北京地磁台的磁环境监测   总被引：1，自引：0，他引：1  

王晓祜  吕智  周江林  张秀玲  燕小渝 《地震地磁观测与研究》2007,28(3):52-61

对北京地磁台建台以来,台站周边环境随着北京城市化进程发生的变化做了较详细的描述.利用几次在台站地磁观测区范围内的地磁场梯度观测资料,分析了台站地磁观测场地磁场梯度的变化情况,并对现有地磁场梯度环境进行了评估.为北京地磁台及全国其他台站,在现有条件下的地磁观测工作提供了有益的参考.  相似文献   

Spatiotemporal dynamics of aboveground primary productivity along a precipitation gradient in Chinese temperate grassland   总被引：2，自引：0，他引：2  

HU ZhongMin    FAN JiangWen  ZHONG HuaPing & YU GuiRui Key Laboratory of Ecosystem Network Observation  Modeling  CERN Center for Synthesis Research  Institute of Geographic Sciences  Natural Resources Research  Chinese Academy of Sciences  Beijing  China  Graduate University of Chinese Academy of Sciences  Beijing  China 《中国科学D辑(英文版)》2007,50(5):754-764

Investigating the spatial and temporal variance in productivity along natural precipitation gradients is one of the most efficient approaches to improve understanding of how ecosystems respond to climate change. In this paper, by using the natural precipitation gradient of the Inner Mongolian Plateau from east to west determined by relatively long-term observations, we analyzed the temporal and spatial dynamics of aboveground net primary productivity (ANPP) of the temperate grasslands covering this region. Across this grassland transect, ANPP increased exponentially with the increase of mean annual precipitation (MAP) (ANPP=24.47e0.005MAP, R2=0.48). Values for the three vegetation types desert steppe, typical steppe, and meadow steppe were: 60.86 gm-2a-1, 167.14 gm-2a-1 and 288.73 gm-2a-1 respectively. By contrast, temperature had negative effects on ANPP. The moisture index (K ), which takes into ac- count both precipitation and temperature could explain the spatial variance of ANPP better than MAP alone (ANPP=2020.34K1.24, R2=0.57). Temporally, we found that the inter-annual variation in ANPP (cal- culated as the coefficient of variation, CV) got greater with the increase of aridity. However, this trend was not correlated with the inter-annual variation of precipitation. For all of the three vegetation types, ANPP had greater inter-annual variation than annual precipitation (PPT). Their difference (ANPP CV/PPT CV) was greatest in desert steppe and least in meadow steppe. Our results suggest that in more arid regions, grasslands not only have lower productivity, but also higher inter-annual variation of production. Climate change may have significant effects on the productivity through changes in precipitation pattern, vegetation growth potential, and species diversity.  相似文献   

混合范数下的最优化反演方法   总被引：4，自引：1，他引：4  

刘海飞  阮百尧  柳建新  吕玉增 《地球物理学报》2007,50(6):1877-1883

在求解地球物理反问题时，通常根据最小二乘准则构造目标函数进行反演，并在实践中得到了广泛的应用.为进一步增强反演的稳健性及减少多解性，不损失反演结果的分辨率，本文提出了混合范数下的最优化反演方法，它根据数据和模型可能服从不同的概率分布，对数据空间和模型空间采用不同的范数来构造目标函数.在给出目标函数的基础上，导出了混合范数下的线性反演方程.由于该线性反演方程的复杂性，我们采用混合范数下迭代再加权共轭梯度法进行求解.最后，通过对模拟的电阻率数据进行反演，验证了本文计算方法是可行的.  相似文献   

Tectonic thermal history and its significance on the formation of oil and gas accumulation and mineral deposit in Ordos Basin   总被引：1，自引：0，他引：1  

REN ZhanLi  ZHANG Sheng  GAO ShengLi  CUI JunPing  XIAO YuanYuan  XIAO Hui 《中国科学D辑(英文版)》2007,50(Z2):27-38

The analyzing data on stratigraphic temperature measurement , thermal conductivity of the strata and radioactive heat production rate show that the present average geothermal gradient in the Ordos Basin is 2.93℃/100 m, and the average heat flow value is 61.78 mW/m2, which belongs to the mesothermal basin, and the value of the present geothermal gradient and heat flow in the east is higher than that in the west. The sandstone radioactive heat production rate of Zhiluo Group in Dongsheng Uranium deposits of Yimeng uplift is obviously higher in the mudstone, indicating that there exists a uranium anomaly. Based on studies of the present thermal field of the basin, the late-Mesozoic paleotemperature and paleogeothermal gradient are determined by using different kinds of paleotemperature methods. According to the anomaly of the late-Mesozoic paleotemperature gradient and magmatic event age, there was a tectonic thermal event in the early Cretaceous epoch of late-Mesozoic. This article rebuilds tectonic thermal history of different tectonic units by thermal history simulation using basin simulating software. The evolution of oil-gas and coal, and accumulation (mineralization) of mineral uranium are all controlled by the tectonic thermal history in the Ordos basin, especially by the tectonic thermal event that happened in the late Mesozoic. For both the gas source rocks of upper Paleozoic group and lower paleozoic group, the gas was largely generated in the early Cretaceous epoch of the late Mesozoic. The main petroleum generation period for Yanchang Group in Triassic system is the early Cretaceous epoch too, and the highest thermal maturity of the coal of Permo-Carboniferous, Triassic, and Jurassic reaches is the early Cretaceous epoch also. Early Cretaceous epoch is still one of the most important mineralizing periods of uranium.  相似文献   

基于小波增强的改进多尺度形态梯度边缘检测算法   总被引：7，自引：1，他引：7  

费浦生  王文波 《武汉大学学报(信息科学版)》2007,32(2):120-123

在形态学梯度边缘检测算子的基础上，综合多结构元和多尺度算法的特性，提出了一种基于小波增强的多结构元、多尺度边缘检测方法，用不同取向的结构元素对图像进行多尺度检测，并综合各尺度下的边缘，得到了噪声存在下的理想边缘。实验表明，本文方法边缘定位准确、轮廓清晰，保留了更多的图像细节，具有较强的抗噪能力。  相似文献   

Solving Three Types of Satellite Gravity Gradient Boundary Value Problems by Least-Squares     

XU Xinyu LI Jiancheng ZOU Xiancai CHU Yonghai 《地球空间信息科学学报》2007,10(3):168-172

The principle and method for solving three types of satellite gravity gradient boundary value problems by least-squares are discussed in detail. Also, kernel function expressions of the least-squares solution of three geodetic boundary value problems with the observations {Γ zz },{Γ xz , Γ yz} and {Γ xx -Γ yy ,2 Γxy}are presented. From the results of recovering gravity field using simulated gravity gradient tensor data, we can draw a conclusion that satellite gravity gradient integral formulas derived from least-squares are valid and rigorous for recovering the gravity field.  相似文献   

A simple solution for drainage through a 2-dimensional hydraulic fill stope     

Nagaratnam Sivakugan  Kelda S. Rankine 《Geotechnical and Geological Engineering》2006,24(5):1229-1241

Inadequate drainage has been attributed as the major cause of failure of several hydraulic fill stopes that have claimed lives. Therefore it is necessary to be able to predict the pore water pressure developments and flow rates throughout the filling operation. There are computer programmes that can simulate the hydraulic filling of a mine stope and enable computations of the pore water pressures, flow rates and hydraulic gradients at any time. This paper presents a simple analytical solution for estimating the maximum pore water pressure within the stope, flow rate and the hydraulic gradients at the entry and exit. The proposed solutions are verified against solutions derived from FLAC, a finite difference software, and the agreement is found to be excellent. A simple equation for the hydraulic gradient at the top of the stope, as a function of the height of water within the fill, is also presented.  相似文献   

均匀和梯度介质中等时面(线)的几何特征分析     

YE Yun-fei 《吉林大学学报(地球科学版)》2006,(Z2)

等时面是地震波时间场的等值面,是Kirchhoff型数值模拟及Kirchhoff型偏移与反偏移的数据叠加或数据分布曲面,其几何形状和局部曲率对于Kirchhoff型真振幅偏移和反偏移中的加权函数计算和成像效果具有重要的影响。本文推导了均匀和梯度介质中的等时线公式并计算了二维均匀和梯度介质中等时线的几何特征。  相似文献   

城市化与西北地区经济发展的互动关系分析   总被引：4，自引：7，他引：4  

赵雪雁 《干旱区地理》2006,29(1):150-155

从各国的经验来看,城市化与区域经济发展存在着强烈的互动关系。本文详细分析了西北地区城市化与人均GDP、经济发展水平、经济发展速度的关系。结果表明:(1)西北地区城市化水平与人均GDP的关系符合国际一般规律,呈对数关系;(2)西北地区城市化水平的地区差异与地区资金投入量、消费和收入的关系密切;(3)西北地区城市化水平与经济发展水平间的相关关系存在较大的区域差异;(4)不同的时段造成西北地区省际城市化水平差异的主要因子不同;(5)与经济增长速度相比,西北五省区的城市化速度仍存在不同程度的滞后。  相似文献   

Modern Diatom Assemblages in Surface Sediments from Estuarine Systemsin the Southeastern Buenos Aires Province, Argentina   总被引：1，自引：0，他引：1  

Gabriela S. Hassan  Marcela A. Espinosa  Federico I. Isla 《Journal of Paleolimnology》2006,35(1):39-53

Paleoecological reconstructions of Holocene sea-level changes in Argentinean coastal regions were based mainly on ecological data gathered from other regions, as there was a lack of information on modern estuarine diatom distributions. The aim of the present work was to assess the spatial variation of diatom assemblages in two representative estuaries of Argentina in order to gather ecological information for paleoecological reconstructions in the region. The two selected estuaries have different geomorphologic features and salinity regimes: Mar Chiquita Lagoon is shallow, which prevents the development of a stable salinity gradient as it occurs in the Quequén Grande River. Surface sediment samples were taken from selected stations representative of the environmental gradient from the inlet to the inner reaches of both estuaries. Cluster analysis defined three diatom zones at Mar Chiquita: marine/brackish assemblages dominate the inlet (zone I), where salinity, tidal range and current speed are higher. The brackish/freshwater tychoplankton Staurosira construens var. venter and Staurosirella pinnata dominate the inner lagoon (zone II), where environmental conditions are very variable and concentrations of suspended sediments are higher. Brackish/freshwater euryhaline diatoms dominate the headwaters (zone III). On the other hand, the Quequén Grande River was divided into three diatom zones: coastal taxa are distributed at the inlet (zone I), while the middle estuary (zone II) is dominated by brackish/freshwater euryhaline taxa. At the upper estuary region (zone III), freshwater diatoms dominate, and the halophobous Nitzschia denticula increased in abundance values. Diatom distributions were most closely related to the salinity gradient at Quequén Grande River than at Mar Chiquita Lagoon. Fossil data of a sequence from Mar Chiquita Lagoon (Las Gallinas Creek) were compared to the modern data set in order to search for analogies between fossil and modern diatom assemblages. DCA results showed that fossil diatom assemblages have modern counterparts. Most diatom assemblages of Las Gallinas Creek fall within Mar Chiquita zone III, representing a shallow brackish/freshwater environment, with low salinity fluctuations (~1–9‰) and no tidal influence. Therefore, our modern diatom data provide useful analogs to interpret paleoenvironments in the region.  相似文献