Numerical analysis of the symmetric methods

Aimed at the initial value problem of the particular second-order ordinary differential equations,y =f(x, y), the symmetric methods (Quinlan and Tremaine, 1990) and our methods (Xu and Zhang, 1994) have been compared in detail by integrating the artificial earth satellite orbits in this paper. In the end, we point out clearly that the integral accuracy of numerical integration of the satellite orbits by applying our methods is obviously higher than that by applying the same order formula of the symmetric methods when the integration time-interval is not greater than 12000 periods.     

ENVIRONMENTAL CHANGE AND ITS IMPACTS ON HUMAN SETTLF, MENT IN THE CHANGJIANG RIVER DELTA IN NEOLITHIC AGE

Dating data, altitude of Neolithic sites, climatic changes from sedimentary records and previous research results were collected and analyzed to detect possible connections between climatic changes and human activities in the Changjiang River Delta in the Neolithic Age. The results indicated that hydrological changes greatly impacted the human activities in the study region. Low-lying geomorphology made the floods and sea level changes become the important factors affecting human activities, especially the altitude change of human settlements. People usually moved to higher places during the periods characterized by high sea level and frequent floods to escape the negative influences from water body expansion, which resulted in cultural hiatus in certain profiles. However, some higher-altitude settlements were not the results of climatic changes but the results of social factors, such as religious ceremony and social status. Therefore, further research will be necessary for the degree and types of impacts of climatic changes on human activities in the study area at that time.     

An analysis of the causes of decadal variations of rainfall in Shandong in summer

The precipitation in Shandong in July, August as well as the whole summer (JJA) and the corresponding 500hPa geopotential height fields are analyzed by means of the SVD (singular value decomposition) methodology. It is found that the general circulations in East Asia and the Western Pacific underwent decadal changes around 1979. The geopotential height, in particular over key areas like the South China Sea and the Philippines, increased after 1979. Corresponding to the changes in the geopotential height, the rainfall in Shandong started to decrease around 1979. The synthesized analysis shows that when the geopotential height at 500hPa level decreases in the key areas, the Western Pacific subtropical high shifts northward and an anticyclonic anomalous cell enforces the southerly flow over Shandong-Korea-Japan, Shandong could experience a wet period. A dry period is likely to occur when the geopotential height increases in these key areas, the subtropical high moves southward or expands westward to a great distance, and a cyclonic anomalous cell controls Shandong. Respective conceptual models for the causative mechanism are obtained for the cases of July, August and the whole summer (JJA).     

Three-dimensional gravity inversion based on 3D U-Net++

The gravity inversion is to restore genetic density distribution of the underground target to be explored for explaining the internal structure and distribution...     

南大洋海冰影像地图投影变换与瓦片切割应用研究

南大洋海冰分布是南极考察过程中影响破冰船航行的重要因素,也是南极研究的重要内容之一。目前国际上不同机构发布的南大洋海冰分布图,大多是球面投影,不能直接用于主流的瓦片地图发布。将极方位立体投影海冰图转换为目前主流的网络墨卡托投影地图,并利用合适的图像重采样方法,按照不同级别比例尺进行瓦片切割和编号存储,最终实现海冰影像地图的发布共享是本文的主要研究内容。笔者对不同的图像重采样方法进行了比较,分析了最邻近点采样方法、双线性内插和双三次卷积重采样方法的优劣,针对本文的研究优选双线性内插方法进行影像地图瓦片的切割,并最终叠加融合在Google地图上,实现了Google底图、准实时海冰影像图与破冰船走航位置的集成显示,为雪龙船的冰区航行提供了重要的数据支撑。     

地形在高大金字塔沙山形成发育过程中的作用——以敦煌鸣沙山-月牙泉地区为例

地形在金字塔沙山形成发育过程中起着重要的作用。金字塔沙山通常形成于山前地带,应属于地形屏障影响下形成的一种沙丘类型。首先,上升气流的发育是山前风阻区气流的主要特征,地形屏障是上升气流发生发展的主要原因。沙山的坡脚、坡中及坡顶分别是上升气流的启动区、发育区及衰退区。上升气流是沙山增高增大发育的主要机制。其次,金字塔沙山多发育于局地环流发育较强的地带,局地环流与区域风况配置是形成复杂沙丘类型的重要因素。本区局地环流偏南风不仅持续时间长,且受到鸣沙山微地形的影响,下坡气流较强。实地观测结果破解了常规气候台观测数据难以揭示上升气流及局地环流对金字塔沙丘形成发育的影响。第三,下附地形在沙山形成发育过程中决定着沙丘发育的“临界尺度”,即丘体达到“临界尺度”的时候,坡面上升气流及风速放大作用逐渐显现,促使丘体增高增大发育,随着沙丘形态与上升气流的互馈作用进一步增强,金字塔沙丘逐渐形成演化为高大沙山。实地观测进一步证实了金字塔沙山是纵向（横向）沙丘形变的一种形式。并提出了金字塔沙山在地形条件下形成演化的一种新模式。     

新疆阿拉套山花岗岩类的岩石化学

新疆阿拉套山南坡东西向展布的花岗岩石的岩石化学研究表明，本区同时存在Ｉ型和Ｓ型两种类型的花岗岩，其分布受构造环境控制，靠近古板块缝合线为Ｉ型花岗岩分布区、远离古板块缝合线为Ｓ型花岗岩分布区。源岩性质和作用强弱等因素可能是造成岩石化学成分差异的原因。     

荒漠生态系统C、N、P生态化学计量研究进展

生态化学计量学是通过研究生物有机体主要元素含量及其比值的变化关系,揭示生态系统各组分间元素循环规律的一门学科,生态化学计量也是荒漠生态系统研究的重要内容。因此,综合掌握水分和养分限制环境下C、N、P生态化学计量的关系对揭示荒漠生态系统植物的限制性元素、土壤营养的供给能力、养分的有效性等都具有重要的意义。基于此,回顾和分析了国内外荒漠生态系统C、N、P生态化学计量最新研究和动态,分别从植物、凋落物、土壤、土壤微生物、土壤酶进行较为系统的评述,讨论了植物-土壤-微生物-酶四者的关系,提出了荒漠生态系统C、N、P生态化学计量的未来研究方向,期望为全面理解固沙植被的演变过程、稳定性维持机制及其科学管理提供理论指导。