榆林地区土地退化机制和调控   总被引：6，自引：0，他引：6  

刘彦随  张晓平  李宪文  Jay GAO 《地理学报(英文版)》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 activites there,The purpose of hias 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 econmomic 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 propsed ,which are studed from the perspective of harmony between nature and economy,and the conception of regional sustainable development.  相似文献   

论大别地块中榴辉岩与围岩的变质关系及区域“递增”变质带的形成     

刘晓春  刘先文  胡克 《吉林大学学报(地球科学版)》1992,(4)

研究表明,大别地块中榴辉岩形成时的变质压力从东南向西北呈递减趋势,由2.8～3.5GPa降至约1.0GPa,而温度变化则不明显,由647～755℃略增至684～829℃.榴辉岩的围岩中某些残留高压矿物或其假象的发现证明它们与榴辉岩一起经历了原地高压变质作用过程.不同地区榴辉岩的退变组合及P—T条件与围岩同步变化,从绿帘角闪岩相、角闪岩相到麻粒岩相,从而表明现今围岩所展示出的“递增”变质带是由榴辉岩相退变质作用造成的,其形成时代可能不早于晚元古代.  相似文献   

流动注射－化学发光法测定钽   总被引：7，自引：0，他引：7  

李先文  王屹  章竹君 《岩矿测试》1994,13(4):245-248

利用Ｔａ对鲁米诺－Ｈ２Ｏ２－Ｋ３Ｆｅ（ＣＮ）６化学发光体系的抑制作用，建立了痕量Ｔａ的化学发光分析法，由流动注射－化学发光仪实现测定。方法的检出限是５．０ｎｇ／ｍｌＴａ（Ｖ）测定范围为０．０１－１μｇ／ｍｌＴａ（Ｖ），测定０．０１μｇ／ｍｌＴａ（Ｖ）１１次的相对标准偏差为３．８％。方法已应用于矿石中Ｔａ的测定。  相似文献   

河南省县级行政区划空间形态特征分析与优化     

李欣  王先文 《测绘工程》2018,(6):69-76

研究行政区划边界的空间形态特征,对研究区域历史,优化区域结构,提高经济水平都具有重要的理论和实际意义。利用分形维数、放射状指数和紧凑度3种定量测度方法,对河南省县级行政区划空间形态特征进行计算和分析,结合河南省社会经济发展数据研究发现,目前部分县级行政区划空间形态存在边界复杂程度高、行政中心边缘化和空间聚集性低等限制区域协调发展的问题。文中研究的方法可以为改善区划空间形态,优化区划边界形状和管理开发区域空间提供决策依据。  相似文献   

安徽庐枞盆地中段重磁电特征及地质意义     

朱将波  汪启年  崔先文 《中国地质调查》2022,9(3):87-95

安徽庐枞盆地是长江中下游成矿带的重要矿集区,其深部火山岩基底性质不明,制约了矿产勘探的开展。通过对庐枞火山岩盆地中段1∶5万高精度重磁数据及大地电磁测深数据进行再处理,探讨该区地球物理场的特征及其地质意义。结果表明: 庐枞火山岩盆地位于NE向古生代地层褶皱带的“鞍部”,火山岩厚度与重力剩余异常幅值变化具有较好的对应关系; 火山岩之下主体为隐伏侵入岩,呈似厚层状,底界面厚度为3~4 km,黄屯—枞阳断裂与罗河断裂是主要的深部岩浆通道。推断盆地内三叠系—石炭系主体被侵位,部分泥盆系—志留系在隐伏侵入岩之下发育。研究成果可为庐枞盆地基础地质研究及找矿预测提供参考。  相似文献   

An alternative approach to calculate the posterior probability of GNSS integer ambiguity resolution     

Xianwen Yu  Jinling Wang  Wang Gao 《Journal of Geodesy》2017,91(3):295-305

When precise positioning is carried out via GNSS carrier phases, it is important to make use of the property that every ambiguity should be an integer. With the known float solution, any integer vector, which has the same degree of freedom as the ambiguity vector, is the ambiguity vector in probability. For both integer aperture estimation and integer equivariant estimation, it is of great significance to know the posterior probabilities. However, to calculate the posterior probability, we have to face the thorny problem that the equation involves an infinite number of integer vectors. In this paper, using the float solution of ambiguity and its variance matrix, a new approach to rapidly and accurately calculate the posterior probability is proposed. The proposed approach consists of four steps. First, the ambiguity vector is transformed via decorrelation. Second, the range of the adopted integer of every component is directly obtained via formulas, and a finite number of integer vectors are obtained via combination. Third, using the integer vectors, the principal value of posterior probability and the correction factor are worked out. Finally, the posterior probability of every integer vector and its error upper bound can be obtained. In the paper, the detailed process to calculate the posterior probability and the derivations of the formulas are presented. The theory and numerical examples indicate that the proposed approach has the advantages of small amount of computations, high calculation accuracy and strong adaptability.  相似文献   

The slanting property of semi-diurnal internal tide propagation in the Pacific Ocean at 1°45′S, 156°E     

BAO Xianwen  ZHANG Yijun  SUN Li  DU Tao  FANG Xinhua 《海洋学报(英文版)》2006,25(4):143-145

By analyzing a data set collected using a moored instrument array and CTD during TOGA-COARE, it is found that there exist remarkable internal tides in the western equatorial Pacific Ocean around 1°45′S,156°E, whose horizontal wavenumber (wavelength), vertical wavenumber, h 156° orizontal propagation speed and vertical propagation speed are 3.3×10-2km-1(210 km),-1.6×10-3m, 2.0 m/s and -3.8 cm/s, respectively, that is, the waveform propagates downwards slantingly. Moreover, the propagating direction rotates statistically clockwise as the depth increases and its cause is unclear.  相似文献   

Analysis of characteristics and mechanism of current system on the west coast of Guangdong of China in summer   总被引：1，自引：2，他引：1  

BAO Xianwen  HOU Yijun  CHEN Changshen  CHEN Fei  SHI Maochong 《海洋学报(英文版)》2005,24(4):1-9

On the basis of data of drifting bottles＇ tracks and the current measured in anchored stations, as well as temperature and salinity observed in cruise investigations and coastal stations, ADCP current data and AVHRR surface sea temperature （SST） data on the western coast of Guangdong, synthetic results of analysis showed that the coastal currents in the west of the mouth of the Zhujiang River were mainly westward in summer, which constituted the north branch of cyclonic gyre in the east of the Qiongzhou Straits. Part of its water flowed westward into the Beibu Gulf through the Qiongzhou Straits. The coastal current pattern was not identical with the traditional current system which flowed westward in the Qiongzhou Straits in winter and eastward in summer. The summertime＇s coastal current was always westward, maybe temporarily turning northeast only when the southwest wind was strong. The important characteristics of coastal current on the western coast of Guangdong, in the Qiongzhou Straits and in the north of the Beibu Gulf were analyzed and their mechanisms also were explained.  相似文献   

Statistical downscaling of IPCC sea surface wind and wind energy predictions for U.S. east coastal ocean,Gulf of Mexico and Caribbean Sea     

YAO Zhigang  XUE Zuo  HE Ruoying  BAO Xianwen  SONG Jun 《中国海洋大学学报(英文版)》2016,15(4):577-582

A multivariate statistical downscaling method is developed to produce regional, high-resolution, coastal surface wind fields based on the IPCC global model predictions for the U.S. east coastal ocean, the Gulf of Mexico(GOM), and the Caribbean Sea. The statistical relationship is built upon linear regressions between the empirical orthogonal function(EOF) spaces of a cross- calibrated, multi-platform, multi-instrument ocean surface wind velocity dataset(predictand) and the global NCEP wind reanalysis(predictor) over a 10 year period from 2000 to 2009. The statistical relationship is validated before applications and its effectiveness is confirmed by the good agreement between downscaled wind fields based on the NCEP reanalysis and in-situ surface wind measured at 16 National Data Buoy Center(NDBC) buoys in the U.S. east coastal ocean and the GOM during 1992–1999. The predictand-predictor relationship is applied to IPCC GFDL model output(2.0?×2.5?) of downscaled coastal wind at 0.25?×0.25? resolution. The temporal and spatial variability of future predicted wind speeds and wind energy potential over the study region are further quantified. It is shown that wind speed and power would significantly be reduced in the high CO_2 climate scenario offshore of the mid-Atlantic and northeast U.S., with the speed falling to one quarter of its original value.  相似文献   

Advances in studies of cloud overlap and its radiative transfer in climate models     

张华  荆现文 《Acta Meteorologica Sinica》2016,30(2):156-168

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