75,353 research outputs found
Dimerization-assisted energy transport in light-harvesting complexes
We study the role of the dimer structure of light-harvesting complex II (LH2)
in excitation transfer from the LH2 (without a reaction center (RC)) to the LH1
(surrounding the RC), or from the LH2 to another LH2. The excited and
un-excited states of a bacteriochlorophyll (BChl) are modeled by a quasi-spin.
In the framework of quantum open system theory, we represent the excitation
transfer as the total leakage of the LH2 system and then calculate the transfer
efficiency and average transfer time. For different initial states with various
quantum superposition properties, we study how the dimerization of the B850
BChl ring can enhance the transfer efficiency and shorten the average transfer
time.Comment: 11 pages, 6 figure
Size dependence of second-order hyperpolarizability of finite periodic chain under Su-Schrieffer-Heeger model
The second hyperpolarizability of
double-bond finite chain of trans-polyactylene is analyzed using the
Su-Schrieffer-Heeger model to explain qualitative features of the
size-dependence behavior of . Our study shows that is
{\it nonmonotonic} with and that the nonmonotonicity is caused by the
dominant contribution of the intraband transition to in polyenes.
Several important physical effects are discussed to reduce quantitative
discrepancies between experimental and our resultsComment: 3 figures, 1 tabl
The X-ray afterglow of GRB 081109A: clue to the wind bubble structure
We present the prompt BAT and afterglow XRT data of Swift-discovered
GRB081109A up to ~ 5\times 10^5 sec after the trigger, and the early
ground-based optical follow-ups. The temporal and spectral indices of the X-ray
afterglow emission change remarkably. We interpret this as the GRB jet first
traversing the freely expanding supersonic stellar wind of the progenitor with
density varying as . Then after approximately 300 sec the
jet traverses into a region of apparent constant density similar to that
expected in the stalled-wind region of a stellar wind bubble or the
interstellar medium (ISM). The optical afterglow data are generally consistent
with such a scenario. Our best numerical model has a wind density parameter
{, a density of the stalled wind ,
and a transition radius cm}. Such a transition
radius is smaller than that predicted by numerical simulations of the stellar
wind bubbles and may be due to a rapidly evolving wind of the progenitor close
to the time of its core-collapse.Comment: 7 pages, 5 figures, 2 tables, MNRAS accepted for publicatio
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