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951.
A 1.5-layer reduced-gravity model forced by wind stress is used to study the bifurcations of the North Equatorial Current(NEC).The authors found that after removing the Ekman drift,the modelled circulations can serve well as a proxy of the SODA circulations on the σθ=25.0 kg m~-3 potential density surface based on available long-term reanalysis wind stress data.The modelled results show that the location of the western boundary bifurcation of the NEC depends on both zonal averaged and local zero wind stress curl latitude.The effects of the anomalous wind stress curl added in different areas are also investigated and it is found that they can change the strength of the Mindanao Eddy(ME),and then influence the interior pathway. 相似文献
952.
The sea cucumber Apostichopus japonicus is a commercially and ecologically important species in China. A total of 3056 potential unigenes were generated after assembling 7597 A. japonicus expressed sequence tags (ESTs) downloaded from Gen-Bank. Two hundred and fifty microsatellite-containing ESTs (8.18%) and 299 simple sequence repeats (SSRs) were detected. The average density of SSRs was 1 per 7.403 kb of EST after redundancy elimination. Di-nucleotide repeat motifs appeared to be the most abundant type with a percentage of 69.90%. Of the 126 primer pairs designed, 90 amplified the expected products and 43 showed polymorphism in 30 individuals tested. The number of alleles per locus ranged from 2 to 26 with an average of 7.0 alleles, and the observed and expected heterozygosities varied from 0.067 to 1.000 and from 0.066 to 0.959, respectively. These new EST-derived microsatellite markers would provide sufficient polymorphism for population genetic studies and genome mapping of this sea cucumber species. 相似文献
953.
该文提出了空间智能平台的概念,阐述了其研究意义和内容,明确了空间智能计算平台核心计算模型的建模对象和目标。在此基础上,分析了宏观数学模型、群体行为模型两种用来构建空间活动模型的建模方法以及适用于空间活动分析的物理环境建模技术。从融合多尺度行为模型、构建城市日常生活模型、验证和校验核心模型以及平衡效率和效果4方面探讨了构建空间智能计算平台的关键技术。从实际功能看,城市空间智能平台是联系宏观复杂问题和微观机制的桥梁,是分析城市问题的工程化实验平台,具有广阔的应用前景。 相似文献
954.
2010年5月,在北京野鸭湖湿地自然保护区选择废弃鱼塘、耕作苜蓿(Medicago)地、撂荒苜蓿地、天然退化湿地和天然湿地作为实验地,其中,天然湿地作为对照。通过土壤种子库萌发实验,对实验地土壤种子库的基本特征以及与地上植被的关系进行了对比研究。结果表明,5种实验地的土壤种子库共有60种植物,隶属于23科46属。其中,萌发物种最多的是菊科(Compositae)、禾本科(Poaceae)和莎草科(Cyperaceae),分别为11种、10种和8种。废弃鱼塘、耕作苜蓿地、撂荒苜蓿地和天然退化湿地种子平均密度为6 885粒/m~2,天然湿地种子的平均密度为16 083粒/m~2,5种实验地的种子库密度差异极显著(n=300,F=4.828,p=0.001<0.05);各实验地的种子库垂直分布有一致的规律性,各实验地0~6 cm土层的种子库密度明显高于6~12 cm土层;各实验地的土壤种子库与地上植被的相似性系数都不高,土壤种子库物种组成的稳定性要高于地上植被。通过研究发现,退化湿地的土壤种子库中有大量的植物种子储藏和湿地植物的种子,这为野鸭湖退化湿地恢复提供了重要的保障,这些潜在的植物种子在野鸭湖退化湿地生态输水过程中会起到应有的恢复作用。建议野鸭湖湿地自然保护区管理部门继续加强退化湿地区域的土壤种子库保护工作,必须重视水环境的恢复、各种人为干扰的消除以及系统保护的加强。 相似文献
955.
The impact of the northward jump and westward movement of the East Asian westerly jet core from the western Pacific Ocean to the Qinghai-Tibet Plateau on precipitation distribution of eastern China is studied. It is concluded that on the one hand, the northward jump of the jet causes the precipitation belt to move northward from the middle and lower reaches of the Yangtze River valley and withdraw during the Mei-yu season; on the other hand, the westward movement of the jet core has no correspondence with withdrawal of the Mei-yu season. However, the earlier or later occurrence of the westward movement of the jet has an influence on the process of the rain belt moving northward than the northward jump of the jet: the rain belt moves northward from the middle-lower Yangtze River valley to the Huaihe River and then to an area between the Yellow River and Huaihe River during years when the time of the westward movement of the jet core is later than that of the northward jump of the jet and from the middle-lower Yangtze River valley to an area between the Yellow River and Huaihe River in other years. Further analysis shows that: (1) The northward jump of the jet and the westward movement of the East Asian westerly jet core causes significant variation of the general atmospheric circulation in middle latitudes and water vapor transport from the western Pacific, but not from the Bay of Bengal. (2) Impact of the northward jump and the westward movement of the East Asian westerly jet core on circulation are different, therefore, water vapor transport from the western Pacific and its impact on the rain belt are different. The earlier or later occurrence of the westward movement of the jet core than the northward jump of the jet causes the process of circulation and water vapor transport to be different which produces a different process of the rain belt moving northward. 相似文献
956.
An adaptive output feedback controller based on neural network feedback-feedforward compensator (NNFFC) which drives a surface ship at high speed to track a desired trajectory is designed. The tracking problem of the surface ship at low speed has been widely investigated. However, the coupling interactions among the forces from each degree of freedom (DOF) have not been considered in general. Furthermore, the influence of the hydrodynamic damping is also simplified into a linear form or neglected. On the contrary, coupling interactions and the nonlinear characteristics of the hydrodynamic damping can never be neglected in high speed maneuvering situation. For these reasons, the influence of the nonlinear hydrodynamic damping on the tracking precision is considered in this paper. Since the hydrodynamic coefficients of the surface ship at high speed are very difficult to be accurately estimated as a prior, it will be compensated by NNFFC as an unknown part of the tracking dynamics system. The stability analysis will be given by the Lyapunov theory. It indicates that the proposed control scheme can guarantee that all the signals in the closed-loop system are uniformly ultimately bounded (UUB), and numerical simulations can illustrate the excellent tracking performance of the surface ship at high speed under the proposed control scheme. 相似文献
957.
在调查隧道K64 +664~ K64+ 674段涌水塌方特征的基础上,从地质结构和地层岩性分析其成因.相应地,建立综合工作程序,采用”超前双排长管棚+小导管+注浆+三台阶法施工+瓦斯监测”的综合方案.对灾害进行处治,效果明显. 相似文献
958.
959.
吉林油田乾146区块经多年开采,已经进入高含水、高采出阶段。通过储层流动单元研究,运用多参数模糊聚类方法将该区高台子油层由好至差划分为A、B、C、D、E 5类储层流动单元。查明了区内主要目的层系各含油小层的储层流动单元发育特征:40、39小层主要发育A、B类优质储层流动单元,42、41、38小层则以C、D、E类储层流动单元为主,各小层储层流动单元类型及展布与初始产能吻合度较高,表明储层流动单元类型的差异是控制本区油气分布的重要因素之一。综合油藏地质特征及油田开发动态数据,对各储层流动单元的注采渗流体系进行了深入剖析,归纳总结出乾146区块高台子油层XII砂组中剩余油分布的5条规律,据此在剩余油分布预测区部署了1口扩边井和2口老区加密井,投产后分别获得了11.2t/d、5.5t/d和8.6t/d的初始产能。 相似文献
960.
Wei-min Ye Zi-yuan Qi Bao Chen Ji Xie Yu Huang Yao-ru Lu Yu-Jun Cui 《Environmental Earth Sciences》2011,64(1):269-276
Karst rocky desertification is a process of land degradation involving serious soil erosion, extensive exposure of basement
rocks. It leads to drastic decrease in soil productivity and formation of a desert-like landscape. In this regard, changes
in climatic conditions are the main origin of the soils degradation. Indeed, soils subjected to successive dry/wet cycling
processes caused by climate change develop swelling and shrinkage deformations which can modify their water retention properties,
thus inducing the degradation of soil–water capacity. The ecological characteristics of cultivation soils in karst areas,
Southwest of China, are extremely easy to be affected by external environmental factors due to its shallow bedding and low
vegetation coverage. Based on the analysis of the climate (precipitation) of this region during the past decades, an experimental
study has been conducted on a cultivated soil obtained from the typical karst area in southwestern China. Firstly, the soil–water
properties have been investigated. The measured soil–water retention curve shows that the air-entry value of the soil is between
50 and 60 kPa, while the residual saturation is about 12%. Based on the experimental results, three identifiable stages of
de-saturation have been defined. Secondly, a special apparatus was developed to investigate the volume change behavior of
the soil with controlled suction cycles. The vapor equilibrium technique was used for the suction control. The obtained results
show that under the effect of dry/wet cycles, (1) the void ratio of the cultivated soil is continuously decreasing, leading
to a gradual soil compaction. (2) The permeability decreases, giving rise to a deterioration of water transfer ability as
well as a deterioration of soil–water retention capacity. It is then obvious that the long-term dry/wet cycling process caused
by the climate change induce a continuously compaction and degradation of the cultivated soil in karst rocky desertification
areas. 相似文献