5,495 research outputs found
A consistency study of coarse-grained dynamical chains through a Nonlinear wave equation of mixed type
A dynamical atomistic chain to simulate mechanical properties of a
one-dimensional material with zero temperature may be modelled by the molecular
dynamics (MD) model. Because the number of particles (atoms) is huge for a MD
model, in practice one often takes a much smaller number of particles to
formulate a coarse-grained approximation. We shall mainly consider the
consistency of the coarse-grained model with respect to the grain (mesh) size
to provide a justification to the goodness of such an approximation. In order
to reduce the characteristic oscillations with very different frequencies in
such a model, we either add a viscous term to the coarse-grained MD model or
apply a space average to the coarse-grained MD solutions for the consistency
study. The coarse-grained solution is also compared with the solution of the
(macroscopic) continuum model (a nonlinear wave equation of mixed type) to show
how well the coarse-grained model can approximate the macroscopic behavior of
the material. We also briefly study the instability of the dynamical atomistic
chain and the solution of the Riemann problem of the continuum model which may
be related to the defect of the atomistic chain under a large deformation in
certain locations.Comment: 25 pages, 15 figure
Enhancement of Optical Nonlinearity Through Anisotropic Microstructures
We investigate the polarization dependence of optical nonlinearity
enhancement for a uniaxial anisotropic composite of metal nanocrystals in a
dielectric host. Three cases are distinguished depending on whether the
polarization is parallel, perpendicular or unpolarized with respect to the axis
of anisotropy. For the parallel polarization, the results show that the 3D
results are qualitatively similar to the 2D case reported recently. For the
perpendicular polarization, the results are markedly different from the
parallel counterpart: In contrast to the absorption, the enhancement factor
actually increases with the anisotropy. Thus the separation of the absorption
and enhancement peaks becomes even more pronounced than the parallel
polarization case. These results indicate a strong polarization dependence of
the nonlinear optical response.Comment: 12 pages, LaTeX format, 9 figures, preliminary results were Reported
in the 2nd Tohwa University International Meeting on Statistical Physics held
on November 4-7, 1997, accepted for publication by Optics Communications on 7
November 199
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