江苏北部开敞淤泥质海岸的侵蚀过程及防护   总被引：9，自引：0，他引：9  

虞志英  张勇 《地理学报》1994,49(2):149-157

开敞淤泥质海岸是淤泥质海岸的主要类型，其自然演变过程，主要受沿海河流泥沙供应条件的制约，一旦泥沙供应消失，海岸往往进入不可逆转的侵蚀过程。江苏北部淤泥质海岸的侵蚀过程，起自１８５５年黄河入海口北归利津入海以后，主要是在近岸破波对岸滩物质的冲刷和潮流的输移扩散作用下进行的。通过对淤泥质海岸动力和沉积物性质的认识和概化，对海岸侵蚀过程作出定量模拟，并对该地区海岸防护工程作出评价和讨论。  相似文献   

Cyclotella-taxa (Bacillariophyceae) in lakes of the Alpine region and their relationship to environmental variables     

Sybille Wunsam  Roland Schmidt  Rolf Klee 《Aquatic Sciences - Research Across Boundaries》1995,57(4):360-386

Surface sediment diatom assemblages for 86 Alpine lakes were analysed focusing on the dominant genusCyclotella and corresponding environmental data. The range of morphological variability of theCyclotella bodanica/radiosa, C. distinguenda, C. ocellata, C. comensis andC. stelligera complexes was documented. Significance tests included in the canonical correspondence analysis (CCA) indicated that total phosphorus, conductivity and surface water temperature were significantly correlated withCyclotella taxa assemblage distribution. Numerical species optima and tolerances were calculated in respect to these significant variables using weighted averaging (WA) regression and calibration. CCA and WA were able to provide information about the environmental preferences of the various morphotypes observed.  相似文献   

Appraisal of regional and index flood quantile estimators     

J. R. Stedinger  L. -H. Lu 《Stochastic Hydrology and Hydraulics》1995,9(1):49-75

Our results illustrate the performance of at-site and regional GEV/PWM flood quantile estimators in regions with different coefficients of variation, degrees of regional heterogeneity, record lengths, and number of sites. Analytic approximations of bias and variance are employed. For realistic GEV distributions and short records, the index-flood quantile estimator performs better than a 2-parameter GEV/PWM quantile estimator with a regional shape parameter, or a 3-parameter at-site GEV/PWM quantile estimator, in both humid and especially in arid regions, as long as the degree of regional heterogeneity is moderate. As regional heterogeneity or record lengths increases, 2-parameter estimators quickly dominate. Flood frequency models that assign probabilities larger than 2% to negative flows are unrealistic; experiments employing such distributions provide questionable results. This appraisal generally demonstrates the value of regionalizing estimators of the shape of a flood distribution, and sometimes the coefficient of variation.  相似文献   

Hybrid Estimation of Semivariogram Parameters   总被引：1，自引：0，他引：1  

Hao Zhang  Dale L. Zimmerman 《Mathematical Geology》2007,39(2):247-260

Two widely used methods of semivariogram estimation are weighted least squares estimation and maximum likelihood estimation. The former have certain computational advantages, whereas the latter are more statistically efficient. We introduce and study a “hybrid” semivariogram estimation procedure that combines weighted least squares estimation of the range parameter with maximum likelihood estimation of the sill (and nugget) assuming known range, in such a way that the sill-to-range ratio in an exponential semivariogram is estimated consistently under an infill asymptotic regime. We show empirically that such a procedure is nearly as efficient computationally, and more efficient statistically for some parameters, than weighted least squares estimation of all of the semivariogram’s parameters. Furthermore, we demonstrate that standard plug-in (or empirical) spatial predictors and prediction error variances, obtained by replacing the unknown semivariogram parameters with estimates in expressions for the ordinary kriging predictor and kriging variance, respectively, perform better when hybrid estimates are plugged in than when weighted least squares estimates are plugged in. In view of these results and the simplicity of computing the hybrid estimates from weighted least squares estimates, we suggest that software that currently estimates the semivariogram by weighted least squares methods be amended to include hybrid estimation as an option.  相似文献   

带权约束参数平差在工程控制网优化中的应用     

鲍峰  程效军 《测绘学报》2002,31(Z1):73-76

介绍用带权约束平差原理编制的工程控制网试验修正法设计和平差程序,并用于设计工程导线和平差变形观测控制网等实际工程的例子,据此提供一些结论和建议.  相似文献   

一种基于GIS的矿产资源潜力评价的自动制图模型     

陈永良  刘大有 《地质论评》2002,48(3):324-329

在基于GIS技术的矿产资源评价工作中,矿产资源潜力评价的自动制图模型通常用来统计综合多源地学信息以便自动圈定成矿远景靶区。在本文中,笔者以人工智能研究领域中的一种不确定推理模型——确定性理论为基础,提出了一种新的矿产资源潜力评价的自动制图模型——合成有矿可信度模型。该模型可以根据研究区各种成矿有利和不利证据的空间分布图,统计生成对应于每一种证据的有矿可信度栅格图,然后,按照特定的有矿可信度合成规则,将所有的有矿可信度栅格图统计综合生成合成有矿可信度栅格图。以该图为依据,可以把研究区内合成有矿可信度相对较高的成矿远景区圈定出来。也可以生成研究区合成有矿可信度等值线图。应用该模型预测了新疆北部多拉纳萨依—阿舍勒地区的多金属成矿远景,并将预测结果与证据加权模型预测结果进行了比较,两种模型的预测结果基本相似,证明了该模型的有效性和实用性。  相似文献   

模糊数学在水化学寻找可地浸铀矿中的应用     

王军 《新疆地质》2002,20(2):167-169

利用水化学找铀，有成本低、效率高、速度快等特点，在寻找可地浸砂岩型铀矿也有明显的效果，但是在找铀过程中仅用水化学成份、氡含量、酸碱度和氧化还原电位等数值进行描述，说明它们与铀矿化的关系，这种单一因素不能综合反映与铀矿化的联系程度，以定量评价铀矿化与上述因素的关系，从而影响了水化学找矿的效果，通过模糊数学方法建立数学模型处理水化学数据，巳知可地浸砂岩型铀矿的特征值为参数进行定量评价未知区铀成矿的前景，使该方法成为今后铀矿预测中一种可靠有效的水文地质方法。  相似文献   

Maximum likelihood environmental calibration and the compute program WACALIB a correction     

H.J.B. Birks 《Journal of Paleolimnology》2001,25(1):111-115

A recently discovered error in the part of the computer program WACALIB that implements maximum likelihood (ML) calibration has been discovered and corrected. The new version of WACALIB has been re-run with all the data-sets from which results based on the earlier version of WACALIB had been published. The new results suggest that ML regression and calibration perform as well or even better than weighted averaging (WA), at least when judged by the apparent root mean squared error. Further work involving cross-validation is required to evaluate more fully the relative performance of WA and ML approaches.  相似文献   

泥浆含砂率对桩基质量的影响     

宋明智  许谷星 《江西地质》2001,15(4):301-304

本文通过对泥浆中颗粒的沉降特性分析，从量上得出泥浆性能对泥浆中颗粒的悬浮携渣能力。泥浆是一流变性的流体，对泥浆性能的把握，应综合考虑，而不偏向于某个指标。提出了在实践中对泥浆的正确使用和泥浆性能取用的建议。  相似文献   

Local spatial interaction modelling based on the geographically weighted regression approach     

Tomoki Nakaya 《GeoJournal》2001,53(4):347-358

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