48,145 research outputs found
Chemical abundance analysis of 19 barium stars
We aim at deriving accurate atmospheric parameters and chemical abundances of
19 barium (Ba) stars, including both strong and mild Ba stars, based on the
high signal-to-noise ratio and high resolution Echelle spectra obtained from
the 2.16 m telescope at Xinglong station of National Astronomical
Observatories, Chinese Academy of Sciences. The chemical abundances of the
sample stars were obtained from an LTE, plane-parallel and line-blanketed
atmospheric model by inputting the atmospheric parameters (effective
temperatures, surface gravities, metallicity and microturbulent velocity) and
equivalent widths of stellar absorption lines. These samples of Ba stars are
giants indicated by atmospheric parameters, metallicities and kinematic
analysis about UVW velocity. Chemical abundances of 17 elements were obtained
for these Ba stars. Their light elements (O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr,
Mn and Ni) are similar to the solar abundances. Our samples of Ba stars show
obvious overabundances of neutron-capture (n-capture) process elements relative
to the Sun. Their median abundances of [Ba/Fe], [La/Fe] and [Eu/Fe] are 0.54,
0.65 and 0.40, respectively. The YI and ZrI abundances are lower than Ba, La
and Eu, but higher than the light elements for the strong Ba stars and similar
to the iron-peak elements for the mild stars. There exists a positive
correlation between Ba intensity and [Ba/Fe]. For the n-capture elements (Y,
Zr, Ba, La), there is an anti-correlation between their [X/Fe] and [Fe/H]. We
identify nine of our sample stars as strong Ba stars with [Ba/Fe]>0.6 where
seven of them have Ba intensity Ba=2-5, one has Ba=1.5 and another one has
Ba=1.0. The remaining ten stars are classified as mild Ba stars with
0.17<[Ba/Fe]<0.54
Effects of microstructure and crystallography on mechanical properties of cold-rolled SAE1078 pearlitic steel
The evolution of the microstructure and crystallography in SAE1078 pearlitic steel sheets under different cold-rolling reductions of up to 90% were quantified using transmission electron microscopy (TEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD). The mechanical properties were determined by tensile testing at room temperature. TEM analysis showed that the pearlite structure was obviously refined with the interlamellar spacing decreasing to about 57 nm at the rolling reduction of 90%. EBSD investigations indicated that the ferrite exhibited a {001}texture in the 90% cold-rolled pearlitic steel. The dislocations were mainly concentrated during cold rolling between the 10% and 70% reduction ratios as the average kernel average misorientation (KAM) angle increased from 0.75° to 1.20°. XRD examination revealed that a transformation from bcc to bct crystal structure of ferrite occurred at 90% rolling reduction due to the supersaturation of carbon. Significant augmentation in the ultimate tensile strength during cold rolling results from the boundary, dislocation, and solid solution strengthening mechanisms
Synergistic and compensatory effects of two point mutations conferring target-site resistance to fipronil in the insect GABA receptor RDL
Insecticide resistance can arise from a variety of mechanisms, including changes to the target site, but is often associated with substantial fitness costs to insects. Here we describe two resistance-associated target-site mutations that have synergistic and compensatory effects that combine to produce high and persistent levels of resistance to fipronil, an insecticide targeting on Îł-aminobytyric acid (GABA) receptors. In Nilaparvata lugens, a major pest of rice crops in many parts of Asia, we have identified a single point mutation (A302S) in the GABA receptor RDL that has been identified previously in other species and which confers low levels of resistance to fipronil (23-fold) in N. lugans. In addition, we have identified a second resistance-associated RDL mutation (R300Q) that, in combination with A302S, is associated with much higher levels of resistance (237-fold). The R300Q mutation has not been detected in the absence of A302S in either laboratory-selected or field populations, presumably due to the high fitness cost associated with this mutation. Significantly, it appears that the A302S mutation is able to compensate for deleterious effects of R300Q mutation on fitness cost. These findings identify a novel resistance mechanism and may have important implications for the spread of insecticide resistance
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Trace doping of multiple elements enables stable battery cycling of LiCoO2 at 4.6 V
LiCoO2 is a dominant cathode material for lithium-ion (Li-ion) batteries due to its high volumetric energy density, which could potentially be further improved by charging to high voltages. However, practical adoption of high-voltage charging is hindered by LiCoO2’s structural instability at the deeply delithiated state and the associated safety concerns. Here, we achieve stable cycling of LiCoO2 at 4.6 V (versus Li/Li+) through trace Ti–Mg–Al co-doping. Using state-of-the-art synchrotron X-ray imaging and spectroscopic techniques, we report the incorporation of Mg and Al into the LiCoO2 lattice, which inhibits the undesired phase transition at voltages above 4.5 V. We also show that, even in trace amounts, Ti segregates significantly at grain boundaries and on the surface, modifying the microstructure of the particles while stabilizing the surface oxygen at high voltages. These dopants contribute through different mechanisms and synergistically promote the cycle stability of LiCoO2 at 4.6 V
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