122 research outputs found
Compacton-like solutions of the hydrodynamic system describing relaxing media
We show the existence of a compacton-like solutions within the relaxing
hydrodynamic-type model and perform numerical study of attracting features of
these solutions
Nanosized carbon forms in the processes of pressure–temperature-induced transformations of hydrocarbons
The products of thermal conversions of naphthalene, anthracene, pentacene, perylene, and coronene at 8 GPa in the temperature range up to 1300 C have been studied by scanning electron and high-resolution transmission electron microscopies. As a result, it has been established that various nanometer-sized carbon species (spherical and coalesced two-core onion-like carbon particles, faceted polyhedral particles, graphitic ribbons, graphitic folds, and nanocrystalline diamonds) are present in the conversion products together with micron-sized crystallites of graphite and diamond. 2006 Elsevier Ltd. All rights reserved
Exciton Dephasing and Thermal Line Broadening in Molecular Aggregates
Using a model of Frenkel excitons coupled to a bath of acoustic phonons in
the host medium, we study the temperature dependence of the dephasing rates and
homogeneous line width in linear molecular aggregates. The model includes
localization by disorder and predicts a power-law thermal scaling of the
effective homogeneous line width. The theory gives excellent agreement with
temperature dependent absorption and hole-burning experiments on aggregates of
the dye pseudoisocyanine.Comment: 11 pages, 3 PostScript figure
Low-temperature quenching of one-dimensional localised Frenkel excitons
We present a theoretical analysis of low-temperature quenching of
one-dimensional Frenkel excitons that are localised by moderate on-site
(diagonal) uncorrelated disorder. Exciton diffusion is considered as an
incoherent hopping over localization segments and is probed by the exciton
fluorescence quenching at point traps. The rate equation is used to calculate
the temperature dependence of the exciton quenching. The activation temperature
of the diffusion is found to be of the order of the width of the exciton
absorption band. We demonstrate that the intra-segment scattering is extremely
important for the exciton diffusion. We discuss also experimental data on the
fast exciton-exciton annihilation in linear molecular aggregates at low
temperatures.Comment: 7 pages, 3 figures, accepted to Chem. Phys. Let
Linear optical properties of one-dimensional Frenkel exciton systems with intersite energy correlations
We analyze the effects of intersite energy correlations on the linear optical
properties of one-dimensional disordered Frenkel exciton systems. The
absorption line width and the factor of radiative rate enhancement are studied
as a function of the correlation length of the disorder. The absorption line
width monotonously approaches the seeding degree of disorder on increasing the
correlation length. On the contrary, the factor of radiative rate enhancement
shows a non-monotonous trend, indicating a complicated scenario of the exciton
localization in correlated systems. The concept of coherently bound molecules
is exploited to explain the numerical results, showing good agreement with
theory. Some recent experiments are discussed in the light of the present
theory.Comment: 18 pages, 3 figues, REVTeX, to appear in Physical Review
FUNDAMENTOS TEÓRICOS DO PROCESSO DE FORMAÇÃO DE CONCEITOS E SUAS IMPLICAÇÕES PARA O ENSINO E APRENDIZAGEM DE QUÍMICA
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