Modelling streamwater chemistry as a mixture of soilwater end-members — An application to the Panola Mountain catchment, Georgia, U.S.A.

1990 ◽  
Vol 116 (1-4) ◽  
pp. 321-343 ◽  
Author(s):  
Richard P. Hooper ◽  
Nils Christophersen ◽  
Norman E. Peters
Keyword(s):  
Streamwater Chemistry ◽  
Mountain Catchment ◽  
End Members

scholarly journals Technical Note: A data-driven method for estimating the composition of end-members from streamwater chemistry observations

2020 ◽  
Author(s):  
Esther Xu Fei ◽  
Ciaran Joseph Harman
Keyword(s):  
Convex Hull ◽  
Technical Note ◽  
Data Driven ◽  
Second Step ◽  
Hydrograph Separation ◽  
Streamwater Chemistry ◽  
Repeated Applications ◽  
End Members ◽  
Time Invariant ◽  
Non Negative Matrix Factorization

Abstract. End-Member Mixing Analysis (EMMA) is a method of interpreting streamwater chemistry variations, and is widely used for chemical hydrograph separation. It is based on the assumption that the streamwater is a mixture of varying contributions from relatively time-invariant source solutions (end-members). These end-members are typically identified by collecting additional measurements of candidate end-members from within the watershed, and comparing these to the observations. This technical note introduces a complementary, data-driven method: Convex-Hull End-Member Mixing Analysis (CHEMMA), to infer the end-member compositions and their associated uncertainties from the streamwater observations alone. The method involves two steps. The first step uses Convex-Hull Non-negative Matrix Factorization (CH-NMF) to infer possible end-member compositions by searching for a simplex that optimally encloses the streamwater observations. The second step uses Constrained K-means Clustering (COP-KMEANS) to classify the results from repeated applications of CH-NMF to analyze the uncertainty associated with the algorithm. In an example application using the 1986 to 1988 Panola Mountain Research Watershed dataset, CHEMMA is able to robustly reproduce the three field-measured end-members found in previous research using only the streawater chemical observations. It also suggests the existence of a fourth end-member. Further work is needed to explore the constraints and capabilities of this approach.

Modelling streamwater chemistry as a mixture of soilwater end-members — A step towards second-generation acidification models

1990 ◽  
Vol 116 (1-4) ◽  
pp. 307-320 ◽  
Author(s):  
Nils Christophersen ◽  
Colin Neal ◽  
Richard P. Hooper ◽  
Rolf D. Vogt ◽  
Sjur Andersen
Keyword(s):  
Second Generation ◽  
Streamwater Chemistry ◽  
End Members

Incommensurate modulated phases of the NbxTa1-xTe4 charge density wave system

1992 ◽  
Vol 50 (1) ◽  
pp. 58-59
Author(s):  
S. Ritchie ◽  
J. C. Bennett ◽  
A. Prodan ◽  
F.W. Boswell ◽  
J.M. Corbett
Keyword(s):  
Charge Density ◽  
Charge Density Wave ◽  
Direct Evidence ◽  
Density Wave ◽  
Wave System ◽  
Modulated Phases ◽  
Metal Atoms ◽  
Incommensurate Modulation ◽  
End Members ◽  
Modulation Wave Vector

A continuous sequence of compounds having composition NbxTa1-xTe4; 0 ≤ x ≤ 1 have been studied by electron diffraction and microscopy. Previous studies have shown that the end members of the series, TaTε4 and NbTε4 possess a quasi-one-dimensional character and exhibit charge density wave (CDW) distortions. In these compounds, the subcell structure is tetragonal with axes (a × a × c) and consists of the metal atoms (Nb or Ta) centered within an extended antiprismatic cage of Te atoms. At room temperature, TaTε4 has a commensurate modulation structure with a 2a × 2a × 3c unit cell. In NbTε4, an incommensurate modulation with × ∼ 16c axes is observed. Preliminary studies of the mixed compounds NbxTα1-xTε4 showed a discontinuous jump of the modulation wave vector commensurate to incommensurate when the Nb dopant concentration x, exceeded x ≃ 0.3, In this paper, the nature of the compositional dependence of is studied in greater detail and evidence is presented for a stepwise variation of . This constitutes the first direct evidence for a Devil's staircase in CDW materials.

Permafrost evolution in a mountain catchment near Santiago de Chile

2021 ◽  
Vol 109 ◽  
pp. 103293
Author(s):  
S. Ruiz Pereira ◽  
C. Marquardt ◽  
E. Beriain ◽  
F. Lambert
Keyword(s):  
Santiago De Chile ◽  
Mountain Catchment

scholarly journals Life among the Craters

2004 ◽  
Vol 213 ◽  
pp. 199-202
Author(s):  
Harrison H. Schmitt
Keyword(s):  
Terrestrial Planets ◽  
The Moon ◽  
Detailed Understanding ◽  
The Earth ◽  
Planetary Mass ◽  
End Members

The Moon forms one end-member in the planetary mass series Earth-Venus-Mars-Mercury-Asteroids-Moon (Weissman 1999). Having a detailed understanding of the nature and evolution of the two end-members of this series, rather than of just the Earth, has increased the value of other data and inferences by orders of magnitude. As a consequence of obtaining an understanding of the evolution of a second planet, we now can look at other terrestrial planets with far greater insight than ever would have been possible otherwise (Fig. 1).

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