Modeling electromechanical properties of layered electrets: Application of the finite-element method

We present calculations on the deformation of two- and three-layer electret systems. The electrical field is coupled with the stress-strain equations by means of the Maxwell stress tensor. In the simulations, two-phase systems are considered, and intrinsic relative dielectric permittivity and Young's modulus of the phases are altered. The numerically calculated electro-mechanical activity is compared to an analytical expression. Simulations are performed on two- and three-layer systems. Various parameters in the model are systematically varied and their influence on the resulting piezoelectricity is estimated. In three-layer systems with bipolar charge, the piezoelectric coefficients exhibit a strong dependence on the elastic moduli of the phases. However, with mono-polar charge, there is no significant piezoelectric effect. A two-dimensional simulation illustrated that higher piezoelectricity coefficients can be obtained for non-uniform surface charges and low Poisson's ratio of phases. Irregular structures considered exhibit low piezoelectric activity compared to two-layer structures.Comment: To be appaer in J Electrostatic

Electric field profiles in electron-beam-charged polymer electrets

A recently developed method, which uses piezoelectrically generated pressure steps for the determination of electric-field profiles in dielectrics, has been applied to electron-beam-charged polyfluoroethylenepropylene (FEP) and polyethyleneterephthalate (PETP) electrets. The results indicate that the technique can be employed to study volume charge effects in thin dielectrics. If properly calibrated, the method provides a quantitative measure of charge-integral functions or electric-field distributions in polymer foils

Origin of temperature dependent conductivity of α\alpha-polyvinylidene fluoride

The conductivity of $\alpha$-polyvinylidene fluoride ($\alpha$-PVDF) is obtained from dielectric measurements performed in the frequency domain at several temperatures. At temperatures above the glass-transition, the conductivity can be interpreted as an ionic conductivity, which confirms earlier results reported in the literature. Our investigation shows that the observed ionic conductivity is closely related to the amorphous phase of the polymer

Participação no grupo cooperativo do movimento da escola moderna: contributos para o desenvolvimento profissional docente

Dissertação apresentada à Escola Superior de Educação de Lisboa para obtenção do grau de Mestre em Ciências da Educação, especialidade Supervisão em EducaçãoO trabalho cooperativo entre os professores tem merecido destaque nos últimos anos, relacionando-se com ajuda mútua (Carneiro, Geller & Nitzke, 2008), onde todos trabalham com o intuito de alcançar objetivos pré definidos entre si (Dillenbourg, 1999) e de obter competências profissionais. Muito embora as práticas de trabalho individual ainda sejam uma tentação para os professores na atualidade há uma maior tendência para trabalharem colaborativamente nas escolas ou em grupos de formação organizados pelas associações de professores. Neste contexto, o estudo que apresentamos tem como finalidade compreender os processos de autoformação cooperada no contexto dos grupos cooperativos do Movimento da Escola Moderna (MEM) e o seu impacto no desenvolvimento profissional docente. Tendo em conta o objeto de estudo, identificaram-se as seguintes questões: i) Que motivações levam os professores a integrar os grupos cooperativos do MEM? ii) Como se organiza e desenvolve a autoformação cooperada nos grupos cooperativos do MEM? iii) Quais os aspetos positivos e constrangimentos identificados pelos professores no trabalho desenvolvido nos grupos cooperativos? iv) Quais as razões que levam os professores a permanecer e a abandonar a sua participação nos grupos cooperativos do MEM? v) Qual o impacto das experiências realizadas no contexto dos grupos cooperativos no desenvolvimento profissional docente? Para o efeito, contámos com a participação de seis professores pertencentes a um grupo cooperativo do MEM. Tendo como referência o objeto de estudo recorremos a uma metodologia de natureza qualitativa e privilegiámos como técnica de recolha de dados a entrevista semiestruturada. Para o tratamento dos dados sustentámo-nos na análise de conteúdo seguindo os passos recomendados para a análise de conteúdo por Bardin (2009). Os resultados do estudo permitiram constatar que o trabalho realizado no seio do grupo cooperativo promove o desenvolvimento profissional docente dado que fomenta a competência reflexiva sobre a prática pedagógica, bem como o desenvolvimento de outras competências da praxis, nomeadamente, a identificação de estratégias mais adequadas à resolução de problemas emergentes do quotidiano profissional do professor.Abstract The cooperative work between teachers has been receiving more attention over the last years, in relation with the mutual assistance (Carneiro, Geller & Nitzke, 2008), where everybody works with an aim to achieve predefined goals, which were created in relation to one another (Dillenbourg, 1999) and to obtain professional skills. Although individual work practices are still tempting to teachers, there is currently a greater trend to work as a group in schools or in training groups organized by teachers’ associations. In this context, this study aims to understand the cooperative self-training processes within the context of MEM’s cooperative groups and their impact in the professional teacher development. Considering the subject of study, the following questions were identified: i) What motivations lead the teachers to integrate MEM’s cooperative groups? ii) How is the cooperative self-training organized and how is it developed within in MEM’s cooperative groups? iii) What are the positive aspects and constraints identified by the teachers within the work developed in the cooperative groups? iv) What are the reasons that lead the teachers to stay or abandon its participation in MEM’s cooperative groups? v) What is the impact of experiences carried in the context of cooperative groups in the professional teacher development? For this purpose, we had the participation of six teachers belonging to one of MEM’s cooperative groups. Keeping the subject of study as a reference, we use a qualitative methodology and gave preference to the semi structured interview as the data collection technique. We based the data processing in the content analysis, following the recommended steps for content analysis by Bardin (2009). The study’s results allowed determining that the executed work promotes the teachers professional development, given that it increases the reflexive competence about the pedagogic practice, as well as the development of other competences of praxis, namely, the identification of the most adequate strategies for the resolution of emerging issues in the teacher’s professional everyday life.N/

Bitstream processing for Embedded Systems using C++ Metaprogramming

Abstract—This paper suggests a new approach for bitstream processing of embedded systems, using a combination of C++ metaprogramming combined with architecture extensions of an customizable embedded processor. Firstly, by using C++ metaprogramming techniques, we are able to code application software that needs to manipulate bitstreams in a very compact manner. Secondly, by using the architecture extensions of the Tensilica embedded processor indirectly via C++ operator overloading, the application code can seamlessly exploit custom architecture extensions. The intention is to do bitstream related processing with low programming effort, while generating runtime efficient code. Compared to other bitstream processing approaches we require no compiler modifications to exploit custom architecture features. Rather we put the bitstream related manipulation functionality into an active library, generated by a C++ metaprogram. I

Origin of the mid-temperature transition in vinylidenefluoride-based ferro-, pyro- and piezoelectric homo-, co- and ter-polymers

status: publishe

Desintegration, Anerkennungsbilanzen und die Rolle sozialer Vergleichsprozesse für unterschiedliche Verarbeitungsmuster

Anhut R, Heitmeyer W. Desintegration, Anerkennungsbilanzen und die Rolle sozialer Vergleichsprozesse für unterschiedliche Verarbeitungsmuster. In: Preyer G, ed. Neuer Mensch und kollektive Identität in der Kommunikationsgesellschaft. Wiesbaden: VS Verlag für Sozialwissenschaften; 2009: 212-236