3,732 research outputs found
Characterizing AGB stars in Wide-field Infrared Survey Explorer (WISE) bands
Since asymptotic giant branch (AGB) stars are bright and extended infrared
objects, most Galactic AGB stars saturate the Wide-field Infrared Survey
Explorer (WISE) detectors and therefore the WISE magnitudes that are restored
by applying point-spread-function fitting need to be verified. Statistical
properties of circumstellar envelopes around AGB stars are discussed on the
basis of a WISE AGB catalog verified in this way. We cross-matched an AGB star
sample with the WISE All-Sky Source Catalog and the Two Mircon All Sky Survey
catalog. Infrared Space Observatory (ISO) spectra of a subsample of WISE AGB
stars were also exploited. The dust radiation transfer code DUSTY was used to
help predict the magnitudes in the W1 and W2 bands, the two WISE bands most
affected by saturation, for calibration purpose, and to provide physical
parameters of the AGB sample stars for analysis. DUSTY is verified against the
ISO spectra to be a good tool to reproduce the spectral energy distributions of
these AGB stars. Systematic magnitude-dependent offsets have been identified in
WISE W1 and W2 magnitudes of the saturated AGB stars, and empirical calibration
formulas are obtained for them on the basis of 1877 (W1) and 1558 (W2) AGB
stars that are successfully fit with DUSTY. According to the calibration
formulae, the corrections for W1 at 5 mag and W2 at 4 mag are and
0.217 mag, respectively. In total, we calibrated the W1/W2 magnitudes of
2390/2021 AGB stars. The model parameters from the DUSTY and the calibrated
WISE W1 and W2 magnitudes are used to discuss the behavior of the WISE
color-color diagrams of AGB stars. The model parameters also reveal that O-rich
AGB stars with opaque circumstellar envelopes are much rarer than opaque C-rich
AGB stars toward the anti-Galactic center direction, which we attribute to the
metallicity gradient of our Galaxy.Comment: 9 pages in two column format, 7 figures, accepted for publication in
A&
Collaborative Deep Reinforcement Learning for Joint Object Search
We examine the problem of joint top-down active search of multiple objects
under interaction, e.g., person riding a bicycle, cups held by the table, etc..
Such objects under interaction often can provide contextual cues to each other
to facilitate more efficient search. By treating each detector as an agent, we
present the first collaborative multi-agent deep reinforcement learning
algorithm to learn the optimal policy for joint active object localization,
which effectively exploits such beneficial contextual information. We learn
inter-agent communication through cross connections with gates between the
Q-networks, which is facilitated by a novel multi-agent deep Q-learning
algorithm with joint exploitation sampling. We verify our proposed method on
multiple object detection benchmarks. Not only does our model help to improve
the performance of state-of-the-art active localization models, it also reveals
interesting co-detection patterns that are intuitively interpretable
An constructive proof for the Umemura polynomials for the third Painlev\'e equation
We are concerned with the Umemura polynomials associated with the third
Painlev\'e equation. We extend Taneda's method, which was developed for the
Yablonskii--Vorob'ev polynomials associated with the second Painlev\'e
equation, to give an algebraic proof that the rational functions generated by
the nonlinear recurrence relation satisfied by Umemura polynomials are indeed
polynomials. Our proof is constructive and gives information about the roots of
the Umemura polynomials.Comment: 20 pages, 3 figure
Dichloropalladium complexes ligated by 4,5-bis(arylimino)pyrenylidenes: Synthesis, characterization, and catalytic behavior towards Heck-reaction
A series of 4,5-bis(arylimino)pyrenylidenylpalladium(II) chloride complexes (C1–C4) were synthesized and characterized by FT-IR and NMR spectroscopy, elemental analysis as well as by single crystal X-ray diffraction for the representative complexes C1 and C3, which revealed a square planar geometry at the palladium center. All palladium complexes exhibited high activity for the Heck cross-coupling reaction, which were effective when conducted in various solvents. Furthermore, the in-situ mixture of palladium dichloride and the ligand (L1) provided an effective catalytic system for the Heck-reaction
Two-Dimensional Topological Insulator State and Topological Phase Transition in Bilayer Graphene
We show that gated bilayer graphene hosts a strong topological insulator (TI)
phase in the presence of Rashba spin-orbit (SO) coupling. We find that gated
bilayer graphene under preserved time-reversal symmetry is a quantum valley
Hall insulator for small Rashba SO coupling , and
transitions to a strong TI when ,
where and are respectively the interlayer potential and tunneling
energy. Different from a conventional quantum spin Hall state, the edge modes
of our strong TI phase exhibit both spin and valley filtering, and thus share
the properties of both quantum spin Hall and quantum valley Hall insulators.
The strong TI phase remains robust in the presence of weak graphene intrinsic
SO coupling.Comment: 5 pages and 4 figure
Topological phases in gated bilayer graphene: Effects of Rashba spin-orbit coupling and exchange field
We present a systematic study on the influence of Rashba spin-orbit coupling,
interlayer potential difference and exchange field on the topological
properties of bilayer graphene. In the presence of only Rashba spin-orbit
coupling and interlayer potential difference, the band gap opening due to
broken out-of-plane inversion symmetry offers new possibilities of realizing
tunable topological phase transitions by varying an external gate voltage. We
find a two-dimensional topological insulator phase and a quantum valley
Hall phase in -stacked bilayer graphene and obtain their effective
low-energy Hamiltonians near the Dirac points. For stacking, we do not
find any topological insulator phase in the presence of large Rashba spin-orbit
coupling. When the exchange field is also turned on, the bilayer system
exhibits a rich variety of topological phases including a quantum anomalous
Hall phase, and we obtain the phase diagram as a function of the Rashba
spin-orbit coupling, interlayer potential difference, and exchange field.Comment: 15 pages, 17figures, and 1 tabl
Centrality and Transverse momentum dependencies of Hadrons in Xe+Xe collisions at TeV from a multi-phase transport model
In this paper, we study and predict the charged-particle pseudorapidity
multiplicity density (), transverse momentum spectra of
identified particles and their ratios in relativistic heavy ion collisions at
the Large Hadron Collider (LHC), using the string-melting version of a
multi-phase transport (AMPT) model with improved quark coalescence method.
Results of the charged-particle pseudorapidity multiplicity density from AMPT
model calculations for Pb+Pb collisions at TeV are
compared with the experimental data. Good agreements are generally found
between theoretical calculations and experimental data. We predict
for Xe+Xe collisions at TeV at
different centralities, and spectra of charged pions, kaons and protons,
and their ratios and in Pb+Pb collisions at
TeV and Xe+Xe collisions at TeV that
are being studied at LHC. The spectra of identified particles in Pb+Pb
collisions from the improved AMPT model are compared and found to be consistent
with results from the iEBE-VISHNU hybrid model with TRENTo initial condition.Comment: 6 pages, 5 figure
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