4,546 research outputs found
Tunable Unidirectional Sound Propagation through a Sonic-Crystal-Based Acoustic Diode
Nonreciprocal wave propagation typically requires strong nonlinear materials to break time reversal symmetry. Here, we utilized a
sonic-crystal-based acoustic diode that had broken spatial inversion
symmetry and experimentally realized sound unidirectional transmission
in this acoustic diode. These novel phenomena are attributed to
different mode transitions as well as their associated different energy
conversion efficiencies among different diffraction orders at two sides
of the diode. This nonreciprocal sound transmission could be
systematically controlled by simply mechanically rotating the square
rods of the sonic crystal. Different from nonreciprocity due to the
nonlinear acoustic effect and broken time reversal symmetry, this new
model leads to a one-way effect with higher efficiency, broader
bandwidth, and much less power consumption, showing promising
applications in various sound devices
Quantum Spin Liquid with Even Ising Gauge Field Structure on Kagome Lattice
Employing large-scale quantum Monte Carlo simulations, we study the extended
model on the kagome lattice. A quantum spin liquid phase
with effective even Ising gauge field structure emerges from the delicate
balance among three symmetry-breaking phases including stripe solid, staggered
solid and ferromagnet. This spin liquid is stabilized by an
extended interaction related to the Rokhsar-Kivelson potential in the quantum
dimer model limit. The phase transitions from the staggered solid to a spin
liquid or ferromagnet are found to be first order and so is the transition
between the stripe solid and ferromagnet. However, the transition between a
spin liquid and ferromagnet is found to be continuous and belongs to the 3D
universality class associated with the condensation of spinons. The
transition between a spin liquid and stripe solid appears to be continuous and
associated with the condensation of visons.Comment: 7 pages, 8 figure
15α,20β-Dihydroxy-6β-methoxy-6,7-seco-6,20-epoxy-1,7-olide-ent-kaur-16-ene
The title compound, C21H30O6, a natural ent-kaurane diterpenoid, was obtained from the medicinal plant Isodon serra. The five rings in the molecule exhibit the expected cis and trans junctions. The three six-membered rings adopt chair, twist-boat and boat conformations, while two five-membered rings adopt envelope conformations. There are two molecules in the asymmetric unit, related by a non-crystallographic twofold screw axis; the main difference is in the different degrees of distortion of ring B. In the crystal, the molecules are linked by intermolecular O—H⋯O hydrogen bonds, forming chains along the b axis
A double neutron star merger origin for the cosmological relativistic fading source PTF11agg?
The Palomar Transient Factory (PTF) team recently reported the discovery of a
rapidly fading optical transient source, PTF11agg. A long-lived scintillating
radio counterpart was identified, but the search for a high energy counterpart
showed negative results. The PTF team speculated that PTF11agg may represent a
new class of relativistic outbursts. Here we suggest that a neutron star
(NS)-NS merger system with a supra-massive magnetar central engine could be a
possible source to power such a transient, if our line of sight is not on the
jet axis direction of the system. These systems are also top candidates for
gravitational wave sources to be detected in the advanced LIGO/Virgo era. We
find that the PTF11agg data could be explained well with such a model,
suggesting that at least some gravitational wave bursts due to NS-NS mergers
may be associated with such a bright electromagnetic counterpart without a
\gamma-ray trigger.Comment: Accepted for publication in ApJ Letter
R3Det: Refined Single-Stage Detector with Feature Refinement for Rotating Object
Rotation detection is a challenging task due to the difficulties of locating
the multi-angle objects and separating them effectively from the background.
Though considerable progress has been made, for practical settings, there still
exist challenges for rotating objects with large aspect ratio, dense
distribution and category extremely imbalance. In this paper, we propose an
end-to-end refined single-stage rotation detector for fast and accurate object
detection by using a progressive regression approach from coarse to fine
granularity. Considering the shortcoming of feature misalignment in existing
refined single-stage detector, we design a feature refinement module to improve
detection performance by getting more accurate features. The key idea of
feature refinement module is to re-encode the position information of the
current refined bounding box to the corresponding feature points through
pixel-wise feature interpolation to realize feature reconstruction and
alignment. For more accurate rotation estimation, an approximate SkewIoU loss
is proposed to solve the problem that the calculation of SkewIoU is not
derivable. Experiments on three popular remote sensing public datasets DOTA,
HRSC2016, UCAS-AOD as well as one scene text dataset ICDAR2015 show the
effectiveness of our approach. Tensorflow and Pytorch version codes are
available at https://github.com/Thinklab-SJTU/R3Det_Tensorflow and
https://github.com/SJTU-Thinklab-Det/r3det-on-mmdetection, and R3Det is also
integrated in our open source rotation detection benchmark:
https://github.com/yangxue0827/RotationDetection.Comment: 13 pages, 12 figures, 9 table
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