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  • 1
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    Earthquake Focal Mechanisms in Yunnan and their Inference on the Regional Stress Field (2013)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2013-08-01
    Description: Using the broadband records from a regional permanent network, we determined the focal mechanisms of 174 small and moderate earthquakes (3.4≤ M w ≤6.0) from January 2008 to March 2011 in Yunnan, China, by fitting the three-component waveforms of P and S waves. Results show that the earthquakes predominantly have strike-slip mechanisms, with occasional normal and very few thrust-faulting events. Most earthquakes occur in the upper crust above 16 km depth. We then derive the regional distribution of the stress field through a damped linear inversion using the focal mechanisms obtained in this study and augmented by the solutions in the Global Centroid Moment Tensor (GCMT) catalog and in Xu et al. (2010) . Inversion results suggest that the entire region is predominantly under a strike-slip faulting regime. Orientations of both maximum and minimum principle axes exhibit a clockwise rotational pattern. The axes of maximum compression are oriented roughly north–south, with a gradual change across the region from trending northwest–southeast in the South China block to trending northeast–southwest in the Indo-China block. This pattern is consistent with the surface horizontal velocity derived from geodetic observations. Localized normal faulting stress regions are observed in the Tengchong volcanic zone and in the Qiao-Jia segment of the Xianshuihe–Xiaojiang fault zone. Online Material: Tables of earthquake catalogs and figures describing stress inversion tests.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 2
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    Earthquake Focal Mechanisms in Yunnan and their Inference on the Regional Stress Field (2013)
    Seismological Society of America
    Details
    Publication Date: 2013-07-31
    Description: Using the broadband records from a regional permanent network, we determined the focal mechanisms of 174 small and moderate earthquakes (3.4〈 or =M (sub w) 〈 or =6.0) from January 2008 to March 2011 in Yunnan, China, by fitting the three-component waveforms of P and S waves. Results show that the earthquakes predominantly have strike-slip mechanisms, with occasional normal and very few thrust-faulting events. Most earthquakes occur in the upper crust above 16 km depth. We then derive the regional distribution of the stress field through a damped linear inversion using the focal mechanisms obtained in this study and augmented by the solutions in the Global Centroid Moment Tensor (GCMT) catalog and in Xu et al. (2010). Inversion results suggest that the entire region is predominantly under a strike-slip faulting regime. Orientations of both maximum and minimum principle axes exhibit a clockwise rotational pattern. The axes of maximum compression are oriented roughly north-south, with a gradual change across the region from trending northwest-southeast in the South China block to trending northeast-southwest in the Indo-China block. This pattern is consistent with the surface horizontal velocity derived from geodetic observations. Localized normal faulting stress regions are observed in the Tengchong volcanic zone and in the Qiao-Jia segment of the Xianshuihe-Xiaojiang fault zone.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America
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  • 3
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    Forward and adjoint simulations of seismic wave propagation on fully unstructured hexahedral meshes (2012)
    Details
    Publication Date: 2021-06-25
    Description: We present forward and adjoint spectral-element simulations of coupled acoustic and (an)elastic seismic wave propagation on fully unstructured hexahedral meshes. Simulations benefit from recent advances in hexahedral meshing, load balancing and software optimization. Meshing may be accomplished using a mesh generation tool kit such as CUBIT, and load balancing is facilitated by graph partitioning based on the SCOTCH library. Coupling between fluid and solid regions is incorporated in a straightforward fashion using domain decomposition. Topography, bathymetry and Moho undulations may be readily included in the mesh, and physical dispersion and attenuation associated with anelasticity are accounted for using a series of standard linear solids. Finite-frequency Fre ́chet derivatives are calculated using adjoint methods in both fluid and solid domains. The software is benchmarked for a layercake model. We present various examples of fully unstructured meshes, snapshots of wavefields and finite-frequency kernels generated by Version 2.0 ‘Sesame’ of our widely used open source spectral-element package SPECFEM3D.
    Description: Published
    Description: 721-739
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Tomography ; Interferometry ; Computational seismology ; Wave propagation ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis ; 05. General::05.01. Computational geophysics::05.01.99. General or miscellaneous ; 05. General::05.01. Computational geophysics::05.01.05. Algorithms and implementation
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Mechanisms of microbial carbon sequestration in the ocean – future research directions (2014)
    COPERNICUS GESELLSCHAFT MBH
    In:  EPIC3Biogeosciences, COPERNICUS GESELLSCHAFT MBH, 11(19), pp. 5285-5306, ISSN: 1726-4170
    Details
    Publication Date: 2014-10-14
    Description: This paper reviews progress on understanding biological carbon sequestration in the ocean with special reference to the microbial formation and transformation of recalcitrant dissolved organic carbon (RDOC), the microbial car bon pump (MCP). We propose that RDOC is a concept with a wide continuum of recalcitrance. Most RDOC compounds maintain their levels of recalcitrance only in a specific environmental context (RDOCt). The ocean RDOC pool also contains compounds that may be inaccessible to microbes due to their extremely low concentration (RDOCc). This differentiation allows us to appreciate the linkage between microbial source and RDOC composition on a range of temporal and spatial scales. Analyses of biomarkers and isotopic records show intensive MCP processes in the Proterozoic oceans when the MCP could have played a significant role in regulating climate. Understanding the dynamics of the MCP in conjunction with the better constrained biological pump (BP) over geological timescales could help to predict future climate trends. Integration of the MCP and the BP will require new research approaches and opportunities. Major goals include understanding the interactions between particulate organic carbon (POC) and RDOC that contribute to sequestration efficiency, and the concurrent determination of the chemical composition of organic carbon, microbial community composition and enzymatic activity. Molecular biomarkers and isotopic tracers should be employed to link water column processes to sediment records, as well as to link present-day observations to paleo-evolution. Ecosystem models need to be developed based on empirical relationships derived from bioassay experiments and field investigations in order to predict the dynamics of carbon cycling along the stability continuum of POC and RDOC under potential global change scenarios. We propose that inorganic nutrient input to coastal waters may reduce the capacity for carbon sequestration as RDOC. The nutrient regime enabling maximum carbon storage from combined POC flux and RDOC formation should therefore be sought.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 5
    Electronic Resource
    Electronic Resource
    Electrical conduction in annealed semi-insulating InP (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 3838-3842 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Variable-temperature current–voltage has been used to study the conduction properties of Fe-doped semi-insulating (SI) InP in the as-grown and annealed states. It is found that the trap-filling (TF) process disappears gradually with lengthening of annealing time. This phenomenon is explained by the decrease of the concentration of the empty Fe deep level (Fe3+) that is caused by the thermally induced donor defect formation. The TF process cannot be observed in annealed undoped and long-time annealed Fe-doped SI InP material. The breakdown field of annealed undoped and Fe-doped SI InP is much lower than that of as-grown Fe-doped InP material. The breakdown field decreases with decreasing of temperature indicating an impact ionization process. This breakdown behavior is also in agreement with the fact that the concentration of the empty deep level in annealed InP is lowered. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372422
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  • 6
    Electronic Resource
    Electronic Resource
    Growth of carbon nanotubes by gas source molecular beam epitaxy (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 1973-1976 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Multiwall carbon nanotubes have been grown by gas source molecular beam epitaxy in the presence of Ni catalyst. Some nanotubes show thinner bases compared with their heads. First- and second-order Raman scattering spectra are used to study the structure of samples with different initial thicknesses of Ni layers. The second-order 2D Raman mode of carbon nanotubes shows a downshift compared with the graphite-like structure. The growth of carbon nanotubes is found to depend on the size of the metal droplets. When the initial Ni layer is either too thick or too thin, few carbon nanotubes are observed. The Raman spectra show graphite and glassy carbon structures for too thick and too thin initial Ni layer films, respectively. Only when a proper range of Ni catalyst film is used, carbon nanotubes could be found. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1337083
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  • 7
    Electronic Resource
    Electronic Resource
    Ge/Si interdiffusion in the GeSi dots and wetting layers (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 4290-4292 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Ge/Si interdiffusion in GeSi dots grown on Si (001) substrate by gas-source molecular beam epitaxy is investigated. Transmission electron microscopy images show that, after annealing, the aspect ratio of the height to base diameter increases. Raman spectra show that the Si–Ge mode redshifts and the intensity of the local Si–Si mode increases with the increase of annealing temperature, which suggests the Ge/Si interdiffusion during annealing. The photoluminescence peaks from the dots and the wetting layers show blueshift due to the atomic intermixing during annealing. The interdiffusion thermal activation energies of GeSi dots and the wetting layers are 2.16 and 2.28 eV, respectively. The interdiffusion coefficient of the dots is about 40 times higher than that of wetting layers and the reasons were discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1403667
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  • 8
    Electronic Resource
    Electronic Resource
    High-quality strain-relaxed SiGe films grown with low temperature Si buffer (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 8279-8283 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-quality strain-relaxed SiGe templates with a low threading dislocation density and smooth surface are critical for device performance. In this work, SiGe films on low temperature Si buffer layers were grown by solid-source molecular beam epitaxy and characterized by atomic force microscope, double-axis x-ray diffraction, photoluminescence spectroscopy, and Raman spectroscopy. Effects of the growth temperature and the thickness of the low temperature Si buffer were studied. It was demonstrated that when using proper growth conditions for the low temperature Si buffer the Si buffer became tensily strained and gave rise to the compliant effect. The lattice mismatch between the SiGe and the Si buffer layer was reduced. A 500 nm Si0.7Ge0.3 film with a low threading dislocation density as well as smooth surface was obtained by this method. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1375801
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  • 9
    Electronic Resource
    Electronic Resource
    Native donors and compensation in Fe-doped liquid encapsulated Czochralski InP (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 86-90 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Undoped and Fe-doped liquid encapsulated Czochralski (LEC) InP has been studied by Hall effect, current–voltage (I–V), and infrared absorption (IR) spectroscopy. The results indicate that a native hydrogen vacancy complex donor defect exists in as-grown LEC InP. By studying the IR results, it is found that the concentration of this donor defect in Fe-doped InP is much higher than that in undoped InP. This result is consistent with the observation that a much higher concentration of Fe2+ than the apparent net donor concentration is needed to achieve the semi-insulating (SI) property in InP. By studying the I–V and IR results of Fe-doped InP wafers sliced from different positions on an ingot, the high concentration of Fe2+ is found to correlate with the existence of this hydrogen complex. The concentration of this donor defect is high in wafers from the top of an ingot. Correspondingly, a higher concentration of Fe2+ can be detected in these wafers. These results reveal the influence of the complex defect on the compensation and uniformity of Fe-doped SI InP materials. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1331644
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  • 10
    Electronic Resource
    Electronic Resource
    Harmonic mixing at mm waveband in a high temperature superconducting grain boundary Josephson junction (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2286-2288 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using a high Tc superconducting grain boundary Josephson junction, harmonic mixing experiments in the mm waveband were carried out, aiming at as large a harmonic number and as high a signal frequency as possible. The dependencies of intermediate frequency output on dc bias, harmonic number, frequency of local oscillator (LO), and other parameters were carefully studied. Until now, our best result was the mixing between the signal at 95 GHz and the 105th harmonic of LO at about 900 MHz. Preliminary experiments using a high Tc harmonic mixer and phase-locking loop were tried to stabilize the frequency of a mm wave source.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356293
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