42,047 research outputs found
Manipulation of the dynamics of many-body systems via quantum control methods
We investigate how dynamical decoupling methods may be used to manipulate the
time evolution of quantum many-body systems. These methods consist of sequences
of external control operations designed to induce a desired dynamics. The
systems considered for the analysis are one-dimensional spin-1/2 models, which,
according to the parameters of the Hamiltonian, may be in the integrable or
non-integrable limits, and in the gapped or gapless phases. We show that an
appropriate control sequence may lead a chaotic chain to evolve as an
integrable chain and a system in the gapless phase to behave as a system in the
gapped phase. A key ingredient for the control schemes developed here is the
possibility to use, in the same sequence, different time intervals between
control operations.Comment: 10 pages, 3 figure
Fluctuating local moments, itinerant electrons and the magnetocaloric effect: the compositional hypersensitivity of FeRh
We describe an ab-initio Disordered Local Moment Theory for materials with
quenched static compositional disorder traversing first order magnetic phase
transitions. It accounts quantitatively for metamagnetic changes and the
magnetocaloric effect. For perfect stoichiometric B2-ordered FeRh, we calculate
the transition temperature of the ferromagnetic-antiferromagnetic transition to
be 495K and a maximum isothermal entropy change in 2 Tesla of J~K~kg. A large (40\%) component of is
electronic. The transition results from a fine balance of competing electronic
effects which is disturbed by small compositional changes - e.g. swapping just
2\% Fe of `defects' onto the Rh sublattice makes drop by 290K. This
hypersensitivity explains the narrow compositional range of the transition and
impurity doping effects.Comment: 11 pages, 4 figure
Knizhnik-Zamolodchikov-Bernard equations connected with the eight-vertex model
Using quasiclassical limit of Baxter's 8 - vertex R - matrix, an elliptic
generalization of the Knizhnik-Zamolodchikov equation is constructed. Via
Off-Shell Bethe ansatz an integrable representation for this equation is
obtained. It is shown that there exists a gauge transformation connecting this
equation with Knizhnik-Zamolodchikov-Bernard equation for SU(2)-WZNW model on
torus.Comment: 20 pages latex, macro: tcilate
Desenvolvimento de revestimentos poliméricos para liberação controlada de ureia.
Entrada padronizada: RIBEIRO, C
Calibração do sensor de capacitância IRRIGAP® para a medida da umidade em solo do Semiárido.
O monitoramento do conteúdo de água do solo fornece a informação sobre o volume de água nele armazenado, sendo que tal procedimento pode ser realizado por métodos diretos e indiretos. Dentre entes últimos, destacam-se aqueles baseados na relação existente entre as propriedades dielétricas e a umidade do solo. Contudo, sendo um método indireto de estimativa da umidade do solo, a utilização de sonda de capacitância requer calibração para a estimativa deste parâmetro na condição local de instalação, de modo a incrementar a sua precisão. Este trabalho teve como objetivo a determinação das curvas de calibração para o sensor capacitivo IRRIGAP®, em condições de laboratório, sendo esta referente às amostras de solo coletadas em três diferentes intervalos de profundidade (0,2-0,3 m, 0,5-0,6 m, 0,8-0,9 m) em um Neossolo Quartzarênico, de uma área irrigada em Petrolina-PE. Tanto o modelo linear quanto o modelo quadrático podem representar a relação entre umidade do solo e tensão do sensor, com altos ajustes
Suppression of Anderson localization of light and Brewster anomalies in disordered superlattices containing a dispersive metamaterial
Light propagation through 1D disordered structures composed of alternating
layers, with random thicknesses, of air and a dispersive metamaterial is
theoretically investigated. Both normal and oblique incidences are considered.
By means of numerical simulations and an analytical theory, we have established
that Anderson localization of light may be suppressed: (i) in the long
wavelength limit, for a finite angle of incidence which depends on the
parameters of the dispersive metamaterial; (ii) for isolated frequencies and
for specific angles of incidence, corresponding to Brewster anomalies in both
positive- and negative-refraction regimes of the dispersive metamaterial. These
results suggest that Anderson localization of light could be explored to
control and tune light propagation in disordered metamaterials.Comment: 4 two-column pages, 3 figure
Creation of a dipolar superfluid in optical lattices
We show that by loading a Bose-Einstein condensate (BEC) of two different
atomic species into an optical lattice, it is possible to achieve a
Mott-insulator phase with exactly one atom of each species per lattice site. A
subsequent photo-association leads to the formation of one heteronuclear
molecule with a large electric dipole moment, at each lattice site. The melting
of such dipolar Mott-insulator creates a dipolar superfluid, and eventually a
dipolar molecular BEC.Comment: 4 pages, 2 eps figure
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