Novel critical phenomena in optimization driven processes on networks

The work presented in this Ph.D thesis was developed in the context of complex network theory, from a statistical physics standpoint. We examine two distinct problems in this research field, taking a special interest in their respective critical properties. In both cases, the emergence of criticality is driven by a local optimization dynamics. Firstly, a recently introduced class of percolation problems that attracted a significant amount of attention from the scientific community, and was quickly followed up by an abundance of other works. Percolation transitions were believed to be continuous, until, recently, an 'explosive' percolation problem was reported to undergo a discontinuous transition, in [93]. The system's evolution is driven by a metropolis-like algorithm, apparently producing a discontinuous jump on the giant component's size at the percolation threshold. This finding was subsequently supported by number of other experimental studies [96, 97, 98, 99, 100, 101]. However, in [1] we have proved that the explosive percolation transition is actually continuous. The discontinuity which was observed in the evolution of the giant component's relative size is explained by the unusual smallness of the corresponding critical exponent, combined with the finiteness of the systems considered in experiments. Therefore, the size of the jump vanishes as the system's size goes to infinity. Additionally, we provide the complete theoretical description of the critical properties for a generalized version of the explosive percolation model [2], as well as a method [3] for a precise calculation of percolation's critical properties from numerical data (useful when exact results are not available). Secondly, we study a network flow optimization model, where the dynamics consists of consecutive mergings and splittings of currents flowing in the network. The current conservation constraint does not impose any particular criterion for the split of current among channels outgoing nodes, allowing us to introduce an asymmetrical rule, observed in several real systems. We solved analytically the dynamic equations describing this model in the high and low current regimes. The solutions found are compared with numerical results, for the two regimes, showing an excellent agreement. Surprisingly, in the low current regime, this model exhibits some features usually associated with continuous phase transitions.

Characterization of water-soluble organic matter from urban aerosols

Water-soluble organic matter (WSOM) from atmospheric particles comprises a complex array of molecular structures that play an important role on the physic-chemical properties of atmospheric particles and, therefore, are linked to several global-relevant atmospheric processes which impact the climate and public health. Due to the large variety of sources and formation processes, adequate knowledge on WSOM composition and its effects on the properties of atmospheric aerosol are still limited. Therefore, this thesis aims at providing new insights on the molecular composition of WSOM from fine atmospheric aerosols typical of an urban area (Aveiro, Portugal). In a first step, adsorption phenomena of semivolatile organic compounds on quartz fibre filters employed in the collection of atmospheric aerosols were assessed. Afterwards, atmospheric aerosol samples were collected during fifteen months, on a weekly basis. A mass balance of aerosol samples was performed in order to set the relative contribution of elemental carbon, WSOM and water-insoluble organic matter to the aerosol mass collected at the urban area of Aveiro, with a special focus on the assessment of the influence of different meteorological conditions. In order to assess the chemical complexity of the WSOM from urban aerosols, their structural characteristics were studied by means of Fourier transform infrared infrared - Attenuated Total Reflectance (FTIR-ATR) and solid-state cross polarization with magic angle spinning 13C nuclear magnetic resonance (CPMAS 13C NMR) spectroscopies, as well as their elemental composition. The structural characterization of aerosol WSOM samples collected in the urban area highlighted a highly complex mixture of functional groups. It was concluded that aliphatic and aromatic structures, hydroxyl groups and carboxyl groups are characteristic to all samples. The semi-quantitative assessment of the CPMAS 13C NMR data showed different distributions of the various functional groups between the aerosol samples collected at different seasons. Moreover, the presence of signals typical of lignin-derived structures in both CPMAS 13C NMR and FTIR-ATR spectra of the WSOM samples from the colder seasons, highlights the major contribution of biomass burning processes in domestic fireplaces, during low temperature conditions, into the bulk chemical properties of WSOM from urban aerosols. A comprehensive two-dimensional liquid chromatography (LC x LC) method, on-line coupled to a diode array, fluorescence, and evaporative light scattering detectors, was employed for resolving the chemical heterogeneity of the aerosol WSOM samples and, simultaneously, to map the hydrophobicity versus the molecular weight distribution of the samples. The LC x LC method employed a mixed-mode hydrophilic interaction column operating under aqueous reversed phase mode in the first dimension, and a size-exclusion column in the second dimension, which was found to be useful for separating the aerosol WSOM samples into various fractions with distinct molecular weight and hydrophobic features. The estimative of the average molecular weight (Mw) distribution of the urban aerosol WSOM samples ranged from 48 to 942 Da and from 45 to 1241 Da in terms of UV absorption and fluorescence detection, respectively. Findings suggest that smaller Mw group fractions seem to be related to a more hydrophobic nature.

Turismo sustentável e educação ambiental nos parques naturais de Montesinho e Douro Internacional

Esta Tese insere-se no âmbito das Ciências e Engenharia do Ambiente e aborda as temáticas do Turismo Sustentável, Educação Ambiental e Áreas Protegidas. Na atualidade o turismo é considerado como um dos fenómenos sociais e económicos mais importantes e um instrumento com grande importância para o desenvolvimento dos países e regiões. A discussão em torno do conceito de turismo sustentável, embora nem sempre coincidentes, orienta para uma conceção onde a componente ambiental, social e económica constituem as principais dimensões que devem ser consideradas no seu desenvolvimento. As áreas protegidas são territórios cuja principal função é conservação do ambiente. Estes espaços protegidos possuem um conjunto de recursos que os potenciam para o desenvolvimento do turismo sustentável e educação ambiental contribuindo, desta forma, para o desenvolvimento sustentado das regiões. Atualmente o turismo sustentável e a educação ambiental são uma realidade cada vez mais presente nas áreas protegidas contribuindo com benefícios sociais, económicos e para o desenvolvimento sustentável das regiões. Pretendeu-se com este trabalho analisar as opiniões e perceções dos visitantes, dos responsáveis dos empreendimentos turísticos, das associações locais e os dirigentes políticos, sobre o turismo sustentável e educação ambiental nos Parques Naturais de Montesinho e Douro Internacional com vista à apresentação de iniciativas para o seu desenvolvimento.Para a concretização deste desiderato geral foi selecionada uma metodologia que englobou, por um lado, uma análise empírica, através da implementação de inquérito por questionários aos visitantes dos Parques Naturais de Montesinho e Douro Internacional. A recolha de informação junto dos empreendimentos turísticos e associações locais, inseridos nos territórios dos parques naturais. Por outro lado, o inquérito por entrevista foi o instrumento de recolha de informação utilizado junto dos responsáveis políticos dos Concelhos que integram os Parques Naturais de Montesinho e Douro Internacional. Dos resultados obtidos, destaca-se que os visitantes, na maioria, são pessoas que visitaram estes parques pela primeira ou segunda vez, não ficam alojados na área e visitaram o parque acompanhados. Salienta-se a opinião favorável, destes, sobre a existência de áreas protegidas em Portugal e sobre a contribuição que estas podem dar para a conservação do ambiente, representando um recurso importante para as gerações futuras. Destaca-se, também, a opinião positiva sobre a visita aos parques e a consideração de que é importante o desenvolvimento do turismo e da educação ambiental. Em relação aos empreendimentos turísticos que participaram no estudo verificou-se que são, principalmente da tipologia de espaço rural. Além da oferta de alojamento, alguns empreendimentos turísticos disponibilizam atividades turísticas nos parques. Os responsáveis são da opinião que os parques são uma mais-valia para a região e tem uma opinião favorável sobre o desenvolvimento do turismo sustentável nas áreas em estudo. No que concerne às associações, verificou-se que as atividades que desenvolvem não estão vocacionadas para o turismo e educação ambiental. No entanto, estas associações também consideram importante a existência dos parques na região e que o turismo sustentável e a educação ambiental são duas componentes complementares que podem contribuir para o desenvolvimento sustentável das áreas dos parques. A opinião dos dirigentes dos municípios que integram os parques naturais de Montesinho e Douro Internacional orienta-se no mesmo sentido. Estes são de opinião que é necessário desenvolver uma estratégia e implementar medidas para o desenvolvimento do turismo sustentável nos parques naturais. Esperamos que os resultados desta investigação possam, de alguma forma, contribuir para orientar as iniciativas e ações de desenvolvimento do turismo sustentável e educação ambiental dos diversos agentes que atuam nos Parques Naturais de Montesinho e Douro Internacional.

Formação de professores e atividades práticas de astronomia no 1º CEB

Os estudos sobre astronomia e educação em astronomia com professores em serviço são escassos e o seu aumento significativo, nos últimos anos, denota a importância desta área na literacia científica dos cidadãos. Há uma necessidade de divulgar esse conhecimento para superar algumas dificuldades, tais como, a prevalência de conceções alternativas e a falta de implementação de atividades práticas no 1º Ciclo do Ensino Básico. Neste contexto, foi implementado um estudo quasi-experimental com professores e alunos dos 3º e 4º anos de escolaridade de escolas da costa norte de Portugal, que integrou aplicação de questionários diagnósticos em mais de um momento, e uma ação de formação sobre astronomia, para professores. A intenção era verificar se as conceções em relação à astronomia, de professores e alunos, estavam em conformidade com as descritas na literatura, e se a ação de formação, com base em atividades práticas, concebidas com materiais acessíveis e adequadas para colocar em prática com os alunos, foi resposta para melhorar os seus conhecimentos científicos e a prática docente. A análise dos dados a partir do pré-teste revelou conceções alternativas de acordo com a literatura. Os resultados verificados no pós-teste, administrado um ano mais tarde, para o grupo experimental de professores, e comparados com os do grupo de controlo, mostraram que a totalidade dos elementos do grupo experimental evidenciaram uma melhoria significativa no conhecimento científico e uma mudança concetual, devido ao desenvolvimento profissional implementado. Também se verificou que a realização de atividades práticas, através de metodologia de investigação, permitiu que os alunos pudessem compreender como funciona a ciência, o que se traduziu em progresso ao nível das aprendizagens e atitudes. A prática efetiva de atividades hands-on e minds-on parece ser uma maneira apropriada para construir e reforçar o conhecimento científico nesta área, acerca de fenómenos não observáveis. Advoga-se, assim, a importância da formação de professores ao longo da carreira docente como forma de atualizar o processo de ensino e aprendizagem, tendo em vista uma escola capaz de preparar os alunos para uma sociedade cada vez mais exigente e influenciada pela constante mudança no conhecimento proporcionado pelo desenvolvimento científico e tecnológico.

Alkali-free bioactive glasses for bone regeneration

Bioactive glasses and glass-ceramics are a class of third generation biomaterials which elicit a special response on their surface when in contact with biological fluids, leading to strong bonding to living tissues. The purpose of the present study was to develop diopside based alkali-free bioactive glasses in order to achieve good sintering behaviour, high bioactivity, and a dissolution/ degradation rates compatible with the target applications in bone regeneration and tissue engineering. Another aim was to understand the structure-property relationships in the investigated bioactive glasses. In this quest, various glass compositions within the Diopside (CaMgSi2O6) – Fluorapatite (Ca5(PO4)3F) – Tricalcium phosphate (3CaO•P2O5) system have been investigated. All the glasses were prepared by melt-quenching technique and characterized by a wide array of complementary characterization techniques. The glass-ceramics were produced by sintering of glass powders compacts followed by a suitable heat treatment to promote the nucleation and crystallization phenomena. Furthermore, selected parent glass compositions were doped with several functional ions and an attempt to understand their effects on the glass structure, sintering ability and on the in vitro bio-degradation and biomineralization behaviours of the glasses was made. The effects of the same variables on the devitrification (nucleation and crystallization) behaviour of glasses to form bioactive glass-ceramics were also investigated. Some of the glasses exhibited high bio-mineralization rates, expressed by the formation of a surface hydroxyapatite layer within 1–12 h of immersion in a simulated body fluid (SBF) solution. All the glasses showed relatively lower degradation rates in comparison to that of 45S5 Bioglass®. Some of the glasses showed very good in vitro behaviour and the glasses co-doped with zinc and strontium showed an in vitro dose dependent behaviour. The as-designed bioactive glasses and glass–ceramic materials are excellent candidates for applications in bone regeneration and for the fabrication of scaffolds for tissue engineering.

Organic contaminants in urban soils: major inputs and potential risks

Urban soil quality may be severely affected by hydrophobic organic contaminants (HOCs), impairing environmental quality and human health. A comprehensive study was conducted in two contrasting Portuguese urban areas (Lisbon and Viseu) in order to assess the levels and potential risks of these contaminants, to identify sources and study their behaviour in soils. The concentrations of HOCs were related to the size of the city, with much higher contamination levels observed in Lisbon urban area. Source apportionment was performed by studying the HOCs profiles, their relationship with potentially toxic elements and general characteristics of soil using multivariate statistical methods. Lisbon seems to be affected by nearby sources (traffic, industry and incineration processes) whereas in Viseu the atmospheric transport may be playing an important role. In a first tier of risk assessment (RA) it was possible to identify polycyclic aromatic hydrocarbons (PAHs) in Lisbon soils as a potential hazard. The levels of PAHs in street dusts were further studied and allowed to clarify that traffic, tire and pavement debris can be an important source of PAHs to urban soils. Street dusts were also identified as being a potential concern regarding human and environmental health, especially if reaching the nearby aquatic bodies. Geostatistical tools were also used and their usefulness in a RA analysis and urban planning was discussed. In order to obtain a more realistic assessment of risks of HOCs to environment and human health it is important to evaluate their available fraction, which is also the most accessible for organisms. Therefore, a review of the processes involved on the availability of PAHs was performed and the outputs produced by the different chemical methods were evaluated. The suitability of chemical methods to predict bioavailability of PAHs in dissimilar naturally contaminated soils has not been demonstrated, being especially difficult for high molecular weight compounds. No clear relationship between chemical and biological availability was found in this work. Yet, in spite of the very high total concentrations found in some Lisbon soils, both the water soluble fraction and the body residues resulting from bioaccumulation assays were generally very low, which may be due to aging phenomena. It was observed that the percentage of soluble fraction of PAHs in soils was found to be different among compounds and mostly regulated by soil properties. Regarding bioaccumulation assays, although no significant relationship was found between soil properties and bioavailability, it was verified that biota-to-soil bioaccumulation factors were sample dependent rather than compound dependent. In conclusion, once the compounds of potential concern are targeted, then performing a chemical screening as a first tier can be a simple and effective approach to start a RA. However, reliable data is still required to improve the existing models for risk characterization.

Phase transitions and nonlinear phenomena in neuronal network models

Communication and cooperation between billions of neurons underlie the power of the brain. How do complex functions of the brain arise from its cellular constituents? How do groups of neurons self-organize into patterns of activity? These are crucial questions in neuroscience. In order to answer them, it is necessary to have solid theoretical understanding of how single neurons communicate at the microscopic level, and how cooperative activity emerges. In this thesis we aim to understand how complex collective phenomena can arise in a simple model of neuronal networks. We use a model with balanced excitation and inhibition and complex network architecture, and we develop analytical and numerical methods for describing its neuronal dynamics. We study how interaction between neurons generates various collective phenomena, such as spontaneous appearance of network oscillations and seizures, and early warnings of these transitions in neuronal networks. Within our model, we show that phase transitions separate various dynamical regimes, and we investigate the corresponding bifurcations and critical phenomena. It permits us to suggest a qualitative explanation of the Berger effect, and to investigate phenomena such as avalanches, band-pass filter, and stochastic resonance. The role of modular structure in the detection of weak signals is also discussed. Moreover, we find nonlinear excitations that can describe paroxysmal spikes observed in electroencephalograms from epileptic brains. It allows us to propose a method to predict epileptic seizures. Memory and learning are key functions of the brain. There are evidences that these processes result from dynamical changes in the structure of the brain. At the microscopic level, synaptic connections are plastic and are modified according to the dynamics of neurons. Thus, we generalize our cortical model to take into account synaptic plasticity and we show that the repertoire of dynamical regimes becomes richer. In particular, we find mixed-mode oscillations and a chaotic regime in neuronal network dynamics.

Evaluation of the matabolic response of osteosarcoma cells to conventional and new anticancer drugs by NMR metabolomics

The main scope of this work was to evaluate the metabolic effects of anticancer agents (three conventional and one new) in osteosarcoma (OS) cells and osteoblasts, by measuring alterations in the metabolic profile of cells by nuclear magnetic resonance (NMR) spectroscopy metabolomics. Chapter 1 gives a theoretical framework of this work, beginning with the main metabolic characteristics that globally describe cancer as well as the families and mechanisms of action of drugs used in chemotherapy. The drugs used nowadays to treat OS are also presented, together with the Palladium(II) complex with spermine, Pd2Spm, potentially active against cancer. Then, the global strategy for cell metabolomics is explained and the state of the art of metabolomic studies that analyze the effect of anticancer agents in cells is presented. In Chapter 2, the fundamentals of the analytical techniques used in this work, namely for biological assays, NMR spectroscopy and multivariate and statistical analysis of the results are described. A detailed description of the experimental procedures adopted throughout this work is given in Chapter 3. The biological and analytical reproducibility of the metabolic profile of MG-63 cells by high resolution magic angle spinning (HRMAS) NMR is evaluated in Chapter 4. The metabolic impact of several factors (cellular integrity, spinning rate, temperature, time and acquisition parameters) on the 1H HRMAS NMR spectral profile and quality is analysed, enabling the definition of the best acquisition parameters for further experiments. The metabolic consequences of increasing number of passages in MG-63 cells as well as the duration of storage are also investigated. Chapter 5 describes the metabolic impact of drugs conventionally used in OS chemotherapy, through NMR metabolomics studies of lysed cells and aqueous extracts analysis. The results show that MG-63 cells treated with cisplatin (cDDP) undergo a strong up-regulation of lipid contents, alterations in phospholipid constituents (choline compounds) and biomarkers of DNA degradation, all associated with cell death by apoptosis. Cells exposed to doxorubicin (DOX) or methotrexate (MTX) showed much slighter metabolic changes, without any relevant alteration in lipid contents. However, metabolic changes associated with altered Krebs cycle, oxidative stress and nucleotides metabolism were detected and were tentatively interpreted at the light of the known mechanisms of action of these drugs. The metabolic impact of the exposure of MG-63 cells and osteoblasts to cDDP and the Pd2Spm complex is described in Chapter 6. Results show that, despite the ability of the two agents to bind DNA, the metabolic consequences that arise from exposure to them are distinct, namely in what concerns to variation in lipid contents (absent for Pd2Spm). Apoptosis detection assays showed that, differently from what was seen for MG-63 cells treated with cDDP, the decreased number of living cells upon exposure to Pd2Spm was not due to cell death by apoptosis or necrosis. Moreover, the latter agent induces more marked alterations in osteoblasts than in cancer cells, while the opposite seemed to occur upon cDDP exposure. Nevertheless, the results from MG-63 cells exposure to combination regimens with cDDP- or Pd2Spm-based cocktails, described in Chapter 7, revealed that, in combination, the two agents induce similar metabolic responses, arising from synergy mechanisms between the tested drugs. Finally, the main conclusions of this thesis are summarized in Chapter 8, and future perspectives in the light of this work are presented.