Helmert方差分量估计结果的方差一致性检验实质   总被引：9，自引：0，他引：9  

刘长建  马高峰 《测绘学院学报》2002,19(2):96-98

Helmert方差分量估计是合理确定不同类观测值或不同种精度观测值权比的常用方法。文中从方差一致性检验的角度分析了Helmert方差分量估计迭代收敛结果的实质，指出了其检验统计量即为X^2(r)分布密度取得最大值的点；并指出当同时还存在其它平差模型误差时，Helmert方差分量估计也可能收敛，且收敛结果的检验实质并没改变，但收敛结果却已失真。  相似文献   

Contribution des réseaux de neurones artificiels (RNA) à la caractérisation des pollutions de sol. Exemples des pollutions en hydrocarbures aromatiques polycycliques (HAP)Artificial Neural Networks (ANNs) characterisation of soil pollution: the Polycyclic Aromatic Hydrocarbons (PAHs) case study     

Adrian Dan  Jasha Oosterbaan  Philippe Jamet 《Comptes Rendus Geoscience》2002,334(13):957-965

We develop the ANNs (Artificial Neural Networks) method to explore contaminant concentration profiles observed in soils of polluted sites. ANNs are particularly efficient in simultaneous analysis of numerous parameters and in identification of complex relations involving field data. Applying the ANN models on a PAH (Polycyclic Aromatic Hydrocarbon) database, we extracted the most characteristic components of known contaminations and applied it to identify the source type of similar polluted sites. The performed tests prove the generalisation capability of the selected ANN model. To cite this article: A. Dan et al., C. R. Geoscience 334 (2002) 957–965.  相似文献   

西北干旱区野生植物及野生药材资源保护中的资源法规分析   总被引：2，自引：0，他引：2  

张蓬涛  李香云 《干旱区地理》2002,25(1):35-39

西北地区野生药材资源和野生植物资源的滥采乱挖不仅引起了资源的迅速衰竭，而且还破坏了当地的草地资源，区域的生态环境也随之渐趋恶化。从产权制度、许可制度、保护制度等资源法律制度入手分析了滥采乱挖屡禁不止的主要原因，并进而提出了加强资源法制建设的多种途径和对策：（1）完善资源产权制度，实现资源产权的具体化、实体化；（2）依法行政，实现资源开发利用和经营的法制化管理；（3）重新审视资源的价值，合理确定资源的保护级别；（4）加强资源法制宣传，提高群众的法律意识。  相似文献   

沙坡头人工固沙区草本层片组成及其动态研究   总被引：1，自引：3，他引：1  

袁建立  张景光  王刚 《中国沙漠》2002,22(6):623-627

通过跟踪观测一年生植物层片在一个生长周期内种类组成及其重要值的变化,并分析变化的生态学机理,得出如下结论:①在固沙区草本层片内,小画眉草的多度、盖度和重要值在群落中所占比例较大,是群落优势种;②在充足的降雨后,一年生植物都突发性萌发,但随着降雨的减少,层片内的一年生植物种群都呈衰退之势,其中小画眉草和虎尾草种群急剧减少,狗尾草、雾冰藜和虫实种群减少幅度不大.在生长后期由于降雨增多且较为均匀,层片内各物种种群数量变化不大,各自完成生活史;③狗尾草、雾冰藜和虫实在整个生长季节种群的数量和频度变化幅度较小,其相对盖度随着时间的推移呈渐次增长之势;④草本层片的变化动态与降雨有较大的相关性.  相似文献   

Biomass estimation for native perennial grasses in the plain of Mendoza, Argentina     

J. C. Guevara  J. M. Gonnet  O. R. Estevez 《Journal of Arid Environments》2002,50(4):613

Plant allometric relationships were studied at the end of the 1999–2000 growing season for eight grasses. Logarithmic regressions were developed relating above-ground biomass to dimensional measurements or to tiller density. Basal diameters (the longest and the greatest perpendicular to the first) and plant height (defined as that reached by vegetative tillers) were recorded on individual plants of tussock grasses. The number of tillers per 1 m² plot was counted for a rhizomatous grass. Our study proved that regression models including basal area or a combination of basal area and height as independent variables gave a good fit to the biomass data for tussock grasses. Density of tillers proved to be a good predictor of biomass for a rhizomatous species. A validation test using 20% of the data not used for estimating the regression equations indicated that these models made accurate prediction of grass biomass. Further work is needed to prove if there are year-to-year differences between models.  相似文献   

多元p－范极大似然平差   总被引：4，自引：1，他引：4  

於宗俦  孙海燕  陈之中 《测绘学报》1996,(4)

本文详细推导了在概括平差函数模型下多元ｐ－范极大似然平差的基础方程以及求解参数估值的计算公式。本文提出的平差方法是一种包含最小二乘法，Ｌ１、Ｌｐ（ｐ＞１）最小平差法的更一般的方法。它只需对观测误差母体作单峰、对称的假设。此方法在给出位置参数、尺度参数的估值的同时，还能对误差母体分布作出估计  相似文献   

历史地震在核工程安全性评价中的应用     

常向东 《地震研究》1996,19(3):315-320

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Chemical characterization of Lower Devonian vascular plants     

Greg Ewbank  Dianne Edwards  Geoffrey D. Abbott 《Organic Geochemistry》1996,25(8):461-473

Vegetative remains of three coalified Lower Devonian vascular plants (Zosterophyllum, Psilophyton, Renalia) were analyzed using flash pyrolysis-gas chromatography-mass spectrometry. The distributions of pyrolysis products are compared with those from younger vascular plant fossil xylem (Cordaixylon, Callixylon) and cuticle (Pachypteris). The likelihood of the chemical preservation of characteristic higher plant macromolecules (e.g., lignin and cutan) in the Lower Devonian plant fossils is considered in light of this comparison and associated thermal maturity assessments. Reflectance values from vitrinite-like macerals, which may not be vitrinite sensu stricto in the Lower Devonian host rocks for the fossils selected for this study, are shown to provide a reasonable assessment of the thermal maturity of these early vascular plant fossils. Although lignin altered through burial maturation is the most likely source of the prominent alkylphenols and aromatic hydrocarbons in the Lower Devonian tracheophyte flash pyrolysates, a contribution from thermally modified tannins cannot be ruled out. Comparison of the highly aliphatic pyrolysates from the Zosterophyllum and Psilophyton axes with that of a thermally mature fossil gymnosperm leaf revealed that cutan was an important component in the Devonian plant remains. This is the earliest chemical evidence for the presence of cutan in vascular plants.  相似文献   

频率域电磁测深资料处理软件包     

汤井田  何继善  鲍光淑 《物探与化探》1994,18(1):46-49

本文利用混合语言编程技术,设计编制了频率域电磁测深资料处理程序包,描述了程序各功能模块的基本功能,给出了利用该软件包对实际数据处理的例子。  相似文献   

大兴安岭北部植被对高胁迫冻土环境及干扰的响应   总被引：9，自引：2，他引：9  

张齐兵 《冰川冻土》1994,16(2):97-103

本文以Ｓｉｍｐｓｏｎ指数，测定了大兴安岭阿木尔林区火灾后植物群落的生态优势度。通过与冻土环境的比较分析得出，植物群落的生态优势度与多年冻土的发育程度之间呈正相关、与物种样性之间呈负相关。并进而提出，多年冻土对该区兴安落叶松林的生长具有直接的高胁迫作用和间接的保护其生物竞争力的双重作用；森林植被则在此高环境压力下采取耐胁迫对策，对干扰也产生双重的响应方式。依此可指导我们在营林实践中有效地利用干扰的正  相似文献