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991.
992.
993.
运用粒度参数分析、黏土矿物含量分析、Flemming三角图示法和Gao-Collins二维的"粒度趋势分析"等方法,对采自莱州湾海域的表层沉积物样品和黏土矿物样品进行分析,了解了该研究区域的沉积环境及沉积物的运移趋势。研究区由岸向海沉积物类型大致依次为砂-粉砂质砂-砂质粉砂-粉砂-黏土质粉砂,并且研究区表层沉积物在近岸区域呈现较为明显的平行岸线的条带状特征;同时沉积物的平均粒径、分选系数、偏态、峰态等粒度参数也呈现出良好的正相关性或负相关性;研究区黏土矿物为伊利石、蒙脱石、绿泥石、高岭石,除伊利石分布大致为黄河三角洲近岸低,向研究区东北方向逐渐升高外,其余的黏土矿物都表现出了近岸高,远海低的分布特征,且主要物源为黄河物质输入。Flemming三角图研究区所有采样点大部分分布在Ⅱ区,少部分分布在Ⅲ区,说明研究区整体水动力较强;采样点在A—E区均有分布,但在C、D两区分布最多,说明研究区沉积物粒径较集中。研究区表层沉积物整体呈由岸向海输运的趋势,具体来看,黄河沉积物入海后向北、向东、向南运移,研究区内沉积物的来源是黄河输沙以及周围入海的小河流的输沙和沿岸冲刷的物质。 相似文献
994.
卫星双向时间传递(Two-Way Satellite Time and Frequency Transfer, TWSTFT)是目前精度最高的时间传递方法之一,同时也是参与国际原子时计算的守时实验室之间比较原子时尺度的一种主要方法.提高TWSTFT链路的短期稳定度,降低周日效应对链路时间传递结果的影响,对优化TAI (International Atomic Time)的性能具有现实意义.提出了一种基于条件平差的TWSTFT链路性能优化方法,先依据TWSTFT链路测量噪声水平与谱分析结果建立TWSTFT链路性能优化网络(简称优化网络),再根据优化网络中各链路测量噪声分析结果设置权系数阵,建立条件平差模型.选取亚太地区的中国计量科学研究院(National Institute of Metrology, NIM)-中国科学院国家授时中心(National Time Service Center, NTSC)卫星双向时间传递链路作为待优化链路,以NTSC、NIM以及德国联邦物理技术研究所(Physikalisch-Technische Bundesanstalt,PTB)之间的TWSTFT链路组成优化网络,对优化网络的组网方法和条件平差模型进行实验验证.结果表明,平差后待优化链路短期稳定度得到了改善,同时其受周日效应的影响降低了约24.6%.使用该方法,能够有效提高待优化链路的时间传递性能. 相似文献
995.
Farmland abandonment is a global problem and considered one of the most important areas in land use change research. Farmland abandonment research currently focuses on understanding the factors that affect farmland abandonment and developing scientific models to simulate farmland abandonment. The study reviewed the natural and political factors driving farmland abandonment and summarized the main models for farmland abandonment simulation together with their advantages and disadvantages. We discuss the main ecological effects of farmland abandonment and propose farmland abandonment research directions. The study found that: (1) the influence of labor cost change and ageing labor force on farmland abandonment needs further investigation, (2) simulation models for farmland abandonment must include the decision-making mechanism of individual farmers and focus on macro large-scale abandonment prediction models, and (3) the influence of farmland abandonment on landscape culture must be investigated in detail. 相似文献
996.
Glacial tills are highly compressible soils composed of loosely cemented sandy silt particles. Their role, for instance, as initial filler materials in geo-technical projects along temperate glacier regions warrant a systematic evaluation of their compressive characteristics. As such, we carry out a series of onedimensional compression tests on re-compacted glacial till samples obtained from Tianmo Gully, Tibet, with the aims of evaluating their compressive behavior under controlled initial stress conditions. The yield stress was determined from the void ratio versus consolidation pressure(e-log) planes. Its compression and swelling behaviors were observed during the primary and secondary compressions of the consolidation tests. From the compression curves, a correlation can be found between the consolidation stress and the void index. In addition, we find that the compression curves of glacial tills collapse into a single curve when normalized by the compression index. The experimental results in this study provide a basic understanding of the compression characteristics of the glacial tills in Tibet, China. 相似文献
997.
为查明清水河东侧断裂的产状、性质及其浅部构造特征,跨断裂开展高分辨率的浅层地震探测,获得高信噪比的浅层地震反射叠加剖面。根据浅层地震剖面结果并结合该区域地质资料,对该断裂的浅部构造特征进行分析和讨论。结果表明,清水河东侧断裂为一条走向近SN、倾向E的逆断层,其浅部为由2~3条断层组成的“Y”字形构造,并错断埋深约10~30 m的第四系沉积层,属第四纪以来的隐伏活动断裂。 相似文献
998.
999.
The Antarctic krill(Euphausia superba) is a key species in the Southern Ocean ecosystem and an important link in the food web of the Antarctic ecosystem. The trophic information for this species during the transition from the austral fall to the winter is important to understand its poorly known overwintering mechanisms. However, the few studies on the topic differ in their results, in terms of both spatial and temporal variables. We investigated the size dependence and monthly and regional variation in δ~(13) C and δ~(15) N values of adult krill in the Antarctic Peninsula, in the austral fall(April to May) and the early winter(June). We aimed to examine the trophic variations of krill occurred during this period, and the relationship between krill and their feeding environment in the Antarctic marine ecosystem. The following results were obtained:(1) no significant relationship was observed between size and the δ13 C value of krill, but the δ15 N value of krill presented a remarkable association with size;(2)the δ13 C values of krill increased during the austral fall, but no remarkable variation existed at the onset of winter,and the δ15 N values were not significant different during this period;(3) mean δ15 N values of krill differed significantly between the Bransfield Strait and the South Shetland Islands. Our data imply that adult krill present size-, season-, and region-dependent trophic variation during the transition from austral fall to early winter in the Antarctic Peninsula. 相似文献
1000.