Electrospun Polyaniline-Reduced Graphene Oxide Composite Nanofibers Based High Sensitive Ammonia Gas Sensor

Ammonia is an important gas in many power plants and industrial processes so its detection is of extreme importance in environmental monitoring and process control due to its high toxicity. Ammonia’s threshold limit is 25 ppm and the exposure time limit is 8 h, however exposure to 35 ppm is only secure for 10 min. In this work a brief introduction to ammonia aspects are presented, like its physical and chemical properties, the dangers in its manipulation, its ways of production and its sources. The application areas in which ammonia gas detection is important and needed are also referred: environmental gas analysis (e.g. intense farming), automotive-, chemical- and medical industries. In order to monitor ammonia gas in these different areas there are some requirements that must be attended. These requirements determine the choice of sensor and, therefore, several types of sensors with different characteristics were developed, like metal oxides, surface acoustic wave-, catalytic-, and optical sensors, indirect gas analyzers, and conducting polymers. All the sensors types are described, but more attention will be given to polyaniline (PANI), particularly to its characteristics, syntheses, chemical doping processes, deposition methods, transduction modes, and its adhesion to inorganic materials. Besides this, short descriptions of PANI nanostructures, the use of electrospinning in the formation of nanofibers/microfibers, and graphene and its characteristics are included. The created sensor is an instrument that tries to achieve a goal of the medical community in the control of the breath’s ammonia levels being an easy and non-invasive method for diagnostic of kidney malfunction and/or gastric ulcers. For that the device should be capable to detect different levels of ammonia gas concentrations. So, in the present work an ammonia gas sensor was developed using a conductive polymer composite which was immobilized on a carbon transducer surface. The experiments were targeted to ammonia measurements at ppb level. Ammonia gas measurements were carried out in the concentration range from 1 ppb to 500 ppb. A commercial substrate was used; screen-printed carbon electrodes. After adequate surface pre-treatment of the substrate, its electrodes were covered by a nanofibrous polymeric composite. The conducting polyaniline doped with sulfuric acid (H2SO4) was blended with reduced graphene oxide (RGO) obtained by wet chemical synthesis. This composite formed the basis for the formation of nanofibers by electrospinning. Nanofibers will increase the sensitivity of the sensing material. The electrospun PANI-RGO fibers were placed on the substrate and then dried at ambient temperature. Amperometric measurements were performed at different ammonia gas concentrations (1 to 500 ppb). The I-V characteristics were registered and some interfering gases were studied (NO2, ethanol, and acetone). The gas samples were prepared in a custom setup and were diluted with dry nitrogen gas. Electrospun nanofibers of PANI-RGO composite demonstrated an enhancement in NH3 gas detection when comparing with only electrospun PANI nanofibers. Was visible higher range of resistance at concentrations from 1 to 500 ppb. It was also observed that the sensor had stable, reproducible and recoverable properties. Moreover, it had better response and recovery times. The new sensing material of the developed sensor demonstrated to be a good candidate for ammonia gas determination.

Electricity markets modeling considering complex contracts and aggregators

All over the world, the liberalization of electricity markets, which follows different paradigms, has created new challenges for those involved in this sector. In order to respond to these challenges, electric power systems suffered a significant restructuring in its mode of operation and planning. This restructuring resulted in a considerable increase of the electric sector competitiveness. Particularly, the Ancillary Services (AS) market has been target of constant renovations in its operation mode as it is a targeted market for the trading of services, which have as main objective to ensure the operation of electric power systems with appropriate levels of stability, safety, quality, equity and competitiveness. In this way, with the increasing penetration of distributed energy resources including distributed generation, demand response, storage units and electric vehicles, it is essential to develop new smarter and hierarchical methods of operation of electric power systems. As these resources are mostly connected to the distribution network, it is important to consider the introduction of this kind of resources in AS delivery in order to achieve greater reliability and cost efficiency of electrical power systems operation. The main contribution of this work is the design and development of mechanisms and methodologies of AS market and for energy and AS joint market, considering different management entities of transmission and distribution networks. Several models developed in this work consider the most common AS in the liberalized market environment: Regulation Down; Regulation Up; Spinning Reserve and Non-Spinning Reserve. The presented models consider different rules and ways of operation, such as the division of market by network areas, which allows the congestion management of interconnections between areas; or the ancillary service cascading process, which allows the replacement of AS of superior quality by lower quality of AS, ensuring a better economic performance of the market. A major contribution of this work is the development an innovative methodology of market clearing process to be used in the energy and AS joint market, able to ensure viable and feasible solutions in markets, where there are technical constraints in the transmission network involving its division into areas or regions. The proposed method is based on the determination of Bialek topological factors and considers the contribution of the dispatch for all services of increase of generation (energy, Regulation Up, Spinning and Non-Spinning reserves) in network congestion. The use of Bialek factors in each iteration of the proposed methodology allows limiting the bids in the market while ensuring that the solution is feasible in any context of system operation. Another important contribution of this work is the model of the contribution of distributed energy resources in the ancillary services. In this way, a Virtual Power Player (VPP) is considered in order to aggregate, manage and interact with distributed energy resources. The VPP manages all the agents aggregated, being able to supply AS to the system operator, with the main purpose of participation in electricity market. In order to ensure their participation in the AS, the VPP should have a set of contracts with the agents that include a set of diversified and adapted rules to each kind of distributed resource. All methodologies developed and implemented in this work have been integrated into the MASCEM simulator, which is a simulator based on a multi-agent system that allows to study complex operation of electricity markets. In this way, the developed methodologies allow the simulator to cover more operation contexts of the present and future of the electricity market. In this way, this dissertation offers a huge contribution to the AS market simulation, based on models and mechanisms currently used in several real markets, as well as the introduction of innovative methodologies of market clearing process on the energy and AS joint market. This dissertation presents five case studies; each one consists of multiple scenarios. The first case study illustrates the application of AS market simulation considering several bids of market players. The energy and ancillary services joint market simulation is exposed in the second case study. In the third case study it is developed a comparison between the simulation of the joint market methodology, in which the player bids to the ancillary services is considered by network areas and a reference methodology. The fourth case study presents the simulation of joint market methodology based on Bialek topological distribution factors applied to transmission network with 7 buses managed by a TSO. The last case study presents a joint market model simulation which considers the aggregation of small players to a VPP, as well as complex contracts related to these entities. The case study comprises a distribution network with 33 buses managed by VPP, which comprises several kinds of distributed resources, such as photovoltaic, CHP, fuel cells, wind turbines, biomass, small hydro, municipal solid waste, demand response, and storage units.

O romance histórico

A estrutura desta dissertação divide-se em duas partes. A primeira reside numa reflexão sobre o percurso profissional do investigador, centrada em aspectos relevantes da carreira docente no que concerne à Literatura e ao estudo da Língua. A narrativa autobiográfica produzida permitiu-nos revisitar episódios da vida profissional e as trajectórias e práticas lectivas utilizadas no ensino da poesia, do texto narrativo e dramático, e na exploração do funcionamento da língua ao longo dos anos. Recuperámos e aprofundámos conhecimentos sobre diversos autores do espaço lusófono – Trindade Coelho, Miguel Torga, Jorge Amado, Almeida Garrett, Manuel Lopes, Germano de Almeida, Érico Veríssimo, Jorge Barbosa, Sophia de Mello Breyner Andresen, Almada Negreiros, José Rodrigues Miguéis, Maria Alberta Menéres, Vergílio Ferreira, Luís de Camões, Fernando Pessoa, Gil Vicente e Padre António Vieira - e respectivas periodizações literárias, sempre que possível. Na segunda parte, procurámos reflectir com maior profundidade sobre outra temática do nosso percurso profissional, neste caso, o romance histórico. Para o efeito, necessitámos de pôr em evidência a controversa dicotomia entre modo e género literário, bem como de abordar o binómio História versus Literatura, dado que, o romance histórico, apesar de privilegiar modos de expressão ficcionais, mantem a sua ligação com a História e com a representação de valores e cenários de uma determinada época e sociedade. Tentámos contribuir para a construção de uma definição de romance histórico, distinguindo a narrativa oitocentista e a metaficção histórica pós-moderna. Terminámos o nosso trabalho discorrendo sobre Alexandre Herculano, centrando a nossa focalização nos conceitos de religiosidade, pátria e organização social no romance histórico Eurico, o Presbítero.

Análise do efeito de distúrbios numa cadeia de abastecimento automóvel, com recurso a um modelo de simulação

Dissertação para obtenção do Grau de Mestre em Engenharia e Gestão Industrial

Hierocracia e sacerdotalismo uma diferenciação de conceitos no pensamento político da baixa Idade Média

pp. 11-24

Hermenêutica e filosofia política: para uma nova interpretação dos textos de doutrina política em Portugal na Idade Média (séc. XIII-XV)

pp. 143-155

Tradição e mudança nas literaturas africanas de língua portuguesa

pp. 345-352

Espalhando água. Contributo da ecologia humana para a preservação.

Dissertação apresentada para cumprimento dos requisitos necessários à obtenção do grau de Mestre em Ecologia Humana e Problemas Sociais Contemporâneos.

Complexos de escorpionato: papel biológico como potenciais agentes anti-tumor

Dissertação para obtenção do Grau de Mestre em Genética Molecular e Biomedicina

Momentos em freios e em embraiagens

Dissertação para obtenção do Grau de Mestre em Mestrado Integrado em Engenharia Mecânica

Estratégias de representação do «eu» e do sentir feminino em narrativas de Stefan Zweig, Simone de Beauvoir e Rita Ferro

Dissertação apresentada para cumprimento dos requisitos necessários à obtenção do grau de Mestre em Estudos Portugueses – Estudos Literários.

Modelação de paredes de edifícios pombalinos

Dissertação para obtenção do Grau de Mestre em Engenharia Civil - Perfil Estruturas e Geotecnia

Identidade Territorial de um Bairro Social: O Caso da Quinta Marquês de Abrantes

Dissertação do Mestrado em Gestão do Território ‐ Território e Desenvolvimento

O olhar contemporâneo e o ressurgimento da fotografia documental. Uma abordagem da obra Benditos, de Tiago Santana

Dissertação apresentada para cumprimento dos requisitos necessários à obtenção do grau de Mestre em Ciências da Comunicação

Fixar o instável, palavras em movimento

Trabalho de Projecto apresentado para cumprimento dos requisitos necessários à obtenção do grau de Mestre em Ciências da Comunicação