A HPF AC-AC converter for Permanent Magnet Generator applications

This paper describes the design and development of a high input power-factor (HPF) AC to AC converter for naval applications using Permanent Magnet Generator (PMG). The proposed converter comprises an isolated three-phase uncontrolled multipulse rectification stage directly connected to a single-phase inverter stage, without the use of DC to DC intermediary stage, resulting in more simplicity for the overall circuitry, assuring robustness, reliability and reduced costs. Furthermore, the multipulse rectifier stage is capable to provide high power factor and input currents with low total harmonic distortion (THD). The output voltage of the PMG varies from 260V rms (220 Hz) to 380V rms (360 Hz), depending on load conditions. The output single-phase inverter stage was designed to operate with wide range of DC bus voltage, maintaining 120V rms, 60 Hz output. Measured total harmonic distortion for the AC output voltage represents less than 2%, at 3.6kW nominal linear load. © 2010 IEEE.

Visualizing the ac magnetic susceptibility of superconducting films via magneto-optical imaging

We have established a link between the global ac response and the local flux distribution of superconducting films by combining magnetic ac susceptibility, dc magnetization, and magneto-optical measurements. The investigated samples are three Nb films: a plain specimen, used as a reference sample, and other two films patterned with square arrays of antidots. At low temperatures and small ac amplitudes of the excitation field, the Meissner screening prevents penetration of flux into the sample. Above a certain ac drive threshold, flux avalanches are triggered during the first cycle of the ac excitation. The subsequent periodic removal, inversion, and rise of flux occurs essentially through the already-created dendrites, giving rise to an ac susceptibility signal weakly dependent on the applied field. The intradendrite flux oscillation is followed, at higher values of the excitation field, by a more drastic process consisting of creation of new dendrites and antidendrites. In this more invasive regime, the ac susceptibility shows a clear field dependence. At higher temperatures a smooth penetration occurs, and the flux profile is characteristic of a critical state. We have also shown that the regime dominated by vortex avalanches can be reliably identified by ac susceptibility measurements. © 2011 American Physical Society.

Estudo comparativo ortográfico: uma análise descritivo-comparativa em documentos históricos do século XIX em São Luís do Maranhão

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Quantificação da desintegração de comprimidos por fluxo ótico em seqüências de imagens de biosusceptometria AC

AC Biosusceptometry (ACB) is a low-cost biomagnetic tool that has been successfully applied on pharmaceutical research to evaluate performance of solid dosage forms. The aim of this work was to evaluate the Horn & Shunck method to access tablet disintegration. To evaluate the HS results was record on video a test with a objet moving in a rail with a constant velocity. The desintegration was recorded on video and ACB, which used have seven pairs of detection coils and a pair of excitation coils to mensure the magnetic ux variation. The signals were ampli ed and digitalized to create images, which were restored by Wiener lter, while the video images are converted to gray scale, both are normalized and binarized and had the optical ow estimation calculated by Horn & Schunck (HS) algorithm. All signals and images are processed and developed algorithm on Matlab. During the tests the ve tablets (500mg ferrite, 375mg excipients, compression 10 to 50 kN) were on a becker between of the ACB system and of the video system, and only touching the surface of the water. With all OF maps calculated was realized the sum of the resultants of each, to get a disintegration process resultant for each compression. Whit that was possible observed the disintegration behaves. For the compression force study the HS components of each sequence was sum, take mean and normalized for sequence's max modulo, therefore can be observed a high growing on less compression tablets. We can conclude the HS algorithm is viable to tablets disintegration data collection and whit that was possible to create a tablets disintegration analyzes protocol, which would be useful on desintegration kinetics study

Avaliação de parâmetros farmacêuticos em comprimidos matriciais empregando a técnica de Biosusceptometria AC

Oral administration is widely accepted route for drug delivery and solid dosage forms are commonly employed. The variation of absorption profiles along the human gastrointestinal tract (GIT) and the ability to target drugs by adequate dosage forms to distinct sites is the challenge in the pharmaceutical development of solid dosage forms. AC Biosusceptometry (ACB) is a technique that deserves consideration due to its features, accuracy of results and versatility. The purpose of this work was to evaluate, by employing the AC Biosusceptometer, the rate of swelling of systems matrices consisting of hydrophilic polymer (hydroxypropyl methyl cellulose) and magnetic material. Matrices tablets were evaluated in vitro to a more detailed analysis of kinetics of swelling, in addition to the study and application of mathematical models to correlate the magnetic area variation and the water uptake. All the procedures for qualitative and quantitative analysis of digital signals as well as the magnetic images processing were performed in MatLab® (Mathworks Inc.). ACB technique proved to be useful towards estimating the swelling properties of hydrophilic matrices in vitro, showing a promising capacity for further analyses involving dissolution test and in vivo studies, supporting their innovative potential pharmaceutical applications

Análise de processos biofarmacêuticos em comprimidos magnéticos empregando a Biosuceptometria AC

Ao administrar um fármaco, devem ser considerados fatores como a forma farmacêutica apropriada, a via de administração com maior eficiência e o que será mais bem aceita pelo paciente. Formas farmacêuticas sólidas (FFS), tais como comprimidos, representam a principal escolha, pois são fáceis de preparar, armazenar, transportar e são bem aceitas pelos pacientes. Porém, a absorção dos fármacos administrados em comprimidos depende do processo de desintegração, ou seja, um processo tempo-dependente que ocorre sob a ação de um desintegrante que promove a fragmentação da forma farmacêutica em partículas passíveis de serem dissolvidas e absorvidas. Para uma liberação efetiva do ativo, uns dos critérios relacionados à formulação como a escolha dos excipientes e o tipo de revestimento devem ser considerados. O revestimento com polímeros é utilizado para melhorar a estabilidade do fármaco, mascarar sabor ou para promover a liberação em locais específicos de acordo com a variação do pH. A técnica considerada como “padrão ouro” para monitorar FFS no trato gastrintestinal do homem é a cintilografia, entretanto, métodos alternativos com base na detecção de campo magnético merecem destaque. A técnica de Biosusceptometria de Corrente Alternada (BAC) tem evoluído, apresentando como vantagem ser um método não-invasivo e livre de radiação ionizante. A BAC utiliza bobinas de indução para registrar a variação temporal do fluxo magnético a partir da resposta de um material magnético ingerido, aplicando-se um campo magnético alternado no meio biológico. O objetivo deste estudo é empregar a BAC para avaliar in vitro a influência de três diferentes polímeros de revestimento em diversos parâmetros farmacotécnicos e no processo de desintegração de comprimidos

Aplicação da MTF e FWHM para análise de resolução espacial de sensores de Biossusceptometria AC

Neste trabalho foi analisada a resolução espacial de sensores de Biossusceptometria AC (BAC) correlacionando dois métodos consagrados em análise de resolução, a Função de Transferência Modulada (do inglês MTF) e a Largura à Meia Altura (FWHM) da Função de Espalhamento Pontual (PSF). A partir da aquisição da PSF do sistema, foi possível quantificar a resolução dos sensores pelos dois métodos. Foram analisados sensores de diferentes diâmetros para a obtenção da correlação entre os dois métodos. Foi variada também a corrente, indiretamente, pela variação de voltagem de excitação. Com estas metodologias foi possível avaliar a resolução de maneira pontual dos sensores, sendo possível otimizar a utilização dos sensores de acordo com a medida a ser realizada

Alegria além do recreio: refazendo nossa história na escola

O presente trabalho analisa a contribuição de um projeto extracurricular no que se refere à formação do autoconceito de quatro alunos das séries finais do Ensino Fundamental I, que apresentam problemas de relacionamento no ambiente escolar e que são marginalizados e vítimas de preconceito. A partir dos princípios metodológicos da pesquisa-ação, o referido projeto desenvolveu atividades que contribuem para valorizar a autonomia, o senso coletivo e a humildade e levou em consideração a diversidade e as diferenças que cada aluno possui. As atividades foram divididas em ciclos nos quais os alunos escolhiam os temas de estudo e a partir deles elaborou-se um planejamento e desenvolveu-se uma série de atividades coletivas que culminaram em uma apresentação daquilo que foi construído/apreendido para as respectivas turmas dos alunos envolvidos. O método de coleta de dados baseou-se em conversas informais com os alunos, com os pais e equipe pedagógica da escola; em observações dos alunos e das intervenções dos educadores-pesquisadores no decorrer do projeto e gravadas em audiovisual. A análise dos dados permitiu inferir que o projeto extracurricular denominado “Aprendendo com Alegria” colaborou na construção de um autoconceito positivo dos envolvidos, porém, mostrou-se frágil diante da complexidade de fatores que influenciam na formação do autoconceito dos alunos, como a visão de pessoas significativas como os pais, professores e equipe pedagógica

Switched capacitor DC-DC converters for HVDC applications

DC distribution and transmission provides an efficient, cost effective and reliable alternative to traditional AC systems for offshore wind farm integration. High power DC-DC converters are key components to realise future offshore voltage DC grids and multi-terminal HVDC systems. Different DC-DC converter topologies have been proposed for this application. The aim of this paper is to investigate the viability of Switched Capacitor (SC) converters in high power application particularly the interconnection of offshore windfarms to a medium voltage DC grid. In addition, a comparison of alternative topologies that have been proposed will be presented. Simulation and experimental results are provided to verify the analysis.

CD-ROM Acrobat Journals Using Networks

The available technologies for publishing journals electronically are surveyed. They range from abstract representations, such as SGML, concerned largely with the structure of the document, to formats such as PostScript which faithfully model the layout and the appearance. The issues are discussed in the context of choosing a format for electronically publishing the journal: Electronic Publishing -- Origination, Dissemination and Design. PostScript is neither widely enough available nor standardised enough to be suitable; a bitmapped pages approach suffers from being resolution-dependent in terms of the visual quality achievable. Reasons are put forward for the final choice of Adobe s new PDF document standard for creating electronic versions of the journal.

Effect of weak dipolar interaction on the magnetic properties of Ni nanoparticles assembly analyzed with different protocols

The effect of weak dipolar interactions (DIs) between Ni nanoparticles (NPs) in samples with different Ni concentrations was investigated by performing a detailed characterization of their structural and magnetic properties. From the determination of several physical parameters of Ni NP assemblies, it was found that the ac and dc magnetic susceptibility measurements are valuable for identifying the DIs between NPs while hysteresis loops measurements showed to be very insensitive, provided that the strength of the DI field is much smaller than the maximum coercive field. Therefore, the sensitivity of the observed static and dynamical magnetic properties to the effect of weak DI depends on the measurement protocols used. (C) 2011 American Institute of Physics. [doi:10.1063/1.3556767]

Surface effects in the magnetic properties of crystalline 3 nm ferrite nanoparticles chemically synthesized

We have systematically studied the magnetic properties of ferrite nanoparticles with 3, 7, and 11 nm of diameter with very narrow grain size distributions. Samples were prepared by the thermal decomposition of Fe (acac)(3) in the presence of surfactants giving nanoparticles covered by oleic acid. High resolution transmission electron microscopy (HRTEM) images and XRD diffraction patterns confirms that all samples are composed by crystalline nanoparticles with the spinel structure expected for the iron ferrite. ac and dc magnetization measurements, as well in-field Mossbauer spectroscopy, indicate that the magnetic properties of nanoparticles with 11 and 7 nm are close to those expected for a monodomain, presenting large M(S) (close to the magnetite bulk). Despite the crystalline structure observed in HRTEM images, the nanoparticles with 3 nm are composed by a magnetically ordered region (core) and a surface region that presents a different magnetic order and it contains about 66% of Fe atoms. The high saturation and irreversibility fields in the M(H) loops of the particles with 3 nm together with the misalignment at 120 kOe in the in-field Mossbauer spectrum of surface component indicate a high surface anisotropy for the surface atoms, which is not observed for the core. For T < 10 K, we observe an increase in the susceptibility and of the magnetization for former sample, indicating that surface moments tend to align with applied field increasing the magnetic core size. (C) 2010 American Institute of Physics. [doi:10.1063/1.3514585]

Magnetization studies of binary and ternary Co-rich phases of the Co-Si-B system

CoB, CO(2)B, CoSi, Co(2)Si and CO(5)Si(2)B phases can be formed during heat-treatment of amorphous co-Si-B soft magnetic materials. Thus, it is important to determine their magnetic behavior as a function of applied field and temperature. In this study, polycrystalline single-phase samples of the above phases were produced via arc melting and heat-treatment under argon. The single-phase nature of the samples was confirmed via X-ray diffraction experiments. AC and DC magnetization measurements showed that Co(2)Si and CO(5)Si(2)B phases are paramagnetic. Minor amounts of either Co(2)Si or CoSi(2) in the CoSi-phase sample suggested a paramagnetic behavior of the CoSi-phase, however, it should be diamagnetic as shown in the literature. The diamagnetic behavior of the CoB phase was also confirmed. The paramagnetic behavior of CO(5)Si(2)B is for the first time reported. The magnetization results of the phase CO(2)B have a ferromagnetic signature already verified on previous NMR studies. A detailed set of magnetization measurements of this phase showed a change of the easy magnetization axis starting at 70K, with a temperature interval of about 13K at a very small field of 1 mT. As the strength of the field is increased the temperature interval is enlarged. The strength of field at which the magnetization saturates increases almost linearly as the temperature is increased above 70K. The room temperature total magnetostriction of the CO(2)B phase was determined to be 8 ppm at a field of 1T. (C) 2010 Elsevier B.V. All rights reserved.

Controlo de conversores de potência genéricos por FPGA

Dissertação para obtenção do grau de Mestre em Engenharia Eletrotécnica Ramo de Automação e Eletrónica Industrial

Desenvolvimento e teste de um sistema para caracterização de materiais magnetoelétricos

Dissertação de mestrado integrado em Engenharia Eletrónica Industrial e Computadores