Browsing by Issue Date, starting with "2020-02-01"
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- Ultrasound and radiation-induced catalytic oxidation of 1-phenylethanol to acetophenone with iron-containing particulate catalystsPublication . Soliman, Mohamed Mostafa Aboelhassan; Kopylovich, Maximilian N.; Alegria, Elisabete; Da Costa Ribeiro, Ana Paula; Ferraria, Ana Maria; Rego, Ana; Correia, Luís M. M.; Saraiva, Marta S.; Pombeiro, ArmandoIron-containingparticulatecatalystsof0.1–1 µmsizewerepreparedbywetandball-milling procedures from common salts and characterized by FTIR, TGA, UV-Vis, PXRD, FEG-SEM, and XPS analyses. It was found that when the wet method was used, semi-spherical magnetic nanoparticles were formed, whereas the mechanochemical method resulted in the formation of nonmagnetic microscale needles and rectangles. Catalytic activity of the prepared materials in the oxidation of 1-phenylethanol to acetophenone was assessed under conventional heating, microwave (MW) irradiation, ultrasound (US), and oscillating magnetic field of high frequency (induction heating). In general, the catalysts obtained by wet methods exhibit lower activities, whereas the materials prepared by ball milling afford better acetophenone yields (up to 83%). A significant increase in yield (up to 4 times) was observed under the induction heating if compared to conventional heating. The study demonstrated that MW, US irradiations, and induction heating may have great potential as alternative ways to activate the catalytic system for alcohol oxidation. The possibility of the synthesized material to be magnetically recoverable has been also verified.
- Value addition of agricultural production to meet the sustainable development goalsPublication . Dos Santos, Maria José Palma LampreiaValue addition is the creation of value at different stages, by different actors throughout the value chain by add value of agricultural production. Value added may be related to quality, costs, delivery times, delivery flexibility, and innovativeness of agricultural products, among other characteristics. The size of value added is decided by the end customer’s willingness to pay. Opportunities to add value depend on a number of factors, such as market characteristics; institutional, social, and environmental conditions; and technological capabilities of the actors involved in that process.
- Viscosity measurements of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIM OTf) at high pressures using the vibrating wire techniquePublication . Sequeira, Maria Carolina; Avelino, Helena Maria Da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, J.M.N.A.The goal of the present work is to contribute to the characterization of ionic liquids by measuring their viscosity at high pressures. As 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIM OTf) has been used as a solvent in CO2 capture processes, the temperature and pressure ranges of the measurements cover the intervals used in those processes. Measurements of the viscosity of EMIM OTf along five isotherms in the range (298-358) K and at pressures up to 50 MPa, have been performed using the vibrating wire technique in the forced mode of operation. As far as the authors are aware, these are the first measurements of this ionic liquid at pressures higher than 0.1 MPa, to be published. The viscosity results were correlated with the molar volume, using a modified hard-spheres model. The root mean square (sigma) deviation of the data from the correlation is less than 0.5% The expanded uncertainty of the present viscosity data is estimated as +/- 2.0% at a 95% confidence level. As a complement, the pressure-viscosity coefficient has been calculated within the temperature range of the present results. Previous studies of the influence of the electric conductivity of ionic liquids, including EMIM OTf, in the vibrating wire method, have been taken into account for the present work. Complementary measurements of the density have been performed along seven isotherms in the temperature range from (298-363) K and pressures from (0.1-70) MPa. The density measurements were carried out with an Anton Paar vibrating U-tube densimeter and the raw data were corrected for viscosity effects. The density results were correlated with the temperature and pressure using a modified Tait equation. The expanded uncertainty of the present density data is estimated as +/- 0.2% at a 95% confidence level.
- Uncertainty of shear resistance models: Influence of recycled concrete aggregate on beams with and without shear reinforcementPublication . Pacheco, João; De Brito, Jorge; Chastre, Carlos; Evangelista, LuisThe model uncertainty of the shear resistance equations of three design codes {the current Eurocode 2 (2004), Model Code (2010), and the final draft of the Eurocode 2 (2020)} was investigated for coarse natural and recycled aggregate concrete beams. Databases of beams with and without shear reinforcement were made with clearly defined criteria. The statistics of the model uncertainty of natural and recycled concrete beams were compared and it was found that recycled aggregate incorporation has detrimental effects on the model uncertainty of shear design. Surprisingly, recycled concrete aggregate beams designed following the current version of Eurocode 2 (2004) are safer than those designed using the other codes. This is due to the shear resistance equations of the latter overestimating the aggregate interlock of recycled aggregate. A preliminary partial factor was proposed, offsetting the influence of recycled aggregate on the safety of beam designs. The database of beams with shear reinforcement lacks representativeness but hinted that recycled aggregate incorporation also reduces the safety of this type of shear design. The paper finishes presenting suggestions of experiments that would complement the current knowledge on this topic.
- Picturing agreement between clustering solutions using multidimensional unfolding: An application to greenhouse gas emissions dataPublication . Martins, Ana Alexandra; Cardoso, Maria MargaridaWhen evaluating a clustering solution, we often have to compare alternative solutions - e.g., to address clustering stability or external validity. Each comparison essentially relies on a contingency table referring to a pair of (crisp) clustering solutions. These data is commonly used as an input to: (1) an assignment problem, to match the clusters of the two partitions; (2) determine several indices of agreement; (3) represent the two partitions in a two-dimensional map resorting to Correspondence Analysis. We propose using the Multidimensional Unfolding (MDU) technique to picture the cross-classification data between two partitions, complementing a clustering evaluation analysis and overcoming some limitations of the traditional approaches (1) to (3). This approach relies on a new similarity measure that excludes agreement between clusters due to chance alone. The resulting MDU map is very easy to interpret, picturing agreement between clustering solutions: the further apart are the clusters (represented by points) from the two partitions, the larger the (Euclidean) distances between the corresponding points. Two applications illustrate the relevance of this approach: an application to a data set on UCI Machine Learning Repository to access clustering external validity; and an application to greenhouse gas emissions data to address the temporal stability of clustering solutions, the clusters of European countries, which have homogeneous sources of pollutant emissions, being compared over three years.