2维矢量地图空间目标关系的组合式表达   总被引：9，自引：2，他引：7  

郭庆胜 《测绘学报》2000,29(2):155-161

矢量模式的地图平面空间目标是地图数据处理中常见的,其空间关系的描述与处理非常重要本文首先分析了平面地图上的尺度空间和拓扑空间的统一,以及点和直线段两两相互间的基本空间关系,并以这些基本窨绵组合为基础,试图利用组合式方法区分和描述地图空间点状、线状和面状空间目标两两相互间的空间关系,且得到各类空间关系的种数。  相似文献   

山西天龙山植被及植物资源   总被引：7，自引：0，他引：7  

程占红  张金屯  陈廷贵 《山地学报》2000,18(3):226-230

采用TWINSPAN对天龙山主要植被进行了分类 ,并用DCA方法分析了植物群落间的生态关系 ,描述了九个主要植物群落类型的特征 ,最后介绍了蕴藏于植被中的天然植物资源的类型及其经济用途 ,提出了植物资源开发利用的对策。  相似文献   

基于信息论方法分析我国典型地震动衰减关系          下载免费PDF全文

胡进军  孙健 《世界地震工程》2018,34(2):065-70

近年来我国强震数据逐渐增多,为了比较和分析我国的几个典型地震动衰减关系,采用一种信息论方法,基于实际地震动记录,计算选取的地震动衰减关系模型的对数似然函数值,通过对数似然函数值对模型进行排序,并给出相应的权重及排名,分析了不同衰减关系对地震动的预测能力。研究表明:针对于我国西部强震数据,基于强震动记录建立的衰减关系的预测结果更接近于实测地震动数据。研究结果可为地震动记录信息不完善或缺乏强震数据地区的地震动衰减关系选取提供参考。  相似文献   

沉水植物苦草根系功能性状对基质类型和种植密度的响应及其与个体表现关系     

陈俊格  陈矿  王和云  易春龙  高健  文冬华  张润龙 《湖泊科学》2024,36(1):247-260

根系功能性状体现了植物细根的生长状况及其对外部环境的适应性,然而根系功能性状响应环境变化的时间稳定性如何仍不清楚。苦草(Vallisneria natans)是水体沉水植被修复的先锋种类,细根在其种群重建初期起着重要作用。该研究设计了草垫、草垫+沙子、草垫+黄泥及草垫+底泥4种生长基质和100株/m²以及200株/m²两种种植密度并将其两两组合,以模拟自然生境不同的基质和密度情况,并在不同时期对苦草功能性状指标进行取样测定,通过重复测量二元方差分析研究基质和密度对根系功能指标的影响,并通过线性拟合模型探讨个体水平的生长表现(生物量分配、营养吸收、个体定植)与具体的根系功能性状之间的关系对环境变化的响应。结果表明:所有测量指标均受到基质条件的显著影响,部分根系功能性状指标如根冠比(RSR)、根干重、比根长(SRL)、根比表面积(SRA)、根组织密度(RTD)、根系锚定力和根体积受密度的影响显著。苦草生物量的分配主要受基质条件的影响,对营养的吸收、运输及根系固着能力受基质和密度的共同影响。线性拟合模型表明SRA、RTD、根直径、根表面积以及根体积在个体水平上能一定程度地预测RSR对环境变化的响应,且RTD的预测效果最好;根冠比、SRA、生根数、总根长、根表面积以及根体积在个体水平上能一定程度地预测SRL对环境变化的响应,其中生根数的预测效果最好;SRA、根直径、根表面积以及根体积在个体水平上能一定程度地预测根系锚定力对环境变化的响应,并且SRA的预测效果最好。但是基质和密度在不同时期对苦草根系功能性状的影响方向会发生改变,当用根系功能性状预测植物个体表现时,需要考虑种群重建所处的时期。  相似文献   

THE EFFECTIVE STRESS PRINCIPLE: INCREMENTAL OR FINITE FORM?     

BERNHARD A. SCHREFLER  DARIUSZ GAWIN 《国际地质力学数值与分析法杂志》1996,20(11):785-814

Different expressions of the effective stress principle can be found in the literature, in particular some are written in finite form and others in incremental form. For the purpose of the paper we take for granted that stress–strain relationships exist or can be obtained for the effective stress coming from both formulations. We investigate the consequences of the choice of particular finite or differential forms when they are introduced in a weak form of the linear momentum balance equation of two- of three-phase porous media for its numerical solution. For partially saturated geomaterials the importance of the capillary pressure–saturation relationship is pointed out.  相似文献   

CHOICE OF SAMPLING STRATEGY AND ESTIMATION METHOD FOR CALCULATING NITROGEN AND PHOSPHORUS TRANSPORT IN SMALL LOWLAND STREAMS     

B. KRONVANG  A. J. BRUHN 《水文研究》1996,10(11):1483-1501

As reliable estimates of stream nutrient transport are required for many purposes including trend analysis, mass balances and model development, the impact of sampling strategy and estimation method on the bias and precision of stream nitrogen (N) and phosphorus (P) transport calculations was evaluated. The study was undertaken in two catchments in eastern Denmark. Selection of the most accurate sampling strategy and estimation method, i.e. with the lowest root mean square error (RMSE) was based on random (Monte Carlo) runs for generating replicate data sets from an essentially complete record of the concentration of total N (TN), total P (TP), particulate P (PP) and dissolved P (DP) during a two-year period (June 1987 to June 1989). The evaluation comprised 13 different estimation methods and seven discrete sampling strategies involving three categories (regular, stratified and strata sampling). The regular sampling strategies were more accurate (lower RMSE) during high-flow periods than stratified sampling. The greatest improvement in RMSE for TN, TP, PP and DP transport was obtained when increasing the sampling frequency from 12 each year (monthly) to 18 (monthly in summer and fortnightly in winter) and 26 each year (fortnightly). The increase in accuracy (RMSE) was less when increasing the sampling frequency to 52 (weekly) or 104 (biweekly). Nearly all the methods evaluated underestimated the annual transport of TP and PP, whereas TN and DP were both under- and overestimated. The best method of estimating N and P transport when utilizing discrete sampling was both site- and time-dependent. The overall best and most reproducible (stream to stream, year to year) method for estimating annual transport of TN, TP, PP and DP was a linear interpolation method. When this method was used to derive estimates of annual TN and TP transport based on fortnightly sampling, the RMSE was 1.4–5.4 and 20.2–38.5%, respectively, in the Gelbæk stream and 1.1–4.9 and 10.5–15.0%, respectively, in the Gjern Å stream. Subdividing the hydrograph into two strata (low-flow and high-flow periods) and sampling these strata separately for calculating TP transport was superior to discrete sampling for the smaller of the two catchments. A combination of regular sampling (monthly) and pooled high-flow sampling (eight events out of a total of 43) reduced the RMSE of the annual TP load to 10.4%.  相似文献