Search

Locating and monitoring passive seismic sources provides us important information for studying subsurface rock deformation, injected fluid migration, regional stress conditions as well as fault rupture mechanism. In this paper, we present a novel passive-source monitoring approach using vector-based elastic time-reversal imaging. By solving the elastic wave equation using observed multicomponent records as boundary conditions, we first compute back-propagated elastic wavefields in the subsurface. Then, we separate the extrapolated wavefields into compressional (P -wave) and shear (S -wave) modes using the vector Helmholtz decomposition. A zero-lag cross-correlation imaging condition is applied to the separated pure-mode vector wavefields to produce passive-source images. We compare imaging results using three implementations, that is dot-product, energy and power. Numerical experiments demonstrate that the power imaging condition gives us the highest resolution and is less sensitive to the presence of random noises. To capture the propagation of microseismic fracture and earthquake rupture, we modify the traditional zero-lag cross-correlation imaging condition by summing the multiplication of the separated P and S wavefields within local time windows, which enables us to capture the temporal and spatial evolution of earthquake rupture. 2-D and 3-D numerical examples demonstrate that the proposed method is capable of accurately locating point sources, as well as delineating dynamic propagation of hydraulic fracture and earthquake rupture. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to clarify the size and morphology of transition metal dichalcogenides has an impact on lubrication performance of Cu-based composites. This study is intended to show that Cu-based electrical contact materials containing Nb0.91Ti0.09Se2 have better electrical and tribological properties than those containing NbSe2. The tribological properties of Cu-based with different Ti-dopped NbSe2 content were also discussed.Design/methodology/approach The NbSe2 and Nb0.91Ti0.09Se2 particles were fabricated by thermal solid state reaction method. The powder metallurgy technique was used to fabricate composites with varying Nb0.91Ti0.09Se2 mass fraction. The phase composition of Cu-based composites was identified by X-ray diffraction, and the morphology of NbSe2/Nb0.91Ti0.09Se2 and the worn surface of composites were characterized by scanning electron microscopy and transmission electron microscopy. In addition, the tribological properties of composites were appraised using a ball-on-disk multi-functional tribometer. The data of friction coefficient and resistivity were analyzed and the corresponding conclusion was drawn.Findings In comparison with the pure copper, Cu-based composites containing Nb0.91Ti0.09Se2/NbSe2 had a lower friction coefficient, illustrating the Nb0.91Ti0.09Se2 with nano-size particles prepared in this work is a perfect choice for the fabrication of excellent electrical contact composites. Compared to composites with NbSe2, composites containing Nb0.91Ti0.09Se2 have better tribological and electrical properties.Research limitations/implications Because of the use of thermal solid state reaction method, the size of NbSe2 and Nb0.91Ti0.09Se2 is relatively large. Therefore, the fabrication of finer particles of Nb0.91Ti0.09Se2 is encouraged.Originality/value In this paper, the authors discuss the tribological and electrical properties of Cu-based composites, and the value of optimum obtained as Nb0.91Ti0.09Se2 content is 15 Wt.%. [ABSTRACT FROM AUTHOR]

Higher alcohols synthesis from syngas via Fischer-Tropsch reaction has been studied on activated carbon supported bimetallic CoFe (denoted as CoFe/AC) catalysts. The effect of impregnation strategy on the structure and performance of the catalysts was investigated by means of N 2 adsorption, HRTEM, ex-situ / in-situ XRD, CO adsorption, CO-TPD, XPS and CO hydrogenation. The results showed that the sequentially impregnated 15Co-5Fe/AC catalyst prepared with iron precursor firstly and then cobalt precursor had the highest CO uptake, metal dispersion and the maximum cobalt surface content, resulting in the enhancement of CO hydrogenation activity as well as the yield of mixed alcohols. On the other hand, the selectivity towards higher alcohols (C 2+ ) was hardly affected by the impregnation sequence. It was found that the activated carbon facilitated the formation of Co 2 C species and doping of Fe into the 15Co/AC catalyst promoted the formation of Co-Fe alloy species. Both of Co 2 C and Co-Fe alloy species were observed in all the co-impregnated and sequentially impregnated catalysts after reaction. It was inferred that Co/Co 2 C as well as Co-Fe alloy species might be responsible for the synthesis of alcohols via CO hydrogenation. [ABSTRACT FROM AUTHOR]

Heterogenization of homogeneous catalyst by immobilizing complex on the surface of polymer supports promotes the design of the catalysts which combine the advantages of heterogeneous and homogeneous catalysts. The porous 2-vinyl-functional diphenyl-2-pyridylphosphine (2V-P,N) polymer (POL-2V-P,N) was successfully synthesized under solvothermal conditions. The POL-2V-P,N polymer was characterized by nitrogen physisorption, thermogravimetry (TG), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The heterogenized homogeneous Pd/POL-2V-P,N catalyst was synthesized by immobilizing Pd(OAc) 2 on the POL-2V-P,N, which was used as not only support but also as ligands. The catalyst was investigated by means of 31 P NMR, X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopic (XPS) and FT-IR and tested for the methoxycarbonylation of acetylene. According to the results of 31 P NMR, XPS and EXAFS, there existed coordination bonds between palladium and the exposed phosphorous and nitrogen atoms of the porous POL-2V-P,N support. The XPS and FT-IR results showed that Pd 0 species were present on the Pd/POL-2V-P,N catalyst. The heterogenized Pd/POL-2V-P,N palladium complex catalyst with high surface area and large pore volume displayed excellent activity for the methoxycarbonylation of acetylene as compared with the corresponding homogeneous palladium diphenyl-2-pyridylphosphine complex (Pd-P,N) under the same conditions. The used Pd/POL-2V-P,N catalyst also exhibited excellent activity under the same conditions. In addition, the hot filtration tests indicated that the reaction occurred in a heterogeneous way. [ABSTRACT FROM AUTHOR]