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O setor das telecomunicações encontra-se em transição para a quinta geração de redes sem fios. Esta transição vem acompanhada de novos desafios, nomeadamente o aumento do número de dispositivos conectados. O facto de haver mais dispositivos a consumir mais largura de banda aumentará inevitavelmente o consumo de energia e, consequentemente, a pegada de carbono das redes sem fios, a menos que se aumente a eficiência energética. Face a este desafio, este trabalho tem como objetivo contribuir para o aumento da eficiência energética de antenas altamente dirigidas e flexíveis, na forma de agregados de antenas. As estratégias exploradas neste trabalho centram-se na manipulação dos sinais radiados, o que significa que estes sinais são substancialmente diferentes do sinal a ser transmitido. O sinal transmitido é, contudo, devidamente reconstruido no campo distante. Foram investigadas duas abordagens para gerar os sinais radiados. A primeira abordagem consiste em dividir a antena em duas partes, cada uma das quais radia um sinal modulado em fase, uma vez que estes sinais permitem operar os amplificadores com eficiência máxima. A segunda abordagem consiste em radiar sinais intermitentes (burst signals, em inglês), de modo a que cada burst seja um sinal modulado em fase. Embora a primeira abordagem não tenha vingado, a segunda abordagem permite reduzir o consumo de energia entre 12% e 44% e a potência dissipada entre 73% e 84%, desde que os amplificadores possam ser desligados durante os períodos de inatividade dos sinais intermitentes. The telecommunications sector is currently transiting towards the fifth generation wireless networks. Such a transition comes with new challenges, in particular the growth of the number of connected devices. Having more devices consuming more bandwidth shall unavoidably increase the power consumption of wireless networks, and thus its carbon footprint, unless energy efficiency is increased. For this reason, this work aims to contribute to increasing the energy efficiency of highly directive and flexible antenna transmitters: phased array antennas. The strategies explored in this work focus on manipulating the radiated signals, which means that such signals are substantially different from the signal to be transmitted. The signal to be transmitted is nonetheless correctly reconstructed in the far field. Two approaches for generating the radiated signals were investigated. The first approach consists in partitioning the antenna in two halves, each of which radiates a phased modulated signal, since such signals allow to operate the power amplifiers at maximum efficiency. The second approach consists in radiating burst signals, such that each burst is a phased modulated signal. Although the first approach proved ineffective, the second approach allows reducing power consumption between 12% and 44% and the dissipated power between 73% and 84%, provided that power amplifiers can be switched off during the idle periods of the bursts. Mestrado em Engenharia Física

O setor das telecomunicações encontra-se em transição para a quinta geração de redes sem fios. Esta transição vem acompanhada de novos desafios, nomeadamente o aumento do número de dispositivos conectados. O facto de haver mais dispositivos a consumir mais largura de banda aumentará inevitavelmente o consumo de energia e, consequentemente, a pegada de carbono das redes sem fios, a menos que se aumente a eficiência energética. Face a este desafio, este trabalho tem como objetivo contribuir para o aumento da eficiência energética de antenas altamente dirigidas e flexíveis, na forma de agregados de antenas. As estratégias exploradas neste trabalho centram-se na manipulação dos sinais radiados, o que significa que estes sinais são substancialmente diferentes do sinal a ser transmitido. O sinal transmitido é, contudo, devidamente reconstruido no campo distante. Foram investigadas duas abordagens para gerar os sinais radiados. A primeira abordagem consiste em dividir a antena em duas partes, cada uma das quais radia um sinal modulado em fase, uma vez que estes sinais permitem operar os amplificadores com eficiência máxima. A segunda abordagem consiste em radiar sinais intermitentes (burst signals, em inglês), de modo a que cada burst seja um sinal modulado em fase. Embora a primeira abordagem não tenha vingado, a segunda abordagem permite reduzir o consumo de energia entre 12% e 44% e a potência dissipada entre 73% e 84%, desde que os amplificadores possam ser desligados durante os períodos de inatividade dos sinais intermitentes. The telecommunications sector is currently transiting towards the fifth generation wireless networks. Such a transition comes with new challenges, in particular the growth of the number of connected devices. Having more devices consuming more bandwidth shall unavoidably increase the power consumption of wireless networks, and thus its carbon footprint, unless energy efficiency is increased. For this reason, this work aims to contribute to increasing the energy efficiency of highly directive and flexible antenna transmitters: phased array antennas. The strategies explored in this work focus on manipulating the radiated signals, which means that such signals are substantially different from the signal to be transmitted. The signal to be transmitted is nonetheless correctly reconstructed in the far field. Two approaches for generating the radiated signals were investigated. The first approach consists in partitioning the antenna in two halves, each of which radiates a phased modulated signal, since such signals allow to operate the power amplifiers at maximum efficiency. The second approach consists in radiating burst signals, such that each burst is a phased modulated signal. Although the first approach proved ineffective, the second approach allows reducing power consumption between 12% and 44% and the dissipated power between 73% and 84%, provided that power amplifiers can be switched off during the idle periods of the bursts. Mestrado em Engenharia Física

Localized energy states such as two-color gap solitons are theoretically and numerically predicted in a periodic structure in the presence of a frequency doubling nonlinearity. These parametric solitons exhibit appealing features as compared to the Kerr case. Novel erects such as merging and all-optical buffering are envisaged.

Localized energy states such as two-color gap solitons are theoretically and numerically predicted in a periodic structure in the presence of a frequency doubling nonlinearity. These parametric solitons exhibit appealing features as compared to the Kerr case. Novel erects such as merging and all-optical buffering are envisaged.

Abstract The impact of CO 2 leakage from underground storage formations on shallow water resources is a concerning aspect in CO 2 capture and storage (CCS) risk assessment. In Campo de Calatrava region (Spain), natural CO 2 fluxes from the Earth’s mantle interact with shallow aquifers, resulting in significant changes in their physical and chemical properties. The resultant water is slightly acidic (pH 5.9-6.4), oxidizing, and enriched in iron (up to 6.1×10 -4 mol·L -1 ) and other metals usually found at trace concentrations. Thermodynamic calculations reveal that aqueous Fe(III) carbonate complexes play an important role in the persistence of this high concentration of iron and trace metals in solution.

Abstract The impact of CO 2 leakage from underground storage formations on shallow water resources is a concerning aspect in CO 2 capture and storage (CCS) risk assessment. In Campo de Calatrava region (Spain), natural CO 2 fluxes from the Earth’s mantle interact with shallow aquifers, resulting in significant changes in their physical and chemical properties. The resultant water is slightly acidic (pH 5.9-6.4), oxidizing, and enriched in iron (up to 6.1×10 -4 mol·L -1 ) and other metals usually found at trace concentrations. Thermodynamic calculations reveal that aqueous Fe(III) carbonate complexes play an important role in the persistence of this high concentration of iron and trace metals in solution.

The lack of real integration between the different dimensions of sustainability is highlighted in the literature as one of the main hindrances to lessening the environmental risks and impacts of large-scale development projects. This paper discusses a hypothesis concerning the problems of integration between the different dimensions of sustainability in socio-environmental research into such projects. Differences in modes of knowledge production and the relationships of these with prevailing social positions constitute the crux of the argument. Endeavours to improve translational knowledge and mixed research methodologies (seeking the semi-standardization of research processes) are put forward as approaches to overcoming the above-mentioned obstacles.

The lack of real integration between the different dimensions of sustainability is highlighted in the literature as one of the main hindrances to lessening the environmental risks and impacts of large-scale development projects. This paper discusses a hypothesis concerning the problems of integration between the different dimensions of sustainability in socio-environmental research into such projects. Differences in modes of knowledge production and the relationships of these with prevailing social positions constitute the crux of the argument. Endeavours to improve translational knowledge and mixed research methodologies (seeking the semi-standardization of research processes) are put forward as approaches to overcoming the above-mentioned obstacles.