Suchergebnisse

Doutoramento em Física ; The high dependence of Portugal from foreign energy sources (mainly fossil fuels), together with the international commitments assumed by Portugal and the national strategy in terms of energy policy, as well as resources sustainability and climate change issues, inevitably force Portugal to invest in its energetic self-sufficiency. The 20/20/20 Strategy defined by the European Union defines that in 2020 60% of the total electricity consumption must come from renewable energy sources. Wind energy is currently a major source of electricity generation in Portugal, producing about 23% of the national total electricity consumption in 2013. The National Energy Strategy 2020 (ENE2020), which aims to ensure the national compliance of the European Strategy 20/20/20, states that about half of this 60% target will be provided by wind energy. This work aims to implement and optimise a numerical weather prediction model in the simulation and modelling of the wind energy resource in Portugal, both in offshore and onshore areas. The numerical model optimisation consisted in the determination of which initial and boundary conditions and planetary boundary layer physical parameterizations options provide wind power flux (or energy density), wind speed and direction simulations closest to in situ measured wind data. Specifically for offshore areas, it is also intended to evaluate if the numerical model, once optimised, is able to produce power flux, wind speed and direction simulations more consistent with in situ measured data than wind measurements collected by satellites. This work also aims to study and analyse possible impacts that anthropogenic climate changes may have on the future wind energetic resource in Europe. The results show that the ECMWF reanalysis ERA-Interim are those that, among all the forcing databases currently available to drive numerical weather prediction models, allow wind power flux, wind speed and direction simulations more consistent with in situ wind measurements. It was ...

The entrepreneurship philosophy assimilated shaped perfectly to the new reality provided by the emergence of the new technologies of information and communication, connecting people and organizations and narrowing the distance between them. With this distance shortage, entrepreneurship assumed a more local dimension than ever, promoting the emergence of smaller entrepreneurial ecosystems at a city-level, ceasing to be exclusive to big cities: the digital business ecosystems. These smaller communities are, therefore, unique and, due to the intrinsic factors of its location (society, culture, finance, politics, demography, etc.), validate the premise of placing the city as the center of the study of entrepreneurship. Recently, academical studies have been using this approach to analyze the entrepreneurial activity in cities, with the help of composite indexes which provide numerical comparisons between the cities. However, these studies tend to be focused on matured digital business ecosystems. As such, this dissertation is motivated by such lack of knowledge and analysis of less-matured digital business ecosystems. The aim of this study is to develop a model of comparison of less-matured digital business ecosystem to be applied in the southern and eastern European region and, with its results, analyze the patterns of such region. This dissertation is settled on a solid literature review followed by a study of the region selected to validate the conditions previously established. With this knowledge base, the model is developed following a strategy fitted with the characteristics of less-matured entrepreneurial ecosystems (configuration, themes, variables, weights, data processing and display). The final results are analyzed and used a base to conjecture about the region's entrepreneurial activity. With this study, it was concluded that the strategy defined cannot be the same as the other more general models, and is crucial to attaining reliable results through this model with these particularities. Concerning with the final results, it was concluded that this region has potential to evolve its stage of entrepreneurial maturity, however, it currently lacks entrepreneurial culture and experience to fully enable input conditions to generate outputs aspired.

Intensive agricultural practices leading to habitat degradation represent a major threat to pollinators. Diverse management practices are expected to influence wild pollinator abundance and richness on farms, although their effect in perennial crops is still unclear. In this study, we assessed the impact of management on apple (Malus domestica) pollination on an oceanic island, by comparing conventional (with and without herbicide application) and organic apple orchards. Pollinator visitation and pan trap surveys were carried out in six apple orchards in Terceira Island (Azores) and the landscape composition surrounding orchards was characterized. We also quantified fruit set, seed set and apple weight. We found no significant effect of management on insect visitation rates, whereas there was a negative association with increasing surrounding agricultural land. In contrast, management had an effect on species abundance, richness and diversity at the orchard level. Conventional orchards without herbicides showed higher abundance than the rest, but lower richness and diversity than conventional orchards with herbicides. Management had an effect on fruit set, but not on seed set or fruit weight. Our results suggest that management alone is insufficient for the overall improvement of apple pollination on an oceanic island, while landscape composition may play a relevant role. ; Regional Government of Extremadura in Spain (PO17006); ACORES-01-0145-FEDER-000073 ; info:eu-repo/semantics/publishedVersion

The expansion of marine renewable power is a major alternative for the reduction of greenhouse gases emissions. In Europe, however, the high penetration of offshore wind brings intermittency and power variability into the existing power grid. Offshore solar photovoltaic power is another technological alternative under consideration in the plans for decarbonization. However, future variations in wind, air temperature or solar radiation due to climate change will have a great impact on both renewable energy resources. In this context, this study focusses on the offshore energy assessment off the coast of Western Iberia, a European region encompassing Portugal and the Northwestern part of Spain. Making use of a vast source of data from 35 simulations of a research project called CORDEX, this study investigates the complementarity of offshore wind and solar energy sources with the aim of improving the energy supply stability of this region up to 2040. Although the offshore wind energy resource has proven to be higher than solar photovoltaic resource at annual scale, both renewable resources showed significant spatiotemporal energy variability throughout the western Iberian Peninsula. When both renewable resources are combined, the stability of the energy resource increased considerably throughout the year. The proposed wind and solar combination scheme is assessed by a performance classification method called Delphi, considering stability, resource, risk, and economic factors. The total index classification increases when resource stability is improved by considering hybrid offshore wind-photovoltaic solar energy production, especially along the nearshore water ; X. Costoya is supported by the Spanish Government through a Juan de la Cierva Postdoctoral Fellowship (FJCI-2017-32577). This work was partially supported by Xunta de Galicia under project ED431C 2021/44 (Grupos de Referencia Competitiva) and Ministry of Science and Innovation of the Government of Spain under the project SURVIWEC PID2020-113245RB-I00. D. ...