Soil measurements during HAPEX-Sahel intensive observation period

This article describes measurements made at each site and for each vegetation cover as part of the soils program for the HAPEX-Sahel regional scale experiment. The measurements were based on an initial sampling scheme and included profile soil water content, surface soil water content, soil water potential, infiltration rates, additional measurements on core samples, and grain size analysis. The measurements were used to categorize the state of the surface and profile soil water regimes during the experiment and to derive functional relationships for the soil water characteristic curve, unsaturated hydraulic conductivity function, and infiltration function. Sample results for different supersites and different vegetation covers are presented showing soil water profiles and total soil water storage on days corresponding to the experimental ‘Golden Days’. Sample results are also presented for spatial and temporal distribution of surface moisture content and infiltration tests. The results demonstrate that the major experimental objective of monitoring the supersites during the most rapid vegetative growth stage with the largest change of the surface energy balance following the rainy season was very nearly achieved. Separation of the effects of probable root activity and drainage of the soil profile is possible. The potential for localized advection between the bare soil and vegetation strips of the tiger bush sites is demonstrate

Evaluation of the Ross fast solution of Richards' equation in unfavourable conditions for standard finite element methods

Ross [Ross PJ. Modeling soil water and solute transport - fast, simplified numerical solutions. Agron J 2003;95:1352-61] developed a fast, simplified method for solving Richards' equation. This non-iterative 1D approach, using Brooks and Corey [Brooks RH, Corey AT. Hydraulic properties of porous media. Hydrol. papers, Colorado St. Univ., Fort Collins: 19641 hydraulic functions, allows a significant reduction in computing time while maintaining the accuracy of the results. The first aim of this work is to confirm these results in a more extensive set of problems, including those that would lead to serious numerical difficulties for the standard numerical method. The second aim is to validate a generalisation of the Ross method to other mathematical representations of hydraulic functions. The Ross method is compared with the standard finite element model, Hydrus-1D [Simunek J, Sejna M, Van Genuchten MTh. The HYDRUS-1D and HYDRUS-2D codes for estimating unsaturated soil hydraulic and solutes transport parameters. Agron Abstr 357; 1999]. Computing time, accuracy of results and robustness of numerical schemes are monitored in I D simulations involving different types of homogeneous soils, grids and hydrological conditions. The Ross method associated with modified Van Genuchten hydraulic functions [Vogel T, Cislerova M. On the reliability of unsaturated hydraulic conductivity calculated from the moisture retention curve. Transport Porous Media 1988:3:1-15] proves in every tested scenario to be more robust numerically, and the compromise of computing time/accuracy is seen to be particularly improved on coarse grids. Ross method run from 1.25 to 14 times faster than Hydrus-1D

Evaluation of Diffraction Data from Electron Diffraction Patterns of Natural Polymers Microcrystals

Methods of evaluating electron diffraction data from films is discussed. Noise reduction is accomplished by heuristic averaging of symmetry related data and 3-point averaging. Global background is removed by radial polynomial fit to intermaxima data or by bivariate splinning. Integration is performed by self-convolution of data subarrays or main array quadrant. A user friendly, menu driven program set is described. The program should be usable in a computer controlled electron microscope with 2-D position sensitive detector

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EVALUATION OF DIFFRACTION DATA FROM ELECTRON DIFFRACTION PATTERNS OF NATURAL POLYMER MICROCRYSTALS

Une méthode de traitement de données de diffraction électronique sur film est présentée. La réduction du bruit est obtenue par calcul de la moyenne des valeurs des données correspondant à des points équivalents par symétrie sur la figure de diffraction et par calcul d'une moyenne locale sur 3 points voisins. La soustraction globale du bruit de fond est effectuée après évaluation de celui-ci sous forme de développement polynomial dans le cas d'une approximation de moyenne radiale, sinon sous forme de développement en fonctions splines à 2 dimensions ; cette évaluation utilise les données situées entre les pics. L'intégration des pics est faite par une méthode d'autoconvolution appliquée soit aux valeurs d'intensité de chaque pic pris isolément soit à l'ensemble des données. Le programme a été conçu pour être d'utilisation facile et fonctionne à l'aide d'un menu. Il devrait être utilisable avec un microscope électronique équipé d'un ordinateur et d'un détecteur à localisation spatiale à 2 dimensions.Methods of evaluating electron diffraction data from films is discussed. Noise reduction is accomplished by heuristic averaging of symmetry related data and 3-point averaging. Global background is removed by radial polynomial fit to intermaxima data or by bivariate splinning. Integration is performed by self-convolution of data subarrays or main array quadrant. A user friendly, menu driven program set is described. The program should be usable in a computer controlled electron microscope with 2-D position sensitive detector

High-angle electron diffraction of frozen hydrated collagen.

By using the techniques developed by Taylor et al. [(1975) J. Mol. Biol. 92, 165-167] (freezing of the hydrated specimen before its insertion into the electron microscope and keeping it frozen throughout the diffraction experiment), it was possible to obtain a high-angle electron-diffraction pattern from collagen fibrils. This pattern is in good agreement with that obtained by high-angle X-ray diffraction. Electron diffraction will be very useful to study collagen, because the diffraction pattern from a carefully selected area of one fibril is now feasible