9,988 research outputs found
Nova ocorrência da Cochonilha-do-carmim em Opuntia spp. (Cactaceae) em Santa Catarina, Brasil.
O objetivo deste trabalho foi o levantamento dos inimigos naturais desta cochonilha que infesta Opuntia spp. no litoral de Santa Catarina
Cenários e ações na pesquisa federal em agricultura orgânica no Brasil
bitstream/CNPAB-2010/35702/1/doc257.pd
Closure of Macroscopic Laws in Disordered Spin Systems: A Toy Model
We use a linear system of Langevin spins with disordered interactions as an
exactly solvable toy model to investigate a procedure, recently proposed by
Coolen and Sherrington, for closing the hierarchy of macroscopic order
parameter equations in disordered spin systems. The closure procedure, based on
the removal of microscopic memory effects, is shown to reproduce the correct
equations for short times and in equilibrium. For intermediate time-scales the
procedure does not lead to the exact equations, yet for homogeneous initial
conditions succeeds at capturing the main characteristics of the flow in the
order parameter plane. The procedure fails in terms of the long-term temporal
dependence of the order parameters. For low energy inhomogeneous initial
conditions and near criticality (where zero modes appear) deviations in
temporal behaviour are most apparent. For homogeneous initial conditions the
impact of microscopic memory effects on the evolution of macroscopic order
parameters in disordered spin systems appears to be mainly an overall slowing
down.Comment: 14 pages, LateX, OUTP-94-24
Accuracy of the Semi--Classical Approximation: the Pullen Edmonds Hamiltonian
A test on the numerical accuracy of the semiclassical approximation as a
function of the principal quantum number has been performed for the
Pullen--Edmonds model, a two--dimensional, non--integrable, scaling invariant
perturbation of the resonant harmonic oscillator. A perturbative interpretation
is obtained of the recently observed phenomenon of the accuracy decrease on the
approximation of individual energy levels at the increase of the principal
quantum number. Moreover, the accuracy provided by the semiclassical
approximation formula is on the average the same as that provided by quantum
perturbation theory.Comment: 12 pages, 5 figures (available upon request to the authors), LaTex,
DFPD/93/TH/47, to be published in Nuovo Cimento
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