Support for Rachel Mak

Statement of Work Project: Support for Rachel Mak PI: Chris Jacobsen, Physics & Astronomy For the period, 10/12/12 - 10/14/13, Rachel Mak will be working on two aspects of multivariate statistical analysis methods. These projects are described in outline, since the details will naturally evolve as they are tested. 1. In Extended X-ray Absorption Fine Structure (EXAFS) studies, the kinetic energy of ionized electrons leads to a de Broglie wavelength and self-interference modulation of the absorption coefficient as a function of incident photon energy. This means that when working with a mixture of oxidation states of one element type, it is incorrect to use standard EXAFS analysis of bonding distances. Surprisingly, we have not found any recognition of this problem in the literature. We believe the answer is to use multivariate statistical analysis to first separate the x-ray absorption spectra from the separate oxidation states, and to then subsequently apply EXAFS analysis to the separate absorption spectra. Ms. Mak has data on mixed Arsentic speciation, and is presently adapting analysis methods used for soft x-ray spectromicroscopy to tackle this problem of interest to the study of “real,” heterogeneous materials using hard X rays. 2. In x-ray fluorescence analysis, Dr. Stefan Vogt has developed a program called MAPS that has proven to be very useful for displaying the quantitative distribution of trace elements which can play important roles in biological and environmental science systems. What is problematic in his present analysis approach is the reliance on principal component analysis for pre-processing of the data, with quantitation errors resulting from the lack of a guarantee of positivity in the resulting fluorescence spectra (negative spectra are unphysical in this context). Ms. Mak is working to apply new methods for non-negative matrix factorization to fluorescence spectra, with the potential for increasing the accuracy of quantitation in trace-element studies.