Formation and destruction of striation plasmas in helium glow discharge at medium pressures

The striation plasmas are usually generated within a positive column of glow discharge,where rich and complex physical interactions are involved,especially,in the medium or high pressures.Along these lines,our work aims to thoroughly investigate the formation and destruction of helium striation plasmas at kPa level pressures.The characteristics of the helium striation plasmas,and especially the optical emission properties are explored.The emission lines of 706.52 nm and391.44 nm related to the energetic electrons and the high-energy metastable helium atoms respectively,were focused on in this work.The formation of striation plasmas in a helium glow discharge,is mainly associated with the instability originating from the stepwise ionization of high-energy metastable state atoms,Maxwellization of the electron distribution functions and gas heating.Additionally,the destruction effect of helium striation plasmas is of great significance when a small amount of nitrogen or oxygen is mixed into the discharge plasmas.The reduction of the mean electron energy and the consumption of the high-energy metastable helium atoms are considered as the underlying reasons for the destruction of striation plasmas.

Detecting the linkage between arable land use and poverty using machine learning methods at global perspective

Eradicating extreme poverty is one of the UN’s primary sustainable development goals(SDG).Arable land is related to eradicating poverty(SDG1)and hunger(SDG2).However,the linkage between arable land use and poverty reduction is ambiguous and has seldom been investigated globally.Six indicators of agricultural inputs,crop intensification and extensification were used to explore the relationship between arable land use and poverty.Non-parametric machine learning methods were used to analyze the linkage between agriculture and poverty at the global scale,including the classification and regression tree(CART)and random forest models.We found that the yield gap,fertilizer consumption and potential cropland ratio in protected areas correlated with poverty.Developing countries usually had a ratio of actual to potential yield less than 0.33 and fertilizer consumption less than 7.31 kg/ha.Overall,crop extensification,intensification and agricultural inputs were related to poverty at the global level.

耦合蝶形天线的石墨烯室温太赫兹探测器

高灵敏度、可室温下工作的太赫兹(THz)探测器是太赫兹在生物技术、量子传输、通信、成像等领域得以应用的关键。本文报道了一种石墨烯太赫兹探测器设计方法,该探测器通过将蝶形天线与石墨烯pn结构建至一个器件中,利用蝶形金属天线将波长为110 mm(2.7 THz)的太赫兹远场光汇聚至约800 nm的石墨烯THz吸收层,同时将这蝶形天线的两极设计为两个独立栅极,将800 nm的吸收层转变为可分离光电子的pn结区,通过增强局域光场增加太赫兹吸收,并同时增强光电子分离效率,将正交极化方向的消光比提升了1到2个数量级,在室温下实现了较低的噪声等效功率(NEP)~1 nW·Hz^(−1/2)。这一设计为太赫兹探测提供了新的技术路径。

Spatial pattern of urban-rural integration in China and the impact of geography

Urban-rural integration (URI) is a global challenge that is highly related to inequalities, poverty, economic growth, and other Sustainable Development Goals (SDGs). Existing research has evaluated the extent of URI and explored its influencing factors, but urban-rural linkages are seldom incorporated in evaluation systems, and geographical factors are rarely recognized as the influencing factors. We construct a URI framework including regional economy, rural development, urban-rural linkage, and urban-rural gap. Based on a dataset consisting of 1,669 counties in China in 2020, we reveal the spatial pattern of URI and find a high correlation between the spatial pattern of URI and the relief degree of land surface (RDLS). Using structural equation modeling, we discover that topography has direct ( − 0.18, p < 0.001) and indirect ( − 0.17, p < 0.001) effects on URI. The indirect negative effects are mediated through the infrastructure, and the combination of localized advantages and modern technical conditions could mitigate the negative impact of topography. Finally, we identify 742 counties as lagging regions in URI, which can be clustered into eight types. Our findings could facilitate policy designing for those countries striving for integrated and sustainable development of urban and rural areas.

近30年来中国北方快速城镇化驱动下乡村聚落的变化规律

快速城镇化进程中乡村的系统性衰落已成为全球趋势,面向乡村聚落(RUS)的持续追踪对于量化乡村发展的不平衡、不充分至关重要.本研究提出一种高效的遥感制图模型,用于自动化生产1990~2020年京津冀地区的RUS逐年数据集,并进一步分析了其变化的时空规律。结果表明:(1)从基于位置和基于面积的双重对比验证了模型的有效性,其多年平均精度分别为85%和0.88.(2)过去30年间,京津冀地区的RUS总面积增长了约2561km²,但其平均单体规模在2005年后基本保持稳定(3)过去30年京津冀地区56.3%的县域,其RUS逐年变化类型为“凸增长"模式。总的来看,本研究提出了一种高效的遥感制图模型用以持续追踪RUS的时空变化规律,能够为乡村聚落体系提供更为精细化的时空信息。

重新认知青藏高原围栏禁牧的作用

围栏禁牧是中国政府为恢复青藏高原等地退化草地而采取的一项重要政策.然而,关于围栏对高寒草地生态系统功能和服务及其对牧民生计的影响,人们的认识还很有限.本研究荟萃分析和基于问卷的调查显示,围栏禁牧时间长达4年和8年的时间里可以有效地促进高寒草甸以及草原的地上植被生长,更长时间的围栏并没有带来任何生态和经济效益.研究还发现,围栏限制了野生动物的活动范围,增加了非围栏地区的放牧压力,降低了牧民的满意度,且给地区和国家政府带来了巨大的财政成本.因此,建议在适当的情况下,应鼓励传统的游牧方式来利用草地,在严重退化的草地上应采用短期围栏(4~8年),在重要的野生动物栖息地应避免使用围栏,特别是受保护的大型哺乳动物分布的区域.研究结果可为青藏高原草地可持续管理提供一定的参考.

Industrial development and land use/cover change and their effects on local environment:a case study of Changshu in eastern coastal China

The interactions among industrial development,land use/cover change (LUCC), and environmentaleffects in Changshu in the eastern coastal China wereanalyzed using high-resolution Landsat TM data in 1990,1995, 2000, and 2006, socio-economic data and waterenvironmental quality monitoring data from researchinstitutes and governmental departments. Three phases ofindustrial development in Changshu were examined (i.e.,the three periods of 1990 to 1995, 1995 to 2000, and 2000to 2006). Besides industrial development and rapidurbanization, land use/cover in Changshu had changeddrastically from 1990 to 2006. This change was characterizedby major replacements of farmland by urban and ruralsettlements, artificial ponds, forested and constructed land.Industrialization, urbanization, agricultural structureadjustment, and rural housing construction were themajor socio-economic driving forces of LUCC inChangshu. In addition, the annual value of ecosystemservices in Changshu decreased slightly during 1990-2000, but increased significantly during 2000-2006.Nevertheless, the local environmental quality in Changshu,especially in rural areas, has not yet been improvedsignificantly. Thus, this paper suggests an increasedattention to fully realize the role of land supply inadjustment of environment-friendly industrial structureand urban-rural spatial restructuring, and translating theland management and environmental protection policiesinto an optimized industrial distribution and land-use pattern.