Percorrer por autor "Fernandes, Paulo"
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- Avaliação das doses de Cone Beam Computed Tomography (CBCT) em pediatriaPublication . Sá, Ana Cravo; Campos, Guilherme; Fernandes, Paulo; Di Maria, SalvatoreO CBCT é o tipo de imagem mais utilizado em radioterapia, no entanto não existem recomendações para os diferentes protocolos [1]. As doses provenientes das imagens diárias poderão atingir 1-3% da dose prescrita, aumentando o risco de tumores radio-induzidos, sendo importante aferir para doentes pediátricos [2]. Pretende-se avaliar as doses de CBCT em doentes pediátricos. As medições realizaram-se em dois sistemas de CBCT, com recurso a um fantoma computed tomography dose index (CTDI) e câmaras de ionização de 100 mm [2]. Os protocolos de cabeça, tórax e pélvico foram considerados num total de 60 medições. Utilizou-se o fantoma TOR 18 FG para avaliar a qualidade da imagem. Avaliou-se a razão sinal ruído (RSR) com voltagens entre 40 kV até 150 kV e 25 mA e um tempo de exposição de 50 ms. As simulações Monte Carlo foram realizadas com o software PENELOPE e com recurso a dois fantomas femininos pediátricos de 10 e 15 anos. Entre os dois sistemas de CBCT verificaram-se diferenças de 1,5 mGy por CBCT para o protocolo de cabeça, 10,7 mGy para o protocolo pélvico e 1,5 mGy para o protocolo de tórax. Obteve-se o melhor rácio de RSR para 60 kV. A máxima diferença foi obtida no útero, com uma redução de dose de 93% face aos valores dos parâmetros fornecidos pelo fabricante. Atualmente, existem várias recomendações sobre os parâmetros de aquisição do CBCT e estes variam entre os diferentes países [3]. Vários estudos [2,4] demonstram estratégias de redução de dose dos CBCT que corroboram os nossos resultados. Obteve-se uma redução de dose de 29% para o protocolo de tórax, 39% para protocolo de cabeça e 42% para o protocolo pélvico para uma voltagem de 60 kV.
- Comparison of antimony selenide thin films obtained by electrochemical deposition and selenization of a metal precursorPublication . Shongalova, Aigul; Aitzhanov, Madi; Zhantuarov, Sultan; Urazov, Kazhmukhan; Fernandes, Paulo; Tokmoldin, Nurlan; Correia, Maria RosárioIn this work, we present a study comparing two methods of Sb2Se3 deposition, namely electrochemical deposition and selenization of a thin-film metallic Sb – precursor deposited by magnetron sputtering. The Sb selenization process was carried out in the range of temperatures from 270 ºC to 350 ºC in an argon atmosphere enriched with elemental Se vapor. Electrochemical deposition of Sb2Se3 was performed in a three-electrode cell at constant potential. Following electrochemical deposition, the samples were annealed in argon at temperatures ranging from 270 ºC to 350 ºC. Characterization of the obtained thin films was performed using X-ray diffraction, Raman spectroscopy and optical transmission. Both deposition methods demonstrate successful emergence of the selenide phase, albeit with the presence of varying levels of antimony oxide. The possibility of preferential growth was observed, which is suggested as dependent on growth method and annealing temperature.
- Cu(In,Ga)Se2 based ultrathin solar cells: the pathway from lab rigid to large scale flexible technologyPublication . Lopes, Tomás; Teixeira, Jennifer; Curado, Marco; Ferreira, Bernado; Oliveira, Antonio; Cunha, José; Monteiro, Margarida; Violas, André; Barbosa, João; Sousa, Patricia; Çaha, Ihsan; Borme, Jérôme; Oliveira, Kevin; Ring, Johan; Chen, Wei; Zhou, Ye; Takei, Klara; Niemi, Esko; Francis, Leonard; Edoff, Marika; Brammertz, Guy; Fernandes, Paulo; Vermang, Bart; Salomé, PedroFor the first time, the incorporation of interface passivation structures in ultrathin Cu(In,Ga)Se2 (CIGS) based solar cells is shown in a flexible lightweight stainless-steel substrate. The fabrication was based on an industry scalable lithography technique - nanoimprint lithography (NIL) - for a 15x15 cm2 dielectric layer patterning, needed to reduce optoelectronic losses at the rear interface. The nanopatterning schemes are usually developed by lithographic techniques or by processes with limited scalability and reproducibility (nanoparticle lift-off, spin-coating, etc). However, in this work the dielectric layer is patterned using NIL, a low cost, large area, high resolution, and high throughput technique. To assess the NIL performance, devices with a NIL nanopatterned dielectric layer are benchmarked against electron-beam lithography (EBL) patterning, using rigid substrates. Up to now, EBL is considered the most reliable technique for patterning laboratory samples. The device patterned by NIL shows similar light to power conversion efficiency average values compared to the EBL patterned device - 12.6 % vs 12.3 %, respectively - highlighting the NIL potential for application in the solar cell sector. Moreover, the impact of the lithographic processes, such as different etch by-products, in the rigid solar cells’ figures of merit were evaluated from an elemental point of view via X-ray Photoelectron Spectroscopy and electrically through a Solar Cell Capacitance Simulator (SCAPS) fitting procedure. After an optimised NIL process, the device on stainless-steel achieved an average power conversion efficiency value of 11.7 % - a slightly lower value than the one obtained for the rigid approach, due to additional challenges raised by processing and handling steel substrates, even though scanning transmission electron microscopy did not show any clear evidence of impurity diffusion towards the absorber. Notwithstanding, time-resolved photoluminescence results strongly suggested the presence of additional non-radiative recombination mechanisms in the stainless-steel absorber, which were not detected in the rigid solar cells, and are compatible with elemental diffusion from the substrate. Nevertheless, bending tests on the stainless-steel device demonstrated the mechanical stability of the CIGS-based device up to 500 bending cycles.
- Dose assessment in paediatric CBCT using measurements, MC simulations and image quality analysisPublication . Sá, Ana Cravo; Campos, Guilherme; Pontes, Miguel; Fernandes, Paulo; Di Maria, SalvatoreCurrently in radiotherapy, Image-Guided Radiation Therapy (IGRT) is a cornerstone for achieving submillimeter treatment precision. Cone Beam Computed Tomography (CBCT) is the type of IGRT most commonly used in radiotherapy departments. However, there are no guidelines for the different types of protocols and image parameters used, which leads to different absorbed doses in healthy tissues and this is especially important in paediatric patients. The aim of this study is to assess the doses from CBCT in paediatric patients.
- Estudo experimental das doses por Tomografia Computorizada de Feixe Cónico em radioterapiaPublication . Bonito, André Filipe Anastácio; Sá, Ana Cravo; Ribeiro, Filipa; Campos, Guilherme; Moreno, Lília; Costa, Maria Jesus; Pontes, Miguel; Fernandes, Paulo; Di Maria, SalvatoreA Tomografia Computorizada por Feixe Cónico (TCFC) é usada para verificação dos tratamentos em radioterapia (RT). Contudo, a sua utilização implica uma dose adicional de radiação para o doente o que poderá potenciar preocupações sobre os efeitos tecidulares a longo prazo [1-4]. Objetivos: Pretende-se, avaliar as doses absorvidas por TCFC nos protocolos de cabeça, tórax e pélvico e entre três instituições visando a otimização da exposição do doente à radiação ionizante. Na revisão sistemática de literatura, utilizaram-se 73 fontes científicas. Posteriormente, realizaram-se medições nas instituições para os diferentes protocolos utilizados com recurso a um fantoma e duas câmaras de ionização. Para análise e comparação dos dados utilizou-se o programa Statistical Package for the Social Sciences, versão 29.0.2.0. Os resultados obtidos mostram que as doses nos protocolos pélvicos apresentam maior variabilidade entre as instituições (p=0.01), embora não se verifiquem diferenças significativas nas doses entre as duas câmaras de ionização. O protocolo pélvico demonstra ser o protocolo com maior dose nas três instituições (ẋ=14.45 mGye 𝞼= 2.883 mGy) contrariamente ao protocolo de cabeça (ẋ= 2.25 mGy e 𝞼= 0.997 mGy). Adicionalmente, observam-se diferenças nos parâmetros de aquisição de TCFC entre instituições para o mesmo protocolo sobretudo no valor de miliampere segundo (mAs)[5,6]. A variação dos parâmetros de aquisição entre instituições para o mesmo protocolo, especialmente nos valores de mAs, explica a divergência dos resultados obtidos. O estudo mostra que o protocolo pélvico apresenta uma grande dose e variabilidade entre instituições podendo esta variação ser explicada pela utilização de diferentes parâmetros de aquisição em cada instituição. Neste sentido, serácrucial realizar esta análise de dose para avaliar com exatidão as doses de TCFC em RT [5,6].
- MobiWise: Eco-routing decision support leveraging the Internet of thingsPublication . Aguiar, Ana; Fernandes, Paulo; Guerreiro, Andreia; Tomás, Ricardo; Agnelo, João; Santos, José Luís; Araújo, Filipe; Coelho, Margarida C.; Fonseca, Carlos M.; D'Orey, Pedro; Luís, Manuel; Sargento, SusanaEco-routing distributes traffic in cities to improve mobility sustainability. The implementation of eco-routing in real-life requires a diverse set of information, including different kinds of sensors. These sensors are often already integrated in city infrastructure, some are technologically outdated, and are often operated by multiple entities. In this work, we provide a use case-oriented system design for an eco-routing service leveraging Internet-of-Things (IoT) technologies. The methodology involves six phases: 1) defining an eco-routing use case for a vehicle fleet; 2) formulating a routing problem as a multi-objective optimisation to divert traffic at a relevant hub facility; 3) identifying data sources and processing required information; 4) proposing a microservice-based architecture leveraging IoT technologies adequate to a multi-stakeholder scenario; 5) applying a microscopic traffic simulator as a digital twin to deal with data sparsity; and 6) visually illustrating eco-routing trade-offs to support decision making. We built a proof-of-concept for a mid-sized European city. Using real data and a calibrated digital twin, we would achieve hourly total emissions reductions up to 2.1%, when applied in a car fleet composed of 5% of eco-routing vehicles. This traffic diversion would allow annual carbon dioxide and nitrogen oxides savings of 400 tons and 1.2 tons, respectively.
- Over 100 mV VOC improvement for rear passivated ACIGS ultra‐thin solar cellsPublication . Oliveira, Antonio; Rocha Curado, Marco; Teixeira, J. P.; Tomé, Daniela; Çaha, Ihsan; Oliveira, Kevin; Lopes, Tomás; Monteiro, Margarida; Violas, André; Correira, Maria; Fernandes, Paulo; Deepak, Francis; Edoff, Marika; Salomé, PedroA decentralized energy system requires photovoltaic solutions to meet new aesthetic paradigms, such as lightness, flexibility, and new form factors. Notwithstanding, the materials shortage in the Green Transition is a concern gaining momentum due to their foreseen continuous demand. A fruitful strategy to shrink the absorber thickness, meeting aesthetic and shortage materials consumption targets, arises from interface passivation. However, a deep understanding of passivated systems is required to close the efficiency gap between ultra-thin and thin film devices, and to mono-Si. Herein, a (Ag,Cu)(In,Ga)Se2 ultra-thin solar cell, with 92% passivated rear interface area, is compared with a conventional nonpassivated counterpart. A thin MoSe2 layer, for a quasi-ohmic contact, is present in the two architectures at the contacts, despite the passivated device narrow line scheme. The devices present striking differences in charge carrier dynamics. Electrical and optoelectronic analysis combined with SCAPS modelling suggest a lower recombination rate for the passivated device, through a reduction on the rear surface recombination velocity and overall defects, comparing with the reference solar cell. The new architecture allows for a 2% efficiency improvement on a 640 nm ultra-thin device, from 11% to 13%, stemming from an open circuit voltage increase of 108 mV.