Temporal-Spatial Variation of Surface Suspended Matter and Controlling Factors in the Inner Shelf of the East China Sea in Winter     

MIN Jianxiong  LI Guangxue  DING Dong  QIAO Lulu  MA Yanyan  YANG Gang  ZHANG Yaqi  ZHANG Lei  LI Shuhao 《中国海洋大学学报(英文版)》2019,(1)

Based on the observed surface suspended matter in the East China Sea in February 2007 and June 2015, an empirical model was established using L1 b's band 4 data to retrieve surface suspended matter from the Moderate Resolution Imagine Spectroradiometer Terra imagery. The squared correlation coefficient is 0.8358, and the root mean square error is 0.4285 mg L-1. The model reflects the distribution characteristics of surface suspended matter in the inner shelf of the East China Sea. In this paper, the satellite images of the study area were retrieved in January from 2001 to 2015, and the monthly distribution of surface suspended matter were obtained. The inter-annual distribution of the study area is similar, and the concentration of surface suspended matter is higher near the shore than offshore. A large amount of surface suspended matter is transported southeast under the influence of Zhejiang and Fujian coastal current and Taiwan warm current. Only a small amount of surface suspension can reach the Kuroshio area. The surface suspended matter concentration changes obviously near the estuary because of the effect of differences in the flux of the Yangtze River. Meanwhile, winter monsoon, temperature front, El Ni?o events, and other factors affect the distribution of surface suspended matter in 100 m isobath to coastal water but minimally influence the distribution in 100 m isobath to deep sea.  相似文献   

A biodiversity evaluation framework for restoration of aquatic macrophyte communities in shallow lakes driven by hydrological process management     

Shuhan Li  Tao Sun  Wei Yang  Baoshan Cui  Xinan Yin 《水文研究》2021,35(1):e13983

Macrophyte community diversity and composition respond to ecosystem conservation and local environmental factors. In this study, we developed a multidimensional diversity framework for macrophyte communities, including the taxonomic and functional alpha and beta diversity. We used the framework to explore the relationships among water level regimes and these diversity parameters in a case study of China's Baiyangdian Lake. Analysis of indicators of hydrologic alteration divided the water level from 1959 to 2019 into four regimes (dry, <6.42 m; low, 6.42–7.23 m; medium, 7.23–8.19 m; high, >8.19 m). Alpha and beta diversity were significantly higher in the medium regime than in the low and high regimes. Redundancy analysis indicated that the maximum water depth significantly affected taxonomic alpha diversity, and total nitrogen (TN) and chemical oxygen demand (COD) concentration significantly affected functional alpha diversity, respectively. Mantel tests showed that TN, Secchi depth (SD), and water depth in the high water level regime significantly increased the total beta diversity and turnover components. TN was the main factor that increased total taxonomic beta diversity. Water level regime mainly influenced interspecific relationships by changing the TN and COD concentration. The water level should be maintained between the medium and high water level regimes to promote restoration of the macrophyte community and improve ecosystem stability. The biodiversity evaluation framework would provide a deeper insight into the hydrological process management for restoration of aquatic macrophyte communities in shallow lakes.  相似文献   

Benthic foraminiferal fauna and sediment provenance of Eocene syn-rift sequences in Taiwan: implication for onset of Asian epi-continental marginal seas off China coast     

Huang  Chi-Yue  Shao  Lei  Wang  Ming-Huei  Xue  Wei-Guang  Qiao  Pei-Jun  Cui  Yu-Chi  Hou  Yuan-Li 《Marine Geophysical Researches》2019,40(2):111-127

Marine Geophysical Research - Early Cenozoic rift basins developed commonly on the Mesozoic basement along the SE Asia Continent. However, Eocene–Oligocene sequences were only exposed widely...  相似文献   

Permeability Characteristics of Broken Coal and Rock Under Cyclic Loading and Unloading     

Zhang  Cun  Zhang  Lei 《Natural Resources Research》2019,28(3):1055-1069

Natural Resources Research - During longwall mining, the permeability evaluation in a caving zone is one of the most challenging risks for mine operators because it controls the behavior of gas...  相似文献   

Implementation of a coupled plastic damage distinct lattice spring model for dynamic crack propagation in geomaterials          下载免费PDF全文

Chao Jiang  Gao‐Feng Zhao 《国际地质力学数值与分析法杂志》2018,42(4):674-693

This paper studies dynamic crack propagation by employing the distinct lattice spring model (DLSM) and 3‐dimensional (3D) printing technique. A damage‐plasticity model was developed and implemented in a 2D DLSM. Applicability of the damage‐plasticity DLSM was verified against analytical elastic solutions and experimental results for crack propagation. As a physical analogy, dynamic fracturing tests were conducted on 3D printed specimens using the split Hopkinson pressure bar. The dynamic stress intensity factors were recorded, and crack paths were captured by a high‐speed camera. A parametric study was conducted to find the influences of the parameters on cracking behaviors, including initial and peak fracture toughness, crack speed, and crack patterns. Finally, selection of parameters for the damage‐plasticity model was determined through the comparison of numerical predictions and the experimentally observed cracking features.  相似文献   

Study of the flood control scheduling scheme for the Three Gorges Reservoir in a catastrophic flood          下载免费PDF全文

Shanghong Zhang  Zhu Jing  Wenda Li  Yujun Yi  Yong Zhao 《水文研究》2018,32(11):1625-1634

The Three Gorges Project is the world's largest water conservancy project. According to the design standards for the 1,000‐year flood, flood diversion areas in the Jingjiang reach of the Yangtze River must be utilized to ensure the safety of the Jingjiang area and the city of Wuhan. However, once these areas are used, the economic and life loss in these areas may be very great. Therefore, it is vital to reduce this loss by developing a scheme that reduces the use of the flood diversion areas through flood regulation by the Three Gorges Reservoir (TGR), under the premise of ensuring the safety of the Three Gorges Dam. For a 1,000‐year flood on the basis of a highly destructive flood in 1954, this paper evaluates scheduling schemes in which flood diversion areas are or are not used. The schemes are simulated based on 2.5‐m resolution reservoir topography and an optimized model of dynamic capacity flood regulation. The simulation results show the following. (a) In accord with the normal flood‐control regulation discharge, the maximum water level above the dam should be not more than 175 m, which ensures the safety of the dam and reservoir area. However, it is necessary to utilize the flood diversion areas within the Jingjiang area, and flood discharge can reach 2.81 billion m³. (b) In the case of relying on the TGR to impound floodwaters independently rather than using the flood diversion areas, the maximum water level above the dam reaches 177.35 m, which is less than the flood check level of 180.4 m to ensure the safety of the Three Gorges Dam. The average increase of the TGR water level in the Chongqing area is not more than 0.11 m, which indicates no significant effect on the upstream reservoir area. Comparing the various scheduling schemes, when the flood diversion areas are not used, it is believed that the TGR can execute safe flood control for a 1,000‐year flood, thereby greatly reducing flood damage.  相似文献   

利用超快速精密星历约束的北斗卫星实时精密定轨     

范磊  施闯  李敏 《大地测量与地球动力学》2018,38(9):937-942

以广播星历为起算轨道的北斗卫星实时滤波精密定轨往往需要较长收敛时间，针对此，提出利用超快速精密星历约束的实时精密定轨方法。通过MGEX跟踪网全球分布的51个测站连续7 d的实测数据，利用平方根信息滤波对北斗卫星实时精密轨道进行确定，并以3 d解事后轨道作为参考，评估北斗卫星实时滤波轨道精度。结果表明，利用广播星历作起算轨道时，北斗实时滤波轨道平均需要经过15 h收敛才能达到稳定，而新方法在这段时间内轨道变化较为平稳，未出现明显的收敛现象，并且7 d时间内GEO卫星在切向、法向和径向上RMS分别优于2.5 m、20 cm和30 cm，IGSO和MEO卫星在3个方向上分别优于30 cm、15 cm和10 cm。
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基于“DEM-NDVI-土地覆盖分类”的天山博格达自然遗产地山地垂直带提取与变化分析     

冀欣阳  骆磊  王心源  李丽  万红 《地球信息科学学报》2018,20(9):1350-1360

本文基于Landsat影像数据获取天山博格达自然遗产地土地覆盖分类,结合归一化植被指数（NDVI）和数字高程模型（DEM）构建“DEM-NDVI-土地覆盖分类”散点图分析研究区植被受海拔和坡向的水热空间变化影响的分布特征,通过概率统计分析提取博格达遗产地山地垂直带,并结合研究区的气温、降水数据和NDVI变化特征分析垂直带变化的原因。研究结果表明：① 本文利用“DEM-NDVI-土地覆盖分类”散点图,揭示了研究区1989年和2016年的NDVI值和分类类别随着海拔上升的变化特征,其中NDVI值随着海拔上升呈现“倒U形”变化,而不同分类类别在一定的海拔区间内呈现出聚集效应,且不同分类类别有明显的高程界限。② 1989年和2016年博格达遗产地山地垂直带分带上限分别为：1278 m和1185 m（温带荒漠草原带）、1784 m和1759 m（山地草原带）、2706 m和2730 m（山地针叶林带）、3272 m和3293 m（高山草甸带）、3636 m和3690 m（高山垫状植被带）。③ 博格达遗产地1989年和2016年山地垂直带受区域气温升高和降雨增加的影响有较为明显的改变,其中温带荒漠草原带最为敏感,其上限变化最大,向下收缩93 m;山地针叶林带的分布范围则向两侧扩张49 m;山地草甸带带宽基本保持不变,但整体上移了约20 m;冰雪带则受到全球气候变暖的影响向上退缩54 m。  相似文献   

Regional Characteristics and Causes of Haze Events in Northeast China     

Weiwei Chen  Shichun Zhang  Quansong Tong  Xuelei Zhang  Hongmei Zhao  Siqi Ma  Aijun Xiu  Yuexin He 《中国地理科学(英文版)》2018,28(5):836-850

Northeast China experiences severe atmospheric pollution, with an increasing occurrence of heavy haze episodes. However, the underlying forces driving haze formation during different seasons are poorly understood. In this study, we explored the spatio-temporal characteristics and causes of haze events in Northeast China by combining a range of data sources(i.e., ground monitoring, satellite-based products, and meteorological products). It was found that the ‘Shenyang-Changchun-Harbin(SCH)'city belt was the most polluted area in the region on an annual scale. The spatial distribution of air quality index(AQI) values had a clear seasonality, with the worst pollution occurring in winter, an approximately oval-shaped polluted area around western Jilin Province in spring, and the best air quality occurring in summer and most of the autumn. The three periods that typically experienced intense haze events were Period I from mid-October to mid-November(i.e., late autumn and early winter), Period II from late-December to February(i.e., the coldest time in winter), and Period III from April to mid-May(i.e., spring). During Period I, strong PM_(2.5) emissions from seasonal crop residue burning and coal burning for winter heating were the dominant reasons for the occurrence of extreme haze events(AQI 300). Period II had frequent heavy haze events(200 AQI 300) in the coldest months of January and February, which were due to high PM_(2.5) emissions from coal burning and vehicle fuel consumption, a lower atmospheric boundary layer, and stagnant atmospheric conditions. Haze events in Period III, with high PM_(10) concentrations, were primarily caused by the regional transportation of windblown dust from degraded grassland in central Inner Mongolia and bare soil in western Jilin Province. Local agricultural tilling could also release PM_(10) and enhance the levels of windblown dust from tilled soil. Better control of coal burning, fuel consumption, and crop residue burning in winter and autumn is urgently needed to address the haze problem in Northeast China.  相似文献   

基于分布式控制力矩陀螺的水下航行器轨迹跟踪控制   总被引：2，自引：0，他引：2  

黄道敏  徐瑞昆  唐国元  冯雷  刘智  徐国华 《海洋工程》2018,36(6):69-76

基于控制力矩陀螺群(CMGs)的水下航行器具有低速或零速机动的能力。采用基于分布式CMGs的水下航行器方案,并研究其水平面的轨迹跟踪控制问题。通过全局微分同胚变换将非完全对称的动力学模型解耦成标准欠驱动控制模型,并根据简化的模型构建其轨迹跟踪的误差动力学模型,将轨迹跟踪控制问题转化为误差模型镇定问题。基于一种分流神经元模型和反步法设计了系统的轨迹跟踪控制律,该控制器不需要对任何虚拟控制输入进行求导计算,且能确保跟踪误差的最终一致有界性。仿真结果表明该控制器能够实现在不依赖动力学参数先验知识的情况下对光滑轨迹的有效跟踪。  相似文献