4161 research outputs found
Sort by
The materials of historical monuments: characterisation of the mortars of the Roman aqueduct of Zaghouan-Carthage
No full textABSTRACT: The Zaghouan-Carthage Roman aqueduct was the largest built by the Roman Empire at the time, and its archaeological remains bear witness to the excellence of Roman construction. Its importance over the centuries makes it a unique case study for characterising the different types of mortar used. This work aims to study these materials, considering their functions, especially as structural elements or as render, to relate the chemical and mineralogical characteristics observed to both the function and historical context of the monument. Using a multi-analytical approach, the preservation of samples was prioritised whenever possible. The results indicate that mortars with a structural function have higher silicon contents than those used as render. In the case of water conduit coatings, the mortars were formulated with ground ceramics to develop hydraulic properties and ensure the waterproofing material. However, it was not possible to identify a characteristic pattern related to the historical construction periods
Using the electrical resistivity method in a fractured granitic environment : approaches and pitfalls
No full textRESUMO: O método de resistividade eléctrica teve, durante um longo período do séc. XX, um amplo uso nas suas variantes de sondagem eléctrica e perfil de resistividade. Mais recentemente, conheceu uma evolução no sentido da utilização de dispositivos com eléctrodos múltiplos, com possibilidades de aquisição 2D e 3D. A interpretação de sondagens eléctricas esteve desde sempre associada basicamente a um modelo de terreno com camadas horizontais; em terrenos graníticos, esta situação pode condicionar a forma como o terreno é concebido, o que pode levar a interpretações desfasadas da realidade. Nos casos considerados, numa zona de falha em granitos, a curva de sondagem obtida tem um ajustamento mais próximo da realidade usando um modelo com limites verticais. Numa aquisição 2D, num terreno granítico com uma estruturação quer horizontal quer vertical bastante marcada, a secção obtida com Wenner-Schlumberger apresenta um artefacto, tendo o dipolo-dipolo mostrado uma melhor capacidade de diferenciação do terreno.ABSTRACT: For most of the last century, the electrical resistivity method was used in the two basic techniques of the electrical resistivity sounding and the resistivity profiling. Further development led to the multielectrode devices now in use, with 2D and 3D capabilities. Traditionally, the electrical resistivity sounding requires for its interpretation the assumption of a stratified earth parallel to the surface; the translation of such an earth to the situation of a granitic terrain may affect the way in which the terrain is conceived. Specific situations considered in this work concern a granitic terrain in centre-northern Portugal. In such a geological context, the sounding curve obtained over a 130 m wide fault zone is better interpreted using a model with vertical limits. 2D acquisition and interpretation techniques have brought the capability to overcome the 1D limitations of electrical soundings and to better address terrain lateral heterogeneity; however, even in a 2D survey some issues may arise. A 235 m long 2D acquisition with Wenner-Schlumberger (WS) and dipole-dipole (DD) arrays (in the same place and in sequence) led to inverse model resistivity sections with partially different results: a vertical discontinuity centred at 150 m in the DD section is displaced to 120 m in the WS section. To gain some insight on this issue, apparent resistivity pseudo-sections with WS and DD arrays were obtained from a dike and a bloc models with the same resistivity. WS results for these models put in evidence higher overall apparent resistivity for the bloc case, but apparent resistivity data structure is basically the same for the two models. In the DD case, even though the apparent resistivity sections have a similar geometry, data structure is different: the apparent resistivities in the lower part of the sections,
compared to the ones in the side areas, are, respectively, similar/significantly lower for the bloc/dike cases; and the observable oblique bands show an almost homogeneous symmetric cross-section (bloc) but an heterogeneous character and asymmetric cross-section (dike). A final situation, concerning a field case over a simpler structured horizontally stratified terrain (alluvium) puts in evidence that the inversion algorithm creates a high/low resistivity pair in the zone concerning a surface high apparent resistivity patch. In the above concerned 2D survey, the combined effect data structure/inversion algorithm led to the creation of an artifact in the case of the WS section; the dipole-dipole showed a better capacity for terrain differentiation
Editorial: The biorefineries and application of green technologies for recovering bioactive compounds from microalgae
No full textABSTRACT: Microalgae are attracting growing scientific and industrial interest as a renewable and versatile source of high-value bioactive compounds, including pigments, fatty acids, proteins, and antioxidants. Their rapid growth, ability to adapt to extreme conditions, and rich biochemical composition make them a promising resource for sustainable development across a range of applications. From cosmetics to food supplements, their potential spans multiple industries. Still, the considerable gap between encouraging laboratory research and commercially viable production remains. One of the major challenges lies in developing methods for extracting and preserving these compounds in ways that are both efficient and environmentally responsible
Renewable Energy Production in the Mediterranean: Exploring the Potential for Offshore Wind Development
No full textABSTRACT: This study presents an overview of the current state of the Maritime Spatial Planning among the Mediterranean countries, explores the previous studies on evaluating the offshore wind potential of the Mediterranean region along with the criteria for suitable site selection. Based on a review of the current state of offshore renewable energy, the potential locations offshore wind will be explored for the Mediterranean coastline case study area. The research concludes with a set of critical considerations related to the need for proper synergies establishment among different stakeholders and for cultivating social acceptance and community engagement. The analysis aims to support decision-makers evaluating the potential of the Mediterranean coastal area in supporting the energy transition goal.COST Action CA20109 Modenerlands, supported by COST (European Cooperation in Science and Technology
Simulation of Surface Segregation in Nanoparticles of Pt-Pd Alloys
No full textABSTRACT: Platinum (Pt) and palladium (Pd) are crucial in hydrogen energy technologies, especially in fuel cells, due to their high catalytic activity and chemical stability. Pt-Pd nanoparticles, produced through various methods, enhance catalytic performance based on their size, shape, and composition. These nanocatalysts excel in direct methanol fuel cells (DMFCs) and direct ethanol fuel cells (DEFCs) by promoting alcohol oxidation and reducing CO poisoning. Pt-Pd catalysts are also being explored for their oxygen reduction reaction (ORR) on the cathodic side of fuel cells, showing higher activity and stability than pure platinum. Molecular dynamics (MD) simulations have been conducted to understand the structural and surface energy effects of PdPt nanoparticles, revealing phase separation and chemical ordering, which are critical for optimizing these catalysts. Pd migration to the surface layer in Pt-Pd alloys minimizes the overall potential energy through the formation of Pd surface monolayers and Pt-Pd bonds, leading to a lower surface energy for intermediate compositions compared to that of the pure elements. The potential energy, calculated from MD simulations, increases with a decreasing particle size due to surface creation, indicating higher reactivity for smaller particles. A general contraction of the average distance to the nearest neighbour atoms was determined for the top surface layers within the nanoparticles. This research highlights the significant impact of Pd segregation on the structural and surface energy properties of Pt-Pd nanoparticles. The formation of Pd monolayers and the resulting core-shell structures influence the catalytic activity and stability of these nanoparticles, with smaller particles exhibiting higher surface energy and reactivity. These findings provide insights into the design and optimization of Pt-Pd nanocatalysts for various applications.LNEG, Laboratório Nacional de Energia e Geologia, Portuga
Análise gemológica das origens do rubi: um estudo de caso
No full textABSTRACT: Gemstones are substances of natural, artificial or synthetic origin, which due to their hardness, rarity, uniqueness, diaphaneity and beauty are used as adornments. In the market, ruby is the second most expensive type of gemstone. Depending on its size, it can exceed the value of the diamond, besides being the most valuable colored gem in the market. It is a variety of the mineral corundum, just like sapphire, and it is a form of crystallized alumina (Al2O3) and the responsible for its red color is chromium. There are deposits in many different places around the world, being common the practice of speculating the origin of the ruby based on the shade of red. Provenance strongly impacts the commercial value of the gem. Several faceted rubies were donated to the Federal University of Ceará. This project aims to discover from what regions (countries) the donated rubies are coming, using gemological characteristics. To establish the origin of the specimen collection, the following methods and equipment were used: bibliographic research about rubies characteristics, refractometer to measure refractive indexes, dichroscope for pleochroism analysis, ultraviolet lamp (UV) for determination of fluorescence, and especially the gemological (stereoscopic) microscope to study the types of inclusions in transparent to translucent rubies. Using the methods cited, it was possible to produce, successfully, the gemological characterization of the specimens and deduce, based on strong evidence, what was the geographic origin of the studied specimens. Through microscopy it was deduced that all the faceted stones are natural and the whole collection include stones from the following countries: Burma, Thailand, Pakistan, Sri Lanka and Tanzania. Results are gathered systematizing bibliographic data and analytical results in order to identify the country of origin of the rubies.RESUMO: Gemas são substâncias de origem natural, sintética ou artificial que devido a sua dureza, raridade, singularidade, diafaneidade e beleza são utilizadas como adorno. No mercado, o rubi é a segunda espécie de gema mais cara. Em idêntico tamanho pode superar o valor do diamante, além de ser a gema corada mais valiosa para o mercado. Trata-se de uma variedade do mineral corindo. Tal como a safira, é simplesmente alumina (Al2O3) cristalizada no sistema trigonal e o elemento cromóforo invocado para a aquisição da sua cor vermelha é o crómio. Existem jazidas em diferentes lugares do mundo, sendo comum a prática de especular sobre a procedência dos rubis com base na tonalidade de vermelho que ostentam. A proveniência influência o valor comercial da gema. Este estudo visa estabelecer a origem geográfica dos rubis lapidados doados à Universidade Federal do Ceará, utilizando informação bibliográfica e caraterísticas gemológicas dos diferentes espécimes. Para estabelecer a procedência dos exemplares foram utilizados: bibliografia referente às caraterísticas dos rubis e equipamentos de análise tais como, refratómetro para leitura do índice de refração, dicroscópio para análise do pleocroismo, luz ultravioleta (UV) para estudo da fluorescência e principalmente o microscópio gemológico para estudo dos tipos de inclusões nos rubis. Utilizando os métodos citados, sistematizou-se a caraterização gemológica dos exemplares, procurando deduzir a sua procedência geográfica. Com base na análise microscópica concluiu-se que todos os exemplares são naturais e que a coleção inclui exemplares oriundos dos seguintes países: Birmânia, Paquistão, Sri Lanka, Tailândia e Tanzânia. Em síntese final, numa tabela reúnem-se dados bibliográficos e resultados analíticos relativos às amostras estudadas. Essa tabela também identifica os países de onde provêm os rubis
Sustainability assessment of collagen extraction from fish skins: A comparative life cycle assessment of conventional and NADES-enhanced processes
No full textABSTRACT: Collagen from blue shark skins offers a promising solution to utilize fishery by-products, reducing waste and improving resource efficiency. This study develops green chemistry-based extraction processes to minimize reliance on traditional chemical methods and lower environmental impacts, prioritizing sustainability and circularity. Two methods for collagen extraction are compared: a conventional alkaline-acid process and an innovative approach using natural deep eutectic solvents (NADES). Process simulations were conducted using SuperPro Designer software for the annual production of 500 kg of pure extracted collagen, followed by life cycle assessment (LCA) using SimaPro software and the Ecoinvent database, applying the Environmental Footprint (EF) method. For 1 kg of pure marine collagen from fish skin residues, defined as the Functional Unit, the conventional approach yielded a single-score impact of 48.1 mPt, while the NADES method achieved 41.5 mPt. Subsystem analysis reveals that, in the conventional method, the extraction and purification stages account for most of the environmental impact (43 % and 45 %, respectively). In contrast, the NADES method attributed 94 % of its total environmental impact to extraction stage, primarily due to NADES component production (citric acid, xylitol). Uncertainty analysis suggests that conclusions regarding impact reduction should be drawn with caution due to the environmental impact variability of considered inputs. Nevertheless, the mathematical model underscores the potential of the NADES method to reduce the environmental impact and promote more sustainable bioprocessing. This work offers valuable insights into the life cycle assessment of large-scale bioprocesses using green chemistry, providing a tool for optimization and environmental impact screening.N/
Development and implementation of the data model of the Geological Digital Map of Portugal
No full textRESUMO: O Laboratório Nacional de Energia e Geologia (LNEG) visa disponibilizar a Carta Geológica Digital de Portugal através do seu geoPortal. Este produto tem por base um modelo de dados (MD) que implementa o catálogo hierárquico das unidades geológicas cartografadas em Portugal continental. O MD foi implementado na infraestrutura de dados espaciais (IDE) e integrado com o modelo INSPIRE. A Geodatabase obtida compila a cartografia geológica existente a várias escalas e suporta a harmonização das unidades geológicas, utilizando como base uma legenda comum, contribuindo para uma cartografia geológica contínua. Este artigo descreve as características da Geodatabase e aspetos relacionados com a sua implementação. A infraestrutura obtida possibilita: (i) harmonizar as inconsistências na representação das unidades cartografadas entre cartas geológicas adjacentes; (ii) harmonizar as inconsistências a diferentes escalas de representação; (iii) responder aos requisitos INSPIRE. Permitiu também identificar problemas e incongruências cartográficas e consequente planeamento mais efetivo e eficaz do trabalho de cartografia geológica.ABSTRACT: The Portuguese Geological Survey (LNEG) aims to provide the Geological Digital Map of Portugal (online version) through its geo-Portal. This product is supported by a data model (DM) that implements a hierarchical catalogue of lithostratigraphic and lithodemic units. The DM is linked to an INSPIRE compliant geodatabase. The developed geological model provides a synthesis of published maps, with ongoing steps toward harmonisation and interoperability. This paper describes several aspects of the database implementation and its characteristics. The obtained database allows to: (i) produce a seamless 2D geological map; (ii) solve the inconsistencies that become visible when changing the scale of representation (from 1:25 000 to 1:200 000); (iii) fulfill the INSPIRE requirements. It also highlights some cartographic problems that require further research and field survey to be solved.Projeto GeoON - Informação Geológica e Mineira Online (POCI-05-5762-FSE-000426)
Acumulação potencial de elementos estratégicos em barragens mineiras : da remineração à reabilitação
No full textABSTRACT: Raw materials, from oil to industrial minerals, are essential to the efficient functioning of the world economy. However, the extraction of base metals, for example, allowed the mobilization and accumulation of large amounts of reactive wastes, triggering critical environmental problems. The Iberian Pyrite Belt, one of the largest metallogenetic provinces in the world, is an example of this, as it presents numerous abandoned mining exploitations that were closed without or with inadequate environmental remediation. However, Europe is particularly vulnerable, as it depends on importing these metals. In this context, the present study addresses the theme of remining, assuming premises of rehabilitation and circular economy. The work focused on one of the most Portuguese paradigmatic mining complexes - the São Domingos mine. The methodological protocol was based on drilling to characterize stream sediments. The results revealed an estimate of the economic potential of accumulated sediments, offering a hopeful and optimistic outlook. These suggest reusing critical elements, such as Ag and Sc. The information in this research aims to help the competent authorities build a recovery strategy based on the valorization of resources centered on the circular economy.RESUMO: As matérias-primas, desde o petróleo aos minerais industriais, apresentam-se como essenciais ao funcionamento eficiente da economia mundial. Contudo, a extração de metais básicos, por exemplo, permitiu a mobilização e acumulação de grandes quantidades de rejeitos reativos, desencadeando sérios problemas ambientais. A Faixa Piritosa Ibérica, uma das maiores províncias metalogenéticas do mundo, é exemplo disso, pois apresenta inúmeras antigas explorações mineiras abandonadas, que foram encerradas sem ou com inadequada remediação ambiental. No entanto, a Europa está numa posição particularmente vulnerável, pois encontra-se dependente da importação desses metais. É neste contexto que o presente estudo aborda a temática da remineração, assumindo premissas de reabilitação e economia circular. O trabalho incidiu sobre um dos complexos mineiros portugueses mais paradigmáticos - a mina de São Domingos. O protocolo metodológico baseou-se na caracterização de sedimentos fluviais, através de sondagens. Os resultados revelaram uma estimativa do potencial económico dos sedimentos acumulados. Estes sugerem a possibilidade de reaproveitamento de elementos críticos, como a Ag e o Sc. As
informações contidas nesta investigação visam auxiliar as autoridades competentes a construir uma estratégia de recuperação baseada na valorização de recursos, assente na economia circular
Avaliação da vulnerabilidade da águas subterrânea em aquíferos fraturados de regiões áridas
No full textABSTRACT: Groundwater is the main water source of semi-arid regions. In these areas, it’s crucial to establish appropriate strategies for evaluating the vulnerability of aquifer systems and their potential exposure to contamination, especially in fractured aquifers, which possess a naturally high vulnerability. The aquifer system from Gabès region, southeastern Tunisia, is a fractured medium exposed to intensive agricultural activities with excessive fertilizer use. This study introduces a novel vulnerability index by incorporating the contribution of medium into the DRASTIC vulnerability method. The obtained results reveal the presence of zones with different degrees of vulnerability: very low (9.6%), low (15%), moderate (22.9%), high (21.5%), and very high vulnerability (31%). The spatial distribution of this new vulnerability index proves to be a valuable tool for effective groundwater management and the identification of suitable locations for new wells and boreholes in the region of Gabès.RESUMO: Os aquíferos constituem a principal fonte de água nas regiões semiáridas. Nestas regiões é fundamental a definição de estratégias adequadas na avaliação da vulnerabilidade dos sistemas aquíferos e possível exposição a contaminação, em particular para aquíferos fraturados, face à sua elevada vulnerabilidade natural. O sistema aquífero da região de Gabes, sudeste da Tunísia, é um meio fraturado exposto a atividades agrícolas intensivas com uso excessivo de fertilizantes. Com este trabalho é apresentado um novo índice de vulnerabilidade, resultante da introdução da variável relativa à fracturação do meio no índice de vulnerabilidade DRASTIC. Os resultados obtidos mostram a ocorrência de zonas de vulnerabilidade: muito baixa (9.6%), baixa (15%), moderada (22.9%), elevada (21.5%) a muito elevada (31%). A distribuição espacial deste novo índice de vulnerabilidade é uma importante ferramenta para a gestão adequada da água subterrânea e na localização de novos de poços e furos na região de Gabès