Wurtzite strcture gallium nitride, GaN,a direct bandgap semiconductor (3.4 eV at room temperature),is an ideal material for fabrication of blue/green light emit ti ng diodes, laser diodes,and high power integrated cir...Wurtzite strcture gallium nitride, GaN,a direct bandgap semiconductor (3.4 eV at room temperature),is an ideal material for fabrication of blue/green light emit ti ng diodes, laser diodes,and high power integrated circuits.Recent progress in th in film crystal technique has realized the output of blue semiconductor lasers w i th a lifetime of over 10000 hours under continuous wave operation at room tempe r ature.So far GaN and its ternary indium and aluminum alloys are grown almost uni v ersally on foreign substrates with varying lattice mismatches.The mismatch undou btedly results in a significant dislocation density in the grown films.Hence it is necessary to grow single crystal GaN to be used as substrates for improvement of laser diodes.On the other hand,low dimensional GaN materials such as nanocry stalline powder,nanocrystal assembled bulk(nanophase) and nano wires are very u seful in both fundamental mesoscopic research and future development of GaN nano devices.Here we report our main recent progresses on the crystal growth of GaN a nd the preparation of its low dimensional materials.展开更多
To investigate the seismic passive earth thrust with two-dimensional steady seepage, a general pseudo-dynamic solution was established based on the limit equilibrium analysis. This solution was purposefully applied to...To investigate the seismic passive earth thrust with two-dimensional steady seepage, a general pseudo-dynamic solution was established based on the limit equilibrium analysis. This solution was purposefully applied to a waterfront gravity wall, which retains a submerged backfill with a drainage system along the backfill-structure interface. The wall was assumed to move towards the backfill to the passive failure state. And the theoretical derivation considered the pore pressures induced by the seepage, the excess pore pressures generated by the earthquake and the seismic inertial forces. Thereinto, the hydrostatic and hydrodynamic pressures were calculated by the analytical formulas, while the seismic forces were obtained by the pseudo-dynamic method. In the parametric study, the results indicate that the velocity of shear wave has a more prominent impact on the seismic passive earth thrust than that of primary wave. Both the horizontal and vertical seismic actions decrease the passive earth pressure, but the horizontal one affects the amplitude of the earth pressure coefficient more significantly. Moreover, the soil friction and the wall friction distinctly increase the seismic passive earth pressure just like the static situation. The comparison shows that the results are consistent with the previous work, which verifies its validity.展开更多
文摘Wurtzite strcture gallium nitride, GaN,a direct bandgap semiconductor (3.4 eV at room temperature),is an ideal material for fabrication of blue/green light emit ti ng diodes, laser diodes,and high power integrated circuits.Recent progress in th in film crystal technique has realized the output of blue semiconductor lasers w i th a lifetime of over 10000 hours under continuous wave operation at room tempe r ature.So far GaN and its ternary indium and aluminum alloys are grown almost uni v ersally on foreign substrates with varying lattice mismatches.The mismatch undou btedly results in a significant dislocation density in the grown films.Hence it is necessary to grow single crystal GaN to be used as substrates for improvement of laser diodes.On the other hand,low dimensional GaN materials such as nanocry stalline powder,nanocrystal assembled bulk(nanophase) and nano wires are very u seful in both fundamental mesoscopic research and future development of GaN nano devices.Here we report our main recent progresses on the crystal growth of GaN a nd the preparation of its low dimensional materials.
基金Projects(U1234204,51378463) supported by the National Natural Science Foundation of China
文摘To investigate the seismic passive earth thrust with two-dimensional steady seepage, a general pseudo-dynamic solution was established based on the limit equilibrium analysis. This solution was purposefully applied to a waterfront gravity wall, which retains a submerged backfill with a drainage system along the backfill-structure interface. The wall was assumed to move towards the backfill to the passive failure state. And the theoretical derivation considered the pore pressures induced by the seepage, the excess pore pressures generated by the earthquake and the seismic inertial forces. Thereinto, the hydrostatic and hydrodynamic pressures were calculated by the analytical formulas, while the seismic forces were obtained by the pseudo-dynamic method. In the parametric study, the results indicate that the velocity of shear wave has a more prominent impact on the seismic passive earth thrust than that of primary wave. Both the horizontal and vertical seismic actions decrease the passive earth pressure, but the horizontal one affects the amplitude of the earth pressure coefficient more significantly. Moreover, the soil friction and the wall friction distinctly increase the seismic passive earth pressure just like the static situation. The comparison shows that the results are consistent with the previous work, which verifies its validity.
