10,784 research outputs found
Efficient Image-Space Extraction and Representation of 3D Surface Topography
Surface topography refers to the geometric micro-structure of a surface and
defines its tactile characteristics (typically in the sub-millimeter range).
High-resolution 3D scanning techniques developed recently enable the 3D
reconstruction of surfaces including their surface topography. In his paper, we
present an efficient image-space technique for the extraction of surface
topography from high-resolution 3D reconstructions. Additionally, we filter
noise and enhance topographic attributes to obtain an improved representation
for subsequent topography classification. Comprehensive experiments show that
the our representation captures well topographic attributes and significantly
improves classification performance compared to alternative 2D and 3D
representations.Comment: Initial version of the paper accepted at the IEEE ICIP Conference
201
Dynamics of symmetry breaking during quantum real-time evolution in a minimal model system
One necessary criterion for the thermalization of a nonequilibrium quantum
many-particle system is ergodicity. It is, however, not sufficient in case
where the asymptotic long-time state lies in a symmetry-broken phase but the
initial state of nonequilibrium time evolution is fully symmetric with respect
to this symmetry. In equilibrium one particular symmetry-broken state is chosen
due to the presence of an infinitesimal symmetry-breaking perturbation. We
study the analogous scenario from a dynamical point of view: Can an
infinitesimal symmetry-breaking perturbation be sufficient for the system to
establish a nonvanishing order during quantum real-time evolution? We study
this question analytically for a minimal model system that can be associated
with symmetry breaking, the ferromagnetic Kondo model. We show that after a
quantum quench from a completely symmetric state the system is able to break
its symmetry dynamically and discuss how these features can be observed
experimentally.Comment: 4+3 pages, 3 figures, minor change
Diffusion of a sphere in a dilute solution of polymer coils
We calculate the short time and the long time diffusion coefficient of a
spherical tracer particle in a polymer solution in the low density limit by
solving the Smoluchowski equation for a two-particle system and applying a
generalized Einstein relation (fluctuation dissipation theorem). The tracer
particle as well as the polymer coils are idealized as hard spheres with a
no-slip boundary condition for the solvent but the hydrodynamic radius of the
polymer coils is allowed to be smaller than the direct-interaction radius. We
take hydrodynamic interactions up to 11th order in the particle distance into
account. For the limit of small polymers, the expected generalized
Stokes-Einstein relation is found. The long time diffusion coefficient also
roughly obeys the generalized Stokes-Einstein relation for larger polymers
whereas the short time coefficient does not. We find good qualitative and
quantitative agreement to experiments.Comment: 9 Pages, 6 Figures, J. Chem. Phys. (in print
Oaxaca/Blinder decompositions for nonlinear models
This paper describes the estimation of a general Blinder–Oaxaca decomposition of the mean outcome differential of linear and nonlinear regression models. Departing from this general model, we show how it can be applied to different models with discrete and limited dependent variables.
Three discontinuous Galerkin schemes for the anisotropic heat conduction equation on non-aligned grids
We present and discuss three discontinuous Galerkin (dG) discretizations for
the anisotropic heat conduction equation on non-aligned cylindrical grids. Our
most favourable scheme relies on a self-adjoint local dG (LDG) discretization
of the elliptic operator. It conserves the energy exactly and converges with
arbitrary order. The pollution by numerical perpendicular heat fluxes degrades
with superconvergence rates. We compare this scheme with aligned schemes that
are based on the flux-coordinate independent approach for the discretization of
parallel derivatives. Here, the dG method provides the necessary interpolation.
The first aligned discretization can be used in an explicit time-integrator.
However, the scheme violates conservation of energy and shows up stagnating
convergence rates for very high resolutions. We overcome this partly by using
the adjoint of the parallel derivative operator to construct a second
self-adjoint aligned scheme. This scheme preserves energy, but reveals
unphysical oscillations in the numerical tests, which result in a decreased
order of convergence. Both aligned schemes exhibit low numerical heat fluxes
into the perpendicular direction. We build our argumentation on various
numerical experiments on all three schemes for a general axisymmetric magnetic
field, which is closed by a comparison to the aligned finite difference (FD)
schemes of References [1,2
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