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- The recreational use value of a national forestPublication . Simões, Paula Marisa NunesNational forests and woodlands are some of the environmental public resources that provide a diversity of goods and services to society. Supporting, regulating, provisioning and cultural services are all known to contribute to human well-being. As these services are not traded in regular markets because of the public or semi-public characteristics of the resources involved, their values are largely unknown. However, a deeper knowledge of the related benefits’ value is expected to help to enhance management practices. The research described in this dissertation concentrates on the analysis of the benefits related to recreational activities enjoyed in national forests and in understanding the demand for these environmental services. The research was motivated by the perception that these values are largely unknown, particularly in Portugal. Bussaco National Forest was chosen as the case study area, but the conclusions are likely to be adapted and extended to other national forests. Two non-market valuation techniques, the travel cost method and the contingent behaviour method, are used to estimate the recreational use benefits. The travel cost method, which belongs to the group of revealed preferences techniques, is used to analyse the actual behaviour and enables us to estimate recreational use values in current conditions. The individual version of the method is identified as the most accurate in the present context as we analyse the recreational demand of a forest visited by people living at different distances from it. From the management perspective, it is also important to address how people would behave if new hypothetical conditions were to be observed. It is particularly important to predict the effects on demand resulting from changes in forest access costs and from the deterioration of current conservation conditions due to a forest fire. The contingent behaviour method, which belongs to the group of stated preferences techniques, is applied jointly with the travel cost method to assess the effects of these changes. Count data models corrected for endogenous stratification and ordered models are used in the analysis of the actual visit behaviour. Travel cost, substitute cost, income per capita, visit motivations, on-site time and visit distribution during the year were identified as the main explanatory variables of demand. Price and income elasticity of demand computed using count data models are low. This result is supported by the ordered models, as results show that the change in income/price must be quite significant to modify demand levels. Considering only the current users, the forest recreational use value estimated for the past three years is about €106 700. A count data model and a pseudo-panel specification is used to combine contingent and observed travel behaviour. The analysis reveals that visitors are sensitive to price and quality changes and that in the forest fire scenario the intended number of trips would be seriously reduced, thus imposing an important welfare loss. There are evidences of hypothetical bias in answers to future behaviour if current conditions do not change and signals of strategic bias when changes in management options are in view. There are no signals of these biases when the quality changes are exogenous.
- Estudo bibliométrico da contribuição de Buckley e Casson (1976) na pesquisa em negócios internacionaisPublication . Ferreira, Manuel Portugal; Serra, Fernando Ribeiro; Almeida, Martinho Isnard Ribeiro deNeste artigo, analisou-se a contribuição para a pesquisa em negócios internacionais da obra de Peter Buckley e Mark Casson, de 1976, The future of the multinational enterprise. Nessa obra, os autores conceitualizam uma das teorias fundacionais da pesquisa em negócios internacionais nas últimas três décadas: a teoria da internalização. Neste estudo bibliométrico analisou-se todo o histórico de publicações na revista líder – o Journal of International Business Studies (JIBS) – entre 1976 e 2010, que citam a obra de 1976, de Buckley e Casson. As análises de citações, de cocitações e de temas permitem verificar o impacto da Teoria da Internalização, e de Buckley e Casson (1976) em especial, na pesquisa em negócios internacionais. Conceitualmente fundado na teoria da internalização para o estudo das multinacionais e da internacionalização das empresas, as ramificações estendem-se para domínios diversos da disciplina e consagram essa obra como um dos trabalhos fundamentais das últimas décadas.
- Sequências perfeitas para sistemas de comunicação com acesso múltiplo por divisão de códigoPublication . Pereira, João da SilvaUma sequência perfeita é identificada quando a sua função de autocorrelação periódica é igual a um impulso unitário de Dirac ou quando todos os valores desfasados de autocorrelação são iguais a zero. No design de sequências perfeitas, a dificuldade é conseguir sequências em quantidade suficiente com baixos valores de correlação cruzada. Nesta tese, são propostos novos métodos de construção de grandes conjuntos de sequências perfeitas derivadas de uma transformada discreta e inversa de Fourier (IDFT). Cada novo conjunto de sequências de autocorrelação periódica perfeita tem um valor máximo absoluto de correlação cruzada periódica (MaxCC) estritamente inferior ao pico máximo da autocorrelação (igual ao comprimento N das sequências).Todos os valores MaxCC encontrados são iguais ou muito próximos do limite inferior teórico “raiz quadrada de N”. Não obstante, alguns dos novos conjuntos de sequências perfeitas são ortogonais e também possuem valores MaxCC baixos. Além disso, novos métodos foram sugeridos e permitiram criar ótimos conjuntos de novos códigos bipolares derivados de sequências perfeitas ortogonais e bidimensionais. É do conhecimento geral o quanto é difícil encontrar valores determinísticos tal como o MaxCC para sequências perfeitas ou mesmo para outras famílias de códigos. Este documento fornece um conjunto de novas propriedades sobre sequências perfeitas e demonstrações matemáticas que permitem determinar alguns MaxCC. Adicionalmente, foram encontrados novos limites superiores de probabilidade de erro em função do valor máximo absoluto de correlação cruzada aperiódica. Da mesma forma, a probabilidade de erro foi reescrita com base no rácio de potência de contraste da família de códigos selecionada para um determinado sistema de comunicação CDMA (Code Division Multiple Access) ou OCDMA (Optical Code Division Multiple Access). Diferentes sistemas de comunicação CDMA foram simulados com as novas famílias de sequências perfeitas. Todas as simulações mostraram como as novas sequências perfeitas e sequências quase perfeitas devem ser úteis em sistemas de comunicação. Esta tese apresenta simulações para mostrar o quanto as novas sequências perfeitas podem ser utilizadas em cenários multiusuários num sistema de comunicação CDMA por Rádio Frequência e também num sistema de comunicação OCDMA. Para um sistema OCDMA, os codificadores/descodificadores selecionados foram as SSFBG (Super Structured Fiber Bragg Grating). Este documento mostra que a seleção correta dos conjuntos de códigos escritos nas SSFBG é fundamental e os sinais óticos das SSFBG são muito parecidos com as sequências perfeitas. Todas as novas famílias de sequências perfeitas, sequências perfeitas e ortogonais, e sequências mutuamente ortogonais podem ser aplicadas em sistemas de comunicação OFDM-CDMA (Orthogonal Frequency-Division Multiplexing - Code Division Multiple Access) ou num simples sistema CDMA de comunicação. No futuro, os novos conjuntos de sequências perfeitas poderão ser utilizados em diversos sistemas de comunicação, na geração de sinais para radares e em tecnologias aplicadas a sonares.
- Immobilized heterologous Rhizopus oryzae lipase: A feasible biocatalyst for the production of human milk fat substitutesPublication . Tecelão, Carla; Guillén, Marina; Valero, Francisco; Ferreira-Dias, SuzanaThis work aims at evaluating the potentialities of a heterologous Rhizopus oryzae lipase (rROL) as a feasible biocatalyst, to be used as an alternative to commercial lipases, for the synthesis of Human Milk Fat Substitutes (HMFS). This enzyme was immobilized in three different supports (Accurel® MP 1000, Eupergit® C and Lewatit® VP OC 1600) and tested as catalysts for the acidolysis between tripalmitin and oleic acid, batchwise, at 60 ◦C, in solvent-free medium. The highest molar incorporations of oleic acid in the triacylglycerols were achieved with rROL in Lewatit® VP OC 1600 and Accurel® MP 1000, although the highest immobilization yields were observed with Eupergit® C. Quasi-equilibrium was attained after 6 h or 12 h reaction, with about 30 mol.% and 22 mol.% of oleic acid incorporation, when rROL immobilized in Lewatit and Accurel were used, respectively. Also, 23 h batch operational stability tests were performed: half-life times (t1/2) of 34.5 h and 64.0 h were achieved for rROL immobilized in Accurel® MP 1000 and in Lewatit® VP OC 1600, respectively. An important increase in the operational stability was observed for rROL immobilized in Lewatit after rehydration at the end of each batch (t1/2 = 202 h). Thus, the loss of activity may be explained by a progressive dehydration occurring along the reaction.
- Performance study about biodiesel impact on buses engines using dynamometer tests and fleet consumption dataPublication . Serrano, Luis M.V.; Câmara, Rui M.O.; Carreira, Vasco J.R.; Gameiro da Silva, M.C.The problem of reducing harmful emissions, mainly particulate matter (PM) and nitrogen oxides (NOxs) originated in compression ignition combustion engines, and also the mandatory intention of lowering the CO2 impacts of road transportation define the need to improve our knowledge on biodiesel use in engines. A 6 in line cylinders Volvo engine was submitted to a 100 min cycle with 27 stabilized steps for seven different fuel blends from pure fossil diesel (B0) to pure biodiesel (B100), considering also B10, B15, B20, B30, B50 fuel blends. The cycle imposed tries to simulate a normal use of a bus in an urban and extraurban circuit, considering different engine rotation and loads applied. An analysis on consumption data obtained of a fleet was made. The fleet had near 200 buses, used different fuel blends, and operated in the north of Portugal. Results reveal that the cycle imposed reflects very well the tendency of consumption, allowing to confirm the methodology and also to check influences on consumption, mainly associated with possibilities to decrease CO2 emissions by using some biodiesel blends on buses. This allows increasing the quality of data in vehicle real use and tightening the uncertainties on the actual effects of using biodiesel.
- On categories with semidirect productsPublication . Martins-Ferreira, Nelson; Sobral, ManuelaNecessary and sufficient conditions for a pointed category to admit semidirect products, in the sense of Bourn and Janelidze (1998) [3], are provided and interpreted in terms of protomodularity and exactness of appropriate split chains.
- A Stochastic Dynamic Programming Approach to Optimize Short-Rotation Coppice Systems Management Scheduling: An Application to Eucalypt Plantations under Wildfire Risk in PortugalPublication . Ferreira, Liliana; Constantino, Miguel F.; Borges, José G.; Garcia-Gonzalo, JordiThis article presents and discusses research with the aim of developing a stand-level management scheduling model for short-rotation coppice systems that may take into account the risk of wildfire. The use of the coppice regeneration method requires the definition of both the optimal harvest age in each cycle and the optimal number of coppice cycles within a full rotation. The scheduling of other forest operations such as stool thinning and fuel treatments (e.g., shrub removals) must be further addressed. In this article, a stochastic dynamic programming approach is developed to determine the policy (e.g., fuel treatment, stool thinning, coppice cycles, and rotation length) that maximizes expected net revenues. Stochastic dynamic programming stages are defined by the number of harvests, and state variables correspond to the number of years since the stand was planted. Wildfire occurrence and damage probabilities are introduced in the model to analyze the impact of the wildfire risk on the optimal stand management schedule policy. For that purpose, alternative wildfire occurrence and postfire mortality scenarios were considered at each stage. A typical Eucalyptus globulus Labill. stand in Central Portugal was used as a test case. Results suggest that the proposed approach may help integrate wildfire risk in short-rotation coppice systems management scheduling. They confirm that the maximum expected discounted revenue decreases with and is very sensitive to the discount rate and further suggest that the number of cycles within a full rotation is not sensitive to wildfire risk. Nevertheless, the expected rotation length decreases when wildfire risk is considered.
- Explaining the seismic moment of large earthquakes by heavy and extremely heavy tailed modelsPublication . Felgueiras, Miguel MartinsThe search of physical laws that explain the energy released by the great magnitude earthquakes is a relevant question, since as a rule they cause heavy losses. Several statistical distributions have been considered in this process, namely heavy tailed laws, like the Pareto distribution with shape parameter α ≈ 0. 6667. Yet, for the usually considered Californian region (where earthquakes with moment magnitude, MW, greater than 7. 9 were never registered) the Pareto distribution with index near the above mentioned seems to have a "too heavy" tail for explaining the bigger earthquakes seismic moments. Usually an exponential tapper is applied to the distribution right tail (above the so called corner seismic moment), or another distribution is considered to explain these high seismic moment data (like another Pareto with different shape parameter). The situation is different for other regions where seisms of larger magnitudes do occur, leading to data sets for which heavy or even extremely heavy tailed models are appropriated. The purpose of this paper is to reduce the seismic moment, M0, of the very large earthquakes to particular heavy and extremely heavy tailed distributions. Using world seismic moment information, we apply Pareto, Log-Pareto and extended slash Pareto distributions to the data, truncated for M0 ≥ 1021 Nm and for M0 ≥ 1021. 25 Nm. For these great seisms we conclude that extended slash Pareto is a promising alternative to the more traditional Pareto and Log-Pareto distributions as a candidate to the real model underlying the data.
- Using Peano–Hilbert space filling curves for fast bidimensional ensemble EMD realizationPublication . Costa, Paulo; Barroso, João; Fernandes, Hugo; Hadjileontiadis, Leontios JEmpirical mode decomposition (EMD) is a fully unsupervised and data-driven approach to the class of nonlinear and non-stationary signals. A new approach is proposed, namely PHEEMD, to image analysis by using Peano–Hilbert space filling curves to transform 2D data (image) into 1D data, followed by ensemble EMD (EEMD) analysis, i.e., a more robust realization of EMD based on white noise excitation. Tests’ results have shown that PHEEMD exhibits a substantially reduced computational cost compared to other 2D-EMD approaches, preserving, simultaneously, the information lying at the EMD domain; hence, new perspectives for its use in low computational power devices, like portable applications, are feasible.