15,729 research outputs found
Highly-efficient noise-assisted energy transport in classical oscillator systems
Photosynthesis is a biological process that involves the highly-efficient
transport of energy captured from the sun to a reaction center, where
conversion into useful biochemical energy takes place. Even though one can
always use a quantum perspective to describe any physical process, since
everything follows the laws of Quantum Mechanics, is the use of quantum theory
imperative to explain this high efficiency? Making use of the quantum-classical
correspondence of electronic energy transfer recently introduced by Eisfeld and
Briggs [Phys. Rev. E 85, 046118 (2012)], we show here that the highly-efficient
noise-assisted energy transport described by Rebentrost et al. [New J. Phys.
11, 033003 (2009)], and Plenio and Huelga [New J. Phys. 10, 113019 (2008)], as
the result of the interplay between the quantum coherent evolution of the
photosynthetic system and noise introduced by its surrounding environment, it
can be found as well in purely classical systems. The wider scope of
applicability of the enhancement of energy transfer assisted by noise might
open new ways for developing new technologies aimed at enhancing the efficiency
of a myriad of energy transfer systems, from information channels in
micro-electronic circuits to long-distance high-voltage electrical lines.Comment: 4 pages, 3 figure
Statistical Entropy of Four-Dimensional Extremal Black Holes
String theory is used to count microstates of four-dimensional extremal black
holes in compactifications with and supersymmetry. The result
agrees for large charges with the Bekenstein-Hawking entropy.Comment: 4 pages, harvma
Predicting criticality and dynamic range in complex networks: effects of topology
The collective dynamics of a network of coupled excitable systems in response
to an external stimulus depends on the topology of the connections in the
network. Here we develop a general theoretical approach to study the effects of
network topology on dynamic range, which quantifies the range of stimulus
intensities resulting in distinguishable network responses. We find that the
largest eigenvalue of the weighted network adjacency matrix governs the network
dynamic range. Specifically, a largest eigenvalue equal to one corresponds to a
critical regime with maximum dynamic range. We gain deeper insight on the
effects of network topology using a nonlinear analysis in terms of additional
spectral properties of the adjacency matrix. We find that homogeneous networks
can reach a higher dynamic range than those with heterogeneous topology. Our
analysis, confirmed by numerical simulations, generalizes previous studies in
terms of the largest eigenvalue of the adjacency matrix.Comment: 4 pages, 3 figure
Dynamic facilitation explains democratic particle motion of metabasin transitions
Transitions between metabasins in supercooled liquids seem to occur through
rapid "democratic" collective particle rearrangements. Here we show that this
apparent homogeneous particle motion is a direct consequence of dynamic
facilitation. We do so by studying metabasin transitions in facilitated spin
models and constrained lattice gases. We find that metabasin transitions occur
through a sequence of locally facilitated events taking place over a relatively
short time frame. When observed on small enough spatial windows these events
appear sudden and homogeneous. Our results indicate that metabasin transitions
are essentially "non-democratic" in origin and yet another manifestation of
dynamical heterogeneity in glass formers.Comment: 6 pages, 6 figure
Glassy behaviour in an exactly solved spin system with a ferromagnetic transition
We show that applying simple dynamical rules to Baxter's eight-vertex model
leads to a system which resembles a glass-forming liquid. There are analogies
with liquid, supercooled liquid, glassy and crystalline states. The disordered
phases exhibit strong dynamical heterogeneity at low temperatures, which may be
described in terms of an emergent mobility field. Their dynamics are
well-described by a simple model with trivial thermodynamics, but an emergent
kinetic constraint. We show that the (second order) thermodynamic transition to
the ordered phase may be interpreted in terms of confinement of the excitations
in the mobility field. We also describe the aging of disordered states towards
the ordered phase, in terms of simple rate equations.Comment: 11 page
Visualizing the logistic map with a microcontroller
The logistic map is one of the simplest nonlinear dynamical systems that
clearly exhibit the route to chaos. In this paper, we explored the evolution of
the logistic map using an open-source microcontroller connected to an array of
light emitting diodes (LEDs). We divided the one-dimensional interval
into ten equal parts, and associated and LED to each segment. Every time an
iteration took place a corresponding LED turned on indicating the value
returned by the logistic map. By changing some initial conditions of the
system, we observed the transition from order to chaos exhibited by the map.Comment: LaTeX, 6 pages, 3 figures, 1 listin
Finite sampling effects on generalized fluctuation-dissipation relations for steady states
We study the effects of the finite number of experimental data on the
computation of a generalized fluctuation-dissipation relation around a
nonequilibrium steady state of a Brownian particle in a toroidal optical trap.
We show that the finite sampling has two different effects, which can give rise
to a poor estimate of the linear response function. The first concerns the
accessibility of the generalized fluctuation-dissipation relation due to the
finite number of actual perturbations imposed to the control parameter. The
second concerns the propagation of the error made at the initial sampling of
the external perturbation of the system. This can be highly enhanced by
introducing an estimator which corrects the error of the initial sampled
condition. When these two effects are taken into account in the data analysis,
the generalized fluctuation-dissipation relation is verified experimentally
Fast Simulation of Facilitated Spin Models
We show how to apply the absorbing Markov chain Monte Carlo algorithm of
Novotny to simulate kinetically constrained models of glasses. We consider in
detail one-spin facilitated models, such as the East model and its
generalizations to arbitrary dimensions. We investigate how to maximise the
efficiency of the algorithms, and show that simulation times can be improved on
standard continuous time Monte Carlo by several orders of magnitude. We
illustrate the method with equilibrium and aging results. These include a study
of relaxation times in the East model for dimensions d=1 to d=13, which
provides further evidence that the hierarchical relaxation in this model is
present in all dimensions. We discuss how the method can be applied to other
kinetically constrained models.Comment: 8 pages, 4 figure
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