Willfully controlling the focus of an extracellular stimulus remains a significant challenge in the development of neural prosthetics and therapeutic devices. In part, this challenge is due to the vast set of complex interactions between the electric fields induced by the microelectrodes and the complex morphologies and dynamics of the neural tissue. Overcoming such issues to produce methodologies for targeted neural stimulation requires a system that is capable of (1) delivering precise, localized stimuli a function of the stimulating electrodes and (2) recording the locations and magnitudes of the resulting evoked responses a function of the cell geometry and membrane dynamics. In order to improve stimulus delivery, we developed microfabrication technologies that could specify the electrode geometry and electrical properties. Specifically, we developed a closed-loop electroplating strategy to monitor and control the morphology of surface coatings during deposition, and we implemented pulse-plating techniques as a means to produce robust, resilient microelectrodes that could withstand rigorous handling and harsh environments. In order to evaluate the responses evoked by these stimulating electrodes, we developed microscopy techniques and signal processing algorithms that could automatically identify and evaluate the electrical response of each individual neuron. Finally, by applying this simultaneous stimulation and optical recording system to the study of dissociated cortical cultures in multielectode arrays, we could evaluate the efficacy of excitatory and inhibitory waveforms. Although we found that the proximity of the electrode is a poor predictor of individual neural excitation thresholds, we have shown that it is possible to use inhibitory waveforms to globally reduce excitability in the vicinity of the electrode. Thus, the developed system was able to provide very high resolution insight into the complex set of interactions between the stimulating electrodes and populations of individual neurons.

Thesis (Ph.D.)-- University of Western Sydney, Nepean, 1999. / Includes bibliographical references (leaves 291-308).

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Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Este trabalho objetiva a eletrodeposiÃÃo de Co-Mo sobre substrato de cobre e analisar a influÃncia da densidade de corrente e do pH da soluÃÃo eletrolÃtica durante a eletrodeposiÃÃo. Os revestimentos foram obtidos sob controle galvanostÃtico no intervalo de densidade de corrente de 30 mAcm-2 a 60 mAcm-2 e pH de 6 a 8. Os revestimento de Co-Mo apresentaram morfologia nodular com trincas independente do valor de densidade de corrente e pH usado. Por meio de Energia Dispersiva de Raios-X, o revestimento obtido em 60 mA.cm-2 e pH 8 apresentou maior porcentagem de molibdÃnio, 32%. A anÃlise por DifraÃÃo de Raios-X mostra que os revestimentos sÃo amorfos. A eficiÃncia no processo de eletrodeposiÃÃo à maior quando a densidade de corrente à de 30 mAcm-2 e pH igual a 6. O estudo eletroquÃmico para a corrosÃo foi realizado em meio de soluÃÃo de NaCl e soluÃÃo deHCO3-/CO32-. Entre os tipos de revestimentos nÃo houve diferenÃa nas propriedadescorrosivas, porà , entre os meios, o de HCO3-/CO32- mostrou-se mais agressivo e a composiÃÃo do filme de passivaÃÃo depende do meio agressor. No estudo eletroquÃmico para a reaÃÃo de desprendimento de hidrogÃnio (RDH) utilizou-se o revestimento com maior Ãrea ativa (com maior porcentagem de molibdÃnio). Por meio de curvas de polarizaÃÃo em estado estacionÃrio, realizadas em um intervalo de temperatura de 30 a 60 ÂC, foi possÃvel determinar a energia de ativaÃÃo para a RDH sobre o revestimento de Co-Mo, obtendo-se um valor de 18,41 kJ.mol-1 / This work objective of this work was to electrodeposit Co-Mo on copper substrate and analyze the influence of current density and pH of the electrolytic solution during electrodeposition. Coatings were produced under galvanostatic control in the current density interval of 30 mAcm-2 to 60 mAcm-2 and pH 6 to 8. The Co-Mo coatings presented a nodular morphology with cracks, independently of the value of current density and pH employed. An analysis of the coating obtained with 60 mAcm-2 and pH8 by energy-dispersive X-ray spectroscopy revealed a high percentage of molybdenum, 32%. An X-ray diffraction analysis indicated that the coating were amorphous. The efficiency of the electrodeposition process was highest at a current density of 30 mAcm-2 and pH6. Theelectrochemical corrosion study was carried out in a medium of NaCl solution and of HCO3-/CO32-solution. The corrosion property of the various types of coatings showed no difference, but the HCO3-/CO32- medium was more aggressive and the composition of the passivation film was found to be dependent on the aggressive medium. The coating with the largest active area (containing the highest percentage of molybdenum) was used for the electrochemical study of the hydrogen evolution reaction (HER). Based on steady-state polarization curves carried out in a temperature range of 30 to 60 ÂC it was possible to determine the activation energy for the HDR on the Co-Mo coatings, obtaining a value of 18.41 kJ.mol-1

Avaliação ambiental, biológica e médica foram realizadas em 17 cromadores de 9 galvânicas do Estado de São Paulo, sendo cinco de cromo decorativo e quatro de cromo duro. O ar do ambiente de trabalho foi coletado individual e estacionariamente durante a semana de trabalho. Amostras de urina dos cromadores, foram coletadas no início e final do período de trabalho, encontrando-se uma correlação entre cromo urinário final e cromo no ar de 0,5. Usou-se a Absorção Atômica com Forno de Grafite GFAAS para determinar-se a concentração de cromo no ar ( Cr-ar) e cromo urinário ( Cr-U). O cromo hexavalente Cr (VI) foi extraído dos filtros de membrana de PVC com porosidade 5 µm com o tampão ácido acético/acetato de sódio, com a complexação do Cr (VI) feita por APDC. O complexo foi extraído com MIK. O limite de detecção foi de 1,1 µg/L. O Cr-U foi analisado diretamente por GFAAS com o limite de detecção 0,50 µg/L utilizando-se como modificador de matriz, nitrato de magnésio hexahidratado. Sem o modificador de matriz o limite de detecção foi de 0,14 µg/L. As concentrações de Cr (VI) no ar nas galvânicas de cromo decorativo variaram de 0,3 a 64,6 µg/m3 e nas de cromo duro variaram de 4,1 a 72,8 µg/m3 , mostrando a inadequação de alguns sistemas de exaustão. 60% dos cromadores das galvânicas de cromo duro tinham o septo nasal perfurado e todos os cromadores avaliados clinicamente tinham alterações nas vias aéreas superiores. O Cr-Uf que é utilizado como indicador biológico para compostos solúveis de cromo hexavalente, em muitos casos seus valores deram menores que o Cr-Ui, necessitando-se de estudos mais aprofundados quanto a esse aspecto, para evitar que o trabalhador possa ser prejudicado com resultados nem sempre condizentes com sua exposição. / Environmental, biological and medical evaluations was made in 17th workers of 9 chrome plating plants of the State of Sao Paulo, being 5 of decorative chrome plating and 4 of hard chrome plating. Environmental air samples were individual and stationarily collected during are week. Worker\'s urine samples were collected in the starting and in the end of the working period and it was obtained a correlation of 0,5 between the final urine chromium content and chromium air content. Graphite Furnace Atomic Absorption Spectrometry GFAAS was used for the determination of the chromium levels in the air (Cr-air) and in the urine(Cr-U). The Cr (VI) was extrated of the PVC membrane filters with an acetic acid/sodium acetate buffer and the Cr (VI) was isolated with APDC/MIBK. The detection limit obtained was 1,1 µg/L. The Cr-U was analised directly by GFAAS and the detection limit obtained was 0,50 µg/L, using magnesium Nitrate as matrix modifier and 0,14 µg/L without matrix modifier. The Cr (VI) concentration in the air was in the range of 0,3 to 64,6 µg/m3 in the decorative chrome plating and of 4,1 to 72,8 µg/m3 in the hard chrome plating, showing that the exhaust systems were inadequate. 60% of the workers of the hard chrome plating had perforation in the nasal cartilage and alI workers clinically evaluated presented alterations in the upper respiratory airway. The Cr-Uf that is used as biological indicator for the Cr(VI) soluble compounds, in many cases presented lower levels that the Cr-Ui showing that it is necessary more studies about this subject. In order to present inadequated results concerning the worker\'s exposition.

As doenças bucais ocupacionais e os acidentes de trabalho requerem medidas de prevenção implantadas no sistema de gestão de segurança e saúde no trabalho, a fim de estabelecer um ambiente de trabalho mais seguro. No caso do ambiente de trabalho apresentado no presente estudo, equacionar prevenção de doenças bucais ocupacionais é uma tarefa árdua. A legislação vigente exige da empresa, elaborar e manter um Programa de Prevenção de Riscos Ambientais (PPRA), visando preservar e manter a segurança e saúde de seus trabalhadores, em consonância com as demais normas regulamentadoras e com os demais requisitos legais, adentrando nesta interface a Odontologia do Trabalho. Por meio do conhecimento técnico-científico da Odontologia do Trabalho, este trabalho propõe incluir nas diretrizes para elaboração e implementação de um PPRA em um processo específico de galvanoplastia os riscos químicos com potencial de inferir na saúde bucal do trabalhador. Obtendo a associação entre a identificação no PPRA dos riscos ambientais e dos possíveis agravos e comprometimento da saúde bucal do trabalhador. Concluindo ser viável a contribuição da odontologia do trabalho na elaboração do PPRA visando à prevenção da saúde bucal dos que neste ambiente laboram; sendo necessário o monitoramento do binômio ambiente laboral e saúde bucal do trabalhador, a análise dos critérios para o estabelecimento de limites de tolerância, a eficácia dos equipamentos de proteção e a descrição dos riscos à saúde bucal na ficha de informação de segurança de produto químico. / Oral diseases and occupational accidents require prevention measures to be implemented in the systems of health and safety management at the workplace for a safer work environment. In the case of the work environment presented in this study, the prevention of occupational oral diseases is a daunting task. The current Brazilian legislation requires companies to establish and enforce a program named Occupational Hazard Prevention Program (PPRA) to help keep good safety and health conditions of their workers in line with regulatory standards and other legal requirements. This paper aims to include potentially damaging chemical risks to oral health of workers in the guidelines of the PPRA program and use them in a specific electroplating process. Through technical and scientific research, this work seeks to associate PPRA identification of environmental risks and its hazards to the possible risk of compromising the oral health of workers. It concludes by proving the positive contribution of dentistry labour in PPRA especially in the prevention of oral health damage, the requirement of monitoring the binomial work environment to maintain a good oral health of workers, analysis of criteria to establish tolerance limits, studies to assess efficiency level of equipment, and description of chemical products risks to oral health to be included in the safety guideline forms.

This study focuses on novel approaches to the modeling and construction of devices used in ion beam and vacuum systems. Turbulent computational fluid dynamics simulations were performed to model the air flow into an ion funnel system. The results of these simulations were coupled one-way with electrodynamics simulations of the fields generated by the ion funnel. Using the turbulence kinetic energy (k), a spatially varying estimation of the fluctuating component of the velocity field was calculated. These resulting simulations more accurately predicted the ion transmission through the system. Using fused deposition modeling (FDM) novel construction methods for the ion funnel and the vacuum chamber components the ion funnel system utilizes were developed. An FDM fabricated frame, in the shape of the ion funnel, was quickly and inexpensively produced. This frame supported a flexible printed circuit board that served as both the lenses of the ion funnel and power distribution circuit. The transmission of ions was as good as the traditionally constructed ion funnel. The device cost and weighed less and had lower intrinsic impedance, requiring less power to be driven. FDM was also used to produce vacuum components by post-processing using electroplating. Initial tests to determine whether electroplating would adequately produce a hermetic seal for vacuum components were performed. It was observed that thinner plated components could not withstand the stresses required from the gaskets and flanges to adequately seal, subsequently cracking. Thicker samples adequately sealed against atmosphere and maintained this seal over the entire test period. A proof of concept KF-25 full nipple was produced and processed using electroplating. The device was able to reach and ultimate pressure of 1 x 10-6 Torr, however, it was not able to reach the ultimate pressure of the chamber, which was 5 x 10-7 Torr due to the inability to be adequately cleaned of contaminant water.