Perylene Diimide acceptors: Fabrication and characterization of electron-only, hole-only devices and solar cells

The thrust towards energy conservation and reduced environmental footprint has fueled intensive research for alternative low cost sources of renewable energy. Organic photovoltaic cells (OPVs), with their low fabrication costs, easy processing and flexibility, represent a possible viable alternative. Perylene diimides (PDIs) are promising electron-acceptor candidates for bulk heterojunction (BHJ) OPVs, as they combine higher absorption and stability with tunable material properties, such as solubility and position of the lowest unoccupied molecular orbital (LUMO) level. A prerequisite for trap free electron transport is for the LUMO to be located at a level deeper than 3.7 eV since electron trapping in organic semiconductors is universal and dominated by a trap level located at 3.6 eV. Although the mostly used fullerene acceptors in polymer:fullerene solar cells feature trap-free electron transport, low optical absorption of fullerene derivatives limits maximum attainable efficiency. In this thesis, we try to get a better understanding of the electronic properties of PDIs, with a focus on charge carrier transport characteristics and the effect of different processing conditions such as annealing temperature and top contact (cathode) material. We report on a commercially available PDI and three PDI derivatives as acceptor materials, and its blends with MEH-PPV (Poly[2-methoxy 5-(2-ethylhexyloxy)-1,4-phenylenevinylene]) and P3HT (Poly(3-hexylthiophene-2,5-diyl)) donor materials in single carrier devices (electron-only and hole-only) and in solar cells. Space-charge limited current measurements and modelling of temperature dependent J-V characteristics confirmed that the electron transport is essentially trap-free in such materials. Different blend ratios of P3HT:PDI-1 (1:1) and (1:3) show increase in the device performance with increasing PDI-1 ratio. Furthermore, thermal annealing of the devices have a significant effect in the solar cells that decreases open-circuit voltage (Voc) and fill factor FF, but increases short-circuit current (Jsc) and overall device performance. Morphological studies show that over-aggregation in traditional donor:PDI blend systems is still a big problem, which hinders charge carrier transport and performance in solar cells.

Frequency-domain receiver design for doubly-selective channels

This work is devoted to the broadband wireless transmission techniques, which are serious candidates to be implemented in future broadband wireless and cellular systems, aiming at providing high and reliable data transmission and concomitantly high mobility. In order to cope with doubly-selective channels, receiver structures based on OFDM and SC-FDE block transmission techniques, are proposed, which allow cost-effective implementations, using FFT-based signal processing. The first subject to be addressed is the impact of the number of multipath components, and the diversity order, on the asymptotic performance of OFDM and SC-FDE, in uncoded and for different channel coding schemes. The obtained results show that the number of relevant separable multipath components is a key element that influences the performance of OFDM and SC-FDE schemes. Then, the improved estimation and detection performance of OFDM-based broadcasting systems, is introduced employing SFN (Single Frequency Network) operation. An initial coarse channel is obtained with resort to low-power training sequences estimation, and an iterative receiver with joint detection and channel estimation is presented. The achieved results have shown very good performance, close to that with perfect channel estimation. The next topic is related to SFN systems, devoting special attention to time-distortion effects inherent to these networks. Typically, the SFN broadcast wireless systems employ OFDM schemes to cope with severely time-dispersive channels. However, frequency errors, due to CFO, compromises the orthogonality between subcarriers. As an alternative approach, the possibility of using SC-FDE schemes (characterized by reduced envelope fluctuations and higher robustness to carrier frequency errors) is evaluated, and a technique, employing joint CFO estimation and compensation over the severe time-distortion effects, is proposed. Finally, broadband mobile wireless systems, in which the relative motion between the transmitter and receiver induces Doppler shift which is different or each propagation path, is considered, depending on the angle of incidence of that path in relation to the direction of travel. This represents a severe impairment in wireless digital communications systems, since that multipath propagation combined with the Doppler effects, lead to drastic and unpredictable fluctuations of the envelope of the received signal, severely affecting the detection performance. The channel variations due this effect are very difficult to estimate and compensate. In this work we propose a set of SC-FDE iterative receivers implementing efficient estimation and tracking techniques. The performance results show that the proposed receivers have very good performance, even in the presence of significant Doppler spread between the different groups of multipath components.

Portugal no conselho de segurança das Nações Unidas

The United Nations is an international organization that was created after World War II, whose main objective is to promote cooperation, social and economic development, as well as to ensure international peace and security. The Member States are key actors in the international political system. For that reason they have strategic interests in what regards taking part in the international organizations. They see it as an opportunity to achieve those goals. The United Nations Security Council has a very important role in preserving international peace and security. It is the organ of the United Nations in which fifteen member states are represented: five permanently and ten non-permanently, being that the latter are elected for two years. Participating in the Security Council is a unique opportunity for middle powers like Portugal to promote their national interests and to increase their international visibility. In addition, they can contribute to the world’s destiny during their mandate period. Portugal has exercised his third term as a non-permanent member of the Security Council in 2011-2012 biennium, defeating Canada after a successful campaign carried out by the Portuguese diplomacy. This study analyses the participation of Portugal in the Security Council´s 2011-2012 biennium. It will focus the application process and election and the role of Portugal in the Security Council, especially in its the presidency and its intervention in the presidency of the Sanctions Committee on Libya. Its aim is to show the impact of Portuguese participation in the Security Council for international peace and security, as well as the geopolitical importance for the country of being part of the Security Council.

A comparison analysis of the marketing strategy of Lufthansa and Emirates in Germany

The objective of this paper is to perform an analysis of the marketing strategy of Lufthansa and Emirates in Germany. Since both airlines use a similar approach to increase brand awareness an in-depth analysis is implemented in order to identify potential differences. Hereby, consumer insights about the perception and expectation travellers have in common will be analyzed and assessed with quantitative data. Both airlines are well positioned in terms of their marketing strategy, but when Emirates is strengthen its marketing campaign with that pace, the Gulf carrier will certainly make use of its economic strength and can become a frightening threat for the Lufthansa Group on long-haul destinations. Finally, recommendations for future marketing activities for both airlines will be given.

O contrato de transporte aéreo

The international conventions and agreements on civil liability emerged with the purpose of regulating the liability of the air carrier, bearing in mind two essential factors: i) the need to protect passengers interests, and ii) to ensure the continuous development of an incipient activity by limiting the compensation amounts. This research will focus on the analysis of the nature of the contract of air carriage, as well as the air carrier's liability regime regarding damages endured by passengers that may result from the non-performance of the contract.

A liberalização do mercado energético e o papel das entidades reguladoras

The liberalisation of the energy market goes back to the 1990s, when it was impelled by the European legislator. Since then, three legislative packages, temporarily successive, were approved. Those packages contained the measures to be implemented in order to deepen the internal energy market. Besides the opening up of several national markets to competition, the European legislator aimed the creation of a real internal energy market within the European Union. The unbundling regime was one of the most important steps with respect to the liberalisation process. The introduction of these rules ensured independence to the various market operators. A real and effective right of choice was granted to the consumers so they may choose their electricity and natural gas supplier. Therefore, the activity of comercialisation is subject to competition. However, some activities of the electricity’s and natural gas’ chain of value, namely the activities of transportation and distribution, were kept under regulation rules. Even though it may seem odd, the assignment of important competences and strong powers to a regulatory authority was essential in order to achieve the liberalisation process’ goals. Electricity and natural gas are essential public goods; therefore the market operators are legally bound to public service obligations, such as the security, the universality and the continuity of the supply. The performance of these obligations may become, in some cases, unprofitable for those operators. For such reason, the protection of the consumers’ rights shall only be properly defended if there is a regulatory authority that monitors the behaviour of the operators and sanctions the failure to comply with the public service obligations. Portugal, as a Member State of the European Union, transposed into the national legal order the European directives concerning the liberalisation process. This transposition has caused radical changes to the electricity and natural gas’ national markets. The Entidade Reguladora dos Serviços Energéticos also suffered various mutations in order to keep up with the regulatory demands regarding the liberalisation process.

Implementation and comparison of different switching techniques for shunt active power filters

This paper presents a comparison between three switching techniques that can be used in three-phase four-wire Shunt Active Power Filters (SAPFs). The implemented switching techniques are: Periodic-Sampling (PS), Triangular Carrier Pulse-Width Modulation (TC-PWM) and Space Vector PWM (SVPWM). The comparison between them is made in terms of the compensated currents THD%, implementation complexity, necessary CPU time and SAPF efficiency. To perform this comparison are presented and analyzed several experimental results, obtained with a 20 kVA Shunt Active Power Filter prototype, specially developed for this purpose. The control system of the developed SAPF is based in the p-q Theory with a grid synchronization algorithm p-PLL.

Análise da qualidade do serviço numa empresa transportadora

Dissertação de mestrado integrado em Engenharia e Gestão Industrial

Methanogens, sulphate and heavy metals: a complex system

Anaerobic digestion (AD) is a well-established technology used for the treatment of wastes and wastewaters with high organic content. During AD organic matter is converted stepwise to methane-containing biogasa renewable energy carrier. Methane production occurs in the last AD step and relies on methanogens, which are rather sensitive to some contaminants commonly found in wastewaters (e.g. heavy metals), or easily outcompeted by other groups of microorganisms (e.g. sulphate reducing bacteria, SRB). This review gives an overview of previous research and pilot-scale studies that shed some light on the effects of sulphate and heavy metals on methanogenesis. Despite the numerous studies on this subject, comparison is not always possible due to differences in the experimental conditions used and parameters explained. An overview of the possible benefits of methanogens and SRB co-habitation is also covered. Small amounts of sulphide produced by SRB can precipitate with metals, neutralising the negative effects of sulphide accumulation and free heavy metals on methanogenesis. Knowledge on how to untangle and balance sulphate reduction and methanogenesis is crucial to take advantage of the potential for the utilisation of biogenic sulphide as a metal detoxification agent with minimal loss in methane production in anaerobic digesters.

Effect of the acoustic impedance in ultrasonic emitter transducers using digital modulations

In an underwater environment it is difficult to implement solutions for wireless communications. The existing technologies using electromagnetic waves or lasers are not very efficient due to the large attenuation in the aquatic environment. Ultrasound reveals a lower attenuation, and thus has been used in underwater long-distance communications. The much slower speed of acoustic propagation in water (about 1500 m/s) compared with that of electromagnetic and optical waves, is another limiting factor for efficient communication and networking. For high data-rates and real-time applications it is necessary to use frequencies in the MHz range, allowing communication distances of hundreds of meters with a delay of milliseconds. To achieve this goal, it is necessary to develop ultrasound transducers able to work at high frequencies and wideband, with suitable responses to digital modulations. This work shows how the acoustic impedance influences the performance of an ultrasonic emitter transducer when digital modulations are used and operating at frequencies between 100 kHz and 1 MHz. The study includes a Finite Element Method (FEM) and a MATLAB/Simulink simulation with an experimental validation to evaluate two types of piezoelectric materials: one based on ceramics (high acoustic impedance) with a resonance design and the other based in polymer (low acoustic impedance) designed to optimize the performance when digital modulations are used. The transducers performance for Binary Amplitude Shift Keying (BASK), On-Off Keying (OOK), Binary Phase Shift Keying (BPSK) and Binary Frequency Shift Keying (BFSK) modulations with a 1 MHz carrier at 125 kbps baud rate are compared.

Marine origin polysaccharides in drug delivery systems

Oceans are a vast source of natural substances. In them, we find various compounds with wide biotechnological and biomedical applicabilities. The exploitation of the sea as a renewable source of biocompounds can have a positive impact on the development of new systems and devices for biomedical applications. Marine polysaccharides are among the most abundant materials in the seas, which contributes to a decrease of the extraction costs, besides their solubility behavior in aqueous solvents and extraction media, and their interaction with other biocompounds. Polysaccharides such as alginate, carrageenan and fucoidan can be extracted from algae, whereas chitosan and hyaluronan can be obtained from animal sources. Most marine polysaccharides have important biological properties such as biocompatibility, biodegradability, and anti-inflammatory activity, as well as adhesive and antimicrobial actions. Moreover, they can be modified in order to allow processing them into various shapes and sizes and may exhibit response dependence to external stimuli, such as pH and temperature. Due to these properties, these biomaterials have been studied as raw material for the construction of carrier devices for drugs, including particles, capsules and hydrogels. The devices are designed to achieve a controlled release of therapeutic agents in an attempt to fight against serious diseases, and to be used in advanced therapies, such as gene delivery or regenerative medicine.

Development of Monoolein-based lipofection vectors for therapeutic siRNA delivery

Tese de Doutoramento em Biologia Molecular e Ambiental - Especialidade em Biologia Celular e Saúde

Algumas considerações sobre o princípio da culpa enquanto factor de autonomização do Direito das Contra-ordenações

Dissertação de mestrado em Direito Judiciário

Development of a poly(L-Lactic acid) based drug release system

Dissertação de mestrado em Biofísica e Bionanossistemas

Lipid based nanocarriers for the delivery of the bioactive compound resveratrol

Dissertação de mestrado em Biofísica e Bionanossistemas