10,753 research outputs found
Mining Point Cloud Local Structures by Kernel Correlation and Graph Pooling
Unlike on images, semantic learning on 3D point clouds using a deep network
is challenging due to the naturally unordered data structure. Among existing
works, PointNet has achieved promising results by directly learning on point
sets. However, it does not take full advantage of a point's local neighborhood
that contains fine-grained structural information which turns out to be helpful
towards better semantic learning. In this regard, we present two new operations
to improve PointNet with a more efficient exploitation of local structures. The
first one focuses on local 3D geometric structures. In analogy to a convolution
kernel for images, we define a point-set kernel as a set of learnable 3D points
that jointly respond to a set of neighboring data points according to their
geometric affinities measured by kernel correlation, adapted from a similar
technique for point cloud registration. The second one exploits local
high-dimensional feature structures by recursive feature aggregation on a
nearest-neighbor-graph computed from 3D positions. Experiments show that our
network can efficiently capture local information and robustly achieve better
performances on major datasets. Our code is available at
http://www.merl.com/research/license#KCNetComment: Accepted in CVPR'18. *indicates equal contributio
Observation of Quantized Hall Effect and Shubnikov-de Hass Oscillations in Highly Doped Bi2Se3: Evidence for Layered Transport of Bulk Carriers
Bi2Se3 is an important semiconductor thermoelectric material and a prototype
topological insulator. Here we report observation of Shubnikov-de Hass (SdH)
oscillations accompanied by quantized Hall resistances (Rxy) in highly-doped
n-type Bi2Se3 with bulk carrier concentrations of few 10^19 cm^-3. Measurements
under tilted magnetic fields show that the magnetotransport is 2D-like, where
only the c-axis component of the magnetic field controls the Landau level
formation. The quantized step size in 1/Rxy is found to scale with the sample
thickness, and average ~e2/h per quintuple layer (QL). We show that the
observed magnetotransport features do not come from the sample surface, but
arise from the bulk of the sample acting as many parallel 2D electron systems
to give a multilayered quantum Hall effect. Besides revealing a new electronic
property of Bi2Se3, our finding also has important implications for electronic
transport studies of topological insulator materials.Comment: accepted by Physical Review Letters (2012
Experimental study on discretely modulated continuous-variable quantum key distribution
We present a discretely modulated continuous-variable quantum key
distribution system in free space by using strong coherent states. The
amplitude noise in the laser source is suppressed to the shot-noise limit by
using a mode cleaner combined with a frequency shift technique. Also, it is
proven that the phase noise in the source has no impact on the final secret key
rate. In order to increase the encoding rate, we use broadband homodyne
detectors and the no-switching protocol. In a realistic model, we establish a
secret key rate of 46.8 kbits/s against collective attacks at an encoding rate
of 10 MHz for a 90% channel loss when the modulation variance is optimal.Comment: 7 pages,6 figure
Quantum Hall effect on centimeter scale chemical vapor deposited graphene films
We report observations of well developed half integer quantum Hall effect
(QHE) on mono layer graphene films of 7 mm \times 7 mm in size. The graphene
films are grown by chemical vapor deposition (CVD) on copper, then transferred
to SiO_{2} /Si substrates, with typical carrier mobilities \approx 4000 cm^{2}
/Vs. The large size graphene with excellent quality and electronic homogeneity
demonstrated in this work is promising for graphene-based quantum Hall
resistance standards, and can also facilitate a wide range of experiments on
quantum Hall physics of graphene and practical applications exploiting the
exceptional properties of graphene
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