针对高原湖泊面积监测问题,采用2017年4月和2018年4月的SPOT6遥感影像,结合DEM数据,首先对数据进行图像镶嵌、正射校正和Gram-Schmidt Pan Sharpening算法融合等处理;再利用归一化差异水体指数提取湖泊整体;然后通过高斯低通滤波器突出水体特征,结合目视解译,选取合适的阈值精确划分水体边界;最后统计得到玛旁雍错湖泊的面积。结果表明,截至2018年4月,玛旁雍错湖泊总面积由412万km2减少到411.4万km2,平均退缩率为0.1%。通过分析普兰气象站的气象数据发现,玛旁雍错湖泊的萎缩与当年降水量变化和气温变化有关,降水量减少、气温升高导致湖泊萎缩,说明气象变化对玛旁雍错湖泊面积变化具有一定的影响。
Based on the k.p theory of Luttinger-Kohn and Bir-Pikus,analytical E-k solutions for the valence band of strained wurtzite ZnO materials are obtained.Strain effects on valence band edges and hole effective masses in strained wurtzite ZnO materials are also discussed.In comparison with unstrained ZnO materials,apparent movement of valence band edges such as "light hole band","heavy hole band" and "crystal splitting band" at Γ point is found in strained wurtzite ZnO materials.Moreover,effective masses of "light hole band","heavy hole band" and "crystal splitting band" for strained wurtzite ZnO materials as the function of stress are given.The analytical results can provide a theoretical foundation for the understanding of physics of strained ZnO materials and its applications with the framework for an effective mass theory.
The strain effects of the Zn1-xMgxO substrate on the bands structure of wurtzite Nb-doped Zn O bulk materials have been investigated using fi rst-principles calculations based on density functional theory. Firstly, the band gap increases gradually with increasing Nb contents in unstrained Nb-doped Zn O, which is consistent with the experimental results. Secondly, the band gap decreases with increasing substrate stress in Nb-doped Zn O/Zn1-xMgxO. Splitting energies between HHB(Heavy Hole Band) and LHB(Light Hole Band), HHB and CSB(Crystal Splitting Band) in Zn0.9167Nb0.0833O/Zn1-xMgxO almost remain unchanged with increasing substrate stress, while decrease slightly in Zn0.875Nb0.125O/Zn1-xMgxO. In addition, detailed analysis of the strain effects on the effective masses of electron and hole in Nb-doped Zn O/Zn1-xMgxO is also given.
Band structures in wurtzite bulk ZnO/Zn1-xMgxO are calculated using first-principles based on the framework of generalized gradient approximation to density functional theory with the introduction of the on-site Coulomb interaction. Strain effects on band gap, splitting energies of valence bands, electron and hole effective masses in strained bulk ZnO are discussed. According to the results, the band gap increases gradually with increasing stress in strained ZnO as an Mg content of Zn1..xMgxO substrate less than 0.3, which is consistent with the experimental results. It is further demonstrated that electron mass of conduction band(CB) under stress increases slightly. There are almost no changes in effective masses of light hole band(LHB) and heavy hole band(HHB)along [00k] and [k00] directions under stress, and stress leads to an obvious decrease in effective masses of crystal splitting band(CSB) along the same directions.
Inter valley scattering has a great impact on carrier mobility of strained Si materials,so based on Fermi’s golden rule and the theory of Boltzmann collision term approximation,inter valley phonon scattering mechanism of electrons in nano scale strained Si（101） materials is established under the influence of both energy and stress. It shows that inter valley phonon f2,f3,g3 scattering rates decrease markedly in nano scale strained Si（101） materials with increasing stress.The quantized models can provide valuable references to the understanding of strained Si materials and the research on electron carrier mobility.
