15,038 research outputs found
Coherence and Decoherence in Biological Systems: Principles of Noise Assisted Transport and the Origin of Long-lived Coherences
The quantum dynamics of transport networks in the presence of noisy
environments have recently received renewed attention with the discovery of
long-lived coherences in different photosynthetic complexes. This experimental
evidence has raised two fundamental questions: Firstly, what are the mechanisms
supporting long-lived coherences and secondly, how can we assess the possible
functional role that the interplay of noise and quantum coherence might play in
the seemingly optimal operation of biological systems under natural conditions?
Here we review recent results, illuminate them at the hand of two paradigmatic
systems, the Fenna-Matthew-Olson (FMO) complex and the light harvesting complex
LHII, and present new progress on both questions. In particular we introduce
the concept of the phonon antennae and discuss the possible microscopic origin
or long-lived electronic coherences.Comment: Paper delivered at the Royal Society Discussion Meeting
"Quantum-coherent energy transfer: implications for biology and new energy
technologies", 27 - 28 April 2011 at The Kavli Royal Society International
Centre, Buckinghamshire, UK. Accepted for publication in Philosophical
Transactions of the Royal Society
Spectrally selective fluorescence imaging of Chlorobaculum tepidum reaction centers conjugated to chelator-modified silver nanowires
A polyhistidine tag (His-tag) present on Chlorobaculum tepidum reaction centers (RCs) was used to immobilize photosynthetic complexes on a silver nanowire (AgNW) modified with nickel-chelating nitrilo-triacetic acid (Ni-NTA). The optical properties of conjugated nanostructures were studied using wide-field and confocal fluorescence microscopy. Plasmonic enhancement of RCs conjugated to AgNWs was observed as their fluorescence intensity dependence on the excitation wavelength does not follow the excitation spectrum of RC complexes in solution. The strongest effect of plasmonic interactions on the emission intensity of RCs coincides with the absorption spectrum of AgNWs and is observed for excitation into the carotenoid absorption. From the absence of fluorescence decay shortening, we attribute the emission enhancement to increase of absorption in RC complexes
Dynamical Systems on Networks: A Tutorial
We give a tutorial for the study of dynamical systems on networks. We focus
especially on "simple" situations that are tractable analytically, because they
can be very insightful and provide useful springboards for the study of more
complicated scenarios. We briefly motivate why examining dynamical systems on
networks is interesting and important, and we then give several fascinating
examples and discuss some theoretical results. We also briefly discuss
dynamical systems on dynamical (i.e., time-dependent) networks, overview
software implementations, and give an outlook on the field.Comment: 39 pages, 1 figure, submitted, more examples and discussion than
original version, some reorganization and also more pointers to interesting
direction
Kaluza-Klein Towers in the Early Universe: Phase Transitions, Relic Abundances, and Applications to Axion Cosmology
We study the early-universe cosmology of a Kaluza-Klein (KK) tower of scalar
fields in the presence of a mass-generating phase transition, focusing on the
time-development of the total tower energy density (or relic abundance) as well
as its distribution across the different KK modes. We find that both of these
features are extremely sensitive to the details of the phase transition and can
behave in a variety of ways significant for late-time cosmology. In particular,
we find that the interplay between the temporal properties of the phase
transition and the mixing it generates are responsible for both enhancements
and suppressions in the late-time abundances, sometimes by many orders of
magnitude. We map out the complete model parameter space and determine where
traditional analytical approximations are valid and where they fail. In the
latter cases we also provide new analytical approximations which successfully
model our results. Finally, we apply this machinery to the example of an
axion-like field in the bulk, mapping these phenomena over an enlarged axion
parameter space that extends beyond those accessible to standard treatments. An
important by-product of our analysis is the development of an alternate
"UV-based" effective truncation of KK theories which has a number of
interesting theoretical properties that distinguish it from the more
traditional "IR-based" truncation typically used in the extra-dimension
literature.Comment: 30 pages, LaTeX, 18 figures. Replaced to match published versio
Index to NASA Tech Briefs, 1975
This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs
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