The Songnen Plain lying in the central part of the Northeast China Plain covers an area of about 170 000 km2. There are vast patches of saline land, which are still in the process of enlargement. The spread of saline ...The Songnen Plain lying in the central part of the Northeast China Plain covers an area of about 170 000 km2. There are vast patches of saline land, which are still in the process of enlargement. The spread of saline land has already caused the worsening of ecoenvironment and hindered agricultural development in the region. The paper analyses background factors of natural environment that caused the spread of saline land according to the information of Landsat TM images. The result shows that among the three kinds of lakes the fault lake is the background factor of natural environment that causes the spread of saline land under arid conditions. Its lakebeach meadows could not recover from the excessive utilization in farming and stockraising. The proposed countermeasures to prevent and control the spread of saline land serve as biological steps or water conservancy facilities to protect the lakebeach meadows of the fault lakes from being artificial excessively utilized.展开更多
In the past ten years, Korean language has received a remarkable success in its spread over East Asia, especially in China. There are generally five geographical factors making Korean language achieve in its spread. I...In the past ten years, Korean language has received a remarkable success in its spread over East Asia, especially in China. There are generally five geographical factors making Korean language achieve in its spread. Influenced by the factors of natural environment, economics, immigration, politics and diplomacy, and cultural communication, the spread of Korean shows that the temporal characteristics of language variation and bilingualism, and the spatial characteristics of principle of proximity and population center.展开更多
LoRa(Long Range radio)系统在当前不断发展的低功率广域网(LPWAN)中处于相对领先地位。它的MAC层采用的是基于ALOHA的接入协议。该接入机制虽然简单易实现,但同时也容易加剧冲突和碰撞的发生,降低整个系统的通信性能。因此,需要研究多...LoRa(Long Range radio)系统在当前不断发展的低功率广域网(LPWAN)中处于相对领先地位。它的MAC层采用的是基于ALOHA的接入协议。该接入机制虽然简单易实现,但同时也容易加剧冲突和碰撞的发生,降低整个系统的通信性能。因此,需要研究多个终端同时占用信道资源时的相互干扰情况,而LoRa信号的扩频因子(SF)将决定信号的通信覆盖范围。因此,分析了干扰信号的SF与发送信号的SF相同以及不同时,干扰信号对发送信号解调性能的影响。实验结果表明,相同SF信号间的干扰影响相对较大,而干扰信号使用的SF与发送信号不同时,干扰的影响相对较小。通过理论分析,获得了接收端正确解调时所要求的信干比(SIR)。可见,不同SF的LoRa信号可看作伪正交。展开更多
为明确加拿大一枝黄花(Solidago canadensis)在湖北省的入侵过程和影响因素,该文结合相关报道和实地踏查搜集加拿大一枝黄花的入侵分布点,借助ArcGIS对其历史分布动态进行模拟重建,并利用MaxEnt模型对其扩散动态和影响因素进行了分析。...为明确加拿大一枝黄花(Solidago canadensis)在湖北省的入侵过程和影响因素,该文结合相关报道和实地踏查搜集加拿大一枝黄花的入侵分布点,借助ArcGIS对其历史分布动态进行模拟重建,并利用MaxEnt模型对其扩散动态和影响因素进行了分析。结果表明:(1)加拿大一枝黄花在湖北呈不连续聚集分布,由早期的“跳跃式”入侵演变为由东向西北“渐进式”扩散,其中武汉、咸宁和宜昌中部地区入侵程度最为严重。(2)人类活动是影响加拿大一枝黄花扩散的主要因素,其主要沿着公路、铁路等交通方式实现远距离传播,入侵分布点数量与人类活动强度和路网密度呈正相关。(3)最干季度降水量(Bio_17)、气温季节性变动系数(Bio_4)、最湿季度平均温度(Bio_8)、土壤的酸碱度(t_pH)、土壤表层有机碳含量(t_oc)和海拔(DEM)是影响其生长繁殖的关键生态因子。在t_pH=4.0~7.5、t_oc=0.60%~1.12%的酸性或弱碱性土及Bio_4=880~920、Bio_8>24℃时,加拿大一枝黄花最容易发生入侵,其在湖北省的中、高适生区面积可达75200 km 2。综合其在湖北的历史扩散动态和影响因素认为:加拿大一枝黄花的适生区面积和入侵点均呈现由东向西减少的趋势;人类活动是造成其入侵湖北和扩散的主要因素,而自然因子则直接限制其在入侵点的种群大小和发生面积。该研究为加拿大一枝黄花的风险评估、监测预警和防控治理等技术提供了理论支撑。展开更多
文摘The Songnen Plain lying in the central part of the Northeast China Plain covers an area of about 170 000 km2. There are vast patches of saline land, which are still in the process of enlargement. The spread of saline land has already caused the worsening of ecoenvironment and hindered agricultural development in the region. The paper analyses background factors of natural environment that caused the spread of saline land according to the information of Landsat TM images. The result shows that among the three kinds of lakes the fault lake is the background factor of natural environment that causes the spread of saline land under arid conditions. Its lakebeach meadows could not recover from the excessive utilization in farming and stockraising. The proposed countermeasures to prevent and control the spread of saline land serve as biological steps or water conservancy facilities to protect the lakebeach meadows of the fault lakes from being artificial excessively utilized.
文摘In the past ten years, Korean language has received a remarkable success in its spread over East Asia, especially in China. There are generally five geographical factors making Korean language achieve in its spread. Influenced by the factors of natural environment, economics, immigration, politics and diplomacy, and cultural communication, the spread of Korean shows that the temporal characteristics of language variation and bilingualism, and the spatial characteristics of principle of proximity and population center.
文摘LoRa(Long Range radio)系统在当前不断发展的低功率广域网(LPWAN)中处于相对领先地位。它的MAC层采用的是基于ALOHA的接入协议。该接入机制虽然简单易实现,但同时也容易加剧冲突和碰撞的发生,降低整个系统的通信性能。因此,需要研究多个终端同时占用信道资源时的相互干扰情况,而LoRa信号的扩频因子(SF)将决定信号的通信覆盖范围。因此,分析了干扰信号的SF与发送信号的SF相同以及不同时,干扰信号对发送信号解调性能的影响。实验结果表明,相同SF信号间的干扰影响相对较大,而干扰信号使用的SF与发送信号不同时,干扰的影响相对较小。通过理论分析,获得了接收端正确解调时所要求的信干比(SIR)。可见,不同SF的LoRa信号可看作伪正交。
文摘为明确加拿大一枝黄花(Solidago canadensis)在湖北省的入侵过程和影响因素,该文结合相关报道和实地踏查搜集加拿大一枝黄花的入侵分布点,借助ArcGIS对其历史分布动态进行模拟重建,并利用MaxEnt模型对其扩散动态和影响因素进行了分析。结果表明:(1)加拿大一枝黄花在湖北呈不连续聚集分布,由早期的“跳跃式”入侵演变为由东向西北“渐进式”扩散,其中武汉、咸宁和宜昌中部地区入侵程度最为严重。(2)人类活动是影响加拿大一枝黄花扩散的主要因素,其主要沿着公路、铁路等交通方式实现远距离传播,入侵分布点数量与人类活动强度和路网密度呈正相关。(3)最干季度降水量(Bio_17)、气温季节性变动系数(Bio_4)、最湿季度平均温度(Bio_8)、土壤的酸碱度(t_pH)、土壤表层有机碳含量(t_oc)和海拔(DEM)是影响其生长繁殖的关键生态因子。在t_pH=4.0~7.5、t_oc=0.60%~1.12%的酸性或弱碱性土及Bio_4=880~920、Bio_8>24℃时,加拿大一枝黄花最容易发生入侵,其在湖北省的中、高适生区面积可达75200 km 2。综合其在湖北的历史扩散动态和影响因素认为:加拿大一枝黄花的适生区面积和入侵点均呈现由东向西减少的趋势;人类活动是造成其入侵湖北和扩散的主要因素,而自然因子则直接限制其在入侵点的种群大小和发生面积。该研究为加拿大一枝黄花的风险评估、监测预警和防控治理等技术提供了理论支撑。
