272 research outputs found
Three dimensional photonic Dirac points in metamaterials
Topological semimetals, representing a new topological phase that lacks a
full bandgap in bulk states and exhibiting nontrivial topological orders,
recently have been extended to photonic systems, predominantly in photonic
crystals and to a lesser extent, metamaterials. Photonic crystal realizations
of Dirac degeneracies are protected by various space symmetries, where Bloch
modes span the spin and orbital subspaces. Here, we theoretically show that
Dirac points can also be realized in effective media through the intrinsic
degrees of freedom in electromagnetism under electromagnetic duality. A pair of
spin polarized Fermi arc like surface states is observed at the interface
between air and the Dirac metamaterials. These surface states show linear
k-space dispersion relation, resulting in nearly diffraction-less propagation.
Furthermore, eigen reflection fields show the decomposition from a Dirac point
to two Weyl points. We also find the topological correlation between a Dirac
point and vortex/vector beams in classic photonics. The theoretical proposal of
photonic Dirac point lays foundation for unveiling the connection between
intrinsic physics and global topology in electromagnetism.Comment: 15 pages, 5 figure
Mass Transfer Performance of a Water-Sparged Aerocyclone Reactor and Its Application in Wastewater Treatment
Phenomenological modeling of Geometric Metasurfaces
Metasurfaces, with their superior capability in manipulating the optical
wavefront at the subwavelength scale and low manufacturing complexity, have
shown great potential for planar photonics and novel optical devices. However,
vector field simulation of metasurfaces is so far limited to
periodic-structured metasurfaces containing a small number of meta-atoms in the
unit cell by using full-wave numerical methods. Here, we propose a general
phenomenological method to analytically model metasurfaces made up of
arbitrarily distributed meta-atoms based on the assumption that the meta-atoms
possess localized resonances with Lorentz-Drude forms, whose exact form can be
retrieved from the full wave simulation of a single element. Applied to phase
modulated geometric metasurfaces, our analytical results show good agreement
with full-wave numerical simulations. The proposed theory provides an efficient
method to model and design optical devices based on metasurfaces.Comment: 16 pages, 8 figure
Towards Large-Scale Small Object Detection: Survey and Benchmarks
With the rise of deep convolutional neural networks, object detection has
achieved prominent advances in past years. However, such prosperity could not
camouflage the unsatisfactory situation of Small Object Detection (SOD), one of
the notoriously challenging tasks in computer vision, owing to the poor visual
appearance and noisy representation caused by the intrinsic structure of small
targets. In addition, large-scale dataset for benchmarking small object
detection methods remains a bottleneck. In this paper, we first conduct a
thorough review of small object detection. Then, to catalyze the development of
SOD, we construct two large-scale Small Object Detection dAtasets (SODA),
SODA-D and SODA-A, which focus on the Driving and Aerial scenarios
respectively. SODA-D includes 24828 high-quality traffic images and 278433
instances of nine categories. For SODA-A, we harvest 2513 high resolution
aerial images and annotate 872069 instances over nine classes. The proposed
datasets, as we know, are the first-ever attempt to large-scale benchmarks with
a vast collection of exhaustively annotated instances tailored for
multi-category SOD. Finally, we evaluate the performance of mainstream methods
on SODA. We expect the released benchmarks could facilitate the development of
SOD and spawn more breakthroughs in this field. Datasets and codes are
available at: \url{https://shaunyuan22.github.io/SODA}
N-alkanes phase change materials and their microencapsulation for thermal energy storage::A critical review
Mass Transfer Performance of a Water-Sparged Aerocyclone Reactor and Its Application in Wastewater Treatment
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