6,278 research outputs found
Stellar equilibrium configurations of white dwarfs in the gravity
In this work we investigate the equilibrium configurations of white dwarfs in
a modified gravity theory, na\-mely, gravity, for which and
stand for the Ricci scalar and trace of the energy-momentum tensor,
respectively. Considering the functional form , with
being a constant, we obtain the hydrostatic equilibrium equation for
the theory. Some physical properties of white dwarfs, such as: mass, radius,
pressure and energy density, as well as their dependence on the parameter
are derived. More massive and larger white dwarfs are found for
negative values of when it decreases. The equilibrium configurations
predict a maximum mass limit for white dwarfs slightly above the Chandrasekhar
limit, with larger radii and lower central densities when compared to standard
gravity outcomes. The most important effect of theory for massive
white dwarfs is the increase of the radius in comparison with GR and also
results. By comparing our results with some observational data of
massive white dwarfs we also find a lower limit for , namely, .Comment: To be published in EPJ
Resíduo micropulverizado da moagem a seco de milho não afeta biodisponibilidade de zinco em ratos.
Trabalho apresentado no XV Congresso Latinoamericano de Nutricion e XVI Jornadas de la Sociedad Chilena de Nutrición, 2009, Santiago do Chile
q- Deformed Boson Expansions
A deformed boson mapping of the Marumori type is derived for an underlying
algebra. As an example, we bosonize a pairing hamiltonian in a two
level space, for which an exact treatment is possible. Comparisons are then
made between the exact result, our q- deformed boson expansion and the usual
non - deformed expansion.Comment: 8 pages plus 2 figures (available upon request
Immature development of Spodoptera dolichos (Fabricius) (Lepidoptera: noctuidae).
We provide detailed temporal and morphological parameters of the immature stages of Spodoptera dolichos (Fabricius) larvae fed on artificial diet under controlled conditions (25?±?1°C, 70?±?10% RH, and 14 h photophase). The viability of the egg, larval, pupal, and prepupal stages was 97.5%, 97.0%, 93.1%, and 98.9%, respectively. The average duration of the egg, larval, prepupal, and pupal stages was 5.0, 23.4, 3.2, and 21.5 days, respectively. Females took longer at the larval stage than males, with 10.5% of them having seven instars. The growth rate of female larvae that developed through six and seven instars was 1.72 and 1.54, respectively. Female pupae were significantly larger, exhibiting slower development than males
Composição bromatológica e digestibilidade aparente de alimentos encontrados na região Semiárida brasileira para arraçoamento de tilapia rosa em cultivos.
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Acceleration of the precession frequency for optically-oriented electron spins in ferromagnetic/semiconductor hybrids
Time-resolved Kerr rotation measurements were performed in InGaAs/GaAs
quantum wells nearby a doped Mn delta layer. Our magneto-optical results show a
typical time evolution of the optically-oriented electron spin in the quantum
well. Surprisingly, this is strongly affected by the Mn spins, resulting in an
increase of the spin precession frequency in time. This increase is attributed
to the variation in the effective magnetic field induced by the dynamical
relaxation of the Mn spins. Two processes are observed during electron spin
precession: a quasi-instantaneous alignment of the Mn spins with photo-excited
holes, followed by a slow alignment of Mn spins with the external transverse
magnetic field. The first process leads to an equilibrium state imprinted in
the initial precession frequency, which depends on pump power, while the second
process promotes a linear frequency increase, with acceleration depending on
temperature and external magnetic field. This observation yields new
information about exchange process dynamics and on the possibility of
constructing spin memories, which can rapidly respond to light while retaining
information for a longer period.Comment: 7 pages, 5 figure
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