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  • 1
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    Simultaneous denoising and reconstruction of 5-D seismic data via damped rank-reduction method (2016)
    Oxford University Press
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    Publication Date: 2016-07-20
    Description: The Cadzow rank-reduction method can be effectively utilized in simultaneously denoising and reconstructing 5-D seismic data that depend on four spatial dimensions. The classic version of Cadzow rank-reduction method arranges the 4-D spatial data into a level-four block Hankel/Toeplitz matrix and then applies truncated singular value decomposition (TSVD) for rank reduction. When the observed data are extremely noisy, which is often the feature of real seismic data, traditional TSVD cannot be adequate for attenuating the noise and reconstructing the signals. The reconstructed data tend to contain a significant amount of residual noise using the traditional TSVD method, which can be explained by the fact that the reconstructed data space is a mixture of both signal subspace and noise subspace. In order to better decompose the block Hankel matrix into signal and noise components, we introduced a damping operator into the traditional TSVD formula, which we call the damped rank-reduction method. The damped rank-reduction method can obtain a perfect reconstruction performance even when the observed data have extremely low signal-to-noise ratio. The feasibility of the improved 5-D seismic data reconstruction method was validated via both 5-D synthetic and field data examples. We presented comprehensive analysis of the data examples and obtained valuable experience and guidelines in better utilizing the proposed method in practice. Since the proposed method is convenient to implement and can achieve immediate improvement, we suggest its wide application in the industry.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 2
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    Temperature, doping, and polarization effects on Bi 6p and S 3p states in the BiS_{2} -layered superconductor LaO_{1−x} F_{x} BiS_{2} (2016)
    American Physical Society (APS)
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    Publication Date: 2016-07-26
    Description: Author(s): Y. Y. Chin, H.-J. Lin, Z. Hu, Masanori Nagao, Yongping Du, Xiangang Wan, B.-J. Su, L. Y. Jang, T. S. Chan, H.-Y. Chen, Y. L. Soo, and C. T. Chen The x-ray absorption spectra at the Bi- L 1 and S- K edges of LaO 1 − x F x BiS 2 show a decrease of spectral weight close to the absorption thresholds upon F substitution for O, indicating a reduction of the unoccupied Bi 6 p and S 3 p states, as expected for electron doping. This doping-induced spectral weigh… [Phys. Rev. B 94, 035150] Published Mon Jul 25, 2016
    Keywords: Electronic structure and strongly correlated systems
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
    Published by American Physical Society (APS)
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  • 3
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    Velocity analysis of simultaneous-source data using high-resolution semblance--coping with the strong noise (2015)
    Oxford University Press
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    Publication Date: 2015-12-11
    Description: Direct imaging of simultaneous-source (or blended) data, without the need of deblending, requires a precise subsurface velocity model. In this paper, we focus on the velocity analysis of simultaneous-source data using the normal moveout-based velocity picking approach.We demonstrate that it is possible to obtain a precise velocity model directly from the blended data in the common-midpoint domain. The similarity-weighted semblance can help us obtain much better velocity spectrum with higher resolution and higher reliability compared with the traditional semblance. The similarity-weighted semblance enforces an inherent noise attenuation solely in the semblance calculation stage, thus it is not sensitive to the intense interference. We use both simulated synthetic and field data examples to demonstrate the performance of the similarity-weighted semblance in obtaining reliable subsurface velocity model for direct migration of simultaneous-source data. The migrated image of blended field data using prestack Kirchhoff time migration approach based on the picked velocity from the similarity-weighted semblance is very close to the migrated image of unblended data.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 4
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    Tomographic resolution of plume anomalies in the lowermost mantle (2015)
    Oxford University Press
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    Publication Date: 2015-03-25
    Description: Mantle plumes as well as ‘superplumes’ have been imaged in the lowermost mantle in tomographic studies. To investigate seismic resolution of deep mantle plume anomalies, we use a spectral element method (SEM) to simulate global seismic wave propagation in 3-D wave speed models and measure frequency-dependent P -, S -, Pdiff - and Sdiff -wave traveltime anomalies caused by plume structures in the lowermost mantle. We compare SEM time delay measurements with calculations based on ray theory and show that an anticorrelation between bulk sound wave speed and S -wave speed could be produced as an artifact. This is caused by different wavefront healing effects between P and S waves in thermal plume models. The differences in wave diffraction between the two types of waves depend on epicentral distance and wave frequency. We show that bulk-sound speed structure can not be recovered in ray-theoretical tomographic inversions when the lateral extent of the anomaly is smaller than the size of the Fresnel zone in the lowermost mantle. In addition, an anticorrelation between bulk sound speed and S -wave speed can be produced in ray-theoretical tomography when the size of the anomaly is less than ~2000 km; and, the artifacts become more pronounced as the lateral extent of the plume decreases. This indicates a chemical origin of ‘superplumes’ in the lowermost mantle may not be necessary to explain observed seismic traveltimes of core–mantle diffracted waves. The same set of Pdiff and Sdiff measurements are inverted using finite-frequency tomography based on Born sensitivity kernels. We show that wavefront healing effects can be accounted for in finite-frequency tomography to recover the true velocity model.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 5
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    Rapid lateral variation of P-wave velocity at the base of the mantle near the edge of the Large-Low Shear Velocity Province beneath the western Pacific (2014)
    Oxford University Press
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    Publication Date: 2014-12-25
    Description: We examine P -wave velocity structure at the base of the mantle beneath the western Pacific, near the western edge of the Pacific Large-Low Shear Velocity Province (LLSVP), using high-quality seismograms provided by a large-scale mobile broad-band seismic observation in northeastern China (the NECESSArray project). Forward modelling using the reflectivity method is conducted to explain the variation of P -wave traveltimes as a function of epicentral distance near the core shadow zone. Additionally, PcP–P traveltimes are examined to enlarge the survey area. As a result, a rapid variation of P -wave velocity is detected at the base of the mantle. Regions of thin (20–50 km thick) and low velocity (–2 to –5 per cent) layers at the base of the mantle are intersected by an 80-km-thick region with a high velocity (+2 per cent). A slightly fast region exists at the northwest of the region with the thin low-velocity layer. These layers are typically separated by several hundred kilometres and would be difficult to explain by thermal effects alone. These observations suggest that very complicated thermochemical reactions occur near the edge of the Pacific LLSVP.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 6
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    Angle-resolved photoemission study of the electronic structure of the quantum spin liquid EtMe3Sb[Pd(dmit)2]2 (2014)
    American Physical Society (APS)
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    Publication Date: 2014-02-06
    Description: Author(s): Q. Q. Ge, H. C. Xu, X. P. Shen, M. Xia, B. P. Xie, F. Chen, Y. Zhang, R. Kato, T. Tsumuraya, T. Miyazaki, M. Matsunami, S. Kimura, and D. L. Feng The electronic structure of a quantum spin liquid compound, EtMe3Sb[Pd(dmit)2]2, has been studied with angle-resolved photoemission spectroscopy, together with two other Pd(dmit)2 salts in the valence bond solid or antiferromagnetic state. EtMe3Sb[Pd(dmit)2]2, being a Mott insulator, has its lower H... [Phys. Rev. B 89, 075105] Published Wed Feb 05, 2014
    Keywords: Electronic structure and strongly correlated systems
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
    Published by American Physical Society (APS)
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  • 7
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    Ferromagnetic Weyl fermions in ${\mathrm{CrO}}_{2}$ (2018)
    American Physical Society (APS)
    Details
    Publication Date: 2018-06-01
    Description: Author(s): R. Wang, Y. J. Jin, J. Z. Zhao, Z. J. Chen, Y. J. Zhao, and H. Xu The interplay between symmetry and magnetization directions in ferromagnetic materials provides an exotic platform to investigate the symmetry-protected topological order. In this work, we propose that unexpected ferromagnetic topological features, such as triple fermions and type-I and type-II Weyl... [Phys. Rev. B 97, 195157] Published Thu May 31, 2018
    Keywords: Electronic structure and strongly correlated systems
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
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  • 8
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    Crustal radial anisotropy in Northeast China and its implications for the regional tectonic extension (2016)
    Oxford University Press
    Details
    Publication Date: 2016-08-25
    Description: We obtain high-resolution Rayleigh and Love wave phase velocity maps from ambient noise tomography using data recorded by NECESSArray in Northeast China. The resulting radial anisotropic model from the joint inversion of Rayleigh and Love wave dispersion curves reveals strong relationship between the crustal radial anisotropy and tectonic provinces, that is, strong positive anisotropy ( V sh 〉 V sv ) beneath the Songliao Basin and weak radial anisotropy beneath the Xinmeng Belt and Changbaishan Region. The Songliao Basin experienced widespread crustal extension during the late Mesozoic. We interpret the lower crustal anisotropy beneath the Songliao Basin as a result of ductile deformation during the rifting stage, which may lead to the alignment of anisotropic minerals and the observed strong radial anisotropy at present. In the northern Songliao Basin, where thick syn-rift and post-rift sediments (≥4 km) are believed to be present, we observe a broader lateral distribution of anisotropy with stronger amplitude compared with the southern basin. We suggest that the broader distribution of crustal radial anisotropy in the northern basin could be the consequence of outward lower crustal flow driven by the sedimentary loading during the post-rift stage, which is also proposed by previous numerical modeling.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 9
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    Crustal structure and deformation beneath the NE margin of the Tibetan plateau constrained by teleseismic receiver function data (2015)
    Oxford University Press
    Details
    Publication Date: 2015-11-19
    Description: We analysed a large amount of teleseismic receiver function data recorded by 172 broadband stations in the NE Tibetan plateau and its surrounding areas to investigate the crustal velocity and anisotropy structure beneath the margin. We first applied the modified H – stacking technique to measure the crustal thickness and average Vp / V s ratio, and then employed a joint inversion scheme to measure azimuthal anisotropy of the crust beneath each station. The observed crustal thickness and Vp / Vs ratio exhibit large variations across the study area, varying from 32 to 75.6 km and from 1.601 to 1.864, respectively. We also found significant azimuthal anisotropy within the crust beneath 12 stations, with a splitting time between 0.36 and 1.06s. The fast polarization directions align well with surface structures, and follow the directions of the maximum horizontal tensile stress. The low Vp / Vs ratio and the strong azimuthal anisotropy observed beneath the margin suggest that whole crustal shortening might be the dominant mechanism for producing the thick crust in NE Tibet. We compared the measured seismic anisotropy with those measured from XKS (SKS, PKS and SKKS), and found that crustal anisotropy appears to play an important role in explaining the amount of XKS splitting times. More importantly, the Moho Ps and the XKS share similar fast polarization directions, suggesting a vertically coherent deformation within the lithosphere beneath the margin.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 10
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    Static charge-density-wave order in the superconducting state of La_{2−x} Ba_{x} CuO_{4} (2017)
    American Physical Society (APS)
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    Publication Date: 2017-06-22
    Description: Author(s): V. Thampy, X. M. Chen, Y. Cao, C. Mazzoli, A. M. Barbour, W. Hu, H. Miao, G. Fabbris, R. D. Zhong, G. D. Gu, J. M. Tranquada, I. K. Robinson, S. B. Wilkins, and M. P. M. Dean Charge-density-wave (CDW) correlations feature prominently in the phase diagram of the cuprates, motivating competing theories of whether fluctuating CDW correlations aid superconductivity or whether static CDW order coexists with superconductivity in inhomogeneous or spatially modulated states. Her… [Phys. Rev. B 95, 241111(R)] Published Wed Jun 21, 2017
    Keywords: Electronic structure and strongly correlated systems
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
    Published by American Physical Society (APS)
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