Significant Phonon Drag Enables High Power Factor in the AlGaN/GaN Two-Dimensional Electron Gas

In typical thermoelectric energy harvesters and sensors, the Seebeck effect is caused by diffusion of electrons or holes in a temperature gradient. However, the Seebeck effect can also have a phonon drag component, due to momentum exchange between charge carriers and lattice phonons, which is more difficult to quantify. Here, we present the first study of phonon drag in the AlGaN/GaN two-dimensional electron gas (2DEG). We find that phonon drag does not contribute significantly to the thermoelectric behavior of devices with ~100 nm GaN thickness, which suppress the phonon mean free path. However, when the thickness is increased to ~1.2 $\mu$m, up to 32% (88%) of the Seebeck coefficient at 300 K (50 K) can be attributed to the drag component. In turn, the phonon drag enables state-of-the-art thermoelectric power factor in the thicker GaN film, up to ~40 mW m$^{-1}$ K$^{-2}$ at 50 K. By measuring the thermal conductivity of these AlGaN/GaN films, we show that the magnitude of the phonon drag can increase even when the thermal conductivity decreases. Decoupling of thermal conductivity and Seebeck coefficient could enable important advancements in thermoelectric power conversion with devices based on 2DEGs

Highly sensitive 4H-SiC pressure sensor at cryogenic and elevated temperatures

The slow etching rate of conventional micro-machining processes is hindering the use of bulk silicon carbide materials in pressure sensing. This paper presents a 4H-SiC piezoresistive pressure sensor utilising a laser scribing approach for fast prototyping a bulk SiC pressure sensor. The sensor is able to operate at a temperature range from cryogenic to elevated temperatures with an excellent linearity and repeatability with a pressure of up to 270 kPa. The good optical transparency of SiC material allows the direct alignment between the pre-fabricated piezoresistors and the scribing process to form a diaphragm from the back side. The sensitivities of the sensor were obtained as 10.83 mV/V/bar at 198 K and 6.72 mV/V/bar at 473 K, which are at least a two-fold increment in comparison with other SiC pressure sensors. The high sensitivity and good reliability at either cryogenic and elevated temperatures are attributed to the profound piezoresistive effect in p-type 4H-SiC and the robust p-n junction which prevents the current from leaking to the substrate. This indicates the potential of utilising the laser scribing approach to fabricate highly sensitive bulk SiC pressure sensors for harsh environment applications

Profundidade da experiência, evocação de memórias episódicas e mudança em psicanálise

Dissertação de Mestrado apresentada no ISPA – Instituto Universitário para obtenção de grau de Mestre na especialidade de Psicologia Clínica.Enquadramento: A terapia focada nas emoções (EFT) é uma das terapias com eficácia reconhecida no tratamento da depressão. No entanto, ainda não existe nenhuma revisão de literatura que sintetize os resultados da investigação neste contexto. Objetivo: Fazer uma revisão sistemática dos estudos sobre a terapia focada nas emoções (EFT) no tratamento da depressão. Método: A pesquisa foi realizada em bases de dados eletrónicas (PsycInfo, PsycArticles, PEP, Psychology and Behavioral Sciences Collection e Academic Search Complete), com as palavras-chave Depression e Emotion Focused Therapy. Resultados: Foram encontrados vinte artigos que podem organizar-se em três grandes grupos: estudo da eficácia, análise do processamento emocional e EFT e narrativa. Conclusões: Os estudos sustentam a eficácia da EFT no tratamento da depressão em terapia individual e de casal. A integração da intensidade da expressão emocional, da aliança terapêutica e do processamento das vivências emocionais podem ser promotoras do progresso terapêutico na EFT. A compreensão das narrativas pessoais à luz das emoções pode ser importante para o estabelecimento de estratégias de intervenção mais eficazes no tratamento da depressão.ABSTRACT: Framework: Emotion focused therapy (EFT) is one of the therapies with recognized efficiency in the depression treatment. However, there is still no literature review that synthesizes research results in this context. Purpose: Conduct a systematic review of studies on emotion-focused therapy (FET) in depression treatment. Method: The research was carried out in electronic databases (PsycInfo, PsycArticles, PEP, Psychology and Behavioral Sciences Collection and Academic Search Complete), with the keywords Depression and Emotion Focused Therapy. Results: 20 articles were found, that can be organized into three main groups: efficiency study, analysis of emotional processing and EFT and narrative. Conclusions: The studies support the efficiency of EFT in the treatment of depression in individual and couple therapy. The integration of the intensity of emotional expression, the therapeutic alliance and the processing of emotional experiences can be the promoter of therapeutic progress in EFT. The understanding of personal narratives in the light of emotions may be important for the establishment of more effective intervention strategies in the treatment of depression

Hybrid modelling and control of power electronics

Switched circuits in power electronics by their nature present hybrid behavior. Such circuits can be described by a set of discrete states with associated continuous dynamics. A control objective, usually regulation of the output in the face of disturbances in the continuous system, is accomplished by choosing among discrete states. We describe a hybrid systems perspective of several common tasks in the design and analysis of power electronics. A DC-DC boost converter circuit is presented as an illustrative example, and the extension of this circuit to a multiple output configuration is provided to show the favorable scaling properties and broad utility of the hybrid approach. © Springer-Verlag Berlin Heidelberg 2003.link_to_subscribed_fulltex

Stability Controllers for Sampled Switched Systems

We consider in this paper switched systems, a class of hybrid systems recently used with success in various domains such as automotive industry and power electonics. We propose a state-dependent control strategy which makes the trajectories of the analyzed system converge to finite cyclic sequences of points. Our method relies on a technique of decomposition of the state space into local regions where the control is uniform. We have implemented the procedure using zonotopes, and applied it successfully to several examples of the literature