University of Coimbra
  • Coimbra, Coimbra, Portugal
Recent publications
Composite steel decking concrete slabs are an important structural member in building construction. Research on its thermal behavior should be developed to understand its fire performance. In this paper, a comparison of the temperature distribution in the cross-section of steel decking concrete slabs subjected to fire is made through three different procedures: (a) standardized analytical, (b) experimental and (c) numerical. The analytical method was the one proposed in NBR 14323 standard. The experimental tests corresponding to eight real-scale fire tests on composite slabs carried out by the authors. The numerical tests were done for the same configurations of the experimental tests and used the FEA software Abaqus. Steel decking temperatures obtained with NBR 14323 methodologies showed good convergence with the experimental and numerical ones. The same was not observed for the concrete, positive and negative rebar.
This research intends to show how an analytical cyclic division of a dataset can improve ANN-type models in predicting future situation of different air pollutants in small-sized urban cities. Similar to other sub-tropical cities, the four seasons are not significant but climate characteristics of Macao obviously includes warm and cold seasons. These make it difficult to train the models well. Thus, an effective analytical way of cyclic division of the dataset for a seasonal LSTM modeling can improve the prediction of air quality with the meteorological data. We used data from 2016 to 2020 as input, and the model was trained on a 24-h basis, weekly oscillation frequency and finally grouped into 2 warm and cold seasons. A small-sized urban city was selected to demonstrate this study with 21 meteorological variables, and wavelet decomposition was used to clearly see the obvious oscillation and cycle patterns. The contributions include using LSTM for the prediction of time series with multivariate inputs in Macao and observing how the 2 cyclic division of the time series dataset of air pollutants and meteorological conditions look like. It is also intended to show, using some indicators, why the multivariate dataset should be divided according to the 2 cold/warm seasons. Finally, the result of predicting the concentrations of air pollutants is presented.
Geological remote sensing has been an invaluable means to obtain data to perform geological mapping objectively and with high accuracy. However, there is a significant gap in geological cartography information at 1:50 000 scale throughout the territory in mainland Portugal. The lack of geological mapping is reflected in the geological resources and land management information. This investigation's main objective was to assess the viability of using remote sensing, machine learning and geochemical techniques as proof of concept for the Portuguese context using the Beiras Group (mainland Portugal) as a case study area of 341 km2. Multispectral analysis was carried out in two Landsat-8 images of 2015, one in the winter and the other in the summer. Hyperspectral data were obtained using a 400-1000 nm spectroradiometer applied to 23 rock samples collected in two field campaigns-the first in January and the second in April 2019. Spectral differences were found distinguishing the two main lithological units, where the granites (Granito de Coentral and Granito de Vila Nova) had an increasing wavelength spectra shape throughout the whole VNIR measurements. Geochemical data was carried out using X-ray Fluorescence, where the average quantity of major elements such as Na2O [2.15 %] and CaO [0.41 %] was higher in granites than metasediments: 0.38 % and 0.11 %, respectively. The J48 machine learning algorithm was performed using as input Landsat-8 reflectance data which showed a high success rate in both confusion matrixes (83,72 % and 94,08 %).
A strain-rate potential (SRP) can be used in place of the classical stress potential to describe the response of plastically deforming solids. Orthotropic potentials are typically developed by extending existing isotropic criteria. For mathematical convenience, the construction of orthotropic SRPs using the linear transformation approach often involves a constrain on the fourth-order orthotropic tensor such that the transformed stress (and therefore strain-rate) tensors are deviatoric. This constrain is not however necessary to ensure plastic incompressibility and in fact reduces the number of independent orthotropic coefficients from nine to six, impairing the flexibility of the criterion. In this work, a new definition is proposed for the fourth-order orthotropic strain-rate transformation tensor with no constrains on the original form of the stress transformation tensor counterpart, such that the number of independent orthotropic coefficients is maximum. Based on this idea, as a proof of concept, a more general orthotropic SRP is construct, dual of a quadratic stress potential with a single linear transformation for materials with the same response in tension and compression.
Recent studies highlight the importance of improving the description of the material behavior, particularly for non-proportional loading paths. This work discusses the differences in the stress and strain ratios predicted by different yield criteria, when applied to describe the plastic behavior of an aluminum alloy, submitted to different non-proportional biaxial loading conditions. Reloading with or without unloading is analyzed to highlight the importance of the unloading stage on the stress paths, since the stress state cannot change abruptly for a material undergoing plastic deformation. Although the yield criteria adopted seem to have a small impact on the stress state predicted for each force-controlled loading condition, the influence on the strain path is non-negligible.
Gas barrier properties are very relevant in composite materials for applications so diverse such as food packaging, electronics, or old document restoration. In the present work, four different types of cellulose nanofibres (CNFs), two types of clay minerals used individually (sepiolite) or combined (sepiolite + kaolinite), and the influence of pH, were explored in the production of composite films. Neat CNFs, only mechanically treated or prepared by enzymatic pre-treatment, gave films with good mechanical and barrier properties, but the addition of minerals led to a dramatic loss of these properties. Contrarily, the use of thin and functionalized fibrils (TEMPO-oxidised or cationized CNFs) gave composite films with good mechanical, thermal and barrier properties. Superior oxygen barrier properties (oxygen transmission rate (OTR) < 0.4 cm3 m−2 day−1) were obtained using TEMPO-oxidised CNF and 20% sepiolite, and, in general, for all the composite films containing the TEMPO CNF (OTR ≤ 1.8 cm3 m−2 day−1). The cationic CNF-based composites also showed a very good oxygen barrier (OTR ≤ 8.2 cm3 m−2 day−1). The high oxygen barrier could be explained by the compactness of the films and better entanglement of the more fibrillated nanocelluloses with the mineral particles. A decrease in the pH of the suspensions led to a decrease in the film preparation time, without a major negative impact on the composite film’s properties.
Objectives Studying rib torsion is crucial for understanding the evolution of the hominid ribcage. Interestingly, there are variables of the rib cross section that could be associated with rib torsion and, consequently, with the morphology of the thorax. The aim of this research is to conduct a comparative study of the shape and mineralized tissues of the rib cross section in different hominids to test for significant differences and, if possible, associate them to different thoracic morphotypes. Materials and Methods The sample consists of the rib cross sections at the midshaft taken from 10 Homo sapiens and 10 Pan troglodytes adult individuals, as well as from A. africanus Sts 14. The shape of these rib cross sections was quantified using geometric morphometrics, while the mineralized tissues were evaluated using the compartmentalization index. Subsequently, covariation between both parameters was tested by a Spearman's ρ test, a permutation test and a linear regression. Results Generally, P. troglodytes individuals exhibit rib cross sections that are rounder and more mineralized compared to those of H. sapiens . However, the covariation between both parameters was only observed in typical ribs (levels 3–10). Although covariation was not found in the rib cross sections of Sts 14, their parameters are closer to P. troglodytes . Discussion On the one hand, the differences observed in the rib cross sections between H. sapiens and P. troglodytes might be related to different degrees of rib torsion and, consequently, to different thoracic 3D configurations. These findings can be functionally explained by considering their distinct modes of breathing and locomotion. On the other hand, although the rib cross sections belonging to Sts 14 are more similar to those of P. troglodytes , previous publications determined that their overall morphology is closer to modern humans. This discrepancy could reflect a diversity of post‐cranial adaptations in Australopithecus .
Perceived everyday discrimination is a transversal phenomenon with a negative impact on people’s health. This study aimed to explore the factor structure and psychometric properties of three versions of the Everyday Discrimination Scale, with three different samples: the European Portuguese validation (EDS-PT, considering any reason for discrimination), using a sample of adults from the community (N = 610), a specific version for sexual minority (EDS-SM), with a sample of sexual minority individuals (N = 352), and a specific version for gender minority (EDS-GM), in a sample of gender minority individuals (N = 108). Factor structure and reliability of the different versions were examined. A second-order two-factor model (Everyday discrimination with factor 1 Unfair Treatment and factor 2 Personal Rejection) presented good adjustment and adequate reliability. Furthermore, all versions of EDS revealed weak to moderate correlations with indicators of convergent validity (mental health, satisfaction with life, social safeness, and social support). This study's outcomes provide insights into different types of everyday discrimination and suggest that the EDS-PT, EDS-SM and EDS-GM are valid and reliable measures useful in research and clinical contexts.
La0.67Ca0.2Ba0.13Fe1−xTixO3 samples (x = 0 and 0.03) were synthesized by the auto-combustion method. Analysis of XRD diffractograms revealed that these compounds crystallize in the cubic system with the space group Pm3̄m. The dielectric properties have been studied in the 10²–10⁶ frequency range and the 120–280 K temperature range. Analysis of AC conductivity shows that the conduction mechanisms are of polaronic origin and that they are co-dominated by the NSPT and OLPT models. The monotonic increase in conductivity with increasing temperature results from the reduction of defect centers and the increase in charge carrier mobility. Such variation is consistent with impedance variation at different frequencies and temperatures indicating semiconductor behavior. Nyquist diagrams are characterized by the appearance of semi-circular arcs. These spectra are modeled in terms of equivalent electrical circuits confirming the contribution of grains (Rg//CPEg) and grain boundaries (Rgb//CPEgb). The dielectric analysis showed an evolution of the dielectric constant in accordance with Koop's theory and the phenomenological model of Maxwell–Wagner. The low conductivity and the high values of the real permittivity at low frequency make our compounds potential candidates for energy storage and applications for electronic devices and microwaves.
Untreated swine wastewater (SW) discharge leads to serious consequences such as water quality decreasing related to eutrophication and proliferation of harmful algae containing cyanotoxins, which can cause acute intoxication in humans. The use of untreated pig farming effluent as fertilizer can lead to the accumulation of polluting compounds. Biological treatments can degrade organic matter but have the disadvantage of requiring large areas and high retention times and demonstrating low efficiencies in the degradation of refractory compounds such as pharmaceutical compounds. In this ambit, the performance of four low-cost materials was evaluated for treatment of a swine wastewater using physical–chemical processes such as adsorption and Fenton’s process. The tested materials are two natural resources, red volcanic rock from Canary (RVR) Islands and black volcanic rock (BVR) from Azores, and two industry residues, red mud (RM) and iron filings (IF). Among the tested materials, only IFs are catalytically active for Fenton’s peroxidation. Still, RVR, BVR, and RM were efficient adsorbents removing up to 67% of COD. The combination between adsorption followed by Fenton’s process using IF as catalyst showed interesting results. When RM is applied as adsorbent in the diluted effluent, it was able to remove 67% and 90% of COD for adsorption and adsorption followed by IF Fenton, respectively. At those conditions, the resultant treated effluent accomplishes the requirements for direct discharge in the natural water courses as well as the parameters for water reusing.
An adolescent was referred to the emergency department due to abnormal uterine haemorrhages in the previous 2 months, associated with dizziness in the last month. At observation, she was haemodynamically stable, with good clinical impression, but evident mucocutaneous pallor. Full blood count confirmed a severe anaemia (haemoglobin 47 g/L). She received red blood cell transfusion (10 mL/kg) and started oral oestradiol. She was discharged, with oral oestradiol and oral iron supplementation. Two weeks later, she started treatment with oestradiol and progestin. The patient had a good recovery, without new similar episodes.
Purpose Amorphous solid dispersions (ASD) for nasal delivery offer the opportunity to increase drug release performance, while using polymers with mucoadhesive properties. The aim of the present study was to apply this solubility enhancement technique to a poorly soluble drug for nasal delivery, while comparing two particle engineering strategies, namely spray dried microparticles and chimeral agglomerates, with the corresponding physical blends with crystalline drug. Methods Formulations of piroxicam were manufactured using varied polymer and particle engineering strategies and evaluated through in vitro drug release and ex vivo permeation studies, as well as nasal deposition and in vivo pharmacokinetic studies. Results ASD with hydroxypropyl methylcellulose (HPMC) showed enhanced drug release and permeation, compared to polyvinylpyrrolidone/vinyl acetate formulations and blends. Nasal deposition of HPMC chimeral agglomerates suggested off-target deposition. In vivo pharmacokinetic studies revealed that spray-dried HPMC-containing microparticles exhibited the highest maximum plasma concentration (C max ) and the lowest time to attain it (t max ). In vitro release rate and in vivo absorption rate were correlated as well as t max and in vitro performance. When excluding the formulation with least nasal targeted deposition, in vitro release and ex vivo permeation performance were also correlated with C max and area under the drug concentration-time curve (AUC) from 0 to 1 h, with R ² > 0.89. Conclusion ASD for nasal delivery provide fast drug absorption, which depends on the supersaturation ability of the polymer employed. In vitro-in vivo correlations suggested that in vitro release and ex vivo permeation studies are predictive tools regarding nasal absorption.
The purpose of this chapter is to explore the moderating effect of decentralization on the relationship between management accounting systems and organizational performance. An online survey was used to inquire CFOs of Portuguese SMEs, and data were analyzed through SmartPLS. The results indicate that decentralization moderates the relationship between MAS and organizational performance. This chapter contributes to a better knowledge of the factors that can enhance MAS effectiveness and its influence on the performance of SMEs.
This study uses neuroimaging methods to identify patterns of brain activation among sport fans in reaction to team stimuli. In a whole-brain analysis without selected regions in advance, the purposes were to identify the structures involved when fans are exposed to positive, neutral, and negative events and to learn what events activate more limbic networks. A total of 53 individuals participated in and functional magnetic resonance imaging experiment involving the presentation of videos in various situations. Findings indicate the activation of the cingulate gyrus and other structures of the limbic system, as the hippocampus and parahippocampus. We also found involvement of the ventral tegmental area of the reward system. Additionally, brain activity in emotional regulation and memory areas were more influenced by positive than neutral and negative videos. It was also found the involvement of other areas not directly included in the limbic or reward systems. This study provides the neural basis of fan reactions to team-related stimuli. Sport clubs should be aware that negative content seems to be suppressed from emotional memory and positive videos trigger more emotion and memory areas than neutral and negative videos.
A spectral Favard theorem for bounded banded lower Hessenberg matrices that admit a positive bidiagonal factorization is found. The large knowledge on the spectral and factorization properties of oscillatory matrices leads to this spectral Favard theorem in terms of sequences of multiple orthogonal polynomials of types I and II with respect to a set of positive Lebesgue--Stieltjes measures. Also a multiple Gauss quadrature is proven and corresponding degrees of precision are found. This spectral Favard theorem is applied to Markov chains with (p+2)-diagonal transition matrices, i.e. beyond birth and death, that admit a positive stochastic bidiagonal factorization. In the finite case, the Karlin--McGregor spectral representation is given. It is shown that the Markov chains are recurrent and explicit expressions in terms of the orthogonal polynomials for the stationary distributions are given. Similar results are obtained for the countable infinite Markov chain. Now the Markov chain is not necessarily recurrent, and it is characterized in terms of the first measure. Ergodicity of the Markov chain is discussed in terms of the existence of a mass at 1, which is an eigenvalue corresponding to the right and left eigenvectors.
The investigation of key minerals including zircon, apatite, titanite, rutile, monazite, xenotime, allanite, baddeleyite and garnet can retain critical information about petrogenetic and geodynamic processes and may be utilised to understand complex geological histories and the dynamic evolution of the continental crust. They act as small but often robust petrochronological capsules and provide information about crustal evolution, from local processes to plate tectonics and supercontinent cycles. They offer us insights into processes of magmatism, sedimentation, metamorphism and alteration, even when the original protolith is not preserved. In situ techniques have enabled a more in-depth understanding of trace element behaviour in these minerals within their textural context. This has led to more meaningful ages for many stages of geological events. New developments of analytical procedures have further allowed us to expand our petrochronological toolbox while improving precision and accuracy. Combining multiple proxies with multiple minerals has contributed to new interpretations of the crustal history of our planet.
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11,721 members
Bruno F. O. Nascimento
  • Department of Chemistry
Sandra Correia
  • Centre for Functional Ecology - Science for People & the Planet
Cláudio M. Nunes
  • Department of Chemistry
Rua Larga , 3004-504, Coimbra, Coimbra, Portugal
Head of institution
Amílcar Falcão
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