Grassland degradation is influenced by climate change and human activities,and has become a major obstacle for the development of arid and semi-arid areas,posing a series of environmental and socio-economic problems.A...Grassland degradation is influenced by climate change and human activities,and has become a major obstacle for the development of arid and semi-arid areas,posing a series of environmental and socio-economic problems.An in-depth understanding of the inner relations among grassland vegetation dynamics,climate change,and human activities is therefore greatly significant for understanding the variation in regional environmental conditions and predicting future developmental trends.Based on MODIS(moderate resolution imaging spectroradiometer)NDVI(normalized difference vegetation index)data from 2000 to 2020,our objective is to investigate the spatiotemporal changes of NDVI in the Xilin Gol grassland,Inner Mongolia Autonomous Region,China.Combined with 12 natural factors and human activity factors in the same period,the dominant driving factors and their interactions were identified by using the geographic detector model,and multiple scenarios were also simulated to forecast the possible paths of future NDVI changes in this area.The results showed that:(1)in the past 21 a,vegetation cover in the Xilin Gol grassland exhibited an overall increasing trend,and the vegetation restoration(84.53%)area surpassed vegetation degradation area(7.43%);(2)precipitation,wind velocity,and livestock number were the dominant factors affecting NDVI(the explanatory power of these factors exceeded 0.4).The interaction between average annual wind velocity and average annual precipitation,and between average annual precipitation and livestock number greatly affected NDVI changes(the explanatory power of these factors exceeded 0.7).Moreover,the impact of climate change on NDVI was more significant than human activities;and(3)scenario analysis indicated that NDVI in the Xinlin Gol grassland increased under the scenarios of reduced wind velocity,increased precipitation,and ecological protection.In contrast,vegetation coverage restoration in this area was significantly reduced under the scenarios of unfavorable climate conditions and excessive human activities.This study provides a scientific basis for future vegetation restoration and management,ecological environmental construction,and sustainable natural resource utilization in this area.展开更多
基于In GaP/GaAs HBT工艺设计了一款工作在1. 8 GHz的三级Doherty功率放大器,第一、二级为驱动级,第三级为Doherty放大器。通过分析Doherty结构,在原有基础上重新设计Doherty电路,使用LC元件替代微带线,减小功率分配网络与合路匹配网络...基于In GaP/GaAs HBT工艺设计了一款工作在1. 8 GHz的三级Doherty功率放大器,第一、二级为驱动级,第三级为Doherty放大器。通过分析Doherty结构,在原有基础上重新设计Doherty电路,使用LC元件替代微带线,减小功率分配网络与合路匹配网络的面积,进而缩小整体电路的面积。将输入、输出匹配网络及功分、合路部分集成至基板上,整体封装尺寸5 mm×5 mm。测试结果表明,芯片输入、输出回波损耗优于-15 d B,放大器整体增益优于33 d B,3 d B压缩点输出功率35 d Bm,其中第三级Doherty放大器峰值功率附加效率(PAE) 47. 9%,8 d B回退点的功率附加效率32. 7%。展开更多
基金supported by the National Natural Science Foundation of China(31500384,31971464)the Young Science and Technology Talents Support Program in Inner Mongolia Autonomous Region(NJYT-19-B31)the Liaoning Province Joint Fund Project(2020-MZLH-11)。
文摘Grassland degradation is influenced by climate change and human activities,and has become a major obstacle for the development of arid and semi-arid areas,posing a series of environmental and socio-economic problems.An in-depth understanding of the inner relations among grassland vegetation dynamics,climate change,and human activities is therefore greatly significant for understanding the variation in regional environmental conditions and predicting future developmental trends.Based on MODIS(moderate resolution imaging spectroradiometer)NDVI(normalized difference vegetation index)data from 2000 to 2020,our objective is to investigate the spatiotemporal changes of NDVI in the Xilin Gol grassland,Inner Mongolia Autonomous Region,China.Combined with 12 natural factors and human activity factors in the same period,the dominant driving factors and their interactions were identified by using the geographic detector model,and multiple scenarios were also simulated to forecast the possible paths of future NDVI changes in this area.The results showed that:(1)in the past 21 a,vegetation cover in the Xilin Gol grassland exhibited an overall increasing trend,and the vegetation restoration(84.53%)area surpassed vegetation degradation area(7.43%);(2)precipitation,wind velocity,and livestock number were the dominant factors affecting NDVI(the explanatory power of these factors exceeded 0.4).The interaction between average annual wind velocity and average annual precipitation,and between average annual precipitation and livestock number greatly affected NDVI changes(the explanatory power of these factors exceeded 0.7).Moreover,the impact of climate change on NDVI was more significant than human activities;and(3)scenario analysis indicated that NDVI in the Xinlin Gol grassland increased under the scenarios of reduced wind velocity,increased precipitation,and ecological protection.In contrast,vegetation coverage restoration in this area was significantly reduced under the scenarios of unfavorable climate conditions and excessive human activities.This study provides a scientific basis for future vegetation restoration and management,ecological environmental construction,and sustainable natural resource utilization in this area.
文摘基于In GaP/GaAs HBT工艺设计了一款工作在1. 8 GHz的三级Doherty功率放大器,第一、二级为驱动级,第三级为Doherty放大器。通过分析Doherty结构,在原有基础上重新设计Doherty电路,使用LC元件替代微带线,减小功率分配网络与合路匹配网络的面积,进而缩小整体电路的面积。将输入、输出匹配网络及功分、合路部分集成至基板上,整体封装尺寸5 mm×5 mm。测试结果表明,芯片输入、输出回波损耗优于-15 d B,放大器整体增益优于33 d B,3 d B压缩点输出功率35 d Bm,其中第三级Doherty放大器峰值功率附加效率(PAE) 47. 9%,8 d B回退点的功率附加效率32. 7%。
