Elastic reverse time migration(RTM)uses the elastic wave equation to extrapolate multicomponent seismic data to the subsurface and separate the elastic wavefield into P-and S-waves.P-and S-wave separation is a necessa...Elastic reverse time migration(RTM)uses the elastic wave equation to extrapolate multicomponent seismic data to the subsurface and separate the elastic wavefield into P-and S-waves.P-and S-wave separation is a necessary step in elastic RTM to avoid crosstalk between coupled wavefields.However,the current curl-divergence operator-based separation method has a polarity reversal problem in PS imaging,and vector separation methods often have separation artifacts at the interface,which affects the quality of the imaging stack.We propose a non-artifact P-and S-wave separation method based on the first-order velocity-strain equation.This equation is used for wavefield extrapolation and separation in the first-order staggered-grid finite-difference scheme,and the storage and calculation amounts are consistent with the classical first-order velocity-stress equation.The separation equation does not calculate the partial derivatives of the elastic parameters,and thus,there is no artifact in the separated Pand S-waves.During wavefield extrapolation,the dynamic characteristics of the reflected wave undergo some changes,but the transmitted wavefield is accurate;therefore,it does not affect the dynamic characteristics of the final migration imaging.Through numerical examples of 2 D simple models,part SEAM model,BP model,and 3 D 4-layer model,different wavefield separation methods and corresponding elastic RTM imaging results are analyzed.We found that the velocity-strain based elastic RTM can image subsurface structures well,without spike artifacts caused by separation artifacts,and without polarity reversal phenomenon of the PS imaging.展开更多
We investigate the critical exponents and magnetocaloric effect of Co2-xZrSn polycrystal. The Co2-xZrSn undergoes a second-order ferromagnetism phase transition around the Curie temperature of Tc ~280 K. The critical ...We investigate the critical exponents and magnetocaloric effect of Co2-xZrSn polycrystal. The Co2-xZrSn undergoes a second-order ferromagnetism phase transition around the Curie temperature of Tc ~280 K. The critical behavior in the vicinity of the magnetic phase transition has been investigated by using modified Arrott plot and Kouvel–Fisher methods.The obtained critical exponents, β, γ, and δ can be well described by the scaling theory. The determined exponents of Co2-xZrSn obey the mean-field model with a long-range magnetic interaction. In addition, the maximum magnetic entropy change-?Sm ax M of Co2-xZrSn is about 0.57 J·kg-1·K-1 and the relative cooling power(RCP) is 14.68 J·kg-1 at 50 kOe(1 Oe = 79.5775 A·m-1).展开更多
Electrides are unique materials with the anionic electrons confined to the interstitial sites,expecting important applications in various areas.In this work,the electronic structure and detailed physical properties of...Electrides are unique materials with the anionic electrons confined to the interstitial sites,expecting important applications in various areas.In this work,the electronic structure and detailed physical properties of topological electride Ca_(3)Pb are studied theoretically.By comparing the crystal structures and band structures of Ca_(3)Pb and Ca_(3)PbO,we find that after removing O^(2-)ions from Ca_(3)PbO,the remaining electrons are confined in the vacancies of the Ca6 octahedra centers,playing the role as anions and forming an additional energy band compared with that of Ca_(3)Pb.These interstitial electrons partially result in the low work function of Ca_(3)Pb.Moreover,the calculated mechanic properties imply that Ca_(3)Pb has a strong brittleness.In addition,the dielectric functions and optical properties of Ca_(3)Pb are also analyzed.展开更多
Electrides are unique materials,whose anionic electrons are confined to interstitial voids,and they have broad potential applications in various areas.In contrast to the majority of inorganic electrides,in which the a...Electrides are unique materials,whose anionic electrons are confined to interstitial voids,and they have broad potential applications in various areas.In contrast to the majority of inorganic electrides,in which the anionic electrons primarily consist of s-electrons of metals,electrides with anionic d-electrons are very rare.Based on first-principles electronic structure calculations,we predict that the layered transition metal chalcogenide Hf_(2)Se is a novel electride candidate with anionic d-electrons.Our results indicate that the anionic electrons confined in the Hf_(6) octahedra vacancy between [Hf_(2)Se] layers mainly come from the Hf-5 d orbitals.In addition,the anionic electrons coexist with the Hf-Hf multiple-center metallic bonds located in the center of neighboring Hf_(4) tetrahedra.The calculated work function(3.33 eV) for the(110) surface of Hf_(2)Se is slightly smaller than that of Hf_(2)S,which has recently been reported to exhibit good electrocatalytic performance.Our study of Hf2 Se will enrich the electride family,and promote further research into the physical properties and applications of electrides.展开更多
基金supported by the National Natural Science Foundation of China,Grant No.41774142
文摘Elastic reverse time migration(RTM)uses the elastic wave equation to extrapolate multicomponent seismic data to the subsurface and separate the elastic wavefield into P-and S-waves.P-and S-wave separation is a necessary step in elastic RTM to avoid crosstalk between coupled wavefields.However,the current curl-divergence operator-based separation method has a polarity reversal problem in PS imaging,and vector separation methods often have separation artifacts at the interface,which affects the quality of the imaging stack.We propose a non-artifact P-and S-wave separation method based on the first-order velocity-strain equation.This equation is used for wavefield extrapolation and separation in the first-order staggered-grid finite-difference scheme,and the storage and calculation amounts are consistent with the classical first-order velocity-stress equation.The separation equation does not calculate the partial derivatives of the elastic parameters,and thus,there is no artifact in the separated Pand S-waves.During wavefield extrapolation,the dynamic characteristics of the reflected wave undergo some changes,but the transmitted wavefield is accurate;therefore,it does not affect the dynamic characteristics of the final migration imaging.Through numerical examples of 2 D simple models,part SEAM model,BP model,and 3 D 4-layer model,different wavefield separation methods and corresponding elastic RTM imaging results are analyzed.We found that the velocity-strain based elastic RTM can image subsurface structures well,without spike artifacts caused by separation artifacts,and without polarity reversal phenomenon of the PS imaging.
基金Project supported by the Fundamental Research Funds for the Central Universities(Grant No.2017RC20)the Research Innovation Fund for College Students of Beijing University of Posts and Telecommunications
文摘We investigate the critical exponents and magnetocaloric effect of Co2-xZrSn polycrystal. The Co2-xZrSn undergoes a second-order ferromagnetism phase transition around the Curie temperature of Tc ~280 K. The critical behavior in the vicinity of the magnetic phase transition has been investigated by using modified Arrott plot and Kouvel–Fisher methods.The obtained critical exponents, β, γ, and δ can be well described by the scaling theory. The determined exponents of Co2-xZrSn obey the mean-field model with a long-range magnetic interaction. In addition, the maximum magnetic entropy change-?Sm ax M of Co2-xZrSn is about 0.57 J·kg-1·K-1 and the relative cooling power(RCP) is 14.68 J·kg-1 at 50 kOe(1 Oe = 79.5775 A·m-1).
基金the National Natural Science Foundation of China(Grant No.12074013)the Research Innovation Fund for College Students of Beijing University of Posts and Telecommunications,the Fundamental Research Funds for the Central Universities,Chinathe Research Funds of Renmin University of China(Grant No.20XNH064).
文摘Electrides are unique materials with the anionic electrons confined to the interstitial sites,expecting important applications in various areas.In this work,the electronic structure and detailed physical properties of topological electride Ca_(3)Pb are studied theoretically.By comparing the crystal structures and band structures of Ca_(3)Pb and Ca_(3)PbO,we find that after removing O^(2-)ions from Ca_(3)PbO,the remaining electrons are confined in the vacancies of the Ca6 octahedra centers,playing the role as anions and forming an additional energy band compared with that of Ca_(3)Pb.These interstitial electrons partially result in the low work function of Ca_(3)Pb.Moreover,the calculated mechanic properties imply that Ca_(3)Pb has a strong brittleness.In addition,the dielectric functions and optical properties of Ca_(3)Pb are also analyzed.
基金Supported by the National Natural Science Foundation of China(Grant No.11774424)the Fundamental Research Funds for the Central Universities(Grant No.2017RC20)+3 种基金the Research Funds of Renmin University of China(Grant No.20XNH064)the CAS Interdisciplinary Innovation Teamthe Beijing Natural Science Foundation(Grant No.Z200005)the Research Innovation Fund for College Students of Beijing University of Posts and Telecommunications。
文摘Electrides are unique materials,whose anionic electrons are confined to interstitial voids,and they have broad potential applications in various areas.In contrast to the majority of inorganic electrides,in which the anionic electrons primarily consist of s-electrons of metals,electrides with anionic d-electrons are very rare.Based on first-principles electronic structure calculations,we predict that the layered transition metal chalcogenide Hf_(2)Se is a novel electride candidate with anionic d-electrons.Our results indicate that the anionic electrons confined in the Hf_(6) octahedra vacancy between [Hf_(2)Se] layers mainly come from the Hf-5 d orbitals.In addition,the anionic electrons coexist with the Hf-Hf multiple-center metallic bonds located in the center of neighboring Hf_(4) tetrahedra.The calculated work function(3.33 eV) for the(110) surface of Hf_(2)Se is slightly smaller than that of Hf_(2)S,which has recently been reported to exhibit good electrocatalytic performance.Our study of Hf2 Se will enrich the electride family,and promote further research into the physical properties and applications of electrides.
