12,229 research outputs found
Temporally coherent 4D reconstruction of complex dynamic scenes
This paper presents an approach for reconstruction of 4D temporally coherent
models of complex dynamic scenes. No prior knowledge is required of scene
structure or camera calibration allowing reconstruction from multiple moving
cameras. Sparse-to-dense temporal correspondence is integrated with joint
multi-view segmentation and reconstruction to obtain a complete 4D
representation of static and dynamic objects. Temporal coherence is exploited
to overcome visual ambiguities resulting in improved reconstruction of complex
scenes. Robust joint segmentation and reconstruction of dynamic objects is
achieved by introducing a geodesic star convexity constraint. Comparative
evaluation is performed on a variety of unstructured indoor and outdoor dynamic
scenes with hand-held cameras and multiple people. This demonstrates
reconstruction of complete temporally coherent 4D scene models with improved
nonrigid object segmentation and shape reconstruction.Comment: To appear in The IEEE Conference on Computer Vision and Pattern
Recognition (CVPR) 2016 . Video available at:
https://www.youtube.com/watch?v=bm_P13_-Ds
Scaling of the CKM Matrix in the 5D MSSM
We discuss a five-dimensional Minimal Supersymmetric Standard Model
compactified on a orbifold, looking at, in particular, the one-loop
evolution equations of the Yukawa couplings for the quark sector and various
flavor observables. Different possibilities for the matter fields are
discussed, that is, where they are in the bulk or localised to the brane. The
two possibilities give rise to quite different behaviours. By studying the
implications of the evolution with the renormalisation group of the Yukawa
couplings and of the flavor observables we find that, for a theory that is
valid up to the unification scale, the case where fields are localised to the
brane, with a large , would be more easily distinguishable from
other scenarios.Comment: 12 pages, 8 figures, Extra comments adde
Bubbles and jackets: new scaling bounds in topological group field theories
We use a reformulation of topological group field theories in 3 and 4
dimensions in terms of variables associated to vertices, in 3d, and edges, in
4d, to obtain new scaling bounds for their Feynman amplitudes. In both 3 and 4
dimensions, we obtain a bubble bound proving the suppression of singular
topologies with respect to the first terms in the perturbative expansion (in
the cut-off). We also prove a new, stronger jacket bound than the one currently
available in the literature. We expect these results to be relevant for other
tensorial field theories of this type, as well as for group field theory models
for 4d quantum gravity.Comment: v2: Minor modifications to match published versio
Scalable Full Flow with Learned Binary Descriptors
We propose a method for large displacement optical flow in which local
matching costs are learned by a convolutional neural network (CNN) and a
smoothness prior is imposed by a conditional random field (CRF). We tackle the
computation- and memory-intensive operations on the 4D cost volume by a
min-projection which reduces memory complexity from quadratic to linear and
binary descriptors for efficient matching. This enables evaluation of the cost
on the fly and allows to perform learning and CRF inference on high resolution
images without ever storing the 4D cost volume. To address the problem of
learning binary descriptors we propose a new hybrid learning scheme. In
contrast to current state of the art approaches for learning binary CNNs we can
compute the exact non-zero gradient within our model. We compare several
methods for training binary descriptors and show results on public available
benchmarks.Comment: GCPR 201
Population growth and persistence in a heterogeneous environment: the role of diffusion and advection
The spatio-temporal dynamics of a population present one of the most
fascinating aspects and challenges for ecological modelling. In this article we
review some simple mathematical models, based on one dimensional
reaction-diffusion-advection equations, for the growth of a population on a
heterogeneous habitat. Considering a number of models of increasing complexity
we investigate the often contrary roles of advection and diffusion for the
persistence of the population. When it is possible we demonstrate basic
mathematical techniques and give the critical conditions providing the survival
of a population, in simple systems and in more complex resource-consumer models
which describe the dynamics of phytoplankton in a water column.Comment: Introductory review of simple conceptual models. 45 pages, 15 figures
v2: minor change
Response of the Jovian thermosphere to a transient ‘pulse’ in solar wind pressure
The importance of the Jovian thermosphere with regard to magnetosphere-ionosphere coupling is often neglected in magnetospheric physics. We present the first study to investigate the response of the Jovian thermosphere to transient variations in solar wind dynamic pressure, using an azimuthally symmetric global circulation model coupled to a simple magnetosphere and fixed auroral conductivity model. In our simulations, the Jovian magnetosphere encounters a solar wind shock or rarefaction region and is subsequently compressed or expanded. We present the ensuing response of the coupling currents, thermospheric flows, heating and cooling terms, and the aurora to these transient events. Transient compressions cause the reversal, with respect to steady state, of magnetosphere-ionosphere coupling currents and momentum transfer between the thermosphere and magnetosphere. They also cause at least a factor of two increase in the Joule heating rate. Ion drag significantly changes the kinetic energy of the thermospheric neutrals depending on whether the magnetosphere is compressed or expanded. Local temperature variations appear between View the MathML source for the compression scenario and View the MathML source for the expansion case. Extended regions of equatorward flow develop in the wake of compression events - we discuss the implications of this behaviour for global energy transport. Both compressions and expansions lead to a View the MathML source increase in the total power dissipated or deposited in the thermosphere. In terms of auroral processes, transient compressions increase main oval UV emission by a factor of ∼4.5 whilst transient expansions increase this main emission by a more modest 37%. Both types of transient event cause shifts in the position of the main oval, of up to 1° latitude
(3+1)-dimensional topological phases and self-dual quantum geometries encoded on Heegard surfaces
We apply the recently suggested strategy to lift state spaces and operators
for (2+1)-dimensional topological quantum field theories to state spaces and
operators for a (3+1)-dimensional TQFT with defects. We start from the
(2+1)-dimensional Turaev-Viro theory and obtain a state space, consistent with
the state space expected from the Crane-Yetter model with line defects. This
work has important applications for quantum gravity as well as the theory of
topological phases in (3+1) dimensions. It provides a self-dual quantum
geometry realization based on a vacuum state peaked on a homogeneously curved
geometry. The state spaces and operators we construct here provide also an
improved version of the Walker-Wang model, and simplify its analysis
considerably. We in particular show that the fusion bases of the
(2+1)-dimensional theory lead to a rich set of bases for the (3+1)-dimensional
theory. This includes a quantum deformed spin network basis, which in a loop
quantum gravity context diagonalizes spatial geometry operators. We also obtain
a dual curvature basis, that diagonalizes the Walker-Wang Hamiltonian.
Furthermore, the construction presented here can be generalized to provide
state spaces for the recently introduced dichromatic four-dimensional manifold
invariants.Comment: 27 pages, many figures, v2: minor correction
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