Browsing by Issue Date, starting with "2023-08"
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- Valorização de cinzas de biomassa vegetal para aplicações geotécnicasPublication . Marchiori, Leonardo; Studart, André; Morais, Maria Vitoria; Albuquerque, Antonio; Andrade Pais, Luís; Boscov, Maria Eugenia Gimenez; Cavaleiro, VictorAs cinzas de biomassa vegetal (CBV) têm sido intensamente estudadas para incorporação em solos em obras de terra. Este trabalho tem como objetivo caracterizar química e geotecnicamente cinzas de pinheiros e oliveiras em comparação com um solo de Castelo Branco (Portugal), com a finalidade de aplicações geotécnica. Avaliações físicas, mineralógicas e químicas são necessárias para investigar a origem dos materiais, nomeadamente para determinar se as CBV têm contaminantes, como metais pesados, em sua composição e suas características físicoquímicas. Considerando que há elevadas quantidades de CBV produzidas pelo mundo e um consequente excesso de deposição em aterros sanitários ou queima, a investigação por novas soluções para a sua reutilização é cada vez mais necessária tendo em atenção quesitos atuais de desenvolvimento sustentável, redução do impacto ambiental e economia circula. A engenharia civil, nomeadamente nas áreas da construção, vias, saneamento e geotecnia, oferece várias oportunidades para investigação da aplicação destes resíduos. Neste âmbito, o reforço de solos e a aplicação de liners se destacam, pois podem beneficiar das caraterísticas físico-químicas e mecânicas das CBV para melhorarem parâmetros como a resistência mecânica e permeabilidade. Foram realizados ensaios de caracterização para as CBV e para um solo fraco, nomeadamente distribuição granulometrica, densidade específica dos grãos, limites de Atterberg, composição química por fluorescência de raio-x e mineralogia por difração de raio-x. Este trabalho faz parte de uma investigação mais ampla para desenvolver um material alternativo que possa ser utilizado em obras de terra de revestimento e reforço de solos. Os resultados demonstram que a introdução das CBV em solos pode contribuir para reduzir o peso específico e a plasticidade e melhorar as propriedades mecânicas do material, consequência também do enriquecimento de minerais pozolânicos devido à sua composição química. Desta forma, as CBV deram boas indicações para serem introduzidas em solos em diferentes percentuais, para melhorar as suas propriedades ou para a produção de liners, sendo necessário realizar futuros testes acerca do desempenho mecânico e ensaios de compressibilidade edométrica e compressão triaxial, condutividade hidráulica e potencial de lixiviação de poluentes, de modo a avaliar a sua sustentabilidade e durabilidade e afastar eventuais impactos no ambiente e saúde pública.
- Biological properties of aromatic plants used in folk medicine: a focus on the essential oil of Thymus zygisPublication . Coimbra, Alexandra Teixeira; Duarte, Ana Paula Coelho; Ferreira, Susana Margarida ParaísoFor centuries, plants have been used for a wide variety of purposes, such as treating diseases, food flavouring and preservation and perfumery. The essential oils (EOs) are aromatic, oil-like volatile substances present in different plant materials that have a wide range of biological activities and can be used in different areas, such as chemical, cosmetic, food, perfumery, and pharmaceutical industries and have been used as therapeutic agents since ancient times. Thymus zygis is a widespread plant, mainly used as a culinary flavouring agent, which EO has demonstrated bioactive properties, such as antioxidant and antimicrobial, and that may even enhance the effect of certain antimicrobial agents. Furthermore, the potential application as a food preservative has been described on different matrixes mainly due to its antimicrobial activity against pathogenic and spoilage microorganisms in food. Considering the different applications of EOs, this work aimed to study the composition, antioxidant, and antimicrobial properties and also the cytotoxicity of the EOs of Foeniculum vulgare, Helichrysum stoechas, Mentha pulegium, Pinus pinaster, Ruta graveolens, and Thymus mastichina. The chemical composition, and the bioactive properties of the T. zygis EO were also evaluated with a focus on antimicrobial activity against Staphylococcus aureus and Listeria monocytogenes, and application of the EO in food. The F. vulgare, H. stoechas, M. pulegium, P. pinaster, R. graveolens, T. mastichina and T. zygis EOs showed antioxidant activity acting through inhibition of lipid peroxidation, while only the H. stoechas, M. pulegium and T. zygis EOs scavenged the free radicals of DPPH. M. pulegium and T. zygis EOs showed the strongest antimicrobial activity and only volatiles compounds from these EOs demonstrated inhibitory activity. Regarding the EO cytotoxicity on a fibroblasts cell line, it was observed that the effect was directly proportional to the EOs concentration, in which the highest cytotoxic effect was obtained with the R. graveolens EO. Considering the antimicrobial potential of the EO from T. zygis and since it showed the greater activity among the tested EOs, it was decided to proceed with further evaluation of this EO, thus deepening its bioactive activities, mainly the antibacterial activity against S. aureus and L. monocytogenes. Taking into account that S. aureus is a Gram-positive bacterium that causes a wide variety of clinical infections, from less severe to serious and life-threatening infections and because these are aggravated by antibiotic resistance, the antibacterial activity of T. zygis EO against strains of S. aureus was evaluated. The T. zygis EO demonstrated antimicrobial activity against S. aureus strains with bactericidal effect. The EO of T. zygis also revealed a synergistic or additive effect in combination with the antibiotic’s ampicillin, ciprofloxacin, or vancomycin against S. aureus strains and, in some cases, changed the antibiotic-resistance phenotype from resistant to susceptible. The T. zygis EO inhibit the formation of biofilms by S. aureus and partially eliminate the preformed biofilms even at subinhibitory concentrations. The EO reduced the haemolytic activity of S. aureus SA 03/10 (the only strain tested that causes haemolysis) as well the quorum-sensing in Chromobacterium violaceum biosensor. Therefore, these results demonstrate the good bioactive properties of the T. zygis EO, mainly the antimicrobial activity against S. aureus, revealing its potential to be used as an antibacterial agent and/or as an enhancer of the effect of antibiotics. Since L. monocytogenes is a foodborne Gram-positive bacterium with a high mortality rate and has the ability to survive and replicate in adverse conditions, allowing the wide distribution of this bacterium in different environments and matrices, such as water, soil, and food products, the antimicrobial activity of T. zygis EO against strains of L. monocytogenes was evaluated. The T. zygis EO presented good antibacterial activity against L. monocytogenes with MIC value of 0.05% while showing a bactericidal effect. The EO significantly reduced the biofilm formation with inhibition percentages from 16.85 to 89.86% and also the motility, while not inducing cross-resistance to antibiotics. The concentration of 2× MIC of T. zygis EO reduced the L. monocytogenes counts (initial inoculum of ~106 CFU/mL) in the chicken juice (1.53 log CFU/mL) and the lettuce model (to below the detection limit) after two days of storage. Regarding the sanitizing of fresh vegetables, the use of 0.2% (v/v) of EO for 5 min of immersion, reduce L. monocytogenes and natural microbiota counts for values below the detection limit of the method for iceberg lettuce. For the spinach leaves, L. monocytogenes and the natural microbiota counts were reduced to 4.35 log CFU/mL and in a range of 4.47 to 5.94 log CFU/mL, respectively, when compared with the washing with water. Thus, the T. zygis EO has demonstrated promising antibacterial activity against L. monocytogenes and these results point to the potential use of the T. zygis EO as a natural food preservative or sanitiser for controlling L. monocytogenes and the natural microbiota in food products. Overall, the present study revealed significant bioactive properties of different EOs, highlighting T. zygis EO to be considered in further studies for potential use in food preservation, due to their antioxidant and antimicrobial properties as well as in the control and reduction of the pathogenicity of the L. monocytogenes and S. aureus.
- Water Treatment Sludge as Geotechnical Liner Material: State-of-ArtPublication . Marchiori, Leonardo; Albuquerque, Antonio; Cavaleiro, VictorThe periodical cleaning of the decanters at the plant generates solid wastes called water treatment sludges (WTS), a chemical compound similar to aluminum silicates. WTS’s properties have been studied for geotechnical purpose and it seems to be suitable for producing liner materials for landfills, dams, ponds, and lagoons which store and prevent soil’s infiltration of residues. Liners are usually shaped of soil and geosynthetics, their main properties required are compaction, compressibility and shear strength, chemical compatibility, and hydraulic conductivity. WTS to be considered as a soil substitute, it must be function like a soil, thus, for developing alternative materials, physical, chemical, mechanical, and hydraulic characterization laboratorial parameters are the first step to make viable its reuse. In this sense, the study aims to review the literature over the above-mentioned parameters in order to evaluate WTS as liner material. This review concluded that WTS have high heterogeneity in chemical and mechanical behavior due source of water and treatment processes. WTS’ water affinity affects plasticity behavior, and its incorporation into soils seems to contribute for a composite with pozzolanic characteristics, low specific gravity, finer granulometry, and mechanical stabilization. Although need attention on its chemical compatibility, the influence on shear resistance—increasing internal effective friction angle and decreasing cohesion—and the optimum ratio of introduction within soils for an alternative liner material. Nonetheless, there are lacks in literature over hydraulic conductivity, and long-term behavior, the use of the material in practice must be preceded by pilot tests or experimental landfills.
- Geotechnical Characterization Methodology of Water Treatment Sludge for Production of Liner MaterialPublication . Marchiori, Leonardo; Morais, Maria Vitoria; Albuquerque, Antonio; Cavaleiro, VictorClayey soils and geosynthetic materials are used as low hydraulic conductivity layers and environmental protection barriers in civil engineering works for storing wastes as covering and bottom impermeabilization layer structures, known as liners. Future shortage of clay materials and geosynthetic’s high costs are usual problems, aligned with the need of prevention of environmental impacts associated to wastes by industry infiltrating into groundwater, sustainable solutions are needed. The reuse of industrial waste materials follows directives of the circular economy when this application is expected to reduce construction costs, help preserve natural resources, reduce the use of synthetic materials, reuse industrial waste materials, and contribute to sustainability. Water treatment sludges (WTS) are generated by water treatment plants mainly from periodic washing of the sedimentation tanks and filters and seems to be suitable for a geomaterial replacement. To make it feasible, the most significant factors that need more investigations are index properties, physical and mechanical behavior, chemical compaction and resistance, hydraulic conductivity, and leaching potential. A methodology for different ratios of WTS, soil, and with or without additive needing, along with a laboratorial analysis of water treatment sludge sample were proposed to ensure the expected results and parameters for liner alternative material.
- Computational characterization of the temperature field in coaxial nitrogen injection under supercritical conditionsPublication . Magalhães, Leandro; Silva, A. R. R.; Barata, Jorge M MThe modeling of fluids in the supercritical regime is addressed at conditions characteristic of liquid-propelled rocket engines, whose increasing performance demands paved the way for supercritical conditions. In the present document, nitrogen is used as a surrogate for the commonly encountered oxygen-hydrogen mixture so that turbulence mixing can be looked into without influences from combustion and chemically reacting effects. The temperature field validation on nitrogen coaxial injection at supercritical conditions, with high-velocity ratios (outer-to-inner), where the main (inner) stream is recessed relative to the outer stream, is of paramount importance in the flame stabilization operation of liquid rocket motors. The temperature field is analyzed taking into account varying momentum and velocity ratios, whose increased leads to a reduction of potential core lengths, increasing jet spreading. The results also depict a fundamental influence of thermal effects, dominating over the transport of momentum. The experimental data and large eddy simulation solvers from the literature agree with the estimate of injection velocities at several conditions and comparable to the space shuttle main engine pre-burner.
- Spot price forecasting for best trading strategy decision support in the Iberian electricity marketPublication . Magalhães, Bianca G.; Bento, Pedro M. R.; Pombo, José; Calado, M. do Rosário; Mariano, Sílvio J. P S.The increasing volatility in electricity markets has reinforced the need for better trading strategies by both sellers and buyers to limit the exposure to losses. Accordingly, this paper proposes an electricity trading strategy based on a mid-term forecast of the average spot price and a risk premium analysis based on this forecast. This strategy can help traders (buyers and sellers) decide whether to trade in the futures market (of varying monthly maturity) or to wait and trade in the spot market. The forecast model consists of an Artificial Neural Network trained with the Long Short Term Memory architecture to predict the average monthly spot prices, using only market price-related data as input variables. Statistical analysis verified the correlation and dependency between variables. The forecast model was trained, validated and tested with price data from the Iberian Electricity Market (MIBEL), in particular the Spanish zone, between January 2015 and August 2019. The last year of this period was reserved for testing the performance of the proposed forecast model and trading strategy. For comparison purposes, the results of a forecasting model trained with the Extreme Learning Machine over the same period are also presented. In addition, the forecasted value of the average monthly spot price was used to perform a risk premium analysis. The results were promising, as they indicated benefits for traders adopting the proposed trading strategy, proving the potential of the forecast model and the risk premium analysis based on this forecast.
- Fractal Patch Antenna based on Crystal Photonic applied to Intelligent Transportation Systems in the 40 GHz Millimeter WavebandPublication . Bagheri, Nila; Khan, Bahram; Teixeira, Emanuel; Velez, Fernando J.5G (and beyond) has very high bandwidth, short latency, better quality of service, and the right amount of capacity. Technological breakthroughs in mobile communication systems user equipments operating in the millimeter wavebands imply a high gain to compensate the effect of path loss. In this work, a novel photonic crystal-based microstrip patch antenna array with high gain is designed to be used in the next generation intelligent transportation ssytems, e.g., V2X, and other exciting applications. The Photonic Band Gap (PBG) structure and Finite Element Method were considered. By using the High Frequency Structure Simulation (HFSS) software, a fractal microstrip patch antenna operating in the U-band of the electromagnetic spectrum is conceived and modeled on a two-dimensional photonic crystal. The use of the PBG structure improves the antenna’s gain and bandwidth, while the antenna’s fractal form decreases its size and improves its input impedance. The operational frequency range is 41.72-45.12 GHz with a resonant band centered at 43.26 GHz. The proposed antenna is comprised of a 0.45 mm thick copper ground plane, a 0.9 mm thick FR-4 epoxy substrate with a relative transmittance of 4.4, and a 0.45 mm thick copper antenna patch. The achieved frequency band gain is 8.95 dBi.