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Sousa J.A.,Laboratorio Regional Of Engineering Civil | Reynolds A.M.,Investimentos e Gestao da Agua S.A. | Ribeiro A.S.,National Laboratory for Civil Engineering
Accreditation and Quality Assurance | Year: 2012

The evaluation of measurement uncertainties has been widely applied to the calibration of measurement instruments, whereas its application to tests, despite increasing requirements, is a more recent phenomenon. The generalization of the evaluation of measurement uncertainties to tests has been a gradual process, in line with changes in the requirements of the normative framework that regulates the accreditation of tests laboratories and also as the perceived good practices have evolved. The sole identification of the relevant sources of uncertainty was followed by the requirement to provide a simplified estimate of the measurement uncertainty, and it is now an accepted requirement to properly evaluate the expanded measurement uncertainty associated with any tests. In this study, the evaluation of measurement uncertainty associated with the determination of sulfate in water will be attempted using a procedure that includes linear regression, with the regression parameters provided with associated uncertainties, and a Monte Carlo method applied as a validation tool of the conventional mainstream evaluation method, concerning the approximations in terms of linearization of the model and the assumed shape of the output distribution introduced by this approach. © 2012 Springer-Verlag. Source


Catrinescu C.,University of Madeira | Catrinescu C.,Technical University Gheorghe Asachi | Fernandes C.,University of Madeira | Fernandes C.,Laboratorio Regional Of Engineering Civil | And 2 more authors.
Applied Catalysis A: General | Year: 2013

In this study, we report the use of clay-based catalysts in the methoxylation of limonene, for the selective synthesis of α-terpinyl methyl ether. Na-SAz-1, Ca-SWy-2 and Sap-Ca source clays and a montmorillonite (SD) from Porto Santo, Madeira Archipelago, Portugal were modified by (i) ion-exchange with Al, Fe, Ni and Na and (ii) acid activation, to produce catalysts with markedly different acidic and textural properties. The lack of activity of Ni2+-SAz-1 (with Lewis acidity maximized), provided evidence that the process occurs preferentially on Brönsted acid sites. The catalysts based on the high layer-charge SAz-1 montmorillonite proved to be the most active. Ion-exchange with Al3+, followed by thermal activation at 150°C, afforded the highest number of Brønsted acid sites located in the clay gallery and this coincided with the maximum catalytic activity. The influence of various reaction conditions, to maximize limonene conversion and selectivity, was studied over Al-SAz-1. When the reaction was performed for 20 h at 40°C, the conversion reached 71% with 91% selectivity to the mono-ether. Mild acid activation (1 M HCl, 30 min, reflux) of the raw SAz-1 clay leads to a material with a good catalytic behaviour (slightly inferior to Al-SAz-1), while any increase in the severity of the acid-treatment (6 M HCl, 30 min, reflux), caused a marked decrease in catalytic activity. © 2013 Elsevier B.V. All rights reserved. Source


Forbes A.B.,National Physical Laboratory United Kingdom | Sousa J.A.,Laboratorio Regional Of Engineering Civil
Measurement: Journal of the International Measurement Confederation | Year: 2011

In this paper, we compare uncertainty evaluation procedures based on the measurement and observation equation approaches applied to a class of models covering many practical measuring systems. We derive general conditions for when the two approaches give the same distributions associated with the measurand and give examples of how and where they differ. We argue that while it is possible to interpret the measurement equation approach as determining a state of knowledge distribution for the measurand, for some problems there are conceptual, and for highly nonlinear models, practical difficulties with this interpretation. These conceptual difficulties do not arise if the measurement equation approach is interpreted as characterising the behaviour of a measuring system. The discussion presented here is relevant to the revision of the GUM, currently being undertaken by the Joint Committee for Guides in Metrology. © 2011 Elsevier Ltd. All rights reserved. Source


Vilcocq L.,University of Madeira | Spinola V.,University of Madeira | Moniz P.,National Laboratory of Energy and Geology | Duarte L.C.,National Laboratory of Energy and Geology | And 4 more authors.
Catalysis Science and Technology | Year: 2015

The hydrolysis of hemicellulosic oligosaccharides (OS) was investigated using acid-activated clays (prepared from natural Porto Santo montmorillonite clay) as catalysts. Acid activation was performed in HCl solution or with aluminium exchange. The clay catalysts were characterized by XRD, N2 adsorption isotherms, CEC, FTIR, titration of acid sites in water and adsorption of sugars and disaccharides. They were tested for the hydrolysis of a model compound, maltose, and of OS-rich liquor from rice straw fractionation. The HCl-activated clays were the most efficient catalysts for maltose hydrolysis. It was demonstrated that the hydrolysis of OS into monomer sugars over a clay catalyst is technically feasible and that this reaction leads to the selective removal of glucose, arabinose and acetic acid side groups from the OS structure, thus yielding simpler xylo-oligosaccharide chains. Furthermore, no significant conversion of monomer sugars into furans was observed. This journal is © The Royal Society of Chemistry. Source


Catrinescu C.,University of Madeira | Catrinescu C.,Technical University Gheorghe Asachi | Fernandes C.,University of Madeira | Fernandes C.,Laboratorio Regional Of Engineering Civil | And 2 more authors.
Applied Catalysis A: General | Year: 2015

In this study, we report the use of clay-based catalysts in the methoxylation of α-pinene, for the selective synthesis of α-terpinyl methyl ether, TME. The main reaction products and intermediates were identified by GC-MS. The reaction conditions (stirring rate and catalyst load) that afford a kinetic regime were established. SAz-1 (Cheto, Arizona, USA) source clay and a montmorillonite (SD) from Porto Santo, Madeira Archipelago, Portugal, were modified by ion-exchange with Al3+ to produce catalysts with markedly different acidities and textural properties. The catalysts based on the high layer-charge SAz-1 montmorillonite proved to be the most active. Ion-exchange with Al3+, followed by thermal activation at 150°C, afforded the highest number of Brønsted acid sites - a significant proportion of which were located in the clay gallery - and this coincided with the maximum catalytic activity. The influence of various reaction conditions, to maximize α-pinene conversion and selectivity, was studied over AlSAz-1. When the reaction was performed for 1 h at 60°C, the conversion reached 65% with 65% selectivity towards the mono-ether, TME. Similar conversions and selectivities required up to 50 h over zeolites and other solid acid catalysts. The kinetic dependencies of this reaction on temperature and reagent concentration, over the selected clays were also investigated. It was established that, in the temperature and reagent concentration regime studied, the reaction was first order with respect to α-pinene. The apparent activation energies over the two catalysts, calculated from Arrhenius plots, were almost identical at 72 kJ mol-1. © 2014 Elsevier B.V. All rights reserved. Source

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