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Biomedical subjects

B Ravel

Publications and source records attributed to B Ravel.

7 recordsLinked to original sources
PubMed2005

ATHENA, ARTEMIS, HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT.

A software package for the analysis of X-ray absorption spectroscopy (XAS) data is presented. This package is based on the IFEFFIT library of numerical and XAS algorithms and is written in the Perl programming language using the Perl/Tk graphics toolkit. The programs described here are: (i) ATHENA, a program for XAS data processing, (ii) ARTEMIS, a program for EXAFS data analysis using theoretical standards from FEFF and (iii) HEPHAESTUS, a collection of beamline utilities based on tables of atomic absorption data. These programs enable high-quality data analysis that is accessible to novices while still powerful enough to meet the demands of an expert practitioner. The programs run on all major computer platforms and are freely available under the terms of a free software license.

Algorithms↗
PubMed2003

Diffraction anomalous fine-structure spectroscopy at beamline BM2 at the European Synchrotron Radiation Facility.

Diffraction anomalous fine-structure (DAFS) spectroscopy uses resonant elastic X-rays scattering as an atomic, shell and site-selective probe that provides information on the electronic structure and the local atomic environment as well as on the long-range-ordered crystallographic structure. A DAFS experiment consists of measuring the Bragg peak intensities as a function of the energy of the incoming X-ray beam. The French CRG (Collaborative Research Group) beamline BM2-D2AM (Diffraction Diffusion Anomale Multi-longueurs d'Onde) at the ESRF (European Synchrotron Radiation Facility) has developed a state-of-the-art energy scan diffraction set-up. In this article the requirements for obtaining reliable DAFS data are presented and recent technical achievements are reported.

Algorithms↗
PubMed2001

ATOMS: crystallography for the X-ray absorption spectroscopist.

ATOMS is a user application providing crystallographic functionality useful to x-ray absorption spectroscopists. ATOMS is also a set of reusable, object-oriented software modules written in the Perl programming language providing crystallographic functionality and access to databases of absorption coefficients and anomalous scattering factors. The main use of the ATOMS program is to generate input data for the ab initio, multiple scattering, x-ray absorption spectroscopy code FEFF. However the code offers many additional features, including useful calculations involving absorption coefficients and simulations of Diffraction Anomalous Fine-Structure (DAFS) spectra. Command line, graphical, and web-based interfaces to the code are offered as part of the standard distribution. As Perl runs on a wide variety of common computer platforms, ATOMS itself is a cross platform application. All text presented to the user can be internationalized - support for four languages is currently included in the package. Development of ATOMS is active - a FEFF interface, structure visualization, and additional crystallographic calculations are among the future developments.

Journal Article↗
PubMed2001

Valence selective DAFS measurements of Mn in La1/3Ca2/3MnO3.

The manganese perovskite system La(1-x)Ca(x)MnO3 displays a complex phase diagram of structural, magnetic, and transport properties with varying Ca concentration. At x = 2/3 and at low temperature, the system is antiferromagnetic with Mn4+ and Mn3+ ions occupying special positions in a charge-ordered supperlattice. The charge ordering transition at about 260 K is characterized by the appearance of satellite peaks around certain strong normal lattice reflections. The normal lattice reflections are due to scattering from planes containing Mn4+ and Mn3+ ions in nearly stoichiometric proportion, however the superlattice reflections are due to scattering from planes containing only Mn4+ ions. By measuring Diffraction Anomalous Fine-Structure spectral on a superlattice reflection and its associated normal lattice reflection, it is possible to isolate absorption-like spectra for the two Mn sites. Due to the weak intensity of these superlattice reflections, we were unable to obtain high quality near-edge spectra for the superlattice reflection measured. However, the data offer useful information about the local electronic structures of the two Mn ions.

Journal Article↗