58 research outputs found
XAFS spectroscopy. I. Extracting the fine structure from the absorption spectra
Three independent techniques are used to separate fine structure from the
absorption spectra, the background function in which is approximated by (i)
smoothing spline. We propose a new reliable criterion for determination of
smoothing parameter and the method for raising of stability with respect to
k_min variation; (ii) interpolation spline with the varied knots; (iii) the
line obtained from bayesian smoothing. This methods considers various prior
information and includes a natural way to determine the errors of XAFS
extraction. Particular attention has been given to the estimation of
uncertainties in XAFS data. Experimental noise is shown to be essentially
smaller than the errors of the background approximation, and it is the latter
that determines the variances of structural parameters in subsequent fitting.Comment: 16 pages, 7 figures, for freeware XAFS analysis program, see
http://www.crosswinds.net/~klmn/viper.htm
Deconvolution problems in x-ray absorption fine structure
A Bayesian method application to the deconvolution of EXAFS spectra is
considered. It is shown that for purposes of EXAFS spectroscopy, from the
infinitely large number of Bayesian solutions it is possible to determine an
optimal range of solutions, any one from which is appropriate. Since this
removes the requirement for the uniqueness of solution, it becomes possible to
exclude the instrumental broadening and the lifetime broadening from EXAFS
spectra. In addition, we propose several approaches to the determination of
optimal Bayesian regularization parameter. The Bayesian deconvolution is
compared with the deconvolution which uses the Fourier transform and optimal
Wiener filtering. It is shown that XPS spectra could be in principle used for
extraction of a one-electron absorptance. The amplitude correction factors
obtained after deconvolution are considered and discussed.Comment: 6 two-column pages, 5 eps figures; submitted to J. Phys.: Appl. Phy
Correlation of the local and the macroscopic properties of high-temperature superconductors
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