Mechanism and regulation of land degradation in Yulin district     

LIU Yansui  ZHANG Xiaoping  LI Xianwen  Jay Gao 《地理学报》2003,13(2):217-224

Yulin district is located in the transitional zone between Mu Us Desert and Loess Plateau of northern Shaanxi Province, thus it is particularly vulnerable to degradation due to its fragile ecosystem and intense human activities there. The purpose of this study is to explore the mechanism, process and driving force of land degradation in area with vulnerable eco-environment within the context of increasing population and intensifying human economic activities, and then find out the patterns and countermeasures of how to control them using the economic and technological ways. In detail, this study includes three main sections: the first section analyzes the mechanism, causes and characteristics of land degradation, which can be achieved by the typical field investigations and systematical analysis within the regional natural, social and economic context. Based on the technologies of remote sensing and GIS, and combined with the modeling methods, the second section reveals the change characteristics of land use and its driving force from 1990 to 2000; As to the third section, feasible countermeasures of how to prevent the degradation and rehabilitate the regional ecology are proposed, which are studied from the perspective of harmony between nature and economy, and the conception of regional sustainable development.  相似文献   

郯庐断裂系研究的新进展——兼论东亚北东向走滑断裂系统   总被引：2，自引：0，他引：2  

刘先文  单巨仁 《地球科学进展》1995,10(2):176-182

对郯庐断裂系研究的最新进展作了介绍。郯庐断裂是多期活动，性质多次转换的巨型断裂，最初的启动时间在晚三叠世末，与南北大陆的碰撞有着直接的关系，早期以走滑（左行）运动为主，伴随挤压和拉伸，范围限于华北地块内部，断裂纵向伸展的高峰期为白垩纪到早始新世，这一时期也是裂陷作用最强的时期，始新世以来以挤压作用为主，东亚走滑断裂系各组成断裂性质复杂，不能以中生代左行平移运动简单概括，走滑断裂系的发展和演化与同时  相似文献   

赤道西太平洋1°45′S,156°E海区的半日内潮波特性(英文)     

鲍献文  张义钧  孙丽  杜涛  方欣华 《海洋通报(英文版)》2006,(2)

通过对TOGA-COARE期间的一组锚系仪器阵列资料的分析得出:在赤道西太平洋1°45′S,156°E。海域存在显著的半日潮频内波,它的水平波数(波长)、垂向波数、水平传播速度和垂向传播速度分别约为:3.3×10-2km-1(210km),-1.6×10-3m-1,2.0m/s,-3.8cm/s。波形向斜下方传播,亦即波能向斜上方传输。它在观测点西南方生成后,向东北方向传播,到达观测海区。流速矢量旋转谱水平随深度的变化呈马鞍形,低谷及深处的峰所在深度分别与南赤道流及赤道潜流的南边界所在深度大体一致。旋转椭圆主轴方位角随深度变化,在浅层(40m处)为北偏东30°,到深处(324m)转为东偏南14°。总体上呈东北方向,表明波来自西南方向。  相似文献   

海洋细结构综述     

鲍献文  方欣华 《海洋与湖沼》1994,25(5):552-559

回顾海洋细结构研究发展过程，阐明海洋细结构基本概念，成因和类型，简单介绍几种用于细结构研究的多参数测量仪器，概述细结构谱特性的研究成果及几个解释模式，总结Ｃｏｘ数与Ｒｉｃｈａｒｄｓｏｎ数的统计特性。最后，阐述目前细结构研究的几个焦点问题并预测近期研究的趋势。  相似文献   

The observed currents in summer in the Bohai Sea   总被引：3，自引：0，他引：3  

乔璐  鲍献文  吴德星 《中国海洋湖沼学报》2008,26(2):130-136

A harmonic method was used to analyze the tidal currents observed in summer at 11 stations made from 1996 to 2001 in the Bohai Sea, China. Data was compared among different instruments and intervals. Elliptic elements were calculated based on harmonic constants, of which vertical distributions of the maximum speed and rotation direction were discussed for understanding the characteristics of diurnal and semi-diurnal tidal current components. The results indicate that the maximum speed of M2 tidal current component is much larger than that of K1; the rotation direction of M2 tidal current constituent is clockwise in the central part of the Bohai Sea and in the Laizhou Bay, but anticlockwise in the Liaodong Bay and Bohai Bay. For K1 tidal current constituent, it is clockwise in the central Bohai Sea but anti-clockwise in the Laizhou Bay and Liaodong Bay. The tidal currents in most stations in the Bohai Sea were regular semidiurnal except for those in the central Bohai Sea, being irregular semidiurnal.  相似文献   

A Strain Rate Dependent Constitutive Model for the Lower Silurian Longmaxi Formation Shale in the Fuling Gas Field of the Sichuan Basin,China     

HOU Zhenkun  LI Xianwen  ZHANG Yanming  LIANG Huqing  GUO Ying  CHENG Hanlie  GAO Ruchao 《《地质学报》英文版》2019,93(4):972-981

Shale, as a kind of brittle rock, often exhibits different nonlinear stress-strain behavior, failure and time-dependent behavior under different strain rates. To capture these features, this work conducted triaxial compression tests under axial strain rates ranging from 5×10?6 s?1 to 1×10?3 s?1. The results show that both elastic modulus and peak strength have a positive correlation relationship with strain rates. These strain rate-dependent mechanical behaviors of shale are originated from damage growth, which is described by a damage parameter. When axial strain is the same, the damage parameter is positively correlated with strain rate. When strain rate is the same, with an increase of axial strain, the damage parameter decreases firstly from an initial value (about 0.1 to 0.2), soon reaches its minimum (about 0.1), and then increases to an asymptotic value of 0.8. Based on the experimental results, taking yield stress as the cut-off point and considering damage variable evolution, a new measure of micro-mechanical strength is proposed. Based on the Lemaitre’s equivalent strain assumption and the new measure of micro-mechanical strength, a statistical strain-rate dependent damage constitutive model for shale that couples physically meaningful model parameters was established. Numerical back-calculations of these triaxial compression tests results demonstrate the ability of the model to reproduce the primary features of the strain rate dependent mechanical behavior of shale.  相似文献   

南沙海区温度细结构正态性检验     

方欣华  吴巍  刘煜  鲍献文 《中国海洋大学学报(自然科学版)》2000,30(2):189-194

对南沙海区观测得的部分温度脉动一深度序列作了正态检验。检验时先用根据序列的自回归模型构成的滤波器滤去序列元素间之相关性产生白噪声序列 ,而后用 χ2一拟合优度检验法对此白噪声序列作正态性独立同分布检验并对偏度与峰度作了检验。检验结果表明 ,除少数样本近似正态分布外 ,大多数样本的分布为非正态的 ,这是在样本内小于内波尺度的不可逆细结构所起的作用  相似文献   

Characteristics of coastal trapped waves along the northern coast of the South China Sea during year?1990   总被引：1，自引：0，他引：1  

Yang Ding  Xianwen Bao  Maochong Shi 《Ocean Dynamics》2012,62(9):1259-1285

The structures and evolution of the coastal-trapped waves (CTW) along the northern coast of the South China Sea (SCS) in the year?1990 are studied using observed hourly sea level records collected from four sites around the northern SCS and a three-dimensional numerical model with realistic bathymetry and wind forcing. Analysis of the yearlong records of the observed sea level data indicates that the sea level variations are highly correlated between the stations and the sea level variability propagates southwestward along the coast. The sea level signals traveling from northeast to southwest along the coast with a propagation speed of 5.5–17.9?m?s^?1 during both the typhoon season and the winter month show the characteristics of a CTW. The wave speed is faster between stations Shanwei and Zhapo than that between Xiamen and Shanwei. Sea level variations during both typhoon season and winter month are reasonably well represented by the numerical model. The model runs focused on the wave signals related to typhoons and winter storm show that the CTW propagating southwestward along the coast can be reinforced or decreased by the local wind forcing during its propagation and there are apparent differences in the propagation characteristics between the waves along the mainland and those traveling around Hainan Island. The abrupt change of the shelf width and coastline around Leizhou Peninsula and Hainan Island are responsible for strong scattering of CTWs from one mode into higher modes. The alongshore velocities across different transects associated with CTW are investigated to examine the vertical structures of the waves. The alongshore velocity structures at transects during different events are related to the combined effect of stratification and shelf profile, which can be estimated using the Burger number. The empirical orthogonal function analysis of alongshore velocity and nodal lines of the mode structure suggest mode two CTWs in transect S2 during typhoon season and mode 1 CTWs during winter. Sensitivity model experiments are also performed to demonstrate the effects of local wind and topography on the wave propagation.  相似文献   

M<Subscript>2</Subscript> tidal dynamics in Bohai and Yellow Seas: a hybrid data assimilative modeling study     

Zhigang Yao  Ruoying He  Xianwen Bao  Dexing Wu  Jun Song 《Ocean Dynamics》2012,62(5):753-769

A high-resolution hybrid data assimilative (DA) modeling system is adapted to study the M₂ barotropic tidal characteristics and dynamics in the Bohai and Yellow Seas. In situ data include tidal harmonics extracted from both coastal sea level and bottom pressure observations. The hybrid DA system consists of both forward and inverse models. The former is three-dimensional, finite-difference, nonlinear Regional Ocean Modeling System (ROMS). The latter is a three-dimensional, linearized, frequency-domain, finite-element model TRUXTON. The DA system assimilates in situ observations via the inversion of the barotropic tidal open boundary conditions (OBCs). Model skill is evaluated by comparing misfits between the observed and modeled tidal harmonics. The assimilation scheme is found effective and efficient in correcting the tidal OBCs, which in turn improves ROMS tidal solutions. Up to 50% reduction of model/data misfits is achieved after data assimilation. M₂ co-tidal maps constructed from the posterior (data assimilative) ROMS solutions agree well with observational analysis of (Fang et al. 2004). Detailed analyses on tidal mixing, residual current, energy flux, dissipation, and momentum term balance dynamics are performed for M₂ constituent, revealing complex M₂ tidal characteristics in the study region and the important role of coastal geometry and topography in affecting regional tidal dynamics.  相似文献   

Observed characteristics of the North Yellow Sea water masses in summer     

鲍献文  李娜  吴德星 《中国海洋湖沼学报》2010,28(1):160-170

In this paper, we characterize the North Yellow Sea (NYS) water masses in summer by analyzing temperature and salinity data surveyed in 2006. The Liaonan Coastal Water is characterized by low salinity westward and southward flow paths. The westward path flows parallel to land, turns to the south, then to the southeast adjacent to the mouth of the Lüshun River, where it mixes with other coastal water directly to the southwest. It becomes the main source of low salinity water in the deep water area west of 123°E. The high-salinity Lubei Coastal Water is the remnant of the winter Lubei Coastal Water, which is located mostly in a small area between Yantai and Weihai, and does not originate in the Bohai Sea Coastal Water. The two NYS zones demarcated at 123°E have distinctly different temperature and salinity characteristics. There are two high-salinity centers east of 123°E, whereas there is low-salinity water to the west whose temperature and salinity structures are complex, composed of the coastal water south of Chengshantou, the Liaonan Coastal Water and the Bohai Sea Water.  相似文献