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Transform Approach (transform + approach)
Selected AbstractsQuantitative trace element imaging using PIXE and the nuclear microprobeINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 4 2000C. G. Ryan Abstract The X-ray spectra of pure elements, excited using MeV energy beam of protons from the nuclear microprobe, have known spectra signatures. This makes X-ray spectra for more complex mixtures amenable to decomposition into contributions from the component elements. By devising this procedure as a matrix operation that transforms directly from spectrum vector to elemental concentration vector, the decomposition can be performed very efficiently enabling the real-time projection of the component element signals. In the case of a raster-scanned beam, with data that contain position information for each X-ray event, this approach enables the real-time projection of component element spatial distribution images. This paper describes the matrix transform approach called dynamic analysis (DA), which enables on-line real-time imaging of major and trace elements using proton-induced X-ray emission (PIXE). The method also provides off-line iterative yield corrections to these images to compensate for changing sample composition across an image area. The resulting images are quantitative in two respects: (1) they resolve the pure element components and strongly reject interferences from other elements and (2) they can be directly interrogated for sample composition at each pixel, over areas, or along lines across the image area, with accuracy comparable to microanalytical point analysis methods. The paper describes the DA method, presents tests, and discusses its application to quantitative major and trace element imaging in geology. © 2001 John Wiley & Sons, Inc. Int J Imaging Syst Technol 11, 219,230, 2000 [source] Method of separated form factors for polydisperse vesiclesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2006Jeremy Pencer Use of the Schulz or Gamma distribution in the description of particle sizes facilitates calculation of analytic polydisperse form factors using Laplace transforms, [f(u)]. Here, the Laplace transform approach is combined with the separated form factor (SFF) approximation [Kiselev et al. (2002). Appl. Phys. A, 74, S1654,S1656] to obtain expressions for form factors, P(q), for polydisperse spherical vesicles with various forms of membrane scattering length density (SLD) profile. The SFF approximation is tested against exact form factors that have been numerically integrated over the size distribution, and is shown to represent the vesicle form factor accurately for typical vesicle sizes and membrane thicknesses. Finally, various model SLD profiles are used with the SFF approximation to fit experimental small-angle neutron scattering (SANS) curves from extruded unilamellar vesicles. [source] Measurement of aroma compound self-diffusion in food models by DOSYMAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2004Thierry Gostan Abstract Self-diffusion measurement of solutes in polymer gels has been investigated using pulsed gradient spin echo NMR spectroscopy. However, few data are available on the self-diffusion of small solutes in natural polysaccharide polymers used as thickeners in the food industry. Since aroma diffusion in food matrices could have an impact on flavor release, this is an interesting and economic challenge. Diffusion ordered spectroscopy (DOSY) resolves diffusion data for each component in complex mixtures. We used DOSY with the inverse Laplace transform approach with the maximum entropy algorithm to investigate diffusion of two aroma compounds, ethyl butanoate and linalool, in an ,-carrageenan matrix as the food model. We showed that the self-diffusion coefficient values of small molecules in a polysaccharide matrix could be easily extracted using this method. We then investigated the impact of the gelling state of ,-carrageenan matrices on the self-diffusion of ethyl butanoate. Copyright © 2004 John Wiley & Sons, Ltd. [source] Dispersive properties of photonic crystal waveguide resonatorsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2007T. Sünner Abstract We have investigated the group delay and the dispersion of light propagating through photonic crystal (PhC) resonators defined in 240 nm thick GaAs membranes. The design of the resonators is based on a PhC heterostructure, which combines waveguide sections with different lattice constants along a PhC waveguide. The measurements were performed by detecting the phase shift of a microwave signal which was modulated onto the light of a tunable laser source. The group delay was found to increase linearly with the quality factor of the resonator, in good agreement with the prediction of a model where the PhC resonator is replaced by an equivalent Fabry,Perot resonator. An alternative analysis of the measurements was performed using a Hilbert transform approach. A maximum group delay of 132 ps was observed for a resonator with a quality factor of 82000. The overall length of this resonator was 10.4 ,m, resulting in a propagation speed of 7.88 × 104 m/s (c/3800). The maximum dispersion of the resonator was around 1.7 ns/nm, which is equivalent to 100 km of standard optical fiber. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||