Based on the results of total-energy calculations for embedded clusters using self-consistent-field Xα-scatteredwave method,we determined the tetragonal fine structure of K(Ta_(0.56)Nb_(0.44))O_(3),i.e.,the equilibri...Based on the results of total-energy calculations for embedded clusters using self-consistent-field Xα-scatteredwave method,we determined the tetragonal fine structure of K(Ta_(0.56)Nb_(0.44))O_(3),i.e.,the equilibrium configuration of B-site cations(Ta and Nb)in the ferroelectric phase.Ta is found to have an off-center displacement of about 0.02A along[001].The off-center displacement of Nb is much larger than that of Ta,thus it makes a major contribution to the occurrence of the ferroelectric instability.展开更多
A simple double-well potential model is established.It shows that the nature of the low-frequency dielectric constant in ferroelectrics is the additional hopping of the off-center ions in multi-site potential.The co-o...A simple double-well potential model is established.It shows that the nature of the low-frequency dielectric constant in ferroelectrics is the additional hopping of the off-center ions in multi-site potential.The co-operative effect causes the fact that the Curie-Weiss law is obeyed.The mechanism of the molecular field is clarified.展开更多
In the Ba_(x)Sr_(l-x)TiO_(3) system,the decrease of the grain size causes the suppression of the ferroelectricity and the increase of the relaxation frequency.Barrier heights increase with the increasing grain size.Th...In the Ba_(x)Sr_(l-x)TiO_(3) system,the decrease of the grain size causes the suppression of the ferroelectricity and the increase of the relaxation frequency.Barrier heights increase with the increasing grain size.The result is analogous to magnetic phase transitions in nanocrystals and the solid-solid phase transitions in nanocrystals.展开更多
【目的】针对以往土壤侵蚀研究中空间连续性降水量数据获取困难以及高植被覆盖区植被覆盖管理因子估算精度不高的问题,本研究尝试引入多源遥感数据进行空间尺度的土壤侵蚀评价。【方法】基于GPM_3IMERGM、LANDSAT8影像数据获取的降雨侵...【目的】针对以往土壤侵蚀研究中空间连续性降水量数据获取困难以及高植被覆盖区植被覆盖管理因子估算精度不高的问题,本研究尝试引入多源遥感数据进行空间尺度的土壤侵蚀评价。【方法】基于GPM_3IMERGM、LANDSAT8影像数据获取的降雨侵蚀量因子(R)和植被覆盖管理因子(C)改进了修正土壤流失模型(RUSLE),并利用改进的RUSLE模型完成研究区土壤侵蚀状况遥感制图。【结果】研究区土壤侵蚀总量为5.12×10^(7) t a^(−1),平均土壤侵蚀模数为7.38 t hm^(−2) a^(−1),受土壤侵蚀影响的总面积为1841.86 km^(2),占土地总面积的24.77%。从土壤侵蚀等级来看,侵蚀强度总体表现为微度和轻度,水土保护情况整体良好。空间分布上,不同侵蚀等级的布局呈现出片状分布与点块状分布相结合的特点;广州市中部和南部的行政区较市区外围和北部的行政区而言,侵蚀状况更轻微。【结论】GPM卫星数据和EVI指数的引入显著提高了RUSLE模型中两个关键因子和土壤侵蚀强度的估算精度,其成果可为广州市区域水土保持和生态环境建设工作提供理论依据和实践参考。展开更多
基金Supported by the Doctoral Fund of the State Education Commission of China under Grant No.98042211.
文摘Based on the results of total-energy calculations for embedded clusters using self-consistent-field Xα-scatteredwave method,we determined the tetragonal fine structure of K(Ta_(0.56)Nb_(0.44))O_(3),i.e.,the equilibrium configuration of B-site cations(Ta and Nb)in the ferroelectric phase.Ta is found to have an off-center displacement of about 0.02A along[001].The off-center displacement of Nb is much larger than that of Ta,thus it makes a major contribution to the occurrence of the ferroelectric instability.
基金the State Key Program for Basic Research of Chinathe Research Found for the Doctoral Program of Higher Education。
文摘A simple double-well potential model is established.It shows that the nature of the low-frequency dielectric constant in ferroelectrics is the additional hopping of the off-center ions in multi-site potential.The co-operative effect causes the fact that the Curie-Weiss law is obeyed.The mechanism of the molecular field is clarified.
基金Supported by the Climbing Program of the National Commission of Science and Technology of China
文摘In the Ba_(x)Sr_(l-x)TiO_(3) system,the decrease of the grain size causes the suppression of the ferroelectricity and the increase of the relaxation frequency.Barrier heights increase with the increasing grain size.The result is analogous to magnetic phase transitions in nanocrystals and the solid-solid phase transitions in nanocrystals.
文摘【目的】针对以往土壤侵蚀研究中空间连续性降水量数据获取困难以及高植被覆盖区植被覆盖管理因子估算精度不高的问题,本研究尝试引入多源遥感数据进行空间尺度的土壤侵蚀评价。【方法】基于GPM_3IMERGM、LANDSAT8影像数据获取的降雨侵蚀量因子(R)和植被覆盖管理因子(C)改进了修正土壤流失模型(RUSLE),并利用改进的RUSLE模型完成研究区土壤侵蚀状况遥感制图。【结果】研究区土壤侵蚀总量为5.12×10^(7) t a^(−1),平均土壤侵蚀模数为7.38 t hm^(−2) a^(−1),受土壤侵蚀影响的总面积为1841.86 km^(2),占土地总面积的24.77%。从土壤侵蚀等级来看,侵蚀强度总体表现为微度和轻度,水土保护情况整体良好。空间分布上,不同侵蚀等级的布局呈现出片状分布与点块状分布相结合的特点;广州市中部和南部的行政区较市区外围和北部的行政区而言,侵蚀状况更轻微。【结论】GPM卫星数据和EVI指数的引入显著提高了RUSLE模型中两个关键因子和土壤侵蚀强度的估算精度,其成果可为广州市区域水土保持和生态环境建设工作提供理论依据和实践参考。
