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- Johnson, Lars, et al.
(författare)
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Blind deconvolution of time-of-flight mass spectra from atom probe tomography
- 2013
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 132, s. 60-64
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Tidskriftsartikel (refereegranskat)abstract
- A major source of uncertainty in compositional measurements in atom probe tomography stems from the uncertainties of assigning peaks or parts of peaks in the mass spectrum to their correct identities. In particular, peak overlap is a limiting factor, whereas an ideal mass spectrum would have peaks at their correct positions with zero broadening. Here, we report a method to deconvolute the experimental mass spectrum into such an ideal spectrum and a system function describing the peak broadening introduced by the held evaporation and detection of each ion. By making the assumption of a linear and time-invariant behavior, a system of equations is derived that describes the peak shape and peak intensities. The model is fitted to the observed spectrum by minimizing the squared residuals, regularized by the maximum entropy method. For synthetic data perfectly obeying the assumptions, the method recovered peak intensities to within +/- 0.33 at%. The application of this model to experimental APT data is exemplified with Fe-Cr data. Knowledge of the peak shape opens up several new possibilities, not just for better overall compositional determination, but, e.g., for the estimation of errors of ranging due to peak overlap or peak separation constrained by isotope abundances. (C) 2013 Elsevier By. All rights reserved.
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| 3. |
- Ström, Anna, 1976, et al.
(författare)
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Rheological characterization of acid pectin samples in the absence and presence of monovalent ions
- 2014
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 113, s. 336-343
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Tidskriftsartikel (refereegranskat)abstract
- Pectins are traditionally divided into two groups, high methoxy and low methoxy. The groupings determine the charge of the pectin and the gelation mechanism. However, not as yet extensively studied is the impact on gelation of the distribution of the charges as characterized by an absolute degree of blockiness (DBabs). The aim of this study was to characterize rheologically the acid gelation of a pectin with a high DBabs and a degree of methyl esterification of similar to 37%, in the absence and presence of monovalent ions. The results obtained suggest that a pectin with a blocky charge distribution at pH conditions close to or below the pKa exhibits weak gel-like properties at intermediate frequencies, despite the absence of a permanent network structure. The addition of monovalent ions changed the rheological behavior to resemble that of a strong gel whose properties depended on the type and concentration of the ions.
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