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To improve the interface bonding strength between the substrate and phases in the Ag-based composite, the silver-coated NbSe2 and silver-coated Ti0.09Nb0.91Se2 particles were synthesized by chemical reduction method, and the Ag-based composites were prepared by powder metallurgy. The results show that, the silver particles are uniformly distributed on the surface of the transition metal selenides, and the Ti0.09Nb0.91Se2 particles show the better coating effect. After covering the Ag coating, the contact between the transition metal selenides and the metal matrix silver is increased, leading to the better wettability and the smaller repulsive force between Ag and the transition metal selenide. Moreover, the possibility of the transition metal selenide decomposition in the Ag-based composite materials is greatly reduced after the Ag coating. The densification of the Ag-based composite materials is improved and the interface bonding strength between the Ag substrates and the transition metal selenides is enhanced. Compared with the Ag-based composites with the uncoated NbSe2, the friction properties of the Ag-based composites containing the silver-coated transition metal selenides decrease slightly.

In order to improve the automation degree of the massage robot,the structure design and kinematics analysis of a four fingered,motor-driven robotic hand for massage robot is completed. Each finger has two joints: the first joint and the second joint. And the degree of freedom of the hand is four by connecting the first joints and second joints of index finger,middle finger and ring finger respectively. In addition,the crank-rocker mechanism is creatively adopted to driven the second joint,which is conducive not only to enhance the continuity and the periodicity of pinching manipulation,but to also avoid frequent reversing the rotation of motor,prolonging the service life of the motor. At last,to verify the design,the model of dexterous hand is developed. The rationality and feasibility of the mechanism of hand are proved by ADAMS motion simulation and MATLAB numerical analysis.

Increasing deployment of dense arrays has facilitated detailed structure imaging for tectonic investigation, hazard assessment and resource exploration. Strong velocity heterogeneity and topographic changes have to be considered during passive source imaging. However, it is quite challenging for ray‐based methods, such as Kirchhoff migration or the widely used teleseismic receiver function, to handle these problems. In this study, we propose a 3‐D passive source reverse time migration strategy based on the spectral element method. It is realized by decomposing the time reversal full elastic wavefield into amplitude‐preserved vector P and S wavefields by solving the corresponding weak‐form solutions, followed by a dot‐product imaging condition to get images for the subsurface structures. It enables us to use regional 3‐D migration velocity models and take topographic variations into account, helping us to locate reflectors at more accurate positions than traditional 1‐D model‐based methods, like teleseismic receiver functions. Two synthetic tests are used to demonstrate the advantages of the proposed method to handle topographic variations and complex velocity heterogeneities. Furthermore, applications to the Laramie array data using both teleseismic P and S waves enable us to identify several south‐dipping structures beneath the Laramie basin in southeast Wyoming, which are interpreted as the Cheyenne Belt suture zone and agree with, and improve upon previous geological interpretations. Plain Language Summary: Increasing deployment of dense arrays has allowed detailed structure imaging. However, traditional ray‐based migration methods or 1‐D velocity model‐based receiver function methods may greatly degrade the imaging quality without considering the full wavefield propagation effect and velocity heterogeneities. Therefore, in this study, we develop a 3‐D passive source migration based on the spectral element method, which is capable of handling topographic variations as well as complex velocity heterogeneities for real data applications. Several synthetic tests and applications to the Laramie array data using both teleseismic P and S waves are used to demonstrate the capability of our method to image complex structures, such as subduction and suture zones. Key Points: A 3‐D passive source reverse time migration based on the spectral element method is proposed to image complex structuresAmplitude‐preserved vector P and S wavefields are accurately decomposed by solving corresponding weak‐form solutionsSeveral south‐dipping structures can be identified from P and S migration results beneath the Laramie basin which are interpreted as the Cheyenne Belt suture zone [ABSTRACT FROM AUTHOR]

SUMMARY: For seismographic stations with short acquisition duration, the signal-to-noise ratios (SNRs) of ambient noise cross-correlation functions (CCFs) are typically low, preventing us from accurately measuring surface wave dispersion curves or waveform characteristics. In addition, with noisy CCFs, it is difficult to extract relatively weak signals such as body waves. In this study, we propose to use local attributes to improve the SNRs of ambient noise CCFs, which allows us to enhance the quality of CCFs for stations with limited acquisition duration. Two local attributes: local cross-correlation and local similarity, are used in this study. The local cross-correlation allows us to extend the dimensionality of daily CCFs with computational costs similar to global cross-correlation. Taking advantage of this extended dimensionality, the local similarity is then used to measure non-stationary similarity between the extended daily CCFs with a reference trace, which enables us to design better stacking weights to enhance coherent features and attenuate incoherent background noises. Ambient noise recorded by several broad-band stations from the USArray in North Texas and Oklahoma, the Superior Province Rifting EarthScope Experiment in Minnesota and Wisconsin and a high-frequency nodal array deployed in the northern Los Angeles basin are used to demonstrate the performance of the proposed approach for improving the SNR of CCFs. [ABSTRACT FROM AUTHOR]

The quadratic Wasserstein (W2) metric has been proposed as a promising misfit function to mitigate cycle‐skipping phenomena in full‐waveform inversion. Mathematically, we demonstrate that the smoothness of the W2‐based adjoint source is two orders of magnitude higher than that based on L2‐norm, which guarantees a larger convergence radius of related inverse problems. However, the oscillatory characteristics of seismic signals and subsequent operations of transforming them into probability densities would decrease the accuracy of the optimal transport map T(t) and exacerbate the nonconvexity of the misfit function. To tackle these challenges, we propose the concept of prescribed direction indicator, which indicates the properly matching direction from predictions to observations, in order to correct inaccurate T(t). 1D synthetic examples suggest that reasonable bijection can be constructed through the proposed method. Numerical experiments demonstrate that it works well during optimization procedures, including enlarging the convergence radius of the inverse problem, improving the computational efficiency and enhancing the reliability of inversion results. Plain Language Summary: Full waveform inversion serves as a powerful tool to enhancing our understanding of Earth's interior structure. However, the traditional L2‐norm‐based method often falls into a local minimum due to the well known cycle‐skipping problem. To address this issue, a novel technique named the Quadratic Wasserstein Metric has been proposed, which yields smoother and more reliable results. Nevertheless, a challenge persists regarding the low precision in calculating the optimal transport map. To counteract this problem, we have introduced a tool called the "Prescribed Direction Indicator," which allows us to correct our calculations of the transport map and assist us in identifying the appropriate alignment between predictions and observations. With numerical synthetic experiments, we prove its superiority to the traditional Wasserstein metric in handling seismic inversions across a variety of scales, from small and local to global problems. Key Points: We mathematically prove W2‐based adjoint source's smoothness is two orders higher than L2‐basedWe propose a concept of prescribed direction indicator to correct inaccurate optimal transport map T(t)Numerical experiments demonstrate the superiority of our proposed method compared to the traditional W2 metric [ABSTRACT FROM AUTHOR]

The pseudo-differential operator with symbol | k |α has been widely used in seismic modelling and imaging when involving attenuation, anisotropy and one-way wave equation, which is usually calculated using the pseudo-spectral method. For large-scale problems, applying high-dimensional Fourier transforms to solve the wave equation that includes pseudo-differential operators is much more expensive than finite-difference approaches, and it is not suitable for parallel computing with domain decomposition. To mitigate this difficulty, we present a truncated space-domain convolution method to efficiently compute the pseudo-differential operator |$\sqrt{-\nabla ^2}$|⁠ , and then apply it to viscoacoustic reverse-time migration. Although |$\sqrt{-\nabla ^2}$| is theoretically non-local in the space domain, we take the limited frequency band of seismic data into account, and constrain the approximated convolution stencil to a finite length. The convolution coefficients are computed by solving a least-squares inverse problem in the wavenumber domain. In addition, we exploit the symmetry of the resulting convolution stencil and develop a fast spatial convolution algorithm. The applications of the proposed method in Q -compensated reverse-time migration demonstrate that it is a good alternative to the pseudo-spectral method for computing the pseudo-differential operator |$\sqrt{-\nabla ^2}$|⁠ , with almost the same accuracy but much higher efficiency. [ABSTRACT FROM AUTHOR]

High-precision ages of Cenozoic volcanic rocks in northeast China are widely reported recently. However, the systematic analysis of spatio-temporal distribution of Cenozoic volcanism, which is important for reconstructing and constraining regional tectonic evolution, is still limited. Here, we collected published geochronological data from more than 400 Cenozoic volcanic samples in northeast China. Combined with field observations of volcanic rock samples and three valid 40Ar-39Ar geochronological data obtained in this study, we compile geochronological data in northeast China and explore a new spatio-temporal distribution pattern for the Cenozoic volcanism in order to constrain geodynamic models for northeast China. Our results show that the Cenozoic volcanism in northeast China has a horseshoe-shaped distribution, and the volcanism almost existed from Paleocene to Quaternary, which can be roughly divided into six volcanic belts. Our results suggest that the volcanism in this region is centred on around the Songliao Basin, then migrates eastward, and eventually has end up with a series of intense activity around the Songliao Basin. This may be related to the upwelling of the asthenosphere caused by the subduction of the Pacific plate and the opening of the Japan Sea. Our study also reveals that Chuandishan basalt in Dunhua area formed by Early Oligocene volcanic activity, which differs from the Pliocene or Miocene stratigraphic ages assumed before. [ABSTRACT FROM AUTHOR]

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