排序方式： 共有24条查询结果，搜索用时 15 毫秒
21.
22.
Clemens Reimann Arnold Arnoldussen Peter Englmaier Peter Filzmoser Tor Erik Finne Robert G. Garrett Friedrich Koller Øystein Nordgulen 《Applied Geochemistry》2007
Rock samples and the C-, B- and O-horizons of soils developed on these rocks were collected in forested areas along a 120-km south–north transect in southern Norway, passing through the city of Oslo. Forty samples (1 site/3 km) were analysed for 37 chemical elements (Ag, Al, As, Au, B, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, Hg, K, La, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Sc, Se, Sr, Te, Th, Ti, Tl, U, V, W and Zn) following an aqua regia digestion; pH (water extract) and loss on ignition were also determined. The O-horizon soils were additionally analysed for Pt. Gold is the only element that shows a clear anthropogenic peak in the O-horizon soils collected from the city of Oslo. Silver, Au, Bi, Cd, Hg, Pb, S, Sb, Se and Sr all show a strong enrichment in the O-horizon when compared to the underlying C-horizon or the bedrock along the full length of the transect. Neither geology nor anthropogenic input of elements dominate the observed patterns. The most important factors for the observed element concentrations in the O-horizon are weathering, uptake (or rejection) of elements by plants and the kinetics of decay of the organic material in the O-horizon. Climate, especially temperature and precipitation, has an important influence on the formation and decay rates of the organic soil layer. Acid precipitation will delay the decomposition of the organic layer and lead to a natural enrichment of several metals in the O-horizon. Land use change, deforestation and liming can all increase the decay kinetics of organic matter and thus result in a release of the stored element pool. 相似文献
23.
Outlier Detection for Compositional Data Using Robust Methods 总被引：6，自引：2，他引：4
Outlier detection based on the Mahalanobis distance (MD) requires an appropriate transformation in case of compositional data.
For the family of logratio transformations (additive, centered and isometric logratio transformation) it is shown that the
MDs based on classical estimates are invariant to these transformations, and that the MDs based on affine equivariant estimators
of location and covariance are the same for additive and isometric logratio transformation. Moreover, for 3-dimensional compositions
the data structure can be visualized by contour lines. In higher dimension the MDs of closed and opened data give an impression
of the multivariate data behavior. 相似文献
24.
Karel Hron Peter Filzmoser Patrice de Caritat Eva Fišerová Alžběta Gardlo 《Mathematical Geosciences》2017,49(6):797-814
The log ratio methodology converts compositional data, such as concentrations of chemical elements in a rock, from their original Aitchison geometry to interpretable real orthonormal coordinates, thereby allowing meaningful statistical processing and visualization. However, it must be taken into account that the original concentrations can be flawed by detection limit or imprecision problems that can severely affect the resulting coordinates. This paper aims to construct such orthonormal log ratio coordinates, called weighted pivot coordinates, that capture the relevant relative information about an original component and treat the redundant information in a controlled manner. Theoretical developments are supported by a thorough simulation study. Weighted pivot coordinates are then applied to the geochemical mapping of catchment outlet sediments from the National Geochemical Survey of Australia illustrating their advantage over possible alternatives. 相似文献