302 research outputs found
Locality Preserving Projections for Grassmann manifold
Learning on Grassmann manifold has become popular in many computer vision
tasks, with the strong capability to extract discriminative information for
imagesets and videos. However, such learning algorithms particularly on
high-dimensional Grassmann manifold always involve with significantly high
computational cost, which seriously limits the applicability of learning on
Grassmann manifold in more wide areas. In this research, we propose an
unsupervised dimensionality reduction algorithm on Grassmann manifold based on
the Locality Preserving Projections (LPP) criterion. LPP is a commonly used
dimensionality reduction algorithm for vector-valued data, aiming to preserve
local structure of data in the dimension-reduced space. The strategy is to
construct a mapping from higher dimensional Grassmann manifold into the one in
a relative low-dimensional with more discriminative capability. The proposed
method can be optimized as a basic eigenvalue problem. The performance of our
proposed method is assessed on several classification and clustering tasks and
the experimental results show its clear advantages over other Grassmann based
algorithms.Comment: Accepted by IJCAI 201
Dual Grid Voltage Modulated Direct Power Control of Grid-Connected Voltage Source Converter under Unbalanced Network Condition
Realization of a three-dimensional photonic topological insulator
Confining photons in a finite volume is in high demand in modern photonic
devices. This motivated decades ago the invention of photonic crystals,
featured with a photonic bandgap forbidding light propagation in all
directions. Recently, inspired by the discoveries of topological insulators
(TIs), the confinement of photons with topological protection has been
demonstrated in two-dimensional (2D) photonic structures known as photonic TIs,
with promising applications in topological lasers and robust optical delay
lines. However, a fully three-dimensional (3D) topological photonic bandgap has
never before been achieved. Here, we experimentally demonstrate a 3D photonic
TI with an extremely wide (> 25% bandwidth) 3D topological bandgap. The sample
consists of split-ring resonators (SRRs) with strong magneto-electric coupling
and behaves as a 'weak TI', or a stack of 2D quantum spin Hall insulators.
Using direct field measurements, we map out both the gapped bulk bandstructure
and the Dirac-like dispersion of the photonic surface states, and demonstrate
robust photonic propagation along a non-planar surface. Our work extends the
family of 3D TIs from fermions to bosons and paves the way for applications in
topological photonic cavities, circuits, and lasers in 3D geometries
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