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Persistent URL http://purl.org/net/epubs/work/24224303
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Record Id 24224303
Title Implementation of a Bayesian algorithm into Mantid for the analysis of neutron scattering data to reveal molecular movements
Abstract Data fitting and model selection lie at the very heart of the scientific method, however, these tasks are often tackled via the use of popular (and typically unquestioned) optimization algorithms of limited validity or flexibility. To circumvent these limitations, this work introduces an adaptive Markov chain Monte Carlo method for, through Bayesian Inference, performing fitting of experimental data. This method allows to obtain chi-squared probability density functions without assuming any frequentist supposition, and taking into account correlation between fitting parameters by direct exploration of the parameter space. This work mainly consists in the creation of a powerful fitting tool based on the aforementioned robust inference method. In fact, it is presented the implementation of the algorithm FABADA (Fitting Algorithm for Bayesian Analysis of Data) within the Mantid framework. The power of this algorithm is illustrated by revisiting an overarching and recurring question in the interpretation of quasielastic neutron scattering measurements, that is, how many spectral components may (or may not) be justified by the available experimental data. Finally, an accurate Bayesian analysis is performed over real quasielastic neutron scattering measurements, in order to study the molecular reorientation dynamics of Cladamantane in its plastic phase. A calorimetric study [1] over this compound shows an anomalous heat-capacity behavior around T = 310 K, which is inside the temperature range of the plastically crystalline phase. So, this work has the aim of prove if the molecular dynamics can be related with this phenomenon. The analysis performed shows how, since the consideration of Cl-adamantane such as an oblong shaped molecule, there is variation on the degree of anisotropy of the rotational diffusion approximately at the temperature of interest.
Organisation ISIS , ISIS-IRIS , STFC
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Language English (EN)
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Thesis BSc, Universitat Politècnica de Catalunya, 2016. https://upcommons…quence=1&isAllowed=y 2016