Matérias-primas da plataforma do Mondego para cerâmica

Doutoramento em GeociênciasO presente trabalho divulga os resultados dos estudos levados a efeito nas matérias-primas argilosas que se integram tipologicamente na argila comum, ocorrentes na designada Plataforma do Mondego, Centro de Portugal, na região entre Miranda do Corvo, a SW, e Tábua, a NE. Para tal realizou-se a cartografia superficial dos sedimentos continentais do Cretácico e do Terciário, aí preservados, estabeleceram-se as colunas sedimentares, a nível regional e a nível local, nas áreas de maior potencial reconhecido e, caracterizaram-se as matérias-primas argilosas amostradas, em termos de composição, textura e aptidão cerâmica, objectivando a definição das zonas das jazidas com maior interesse industrial. A informação obtida e compilada, relativa ao caulino e ao feldspato é também apresentada, com vista a uma percepção da potencialidade destas matériasprimas cerâmicas ocorrentes na área. O estudo de caracterização dos materiais argilosos investigados teve como base 53 amostras obtidas em seis regiões da Plataforma do Mondego aqui definidas por motivo de organização do trabalho, segundo os critérios geográfico e geotectónico. As formações de Côja e de Campelo, do Terciário, constituem as unidades onde ocorrem litótipos produtivos, em termos de matéria-prima para a Cerâmica de Barro Vermelho ou Cerâmica de Construção. Relativamente às características texturais e composicionais, em síntese, apresentam-se os factos relevantes seguintes: A matéria-prima argilosa existente na área estudada materializa, granulometricamente, na maioria das amostras, silte, caindo os níveis amostrados com maior percentagem de argila, no domínio do silte argiloso. O défice em fracção argila implica limitações quanto à possibilidade de diversificação de produtos cerâmicos fabricados com estas matérias-primas tal-qual. Os diferentes métodos analíticos utilizados na caracterização mineralógica dos materiais amostrados confirmaram uma composição em termos dos minerais argilosos, consistindo de ilite/mica (em geral, o mais abundante), caulinite e esmectite, interestratificados e clorite. Os minerais não argilosos são quartzo (predominante), feldspato (sobretudo potássico) e hematite, com uma representação baixa. A mineralogia da fracção inferior a 2μm das amostras, não difere das amostras totais, salvo no teor mais elevado dos minerais argilosos e acentuada redução dos minerais não argilosos. Os resultados da análise química por fluorescência de raios X das amostras integrais correlacionam-se com as características mineralógicas observadas através das técnicas analíticas utilizadas. No respeitante às propriedades e comportamento cerâmico verifica-se: Os parâmetros relacionados com a plasticidade indicam que parte das pastas elaboradas com estes materiais argilosos têm uma trabalhabilidade aceitável, mas existem problemas de conformação e acentuada retracção num número significativo de amostras, devido à elevada plasticidade da maioria das amostras. A extrusão é satisfatória a óptima. A RMF e a retracção em seco assumem valores, respectivamente, moderados a baixos e moderados, embora seja necessário ter em conta o procedimento de extrusão dos provetes, sem dispositivo de vácuo. Todas as amostras foram sujeitas a cozedura a 900ºC, e um conjunto seleccionado foi cozido a 1000ºC e a 1100ºC. As fases mineralógicas ocorrentes após cozeduras a 900ºC e 1100ºC foram identificadas num conjunto de amostras, tendo-se evidenciado a coerência dessas fases, com a mineralogia das amostras em seco. Após cozedura a 900ºC, os valores de RMF das amostras satisfazem geralmente os valores mínimos, exigidos para o fabrico de tijolo, abobadilha e, com alguma frequência, de telha, como já se verificava com os valores daquela propriedade em seco. Os valores de retracção seco-cozido são em geral, modestos. A capacidade de absorção de água é maioritariamente elevada. A formação de vidro, sobretudo, condiciona o comportamento destas propriedades por cozedura dos provetes a 1000ºC e a 1100ºC. A coloração predominante em cru das matérias-primas argilosas amostradas é amarelo acastanhado a castanho avermelhado. Após cozedura a 900ºC, há um acentuado escurecimento e incremento no grau de vermelho. As cozeduras a 1000ºC e 1100ºC promovem escurecimento gradual, com ligeira influência na cor. O comportamento dos provetes após as cozeduras cerâmicas revelou-se homogéneo a cada uma das respectivas temperaturas, não se registando também defeitos significativos, nem eflorescências. A análise das amostras em termos composicionais e tecnológicos permitiu destacar as principais características e aspectos distintivos das matériasprimas, nas diferentes regiões definidas objectivando as diferentes potencialidades cerâmicas. Nesta abordagem comparativa foram consideradas só as amostras dos campos silte e silte arenoso, por serem aquelas com maior interesse para a Cerâmica de Construção. Nas colunas sedimentares das regiões de Tábua e Santa Quitéria constata-se a ocorrência de dois ritmos de sedimentação, que embora assumam características específicas em cada região, têm aspectos composicionais e tecnológicos em comum, traduzindo melhor aptidão cerâmica os ritmos inferiores. A conjugação da cartografia realizada com os estudos laboratoriais permite concluir que as regiões de Tábua e de Santa Quitéria serão as que têm maior potencial por explorar, em matéria-prima para Cerâmica de Construção, apesar da primeira já ser intensamente explorada. Na região de Tábua, as amostras têm como fases mineralógicas principais ilite e quartzo na mesma proporção média (35%) e caulinite (média=19%) que regista enriquecimento significativo na fracção argila (média=38%). As argilas desta região registam a cor em cru mais vermelha e pH mais ácido observados. O ritmo de sedimentação inferior, com esmectite e interestratificados e ligeiramente menos quartzoso, apresenta melhores propriedades cerâmicas. A composição mineralógica média das amostras da região de Santa Quitéria é próxima daquela da região de Tábua, mas menos caulinítica, em especial na sequência inferior, na qual o teor médio de caulinite na fracção argila (7%) é o mais baixo observado. Na região de Côja – Arganil, a actividade extractiva é significativa na bacia de Côja. Aqui, a exploração de novas áreas potenciais é condicionada pela cobertura conglomerática e por estruturas tectónicas e não tectónicas relacionadas com comportamento plástico. Na restante área desta região, os recursos argilosos são penalizados por material areno-conglomerático. As amostras desta região distinguem-se das restantes a nível textural pela maior fracção areia e mineralogicamente pela presença de clorite, teor reduzido de caulinite e elevado de feldspato. As potencialidades em barro vermelho na região de Sanguinheda não serão significativas, pois a Formação de Côja é predominantemente arcósica e a Formação de Campelo pouco espessa e conglomerática. As argilas com melhor aptidão cerâmica foram amostradas na região de Miranda do Corvo – Lousã. Na composição, estas amostras são as que contêm maior fracção de argila, maior teor de ilite e caulinite e menor de argilas expansivas. Registam os melhores valores nas características tecnológicas, nomeadamente a RMF e absorção de água. A consistência dos grupos amostrais e ritmos definidos em termos composicionais e tecnológicos é corroborada pelas técnicas de análise estatística multivariada aplicadas, que os identificam. As condições de amostragem na região de Tábua, permitiram a elaboração de uma coluna tipológica, na qual, a partir de uma caracterização expedita de amostras é possível identificar a sua afinidade com os ritmos argilosos definidos e, consequentemente, a sua situação na coluna sedimentar regional e aptidão cerâmica. A cartografia dos recursos argilosos potenciais, elaborada à escala 1:25.000, constitui um dos objectivos principais deste trabalho e nela constam unidades litológicas, nas quais são diferenciadas unidades argilosas tendo também em consideração a tipologia e guias mineralógicos resultantes da caracterização das amostras. As características composicionais destas unidades denotam diferente aptidão cerâmica e, portanto, permitem salientar as zonas com maior interesse económico.The work presented herein discloses the results of the studies undertaken on the clay raw materials that typologically make up common clay, occurring in the usually named Mondego Platform, which is located in the region between Miranda do Corvo, SW, and Tábua, NE (Center region of Portugal). These studies encompassed superficial mapping of the continental sediments of the sedimentary deposits dated of Cretaceous and Tertiary and the description of the sedimentary columns, at both the regional and local scales in the areas of greater recognized potential; the sampled raw materials had been characterised in terms of composition, texture and ceramic aptitude in order to define the zones of the deposits with major industrial significance. The compiled and obtained information, relative to kaolin and feldspar is also presented, to gain an idea of the apparent potential of these ceramic raw materials in the area. The characterization of the investigated clay materials has been based upon 53 samples from six regions of the Mondego Platform herein defined for work organization purposes bearing in mind geographic and geotectonical criteria. The Tertiary Coja and Campelo formations comprise the units where potential lithotypes occur for red firing clays, used for structural clay products or Construction Ceramics. Relatively to the compositional characteristics, in summary, the following relevant facts are presented: The existing clay raw materials in the studied area materialize, in the majority of the samples, silt sized sediments; the sampled raw materials with higher clay percentage belong to the clayey silt domain. The clay fraction deficit implies limitations to the diversification possibility of ceramic products manufactured with these raw materials as they are. The diverse analytical methods used in the mineralogical characterization of the sampled materials confirmed a composition in terms of clay minerals, consisting of illite/mica (usually the most abundant), kaolinite and smectite, interstratified minerals and chlorite. The non clay minerals are quartz (predominant), feldspar (more frequently potash feldspar) and hematite in minor amounts. The mineralogy of the samples particle size fraction< 2μm, does not differ from the total samples, except for the higher amount of clay minerals and significant reduction of non clay minerals. The results of the chemical analysis of the total samples using X-ray fluorescence are correlated with the mineralogical characteristics obtained with the analytical techniques used. With regard to the ceramic properties and behavior, the following results apply: The parameters related with the plasticity indicate that part of the clay mixtures elaborated with these clay materials have an acceptable workability, but problems of conformation and significant shrinkage are observed in a considerable number of samples, due to the high plasticity of the majority of samples. The extrudability is satisfactory to excellent. The bending strength and the dry shrinkage assume values moderate to low, although it is necessary to consider that the studied probes were extruded without a vacuum device. All the samples had been fired at 900ºC, and an assemblage of samples was selected for firing at 1000ºC and 1100ºC. The high temperature mineralogical phases occurring after firing at 900ºC and 1100ºC had been identified in a set of samples, having themselves evidenced the coherence of these phases, with the mineralogy of the dry samples. After firing at 900ºC, the samples’ bending strength values satisfy the minimum generally required for the brick production; a few samples attain minimum bending strength values required for roofing tiles, corresponding with previously obtained dry values. The values of dry-firing shrinkage are in general, low. The water absorption usually is high. The glass formation, over all, conditions these properties’ behavior when probes are fired at 1000ºC and 1100ºC. The predominant raw color of the sampled clay raw materials grades from brownish yellow to reddish brown. After firing at 900ºC, there is an accentuated darkening and an increment in the red hues. Both firings at 1000ºC and 1100ºC bring gradual darkening, with a small influence in the colour. The probes’ behavior after firing is homogeneous at each one of the respective temperatures, revealing no significant flaws, nor efflorescence. The analysis of the samples in compositional and technological terms emphasizes the main characteristics and distinctive aspects of the raw materials in the different selected study areas regarding the different ceramic potential. In this comparative approach only silt and sandy silt samples had been considered because of their higher importance for Construction Ceramics. In the sedimentary columns of Tábua and Santa Quitéria regions the occurrence of two groups of sedimentary layers is shown that even though assuming specific characteristics in each region, they encompass common compositional and technological aspects proving that the ceramic aptitude of the lower layers is better. The combination of the mapping and laboratory studies carried through allows one to conclude that the regions of Tábua and Santa Quitéria are the areas with greater potential for exploration of clay raw materials for Construction Ceramics, although the former area is already being an established red clays extraction centre. In the Tábua region the samples have as main mineralogical phases illite and quartz in the same average ratio (35%) and kaolinite (average=19%), which has a significant enrichment in the clay fraction (average =38%). The clays in this region show the reddest raw colour and the lowest pH values observed. The group of lower sedimentary layers with smectite and interstratified clay minerals and slightly lower quartz content, present the best ceramic properties. The samples average mineralogical composition in the Santa Quitéria region is comparable to the one in the Tábua region but with less kaolinite content especially in the lower layer sequence in which the average kaolinite content in the fraction < 2μm (7%) is the lowest observed. In the Coja - Arganil region, the Coja basin is a significant red clays extraction centre. Here, the exploration of new potential areas is conditioned due to the conglomeratic cover and related tectonic and non-tectonic structures with a plastic behaviour. In the remaining area of this region, the clay resources are penalized by sandy and conglomeratic material. The samples of this region can be distinguished from the rest on a textural basis, a higher sand fraction content and, mineralogicaly, by the presence of chlorite, low kaolinite content and high feldspar content. The potential of red firing clays in the region of Sanguinheda is reduced, because the Coja Formation is predominantly arcosic and the Campelo Formation is thin and conglomeratic. Clays with better ceramic aptitude were sampled in the region of Miranda do Corvo - Lousã. These samples are characterised by a higher clay fraction percentage, illite and kaolinite contents and a minor content of expansive clay minerals. They present the best values in the technological characteristics, namely bending strength and water absorption. The consistency of the samples’ groups and layer sequences defined in compositional and technological terms are corroborated by the multivariate statistic analysis techniques applied, that identify those groups and sequences. The sampling in the region of Tábua, allowed the elaboration of a typological column, in which, from a brief characterization of samples it is possible to identify its affinity with the clay layer sequences defined and, consequently, its position in the regional sedimentary column and ceramic aptitude. The mapping of the potential clay resources, elaborated to the scale 1:25.000, represents one of this work’s main goals, where the defined lithological units encompass clay units which are differentiated also considering the typology and mineralogical guides’ resultant from the characterization of the samples. The compositional characteristics of these units denote different ceramic aptitude and, therefore, they allow pointing out the zones with higher economical potential

MACIÇOS GRANÍTICOS DE ESMOLFE E ANTAS - MATANÇA (PORTUGAL): RECONHECIMENTO, CARACTERIZAÇÃO E DEFINIÇÃO DE ÁREAS COM POTENCIALIDADE PARA EXPLORAÇÃO DE GRANITO ORNAMENTAL

O presente trabalho tem por objetivo o estudo de áreas com potencialidade para produção de pedra ornamental nos maciços graníticos de Esmolfe e Antas-Matança, na região Centro-Norte de Portugal. Os granitos estudados, tardi-hercínicos e de característica calco-alcalina, têm cor cinzenta azulada, granulação média e tendência levemente porfirítica. Apresentam acentuada homogeneidade mineralógica, textural e estrutural e escassos defeitos do ponto de vista ornamental, sendo a principal condicionante à atividade extrativa a fracturação. Procede-se à análise da informação colhida e tratamento estatístico dos dados de fracturação, visando ao conhecimento do estado de compartimentação dos maciços nos níveis superficiais, embora com as reservas inerentes à alietoriedade da rede de fracturação natural. No maciço de Esmolfe, a textura do granito é mais homogênea, apresentando uma granulação mais grosseira e cor mais clara do que o granito de Antas-Matança. Os espaçamentos dos sistemas de fracturas em ambos os maciços são maioritariamente moderados a amplos (1 a 6,25m). A atividade extrativa em Antas-Matança é ainda reduzida, enquanto em Esmolfe é intensa e sem planeamento. A proliferação exagerada de pedreiras, que raramente ultrapassam os níveis superficiais (2 a 3m de profundidade), sem atingir níveis mais promissores, causa um elevado impacto visual. Foram definidas cinco áreas potenciais para exploração de granito ornamental em Antas-Matança e quatro em Esmolfe. ESMOLFE AND ANTAS MATANÇA GRANITIC MASSIFS (PORTUGAL): GENERAL GEOLOGICAL SURFACE STUDY, CHARACTERISATION AND DEFINITION OF POTENTIAL AREAS FOR ORNAMENTAL GRANITE QUARRYING Extended Abstract The present investigation seeks to study the areas with dimension stone potential in the Antas-Matança and Esmolfe massifs, in central northern Portugal. There are two massifs: the Esmolfe massif, with an outcrop area of 12 km2 , is circular with a narrow offshoot to the NE and prolongs itself to the SE until the Antas-Matança massif. This latter massif is elliptic in shape, elongated in an E-W direction, with an outcrop area of approximately 19 km2 . Both granites studied are calc-alkaline, undeformed, blue-grey in colour, medium-grained with a slightly porphyritic tendency. They are regarded as part of the Celorico-Matança granite that has been dated at 252± 9 M.a. (Pinto et al. 1987). The textural characteristics of the granite massifs are relatively homogeneous although variations do occur. The Antas-Matança facies shows some colour variations and heterogeneity in grain size. The Esmolfe facies is more homogeneous, coarser-grained, lighter in colour, due to aggregates of feldspar crystals, than the Antas-Matança facies. Superficial alteration of the Antas-Matança facies is greater than in the Esmolfe facies. Due to the petrographic and textural characteristics of the granite under study, and small defects in terms of dimension stone production, the main limiting factor in defining favourable areas for dimension stone extraction is the fracture density pattern. Hence, this aspect is highlighted. The paper proceeds to analyse field information and statistically treats fracture density data to understand and define the compartmentalisation of the massifs in the upper levels although limited to the inherent randomness of natural fracture patterns. In the Esmolfe massif the main fracture orientation is N15-30º W (total population) in 16 of the 22 lines considered both as main or secondary fracture sets (Table 1). In this system 50% of the fracture spacing are < 1m although there is considerable dispersion. The spacing between main fracture sets varies considerably in most cases with no regularity in spacing patterns. The total population in the Antas-Matança massif shows there to be two main orientation directions 40- 50º and 150-160º that are sub vertical in nature. In both sets spacing is < 1m (65% of total). This implies that the set 40-50º penalises a few of the areas due to high frequencies of closely spaced fractures (< 0.3m). Fracture spacing in both massifs are considered moderate (1-2.5m) to ample (2.5-6.25m). Comparison of the class frequencies of distance between consecutive fractures shows that the distribution of intervals is similar in both the Esmolfe and Antas-Matança massifs where, in the latter, reduced spacing predominates. However, if we compare the average distance frequencies between fractures in the scan-lines, the spacing between fractures in Esmolfe appears to be greater than in Antas-Matança (Fig. 9B). This is mainly due to the high frequency of reduced spacing in the Antas-Matança massif that lowers the average distance between fractures. In Esmolfe, one third of the lines studied, the average spacing is < 2m. These factors, in conjunction with the textural homogeneity of the rock, mineralogical characteristics and other factors, such as favourable topographic conditions, easy access and large reserves demonstrate the high ornamental potential of these granites. The quarrying activity in Esmolfe is intense and chaotic. The exaggerated proliferation of quarries that hardly ever go beyond the superficial levels causes a high negative visual impact. The lack of technical management in the majority of quarries implies that rarely the more promising levels are ever extracted resulting in the premature closure of the quarry. The Esmolfe granite is commercialised under various designations of which Cinza (grey) is the most common. It outcrops generally in large boulders that due to their dimension alone allow the installation of the quarries. Alteration profile is generally < 0.2m. The extraction activity of the Antas-Matança massif is presently restricted to three quarries, being the granite commercialised under the designation Cinza (grey) or Cinzento Antas (Antas grey). The existence of extensive slabs of this facies with a reduced alteration profile creates very favourable conditions for dimension stone extraction. This study shows that the Esmolfe massif has potential for extraction in four areas located SW of Pedras Altas and S of Ponte do Ferreira (Map 1). For the Antas-Matança massif 5 areas are proposed, namely the outcrops nearby Pisão, Lameira area (station A24), Antas and Abrocedo areas (Map 2). The importance of this study is clearly shown not only for territorial land planning uses, in the selection and hierarchisation, of potential areas but also to better plan exploration methodologies (e.g. use of georadar or percussion drilling), if the raw material warrants it

Design of an intrinsically safe series-series compensation WPT system for automotive LiDAR

The earliest and simplest impedance compensation technique used in inductive wireless power transfer (WPT) design is the series-series (SS) compensation circuit, which uses capacitors in series with both primary and secondary coils of an air-gapped transformer. Despite of its simplicity at the resonant condition, this configuration exhibits a major sensitivity to variations of the load attached to the secondary, especially when higher coupling coefficients are used in the design. In the extreme situation that the secondary coil is left at open circuit, the current at the primary coil may increase above the safety limits for either the power converter driving the primary coil or the components in the primary circuit, including the coil itself. An approach often used to minimize this problem is detuning, but this also reduces the electrical efficiency of the power transfer. In low power, fixed-distance stationary WPT, a fair trade-off between efficiency and safety must be verified. This paper aims to consolidate a simple design procedure for such a SS-compensation, exemplifying its use in the prototype of a WPT system for automotive light detection and ranging (LiDAR) equipment. The guidelines herein provided should equally apply to other low power applications.This work has been supported by national funds through FCT—Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2019, and also European Structural and Investment Funds in the FEDER component, through the Operational Competitiveness and Internationalization Programme (COMPETE 2020) [Project nº 037902; Funding Reference: POCI-01-0247-FEDER-037902]

Wireless communication and management system for E-Bike dynamic inductive power transfer lanes

This paper presents the design, implementation, and testing of a wireless communication system for automatic identification of e-bikes and management of their battery charging in the context of dynamic inductive wireless power transfer (DIWPT) lanes. The proposed system checks if an e-bike, uniquely identified by its RFID tag, is authorized to receive energy from the lane coils and acts accordingly. An authentication mechanism was developed based on the use of embedded Wi-Fi boards attached to the coils and communicating with a central HTTP server with a MySQL database. The developed management system also provides other features, such as the recording of the number of lane coils used by each e-bike for billing purposes. The results from experimental tests on a laboratory prototype were used to validate the developed functionalities and assess the quality of service provided by the proposed system.This work was supported by FCT national funds, under the national support to R&D units grant,through the reference project UIDB/04436/2020 and UIDP/04436/2020

Vehicle electrification: technologies, challenges and a global perspective for smart grids

Nowadays, due to economic and climate concerns, the private transportation sector is shifting for the vehicle electrification, mainly supported by electric and hybrid plug-in vehicles. For this new reality, new challenges about operation modes are emerging, demanding a cooperative and dynamic operation with the electrical power grid, guaranteeing a stable integration without omitting the power quality for the grid-side and for the vehicle-side. Besides the operation modes, new attractive and complementary technologies are offered by the vehicle electrification in the context of smart grids, which are valid for both on-board and off-board systems. In this perspective, this book chapter presents a global perspective and deals with challenges for the vehicle electrification, covering the key technologies toward a sustainable future. Among others, the flowing topics are covered: (1) Overview of power electronics structures for battery charging systems, including on-board and off-board systems; (2) State-of-the-art of communication technologies for application in the context of vehicular electrification, smart grids and smart homes; (3) Challenges and opportunities concerning wireless power transfer with bidirectional interface to the electrical grid; (4) Future perspectives about bidirectional power transfer between electric vehicles (vehicle-to-vehicle operation mode); (5) Unified technologies, allowing to combine functionalities of a bidirectional interface with the electrical grid and motor driver based on a single system; and (6) Smart grids and smart homes scenarios and accessible opportunities about operation modes.Fundação para a Ciência e Tecnologia (FCT

A review on power electronics technologies for electric mobility

Concerns about greenhouse gas emissions are a key topic addressed by modern societies worldwide. As a contribution to mitigate such effects caused by the transportation sector, the full adoption of electric mobility is increasingly being seen as the main alternative to conventional internal combustion engine (ICE) vehicles, which is supported by positive industry indicators, despite some identified hurdles. For such objective, power electronics technologies play an essential role and can be contextualized in different purposes to support the full adoption of electric mobility, including on-board and off-board battery charging systems, inductive wireless charging systems, unified traction and charging systems, new topologies with innovative operation modes for supporting the electrical power grid, and innovative solutions for electrified railways. Embracing all of these aspects, this paper presents a review on power electronics technologies for electric mobility where some of the main technologies and power electronics topologies are presented and explained. In order to address a broad scope of technologies, this paper covers road vehicles, lightweight vehicles and railway vehicles, among other electric vehicles.This work has been supported by FCT – Fundação para a Ciência e Tecnologia with-in the Project Scope: UID/CEC/00319/2020. This work has been supported by the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017, and by the FCT Project new ERA4GRIDs PTDC/EEI-EEE/30283/2017. Tiago Sousa is supported by the doctoral scholarship SFRH/BD/134353/2017 granted by FCT

Efficiency comparison of different DC-DC converter architectures for a power supply of a LiDAR system

LiDAR (Light Detection And Ranging) is a technology used to meas-ure distances to objects. Internally, a LiDAR system is constituted by several components, including a power supply, which is responsible to provide the dis-tinct voltage levels necessary for all the components. In this context, this paper presents an efficiency comparison of three different DC-DC converter architec-tures for a LiDAR system, each one composed of three DC-DC converters: in parallel; in cascade; and hybrid (mix of parallel and cascade). The topology of the adopted integrated DC-DC converters is the synchronous buck Switched-Mode Power Supply (SMPS), which is a modified version of the basic buck SMPS topology. Three distinct SMPSs were considered: LM5146-Q1, LM5116, and TPS548A20RVER. These SMPSs were selected according to the require-ments of voltage levels, namely, 12 V, 5 V, and 3.3 V. Along the paper, the prin-ciple of operation of the SMPSs is presented, as well as the evaluation results obtained for different operating powers, allowing to establish a comprehensive efficiency comparison.This work has been supported by national funds through FCT—Fundação para a Ciência e Tecnologia within the Project Scope: UIDB/00319/2020, and also European Structural and Investment Funds in the FEDER component, through the Operational Competitiveness and Internationalization Programme (COMPETE 2020) [Project nº 037902; Funding Reference: POCI-01-0247-FEDER-037902]

Desilusão

ARTE E CULTURA VISUAL é uma revista do Centro de Investigação e de Estudos em Belas-Artes (CIEBA), com a periodicidade de um número anual, a sair no final de cada ano. O âmbito a que se dedica é, como o título faz antever, as artes plásticas e a cultura visual, procurando um discurso reflexivo, diverso, actual, problematizante e orgânico, que permita conferir enfoque aos dispositivos da arte e das imagens artísticas na sua ontologia e nos seus contextos – pontuais ou sistémicos – históricos, culturais, estéticos, institucionais, sociais, e, inclusivamente, económicos e políticos. Centrando- se neste campo de pensamento – e as imagens assumem também uma forma de pensamento –, a revista convoca pensadores pluridisciplinares e artistas que desejem partilhar a sua reflexão e a sua obra. Cada número é dedicado a um tema. Este número é dedicado à DESILUSÃO. Desilusão reporta-se a uma sensação de desapontamento, a um sentimento de frustração ou de decepção. Naturalmente, que este desapontamento implica que antes a si existiu, de alguma forma, uma expectativa, eventualmente uma ilusão, que, por conseguinte, não foi cumprida. Depois do alívio da pandemia, de repente, a guerra foi outra. A Rússia invadia a Ucrânia em Fevereiro. Perdem-se vidas, comentem-se abusos de variada ordem. A guerra seguiu-se à peste, como se voltássemos à Idade Média, a um lugar que nos parecia distante, superado. A desilusão pode, contudo, não se limitar à guerra. Este número de Arte e Cultura Visual procura explorar e interpelar este conceito na sua plural abrangência e significado.info:eu-repo/semantics/publishedVersio