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- Geodetic implications on block formation and geodynamic domains in the South Shetland Islands, Antarctic PeninsulaPublication . Berrocoso, M.; Fernandez-Ros, A.; Prates, Gonçalo; Garcia, A.; Kraus, S.The South Shetland Islands archipelago is dynamically complex due to its tectonic surroundings. Most islands are part of a formerly active volcanic arc, although Deception, Penguin and Bridgeman Islands, as well as several submarine volcanoes, are characterized by active back-arc volcanism. Geodetic benchmarks were deployed and the movement of the lithosphere to which they were fixed measured to provide geodynamic insight for the South Shetland Islands, Bransfield Basin and Antarctic Peninsula area based on surface deformation. These benchmarks' data add spatial and temporal coverage to previous results. The results reveal two different geodynamic patterns, each confined to a distinct part of the South Shetland Islands archipelago. The inferred absolute horizontal velocity vectors for the benchmarks in the northeastern part of the archipelago are consistent with the opening of the Bransfield Basin, while benchmark vectors in the southwestern part of the archipelago are similar to those of the benchmarks on the Antarctic Peninsula. In between, Snow, Deception and Livingston Islands represent a transition zone. In this area, the horizontal velocity vectors relative to the Antarctic plate shift northeastwards from N to NW. Furthermore, the South Shetland Islands benchmarks, except for that at Gibbs (Elephant) Islands, indicate subsidence, which might be a consequence of the slab roll-back at the South Shetland Trench. In contrast, the uplift revealed by the Antarctic Peninsula benchmarks suggests glacial isostatic adjustment after the Larson B ice-shelf breakup. (C) 2015 Elsevier B.V. All rights reserved.
- External control of the Drosophila melanogaster egg to imago development period by specific combinations of 3D low-frequency electric and magnetic fieldsPublication . Makarov, Vladimir I.; Khmelinskii, IgorWe report that the duration of the egg-to-imago development period of the Drosophila melanogaster, and the imago longevity, are both controllable by combinations of external 3-dimensional (3D) low-frequency electric and magnetic fields (LFEMFs). Both these periods may be reduced or increased by applying an appropriate configuration of external 3D LFEMFs. We report that the longevity of D. melanogaster imagoes correlates with the duration of the egg-to-imago development period of the respective eggs. We infer that metabolic processes in both eggs and imago are either accelerated (resulting in reduced time periods) or slowed down (resulting in increased time periods). We propose that external 3D LFEMFs induce electric currents in live systems as well as mechanical vibrations on sub-cell, whole-cell and cell-group levels. These external fields induce media polarization due to ionic motion and orientation of electric dipoles that could moderate the observed effects. We found that the longevity of D. melanogaster imagoes is affected by action of 3D LFEMFs on the respective eggs in the embryonic development period (EDP). We interpret this effect as resulting from changes in the regulation mechanism of metabolic processes in D. melanogaster eggs, inherited by the resulting imagoes. We also tested separate effects of either 3D electric or 3D magnetic fields, which were significantly weaker.
- Macroalgal morphogenesis induced by waterborne compounds and bacteria in coastal seawaterPublication . Grueneberg, Jan; Engelen, Aschwin H.; Costa, Rodrigo; Wichard, ThomasAxenic gametes of the marine green macroalga Ulva mutabilis Foyn (Ria Formosa, locus typicus) exhibit abnormal development into slow-growing callus-like colonies with aberrant cell walls. Under laboratory conditions, it was previously demonstrated that all defects in growth and thallus development can be completely abolished when axenic gametes are inoculated with a combination of two specific bacterial strains originally identified as Roseo-bacter sp. strain MS2 and Cytophaga sp. strain MS6. These bacteria release diffusible morphogenetic compounds (= morphogens), which act similar to cytokinin and auxin. To investigate the ecological relevance of the waterborne bacterial morphogens, seawater samples were collected in the Ria Formosa lagoon (Algarve, Southern Portugal) at 20 sampling sites and tidal pools to assess their morphogenetic effects on the axenic gametes of U. mutabilis. Specifically the survey revealed that sterile-filtered seawater samples can completely recover growth and morphogenesis of U. mutabilis under axenic conditions. Morphogenetic activities of free-living and epiphytic bacteria isolated from the locally very abundant Ulva species (i.e., U. rigida) were screened using a multiwell-based testing system. The most represented genera isolated from U. rigida were Alteromonas, Pseudoalteromonas and Sulfitobacter followed by Psychrobacter and Polaribacter. Several naturally occurring bacterial species could emulate MS2 activity (= induction of cell divisions) regardless of taxonomic affiliation, whereas the MS6 activity (= induction of cell differentiation and cell wall formation) was species-specific and is probably a feature of difficult-to-culture bacteria. Interestingly, isolated bacteroidetes such as Algoriphagus sp. and Polaribacter sp. could individually trigger complete Ulva morphogenesis and thus provide a novel mode of action for bacterial-induced algal development. This study also highlights that the accumulation of algal growth factors in a shallow water body separated from the open ocean by barrier islands might have strong implications to, for example, the wide usage of natural coastal seawater in algal (land based) aquacultures of Ulva.
- Prospecção e defesa da paisagem urbana do Algarve (1965-70): a arquitetura tradicional e a preservação do património urbano na proposta da DGSUPublication . Ribeiro, Vítor; Costa, Miguel Reimão; Aguiar, José; Valverde, IsabelNo contexto da sucessiva redefinição do conceito de património, a arquitetura vernácula tenderá a assumir a sua importância a partir da segunda metade do século passado, alcançando estatuto próprio na Carta sobre o Património Construído Vernáculo de 1999. Em Portugal, adquirem particular relevância os trabalhos desenvolvidos em diferentes âmbitos, desde a antropologia à arquitetura, passando pela agronomia e pela geografia, que culminariam em diferentes sínteses sobre o tema, alargadas a todo o território nacional continental. Essa abordagem só no final dos anos 60 viria a ser ensaiada, à escala da região do Algarve, no pioneiro trabalho desenvolvido pela equipa dirigida pelo Arq.º Cabeça Padrão, no âmbito da Secção de Defesa e Recuperação da Paisagem Urbana da Direcção-Geral dos Serviços de Urbanização (DGSU), sob o título “Prospecção, Preservação e Recuperação de Elementos Urbanísticos e Arquitectónicos Notáveis, em Áreas Urbanas e Marginais Viárias, na Região do Algarve”, constituindo um de três estudos complementares a integrar o Plano Regional do Algarve. Dos 49 volumes projectados a partir de 1965, abrangendo 47 aglomerados urbanos de dimensões muito diversas e maioritariamente localizados na faixa litoral da região, apenas de cerca de metade se conhece hoje o paradeiro. Mas se bem que rapidamente tenham sido remetidos - até muito recentemente -, ao esquecimento dos arquivos, e pese embora o seu carácter datado, constituem um conjunto documental singular de inegável importância, pela metodologia e propostas que encerram, no contexto da evolução histórica dos conceitos e práticas de valorização e conservação patrimonial (em particular no que se refere ao património arquitectónico urbano de carácter vernáculo) e de planeamento e intervenção em áreas urbanas consolidadas. Importância reforçada pelo extenso levantamento fotográfico produzido e onde se fixou um momento histórico charneira documentando o início de profundas transformações - que se acentuariam nas décadas subsequentes -, entre outras razões, por força da emergente importância do turismo. Com a presente comunicação pretende-se resgatar do esquecimento um trabalho verdadeiramente pioneiro (mesmo em termos mundiais) no que se refere à preservação e recuperação da paisagem urbana do Algarve, avaliando a sua metodologia e abordagem particular no âmbito das intervenções em espaço urbano e retomando um processo de análise e caracterização da arquitetura tradicional da região a partir do valioso espólio fotográfico constante neste estudo.
- Coupling tendencies during exploratory behaviours of competing players in rugby union dyadsPublication . Correia, Vanda; Passos, Pedro; Araújo, Duarte; Davids, Keith; Diniz, Ana; Kelso, J. A. ScottThis study investigated interpersonal coordination tendencies in 1vs.1 dyads in rugby union, here expressed by participants' movement velocity towards or away from the sideline as they competed to score or prevent a try. We examined whether coupling tendencies of members of each dyad shaped key performance outcomes (try or successful tackle). Data on movement displacement trajectories of eight male rugby union players (aged 11-12 years) were analysed during performance in 47 trials. To assess coordination tendencies during exploratory behaviours in the dyads, analyses of performance time series data were undertaken using variable time graphs, running correlations and cross-correlations. Results revealed distinct coupling patterns characterised by shifts between synchronous coordination and asynchronous coordination tendencies and uncoordinated actions. Observed behaviours were interpreted as attempts of competing participants to create and perceive possibilities for action while seeking to achieve specific performance goals. Findings also revealed that a variety of patterned relations between participants resulted in different performance outcomes.
- Reflexões sobre o campo do cinema e educaçãoPublication . Pacheco, RaquelNão estamos engatinhando, não estamos no começo, estamos nos arrastando na área. É porque ainda não se encontrou uma maneira adequada, ou mais interessante, de se fazer isso. Apesar do campo já existir há muitos anos, ou melhor, décadas, atualmente continuamos tentando provar que ele é importante. Me parece que existe um vácuo entre quem está fazendo, quem está aprendendo e a relação com o governo e com a escola. Há uma ausência de comunicação. (Índia Martins – Professora de cinema e educação da UFF, 2014) . A afirmação, acima, de Martins dá conta de um problema de base em relação ao campo do cinema e educação no país. Este é o assunto central deste artigo que pretende refletir sobre o cinema e educação enquanto campo baseando-se no trabalho que desenvolvemos ao longo dos últimos anos. Para compreendermos com mais clareza esta temática, primeiro vamos conhecer um pouco da sua história. Em um estudo sobre a relevância do movimento anarquista1 no Brasil e seu envolvimento com o cinema, no início do século XX, em um período que vai dos anos 1901 a 1921, Figueira (2004) faz um relato sobre a introdução e os usos do cinematógrafo pela Igreja, pelo Estado e pela indústria/mercado, na sociedade Brasileira.
- Regenerative memory in time-delayed neuromorphic photonic resonatorsPublication . Romeira, Bruno; Avó, R.; Figueiredo, José; Barland, S.; Javaloyes, JulienWe investigate a photonic regenerative memory based upon a neuromorphic oscillator with a delayed self-feedback (autaptic) connection. We disclose the existence of a unique temporal response characteristic of localized structures enabling an ideal support for bits in an optical buffer memory for storage and reshaping of data information. We link our experimental implementation, based upon a nanoscale nonlinear resonant tunneling diode driving a laser, to the paradigm of neuronal activity, the FitzHugh-Nagumo model with delayed feedback. This proof-of-concept photonic regenerative memory might constitute a building block for a new class of neuron-inspired photonic memories that can handle high bit-rate optical signals.
- Modeling of the lycopene extraction from tomato pulpsPublication . Dolatabadi, Zahra; Rad, Amir Hossien Elhami; Farzaneh, Vahid; Feizabad, Seyed Hashem Akhlaghi; Estiri, Seyed Hossein; Bakhshabadi, HamidThe inputs of this network were the concentration of pectinase and time of incubation, and the outputs were extracted lycopene and the activity of radical scavenging activity. Two different networks were designed for the process under the sonication and without it. For optimal network, networks' transfer functions and different learning algorithms were evaluated and the validity of each one was determined. Consequently, the feedforward neural network with function of logarithmic transfer, Levenberg Marquardt algorithm and 4 neurons in the hidden layer with the correlation coefficient of 0.96 and 0.99 were respectively observed for the treatments under sonication and without it, furthermore, root mean squared error and standard error values were obtained 0.46 and 0.22 respectively for the treatments under sonication and 0.77 and 0.38 without it as respectively optimal networks. The selected networks could determine the chosen responses, individually and in combined effect of both inputs as well (R-2 > 0.98). (C) 2015 Elsevier Ltd. All rights reserved.
- Learning from differences: a strategy for teacher development in respect to student diversityPublication . Messiou, Kyriaki; Ainscow, Mel; Echeita, Gerardo; Goldrick, Sue; Hope, Max; Paes, Isabel; Sandoval, Marta; Simon, Cecilia; Vitorino, TeresaDrawing on evidence gathered as a result of collaborative action research carried out in 8 secondary schools in 3 European countries, this paper proposes an innovative strategy for helping teachers respond positively to learner diversity. The strategy merges the idea of lesson study with an emphasis on listening to the views of students. The research suggests that it is this latter emphasis that makes the difference as far as responding to learner diversity is concerned. It is this that brings a critical edge to the process that has the potential to challenge teachers to go beyond the sharing of existing practices in order to invent new possibilities for engaging students in their lessons. The paper also considers some of the difficulties involved in using this strategy.
- Higher central extensions and cohomologyPublication . Rodelo, Diana; Van der Linden, TimWe establish a Galois-theoretic interpretation of cohomology in semi-abelian categories: cohomology with trivial coefficients classifies central extensions, also in arbitrarily high degrees. This allows us to obtain a duality, in a certain sense, between "internal" homology and "external" cohomology in semiabelian categories. These results depend on a geometric viewpoint of the concept of a higher central extension, as well as the algebraic one in terms of commutators. (C) 2015 Elsevier Inc. All rights reserved.
- Ecotoxicological endpoints, are they useful tools to support ecological status assessment in strongly modified water bodies?Publication . Palma, Patrícia; Ledo, L.; Alvarenga, P.Although man-made reservoirs represent an important water supply source in countries where water scarcity has become a problem, little work has been done on the evaluation of their ecological status. Taking this in account, the general aim of this study was to assess the usefulness of ecotoxicological endpoints in the potential ecological status characterization of water reservoirs, with the purpose of their possible integration in evaluation programs developed under the Water Framework Directive (WFD). To achieve this purpose, a group of bioassays were selected to evaluate both water and sediment compartments at the Alqueva reservoir (the biggest from the Iberian Peninsula), with representative species from different taxonomic and functional groups: Vibrio fischeri, Thamnocephalus platyurus, Daphnia magna and Heterocypris incongruens. The ecotoxicological assessment showed that sublethal endpoints (e.g., luminescence, growth or reproduction), would be more useful and sensitive to identify toxicity patterns in this type of water body. In general, the results from this ecotoxicological tool-box agreed with the potential ecological status established according to the WFD, which indicates that the bioassays complement the ecological assessment. Furthermore, the use of an ecotoxicological approach can be extremely useful, especially in cases where the biotic indices are difficult to establish, such as in man-made reservoirs. However, when pollutant concentrations are very low, and/or when nutrients and organic matter concentrations are high, the two approaches do not fit, requiring further research to determine which organisms are more sensitive and the best biotic indices to use under those conditions. (C) 2015 Elsevier B.V. All rights reserved.
- In vivo metabolism of unsaturated fatty acids in Sepia officinalis hatchlingsPublication . Reis, Diana; Rodriguez, C.; Acosta, N. G.; Almansa, E.; Tocher, D. R.; Andrade, José Pedro; Sykes, António V.The transition of Sepia officinalis culture to industrial large scale has been hampered due to bottlenecks related to the limited knowledge on nutritional physiology of the species. Determination of the endogenous ability of S. officinalis hatchlings to metabolise unsaturated fatty acids (FA) may provide new insight on the capability of hatchlings to biosynthesise different FA, as well as lipid classes containing essential fatty acids (EFA). In the present study, cuttlefish hatchlings were incubated with [1-C-14] FA including C18 FA (18:1n-9, 18:2n-6, 18:3n-3) and long-chain polyunsaturated fatty acids (LC-PUFA) (20: 4n-6 (ARA), 20:5n-3 (EPA) or 22:6n-3 (DHA)), which were added individually as potassium salts bound to bovine serumalbumin. As a result, it was possible to investigate the in vivo FAmetabolismof S. officinalis hatchlings by following the incorporation of specific [1-C-14] FA, which points to the suitability of this methodology to study lipid metabolism of newly hatched cephalopods. The majority of radioactivity incorporated was recovered esterified into polar lipids (PL). A pattern was detected, where [1-C-14] DHA, [1-C-14] C18 FA and their metabolic products were preferentially esterified into phosphatidylcholine, whereas [1-C-14] ARA and [1-C-14] EPA were mainly esterified into phosphatidylethanolamine. [1-C-14] C18 FA were the most transformed FA with several metabolites produced by elongation and possible desaturation being obtained. As a contrary the radioactivity incorporated into hatchling total lipid (TL) from supplemented [1-C-14] LC-PUFA only one elongation product was recovered from the three substrates, except for [1-C-14] ARA, where an unidentified product was also detected. The present in vivo results indicated that S. officinalis hatchlings may have capability for the first steps in the biosynthesis of ARA and EPA from 18: 2n-6 and 18: 3n-3, respectively, including the existence of a desaturase potentially involved. Nonetheless, considering the low desaturation rates detected, this process may not be sufficient to cover EFA demands during development of this species. Therefore, dietary ARA and EPA, as well as DHA, should be supplied during the hatchling stage of Sepia. While designing an inert diet, which ensures normal growth and development of this species during the hatchling stage, the C18 FA and LC-PUFA levels and ratios should be considered, since the esterification pattern detected in the present study suggested competition between these FA for esterification into specific lipid classes. Moreover, considering the observed esterification pattern of LC-PUFA into different lipid classes, it is likely that the DHA/EPA/ARA ratio, rather than DHA/EPA or EPA/ARA ratios, would be of great importance for S. officinalis hatchling development. (C) 2015 Elsevier B.V. All rights reserved.
- Corrigendum to “Evidence for the conservation of miR-223 in zebrafish (Danio rerio): Implications for function” [Gene 566/1 (2015) 54–62]Publication . Roberto, Vania Palma; Tiago, Daniel; Gautvik, K.; Cancela, M. LeonorThe authors regret to inform that the zebrafish fbxw7 primers sequences in Supplementary Table S1, and the zebrafish stmn1a accession number in Table 1, were incorrectly introduced. Please consider the following corrections:
- Corporate social responsibility in tourism: The case of Zoomarine AlgarvePublication . Contreiras, Joaquim; Machado, Virgílio; Duarte, Ana PatríciaThis study had a threefold purpose. First, it sought to examine the opinion of three important stakeholders – employees, visitors and members of the local community – about the corporate social responsibility (CSR) practices of the theme park, Zoomarine Algarve. Second, this study evaluated the perceptions of the public regarding the impact of the company’s activities on regional development and environmental awareness. Last, the study sought to understand if stakeholders’ opinions regarding this company’s engagement in CSR practices are related to the impacts attributed to Zoomarine Algarve’s regular functions. The methodology comprised quantitative research based on a survey administered to convenience samples of the target groups (n = 405). The results reveal that stakeholders have an extremely positive view of the theme park’s engagement in CSR practices and feel that it contributes significantly to regional development, as well as to raising the environmental awareness of visitors and local communities. The findings also show that perceptions of CSR engagement are positively related with perceived impacts.
- Transcriptional regulation of gilthead seabream bone morphogenetic protein (BMP) 2 gene by bone- and cartilage-related transcription factorsPublication . Marques, Cátia L.; Cancela, Leonor; Laizé, VincentBone morphogenetic protein (BMP) 2 belongs to the transforming growth factor (3 (TGF(3) superfamily of cytokines and growth factors. While it plays important roles in embryo morphogenesis and organogenesis, BMP2 is also critical to bone and cartilage formation. Protein structure and function have been remarkably conserved throughout evolution and BMP2 transcription has been proposed to be tightly regulated, although few data is available. In this work we report the cloning and functional analysis of gilthead seabream BMP2 promoter. As in other vertebrates, seabream BMP2 gene has a 5' non-coding exon, a feature already present in DPP gene, the fruit fly ortholog of vertebrate BMP2 gene, and maintained throughout evolution. In silico analysis of seabream BMP2 promoter revealed several binding sites for bone and cartilage related transcription factors (TFs) and their functionality was evaluated using promoter-luciferase constructions and TF-expressing vectors. Runt -related transcription factor 3 (RUNX3) was shown to negatively regulate BMP2 transcription and combination with the core binding factor beta (CBF(3) further reduced transcriptional activity of the promoter. Although to a lesser extent, myocyte enhancer factor 2C (MEF2C) had also a negative effect on the regulation of BMP2 gene transcription, when associated with SRY (sex determining region Y)-box 9 (SOX9b). Finally, v-ets avian erythroblastosis virus E26 oncogene homolog 1 (ETS1) was able to slightly enhance BMP2 transcription. Data reported here provides new insights toward the better understanding of the transcriptional regulation of BMP2 gene in a bone and cartilage context. (C) 2015 Elsevier B.V. All rights reserved.
- High-glucose feeding of gilthead seabream (Sparus aurata) larvae: effects on molecular and metabolic pathwaysPublication . Rocha, Filipa; Dias, Jorge; Geurden, Inge; Dinis, Maria Teresa; Panserat, Stephane; Engrola, S.Nutritional programming has begun to arouse interest as a novel tool to alter specific metabolic pathways or functions in farmed animals. The aim of the present study was to explore the potential of early glucose stimuli to induce changes in nutrient metabolism of gilthead seabream. Nutritional conditioning was performed by delivering glucose-rich feed at three distinct recurrent periods of larval feeding regime: during first-feeding with rotifers (3 days after hatching, DAH) and mid-feeding with Artemia metanauplii (20DAH) and the beginning of inert diet feeding (30DAH), called the Recurrent treatment (REC). As opposed, the control treatment (CTRL) did not experience any glucose stimuli. At post-larval stage (from 50 to 60DAH), both treatments were challenged with a high-carbohydrate diet (50%). The immediate response to the early stimuli was assessed through gene expression of metabolic markers and by nutrient metabolism using [C-14] tracers. Each dietary stimulus induced metabolic changes on REC larvae, shown by altered expression of some genes, including those involved in glycolysis, and by a different pattern of glucose utilization. However, none of the molecular adaptations (except G6PDH gene) were persistent in the viscera and muscle of challenged post-larvae from REC group. In contrast, the glucose metabolism of challenged REC post-larvae revealed a shift towards a higher catabolism and lower glucose retention in tissues, compared to the CTRL group, suggesting an improvement of glucose oxidation pathways. In addition, the REC group showed a higher bio-conversion of glucose into lipids, indicating enhanced hepatic lipogenesis. The early stimuli did not affect the relative retention or use of amino acids or the growth and survival of challenged fish, up to 60DAH. In summary, although not substantiated at a molecular level, our data reveal that a recurrent high-glucose stimulus during larval stages affects the short-term modulation of pathways for glucose utilization in gilthead seabream. (C) 2015 Elsevier B.V. All rights reserved.
- O ensino profissional face ao ensino regular no sistema educacional português ao nível do ensino secundárioPublication . Narciso, Eugénia Susana Sério; Barradas, Álvaro; Vilhena, Carla CardosoO presente relatório descreve de forma detalhada o meu percurso profissional enquanto docente do sistema educativo português no período compreendido entre 2005 e 2013. São apresentadas várias tipologias de cursos com os quais trabalhei e é feita uma análise global e pessoal das práticas letivas associadas a esses percursos, assim como dos métodos de avaliação e planificação utilizados. Posteriormente é feita uma análise às ofertas educativas existentes no ensino secundário em Portugal, nomeadamente a vertente profissional e regular, permitindo uma distinção dos percursos ao nível do seu funcionamento, metas e objetivos, público-alvo, tipos de avaliação e certificação, com base na análise da legislação e documental.
- Diversity and specificity of the marine sponge microbiome as inspected by next generation sequencingPublication . Soares, André Rodrigues; Costa, Rodrigo da Silva; Reis, Margarida P.Sponges are early-branching metazoans whose hosted microbial communities are currently seen as highly fruitful sources of microbial ecological, evolutionary and metabolic novelties.
- Thermally stimulated currents on oxide based TFTsPublication . Cabrita, Fábio Emanuel Sousa; Gomes, Henrique L.Óxidos amorfos semiconductores têm assumido um papel de liderança para aplicações em Transístores de Filme Fino (TFTs). Este tipo de transístores tem aplicações em ecrãs planos que usam Díodos Emissores de Luz (LEDs). Os TFTs controlam a activação de cada pixel luminoso. Em teoria os óxidos semiconductores podem ser fabricados em substratos de grandes dimensões, e eventualmente num futuro próximo, em substratos flexíveis de baixo custo, como o plástico e o papel. Esta possibilidade torna esta tecnologia um competidor direto com a electrónica orgânica, em particular onde o desempenho e o custo são um requisito essencial. Esta dissertação apresenta a caracterização eléctrica de um conjunto de Transístores de Efeito de Campo (FET) com base em filme finos de óxidos amorfos. Apresenta os métodos de fabrico, os materiais usados, estrutura física, modo de funcionamento e as características eléctricas. TFTs com base em óxidos semiconductores sofrem de um conjunto de problemas que afectam o seu desempenho. Uma das instabilidades é a alteração das propriedades eléctricas quando expostos à luz. Este problema é tanto mais grave já que umas das aplicações dos TFTs é justamente em ecrãs. O objectivo principal desta dissertação é identificar a origem física da instabilidade à luz. Com este objectivo usou-se um conjunto de técnicas eléctricas desenhadas para obter informação sobre os estados electrónicos que são induzidos quando o TFT é exposto à luz. Um das técnicas usadas foi o método das Correntes Termo Estimuladas (TSC). O óxido semiconductor em estudo foi o Zinc Tin Oxide (ZTO). Os resultados obtidos permitiram concluir que a luz induz um estado electrónico no semiconductor. Este estado electrónico comporta-se como um dopante e aumenta a condutividade eléctrica do material. As TSCs permitiram ainda identificar que este dopante esta energeticamente localizado a 0.14 eV da banda de condução do semicondutor. O estado induzido pela luz é muito mais raso que o estado responsável pela condução eléctrica normal, quando o TFT não é exposto à luz. TFTs não expostos à luz mostram um processo de condução termicamente ativado mas com uma energia de activação de 0.22 eV. Os estados electrónicos induzidos pela luz tem um tempo de vida de algumas horas. Este tempo de vida é suficientemente longo para considerar a possibilidade de usar este efeito em foto-sensores do tipo Charge-Coupled Devices (CCD) ou em memórias ópticas. Desta forma um efeito que é prejudicial pode ser convertido numa aplicação prática.
- Light-induced effects on oxide based thin film transistorsPublication . Cardoso, André Lança; Gomes, Henrique L.Este trabalho incidiu sobre a análise elétrica dos transístores com base em óxidos semicondutores. Esta é uma área emergente e tecnologicamente relevante. Numa primeira fase a dissertação aborda com detalhe, os aspetos essenciais dos transístores com base em óxido semiconductor: Discute-se a sua origem, estrutura, os métodos de fabrico e as aplicações. Depois desta introdução, os efeitos da exposição à luz nas propriedades elétricas dos transístores são apresentados e discutidos em detalhe. Foram estudados transístores preparados através de uma solução líquida de ureia. Este processo de fabrico torna possível imprimir ou depositar o semicondutor em substratos flexíveis e de baixo custo, abrindo um conjunto de novas oportunidades para tecnologia eletrónica com base em óxidos amorfos semicondutores. Até recentemente esta possibilidade de imprimir eletrónica era apenas possível com transístores orgânicos. Os problemas relacionados com a exposição de luz em transístores de óxidos amorfos tem sido estudados na literatura e atribuídos a interação de cargas elétricas com defeitos no semiconductor. Este tipo de defeito é conhecido por lacunas de oxigénio. Estes defeitos eletrónicos foto-induzidos afetam a performance do transístor e modificam temporariamente os seus parâmetros, nomeadamente a mobilidade de efeito de campo, a tensão de arranque, a condutividade elétrica, as correntes de fuga e a estabilidade operacional. Os resultados obtidos nesta dissertação mostram que a exposição prolongada à luz com energia igual ou superior ao hiato do ZTO induzem estados dopantes duradouros. Estes estados dopantes estão localizados aproximadamente a 0.14 eV do limite da banda de condução. É proposto que as espécies químicas responsáveis pelos estados induzidos pela luz, sejam os espaços não ocupados do oxigénio ionizado. Porém, mais experiências são precisas para provar esta proposta. A iluminação afeta também a estabilidade operacional do transístor. Transístores submetidos à iluminação sofre de uma rápida variação da tensão de arranque. Transístores fabricados usando ureia são mais instáveis do que que transístores fabricados usando técnicas de sublimação térmica. Estas diferenças de comportamento são atribuídas à presença de defeitos eletricamente ativos. Sugere-se que estes defeitos estão localizados na interface entre o dielétrico e semicondutor. Estudos da corrente que flui no transístor em função da temperatura revelam um comportamento anómalo. Foram detetadas dois tipos de anomalias uma devido aos estado induzidos pela luz e outra causada pela presença de uma quantidade residual de água na superfície do dielétrico.
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