19,079 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.
Experiência de capacitação de empregados com atividades em laboratório na Embrapa Amazônia Oriental.
Editores técnicos: Nádia Elígia Pinto Paracampo, Laura Figueiredo Abreu. XIII MET
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
New Cosmic Accelerating Scenario without Dark Energy
We propose an alternative, nonsingular, cosmic scenario based on
gravitationally induced particle production. The model is an attempt to evade
the coincidence and cosmological constant problems of the standard model
(CDM) and also to connect the early and late time accelerating stages
of the Universe. Our space-time emerges from a pure initial de Sitter stage
thereby providing a natural solution to the horizon problem. Subsequently, due
to an instability provoked by the production of massless particles, the
Universe evolves smoothly to the standard radiation dominated era thereby
ending the production of radiation as required by the conformal invariance.
Next, the radiation becomes sub-dominant with the Universe entering in the cold
dark matter dominated era. Finally, the negative pressure associated with the
creation of cold dark matter (CCDM model) particles accelerates the expansion
and drives the Universe to a final de Sitter stage. The late time cosmic
expansion history of the CCDM model is exactly like in the standard
CDM model, however, there is no dark energy. This complete scenario is
fully determined by two extreme energy densities, or equivalently, the
associated de Sitter Hubble scales connected by , a result that has no correlation with the cosmological constant
problem. We also study the linear growth of matter perturbations at the final
accelerating stage. It is found that the CCDM growth index can be written as a
function of the growth index, . In this
framework, we also compare the observed growth rate of clustering with that
predicted by the current CCDM model. Performing a statistical test
we show that the CCDM model provides growth rates that match sufficiently well
with the observed growth rate of structure.Comment: 12 pages, 3 figures, accepted for publication by Phys. Rev. D. (final
version, some references have corrected). arXiv admin note: substantial text
overlap with arXiv:1106.193
Crescimento da bananeira cv. Prata Anã sob diferentes regimes de irrigação com déficit.
A escassez dos recursos hídricos obriga cada vez mais o uso eficiente do recurso água, isto é, incrementar a produção por unidade de água consumida. Sendo assim, o objetivo desse trabalho foi avaliar o crescimento vegetativo e as variáveis de produção da cultivar Prata Anã submetida a déficit hídrico em diferentes fases fenológicas. O presente trabalho foi conduzido nos campos experimentais da Embrapa Mandioca e Fruticultura, no município de Cruz das Almas ? BA (12º48?S; 39º06?W; 225 metros)
Dynamics and stability of Bose-Einstein solitons in tilted optical lattices
Bloch oscillations of Bose-Einstein condensates realize sensitive matter-wave
interferometers. We investigate the dynamics and stability of bright-soliton
wave packets in one-dimensional tilted optical lattices with a modulated
mean-field interaction . By means of a time-reversal argument, we prove
the stability of Bloch oscillations of breathing solitons that would be
quasistatically unstable. Floquet theory shows that these breathing solitons
can be more stable against certain experimental perturbations than rigid
solitons or even non-interacting wave packets.Comment: final, published versio
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
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