Matemática e Estatística / Mathematics and Statistics
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Percorrer Matemática e Estatística / Mathematics and Statistics por Domínios Científicos e Tecnológicos (FOS) "Ciências Naturais"
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- Hydrogenolysis of Xylitol to value added products: a mathematical approachPublication . Ndlovu, Thandokuhle Quinton; Costa, Fernando Pestana da; Magagula, Vusi; Shozi, MzamoIn this paper we mathematically investigate the kinetics underlying the hydrogenolysis of xylitol over a metal based catalyst by using ordinary differential equations. The primary motivation for mathematically investigating this reaction lies on the fact that some of the value added products from this reaction are sourced from fossil fuels, which are not environmentally friendly. They have been reported by different researchers that they are the primary drive of global warming which leads to climate change, which causes severe disturbances in the Earth´s natural systems and economies. Xylitol, on the other hand, which is readily available from biomass have been reported as an alternative raw material for some of the value added products. A reaction mechanism proposed from experimental data is used to formulate a system of ordinary differential equations which is then analyzed using some qualitative analysis tools from mathematics. Numerical simulations are performed to try and ascertain the long time behavior of the system's solutions. Results showed that the solutions to the system approaches a lower dimensional invariant set with X_k=0 for k=1,...,8 and X_k>0 for k=9, 10, 11. These numerical results were found to be in agreement with the experimental results from the chemistry point of view. Therefore, it is believed that this model can be extended for use in other sugar alcohols higher than xylitol, like sorbitol as means to maximize the yields of the desired products.
- Spatial and multivariate statistics in assessing water quality in the North SeaPublication . Ody, Christopher; Ramos, Maria do Rosário; Carolino, Elisabete Teresa Mata Almeida; Gervasi , O.; Murgante , B.; Garau , C.; Taniar, D.; Rocha , A. M. A. C.; Lago , M. N. FaginasThe Southern North Sea region plays a vital role for both the economy and society of the surrounding countries. Analyzing the quality of your water is a critical process that involves an assessment of physical, chemical, and biological parameters, essential to guarantee environmental sustainability and the health of local communities and marine ecosystems. Using Multivariate and Spatial Statistics methods, this study seeks to identify spatial patterns and autocorrelations to assess water quality in that region. The data set used was taken on a scientific cruise carried out in December 2020 aboard the RV Meteor vessel, led by a team of German researchers. The raw data went through pretreatment guided by the Data Quality Control protocol of SeaDataNet, an international oceanography project aimed at making European maritime data available. Spike and gradient tests were performed, in addition to data standardization and imputation through inverse distance weighting interpolation. For a better understanding of the scientific area, the data were aggregated by zones for certain analyses, and were sometimes considered globally. An exploratory spatial data analysis (ESDA) was carried out in order to summarize its main characteristics. A reduction in the dimensionality of the original data was carried out through principal component analysis as an auxiliary tool for spatial analysis. The Spatial autocorrelation is analyzed by calculating global and local Moran’s I Statistics. The outcomes indicate a significant spatial autocorrelation for all variables considered in the freshwater areas and a notable range flattening of the variables in the open sea areas, which possibly caused the lack of significant spatial autocorrelation in those areas.