Vol. 516 (May 10
Projeto valoriza bioma cerrado.
Os objetivos almejados foram propor sistemas agroflorestais agroecológicos temáticos; alternativas econômicas e sociais viáveis e participativas e de recuperação de áreas degradadas com espécies nativas e potencialmente utilizáveis para exploração econômica e sustentável. Estudar e desenvolver conhecimento ecológico, bioquímico e molecular e o manejo fitotécnico de espécies nativas componentes do sistema agroflorestal e desenvolver estudos fisiológicos, bioquímicos, ecológicos, econômicos e sociais. E também promover a educação ambiental participativa de crianças, jovens e adultos.bitstream/item/46248/1/projetobc.pd
Strong evidences for a nonextensive behavior of the rotation period in Open Clusters
Time-dependent nonextensivity in a stellar astrophysical scenario combines
nonextensive entropic indices derived from the modified Kawaler's
parametrization, and , obtained from rotational velocity distribution. These
's are related through a heuristic single relation given by , where is the cluster age. In a nonextensive
scenario, these indices are quantities that measure the degree of
nonextensivity present in the system. Recent studies reveal that the index
is correlated to the formation rate of high-energy tails present in the
distribution of rotation velocity. On the other hand, the index is
determined by the stellar rotation-age relationship. This depends on the
magnetic field configuration through the expression , where
and denote the saturation level of the star magnetic field and its
topology, respectively. In the present study, we show that the connection
is also consistent with 548 rotation period data for single
main-sequence stars in 11 Open Clusters aged less than 1 Gyr. The value of
2.5 from our unsaturated model shows that the mean magnetic field
topology of these stars is slightly more complex than a purely radial field.
Our results also suggest that stellar rotational braking behavior affects the
degree of anti-correlation between and cluster age . Finally, we suggest
that stellar magnetic braking can be scaled by the entropic index .Comment: 6 pages and 2 figures, accepted to EPL on October 17, 201
Using a flocculent brewer’s yeast strain of Saccharomyces cerevisiae in the removal of heavy metals
Fundação para a Ciência e a Tecnologia (FCT) - POCTI/CTA/47875/2002, (SFRH/BD/31755/2006)Fundo Europeu de Desenvolvimento Regional (FEDER
Removal of heavy metals using cells of Saccharomyces cerevisiae as a green technology
Anthropogenic activities are largely responsible for the release of heavy metals in the environment.
Unlike organic pollutants, heavy metals are not degraded and remain indefinitely in the ecosystem,
which poses a different kind of challenge for remediation.
Municipal sanitary sewers are not designed to treat toxic wastes, such as industrial effluents containing
heavy metals. Thus, heavy metals should be removed in a “previous step”, from these metalladen
effluents before they are released into the water body or sent to a municipal treatment plant.
Conventional physicochemical technologies are not environmental friendly, fully efficient or present
very high costs when applied to large volume of wastewaters containing low metal concentration (1-
100 mg/l). The disadvantages of these available “best treatment technologies”, associated with the
increase of environmental regulations, have compelled the search for alternative, low-cost and efficient
processes for the detoxification of metal-bearing wastewaters.
The advantages and the current knowledge of the mechanisms of metal removal by yeast cells of
Saccharomyces cerevisiae will be presented. The use of live or dead biomass and the influence of
biomass inactivation processes or the modification of the yeast surface on the metal accumulation
characteristics will be outlined. The importance of the physico-chemical characteristics of the effluents
and the role of chemical speciation as a tool for predicting and optimising metal removal will be
highlighted. The use of yeast cells as the only treatment process of real effluents or in a “polishing” step,
after the chemical treatment of the raw effluent to remove the bulk of the metal will be presented. The
problem of biomass separation, after treatment of the effluents, and the use of flocculent characteristics
of yeast cells, as an alternative process of cell-liquid separation, will also be discussed. The convenient
management of the contaminated biomass and the advantages of the selective recovery of heavy
metals in the development of a closed cycle without residues (green technology) will be presented
An extended formalism for preferential attachment in heterogeneous complex networks
In this paper we present a framework for the extension of the preferential
attachment (PA) model to heterogeneous complex networks. We define a class of
heterogeneous PA models, where node properties are described by fixed states in
an arbitrary metric space, and introduce an affinity function that biases the
attachment probabilities of links. We perform an analytical study of the
stationary degree distributions in heterogeneous PA networks. We show that
their degree densities exhibit a richer scaling behavior than their homogeneous
counterparts, and that the power law scaling in the degree distribution is
robust in presence of heterogeneity
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