6,258 research outputs found
DIVE in the cosmic web: voids with Delaunay Triangulation from discrete matter tracer distributions
We present a novel parameter-free cosmological void finder (\textsc{dive},
Delaunay TrIangulation Void findEr) based on Delaunay Triangulation (DT), which
efficiently computes the empty spheres constrained by a discrete set of
tracers. We define the spheres as DT voids, and describe their properties,
including an universal density profile together with an intrinsic scatter. We
apply this technique on 100 halo catalogues with volumes of 2.5\,Gpc
side each, with a bias and number density similar to the BOSS CMASS Luminous
Red Galaxies, performed with the \textsc{patchy} code. Our results show that
there are two main species of DT voids, which can be characterised by the
radius: they have different responses to halo redshift space distortions, to
number density of tracers, and reside in different dark matter environments.
Based on dynamical arguments using the tidal field tensor, we demonstrate that
large DT voids are hosted in expanding regions, whereas the haloes used to
construct them reside in collapsing ones. Our approach is therefore able to
efficiently determine the troughs of the density field from galaxy surveys, and
can be used to study their clustering. We further study the power spectra of DT
voids, and find that the bias of the two populations are different,
demonstrating that the small DT voids are essentially tracers of groups of
haloes.Comment: 12 pages, 13 figure
Improved Antireflection Properties of an Optical Film Surface with Mixing Conical Subwavelength Structures
Based on finite difference time domain method, an optical film surface with mixing conical subwavelength structures is numerically investigated to improve antireflection property. The mixing conical subwavelength structure is combined with the pure periodic conical subwavelength structures and the added small conical structures in the gap between the pure periodic conical subwavelength structures. The antireflection properties of two types of subwavelength structures with different aspect ratios in spectral range of 400–800 nm are analyzed and compared. It is shown that, for the mixing type, the average reflectance is decreased and the variances of the reflectance are evidently smaller. When the added structure with a better aspect ratio exists, the average reflectance of the surface can be below 0.30%. Obviously, the antireflection properties of the optical film surface with mixing conical subwavelength structures can be improved
Thermally-Switchable Metalenses Based on Quasi-Bound States in the Continuum
Dynamic wavefront shaping with optical metasurfaces has presented a major
challenge and inspired a large number of highly elaborate solutions. Here, we
experimentally demonstrate thermo-optically reconfigurable, nonlocal
metasurfaces using simple device architectures and conventional CMOS-compatible
dielectric materials. These metasurfaces support quasi-bound states in the
continuum (q-BICs) derived from symmetry breaking and encoded with a spatially
varying geometric phase, such that they shape optical wavefront exclusively on
spectrally narrowband resonances. Due to the enhanced light-matter interaction
enabled by the resonant q-BICs, a slight variation of the refractive index
introduced by heating and cooling the entire device leads to a substantial
shift of the resonant wavelength and a subsequent change to the optical
wavefront associated with the resonance. We experimentally demonstrate a
metalens modulator, the focusing capability of which can be thermally turned on
and off, and reconfigurable metalenses, which can be thermo-optically switched
to produce two distinct focal patterns. Our devices offer a pathway to realize
reconfigurable, multifunctional meta-optics using established manufacturing
processes and widely available dielectric materials that are conventionally not
considered "active" materials due to their small thermo-optic or electro-optic
coefficients
Supervised Collective Classification for Crowdsourcing
Crowdsourcing utilizes the wisdom of crowds for collective classification via
information (e.g., labels of an item) provided by labelers. Current
crowdsourcing algorithms are mainly unsupervised methods that are unaware of
the quality of crowdsourced data. In this paper, we propose a supervised
collective classification algorithm that aims to identify reliable labelers
from the training data (e.g., items with known labels). The reliability (i.e.,
weighting factor) of each labeler is determined via a saddle point algorithm.
The results on several crowdsourced data show that supervised methods can
achieve better classification accuracy than unsupervised methods, and our
proposed method outperforms other algorithms.Comment: to appear in IEEE Global Communications Conference (GLOBECOM)
Workshop on Networking and Collaboration Issues for the Internet of
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