29,940 research outputs found
The radial abundance gradient of oxygen towards the Galactic anticentre
We present deep optical spectroscopy of eight HII regions located in the
anticentre of the Milky Way. The spectra were obtained at the 10.4m GTC and
8.2m VLT. We determined Te([NII]) for all objects and Te([OIII]) for six of
them. We also included in our analysis an additional sample of 13 inner-disc
Galactic Hii regions from the literature that have excellent T_e
determinations. We adopted the same methodology and atomic dataset to determine
the physical conditions and ionic abundances for both samples. We also detected
the CII and OII optical recombination lines in Sh 2-100, which enables
determination of the abundance discrepancy factor for this object. We found
that the slopes of the radial oxygen gradients defined by the HII regions from
R_25 (= 11.5 kpc) to 17 kpc and those within R_25 are similar within the
uncertainties, indicating the absence of flattening in the radial oxygen
gradient in the outer Milky Way. In general, we found that the scatter of the
O/H ratios of Hii regions is not substantially larger than the observational
uncertainties. The largest possible local inhomogeneities of the oxygen
abundances are of the order of 0.1 dex. We also found positive radial gradients
in Te([O III]) and Te([N II]) across the Galactic disc. The shapes of these
temperature gradients are similar and also consistent with the absence of
flattening of the metallicity distribution in the outer Galactic disc.Comment: 20 pages, 11 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
An integrated bayesian approach for effective multi-truth discovery
Truth-finding is the fundamental technique for corroborating reports from multiple sources in both data integration and collective intelligent applications. Traditional truthfinding methods assume a single true value for each data item and therefore cannot deal will multiple true values (i.e., the multi-truth-finding problem). So far, the existing approaches handle the multi-truth-finding problem in the same way as the single-truth-finding problems. Unfortunately, the multi-truth-finding problem has its unique features, such as the involvement of sets of values in claims, different implications of inter-value mutual exclusion, and larger source profiles. Considering these features could provide new opportunities for obtaining more accurate truthfinding results. Based on this insight, we propose an integrated Bayesian approach to the multi-truth-finding problem, by taking these features into account. To improve the truth-finding efficiency, we reformulate the multi-truthfinding problem model based on the mappings between sources and (sets of) values. New mutual exclusive relations are defined to reflect the possible co-existence of multiple true values. A finer-grained copy detection method is also proposed to deal with sources with large profiles. The experimental results on three real-world datasets show the effectiveness of our approach.Xianzhi Wang, Quan Z. Sheng, Xiu Susie Fang, Lina Yao, Xiaofei Xu, Xue L
Optical properties of TlNi2Se2: Observation of pseudogap formation
The quasi-two-dimensional nickel chalcogenides is a newly
discovered superconductor. We have performed optical spectroscopy study on
single crystals over a broad frequency range at various
temperatures. The overall optical reflectance spectra are similar to those
observed in its isostructure . Both the suppression in
and the peaklike feature in suggest the progressive
formation of a pseudogap feature in the midinfrared range with decreasing
temperatures, which might be originated from the dynamic local fluctuation of
charge-density-wave (CDW) instability. We propose that the CDW instability in
is driven by the saddle points mechanism, due to the existence of
van Hove singularity very close to the Fermi energy.Comment: 5 pages, 4 figure
Nodeless superconductivity in IrPtTe with strong spin-orbital coupling
The thermal conductivity of superconductor IrPtTe
( = 0.05) single crystal with strong spin-orbital coupling was measured down
to 50 mK. The residual linear term is negligible in zero magnetic
field. In low magnetic field, shows a slow field dependence. These
results demonstrate that the superconducting gap of IrPtTe is
nodeless, and the pairing symmetry is likely conventional s-wave, despite the
existence of strong spin-orbital coupling and a quantum critical point.Comment: 5 pages, 4 figure
Approximate truth discovery via problem scale reduction
Many real-world applications rely on multiple data sources to provide information on their interested items. Due to the noises and uncertainty in data, given a specific item, the information from different sources may conflict. To make reliable decisions based on these data, it is important to identify the trustworthy information by resolving these conflicts, i.e., the truth discovery problem. Current solutions to this problem detect the veracity of each value jointly with the reliability of each source for every data item. In this way, the efficiency of truth discovery is strictly confined by the problem scale, which in turn limits truth discovery algorithms from being applicable on a large scale. To address this issue, we propose an approximate truth discovery approach, which divides sources and values into groups according to a userspecified approximation criterion. The groups are then used for efficient inter-value influence computation to improve the accuracy. Our approach is applicable to most existing truth discovery algorithms. Experiments on real-world datasets show that our approach improves the efficiency compared to existing algorithms while achieving similar or even better accuracy. The scalability is further demonstrated by experiments on large synthetic datasets.Xianzhi Wang, Quan Z. Sheng, Xiu Susie Fang, Xue Li, Xiaofei Xu, and Lina Ya
Pressure Effect on the superconducting properties of LaO_{1-x}F_{x}FeAs(x=0.11) superconductor
Diamagnetic susceptibility measurements under high hydrostatic pressure (up
to 1.03 GPa) were carried out on the newly discovered Fe-based superconductor
LaO_{1-x}F_{x}FeAs(x=0.11). The transition temperature T_c, defined as the
point at the maximum slope of superconducting transition, was enhanced almost
linearly by hydrostatic pressure, yielding a dT_c/dP of about 1.2 K/GPa.
Differential diamagnetic susceptibility curves indicate that the underlying
superconducting state is complicated. It is suggested that pressure plays an
important role on pushing low T_c superconducting phase toward the main
(optimal) superconducting phase.Comment: 7 pages, 4 figure
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