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111.
Journal of Geographical Sciences - Rocky desertification poverty (RDP) refers to rural poverty triggered or exacerbated by rocky desertification, which deprives farmers of opportunities for... 相似文献
112.
Ji Yang Ying-Xi Zuo Zheng LOU Jing-Quan Cheng Qi-Zhou Zhang Sheng-Cai Shi Jia-Sheng Huang Qi-Jun Yao Zhong Wang 《天体物理学报》2013,(12):1493-1508
As the highest, coldest and driest place in Antarctica, Dome A provides exceptionally good observing conditions for ground-based observations over terahertz wavebands. The 5 m Dome A Terahertz Explorer (DATES) has been proposed to explore new terahertz windows, primarily over wavelengths between 350 and 200 pm. DATE5 will be an open-air, fully-steerable telescope that can function by unmanned operation with remote control. The telescope will be able to endure the harsh polar environment, including high altitude, very low temperature and very low air pressure. The unique specifications, including high accuracies for surface shape and pointing and fully automatic year-around remote operation, along with a stringent limit on the periods of on-site assembly, testing and maintenance, bring a number of challenges to the design, construction, assembly and operation of this telescope. This paper intro- duces general concepts related to the design of the DATE5 antenna. Beginning from an overview of the environmental and operational limitations, the design specifications and requirements of the DATE5 antenna are listed. From these, major aspects on the conceptual design studies, including the antenna optics, the backup structure, the pan- els, the subreflector, the mounting and the antenna base structure, are explained. Some critical issues of performance are justified through analyses that use computational fluid dynamics, thermal analysis and de-icing studies, and the proposed approaches for test operation and on-site assembly. Based on these studies, we conclude that the specifications of the DATE5 antenna can generally be met by using enhanced technological approaches. 相似文献
113.
几种海洋蓝藻生长条件的研究 总被引:4,自引:0,他引:4
对Synechococcus bacillaris,Oscillatoria lud,Schizothrix calcicola,Spirulina platensis等4各海洋蓝藻的生长条件的研究表明,除S.platensis外,其他3种蓝藻在“f/2”培养基中生长良好,外源生长因子对生长有不同程度的促进作用。S.bacillaris适应较高光强,其温度和pH最适范围较窄,S.calcicola 相似文献
114.
Effects of grazing and climate change on species diversity in sandy grassland, Inner Mongolia, China
To understand the effects of animal grazing activities and climate change on sandy grassland vegetation in northern China, a field grazing and protected enclosure experiment was conducted from 1992 through 2006 in Horqin Sand Land, Inner Mongolia. The results showed that (1) the grazing was primary responsible for changes of the vegetation richness and diversity in the grazing grassland and that changing climate was the main reason for changes in the species richness and diversity in the grassland protected from grazing; (2) light and moderate grazing can promote restoration of the richness and the diversity in the degraded grassland, and heavy grazing could result in a decrease of the richness and diversity; (3) heavy grazing can result in significant decrease of the perennial diversity, and moderate and light grazing promotes increase of the perennial diversity; the grazing, whether heavy or moderate and light grazing, was beneficial to increase of the annual diversity; (4) heavy grazing was not beneficial to diversity of Graminean and Chenopodiaceae, and moderate and light grazing was favorable the diversity of Compositae and Chenopodiaceae; (5) the warm-humid climate was favorable to increase of the richness and the diversity, and the warm-drought climate could result in decease of the richness and the diversity; (6) increased precipitation was favorable to perennial diversity and the diversity of Graminean, Leguminosae, and Compositae, and decreased precipitation had few effects on the annual diversity and Chenopodiaceae diversity. 相似文献
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HuaiMin Xue YingGeng Wang Fang Ma Cheng Wang DeEn Wan YanLong Zuo 《中国科学D辑(英文版)》2009,52(11):1756-1770
The Taiping-Huangshan composite intrusion is a unique complex with characteristics changing from calc-alkaline (Taiping intrusion)
to alkaline (Huangshan intrusion). Huangshan intrusion samples show a spectacular tetrad effect in their REE distribution
patterns as well as non-CHARAC (charge-and-radius-controlled) trace element behavior, indicating a highly evolved late-stage
magma component. This composite intrusion provides a rare opportunity to investigate the variance of tectonic setting and
lithospheric thinning of the southeastern Yangtze Craton in late Mesozoic era. Zircon SHRIMP U-Pb analyses yield an emplacement
age of 140.6±1.2 Ma for the Taiping intrusion, and ages of 127.7±1.3, 125.7±1.4, 125.1±1.5, and 125.2±5.5 Ma for four samples
from the Huangshan intrusion respectively. The ages for four different phases of the Huangshan intrusion agree within their
small analytical errors, indicating that the emplacement was in a short time. The Taiping and Huangshan intrusions are intimately
associated, but there is about 15 Ma interval between their intrusion, and the magma characters change from calc-alkaline
to alkaline without transition. This probably corresponds to lithospheric thinning of the southeastern Yangtze Craton. This
event possibly happened from about 141 Ma (the emplacement age of the Taiping intrusion), to 128 Ma (start of emplacement
of the Huangshan intrusion). The thinning mechanism is dominantly delamination. 相似文献
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119.
黄土高原表土磁化率与气候要素的定量关系研究 总被引:1,自引:0,他引:1
黄土高原地区已建立多个表土低频磁化率-气候转换函数,为黄土古气候定量重建提供了关键方法.但是表土磁化率变化的气候控制因素的系统研究尚未开展;同时,低频磁化率部分受到沉积作用的影响,需要寻找气候意义更明确的指标.我们系统采集了黄土高原及周边地区的表土样品,运用相关、回归和因子分析等方法,研究了不同气候要素及其季节变化对表土磁化率和频率磁化率的控制作用.结果显示,湿度是控制黄土高原表土磁化率的主要因素,温度的影响相对较小;降水的季节分配也有影响,月降水变率较小的地区磁化率较高.在此基础上,选择反映成壤磁性颗粒组分的频率磁化率,建立了频率磁化率-年均降水量的转换函数,为黄土古气候定量估算提供了新的途径. 相似文献
120.