7,669 research outputs found
Linear, third- and fifth-order nonlinear spectroscopy of a charge transfer system coupled to an underdamped vibration
We study hole, electron and exciton transport in a charge transfer system in
the presence of underdamped vibrational motion. We analyze the signature of
these processes in the linear and third-, and fifth-order nonlinear electronic
spectra. Calculations are performed with a numerically exact hierarchical
equations of motion method for an underdamped Brownian oscillator spectral
density. We find that combining electron, hole and exciton transfer can lead to
non-trivial spectra with more structure than with excitonic coupling alone.
Traces taken during the waiting time of a two-dimensional spectrum are
dominated by vibrational motion and do not reflect the electron, hole, and
exciton dynamics directly. We find that the fifth-order nonlinear response is
particularly sensitive to the charge transfer process. While third-order 2D
spectroscopy detects the correlation between two coherences, fifth-order 2D
spectroscopy (2D population spectroscopy) is here designed to detect
correlations between the excited states during two different time periods
Correlated fluctuations in the exciton dynamics and spectroscopy of DNA
The absorption of ultraviolet light creates excitations in DNA, which
subsequently start moving in the helix. Their fate is important for an
understanding of photo damage, and is determined by the interplay of electronic
couplings between bases and the structure of the DNA environment. We model the
effect of dynamical fluctuations in the environment and study correlation,
which is present when multiple base pairs interact with the same mode in the
environment. We find that the correlations strongly affect the exciton
dynamics, and show how they are observed in the decay of the anisotropy as a
function of a coherence and a population time in a non-linear optical
experiment
Quantitative Inter-channel Calibration of SHOALS Signals for Consistent Bottom Segmentation and Characterization
Predicting the Success of Invasive Species in the Great Bay Estuarine Researve
The University of New Hampshire Zoology Department reports on a study designed to continue monitoring the distribution of invasive species in the Great Bay Estuary and to carry out laboratory experiments designed to test the effects of salinity on ascidian mortality and determine predators of ascidian species. Researchers collected presence/absence and abundance data of invasive species at four sites within the Great Bay Estuarine System. The report gives a brief description of the results of the monitoring program to compare results obtained from 2006 to 2007 and to assess the response of ascidians to varying salinity and predators. This report specifically includes monitoring data from 2007 and results of laboratory and field experiments examining the effects of salinity and predators on ascidian distribution
Does settlement plate material matter? The influence of substrate type on fouling community development
Benthic community composition and ascidian abundance can differ dramatically between adjacent man-made and natural substrates. Although multiple factors, including light exposure, surface orientation, predation exposure, and habitat type, are known to contribute to these patterns, few studies have directly tested the influence of substrate identity on community development. We compared fouling communities on settlement plates composed of commonly occurring natural (granite) and artificial (concrete, high density polyethylene, and PVC) marine materials deployed from late May to mid November 2014 from a floating dock in Newcastle, NH. We sought to determine if observed patterns resulted from differential recruitment onto substrate materials or post-settlement survival and growth. To do this, half of the plates were cleaned during bi-weekly examinations, and half were left un-cleaned. Preliminary analyses indicate that community composition differs between substrate types. These results will help us understand how substrate features contribute to non-native species establishment and habitat dominance, and may inform decisions regarding material usage in marine construction. These findings also underline the importance of settlement substrate choice in scientific studies, as plate material may influence experimental conclusions
On finite-size Lyapunov exponents in multiscale systems
We study the effect of regime switches on finite size Lyapunov exponents
(FSLEs) in determining the error growth rates and predictability of multiscale
systems. We consider a dynamical system involving slow and fast regimes and
switches between them. The surprising result is that due to the presence of
regimes the error growth rate can be a non-monotonic function of initial error
amplitude. In particular, troughs in the large scales of FSLE spectra is shown
to be a signature of slow regimes, whereas fast regimes are shown to cause
large peaks in the spectra where error growth rates far exceed those estimated
from the maximal Lyapunov exponent. We present analytical results explaining
these signatures and corroborate them with numerical simulations. We show
further that these peaks disappear in stochastic parametrizations of the fast
chaotic processes, and the associated FSLE spectra reveal that large scale
predictability properties of the full deterministic model are well approximated
whereas small scale features are not properly resolved.Comment: Accepted for publication in Chao
An efficient tool to calculate two-dimensional optical spectra for photoactive molecular complexes
We combine the coherent modified Redfield theory (CMRT) with the equation of
motion-phase matching approach (PMA) to calculate two-dimensional photon echo
spectra for photoactive molecular complexes with an intermediate strength of
the coupling to their environment. Both techniques are highly efficient, yet
they involve approximations at different levels. By explicitly comparing with
the numerically exact quasi-adiabatic path integral approach, we show for the
Fenna-Matthews-Olson complex that the CMRT describes the decay rates in the
population dynamics well, but final stationary populations and the oscillation
frequencies differ slightly. In addition, we use the combined CMRT+PMA to
calculate two-dimensional photon-echo spectra for a simple dimer model. We find
excellent agreement with the exact path integral calculations at short waiting
times where the dynamics is still coherent. For long waiting times, differences
occur due to different final stationary states, specifically for strong
system-bath coupling. For weak to intermediate system-bath couplings, which is
most important for natural photosynthetic complexes, the combined CMRT+PMA
gives reasonable results with acceptable computational efforts
Coherent exciton dynamics in the presence of underdamped vibrations
Recent ultrafast optical experiments show that excitons in large biological
light-harvesting complexes are coupled to molecular vibration modes. These
high-frequency vibrations will not only affect the optical response, but also
drive the exciton transport. Here, using a model dimer system, the frequency of
the underdamped vibration is shown to have a strong effect on the exciton
dynamics such that quantum coherent oscillations in the system can be present
even in the case of strong noise. Two mechanisms are identified to be
responsible for the enhanced transport efficiency: critical damping due to the
tunable effective strength of the coupling to the bath, and resonance coupling
where the vibrational frequency coincides with the energy gap in the system.
The interplay of these two mechanisms determines parameters responsible for the
most efficient transport, and these optimal control parameters are comparable
to those in realistic light-harvesting complexes. Interestingly, oscillations
in the excitonic coherence at resonance are suppressed in comparison to the
case of an off-resonant vibration
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