22,884 research outputs found
Doped AB_2 Hubbard Chain: Spiral, Nagaoka and RVB States, Phase Separation and Luttinger Liquid Behavior
We present an extensive numerical study of the Hubbard model on the doped
AB chain, both in the weak coupling and the infinite-U limit. Due to the
special unit cell topology, this system displays a rich variety of phases as
function of hole doping () away from half-filling. Near half-filling,
spiral states develop in the weak coupling regime, while Nagaoka itinerant
ferromagnetism is observed in the infinite-U limit. For higher doping the
system phase-separates before reaching a Mott insulating phase of short-range
RVB states at . Moreover, for we observe a crossover,
which anticipates the Luttinger liquid behavior for .Comment: 11 pages, 13 figure
Magnetism and Electronic Correlations in Quasi-One-Dimensional Compounds
In this contribution on the celebration of the 80th birthday anniversary of
Prof. Ricardo Ferreira, we present a brief survey on the magnetism of
quasi-one-dimensional compounds. This has been a research area of intense
activity particularly since the first experimental announcements of magnetism
in organic and organometallic polymers in the mid 80s. We review experimental
and theoretical achievements on the field, featuring chain systems of
correlated electrons in a special AB2 unit cell structure present in inorganic
and organic compounds
Coherent and semiclassical states in magnetic field in the presence of the Aharonov-Bohm solenoid
A new approach to constructing coherent states (CS) and semiclassical states
(SS) in magnetic-solenoid field is proposed. The main idea is based on the fact
that the AB solenoid breaks the translational symmetry in the xy-plane, this
has a topological effect such that there appear two types of trajectories which
embrace and do not embrace the solenoid. Due to this fact, one has to construct
two different kinds of CS/SS, which correspond to such trajectories in the
semiclassical limit. Following this idea, we construct CS in two steps, first
the instantaneous CS (ICS) and the time dependent CS/SS as an evolution of the
ICS. The construction is realized for nonrelativistic and relativistic spinning
particles both in (2+1)- and (3+1)- dimensions and gives a non-trivial example
of SS/CS for systems with a nonquadratic Hamiltonian. It is stressed that CS
depending on their parameters (quantum numbers) describe both pure quantum and
semiclassical states. An analysis is represented that classifies parameters of
the CS in such respect. Such a classification is used for the semiclassical
decompositions of various physical quantities.Comment: 35 pages, 2 figures. Some typos in (77), (101), and (135) corrected
with respect to the published version. Results unchange
The importance of measuring skin resistance for electrical nociceptive stimulation in standing horses
Scalar and Spinor Particles in the Spacetime of a Domain Wall in String Theory
We consider scalar and spinor particles in the spacetime of a domain wall in
the context of low energy effective string theories, such as the generalized
scalar-tensor gravity theories. This class of theories allows for an arbitrary
coupling of the wall and the (gravitational) scalar field. First, we derive the
metric of a wall in the weak-field approximation and we show that it depends on
the wall's surface energy density and on two post-Newtonian parameters. Then,
we solve the Klein-Gordon and the Dirac equations in this spacetime. We obtain
the spectrum of energy eigenvalues and the current density in the scalar and
spinor cases, respectively. We show that these quantities, except in the case
of the energy spectrum for a massless spinor particle, depend on the parameters
that characterize the scalar-tensor domain wall.Comment: LATEX file, 21 pages, revised version to appear in Phys. Rev.
Ecofisiologia de plantas da caatinga.
O Nordeste brasileiro abrange uma área de 1.600.000 km2 dos quais aproximadamente 1.083.790 km2 corresponde a área da zona semi-árida, que se caracteriza basicamente pela escassez, irregularidade e má distribuição das chuvas. As chuvas que caem sobre a região variam entre, 300mm a 950 mm por ano, com 80% da precipitação ocorrendo num período de cinco a seis meses. (Embrapa, 2000). A evapotranspiração potencial na região é considerada uma das mais altas do mundo alcançando uma média anual de aproximadamente 2.000 mm. Esta situação é influenciada pela ocorrência de forte insolação altas temperaturas ( médias anuais de 23 a 28 oC ) e umidade relativa em torno de 50% (Valdivieso e Cordeiro, 1985). Os solos do semi-árido são geralmente rasos, deficientes em matéria orgânica, com baixos teores de fósforo e de médio a alto, de potássio
Sedative and antinociceptive effects of different combinations of detomidine and methadone in standing horses
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