2,169 research outputs found
Cold atom realizations of Brownian motors
Brownian motors are devices which "rectify" Brownian motion, i.e. they can
generate a current of particles out of unbiased fluctuations. Brownian motors
are important for the understanding of molecular motors, and are also promising
for the realization of new nanolelectronic devices. Among the different systems
that can be used to study Brownian motors, cold atoms in optical lattices are
quite an unusual one: there is no thermal bath and both the potential and the
fluctuations are determined by laser fields. In this article recent
experimental implementations of Brownian motors using cold atoms in optical
lattices are reviewed
Recombination in polymer-fullerene bulk heterojunction solar cells
Recombination of photogenerated charge carriers in polymer bulk
heterojunction (BHJ) solar cells reduces the short circuit current (Jsc) and
the fill factor (FF). Identifying the mechanism of recombination is, therefore,
fundamentally important for increasing the power conversion efficiency. Light
intensity and temperature dependent current-voltage measurements on polymer BHJ
cells made from a variety of different semiconducting polymers and fullerenes
show that the recombination kinetics are voltage dependent and evolve from
first order recombination at short circuit to bimolecular recombination at open
circuit as a result of increasing the voltage-dependent charge carrier density
in the cell. The "missing 0.3V" inferred from comparison of the band gaps of
the bulk heterojunction materials and the measured open circuit voltage at room
temperature results from the temperature dependence of the quasi-Fermi-levels
in the polymer and fullerene domains - a conclusion based upon the fundamental
statistics of Fermions.Comment: Accepted for publication in Physical Review B.
http://prb.aps.org/accepted/B/6b07cO3aHe71bd1b149e1425e58bf2868cda2384d?ajax=1&height=500&width=50
The effect of Coulombic friction on spatial displacement statistics
The phenomenon of Coulombic friction enters the stochastic description of dry
friction between two solids and the statistic characterization of vibrating
granular media. Here we analyze the corresponding Fokker-Planck equation
including both velocity and spatial components, exhibiting a formal connection
to a quantum mechanical harmonic oscillator in the presence of a delta
potential. Numerical solutions for the resulting spatial displacement
statistics show a crossover from exponential to Gaussian displacement
statistics. We identify a transient intermediate regime that exhibits
multiscaling properties arising from the contribution of Coulombic friction.
The possible role of these effects during observations in diffusion experiments
is shortly discussed.Comment: 11 pages, 9 figure
A New Partnership: The Society for Acupuncture Research and the Journal of Alternative and Complementary Medicine
published_or_final_versio
Anomalous diffusion in quantum Brownian motion with colored noise
Anomalous diffusion is discussed in the context of quantum Brownian motion
with colored noise. It is shown that earlier results follow simply and directly
from the fluctuation-dissipation theorem. The limits on the long-time
dependence of anomalous diffusion are shown to be a consequence of the second
law of thermodynamics. The special case of an electron interacting with the
radiation field is discussed in detail. We apply our results to wave-packet
spreading
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