2,581 research outputs found
Variation characteristics of anchor’s dynamic testing signal on the conditions of tensile load
Non-destructive testing for rock bolts in this study considers loads typical of anchors in practical engineering. The non-destructive testing experiment has been conducted for bolts under various load levels with variation characteristics of the dynamic testing signal and analyzed based on the stress wave reflection method. This research indicates that reflection signals of the fixed end section are relatively strong while reflection signals of the bottom section are relatively weak, regardless of bolt bearing loads, due to the effect of transmission, reflection and attenuation of the stress wave. The dynamic signal features obvious cycles in addition to the comparatively regular waveform in no-load cases as, with increasing load, dynamic signals become increasingly unstable while mechanical properties change in the anchor rod, anchor medium and the interface. The combination method of wavelet decomposition and multi-scale is applied to the test signal analysis to improve readability and accuracy of the signal. This research indicates that wavelet analysis interacts with non-stationary signals effectively, creating a solution for the reducing signal-noise ratio caused by the load. Obviously, it can also additionally read out the reflected signal of the bottom section, thereby improving the accuracy of anchoring quality interpretation
Large spin Hall conductivity and excellent hydrogen evolution reaction activity in unconventional PtTe1.75 monolayer
Two-dimensional (2D) materials have gained lots of attention due to the
potential applications. In this work, we propose that based on first-principles
calculations, the (22) patterned PtTe monolayer with kagome lattice
formed by the well-ordered Te vacancy (PtTe) hosts large spin Hall
conductivity (SHC) and excellent hydrogen evolution reaction (HER) activity.
The unconventional nature relies on the band representation (BR) of the
highest valence band without SOC. The large SHC comes from the Rashba
spin-orbit coupling (SOC) in the noncentrosymmetric structure induced by the Te
vacancy. Even though it has a metallic SOC band structure, the
invariant is well defined due to the existence of the direct band gap and is
computed to be nontrivial. The calculated SHC is as large as 1.25 at the Fermi level (). By tuning the
chemical potential from to eV, it varies rapidly and
monotonically from to 3.1. In addition, we also find the Te vacancy in the patterned
monolayer can induce excellent HER activity. Our results not only offer a new
idea to search 2D materials with large SHC, i.e., by introducing
inversion-symmetry breaking vacancies in large SOC systems, but also provide a
feasible system with tunable SHC (by applying gate voltage) and excellent HER
activity
The growth of graphene on Ni–Cu alloy thin films at a low temperature and its carbon diffusion mechanism
Carbon solid solubility in metals is an important factor affecting uniform graphene growth by chemical vapor deposition (CVD) at high temperatures. At low temperatures, however, it was found that the carbon diffusion rate (CDR) on the metal catalyst surface has a greater impact on the number and uniformity of graphene layers compared with that of the carbon solid solubility. The CDR decreases rapidly with decreasing temperatures, resulting in inhomogeneous and multilayer graphene. In the present work, a Ni–Cu alloy sacrificial layer was used as the catalyst based on the following properties. Cu was selected to increase the CDR, while Ni was used to provide high catalytic activity. By plasma-enhanced CVD, graphene was grown on the surface of Ni–Cu alloy under low pressure using methane as the carbon source. The optimal composition of the Ni–Cu alloy, 1:2, was selected through experiments. In addition, the plasma power was optimized to improve the graphene quality. On the basis of the parameter optimization, together with our previously-reported, in-situ, sacrificial metal-layer etching technique, relatively homogeneous wafer-size patterned graphene was obtained directly on a 2-inch SiO2 /Si substrate at a low temperature (~600◦ C)
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