5,895 research outputs found
Nonequilibrium Phase Transitions in Directed Small-World Networks
Many social, biological, and economic systems can be approached by complex
networks of interacting units. The behaviour of several models on small-world
networks has recently been studied. These models are expected to capture the
essential features of the complex processes taking place on real networks like
disease spreading, formation of public opinion, distribution of wealth, etc. In
many of these systems relations are directed, in the sense that links only act
in one direction (outwards or inwards). We investigate the effect of directed
links on the behaviour of a simple spin-like model evolving on a small-world
network. We show that directed networks may lead to a highly nontrivial phase
diagram including first and second-order phase transitions out of equilibrium.Comment: 4 pages, RevTeX format, 4 postscript figs, uses eps
Lyapunov vectors and excited energy levels of the directed polymer in random media
The scaling behavior of the excited energy levels of the directed polymer in
random media is analyzed numerically. We find that the spatial correlations of
polymer energies scale as for small enough wavenumbers
with a nontrivial exponent . The equivalence between the
stochastic-field equation that describes the partition function of the directed
polymer and that governing the time evolution of infinitesimal perturbations in
space-time chaos is exploited to connect this exponent with the
spatial correlations of Lyapunov vectors reported in the literature. The
relevance of our results for other problems involving optimization in random
systems is discussed
Oblique surface waves at an interface of metal-dielectric superlattice and isotropic dielectric
We investigate the existence and the dispersion characteristics of surface
waves that propagate at an interface between metal-dielectric superlattice and
isotropic dielectric. Within the long wavelength limit, when the
effective-medium approximation is valid, the superlattice behaves like a
uniaxial plasmonic crystal with the main optical axes perpendicular to the
metal-dielectric interfaces. We demonstrate that if such a semi-infinite
plasmonic crystal is cut normally to the layer interfaces and brought into the
contact with semi-infinite dielectric, a new type of surface modes can appear.
The propagation of such modes obliquely to the optical axes occurs under
favorable conditions that regard thicknesses of the layers, as well as the
proper choice of dielectric permittivity of the constituent materials. We show
that losses within the metallic layers can be substantially reduced by making
the layers sufficiently thin. At the same time, a dramatic enlargement of the
range of angles for oblique propagation of the new surface modes is observed.
This can lead, however, to the field non-locality and consequently to the
failure of the effective-medium approximation.Comment: 4 pages, 3 figure
NR-SLAM: Non-Rigid Monocular SLAM
In this paper we present NR-SLAM, a novel non-rigid monocular SLAM system
founded on the combination of a Dynamic Deformation Graph with a Visco-Elastic
deformation model. The former enables our system to represent the dynamics of
the deforming environment as the camera explores, while the later allows us to
model general deformations in a simple way. The presented system is able to
automatically initialize and extend a map modeled by a sparse point cloud in
deforming environments, that is refined with a sliding-window Deformable Bundle
Adjustment. This map serves as base for the estimation of the camera motion and
deformation and enables us to represent arbitrary surface topologies,
overcoming the limitations of previous methods. To assess the performance of
our system in challenging deforming scenarios, we evaluate it in several
representative medical datasets. In our experiments, NR-SLAM outperforms
previous deformable SLAM systems, achieving millimeter reconstruction accuracy
and bringing automated medical intervention closer. For the benefit of the
community, we make the source code public.Comment: 12 pages, 7 figures, submited to the IEEE Transactions on Robotics
(T-RO
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