5,240 research outputs found
Langevin approach to generate synthetic turbulence
We present an analytical scheme, easily implemented numerically, to generate
synthetic Gaussian turbulent flows by using a linear Langevin equation, where
the noise term acts as a stochastic stirring force. The characteristic
parameters of the velocity field are well introduced, in particular the
kinematic viscosity and the spectrum of energy. As an application, the
diffusion of a passive scalar is studied for two different energy spectra.
Numerical results are compared favorably with analytical calculations.Comment: 7 pages, REVTEX, 6 figures. To appear in Physics of Fluids (April
1997
Front dynamics in turbulent media
A study of a stable front propagating in a turbulent medium is presented. The
front is generated through a reaction-diffusion equation, and the turbulent
medium is statistically modeled using a Langevin equation. Numerical
simulations indicate the presence of two different dynamical regimes. These
regimes appear when the turbulent flow either wrinkles a still rather sharp
propagating interfase or broadens it. Specific dependences of the propagating
velocities on stirring intensities appropriate to each case are found and
fitted when possible according to theoretically predicted laws. Different
turbulent spectra are considered.Comment: 8 pages, REVTEX, 6 postscript figures included. To appear in Phys.
Fluids (1997
Nonequilibrium transitions induced by multiplicative noise
A new simple model exhibiting a noise-induced ordering transition (NIOT) and
a noise-induced disordering transition (NIDT), in which the noise is purely
multiplicative, is presented. Both transitions are found in two as well as in
one dimension (where they had not been previously reported). We show
analytically and numerically that the critical behavior of these two
transitions is described by the so called multiplicative noise(MN) universality
class. A computation of the set of critical exponents is presented in both
, and (where they have not been previously measured).Comment: 4 pages, 2 figures, Late
Heat Fluctuations in Brownian Transducers
Heat fluctuation probability distribution function in Brownian transducers
operating between two heat reservoirs is studied. We find, both analytically
and numerically, that the recently proposed Fluctuation Theorem for Heat
Exchange [C. Jarzynski and D. K. Wojcik, Phys. Rev. Lett. 92, 230602 (2004)]
has to be modified when the coupling mechanism between both baths is
considered. We also extend such relation when external work is present. Our
work fixes the domain of applicability of the theorem in more realistic
operating systems.Comment: Comments are welcom
White noise flashing Brownian pump
A Brownian pump of particles powered by a stochastic flashing ratchet
mechanism is studied. The pumping device is embedded in a finite region and
bounded by particle reservoirs. In the steady state, we exactly calculate the
spatial density profile, the concentration ratio between both reservoirs and
the particle flux. A simple numerical scheme is presented allowing for the
consistent evaluation of all such observable quantities
The effect of vacancy-induced magnetism on electronic transport in armchair carbon nanotubes
The influence of local magnetic moment formation around three kinds of
vacancies on the electron conduction through metallic single-wall carbon
nanotubes is studied by use of the Landauer formalism within the coherent
regime. The method is based on the single-band tight-binding Hamiltonian, a
surface Green's function calculation, and the mean-field Hubbard model. The
numerical results show that the electronic transport is spin-polarized due to
the localized magnetic moments and it is strongly dependent on the geometry of
the vacancies. For all kinds of vacancies, by including the effects of local
magnetic moments, the electron scattering increases with respect to the
nonmagnetic vacancies case and hence, the current-voltage characteristic of the
system changes. In addition, a high value for the electron-spin polarization
can be obtained by applying a suitable gate voltage.Comment: 6 pages, 6 figure
Weak disorder: anomalous transport and diffusion are normal yet again
Particles driven through a periodic potential by an external constant force
are known to exhibit a pronounced peak of the diffusion around a critical force
that defines the transition between locked and running states. It has recently
been shown both experimentally and numerically that this peak is greatly
enhanced if some amount of spatial disorder is superimposed on the periodic
potential. Here we show that beyond a simple enhancement lies a much more
interesting phenomenology. For some parameter regimes the system exhibits a
rich variety of behaviors from normal diffusion to superdiffusion, subdiffusion
and even subtransport.Comment: Substantial improvements in presentatio
Transverse transport in graphite
Graphite is a layered material showing a strong anisotropy. Among the
unconventional properties reported by experiments, the electronic transport
along the c-axis, which has direct implications in order to build graphitic
devices, remains a controversial topic. We study the influence of inelastic
scattering on the electron tunnelling between layers. In the presence of
electron electron interactions, tunnelling processes are modified by inelastic
scattering events.Comment: 9 pages, no figures Proceedings of the Graphene Conference, MPI PKS
Dresden, September 200
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