7,434 research outputs found
An independent test of the photometric selection of white dwarf candidates using LAMOST DR3
In Gentile Fusillo et al. (2015) we developed a selection method for white
dwarf candidates which makes use of photometry, colours and proper motions to
calculate a probability of being a white dwarf (Pwd). The application of our
method to the Sloan Digital Sky Survey (SDSS) data release 10 resulted in
nearly 66,000 photometrically selected objects with a derived Pwd,
approximately 21000 of which are high confidence white dwarf candidates. Here
we present an independent test of our selection method based on a sample of
spectroscopically confirmed white dwarfs from the LAMOST (Large Sky Area
Multi-Fiber Spectroscopic Telescope) survey. We do this by cross matching all
our 66,000 SDSS photometric white dwarf candidates with the over 4
million spectra available in the third data release of LAMOST. This results in
1673 white dwarf candidates with no previous SDSS spectroscopy, but with
available LAMOST spectra. Among these objects we identify 309 genuine white
dwarfs. We find that our Pwd can efficiently discriminate between confirmed
LAMOST white dwarfs and contaminants. Our white dwarf candidate selection
method can be applied to any multi-band photometric survey and in this work we
conclusively confirm its reliability in selecting white dwarfs without recourse
to spectroscopy. We also discuss the spectroscopic completeness of white dwarfs
in LAMOST, as well as deriving effective temperatures, surface gravities and
masses for the hydrogen-rich atmosphere white dwarfs in the newly identified
LAMOST sample.Comment: 10 pages, 7 figures. Accepted for publication in MNRAS. The full
catalogue presented in table 4 is available at
http://www2.warwick.ac.uk/fac/sci/physics/research/astro/catalogues/SDSS_WD_candidates_with_LAMOST_spectra.cs
A comprehensive study of the open cluster NGC 6866
We present CCD photometry of the field of the open cluster NGC 6866.
Structural parameters of the cluster are determined utilizing the stellar
density profile of the stars in the field. We calculate the probabilities of
the stars being a physical member of the cluster using their astrometric data
and perform further analyses using only the most probable members. The
reddening and metallicity of the cluster were determined by independent
methods. The LAMOST spectra and the ultraviolet excess of the F and G type
main-sequence stars in the cluster indicate that the metallicity of the cluster
is about the solar value. We estimated the reddening
mag using the vs two-colour diagram. The distance modula, the
distance and the age of NGC 6866 were derived as mag,
pc and Myr, respectively, by fitting
colour-magnitude diagrams of the cluster with the PARSEC isochrones. The
Galactic orbit of NGC 6866 indicates that the cluster is orbiting in a slightly
eccentric orbit with . The mass function slope was
derived by using the most probable members of the cluster.Comment: 14 pages, including 16 figures and 7 tables, accepted for publication
in MNRAS. Table 4 in the manuscript will be published electronicall
Bounds of Efficiency at Maximum Power for Normal-, Sub- and Super-Dissipative Carnot-Like Heat Engines
The Carnot-like heat engines are classified into three types (normal-, sub-
and super-dissipative) according to relations between the minimum irreversible
entropy production in the "isothermal" processes and the time for completing
those processes. The efficiencies at maximum power of normal-, sub- and
super-dissipative Carnot-like heat engines are proved to be bounded between
and , and , 0 and
, respectively. These bounds are also shared by linear, sub-
and super-linear irreversible Carnot-like engines [Tu and Wang, Europhys. Lett.
98, 40001 (2012)] although the dissipative engines and the irreversible ones
are inequivalent to each other.Comment: 1 figur
Phenolic Characterisation and Antioxidant Capacity of Young Wines Made From Different Grape Varieties Grown in Helanshan Donglu Wine Zone (China)
The Helanshan Donglu wine zone (China) is one of the most successful wine region of China, and the phenolic characterisation and antioxidant capacity of the primarily young, monovarietal wines from there were evaluated. The result showed that Helanshan Donglu wines contained abundant phenolic compounds, especially flavan-3-ols, and possessed high antioxidant capacity. In different grape varieties, the phenolic profiles varied greatly in both red and white wines. For red wines, Cabernet Sauvignon represented the highest total phenols (2 631 mg/L GAE), total flavonoids (1 840.83 mg/L CTE) and antioxidant capacity. Gamay and Cabernet Gernischt possessed the highest total flavan-3-ols (1 108.08 mg/L CTE) and total anthocyanins (258.78 mg/L CGE). Amongst the white wines, Chardonnay and Chenin blanc showed the highest phenolic contents and antioxidant capacity. (+)-Catechin and (-)-epicatechin were dominant phenolic constituents in both the red and white wines. Gallic acid and salicylic acid were the second most abundant in red wines, while gentisic acid was the second most abundant in white wines
Neutron scattering and muon-spin spectroscopy studies of the magnetic triangular-lattice compounds LaNiWO ( = Sr, Ba)
We report on the geometrically frustrated two-dimensional triangular-lattice
magnets LaNiWO ( = Sr, Ba) studied mostly by means of
neutron powder diffraction (NPD) and muon-spin rotation and relaxation
(SR) techniques. The chemical pressure induced by the Ba-for-Sr
substitution suppresses the ferromagnetic (FM) transition from 6.3 K in the
Ba-compound to 4.8 K in the Sr-compound. We find that the space
group reproduces the NPD patterns better than the previously reported
space group. Both compounds adopt the same magnetic structure with
a propagation vector , in which the Ni
magnetic moments are aligned ferromagnetically along the -axis. The
zero-field {\textmu}SR results reveal two distinct internal fields (0.31 and
0.10 T), caused by the long-range ferromagnetic order. The small transverse
muon-spin relaxation rates reflect the homogeneous internal field distribution
in the ordered phase and, thus, further support the simple FM arrangement of
the Ni moments. The small longitudinal muon-spin relaxation rates, in
both the ferromagnetic- and paramagnetic states of ALaNiWO,
indicate that spin fluctuations are rather weak. Our results demonstrate that
chemical pressure indeed changes the superexchange interactions in
LaNiWO compounds, with the FM interactions being dominant.Comment: 8 pages, 7 figures; accepted by Phys. Rev. Material
Mass Hierarchy Determination Using Neutrinos from Multiple Reactors
We report the results of Monte Carlo simulations of a medium baseline reactor
neutrino experiment. The difference in baselines resulting from the 1 km
separations of Daya Bay and Ling Ao reactors reduces the amplitudes of 1-3
oscillations at low energies, decreasing the sensitivity to the neutrino mass
hierarchy. A perpendicular detector location eliminates this effect. We
simulate experiments under several mountains perpendicular to the Daya Bay/Ling
Ao reactors, considering in particular the background from the TaiShan and
YangJiang reactor complexes. In general the hierarchy can be determined most
reliably underneath the 1000 meter mountain BaiYunZhang, which is 44.5 km from
Daya Bay. If some planned reactors are not built then nearby 700 meter
mountains at 47-51 km baselines gain a small advantage. Neglecting their low
overhead burdens, hills near DongKeng would be the optimal locations. We use a
weighted Fourier transform to avoid a spurious dependence on the high energy
neutrino spectrum and find that a neural network can extract quantities which
determine the hierarchy marginally better than the traditional RL + PV.Comment: 22 pages, added details on the neural network (journal version
Enhancing Performance of Nonfullerene Acceptors via Side-Chain Conjugation Strategy
A side-chain conjugation strategy in the design of nonfullerene electron acceptors is proposed, with the design and synthesis of a side-chain-conjugated acceptor (ITIC2) based on a 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]di(cyclopenta-dithiophene) electron-donating core and 1,1-dicyanomethylene-3-indanone electron-withdrawing end groups. ITIC2 with the conjugated side chains exhibits an absorption peak at 714 nm, which redshifts 12 nm relative to ITIC1. The absorption extinction coefficient of ITIC2 is 2.7 × 105m−1 cm−1, higher than that of ITIC1 (1.5 × 105m−1 cm−1). ITIC2 exhibits slightly higher highest occupied molecular orbital (HOMO) (−5.43 eV) and lowest unoccupied molecular orbital (LUMO) (−3.80 eV) energy levels relative to ITIC1 (HOMO: −5.48 eV; LUMO: −3.84 eV), and higher electron mobility (1.3 × 10−3 cm2 V−1 s−1) than that of ITIC1 (9.6 × 10−4 cm2 V−1 s−1). The power conversion efficiency of ITIC2-based organic solar cells is 11.0%, much higher than that of ITIC1-based control devices (8.54%). Our results demonstrate that side-chain conjugation can tune energy levels, enhance absorption, and electron mobility, and finally enhance photovoltaic performance of nonfullerene acceptors
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