15,508 research outputs found
Density-functionals not based on the electron gas: Local-density approximation for a Luttinger liquid
By shifting the reference system for the local-density approximation (LDA)
from the electron gas to other model systems one obtains a new class of density
functionals, which by design account for the correlations present in the chosen
reference system. This strategy is illustrated by constructing an explicit LDA
for the one-dimensional Hubbard model. While the traditional {\it ab initio}
LDA is based on a Fermi liquid (the electron gas), this one is based on a
Luttinger liquid. First applications to inhomogeneous Hubbard models, including
one containing a localized impurity, are reported.Comment: 4 pages, 4 figures (final version, contains additional applications
and discussion; accepted by Phys. Rev. Lett.
On the algebraic Bethe ansatz: Periodic boundary conditions
In this paper, the algebraic Bethe ansatz with periodic boundary conditions
is used to investigate trigonometric vertex models associated with the
fundamental representations of the non-exceptional Lie algebras. This
formulation allow us to present explicit expressions for the eigenvectors and
eigenvalues of the respective transfer matrices.Comment: 36 pages, LaTex, Minor Revisio
D3 instantons in Calabi-Yau orientifolds with(out) fluxes
We investigate the instanton effect due to D3 branes wrapping a four-cycle in
a Calabi-Yau orientifold with D7 branes. We study the condition for the nonzero
superpotentials from the D3 instantons. For that matter we work out the zero
mode structures of D3 branes wrapping a four-cycle both in the presence of the
fluxes and in the absence of the fluxes. In the presence of the fluxes, the
condition for the nonzero superpotential could be different from that without
the fluxes. We explicitly work out a simple example of the orientifold of with a suitable flux to show such behavior. The effects of
D3-D7 sectors are interesting and give further constraints for the nonzero
superpotential. In a special configuration where D3 branes and D7 branes wrap
the same four-cycle, multi-instanton calculus of D3 branes could be reduced to
that of a suitable field theory. The structure of D5 instantons in Type I
theory is briefly discussed.Comment: 17 pages; Typos corrected, arguments improved and references adde
Deposition of tin film on carbon steel bandsaw blades by the cold plasma tecnique.
Disponível online. Resumo
Otimização e validação de método para determinação de ácidos orgânicos em vinhos por cromatografia líquida de alta eficiência.
Reagentes e soluções analíticas; Instrumentação e condição cromatográfica; Estabilidade dos padrões analíticos e da fase móvel; Validação do método; Preparação das amostras de vinho
Accelerating Cold Dark Matter Cosmology ()
A new kind of accelerating flat model with no dark energy that is fully
dominated by cold dark matter (CDM) is investigated. The number of CDM
particles is not conserved and the present accelerating stage is a consequence
of the negative pressure describing the irreversible process of gravitational
particle creation. A related work involving accelerating CDM cosmology has been
discussed before the SNe observations [Lima, Abramo & Germano, Phys. Rev. D53,
4287 (1996)]. However, in order to have a transition from a decelerating to an
accelerating regime at low redshifts, the matter creation rate proposed here
includes a constant term of the order of the Hubble parameter. In this case,
does not need to be small in order to solve the age problem and the
transition happens even if the matter creation is negligible during the
radiation and part of the matter dominated phase. Therefore, instead of the
vacuum dominance at redshifts of the order of a few, the present accelerating
stage in this sort of Einstein-de Sitter CDM cosmology is a consequence of the
gravitational particle creation process. As an extra bonus, in the present
scenario does not exist the coincidence problem that plagues models with
dominance of dark energy. The model is able to harmonize a CDM picture with the
present age of the universe, the latest measurements of the Hubble parameter
and the Supernovae observations.Comment: 9 pages, 6 figures, typos corrected, references added, discussion in
Appendix B extende
Otimização e validação de método para determinação de ácidos orgânicos em vinhos por cromatografia líquida de alta eficiência.
The organic acids (tartaric, malic, citric, lactic and succinic) are de main components responsible for the acidity in the wine. This method for simultaneous determination of organic acids and interfering peaks in wines can be achieved in 16 min. The sample preceded by a dilution and filtration step. The chromatographic separation required one reversed phase column, isocratic mobile phase (acetonitrila, formic acid in water) and detection wavelength was set at 212 nm. The validation confirmed good repeatability, recovery and application in red and white wines.Nota técnica
Evaluation of ripening Vitis vinifera grown in Northeastern Brazil.
This study aimed to determine physical characteristics and chemical composition of grapes cvs. Syrah and Tempranillo, during maturation
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