Th. doct.-ing.--Génie chim.--Grenoble--I.N.P.G., 1984. N°: DI 487.

Made available in DSpace on 2014-06-11T19:25:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2001-02-05Bitstream added on 2014-06-13T20:33:17Z : No. of bitstreams: 1 cavalheiro_acv_me_araiq.pdf: 1614169 bytes, checksum: f41935b142e7cfa5cc1b9bce0d334cee (MD5) / No presente trabalho estudou-se a construção, caracterização e aplicação físico-química do eletrodo Pt|Hg|Hg2Ox|Grafite, sensível ao íon oxalato (Ox), em meio de NaNO3 a (25,0 ± 0,1) ºC, no intervalo de força iônica compreendido entre 0,300 e 1,200 mol L-1, cujos experimentos foram conduzidos no menor intervalo de tempo possível. Os dados potenciométricos foram adquiridos a cada 30s, onde o coeficiente angular médio das curvas analíticas foi de 28,4 mV/dec, com um intervalo útil de concentração de 0,0348 a 0,0669 mol L-1. Os valores de coeficiente molar de atividade do íon oxalato (yOx) em meio de NaNO3 foram maiores do que os respectivos valores em meio de NaClO4 (obtidos em trabalho anterior), para as mesmas forças iônicas devido às características intrínsecas de cada eletrólito. O eletrodo apresenta resposta repetitiva, em função do tempo de uso, em meio de NaClO4 por um período superior a oito meses, enquanto que em meio de NaNO3, apresenta diminuição na sua sensibilidade de cerca de 50%, para 0,500 mol L-1 (NaNO3), em 75 dias. As micrografias das superfícies das pastilhas sensoras utilizadas em meio de NaClO4 não apresentaram alteração. Todavia as utilizadas em meio de NaNO3 mostraram alterações significativas após cerca de trinta horas consecutivas de imersão em solução contendo Na2Ox, entretanto, tais alterações não foram observadas até cerca de quatro horas de imersão. / An oxalate sensitive electrode based on Pt|Hg|Hg2Ox|Grafite matrix was studied in conditions as follows: 0.300 – 1.200 mol L-1 NaNO3 interval of ionic strength, at (25.0 ± 0.1) ºC. All experiments were carried out in the shortest time interval. The potenciometric data was acquired at each 30s, where the medium angular coefficient of the analytical curves was of 28.4 mV/dec, with an useful interval of concentration of 0.0348 to 0.0669 mol L-1. The values of single molar ion activity coefficients associated to oxalate ion (yOx) in NaNO3 media were higher than those obtained in previous work in NaClO4 media, in the same ionic strength due to the intrinsic characteristics of each electrolyte. The electrode presents repetitive response in NaClO4 media during eight months. In sodium nitrate media, it presents decrease in sensibility of about 50%, for 0.500 mol L-1 NaNO3 during 75 days. The surfaces of the tablet sensors used in NaClO4 media did not present any alteration. On the other way, the tablets showed significant alterations on surface after thirty hours of continuous immersion in solution containing Na2Ox and NaNO3. However, there are no significant alterations after fours hours under immersion.

The objective of this thesis is to provide additional insight into the electrode array-nerve fibre interface that exists in the implanted cochlea and to facilitate investigation of new electrode arrays in interaction with the cochlea and auditory nerve fibres. The focus is on potential distributions and excitation profiles generated by different electrode array types and factors that could have an influence on these distributions and profiles. Research contributions made by the thesis are the creation of a detailed 3-D model of the implanted cochlea that accurately predicts measurable effects in cochlear implant wearers and facilitates effortless simulation of existing and new electrode array variations; the establishment of the important anatomical structures required in a 3-D representation of the implanted cochlea; establishment of evidence that array location is the primary parameter that controls spread of excitation; definition of the critical focussing intensity of intracochlear electrode pairs; confirmation thatmonopolar stimulation could deliver focussed stimulation to approximately the same degree than that delivered by widely spaced electrode configurations and that the use of monopolar configurations over bipolar configurations are therefore advantageous under certain conditions; explanation of the effect that encapsulation tissue around cochlear implant electrodes could have on neural excitation profiles; extension of the information available on the focussing ability of multipolar intracochlear electrode configurations; and establishment of evidence that a higher lateral electrode density could facilitate better focussing of excitation, continuous shaping of excitation profiles and postoperative customization of electrode arrays for individual implant wearers. / Dissertation (PhD(Electronic Engineering))--University of Pretoria, 2001. / Electrical, Electronic and Computer Engineering / Unrestricted

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