343 research outputs found
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Pinning and depinning of a classic quasi-one-dimensional Wigner crystal in the presence of a constriction
We studied the dynamics of a quasi-one-dimensional chain-like system of
charged particles at low temperature, interacting through a screened Coulomb
potential in the presence of a local constriction. The response of the system
when an external electric field is applied was investigated. We performed
Langevin molecular dynamics simulations for different values of the driving
force and for different temperatures. We found that the friction together with
the constriction pins the particles up to a critical value of the driving
force. The system can depin \emph{elastically} or \emph{quasi-elastically}
depending on the strength of the constriction. The elastic (quasi-elastic)
depinning is characterized by a critical exponent
(). The dc conductivity is zero in the pinned regime, it has
non-ohmic characteristics after the activation of the motion and then it is
constant. Furthermore, the dependence of the conductivity with temperature and
strength of the constriction was investigated in detail. We found interesting
differences between the single and the multi-chain regimes as the temperature
is increased.Comment: 18 pages, 16 figures, accepted for publication in PR
Generalized Drude model: Unification of ballistic and diffusive electron transport
For electron transport in parallel-plane semiconducting structures, a model
is developed that unifies ballistic and diffusive transport and thus
generalizes the Drude model. The unified model is valid for arbitrary magnitude
of the mean free path and arbitrary shape of the conduction band edge profile.
Universal formulas are obtained for the current-voltage characteristic in the
nondegenerate case and for the zero-bias conductance in the degenerate case,
which describe in a transparent manner the interplay of ballistic and diffusive
transport. The semiclassical approach is adopted, but quantum corrections
allowing for tunneling are included. Examples are considered, in particular the
case of chains of grains in polycrystalline or microcrystalline semiconductors
with grain size comparable to, or smaller than, the mean free path. Substantial
deviations of the results of the unified model from those of the ballistic
thermionic-emission model and of the drift-diffusion model are found. The
formulation of the model is one-dimensional, but it is argued that its results
should not differ substantially from those of a fully three-dimensional
treatment.Comment: 14 pages, 5 figures, REVTEX file, to appear in J. Phys.: Condens.
Matte
Anomalous Drude Model
A generalization of the Drude model is studied. On the one hand, the free
motion of the particles is allowed to be sub- or superdiffusive; on the other
hand, the distribution of the time delay between collisions is allowed to have
a long tail and even a non-vanishing first moment. The collision averaged
motion is either regular diffusive or L\'evy-flight like. The anomalous
diffusion coefficients show complex scaling laws. The conductivity can be
calculated in the diffusive regime. The model is of interest for the
phenomenological study of electronic transport in quasicrystals.Comment: 4 pages, latex, 2 figures, to be published in Physical Review Letter
Directional statistics and filtering using libDirectional
In this paper, we present libDirectional, a MATLAB library for directional statistics and directional estimation. It supports a variety of commonly used distributions on the unit circle, such as the von Mises, wrapped normal, and wrapped Cauchy distributions. Furthermore, various distributions on higher-dimensional manifolds such as the unit hypersphere and the hypertorus are available. Based on these distributions, several recursive filtering algorithms in libDirectional allow estimation on these manifolds. The functionality is implemented in a clear, well-documented, and object-oriented structure that is both easy to use and easy to extend
Linear functional electromagnetic constitutive relations and plane waves in a hemihedral isotropic material
Optical activity induced by curvature in a gravitational pp-wave background
We study optical activity induced by curvature. The optical activity model we
present has two phenomenological gyration parameters, within which we analyze
three model cases, namely, an exactly integrable model, the Landau-Lifshitz
model and the Fedorov model, these latter two are solved in the short
wavelength approximation. The model background is a gravitational pp-wave. The
solutions show that the optical activity induced by curvature leads to Faraday
rotation.Comment: 16 pages, late
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