The influence of polarization-induced electric fields on the electron distribution and the optical properties of intersubband transitions （ISBT） in AlxGa（1-x）N/GaN coupled double quantum wells （DQWs） is investig...The influence of polarization-induced electric fields on the electron distribution and the optical properties of intersubband transitions （ISBT） in AlxGa（1-x）N/GaN coupled double quantum wells （DQWs） is investigated by self-consistent calculation. It is found that the polarization-induced potential drop leads to an asymmetric potential profile of AlxGa（1-x）N/GaN DQWs even though the two wells have the same width and depth. The polarization effects result in a very large Stark shift between the odd and even order subbands,thus shortening the wavelength of the ISBT between the first odd order and the second even order （1odd-2 ） subbands. Meanwhile, the electron distribution becomes asymmetric due to the polarization effects, and the absorption coefficient of the 1odd-2 ISBT decreases with increasing polarization field discontinuity.展开更多
Triplicate waveform modeling is used to resolve SH （Vs） and P （Vp） wave velocity structures in the upper mantle transition zone （TZ） beneath northwestern （NW） Tibet. Focal depth move out stacking is proposed t...Triplicate waveform modeling is used to resolve SH （Vs） and P （Vp） wave velocity structures in the upper mantle transition zone （TZ） beneath northwestern （NW） Tibet. Focal depth move out stacking is proposed to enhance the identification of triplicate phases, and can be used to test consistency of our data. Our results show that the Vs and Vp structures are decorrelated, and that a large Vs jump occurred across the 660-km discontinuity, with a small Vs gradient above it. Conversely, the Vp model is characterized by a relatively small contrast across the discontinuity, accompanied by a high Vp gradient in the TZ. There seem no significant depth anomalies of the 660-kin discontinuity in both models. The seismic structures in TZ beneath NW Tibet are similar to recent studies beneath the central Qiangtang and western Lhasa terrains. Taking the lower TZ structures under India as references, Vs is normal but Vp appears slightly high, and thus a high ratio of Vp/Vs was indicated beneath NW Tibet. Combined results with experiment information from mineral studies, we suggest that the differential anomalies of Vp and Vs can be attributed to a chemical heterogeneity, such as increased A1 content in the lower TZ. Considering the tectonic evolution of Tibet, the chemical heterogeneity may be associated with subduction or detachment of the Tethys oceanic slab.展开更多
High-pressure polymorphs of olivine and enstatite are major constituent minerals in the mantle transition zone （MTZ）. The phase transformations of olivine and enstatite at pressure and temperature conditions corresp...High-pressure polymorphs of olivine and enstatite are major constituent minerals in the mantle transition zone （MTZ）. The phase transformations of olivine and enstatite at pressure and temperature conditions corresponding to the lower part of the MTZ are import for understanding the nature of the 660 km seismic discontinuity. In this study, we determine phase transfor- mations of olivine （MgSi204） and enstatite （MgSiO3） systematiclly at pressures between 21.3 and 24.4 GPa and at a constant temperature of 1600~C. The most profound discrepancy between olivine and enstatite phase transformation is the occurency of perovskite. In the olivine system, the post-spinel transformation occures at 23.8 GPa, corresponding to a depth of 660 km. In contrast, perovskite appears at 〈23 GPa （640 km） in the enstatite splitting of the 660 km seismic discountinuity under eastern China. system. The -1 GPa gap could explain the uplifting and/orsplitting of the 660 km seismic discountinuity under eastern China.展开更多
文摘The influence of polarization-induced electric fields on the electron distribution and the optical properties of intersubband transitions （ISBT） in AlxGa（1-x）N/GaN coupled double quantum wells （DQWs） is investigated by self-consistent calculation. It is found that the polarization-induced potential drop leads to an asymmetric potential profile of AlxGa（1-x）N/GaN DQWs even though the two wells have the same width and depth. The polarization effects result in a very large Stark shift between the odd and even order subbands,thus shortening the wavelength of the ISBT between the first odd order and the second even order （1odd-2 ） subbands. Meanwhile, the electron distribution becomes asymmetric due to the polarization effects, and the absorption coefficient of the 1odd-2 ISBT decreases with increasing polarization field discontinuity.
基金supported by the National Natural Science Foundation of China (Grant Nos. 40604009, 40574040, 40704011 and 40974061)
文摘Triplicate waveform modeling is used to resolve SH （Vs） and P （Vp） wave velocity structures in the upper mantle transition zone （TZ） beneath northwestern （NW） Tibet. Focal depth move out stacking is proposed to enhance the identification of triplicate phases, and can be used to test consistency of our data. Our results show that the Vs and Vp structures are decorrelated, and that a large Vs jump occurred across the 660-km discontinuity, with a small Vs gradient above it. Conversely, the Vp model is characterized by a relatively small contrast across the discontinuity, accompanied by a high Vp gradient in the TZ. There seem no significant depth anomalies of the 660-kin discontinuity in both models. The seismic structures in TZ beneath NW Tibet are similar to recent studies beneath the central Qiangtang and western Lhasa terrains. Taking the lower TZ structures under India as references, Vs is normal but Vp appears slightly high, and thus a high ratio of Vp/Vs was indicated beneath NW Tibet. Combined results with experiment information from mineral studies, we suggest that the differential anomalies of Vp and Vs can be attributed to a chemical heterogeneity, such as increased A1 content in the lower TZ. Considering the tectonic evolution of Tibet, the chemical heterogeneity may be associated with subduction or detachment of the Tethys oceanic slab.
基金financially supported by the Sinoprobe-0801National Natural Science Foundation of China(Grant Nos.41002068&41174076)
文摘High-pressure polymorphs of olivine and enstatite are major constituent minerals in the mantle transition zone （MTZ）. The phase transformations of olivine and enstatite at pressure and temperature conditions corresponding to the lower part of the MTZ are import for understanding the nature of the 660 km seismic discontinuity. In this study, we determine phase transfor- mations of olivine （MgSi204） and enstatite （MgSiO3） systematiclly at pressures between 21.3 and 24.4 GPa and at a constant temperature of 1600~C. The most profound discrepancy between olivine and enstatite phase transformation is the occurency of perovskite. In the olivine system, the post-spinel transformation occures at 23.8 GPa, corresponding to a depth of 660 km. In contrast, perovskite appears at 〈23 GPa （640 km） in the enstatite splitting of the 660 km seismic discountinuity under eastern China. system. The -1 GPa gap could explain the uplifting and/orsplitting of the 660 km seismic discountinuity under eastern China.
