54,490 research outputs found
From 3D Point Clouds to Pose-Normalised Depth Maps
We consider the problem of generating either pairwise-aligned or pose-normalised depth maps from noisy 3D point clouds in a relatively unrestricted poses. Our system is deployed in a 3D face alignment application and consists of the following four stages: (i) data filtering, (ii) nose tip identification and sub-vertex localisation, (iii) computation of the (relative) face orientation, (iv) generation of either a pose aligned or a pose normalised depth map. We generate an implicit radial basis function (RBF) model of the facial surface and this is employed within all four stages of the process. For example, in stage (ii), construction of novel invariant features is based on sampling this RBF over a set of concentric spheres to give a spherically-sampled RBF (SSR) shape histogram. In stage (iii), a second novel descriptor, called an isoradius contour curvature signal, is defined, which allows rotational alignment to be determined using a simple process of 1D correlation. We test our system on both the University of York (UoY) 3D face dataset and the Face Recognition Grand Challenge (FRGC) 3D data. For the more challenging UoY data, our SSR descriptors significantly outperform three variants of spin images, successfully identifying nose vertices at a rate of 99.6%. Nose localisation performance on the higher quality FRGC data, which has only small pose variations, is 99.9%. Our best system successfully normalises the pose of 3D faces at rates of 99.1% (UoY data) and 99.6% (FRGC data)
The formation of spiral arms and rings in barred galaxies
We propose a theory to explain the formation of both spirals and rings in
barred galaxies using a common dynamical framework. It is based on the orbital
motion driven by the unstable equilibrium points of the rotating bar potential.
Thus, spirals, rings and pseudo-rings are related to the invariant manifolds
associated to the periodic orbits around these equilibrium points. We examine
the parameter space of three barred galaxy models and discuss the formation of
the different morphological structures according to the properties of the bar
model. We also study the influence of the shape of the rotation curve in the
outer parts, by making families of models with rising, flat or falling rotation
curves in the outer parts. The differences between spiral and ringed structures
arise from differences in the dynamical parameters of the host galaxies.Comment: 6 pages, 3 figures, conference proceedings of "Semaine de
l'Astrophysique Francaise", Grenoble 2007, eds. J. Bouvier, A. Chalabaev, C.
Charbonne
Efficient harmonic oscillator chain energy harvester driven by colored noise
We study the performance of an electromechanical harmonic oscillator chain as
an energy harvester to extract power from finite-bandwidth ambient random
vibrations, which are modelled by colored noise. The proposed device is
numerically simulated and its performance assessed by means of the net
electrical power generated and its efficiency in converting the external
noise-supplied power into electrical power. Our main result is a much enhanced
performance, both in the net electrical power delivered and in efficiency, of
the harmonic chain with respect to the popular single oscillator resonator. Our
numerical findings are explained by means of an analytical approximation, in
excellent agreement with numerics
The Directed Closure Process in Hybrid Social-Information Networks, with an Analysis of Link Formation on Twitter
It has often been taken as a working assumption that directed links in
information networks are frequently formed by "short-cutting" a two-step path
between the source and the destination -- a kind of implicit "link copying"
analogous to the process of triadic closure in social networks. Despite the
role of this assumption in theoretical models such as preferential attachment,
it has received very little direct empirical investigation. Here we develop a
formalization and methodology for studying this type of directed closure
process, and we provide evidence for its important role in the formation of
links on Twitter. We then analyze a sequence of models designed to capture the
structural phenomena related to directed closure that we observe in the Twitter
data
Scanning tunneling microscopy of adsorbed molecules on metalic surfaces for nearly localized atomic states
We consider a Hubbard-Anderson model which describes localized orbitals in
five different sites hybridized both among themselves and with a continuum of
extended states. A square planar geometry with an atom at the center is used to
represent TBrPP-Co molecules. When the renormalized effective hopping between
sites is small compared with a Kondo energy scale determined by the
sitecontinuum hybridization, the system can be described as a set of
independent Kondo resonances, rather than molecular states. We study the
crossover between both regimes and analyze the spectral density of conduction
electrons as a function of position. The results are in qualitative agreement
with measurements of the differential conductance in a system with TBrPP-Co
molecules adsorbed on a Cu(111) surface.Comment: 5 pages, 4 figure
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