61,490 research outputs found
Counting with Focus for Free
This paper aims to count arbitrary objects in images. The leading counting
approaches start from point annotations per object from which they construct
density maps. Then, their training objective transforms input images to density
maps through deep convolutional networks. We posit that the point annotations
serve more supervision purposes than just constructing density maps. We
introduce ways to repurpose the points for free. First, we propose supervised
focus from segmentation, where points are converted into binary maps. The
binary maps are combined with a network branch and accompanying loss function
to focus on areas of interest. Second, we propose supervised focus from global
density, where the ratio of point annotations to image pixels is used in
another branch to regularize the overall density estimation. To assist both the
density estimation and the focus from segmentation, we also introduce an
improved kernel size estimator for the point annotations. Experiments on six
datasets show that all our contributions reduce the counting error, regardless
of the base network, resulting in state-of-the-art accuracy using only a single
network. Finally, we are the first to count on WIDER FACE, allowing us to show
the benefits of our approach in handling varying object scales and crowding
levels. Code is available at
https://github.com/shizenglin/Counting-with-Focus-for-FreeComment: ICCV, 201
Quantum Theory of Orbital Magnetization and its Generalization to Interacting Systems
Based on standard perturbation theory, we present a full quantum derivation
of the formula for the orbital magnetization in periodic systems. The
derivation is generally valid for insulators with or without a Chern number,
for metals at zero or finite temperatures, and at weak as well as strong
magnetic fields. The formula is shown to be valid in the presence of
electron-electron interaction, provided the one-electron energies and wave
functions are calculated self-consistently within the framework of the exact
current and spin density functional theory.Comment: Accepted by Phys. Rev. Let
Quantum temporal imaging: application of a time lens to quantum optics
We consider application of a temporal imaging system, based on the
sum-frequency generation, to a nonclassical, in particular, squeezed optical
temporal waveform. We analyze the restrictions on the pump and the phase
matching condition in the summing crystal, necessary for preserving the quantum
features of the initial waveform. We show that modification of the notion of
the field of view in the quantum case is necessary, and that the quantum field
of view is much narrower than the classical one for the same temporal imaging
system. These results are important for temporal stretching and compressing of
squeezed fields, used in quantum-enhanced metrology and quantum communications.Comment: 9 pages, 3 figure
Simulation and detection of Dirac fermions with cold atoms in an optical lattice
We propose an experimental scheme to simulate and observe relativistic Dirac
fermions with cold atoms in a hexagonal optical lattice. By controlling the
lattice anisotropy, one can realize both massive and massless Dirac fermions
and observe the phase transition between them. Through explicit calculations,
we show that both the Bragg spectroscopy and the atomic density profile in a
trap can be used to demonstrate the Dirac fermions and the associated phase
transition.Comment: 4 pages; Published versio
Vibration Induced Non-adiabatic Geometric Phase and Energy Uncertainty of Fermions in Graphene
We investigate geometric phase of fermion states under relative vibrations of
two sublattices in graphene by solving time-dependent Sch\"{o}dinger equation
using Floquet scheme. In a period of vibration the fermions acquire different
geometric phases depending on their momenta. There are two regions in the
momentum space: the adiabatic region where the geometric phase can be
approximated by the Berry phase and the chaotic region where the geometric
phase drastically fluctuates in changing parameters. The energy of fermions due
to vibrations shows spikes in the chaotic region. The results suggest a
possible dephasing mechanism which may cause classical-like transport
properties in graphene.Comment: 9 pages, 5 figure
Proliferation of metallic domains caused by inhomogeneous heating near the electrically-driven transition in VO nanobeams
We discuss the mechanisms behind the electrically driven insulator-metal
transition in single crystalline VO nanobeams. Our DC and AC transport
measurements and the versatile harmonic analysis method employed show that
non-uniform Joule heating causes phase inhomogeneities to develop within the
nanobeam and is responsible for driving the transition in VO. A
Poole-Frenkel like purely electric field induced transition is found to be
absent and the role of percolation near and away from the electrically driven
transition in VO is also identified. The results and the harmonic
analysis can be generalized to many strongly correlated materials that exhibit
electrically driven transitions
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