High-resolution seismic reflection investigation of gas accumulation and seepage in the tidal channels of the Ria of Aveiro barrier lagoon (Portugal)

O metano é um gás de estufa potente e uma importante fonte de energia. A importância global e impacto em zonas costeiras de acumulações e escape de gás metano são ainda pouco conhecidas. Esta tese investiga acumulações e escape de gás em canais de maré da Ria de Aveiro com dados de cinco campanhas de reflexão sísmica de alta resolução realizadas em 1986, 1999, 2002 e 2003. Estas incluem três campanhas de Chirp (RIAV99, RIAV02 e RIAV02A) e duas campanhas de Boomer (VOUGA86 e RIAV03). O processamento dos dados de navegação incluíram filtros de erros, correcções de sincronização de relógios de sistemas de aquisição de dados, ajuste de “layback” e estimativa da posição de “midpoint”. O processamento do sinal sísmico consistiu na correcção das amplitudes, remoção de ruído do tipo “burst”, correcções estáticas, correcção do “normal move-out”, filtragem passabanda, desconvolução da assinatura e migração Stolt F-K. A análise da regularidade do trajecto de navegação, dos desfasamentos entre horizontes e dos modelos de superfícies foi utilizada para controlo de qualidade, e permitiu a revisão e melhoria dos parâmetros de processamento. A heterogeneidade da cobertura sísmica, da qualidade do sinal, da penetração e da resolução, no seu conjunto constrangeram o uso dos dados a interpretações detalhadas, mas locais, de objectos geológicos da Ria. É apresentado um procedimento para determinar a escolha de escalas adequadas para modelar os objectos geológicos, baseado na resolução sísmica, erros de posicionamento conhecidos e desfasamentos médios entre horizontes. As evidências de acumulação e escape de gás na Ria de Aveiro incluem turbidez acústica, reflexões reforçadas, cortinas acústicas, domas, “pockmarks” e alinhamentos de “pockmarks” enterradas, horizontes perturbados e plumas acústicas na coluna de água (flares). A estratigrafia e a estrutura geológica controlam a distribuição e extensão das acumulações e escape de gás. Ainda assim, nestes sistemas de baixa profundidade de água, as variações da altura de maré têm um impacto significativo na detecção de gás com métodos acústicos, através de alterações nas amplitudes originais de reflexões reforçadas, turbidez acústica e branqueamento acústico em zonas com gás. Os padrões encontrados confirmam que o escape de bolhas de gás é desencadeado pela descida da maré. Há acumulações de gás em sedimentos Holocénicos e no substrato de argilas e calcários do Mesozóico. Evidências directas de escape de gás em sondagens em zonas vizinhas, mostraram gás essencialmente biogénico. A maioria do gás na área deve ter sido gerado em sedimentos lagunares Holocénicos. No entanto, a localização e geometria de estruturas de escape de fluidos em alguns canais de maré, seguem o padrão de fracturas do substrato Mesozóico, indicando uma possível fonte mais profunda de gás e que estas fracturas funcionam como condutas preferenciais de migração dos fluidos e exercem um controlo estrutural na ocorrência de gás na Ria.

Metodologia de selecção de materiais em design: base de dados nacional

Desde a Pré-História que a escolha de materiais esteve relacionada com a Arte. Mais tarde, durante a Idade Moderna vai ganhando uma importância cada vez maior. Atingida que foi a Idade Contemporânea, nomeadamente após a Revolução Industrial e durante a Segunda Guerra Mundial, devido ao aumento do número de materiais disponíveis, é que se pode falar de uma verdadeira seleção de materiais. É também após a Revolução Industrial que se clarificam as relações entre a evolução dos materiais e os movimentos e correntes das Artes Plásticas. Neste contexto, estudaram-se as interligações entre o processo de design e as metodologias de seleção, assim como as diversas tipologias de ferramentas existentes para esse efeito. Deste estudo, consideradas as respetivas vantagens e limitações, foi possível identificar bases de dados essencialmente técnicas, ou ao invés, ferramentas para inspiração com muitas imagens e pouca informação sobre as propriedades dos materiais. Para completar este levantamento crítico sobre processos e ferramentas de seleção, inquiriram-se cinquenta e três profissionais que trabalhavam em diferentes gabinetes de design portugueses. As perguntas dirigidas aos designers portugueses versaram sobre problemas relacionados com a escolha de materiais, abrangendo o tipo de matériasprimas empregues, processos utilizados e a qualidade da informação obtida. Na sequência deste estudo, verificou-se a existência de diversas lacunas relativamente aos meios disponíveis, rotinas de seleção, qualidade da informação existente e metodologias utilizadas. Foi neste contexto que se iniciou o projeto de criação de uma nova metodologia suportada por uma ferramenta digital. Os principais aspetos inovadores são: uma melhor interligação entre a metodologia de design e o processo de seleção de materiais e a sua sincronização; a informação necessária em cada etapa e o destaque dos fatores catalisadores da seleção de materiais. Outro elemento inovador foi a conjugação de três formas deferentes de seleção de materiais numa só ferramenta (a geral, a visual e a específica) e a hipótese de aceder a diferentes graus de informação. A metodologia, no contexto dos recursos disponíveis, foi materializada sob a forma de ferramenta digital (ptmaterials.com). O protótipo foi aferido com testes de usabilidade de cariz heurístico, com a participação de dezanove utilizadores. Foram detetadas diversas falhas de interação que condicionaram a liberdade e o controlo da navegação no seio da interface. Os utilizadores também mencionaram a existência de lacunas na prevenção de erros e a ligação do sistema à lógica habitual de outras aplicações já existentes. No entanto, também constituiu um estímulo a circunstância da maioria dos designers avaliarem o sistema como eficaz, eficiente, satisfatório e confirmarem o interesse da existência dos três tipos de seleção. Posteriormente, ao analisar os restantes resultados dos testes de usabilidade, também foram evidenciadas as vantagens dos diferentes tipos de informação disponibilizada e a utilidade de uma ferramenta desta natureza para a Indústria e Economia Nacionais. Esta ferramenta é apenas um ponto de partida, existindo espaço para melhorar a proposta, apesar da concretização de uma ferramenta digital ser um trabalho de grande complexidade. Não obstante se tratar de um protótipo, esta ferramenta está adequada aos dias de hoje e é passível de evoluir no futuro, tendo também a possibilidade de vir a ser preferencialmente utilizada por outros países de língua portuguesa.

Ultrasonic location system

Esta tese apresenta um sistema de localização baseado exclusivamente em ultrassons, não necessitando de recorrer a qualquer outra tecnologia. Este sistema de localização foi concebido para poder operar em ambientes onde qualquer outra tecnologia não pode ser utilizada ou o seu uso está condicionado, como são exemplo aplicações subaquáticas ou ambientes hospitalares. O sistema de localização proposto faz uso de uma rede de faróis fixos permitindo que estações móveis se localizem. Devido à necessidade de transmissão de dados e medição de distâncias foi desenvolvido um pulso de ultrassons robusto a ecos que permite realizar ambas as tarefas com sucesso. O sistema de localização permite que as estações móveis se localizem escutando apenas a informação em pulsos de ultrassons enviados pelos faróis usando para tal um algoritmo baseado em diferenças de tempo de chegada. Desta forma a privacidade dos utilizadores é garantida e o sistema torna-se completamente independente do número de utilizadores. Por forma a facilitar a implementação da rede de faróis apenas será necessário determinar manualmente a posição de alguns dos faróis, designados por faróis âncora. Estes irão permitir que os restantes faróis, completamente autónomos, se possam localizar através de um algoritmo iterativo de localização baseado na minimização de uma função de custo. Para que este sistema possa funcionar como previsto será necessário que os faróis possam sincronizar os seus relógios e medir a distância entre eles. Para tal, esta tese propõe um protocolo de sincronização de relógio que permite também obter as medidas de distância entre os faróis trocando somente três mensagens de ultrassons. Adicionalmente, o sistema de localização permite que faróis danificados possam ser substituídos sem comprometer a operabilidade da rede reduzindo a complexidade na manutenção. Para além do mencionado, foi igualmente implementado um simulador de ultrassons para ambientes fechados, o qual provou ser bastante preciso e uma ferramenta de elevado valor para simular o comportamento do sistema de localização sobre condições controladas.

Control design for multicast-aware class-based networks

The expectations of citizens from the Information Technologies (ITs) are increasing as the ITs have become integral part of our society, serving all kinds of activities whether professional, leisure, safety-critical applications or business. Hence, the limitations of the traditional network designs to provide innovative and enhanced services and applications motivated a consensus to integrate all services over packet switching infrastructures, using the Internet Protocol, so as to leverage flexible control and economical benefits in the Next Generation Networks (NGNs). However, the Internet is not capable of treating services differently while each service has its own requirements (e.g., Quality of Service - QoS). Therefore, the need for more evolved forms of communications has driven to radical changes of architectural and layering designs which demand appropriate solutions for service admission and network resources control. This Thesis addresses QoS and network control issues, aiming to improve overall control performance in current and future networks which classify services into classes. The Thesis is divided into three parts. In the first part, we propose two resource over-reservation algorithms, a Class-based bandwidth Over-Reservation (COR) and an Enhanced COR (ECOR). The over-reservation means reserving more bandwidth than a Class of Service (CoS) needs, so the QoS reservation signalling rate is reduced. COR and ECOR allow for dynamically defining over-reservation parameters for CoSs based on network interfaces resource conditions; they aim to reduce QoS signalling and related overhead without incurring CoS starvation or waste of bandwidth. ECOR differs from COR by allowing for optimizing control overhead minimization. Further, we propose a centralized control mechanism called Advanced Centralization Architecture (ACA), that uses a single state-full Control Decision Point (CDP) which maintains a good view of its underlying network topology and the related links resource statistics on real-time basis to control the overall network. It is very important to mention that, in this Thesis, we use multicast trees as the basis for session transport, not only for group communication purposes, but mainly to pin packets of a session mapped to a tree to follow the desired tree. Our simulation results prove a drastic reduction of QoS control signalling and the related overhead without QoS violation or waste of resources. Besides, we provide a generic-purpose analytical model to assess the impact of various parameters (e.g., link capacity, session dynamics, etc.) that generally challenge resource overprovisioning control. In the second part of this Thesis, we propose a decentralization control mechanism called Advanced Class-based resource OverpRovisioning (ACOR), that aims to achieve better scalability than the ACA approach. ACOR enables multiple CDPs, distributed at network edge, to cooperate and exchange appropriate control data (e.g., trees and bandwidth usage information) such that each CDP is able to maintain a good knowledge of the network topology and the related links resource statistics on real-time basis. From scalability perspective, ACOR cooperation is selective, meaning that control information is exchanged dynamically among only the CDPs which are concerned (correlated). Moreover, the synchronization is carried out through our proposed concept of Virtual Over-Provisioned Resource (VOPR), which is a share of over-reservations of each interface to each tree that uses the interface. Thus, each CDP can process several session requests over a tree without requiring synchronization between the correlated CDPs as long as the VOPR of the tree is not exhausted. Analytical and simulation results demonstrate that aggregate over-reservation control in decentralized scenarios keep low signalling without QoS violations or waste of resources. We also introduced a control signalling protocol called ACOR Protocol (ACOR-P) to support the centralization and decentralization designs in this Thesis. Further, we propose an Extended ACOR (E-ACOR) which aggregates the VOPR of all trees that originate at the same CDP, and more session requests can be processed without synchronization when compared with ACOR. In addition, E-ACOR introduces a mechanism to efficiently track network congestion information to prevent unnecessary synchronization during congestion time when VOPRs would exhaust upon every session request. The performance evaluation through analytical and simulation results proves the superiority of E-ACOR in minimizing overall control signalling overhead while keeping all advantages of ACOR, that is, without incurring QoS violations or waste of resources. The last part of this Thesis includes the Survivable ACOR (SACOR) proposal to support stable operations of the QoS and network control mechanisms in case of failures and recoveries (e.g., of links and nodes). The performance results show flexible survivability characterized by fast convergence time and differentiation of traffic re-routing under efficient resource utilization i.e. without wasting bandwidth. In summary, the QoS and architectural control mechanisms proposed in this Thesis provide efficient and scalable support for network control key sub-systems (e.g., QoS and resource control, traffic engineering, multicasting, etc.), and thus allow for optimizing network overall control performance.

Cooperative positioning for heterogeneous wireless systems

Future emerging market trends head towards positioning based services placing a new perspective on the way we obtain and exploit positioning information. On one hand, innovations in information technology and wireless communication systems enabled the development of numerous location based applications such as vehicle navigation and tracking, sensor networks applications, home automation, asset management, security and context aware location services. On the other hand, wireless networks themselves may bene t from localization information to improve the performances of di erent network layers. Location based routing, synchronization, interference cancellation are prime examples of applications where location information can be useful. Typical positioning solutions rely on measurements and exploitation of distance dependent signal metrics, such as the received signal strength, time of arrival or angle of arrival. They are cheaper and easier to implement than the dedicated positioning systems based on ngerprinting, but at the cost of accuracy. Therefore intelligent localization algorithms and signal processing techniques have to be applied to mitigate the lack of accuracy in distance estimates. Cooperation between nodes is used in cases where conventional positioning techniques do not perform well due to lack of existing infrastructure, or obstructed indoor environment. The objective is to concentrate on hybrid architecture where some nodes have points of attachment to an infrastructure, and simultaneously are interconnected via short-range ad hoc links. The availability of more capable handsets enables more innovative scenarios that take advantage of multiple radio access networks as well as peer-to-peer links for positioning. Link selection is used to optimize the tradeo between the power consumption of participating nodes and the quality of target localization. The Geometric Dilution of Precision and the Cramer-Rao Lower Bound can be used as criteria for choosing the appropriate set of anchor nodes and corresponding measurements before attempting location estimation itself. This work analyzes the existing solutions for node selection in order to improve localization performance, and proposes a novel method based on utility functions. The proposed method is then extended to mobile and heterogeneous environments. Simulations have been carried out, as well as evaluation with real measurement data. In addition, some speci c cases have been considered, such as localization in ill-conditioned scenarios and the use of negative information. The proposed approaches have shown to enhance estimation accuracy, whilst signi cantly reducing complexity, power consumption and signalling overhead.

All-optical routing functionalities

All-optical solutions for switching and routing packet-based traffic are crucial for realizing a truly transparent network. To meet the increasing requirements for higher bandwidth, such optical packet switched networks may require the implementation of digital functions in the physical layer. This scenario stimulated us to research and develop innovative high-speed all-optical storage memories, focusing mainly on bistables whose state switching is triggered by a pulsed clock signal. In clocked devices, a synchronization signal is responsible for controlling the enabling of the bistable. This thesis also presents novel solutions to implement optical logic gates, which are basic building blocks of any processing system and a fundamental element for the development of complex processing functionalities. Most of the proposed schemes developed in this work are based on SOA-MZI structures due to their inherent characteristics such as, high extinction ratio, high operation speed, high integration capability and compactness. We addressed the experimental implementation of an all-optical packet routing scheme, with contention resolution capability, using interconnected SOAMZIs. The impact on the system performance of the reminiscent power of the blocked packets, from the non ideal switching performed by the SOA-MZIs, was also assessed.

Communication between nodes for autonomic and distributed management

Over the last decade, the most widespread approaches for traditional management were based on the Simple Network Management Protocol (SNMP) or Common Management Information Protocol (CMIP). However, they both have several problems in terms of scalability, due to their centralization characteristics. Although the distributed management approaches exhibit better performance in terms of scalability, they still underperform regarding communication costs, autonomy, extensibility, exibility, robustness, and cooperation between network nodes. The cooperation between network nodes normally requires excessive overheads for synchronization and dissemination of management information in the network. For emerging dynamic and large-scale networking environments, as envisioned in Next Generation Networks (NGNs), exponential growth in the number of network devices and mobile communications and application demands is expected. Thus, a high degree of management automation is an important requirement, along with new mechanisms that promote it optimally and e ciently, taking into account the need for high cooperation between the nodes. Current approaches for self and autonomic management allow the network administrator to manage large areas, performing fast reaction and e ciently facing unexpected problems. The management functionalities should be delegated to a self-organized plane operating within the network, that decrease the network complexity and the control information ow, as opposed to centralized or external servers. This Thesis aims to propose and develop a communication framework for distributed network management which integrates a set of mechanisms for initial communication, exchange of management information, network (re) organization and data dissemination, attempting to meet the autonomic and distributed management requirements posed by NGNs. The mechanisms are lightweight and portable, and they can operate in di erent hardware architectures and include all the requirements to maintain the basis for an e cient communication between nodes in order to ensure autonomic network management. Moreover, those mechanisms were explored in diverse network conditions and events, such as device and link errors, di erent tra c/network loads and requirements. The results obtained through simulation and real experimentation show that the proposed mechanisms provide a lower convergence time, smaller overhead impact in the network, faster dissemination of management information, increase stability and quality of the nodes associations, and enable the support for e cient data information delivery in comparison to the base mechanisms analyzed. Finally, all mechanisms for communication between nodes proposed in this Thesis, that support and distribute the management information and network control functionalities, were devised and developed to operate in completely decentralized scenarios.

In search of reliable centimeter-level indoor positioning: a smartphone-based approach

This thesis describes the design and implementation of a reliable centimeter-level indoor positioning system fully compatible with a conventional smartphone. The proposed system takes advantage of the smartphone audio I/O and processing capabilities to perform acoustic ranging in the audio band using non-invasive audio signals and it has been developed having in mind applications that require high accuracy, such as augmented reality, virtual reality, gaming and audio guides. The system works in a distributed operation mode, i.e. each smartphone is able to obtain its own position using only acoustic signals. To support the positioning system, a Wireless Sensor Network (WSN) of synchronized acoustic beacons is used. To keep the infrastructure in sync we have developed an Automatic Time Synchronization and Syntonization (ATSS) protocol with a standard deviation of the sync offset error below 1.25 μs. Using an improved Time Difference of Arrival (TDoA) estimation approach (which takes advantage of the beacon signals’ periodicity) and by performing Non-Line-of-Sight (NLoS) mitigation, we were able to obtain very stable and accurate position estimates with an absolute mean error of less than 10 cm in 95% of the cases and a mean standard deviation of 2.2 cm for a position refresh period of 350 ms.

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.