Channel and frequency offset estimation schemes for multicarrier systems

Doutoramento em Engenharia ElectrotécnicaO presente trabalho aborda o problema da estimação de canal e da estimação de desvio de frequência em sistemas OFDM com múltiplas configurações de antenas no transmissor e no receptor. Nesta tese é apresentado o estudo teórico sobre o impacto da densidade de pilotos no desempenho da estimação de canal em sistemas OFDM e são propostos diversos algoritmos para estimação de canal e estimação de desvio de frequência em sistemas OFDM com antenas únicas no transmissor e receptor, com diversidade de transmissão e MIMO. O estudo teórico culmina com a formulação analítica do erro quadrático médio de um estimador de canal genérico num sistema OFDM que utilize pilotos dedicados, distribuidos no quadro transmitido em padrões bi-dimensionais. A formulação genérica é concretizada para o estimador bi-dimensional LS-DFT, permitindo aferir da exactidão da formulação analítica quando comparada com os valores obtidos por simulação do sistema abordado. Os algoritmos de estimação investigados tiram partido da presença de pilotos dedicados presentes nos quadros transmitidos para estimar com precisão os parâmetros pretendidos. Pela sua baixa complexidade, estes algoritmos revelam-se especialmente adequados para implementação em terminais móveis com capacidade computacional e consumo limitados. O desempenho dos algoritmos propostos foi avaliado por meio de simulação do sistema utilizado, recorrendo a modelos aceites de caracterização do canal móvel multipercurso. A comparação do seu desempenho com algoritmos de referência permitir aferir da sua validade. ABSTRACT: The present work focus on the problem of channel estimation and frequency offset estimation in OFDM systems, with different antenna configurations at both the transmitter and the receiver. This thesis presents the theoretical study of the impact of the pilot density in the performance of the channel estimation in OFDM systems and proposes several channel and frequency offset algorithms for OFDM systems with single antenna at both transmitter and receiver, with transmitter diversity and MIMO. The theoretical study results in the analytical formulation of the mean square error of a generic channel estimator for an OFDM system using dedicated pilots, distributed in the transmitted frame in two-dimensional patterns. The generic formulation is implemented for the two-dimensional LS-DFT estimator to verify the accuracy of the analytical formulation when compared with the values obtained by simulation of the discussed system. The investigated estimation algorithms take advantage of the presence of dedicated pilots present in the transmitted frames to accurately estimate the required parameters. Due to its low complexity, these algorithms are especially suited for implementation in mobile terminals with limited processing power and consumption. The performance of the proposed algorithms was evaluated by simulation of the used system, using accepted multipath mobile channel models. The comparison of its performance with the one of reference algorithms measures its validity

Internship supervisors' perception of the radiography students in clinical environment

The main goal of this research was to identify and describe the perception of internship supervisors of the radiography students in clinical environment about their competencies, skills and characteristics

Interchanging knowledge and experiments in a learning community in a view of collaborative work

Conferência realizada, em Lisboa, de 8-9 de Novembro de 2007.In this work we describe and analyze an experiment based in a programme of permanent seminars – e-DCET organized with the objective of developing practices of collaborative work inside the Departamento de Ciências Exactas e Tecnológicas (Universidade Aberta - Portugal), valuing the active sharing of pedagogic practices and knowledge at a variety of levels. Various themes were discussed and analyzed, among them we highlighted some experiences of online teaching in formal and non-formal contexts, user management in Moodle LMS, news from international e-learning meetings, visual representations and teaching chemistry online, pseudo-code as a communication language using Notetab and interactive materials in teaching mathematics

O papel das redes sociais na orientação clínica em estudantes de licenciatura

O ensino clínico e os papéis dos diversos intervenientes constituem um elemento primordial na formação dos alunos, promovendo a sua aprendizagem e consequentemente o seu futuro como profissionais. Este trabalho, visa à identificação e compreensão de determinadas competências e momentos que são valorizados para o sucesso do aluno estagiário de um curso superior, que emergem de conhecimento obtido a partir de redes sociais informais, bem como o nível das expetativas que os atores sociais apresentam em relação à capacidade e desenvolvimento dos mesmos no futuro

Canopy insect herbivores in the Azorean Laurisilva forests: key host plant species in a highly generalist insect community

Copyright © ECOGRAPHY 2005.This article explores patterns of insect herbivore distribution in the canopy of the Laurisilva forests on seven islands in the Azores archipelago. To our knowledge, this is one of the first extensive studied of this type in tree or shrub canopies of oceanic island ecosystems. One of the most frequently debated characteristics of such ecosystems is the likely prevalence of vague, ill-defined niches due to taxonomic disharmony, which may have implications for insect-plant interactions. For instance, an increase in ecological opportunities for generalist species is expected due to the lack of predator groups and reduced selection for chemical defence in host plants. The following two questions were addressed: 1) Are specialists rare species, and insect herbivore species randomly distributed among host plant species in the Azores? 2) Are the variances in insect herbivore species composition, frequency and richness explained by host plants or by regional island effects? We expect a proportional distribution of herbivore species between host plants, influenced by host frequency and distinct island effects; otherwise, deviation from expectation might suggest habitat preference for specific host tree crowns. Canopy beating tray samples were performed on seven islands, comprising 50 transects with 1 to 3 plant species each (10 replicates per species), giving 1320 samples from ten host species trees or shrubs in total. From a total of 129 insect herbivore species, a greater number of herbivore species was found on Juniperus brevifolia (s=65) and Erica azorica (s=53). However, the number of herbivore species per individual tree crown was higher for E. azorica than for any other host, on all islands, despite the fact that it was only the fourth more abundant plant. In addition, higher insect species richness and greater insect abundance were found on the trees of Santa Maria Island, the oldest in the archipelago. Insect species composition was strongly influenced by the presence of E. azorica, which was the only host plant with a characteristic fauna across the archipelago, whereas the fauna of other plant crowns was grouped by islands. The great insect occurrence on E. azorica reflects strong habitat fidelity, but only four species were clearly specialists. Our findings indicate a broadly generalist fauna. The simplicity of Azorean Laurisilva contributed to the understanding of insect-plant mechanisms in canopy forest habitats

VLCLighting - A Collaborative Research Project on Visible Light Communication

This paper describes a collaborative research project on Visible Light Communications for lighting infrastructures. It is being developed by the Integrated Circuits and Mobile Network groups in Instituto de Telecomunicações, Aveiro site, and expects to deliver a VLC demonstrator transmitting video and data in real-time by the end of 2016. Another main goal is to develop this system to be modular in order to enable collaboration with other groups with interest in this field, offering the academic community a real-time test bed to evaluate the performance of different modules, algorithms and optical front-ends, which is currently not available

Age constraints on the Late Cretaceous alkaline magmatism on the West Iberian Margin

The onshore sector of theWest Iberian Margin (WIM) was the locus of several cycles of magmatic activity during the Mesozoic, the most voluminous of which was of alkaline nature and occurred between 70 and 100 Ma. This cycle took place in a post-rift environment, during the 35 counter-clockwise rotation of Iberia and initiation of the alpine compression. It includes the subvolcanic complexes of Sintra, Sines, and Monchique, the volcanic complex of Lisbon and several other minor intrusions, covering an area of approximately 325 km2. Previous cycles were tholeiitic and transitional in nature, occuring around 200 Ma and 130–135 Ma, respectively. New LA-ICP-MS U-Pb, 40Ar/39Ar, K-Ar and Rb-Sr ages on several intrusions distributed along the onshore WIM are presented, which combined with reviously published data allows us to constrain the duration of the Late Cretaceous alkaline cycle to circa 22 Ma (94–72 Ma) and define two pulses of magmatic activity. The first one (94–88 Ma) occurred during the opening of the Bay of Biscay and consequent rotation of Iberia and clusters above N38 200 . The second pulse (75–72 Ma) has a wider geographical distribution, from N37 to N39 . This final pulse occurred during the initial stages of the Alpine orogeny in Iberia that led to the formation of the Pyrenees and Betics and to tectonic inversion of the Mesozoic basins. Isotope and trace element geochemistry point to a sublithospheric source for the alkaline magmatism that clearly distinguishes it from the previous cycles which had an important lithospheric mantle component. Also, it allows the discrimination between the two different alkaline pulses in terms of trace element abundance and residual mantle minerology. It is speculated that these differences might be the result of distinct magma ascent rates due to either more or less favourable tectonic settings that avoided or allowed the interaction with metasomatized lithosphere and equilibration with K rich minerals like amphibole and/or phlogopite

Concurso de Pontes de Esparguete: Engenho e Criatividade

O principal objectivo do concurso de Pontes de Esparguete promovido pelos Departamentos de Engenharia Electromecânica e de Engenharia Civil é incentivar as capacidades criativas dos alunos aplicando os conhecimentos adquiridos no projecto de uma ponte executada com um material tão comum como o esparguete. Este evento visa aumentar o interesse dos alunos pela criatividade/investigação e pela procura de soluções engenhosas para os problemas propostos. Trata-se de um concurso já com nove edições, tendo sido o precursor em Portugal de eventos similares promovidos por outras instituições de Ensino Superior, Secundário e Básico. Neste artigo é apresentada a evolução do evento desde a sua génese, tanto ao nível das soluções encontradas pelos alunos para consecutivamente quebrarem os recordes de resistência, como pela motivação demonstrada na participação neste tipo de concursos didácticos destinados ao ensino da engenharia.info:eu-repo/semantics/publishedVersio

Relação entre o número de espécies e o número de táxones de alto nível para a fauna de artrópodes dos Açores

Nesta contribuição pretendemos avaliar a aplicação dos modelos RESTAN, "Relação entre o número de Espécies e o número de Táxones de Alto Nível", à fauna de artrópodes de vários habitats das ilhas dos Açores. Utilizámos várias bases de dados recentemente obtidas baseadas em amostragens estandardizadas de artrópodes epígeos do solo em florestas de áreas protegidas, artrópodes fitófagos e predadores de pastagens semeadas e semi-naturais e artrópodes da copa da árvore endémica Juniperus brevifolia. Os modelos RESTAN são aplicados não só usando dados puramente taxonómicos, mas igualmente agrupando os taxa em termos de estratégias ecológicas (e.g. herbívoros, predadores) e de colonização das ilhas (e.g. endémicos). Deste modo pensamos poder avaliar a aplicabilidade destes modelos em estudos de estrutura de comunidades e de conservação. Para os Açores, a aplicação dos modelos RESTAN constitui uma forma muito prática e eficaz de obter estimativas de diversidade. De facto, em todas as matrizes de dados analisadas a riqueza de espécies pode ser estimada eficazmente usando apenas a riqueza em géneros, sendo a relação linear. Ao nível da família, os modelos estimadores possuem um menor poder explicativo e são melhor explicados por uma função exponencial. O escalonamento de Reservas Florestais Naturais dos Açores em termos de biodiversidade de artrópodes endémicos pode ser efectuado usando informação taxonómica ao nível do género. A aplicação de métodos de estimativa rápida de biodiversidade fica assim facilitada, podendo usar-se parataxonomistas bem treinados para o processo de triagem do grande número de amostras geralmente necessárias em estudos ecológicos. Discute-se igualmente a aplicabilidade dos modelos RESTAN a dados de diversidade alfa, beta e gama.ABSTRACT: In this contribution we examine the predictive power of numbers of higher taxa (orders, families and genera) as surrogates of species richness ("RESTAN" models – models based on linear relationship between species and higher taxa numbers) for the Azorean arthropod fauna. Recently, two large entomological and ecological studies were performed in the Azores, using standardized sampling protocols to estimate the diversity of arthropods in grassland and native forests. We use datasets available from those studies to address a few technical questions: A. what is the impact of using several measures of diversity (alpha, gamma and beta species diversity; Shannon-Wiener index of diversity; Evenness) based on numbers of families and genera for canopy arthropods? For instance, could be predicted that values of beta-diversity decrease with the use of higher-taxa estimates. All the measures of diversity could be used, being the genera the best predictor; B. how well behave the RESTAN models for functional groups of species like grass-feeding and web-building spiders in grasslands? The predictive power of higher-taxa is low using web-building spiders, due to few families being envolved and some genera having many species locally represented; C. assuming at least one sample with no species then there will be also no highertaxa in that sample. Consequently, the curve of the relationship between highertaxa richness and species richness should be anchored to the origin (y= bx). What is the predictive value of this model in comparison with the linear (y =a + bx), log-log (log y = a + b log x) and exponential (y = A • e b x) models? The best fit was obtained with the linear model for the genus-species relationship, but the variables are not normally distributed and the log-log model should be preferable. For the family-species relationship the exponential model is the best. The linear model anchored to the origin (y =bx) has some statistical pitfalls and was of less predictive value; D. in conservation studies what is the predictive value of higher-taxa in ranking protected areas? We found that the numbers of arthropod genera could successfully rank the Natural Forest Reserves as well as numbers of species (using endemic species dataset). We found that in the Azores the predictions of species richness using higher-taxa are quite reasonable, mainly because of low levels of diversity. Therefore, costeffective studies could use only genera, since the species richness of arthropods could be predicted reasonably closely from their genus-level richness. Family and order-level data were less informative for all datasets. We suggest that in the Azores as a consequence of the low levels of species diversification with a great proportion of monospecific genera, the use of parataxonomists trained in genus-level identification could be appropriate for sorting large numbers of ecological samples

Adverse effects of levomepromazine in sheep

Variações do hemograma, frequência cardiorrespiratória, temperatura retal e movimentos ruminatórios foram estudados, antes e após a aplicação de levomepromazina em oito ovinos separados em dois lotes de igual número. O primeiro lote recebeu a droga por via intramuscular (2 mg/kg) e o segundo pela via intravenosa (1 mg/kg). As amostras sanguíneas e os sintomas clínicos foram colhidos antes e aos 15, 30 e 60 minutos após a aplicação do fármaco. Em todos os animais evidenciou-se a diminuição do número de eritrócitos (8,57 - 7,32 milhões/mm3) e dos valores do hematócrito (32,37 - 27,12%), eosinopenia (708,75 - 452,50 mm3) e neutrofilia (2.337,50 - 3.345,00 mm3). A taxa de leucócitos e linfócitos permaneceu praticamente constante. A frequência cardíaca e respiratória diminuiu nos primeiros 15 minutos (130 - 118 bat./min. e 97,50 - 49,87 mov./min.), aumentando logo após (132 - 143 bat./min. e 60,00 - 68,75 mov./min.). A temperatura retal e os movimentos de rúmen permaneceram sem alteração.Change of hemogram, cardiopulmonary frequency, rectal temperature and rumen motility was studied prior and post application of levomepromazine in eight sheep divided into two groups of equal number. The first group received intramuscularly (2 mg/kg) and the second intravenously (1 mg/kg). The blood samples and the clinical symptoms were gathered prior. 15, 30 and 60 minutes post the drug application. In all animals a decrease of erythrocyte number (8.57 - 7.32 million/mm3) and haematocrit values (32.37 - 27.12%) was observed. Eosinopenia (708.75 - 452.50 mm3) and neutrophilia (2,337.50 - 3,345.00 mm3) were also observed. The leukocytes and lymphocytes counts remained constant. The cardiac and pulmonary frequency decreased 15 minutes after the drug application (130 - 118 bat./min and 97.60 - 49.87 mov./min.). After this time increase (132- 143 bat./min. and 60.00-68.75 mov./min.) was observed. The rectal temperature and rumem motility rate remained practically constant during the experiment