Browsing by Issue Date, starting with "2021-01"
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- Coastline evolution of the Portuguese south eastern coast: a high-resolution approach in a 65 years’ time-windowPublication . Nave, Silvia; Rebêlo, LuísAbstract. The coast, as the interface between land and sea, is a highly dynamic area, endangered by erosion and flooding, particularly at times of sea-level rise. At the present context of climate change, the use of scientific knowledge to understand coastal dynamics and coastal evolution assessment through time is essential to find a suitable management response for a successful adaptive coastal governance. It is proposed that the obtained high-resolution and long-term coastline change dataset is of crucial impor tance to improve the knowledge on mesoscale evolution of the Portuguese south-eastern coast, from Ancão to Vila Real de Santo António (VRSA), a 55 km long coastal stretch. The evolutionary trend, from 1950 to 2015, points to a general seaward progradation at the western (Barreta island) and eastern (Cacela peninsula – VRSA) sectors, and mostly an erosional trend at the central barrier island system (Culatra, Tavira and Cabanas islands). Moreover, a considerable average landward displacement of approximately 130 m is observed at Cabanas island. Regarding overall coastline movement, seaward displacement prevails, with a prograding coastline occupying approximately 54% of the studied sector even though this is mostly associated with human intervention on the coast. The exception is the Manta Rota - Monte Gordo sector where accumulation is likely related to natural processes. Considering the significant influence man-made interventions have had on the coastline evolution, it is believed that the natural evolutionary pattern would point to an overall erosional trend in the islands sector and a progradational trend from Manta Rota to VRSA beach.
- Decarbonization of electricity systems in Europe: market design challengesPublication . Strbac, Goran; Papadaskalopoulos, Dimitrios; Chrysanthopoulos, Nikolaos; Estanqueiro, Ana; Algarvio, Hugo; Lopes, Fernando; Vries, Laurens de; Morales-España, Germán; Sijm, Jos; Hernandez-Serna, Ricardo; Kiviluoma, Juha; Helistö, NiinaABSTRACT: Driven by climate change concerns, Europe has taken significant initiatives toward the decarbonization of its energy system. The European Commission (EC) has set targets for 2030 to achieve at least 40% reduction in greenhouse gas emissions with respect to the 1990 baseline level and cover at least 32% of the total energy consumption in the European Union (EU) through renewable energy sources, predominantly wind and solar generation. However, these technologies are inherently characterized by high variability, limited predictability and controllability, and lack of inertia, significantly increasing the balancing requirements of the system with respect to historical levels. The flexibility burden is currently carried by flexible fossil-fueled conventional generators (mainly gas), which are required to produce significantly less energy (as low operating cost and CO2-free renewable and nuclear generation are prioritized in the merit order) and operate part loaded with frequent startup and shut-down cycles, with devastating effects on their cost efficiency.
- Permian stratigraphy and palynology of the Lower Karoo Group in Mozambique: a 2020 perspectivePublication . Lopes, Gilda; Pereira, Zélia; Fernandes, Paulo; Marques, João; Mendes, Márcia; Götz, Annette E.ABSTRACT: In the past decade, the increase in the number of palynological works in Mozambique documents the significance of palynology in dating the late Palaeozoic basins in this region of southwestern Gondwana. The new information gained mainly from the study of the Moatize-Minj ova Coal Basin is the basis for a better understanding of the regional biostratigraphy, as well as of palaeoenvironmental and palaeoclimatic conditions during the Permian. Here we provide a review on the Permian palynostratigraphy and its implications for lithostratigraphic correlation of Lower Karoo basins in Mozambique. The new biostratigraphic information leads to the conclusion that an age update for the lithostratigraphic units established for the Lower Karoo in Mozambique (Virzi, Moatize, and Matinde formations) is most needed. The Cisuralian palynological association in Mozambique is characterized by long-range taxa recorded since the middle Cisuralian (Sakmarian to Artinskian) (Alisporites spp., Cannanoropollis spp., Horriditriletes spp., Laevigatosporites spp., Potonieisporites spp., Protohaploxypinus spp.). Several first occurrences are also recorded in the late Cisuralian (Kungurian) (e. g., Cirratriradites africanensis, Marsupipollenites triradiatus, and Vittatina spp.). The Guadalupian association is mainly characterized by taxa that extend their range since the Cisuralian (e. g., Alisporites spp., Cirratriradites africanensis, Guttulapollenites hannonicus, Horriditriletes ramosus, Kraeuselisporites enormis, Lueckisporites virkkiae, Limitisporites monstruosus, Marsupipollenites striatus, M. triradiatus, Pakhapites fusus, Platysaccus papilionis, Thymospora pseudothiessenii, and Weylandites lucifer), with only few first occurrences (Lueckisporites virkkiae, Striatopodocarpites cancellatus, and S. fusus) and last occurrences (Cirratriradites africanensis, Limitisporites monstruosos) being recorded. The Lopingian palynological association includes most of the taxa described for the Guadalupian. In contrast, Corisaccites alutas, Indotriradites niger, Klausipollenites schaubergeri, Lunatisporites pellucidus, Osmundacidites senectus, Polypodiisporites spp., P. mutabilis, and Protohaploxypinus microcorpus are recorded for the first time. Indication of the proximity to the Permian-Triassic Boundary is supported by the occurrence of Klausipollenites schaubergeri, Protohaploxypinus microcorpus, and Osmundacidites senectus in the upper part of the Matinde Formation. Based on the palynological data, the oldest rock unit, the Virzi Formation, was deposited in the Permian (middle Cisuralian), and no older sedimentary rocks are currently known for the Lower Karoo Group in Mozambique. The palynological associations described also indicate that the Authors' deposition of the Moatize Formation occurred from the middle Cisuralian to the latest Guadalupian/early Lopingian, whilst the deposition of the Matinde Formation lasted from the late Guadalupian to the latest Lopingian. Thus, the boundary between both formations is assumed to be diachronous.
- The effects of mechanical alloying on the physical and thermal properties of CuCrFeTiV alloyPublication . Antão, Francisco; Dias, Marta; Correia, J.B.; Galatanu, Andrei; Galatanu, M.; Mardolcar, U. V.; Myakush, A.; Cruz, M. M.; Casaca, António; Silva, R.C. da; Alves, E.ABSTRACT: The present work reports the production and key properties of the CuCrFeTiV high entropy alloy synthetized mechanical alloying and spark plasma sintering. The milled powders and the as-sintered samples were analysed through scanning electron microscopy, coupled with energy dispersive X-ray spectroscopy and particle induced X-ray emission. Magnetic properties together with electrical resistivity, thermal conductivity, specific heat differential thermal analysis were also evaluated on the consolidated samples. The powders reveal an increasing content in iron as the millings are prolonged up to 20 h. The elemental composition of the sintered alloy, determined through particle induced X-ray emission, confirms the final composition after mechanical alloying with an increase of iron and a decrease in the remaining elements. Furthermore, although the alloy presents electrical resistivity typical of a high entropy alloy, a ferromagnetic behaviour was found, consistently with major Fe content as detected in prior observations. Finally, thermal measurements show that this CuCrFeTiV entropy alloy possesses thermal properties suitable for its potential use as thermal barriers.
- Geologia e geocronologia U-Pb SHRIMP do ortognaisse Caiongo – domínio São José Campestre, província Borborema, nordeste do BrasilPublication . Dáttoli, Luan; Oliveira, Saulo; Cunha, A.; Matos Arouca Júnior, Ramon; Rocha, D.O Ortognaisse Caiongo faz parte do contexto geológico da porção norte da Província Borborema, mais precisamente no Domínio São José do Campestre. Trata-se de um corpo de formato sigmoidal, alojado entre as Zonas de Cisalhamento Picuí – João Câmara e Lajes-Pintadas com cerca de 44 km2 de área aflorante. Suas fácies possuem textura facoidal, e composição variando entre sienogranítica a álcali-feldspato granítica. São rochas leucocráticas a mesocráticas, com feldspatos potássicos que chegam a 5 cm. Geoquimicamente essas rochas apresentam composição metaluminosa e shoshonítica, e concentração de elementos traços semelhantes aos encontrados em granitoides do tipo A. Possui idade de cristalização do protólito paleoproterozoico (2,223 ± 32 Ma). O εNd (t) de -0,25, além de sua idade TDM de 2,430 Ma, sugere alguma contaminação crustal na formação do protólito desta rocha.
- Geology of the recently discovered massive and stockwork sulphide mineralization at Semblana, Rosa Magra and Monte Branco, Neves–Corvo mine region, Iberian Pyrite Belt, PortugalPublication . Pereira, Zélia; Matos, João Xavier; Solá, A. Rita; Batista, Maria Joao; Salgueiro, Rute; Rosa, Carlos; Albardeiro, Luis; Mendes, Márcia; Morais, Igor; de Oliveira, Daniel Pipa Soares; Pacheco, Nelson; Araújo, Vítor; Castelo Branco, José M.; Neto, Rodrigo; Lains Amaral, João; Inverno, Carlos; Oliveira, José T.Abstract The recently discovered massive and stockwork sulphide mineralization of Semblana-Rosa Magra and Monte Branco, situated ESE of the Neves–Corvo volcanogenic massive sulphide (VMS) deposit in the Iberian Pyrite Belt (IPB) is presented. Geological setting and tectonic model is discussed based on proxies such as palynostratigraphy and U–Pb zircon geochronology. The mineralization is found within the IPB Volcano-Sedimentary Complex (VSC) Lower sequence, which includes felsic volcanic rocks (rhyolites) with U–Pb ages in zircons of 359.6 ± 1.6 Ma, and black shales of the Neves Formation of late Strunian age. Massive sulphides are enveloped by these shales, implying that felsic volcanism, mineralization and shale sedimentation are essentially coeval. This circumstance is considered highly prospective, as it represents an important exploration vector to target VMS mineralization across the IPB, in areas where the Lower VSC sequence is present. The Upper VSC sequence, with siliciclastic and volcanogenic sedimentary rocks of middle–late Visean age, shows no massive mineralization but a late Tournaisian (350.9 ± 2.3 Ma) volcanism with disseminated sulphides was also identified. Nevertheless, stratigraphic palynological gaps were found within the Strunian and in the Tournaisian sediments, between the Lower and Upper VSC sequences, reflecting probable erosion and uplift mechanisms linked with extensional tectonics. The Semblana and Monte Branco deposits and the Rosa Magra stockwork are enclosed by tectonic sheets that dismembered the VSC sequence in a fold-and-thrust tectonic complex, characteristic of the NE Neves–Corvo region. The methodologies used allow a geological comparison between Neves–Corvo and other IPB mine regions such as Lousal–Caveira, Herrerias, Tharsis and Aznalcollar.
- Assessment of the effect of autohydrolysis treatment in banana’s pseudostem pulpPublication . Díaz, Sara; Ortega, Zaida; Benítez Vega, Antonio Nizardo; Costa, Diogo; Carvalheiro, Florbela; Fernandes, M. C.; Duarte, Luís C.ABSTRACT: Banana's pseudostem pulp (BPP) is a potential by-product obtained in the mechanical fiber extraction of banana's pseudostem. Its chemical characterization revealed to have an interesting composition, with a high polysaccharides content and low content in lignin, which makes it particularly relevant for the biorefinery's biochemical platform. Autohydrolysis pretreatment, studied under isothermal (140 degrees C) and non-isothermal conditions (140-220 degrees C), yielded oligosaccharides, mainly gluco-oligosaccharides, as the main soluble products. The highest oligosaccharides production (24 g/100 g raw material) was obtained at a severity factor of 2.3. Autohydrolysis pretreatment effectively disrupted the structure of the material, inducing an improvement of the enzymatic digestibility from 73% for the raw material up to 90% for the most severe conditions. Two stage autohydrolysis, with increasing severity, was also studied, allowing to obtain a higher amount of oligosaccharides (32 g/100 g raw material) and higher digestibility of the remaining solid (up to 97%).