522 research outputs found
Ab initio molecular dynamics simulations of Aluminum solvation
The solvation of Al and its hydrolyzed species in water clusters has been
studied by means of ab initio molecular dynamics simulations. The hexa-hydrate
aluminum ion formed a stable complex in the finite temperature cluster
simulation of one aluminum ion and 16 waters. The average dipole moment of
strongly polarized hydrated water molecules in the first solvation shell of the
hexa-hydrate aluminum ion was found to be 5.02 Debye. The deprotonated
hexa-hydrate complex evolves into a tetra-coordinated aluminate ion with two
water molecules in the second solvation shell forming hydrogen bonds to the
hydroxyl groups in agreement with the observed coordination.Comment: 12 pages in Elsevier LaTeX, 5 figures in Postscript, 2 last figures
are in color, submitted to Chemical Physics Letter
Fredholm methods for billiard eigenfunctions in the coherent state representation
We obtain a semiclassical expression for the projector onto eigenfunctions by
means of the Fredholm theory. We express the projector in the coherent state
basis, thus obtaining the semiclassical Husimi representation of the stadium
eigenfunctions, which is written in terms of classical invariants: periodic
points, their monodromy matrices and Maslov indices.Comment: 12 pages, 10 figures. Submitted to Phys. Rev. E. Comments or
questions to [email protected]
Long-lived oscillons from asymmetric bubbles
The possibility that extremely long-lived, time-dependent, and localized
field configurations (``oscillons'') arise during the collapse of asymmetrical
bubbles in 2+1 dimensional phi^4 models is investigated. It is found that
oscillons can develop from a large spectrum of elliptically deformed bubbles.
Moreover, we provide numerical evidence that such oscillons are: a) circularly
symmetric; and b) linearly stable against small arbitrary radial and angular
perturbations. The latter is based on a dynamical approach designed to
investigate the stability of nonintegrable time-dependent configurations that
is capable of probing slowly-growing instabilities not seen through the usual
``spectral'' method.Comment: RevTeX 4, 9 pages, 11 figures. Revised version with a new approach to
stability. Accepted to Phys. Rev.
Universality of the Lyapunov regime for the Loschmidt echo
The Loschmidt echo (LE) is a magnitude that measures the sensitivity of
quantum dynamics to perturbations in the Hamiltonian. For a certain regime of
the parameters, the LE decays exponentially with a rate given by the Lyapunov
exponent of the underlying classically chaotic system. We develop a
semiclassical theory, supported by numerical results in a Lorentz gas model,
which allows us to establish and characterize the universality of this Lyapunov
regime. In particular, the universality is evidenced by the semiclassical limit
of the Fermi wavelength going to zero, the behavior for times longer than
Ehrenfest time, the insensitivity with respect to the form of the perturbation
and the behavior of individual (non-averaged) initial conditions. Finally, by
elaborating a semiclassical approximation to the Wigner function, we are able
to distinguish between classical and quantum origin for the different terms of
the LE. This approach renders an understanding for the persistence of the
Lyapunov regime after the Ehrenfest time, as well as a reinterpretation of our
results in terms of the quantum--classical transition.Comment: 33 pages, 17 figures, uses Revtex
Análise da variabilidade genética de acessos de Psidium spp. (Myrtaceae) avaliados quanto à reação a Meloidogyne enterolobii¹
Holographic dark energy in a non-flat universe with Granda-Oliveros cut-off
Motivated by Granda and Oliveros (GO) model, we generalize their work to the
non-flat case. We obtain the evolution of the dark energy density, the
deceleration and the equation of state parameters for the holographic dark
energy model in a non-flat universe with GO cut-off. In the limiting case of a
flat universe, i.e. , all results given in GO model are obtained.Comment: 11 pages, 5 figure
Biological treatments in allergy: Prescribing patterns and management of hypersensitivity reactions
Clinical Communication
Influência da irrigação no ciclo do abacaxizeiro cv. Pérola em área de tabuleiro costeiro da Bahia
Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory
Atmospheric parameters, such as pressure (P), temperature (T) and density,
affect the development of extensive air showers initiated by energetic cosmic
rays. We have studied the impact of atmospheric variations on extensive air
showers by means of the surface detector of the Pierre Auger Observatory. The
rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find
that the observed behaviour is explained by a model including the effects
associated with the variations of pressure and density. The former affects the
longitudinal development of air showers while the latter influences the Moliere
radius and hence the lateral distribution of the shower particles. The model is
validated with full simulations of extensive air showers using atmospheric
profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle
Physic
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