3,639 research outputs found
Enhanced superconductivity at the interface of W/SrRuO point contact
Differential resistance measurements are conducted for point contacts (PCs)
between tungsten tip approaching along the axis direction and the
plane of SrRuO single crystal. Three key features are found.
Firstly, within 0.2 mV there is a dome like conductance enhancement due to
Andreev reflection at the normal-superconducting interface. By pushing the W
tip further, the conductance enhancement increases from 3\% to more than 20\%,
much larger than that was previously reported, probably due to the pressure
exerted by the tip. Secondly, there are also superconducting like features at
bias higher than 0.2 mV which persists up to 6.2 K, resembling the enhanced
superconductivity under uniaxial pressure for bulk SrRuO crystals
but more pronounced here. Third, the logarithmic background can be fitted with
the Altshuler-Aronov theory of tunneling into quasi two dimensional electron
system, consistent with the highly anisotropic electronic system in
SrRuO.Comment: prb style, 9 pages, 8 fig
An Adaptive Skin Detection Approach of Face Images with Unequal Luminance, Color Excursion, and Background Interference
Face detection and recognition are affected greatly by unequal luminance, color excursion and background interference. For improving skin detection rates of color face images in the presence of unequal luminance, color excursion and background interference, this paper proposes an approach for automatic skin detection. This approach globally corrects the color excursion using the X, Y, Z color components. Then it establishes a self-adaptive nonlinear amendment function using the a', b'and L' components, and locally corrects the R, G, B color components of row-column transformed sub-block images to balance the global luminance and color. Finally, it constructs an L'a'b'three-dimensional semi-supervised dual-probability skin model, based on which automatic skin detection can be realized. The experimental results demonstrated that this approach has great adaptability, a high detection rate and speed
Influence of chemistry and structure on interfacial segregation in NbMoTaW with high-throughput atomistic simulations
Refractory multi-principal element alloys exhibiting promising mechanical
properties such as excellent strength retention at elevated temperatures have
been attracting increasing attention. Although their inherent chemical
complexity is considered a defining feature, a challenge arises in predicting
local chemical ordering, particularly in grain boundary regions with enhanced
structural disorder. In this study, we use atomistic simulations of a large
group of bicrystal models to sample a wide variety of interfacial sites (grain
boundary) in NbMoTaW and explore emergent trends in interfacial segregation and
the underlying structural and chemical driving factors. Sampling hundreds of
bicrystals along the [001] symmetric tilt axis and analyzing more than one
hundred and thirty thousand grain boundary sites with a variety of local atomic
environments, we uncover segregation trends in NbMoTaW. While Nb is the
dominant segregant, more notable are the segregation patterns that deviate from
expected behavior and mark situations where local structural and chemical
driving forces lead to interesting segregation events. For example, incomplete
depletion of Ta in low-angle boundaries results from chemical pinning due to
favorable local compositional environments associated with chemical short-range
ordering. Finally, machine learning models capturing and comparing the
structural and chemical features of interfacial sites are developed to weigh
their relative importance and contributions to segregation tendency, revealing
a significant increase in predictive capability when including local chemical
information. Overall, this work, highlighting the complex interplay between
local grain boundary structure and chemical short-range ordering, suggest
tunable segregation and chemical ordering by tailoring grain boundary structure
in multi-principal element alloys
Evolutionary Consequences of Dusty Tori in Active Galactic Nuclei
Deep surveys of {\em Chandra} and {\em HST} (Hubble Space Telescope) show
that active galactic nucleus (AGN) populations are changing with hard X-ray
luminosities. This arises an interesting question whether the dusty torus is
evolving with the central engines. We assemble a sample of 50 radio-quiet PG
quasars to tackle this problem. The covering factors of the dusty tori can be
estimated from the multiwavelength continuum. We find they are strongly
correlated with the hard X-ray luminosity. Interestingly this correlation
agrees with the fraction of type II AGNs discovered by {\em Chandra} and {\em
HST}, implying strong evidence for that the AGN population changing results
from the evolution of the tori. We also find that the frequencies of the dips
around 1m in the continuum correlate with the covering factors in the
present sample, indicating the dip frequencies are adjusted by the covering
factors. In the scenario of fueling black hole from the torus, the covering
factor is a good and the dip frequency is a potential indicator of the torus
evolution.Comment: 4 pages in emulateapj5.sty. Accepted by ApJ Letter
From High-Entropy Ceramics to Compositionally-Complex Ceramics: A Case Study of Fluorite Oxides
Using fluorite oxides as an example, this study broadens high-entropy
ceramics (HECs) to compositionally-complex ceramics (CCCs) or multi-principal
cation ceramics (MPCCs) to include medium-entropy and/or non-equimolar
compositions. Nine compositions of compositionally-complex fluorite oxides
(CCFOs) with the general formula of (Hf1/3Zr1/3Ce1/3)1-x(Y1/2X1/2)xO2-delta (X
= Yb, Ca, and Gd; x = 0.4, 0.148, and 0.058) are fabricated. The phase
stability, mechanical properties, and thermal conductivities are measured.
Compared with yttria-stabilized zirconia, these CCFOs exhibit increased cubic
phase stability and reduced thermal conductivity, while retaining high Young's
modulus (~210 GPa) and nanohardness (~18 GPa). Moreover, the
temperature-dependent thermal conductivity in the non-equimolar CCFOs shows an
amorphous-like behavior. In comparison with their equimolar high-entropy
counterparts, the medium-entropy non-equimolar CCFOs exhibit even lower thermal
conductivity (k) while maintaining high modulus (E), thereby achieving higher
E/k ratios. These results suggest a new direction to achieve
thermally-insulative yet stiff CCCs (MPCCs) via exploring non-equimolar and/or
medium-entropy compositions.Comment: 39 pages; 8 + 5 figures; Accepted for publications in Journal of the
European Ceramic Society (1/7/2020
Highly selective oxidation of benzene to phenol with air at room temperature promoted by water
Phenol is one of the most important fine chemical intermediates in the synthesis of plastics and drugs with a market size of ca. $30b1 and the commercial production is via a two-step selective oxidation of benzene, requiring high energy input (high temperature and high pressure) in the presence of a corrosive acidic medium, and causing serious environmental issues2-5. Here we present a four-phase interface strategy with well-designed Pd@Cu nanoarchitecture decorated TiO2 as a catalyst in a suspension system. The optimised catalyst leads to a turnover number of 16,000-100,000 for phenol generation with respect to the active sites and an excellent selectivity of ca. 93%. Such unprecedented results are attributed to the efficient activation of benzene by the atomically Cu coated Pd nanoarchitecture, enhanced charge separation, and an oxidant-lean environment. The rational design of catalyst and reaction system provides a green pathway for the selective conversion of symmetric organic molecules
Chemical order transitions within extended interfacial segregation zones in NbMoTaW
Interfacial segregation and chemical short-range ordering influence the
behavior of grain boundaries in complex concentrated alloys. In this study, we
use atomistic modeling of a NbMoTaW refractory complex concentrated alloy to
provide insight into the interplay between these two phenomena. Hybrid Monte
Carlo and molecular dynamics simulations are performed on columnar grain models
to identify equilibrium grain boundary structures. Our results reveal extended
near-boundary segregation zones that are much larger than traditional
segregation regions, which also exhibit chemical patterning that bridges the
interfacial and grain interior regions. Furthermore, structural transitions
pertaining to an A2-to-B2 transformation are observed within these extended
segregation zones. Both grain size and temperature are found to significantly
alter the widths of these regions. Analysis of chemical short-range order
indicates that not all pairwise elemental interactions are affected by the
presence of a grain boundary equally, as only a subset of elemental clustering
types are more likely to reside near certain boundaries. The results emphasize
the increased chemical complexity that is associated with near-boundary
segregation zones and demonstrate the unique nature of interfacial segregation
in complex concentrated alloys
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