5,640 research outputs found
Supermassive black holes as the regulators of star formation in central galaxies
We present a relationship between the black hole mass, stellar mass, and star
formation rate of a diverse group of 91 galaxies with dynamically-measured
black hole masses. For our sample of galaxies with a variety of morphologies
and other galactic properties, we find that the specific star formation rate is
a smoothly decreasing function of the ratio between black hole mass and stellar
mass, or what we call the specific black hole mass. In order to explain this
relation, we propose a physical framework where the gradual suppression of a
galaxy's star formation activity results from the adjustment to an increase in
specific black hole mass and, accordingly, an increase in the amount of
heating. From this framework, it follows that at least some galaxies with
intermediate specific black hole masses are in a steady state of partial
quiescence with intermediate specific star formation rates, implying that both
transitioning and steady-state galaxies live within this region known as the
"green valley." With respect to galaxy formation models, our results present an
important diagnostic with which to test various prescriptions of black hole
feedback and its effects on star formation activity.Comment: 15 pages, 4 figures, 2 tables. Accepted for publication in The
Astrophysical Journa
Measurement of miniband parameters of a doped superlattice by photoluminescence in high magnetic fields
We have studied a 50/50\AA superlattice of GaAs/AlGaAs
composition, modulation-doped with Si, to produce
cm electrons per superlattice period. The modulation-doping was tailored
to avoid the formation of Tamm states, and photoluminescence due to interband
transitions from extended superlattice states was detected. By studying the
effects of a quantizing magnetic field on the superlattice photoluminescence,
the miniband energy width, the reduced effective mass of the electron-hole
pair, and the band gap renormalization could be deduced.Comment: minor typing errors (minus sign in eq. (5)
Determination of phytoextraction potential of plant speciesfor toxic elements in soils of abandoned sulphide-mining areas
This study has determined contamination levels in soils and plants from the Sa˜o Domingos mining area, Portugal, by k0-INAA. Total concentrations of As, Sb, Cr, Hg, Cu, Zn and Fe in soils were very high, exceeding the maximum limits in Portuguese legislation. Concentrations of toxic elements like As, Sb and Zn were highest in roots of Erica andevalensis, Juncus acutus, Agrostis castellana and Nicotiana glauca. Additionally, As, Br, Cr, Fe, Sb and Zn in all organs of most plants were above toxicity levels.
Those species that accumulated relatively high concentrations of toxic elements in roots (and tops) may be cultivated for phytostabilisation of similar areas
Avaliação in vivo da qualidade protéica do champignon do Brasil (Agaricus brasiliensis Wasser et al.).
Objetivo: O trabalho aqui descrito trata da avaliação de uma dieta experimental contendo Champingnon do Brasil (Agaricus brasiliensis) como fonte de proteína em um modelo experimental de ratos. Métodos: Para este propósito, foram selecionados 24 ratos Wistar machos, recém desmamados (21 dias) divididos em 3 grupos de 8 animais cada, que foram alimentados com uma dieta padrão de caseína, ou com uma dieta experimental de proteína de Agaricus brasiliensis ambas contendo 10% de proteína e isoenergéticas ou ainda, com uma dieta com muito baixo teor de proteína. O ensaio biológico foi realizado em 28 dias, ao longo dos quais se determinou a concentração de nitrogênio na urina e nas fezes, além dos cálculos do Quociente de Eficiência Alimentar (ganho de peso dividido pelo consumo de dieta), do Quociente de Eficiência Protéica (ganho de peso dividido pelo consumo de proteína), da Razão Protéica Líquida (ganho de peso corrigido dividido pelo consumo de proteína) e da Digestibilidade Verdadeira. Resultados: Os resultados demonstraram que quando o Champignon do Brasil foi utilizado como fonte exclusiva de proteína na dieta, os índices de qualidade protéica apresentaram-se baixos (Quociente de Eficiência Alimentar= 0,08, Quociente de Eficiência Protéica=0,92 e Razão Protéica Líquida=3,00), quando comparados com a dieta padrão caseína (Quociente de Eficiência Alimentar=0,30, Quociente de Eficiência Protéica=3,05 e Razão Protéica Líquida=4,21). Os índices obtidos para o grupo Agaricus mostraram-se comparáveis àqueles 536 | G.S. HENRIQUES et al. Revista de Nutrição Rev. Nutr., Campinas, 21(5):535-543, set./out., 2008 apresentados por alguns tipos de proteína vegetal e podem ser explicados por sua limitação em aminoácidos essenciais, notadamente a lisina e a leucina, respectivamente primeiro e segundo aminoácido limitante. Conclusão: Os dados apontam para a utilização da proteína do Agaricus brasiliensis como uma boa fonte para complementação protéica, quando combinada com outras culturas vegetais comuns na dieta típica brasileira
Al-containing MCM-41 type materials prepared by different synthesis methods: hydrothermal stability and catalytic properties
Al-containing MCM-41 type materials were prepared by three different synthesis methods
(aluminum grafting on the calcined MCM-41, pH adjustment during the crystallization period
and crystallization in the presence of zeolite seeds). The samples were characterized by
powder XRD, nitrogen adsorption, 27Al MAS NMR and FTIR with pyridine as probe
molecule. All the samples exhibit a high hydrothermal stability at high temperature just with a
minor structural degradation. N2 adsorption data obtained for the sample prepared from a gel
containing zeolite seeds suggest a higher structural resistance to the hydrothermal treatment in
comparison with the samples prepared by other methods. A different type of pyridine
adsorbed, probably interacting simultaneously with a Brönsted and a Lewis acid site, is
observed upon pyridine adsorption. This type of adsorption is stronger for the sample
prepared in the presence of zeolite seeds and is not observed on Al-grafted MCM-41.
2
The catalytic activity towards the isomerization of α-pinene depends mainly on the number of
Brönsted acid sites. The data obtained in this study strongly indicate that for this type of
materials, the Lewis acid sites do not influence the selectivity for the isomerization products
Determinação da glicemia e índice glicêmico do cogumelo Agaricus brasiliensis em modelo de ratos Wistar normais e efeitos diabéticos por aplicação de estreptozotocina.
Trabalho apresentado no XV Congresso Latinoamericano de Nutricion e XVI Jornadas de la Sociedad Chilena de Nutrición, 2009, Santiago do Chile
Amino acid and mineral composition of yellow and red peachpalm flour (Bactris gasipaes Kunth. Var. Gasipaes Henderson).
Comparison between ingestion of yellow and red peachpalm flour (Bactris gasipaes Kunth. Var. GasipaesHenderson) over glycemic behavior in diabetic and non-diabetic wistar rats.
Imaging of pancreas transplantation and its complications
Abstract
Pancreas transplantation is an effective treatment for type 1 diabetes mellitus and is being increasingly performed worldwide. Early recognition of graft-related complications is fundamental for graft survival; thus, radiologists must be aware of the transplantation technique, pancreas-graft imaging and postoperative complications. We present normal pancreas-graft imaging appearances and the imaging features of postoperative complications
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