Sample records for electrodes
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1

Eletrodos fabricados por "silk-screen"/ Screen-printed electrodes

Nascimento, Valberes B.; Angnes, Lúcio
1998-10-01

Resumo em inglês A review dealing with the use of screen-printing technology to manufacture disposable electrodes is presented, covering in details virtually all the publications in the area up to early 1997 and including 206 references. The elements and different strategies on constructing modified electrodes are highlighted. Commercial and Home-made ink recipes are discussed. Microelectrode arrays, built by the combination of photostructuring and screen-printing technologies to the mass production of advanced disposable sensors, are also discussed. Future research trends are predicted.

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2

Eletrodos artesanais para voltametria/ Homemade electrodes for voltammetry

Silva, Reinaldo Carvalho; Souza, Ivan Gonçalves de
1998-07-01

Resumo em inglês This paper describes the construction and performance of homemade electrodes for voltammetric purpose using cheap materials, like pipette tips and asbestos fiber. A good cost-to-benefit relation makes this devices specially designed for student use, expecting to improve the broadcasting of electroanalytical methods in Brazilian schools.

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3

Eletrodos modificados com DNA: uma nova alternativa em eletroanálise/ DNA-modified electrodes: a new alternative for electroanalysis

La-Scalea, Mauro A.; Serrano, Silvia H. P.; Gutz, Ivano G. R.
1999-06-01

Resumo em inglês The first studies about DNA electrochemistry appeared at the end of the fifties. The voltammetric techniques became important tool for the DNA conformational analysis, producing evidences about DNA double helix polimorphism. The new techniques based on electrodes modification with nucleic acid enlarged the use of the electrochemical methods on the DNA research. DNA electrochemical biosensors are able to detect specific sequences of DNA bases, becoming important alternativ (mais) e for the diagnosis of disease, as well as in the carcinogenic species determination. Besides, the use of DNA biosensors in the mechanism study of biological drug actions can be useful for drug design.

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4

Eletrodos quimicamente modificados aplicados à eletroanálise: uma breve abordagem/ Chemically modified electrodes applyes to electroanalysis: a brief presentation

Souza, Maria de Fátima Brito
1997-04-01

Resumo em inglês Chemically modified electrodes (CMEs) have been subject of considerable attention since its inception about 23 years ago. CMEs result of a deliberate immobilization of a modifier agent onto the electrode surface obtained through chemical reactions, chemisorption, composite formation or polymer coating. This immobilization seeks transfer the physicochemical properties of the modifier to the electrode surface and thus to dictate and control the behavior of the electrode/sol (mais) ution interface. In recent years the interest in CMEs has increased particularly to enhance the sensitivity and/or the selectivity of electroanalytical techniques. In general higher sensitivity and/or selectivity may be achieved by exploiting one or more of the following phenomena: electrocatalysis, preconcentration and interferents exclusion. This paper deals with the application of CMEs in electroanalysis, including a brief presentation of the more general procedures that have been employed for the modification of electrode surfaces.

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5

Eletrodos positivos tubulares para baterias chumbo ácidas produzidas com material ativo nanométrico/ Lead acid batteries tubular positive electrodes assembled with nanometric active material

Impinnisi, Patrício R; Andrade, Juliano de; Palmer, Rodrigo V
2011-01-01

Resumo em inglês Conventional stationary lead acid batteries positive tubular plates have a specific capacity of about 120 Ah/kg. This value represents an active material utilization coefficient of 50%. The production of these plates includes some initial processes to generate the active PbO2 from a precursor material. In the present work it will be presented a proper and novel methodology to assemble tubular plates directely with nanometric powder of PbO2 particles. The utilization coeff (mais) icient of these plates was about 80%, and they were able to endure more than 130 severe duty cycles. This high utilization coefficient is a higly desirable feature for electric vehicles batteries.

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6

Eletrodos modificados com polímeros perfluorados e sulfonados: aplicações em análises ambientais/ Perfluorinated and sulfonated polymers modified electrodes: applications to environmental analysis

Fungaro, Denise Alves; Brett, Christopher M. A.
2000-12-01

Resumo em inglês Perfluoro and sulfonated ion-exchange polymers are recognized as a very useful material for various mechanistic studies and applications in electrochemistry. These polymers are characterized by high equivalent weights and by a low number of ion-exchange sites interposed between long organic chains. The solubility enables a preparation of stable polyelectrolyte films on the electrode surface. Examples of the determination of trace metals and organic componds in real environmental samples are presented.

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7

Eletrodos de pasta de carbono modificados com ácidos húmicos: estudo e determinação de metais em meio aquoso/ Carbon paste electrodes modified with humic acids: study and determination of metals in aqueous solution

Crespilho, Frank Nelson; Rezende, Maria Olímpia Oliveira
2004-12-01

Resumo em inglês Since 1992, the carbon paste electrodes modified with humic acids have been used for studying the behavior of metals in aqueous solutions. Many parameters influence the performance of the electrodes, such as the humic acid ratio, the nature of the humic acid, the accumulation time, the pH, the scan rate, and the preparation of the electrodes itself. There are various methos of preparing the electrodes. The goal of this paper is to review some of them. The advantages of us (mais) ing electrodes modified with humic acids as electrochemical sensors for evaluating metals in aqueous solution are stressed.

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8

Eletrodos modificados por hidróxido de níquel: um estudo de revisão sobre suas propriedades estruturais e eletroquímicas visando suas aplicações em eletrocatálise, eletrocromismo e baterias secundárias/ Nickel hydroxide modified electrodes: a review study concerning its structural and electrochemical properties aiming the application in electrocatalysis, electrochromism and secondary batteries

Vidotti, Marcio; Torresi, Roberto; Torresi, Susana I. Córdoba de
2010-01-01

Resumo em inglês The present review paper describes the main features of nickel hydroxide modified electrodes covering its structural and electrochemical behavior and the newest advances promoted by nanostructured architectures. Important aspects such as synthetic procedures and characterization techniques such as X-Ray diffraction, Raman and Infrared spectroscopy, Electronic Microscopy and many others are detailed herein. The most important aspect concerning nickel hydroxide is related t (mais) o its great versatility covering different fields in electrochemical-based devices such as batteries, electrocatalytic systems and electrochromic electrodes, the fundamental issues of these devices are also commented. Finally, some of the newest advances achieved in each field by the incorporation of nanomaterials will be shown.

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9

Utilização de eletrodos potenciométricos de amálgama em estudos de complexação de substâncias húmicas/ The use of potentiometric amalgam electrodes for complexation studies of humic substances

Abate, Gilberto; Masini, Jorge C.
1999-09-01

Resumo em inglês Potentiometric amalgam electrodes of lead, cadmium, and zinc are proposed to study the complexation properties of commercial and river sediment humic acids. The copper complexation properties of both humic acids were studied in parallel using the solid membrane copper ion-selective electrode (Cu-ISE). The complexing capacity and the averaged conditional stability constants were determined at pH 6.00 ± 0.05 in medium of 2x10-2 mol L-1 sodium nitrate, using the Scatchard m (mais) ethod. The lead and cadmium amalgam electrodes presented a Nernstian behavior from 1x10-5 to 1x10-3 moles L-1 of total metal concentration, permitting to perform the complexation studies using humic acid concentrations around of 20 to 30 mg L-1, that avoids colloidal aggregation. The zinc amalgam electrode showed a subnernstian linear response in the same range of metal concentrations. The Scatchard graphs for both humic acids suggested two classes of binding sites for lead and copper and one class of binding site for zinc and cadmium.

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10

Testes de desempenho de eletrodos: eletrodos de referência/ Performance tests for electrodes: reference eletrodes

Silva Jr., Ademário Íris da; Araújo Filho, Hiram da Costa; Silva, Reinaldo Carvalho
2000-08-01

Resumo em inglês This paper is designed to divulge some tests found in books, articles and international technical standards, by means of which it is possible to evaluate the performance of reference electrode widely used in potentiometric and voltammetric methods. The reference potential (Eref), junction resistance (Rj), the ability of keeping up the potential when current is flowing (polarizability), and of generating junction potentials (Ej) are applied to some commercial electrodes. T (mais) he results obtained are amply discussed and some corrective procedures are suggested when the electrode fails.

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11

Preparação de eletrodos opticamente transparentes/ Preparation of optically transparent electrodes

Cardoso, William da Silva; Longo, Claudia; De Paoli, Marco-Aurelio
2005-03-01

Resumo em inglês A simple experiment for the preparation of transparent conducting glass electrodes by deposition of pure and fluorine doped SnO2 films is described. This procedure was tested in the undergraduate inorganic course at IQ-UNICAMP. The success in achieving a conducting layer was easily checked using the standard probes of a volt-ohm meter. The optical transmittance and thickness were studied by UV-vis spectrophotometry. To discuss the experimental results we place significant (mais) emphasis on molecular orbital and energy band model theories. The undergraduate students can also discuss the concepts related to the electronic properties of solids and to interesting new materials, such as transparent conducting films, which are the subject of significant current research and technological applications.

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12

Preparação e caracterização de eletrodos de Pt e Pd modificados por poli-{trans-[RuCl2(vpy)4]} empregando espectroscopia de impedância eletroquímica/ Preparation and characterization of modified electrodes of Pt and Pd by poly-{trans-[RuCl2(vpy)4]} employing electrochemical impedance spectroscopy

Paula, M.M.S.; Zanini, L.C.; Martini, E.; Franco, C.V.
2008-06-01

Resumo em português Polímeros redox vêm sendo amplamente empregados na preparação de eletrodos modificados em virtude de suas propriedades eletrocatalíticas. Este trabalho descreve a preparação e caracterização de eletrodos modificados de Pt e Pd, por eletrodeposição redutiva de trans-[RuCl2(vpy)4]. Os eletrodos preparados foram caracterizados por espectroscopia de impedância eletroquímica em diferentes potenciais dc. O circuito equivalente simulado para o eletrodo Pt/poli-trans (mais) -[RuCl2(vpy)4] em -186 mV dc é semelhante a um circuito R1(R2Q)C. Os diagramas de Nyquist não mostram diferenças significativas entre os eletrodos de Pt/poli-trans-[RuCl2(vpy)4] e Pd/poli-trans-[RuCl2(vpy)4]. Os gráficos obtidos para diferentes substratos, Pt e Pd, são semelhantes em formato, mas apresentam diferenças no valor de RΩ, sendo maior em Pd. Isto pode ser indicativo de maior queda ôhmica no sistema Pd/filme/solução. Os diagramas de impedâncias obtidos para o filme polimérico poli-{trans-[RuCl2(vpy)4]}, depositados sobre Pt ou Pd, variam de acordo com o potencial dc, em torno da onda voltamétrica do par redox Ru2+/3+. A inclinação da reta que representa a difusão de Warburg é maior no eletrodo de Pd, mostrando que nesse sistema ocorre um controle difusional maior. Resumo em inglês Redox polymers has been highly employed in preparation of modified electrodes and yours electrocatalytic properties studied. This work describes the preparation of modified Pt and Pd electrodes by polymers by cathodic electrodeposition of trans-[RuCl2(vpy)4]. The electrodes were characterized by electrochemical impedance spectroscopy at different dc potentials. The equivalent circuit which simulated electrochemical impedance data obtained for the electrode Pt/poly-trans-[ (mais) RuCl2(vpy)4] at -186 mV dc was R1(R2Q)C. From Nyquist plots, no significant differences between Pt/poly-trans-[RuCl2(vpy)4] and Pd/poly-trans-[RuCl2(vpy)4] electrodes could be observed. The plots corresponding to different substrates, Pt and Pd, show similar shape, but the RΩ value is higher in Pd electrode. Probably, this can be indication of ohmic fall higher in the Pd/film/solution system. The impedance plots obtained to the polymeric film trans-[RuCl2(vpy)4], deposited on Pt or Pd, vary with the dc potential closely the voltammetric wave of the Ru2+/3+ redox couple. The inclination of the plot corresponding the Warburg diffusion in the Pd electrode is higher than Pt electrode, showing a diffusional control.

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13

Atividade eletrocatalítica de eletrodos compostos por Pt, RuO2 e SnO2 para a eletrooxidação de formaldeído e ácido fórmico/ Electrocatalytical activity of Pt, SnO2 and RuO2 mixed electrodes for the electrooxidation of formic acid and formaldehyde

Profeti, L.P.R.; Profeti, D.; Olivi, P.
2005-01-01

Resumo em português A atividade eletrocatalítica para a oxidação de ácido fórmico e formaldeído em eletrodos binários de Pt e SnO2 e ternários de Pt, RuO2 e SnO2 em diferentes composições, foi investigada através das técnicas de voltametria cíclica e cronoamperometria. Os materiais foram preparados por decomposição térmica de precursores poliméricos na temperatura de 400°C. Os experimentos de voltametria cíclica mostraram que os eletrodos mistos proporcionaram uma dimin (mais) uição de ~100 mV (ERH) no potencial de pico de oxidação das moléculas orgânicas em relação ao eletrodo contendo somente Pt e indicaram que a composição Pt0,6Ru0,2Sn0,2Oy possui maior densidade de corrente de oxidação em potenciais inferiores ao potencial de pico. Os experimentos de cronoamperometria confirmam a contribuição da adição de SnO2 e RuO2 para o aumento da atividade catalítica em menores valores de potencial. Resumo em inglês The electrocatalytical activity of binary electrodes of Pt and SnO2 and ternary electrodes of Pt and SnO2 and RuO2 for the electrooxidation of formic acid and formaldehyde was investigated by cyclic voltammetry and chronoamperometry techniques. The electrode materials were prepared by the thermal decomposition of polymeric precursors at 400 ºC. The cyclic voltammetry results showed that the methanol electrooxidation process presents peak potentials for those electrodes a (mais) pproximately 100 mV lower than the values obtained for metallic platinum electrodes. The Pt0.6Ru0.2Sn0.2Oy electrodes presented the highest current density values for potentials lower than the peak potential values. The chronoamperometric experiments also showed that the addition of SnO2 and RuO2 contributed for the enhancement of the electrode activity in low potential values. The preparation method was found to be useful to obtain high active materials.

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14

Estudo comparativo de eletrodos comerciais para soldagem subaquática molhada/ Comparative study of commercial electrodes for underwater wet welding

Bracarense, Alexandre Q.; Pessoa, Ezequiel C.; Santos, Valter R. dos; Monteiro, Maurício J.; Rizzo, Fernando C.; Paciornik, Sidnei; Reppold, Ricardo; Domingues, José R.; Vieira, Leonardo A.
2010-12-01

Resumo em português Com o objetivo de fornecer subsídios para a seleção de consumíveis para a soldagem molhada foram determinadas algumas propriedades do metal de solda a partir de juntas soldadas em água doce com eletrodos revestidos comerciais específicos para este fim. As soldas foram realizadas em tanque a 0,5m de profundidade por dispositivo de soldagem por gravidade. Foram levantados dados que auxiliem a eleger os consumíveis de melhor desempenho para serem testados em maiores p (mais) rofundidades. Foram realizados os seguintes testes e avaliações: caracterização microestrutural, análise e quantificação das inclusões, composição química do metal de solda, dureza Vickers, hidrogênio difusível e avaliação da soldabilidade. Os resultados obtidos permitem classificar os consumíveis testados em dois grupos com características bem distintas. No primeiro grupo está o único eletrodo do tipo oxidante e no segundo grupo estão os quatro eletrodos do tipo rutílico testados. Quanto às propriedades mecânicas e às características operacionais, os eletrodos do tipo rutílico apresentaram os melhores resultados. Por outro lado, o eletrodo oxidante testado produziu soldas com mais baixo teor de hidrogênio difusível e, portanto, menor risco potencial de provocar trincas a frio. As diferenças de propriedades entre os eletrodos testados são evidenciadas e discutidas no presente trabalho. Resumo em inglês With the objective to supply subsidies to select ferritic electrodes for underwater wet welding, some weld metal characteristics of commercial electrodes were determined. The welding trials were carried out at 0.5m fresh water depth in an aquarium, using a gravity device for welding. The study aimed also to obtain data to help to elect the consumables of best performance to be tested in higher depths. The following characterizations were performed: microstructural analysi (mais) s, quantification of inclusions, weld metal and inclusions chemical composition, mechanical properties, diffusible hydrogen and weldability evaluation. The obtained results helped to classify the tested consumables in two groups with quite different characteristics. The first group is composed of one oxidizing type electrode and the second one is composed of four rutile type electrodes. Regarding to hydrogen in the weld metal, the obtained results show that the oxidizing electrode is able to produce welds with considerable low diffusible hydrogen content. As a consequence, smaller potential risk of cold cracking is expected when using this electrode. Meantime, regarding to the arc stability and other operational indicators, the oxidizing electrode presented inferior performance. Considering mechanical properties, the rutile electrodes presented the best results. The properties differences among the electrodes tested are shown and discussed in the present work.

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15

Implantação estereotáxica de eletrodos profundos por ressonância magnética para cirurgia de epilepsia/ MRI-guided stereotactic implantation of depth electrodes in epilepsy surgery

MENESES, MURILO S.; FOLLADOR, FLÁVIA R.; ARRUDA, WALTER O.; SANTOS, HERALDO L.; YONESAWA, DÉBORA; HUNHEVICZ, SONIVAL C.
1999-09-01

Resumo em português Apresentamos o caso de uma paciente com epilepsia refratária ao tratamento medicamentoso e submetida à monitorização em vídeo-eletrencefalografia por eletrodos de profundidade intracerebrais. A história, o exame clínico, a ressonância magnética (RM), a vídeo-eletrencefalografia e o estudo neuropsicológico não foram suficientes para a determinação da área cerebral de origem das crises convulsivas. Eletrodos de profundidade intracerebrais colocados por estere (mais) otaxia guiada por RM possibilitaram o registro de forma muito clara da atividade epileptiforme, determinando com precisão a área cerebral epileptogênica a ser removida por cirurgia. Após lobectomia temporal anterior direita com amígdalo-hipocampectomia realizada há três meses, a paciente permanece sem crises convulsivas. Segundo informações obtidas durante o último Congresso da Liga Brasileira de Epilepsia, esta é a primeira cirurgia estereotáxica para colocação de eletrodos de profundidade intracerebrais em epilepsia no Brasil. Resumo em inglês We present the case of a 40-year-old woman with refractory epilepsy since aged 18, who was submitted to video-EEG monitoring with intracerebral depth electrodes. The clinical history and examination, magnetic resonance image (MRI), video-EEG and neuropsychological study did not allow the determination of the cerebral onset of epileptic seizures. Depth electrodes inserted by MRI-guided stereotaxis allowed the recording of the epileptic activity and thus showed quite accura (mais) tely the area of the brain to be surgically resected. She underwent a right anterior temporal lobectomy with amygdalohippocampectomy. The immediate postoperative period was uneventful and she is without epileptic seizures after three months of follow-up. The average pre-operative free-seizure period was two weeks. To our knowledge, this is the first stereotactic surgery for insertion of depth intracerebral electrodes in epilepsy in Brazil.

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16

Tendências em modificação de eletrodos amperométricos para aplicações eletroanalíticas/ Trends in amperometric electrodes modification for electroanalytical applications

Pereira, Arnaldo César; Santos, Antonio de Santana; Kubota, Lauro Tatsuo
2002-11-01

Resumo em inglês The most relevant advances on the analytical applications of chemically modified electrodes (CME) are presented. CME have received great attention due to the possibility of electrode surface modification including chemisorption, composite generation and polymer coating. In recent years, the interest in CME has increased overall to improve the sensitivity and selectivity of the electroanalytical probes, considering the electron mediator incorporation and the new conducting (mais) polymers development. The general procedures employed for the electrode modification and the operational characteristics of some electrochemical sensors are discussed.

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17

Aplicações eletroanalíticas com eletrodos de prata confeccionados a partir de CDs graváveis/ Electroanalytical applications of silver electrodes built from recordable CDs

Richter, Eduardo M.; Jesus, Dosil P. de; Neves, Carlos A.; Lago, Claudimir L. do; Angnes, Lúcio
2003-12-01

Resumo em inglês This paper presents a new way for the construction of silver electrodes utilizing recordable CDs. The new electrodes were explored for the quantification of chloride (by potentiometry/FIA), cyanide (by amperometry/FIA) and for lead analysis (by square wave voltammetry). For the flowing measurements, a digital multimeter, connected to a microcomputer (via RS 232 interface) was used to collect directly the potential signal (for Cl- measurements) or to take the output signal (mais) from a potentiostat (for CN- measurements). The square wave voltammetry analysis was performed in a commercial instrument. The results shown good performance of the new electrodes and the detection limit (s/n = 3) attained for these three analytes were: 0.2, 50, and 200 µg L-1 for Pb2+, Cl-, and CN- respectively.

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18

Uma célula simples para adaptação de eletrodos seletivos comerciais em sistemas de análises em fluxo/ A simple cell for assembling commercial ion-selective electrodes in continuous flow analyzers

Marin, Maria Angélica Bonadiman; Ganzarolli, Edgard Moreira; Queiróz, Roldão Rooseveld Urzêdo de; Souza, Ivan Gonçalves de
1998-11-01

Resumo em inglês A simple flow cell for potentiometric detection is described. It was assembled by making use of two perspex pieces fixed together by means of four screws, and allow the connection of plane membrane conventional electrodes to flow system. Details about its construction are presented. The device performance was evaluated by making use of a cyanide ion-selective electrode. The relative standard deviation was about 0.5% with a detection limit of 8.0 x 10-6 mol CN- dm-3. Under experimental conditions, the linear range was 10-5 to10-2 mol dm-3.

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19

Reação de geração de oxigênio em eletrodos de Mn2O3 suportados em aço inoxidável/ Oxygen evolution reaction on Mn2O3 electrodes supported on stainless steel

Varela, Hamilton; Câmara, Giuseppe A.; Scatena Júnior, Hélio; Gonzalez, Ernesto R.
2000-12-01

Resumo em inglês A study of the kinetics of oxygen evolution in alkaline conditions from ceramic films of Mn2O3 supported on stainless steel was carried out. This study has been done through the determination of transfer coefficients, Tafel slopes and exchange currents using potentiodynamic and quasi-potentiostatic measurements. The activation energy was determined as a function of the overpotential and, additionally, the electrode active surface was estimated. The results are consistent (mais) with data already published for other electrodes, implying that the methods used in this work were reliable and precise.

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20

Otimizaçâo das condições de preparação de eletrodos à base de carbono cerâmico utilizando-se planejamento fatorial/ Optimization of electrodes conditions preparation based carbon ceramic using factorial design

Skeika, Tatiane; Pessoa, Christiana; Fujiwara, Sergio Toshio; Nagata, Noemi
2010-01-01

Resumo em inglês Different parameters of carbon ceramic electrodes (CCE) preparation, such as type of precursor, carbon material, catalyst amount, among others, significantly influence the morphological properties and consequently their electrochemical responses. This paper describes a 2³ factorial design (2 factors and 3 levels with central point replicates), which the factors analyzed were catalyst amount (HCl 12 mol L-1), graphite/precursor ratio, and precursor type (TEOS - tetraethox (mais) ysilane and MTMOS - methyltrimetoxysilane). The design resulted in a significant third order interaction for peak current values (Ipa) and a second order interaction for potential difference (ΔE), between thefactors studied, which could not be observed when using an univariated study.

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21

Preparação e caracterização de eletrodos monocristalinos/ Preparation and characterization of single crystal electrodes

Perez, Joelma; Villullas, Hebe M.; Gonzalez, Ernesto R.
1997-10-01

Resumo em inglês Studies of the kinetics of electrocatalytic reactions on well oriented single crystal surfaces have demonstrated the influence of surface structure on the rate and mechanisms of many electrochemical processes. The preparation and characterization of these surfaces is the first step in this type of studies. In this paper, a methodology employed in order to ensure the quality and cleanliness of single crystals and their utilization as rotating electrodes is described.

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22

Eletrocatálise da reação de redução de oxigênio sobre eletrodos de grafite modificados com ftalocianina tetracarboxilada de ferro/ Eletrocatalysis of the oxygen reduction reaction on graphite electrodes modified with iron tetracarboxyphthalocyanine

Chaves, J. A. P.; Araújo, M. F. A.; Varela Júnior, J. de J. G.; Tanaka, A. A.
2003-01-01

Resumo em português Este trabalho apresenta um estudo das propriedades eletroquímicas de eletrodos de grafite modificados, em níveis de monocamadas, com ftalocianina tetracarboxilada de ferro, FeTcPc, em soluções aquosas. Em meio alcalino, os eletrodos modificados apresentaram alta atividade eletrocatalítica para a reação de redução de oxigênio, comparável com a do eletrodo de platina. A reação processa-se de acordo com uma cinética de primeira ordem com relação ao oxigênio (mais) dissolvido, um mecanismo envolvendo 4 elétrons e associado com o processo redox Fe(3+)TcPc/Fe(2+)TcPc. Resumo em inglês This work presents a study of the electrochemical properties of pyrolytic graphite electrodes modified, at monolayer levels, with iron tetracarboxylated phthalocyanine, FeTcPc, in aqueous solutions. In alkaline media, the modified electrodes presented high electrocatalytic activity towards the oxygen reduction reaction, and comparable to that showed by platinum electrodes. The reaction proceeds according to a first order reaction with respect to dissolved oxygen, a mechanism involving 4 electrons and associated with the Fe(3+)TcPc/Fe(2+)TcPc redox process.

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23

Eletroxidação do etanol em eletrodos de Ti/IrO2/ Electro-oxidation of ethanol in Ti/IrO2

Fidelis, Carlos H.V.; Donate, Paulo M.; Andrade, Adalgisa R. de
2001-02-01

Resumo em inglês It has been carried out an investigation of ethanol electro-oxidation on Ti/IrO2 electrodes. The experimental results show a high selectivity towards acetaldehyde formation thus, offering potential advantages in cost and availability of raw material. It has been observed that the electrode is partially blocked by a film formed after the oxidation of the starting material which can be removed by pulse technique between RDO and RDH onset. The mechanism and the selectivity of the product formed is presented.

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24

Hidrogenação eletrocatalítica de substratos orgânicos utilizando eletrodos modificados poliméricos contendo partículas de Ni/Pd e Ni/Pt/ Electrocatalytic hydrogenation of organic substrates on polymer modified electrodes embedding Ni/Pd and Ni/Pt particles

Purgato, Fabiana L. S.; Romero, José R.; Abrantes, Luisa M.
2009-01-01

Resumo em inglês Novel modified electrodes bearing dispersed Pd and Pt particles have been prepared from poly (allyl ether of the p-benzenesulfonic acid) films with incorporated nickel particles making use of galvanic displacement reactions. The SEM analysis of the new modified electrodes revealed efficient deposition of Pd but weak up-take of Pt. Electrocatalytic hydrogenation of several classes of organic substrates were carried out using the MEs Ni, Ni/Pd and Ni/Pt. The Ni/Pd ME showed (mais) to be the best of them for the hydrogenation of double, triple and carbonyl bonds. The complete hydrogenation of the aromatic rings for the well-adsorbed substrates acetophenone and benzophenone is noteworthy.

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25

Recentes avanços e novas perspectivas dos eletrodos íon-seletivos/ Recent advances and new perspectives of ion-selective electrodes

Torres, Karin Yanet Chumbimuni; Marzal, Percy Calvo; Kubota, Lauro Tatsuo; Bakker, Eric
2006-10-01

Resumo em inglês This paper describes the recent progress in the development of polymeric membranes for ion-selective electrodes. The importance of knowing the mechanism of potential development in membranes for ion-selective electrodes to reach lower detection limits and improve selectivity are discussed. Recent advances and future trends of research on ion-selective electrodes are also reported.

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26

Despolarizador eletrônico de eletrodos/ Eletronic depolarizer for electrodes

Li, Rosamaria Wu Chia; Campioti, Decio Arrais; Pardini, Vera Lúcia; Gruber, Jonas
1999-12-01

Resumo em inglês This paper presents the design of a simple apparatus that periodically switches off both working and auxiliary electrodes short-circuiting them for a couple of seconds. Depolarization takes place and the initial current is re-established.

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27

Estudo de efeito dos sais precursores sobre as propriedades eletrocatalíticas de eletrodos de Ti-SnO2/Sb preparados por decomposição térmica/ Study of the effect of precursor salts on the electrocatalytic properties of Ti-SnO2/Sb electrodes prepared by thermal decomposition

Andrade, Leonardo Santos; Rocha-Filho, Romeu C.; Bocchi, Nerilso; Biaggio, Sonia R.
2004-12-01

Resumo em inglês The physical and electrochemical properties of Ti-SnO2/Sb electrodes obtained by the thermal decomposition of solutions of the precursor salts SnCl2×2H2O/SbCl3 and SnSO4/Sb2(SO4)3 were investigated. The reversibility of the cyclic voltammetric response of the Fe(CN)6(4-)/Fe(CN)6(3-) redox couple was assessed using the obtained electrodes. Their catalytic activity for the oxygen-evolving reaction and maximum capacity for electronic transfer were also evaluated by potentia (mais) l and current linear scans in 0.5 mol L-1 H2SO4. Additionally, scanning electron microscopy analyses allowed the visualization of the morphology of the oxide films obtained. The best results were presented by the electrodes obtained from the chloride salt precursors.

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Correlação entre a estrutura atômica superficial e o processo de adsorção-dessorção reversível de hidrogênio em eletrodos monocristalinos Pt(111), Pt(100) e Pt(110)/ The correlation between the atomic surface structure and the reversible adsorption-desorption of hydrogen on single crystal Pt (111), Pt (100) and Pt (110) electrodes

Santos, Valderi Pacheco dos; Tremiliosi Filho, Germano
2001-12-01

Resumo em inglês Platinum is widely used as electrode in electrocatalytic processes, however the use of polycrystalline electrodes introduces a series of variables in the electrochemical system due to the aleatory contribution of all the crystallographic orientations with different surface packing of atoms. Single crystal platinum electrodes of low Miller index present surface structure of high regularity and serve as model to establish a correlation among the macroscopic and microscopic (mais) properties of the electrochemical interface. Therefore, the main aim of this work is the study of the voltammetric profiles of the reversible adsorption-desorption of hydrogen on Pt(100), Pt(110) and Pt(111), in order to correlate the electrochemical properties of each different orientation with the surface atomic structure.

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Comportamento eletroquímico da N-nitrosotiazolidina ácido carboxílico sobre eletrodos de ouro e mercúrio/ Electrochemical behavior of N-nitrosothiazolidine carboxilic acid on gold and mercury electrodes

Codognoto, Lucia; Reyes, Felix G. R.; Winter, Eduardo; Rath, Susanne
2008-01-01

Resumo em inglês The electrochemical behavior of N-nitrosothiazolidine carboxylic acid (NTAC) on gold and hanging mercury electrodes, using the cyclic and square wave voltammetries, was studied. Whereas NTAC suffer reduction in a single step on the mercury electrode, two peaks appears on the cyclic voltammograms on the gold electrode, one anodic peak overlaying the gold oxide process at 1.2 V and one cathodic peak at -0.41 V vs Ag/AgCl, KCl 3.0 mol L-1. The cathodic peak depends on the pr (mais) evious oxidation of NTAC at the electrode surface, presents irreversible and adsorption controlled characteristics and it is suitable for quantitative purposes.

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Estudo anatômico da cóclea para confecção de instrumental para a cirurgia de implante coclear com 2 feixes de eletrodos em cócleas ossificadas/ Cochlear anatomy study used to design surgical instruments for cochlear implants with two bundles of electrodes in ossified cochleas

Bogar, Mariana; Bento, Ricardo Ferreira; Tsuji, Robinson Koji
2008-04-01

Resumo em português A ossificação da cóclea, decorrente principalmente de meningite, impede a inserção completa do implante coclear convencional. Os implantes com 2 feixes de eletrodos mais curtos do que o convencional foram desenvolvidos especialmente para cócleas ossificadas. Porém, durante essa cirurgia há um grande risco de lesão da artéria carótida interna (ACI). Portanto, a medida da profundidade das cocleostomias para inserir os dois feixes de eletrodos aumentaria a seguran (mais) ça desse procedimento. OBJETIVOS: 1) Obter as distâncias entre as cocleostomias e a ACI em ossos temporais de cadáver; 2) Confeccionar instrumento que possa ser usado na cirurgia de implante coclear com 2 feixes de eletrodos. FORMA DE ESTUDO: Experimental prospectivo. MATERIAL E MÉTODO: Em 21 ossos de cadáveres foi realizada: 1) mastoidectomia cavidade aberta; 2) cocleostomias nos giros basal e médio da cóclea; 3) identificação da ACI; 4) medida da distância entre as cocleostomias e a artéria. RESULTADOS: A medida média ± desvio padrão obtida para o túnel superior foi 8,2 ± 1,1mm e para o túnel inferior foi 8,1± 1,3mm. A menor distância encontrada foi 6,5mm para o túnel superior e 6,0mm para o túnel inferior. CONCLUSÃO: Apesar dos parâmetros calculados concluímos que a melhor medida para ser considerada na confecção do instrumento cirúrgico serão as mínimas medidas obtidas em cada um dos giros cocleares, pois é a maneira mais segura para evitar a lesão da ACI, que pode ser fatal. Resumo em inglês Cochlear ossification, mainly secondary to meningitis, prevents the complete conventional cochlear implant insertion. Implants with two electrode bundles shorter than the conventional ones were specifically developed for ossified cochleas. However, during surgery there is a high risk of damaging the internal carotid artery (ICA). Therefore, measuring cochleostomy depth in order to insert the two electrode bundles would greatly increase the procedure's safety. AIMS: 1) Fin (mais) d the distances between cochleostomies and ICA in cadaver temporal bones. 2) Design an instrument that can be used in cochlear implant surgery to introduce an implant with two bundles of electrodes. STUDY DESIGN: Experimental prospective. MATERIALS AND METHODS: In 21 temporal bones from cadavers we performed: 1) canal wall down mastoidectomy; 2) cochleostomy in the cochlear basal and middle turns; 3) ICA identification; 4) Length determination between the cochleostomies and the artery. RESULTS: the average distance ± standard deviation obtained for the upper tunnel was of 8.2 ± 1.1 mm and for the lower tunnel it was of 8.1± 1.3 mm. The shortest distance found was of 6.5 mm for the upper tunnel and 6.0 mm for the lower tunnel. CONCLUSION: Despite the values calculated, we concluded that the best value to be considered in creating a surgical instrument are the minimum lengths obtained for each one of the cochlear turns, because this is the safest way to avoid damaging the ICA, that can be fatal.

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Potencialidades do uso de ultrassom na determinação do pesticida carbaril empregando eletrodos de diamante/ Ultrasound potentialities on the determination of the pesticide carbaryl using diamond electrodes

Garbellini, Gustavo S.; Avaca, Luis A.; Salazar-Banda, Giancarlo R.
2010-01-01

Resumo em inglês The potentiality of the use of ultrasound radiation in association with a boron-doped diamond electrode was evaluated on the voltammetric determination of the pesticide carbaryl. Improvements in the sensitivity, limit of detection and reproducibility of the measurements were observed due to both, the enhancement of mass transport and the cleaning of the electrode surface provided by ultrasound. Satisfactory recovery levels for carbaryl in pure water (96-98%) and pineapple (mais) juice (89-92%) for quiescent and sonovoltammetric methodologies were obtained. These methodologies can be alternative tools for the analyses of pesticides in fruit samples, mainly the insonated condition that improve the analytical performance and dispense intermediary cleanings of the electrode surface.

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Hidrogenação eletrocatalítica de substratos orgânicos: estudo da eficiência dos metais nobres níquel, paládio e platina usando eletrodos modificados/ Electrocatalytic hydrogenation of organic substrates: study of the efficiency of the nickel, paladium and platinum noble metals using modified electrodes

Pontólio, José Olavo S.; Purgato, Fabiana L. S.; Romero, José R.
2004-08-01

Resumo em inglês Nickel, palladium and platinum micro-crystals were dispersed in films covering a vitreous carbon plate electrode by ion exchange followed by electroreduction of their ions. These modified electrodes were used in the electrocatalytic hydrogenation of several substrates of different classes and their efficiency is reported. A comparison among them was performed based on the structural characteristics of the metals. A modified electrode containing platinum showed to be more efficient than a palladium modified electrode and the one of nickel was the less efficient.

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Avaliação da atividade mioelétrica do trato gastrointestinal em cães: avaliação de um sistema de fixação de eletrodos na parede abdominal/ Gastrointestinal myoelectric activity in dogs: evaluation of a fixation system of electrodes on the abdominal wall

Ferraz, Álvaro Antônio Bandeira; Coelho, Antônio Roberto de Barros; Leão, Cristiano de Souza; Campos, Josemberg Marins; Câmara Neto, Renato Dornelas; Bacelar, Tércio Souto
2002-01-01

Resumo em português OBJETIVO: A implantação de eletrodos intra-abdominais para captura de sinais de onda elétrica constitui instrumento de estudo da atividade mioelétrica do tubo gastrointestinal. O deslocamento destes eletrodos do local de implantação ocorre com certa freqüência em animais de experimentação não anestesiados, devido aos movimentos da musculatura diafragmática, abdominal, do peristaltismo gastrintestinal e sobretudo aos hábitos inerentes à espécie de animal est (mais) udada, particularmente presentes em caninos. No referido estudo foi proposto um procedimento que proporciona estabilidade ao referido sistema utilizando-se recursos simples e de custos irrelevantes. MÉTODOS: Os autores apresentam através de diagramas e fotos um sistema de ancoração dos eletrodos elétricos na pele dos animais com botões. RESULTADOS: Foram realizados 5 experimentos, fixando-se em cada animal 3 eletrodos bipolares. Os animais foram mantidos em repouso até a completa recuperação do íleo paralítico. Não foi identificado nos animais estudados nenhuma migração dos eletrodos. CONCLUSÃO: O procedimento proposto é eficiente, simples, de fácil confecção e permite o monitoramento da atividade mioelétrica, em cães não anestesiados, por períodos de tempo prolongado. Resumo em inglês OBJECTIVE: The use of intra-abdominal electrodes in the study of gastrointestinal electrical wave is an important instrument of the gastrointestinal mioelectric activity. However, the dislocations of the electrodes in non-anaesthetized animals due to diaphragmatic muscle movements, gastrointestinal movements and mainly due to the animals habits, especially in dogs. The study has the objective to demonstrate a procedure that stabilize the system using simple resources an i (mais) rrelevant cost. METHODS: The authors demonstrate under diagrams and picture a fixed system to fix the electrical electrodes through the animal skin using bottoms. RESULTS: The system was used in 5 animals. Each animal had 3 bipolar electrodes. During the study it was not identified any electrode migration. The animals was kept resting until the complete recovery of the postoperative ileus. CONCLUSION: The procedure proposed is efficient, simple, and easy to be made and allow an acquisition of the mioelectric activity, in dogs not anaesthetized, for long periods.

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Construção e aplicação de eletrodo de aço inoxidável UNS S31254 como eletrodo indicador em titulações condutimétricas/ Construction and application of UNS S31254 stainless steel as indicator electrode in conductimetric tritations

Terra, Lúcia Helena; Torres, Nivaldo; Agostinho, Silvia Maria Leite
2003-01-01

Resumo em inglês UNS S31254 SS electrodes have been built to substitute platinum in conductimetric titrations. The electrodes were tested in both acid-basic titration (chloridric acid and sodium hydroxide) and precipitation titration (sodium chloride and argentum nitrate as titrant). The practical application was exemplified from conductimetric tritations of HF ¾ HNO3 mixtures used in metalurgical industry to passivate stainless steels. The results were com (mais) pared with those obtained using commercial platinum electrodes. The equivalent volumes obtained were comparable within 3% experimental error. Its application depends on the nature of electrolyte. These results have shown that stainless steel, less expensive than platinum (about three order of magnitude), can substitute platinum electrodes in routine analyses and didactic laboratories.

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Construção artesanal de um eletrodo íon seletivo a chumbo(II): uma alternativa para disciplinas experimentais/ Homemade construction of a lead(II) ion selective electrode: an alternative to experimental subjects

Silva, Jonatas Gomes da; Lehmkuhl, Arilson; Alcanfor, Silvia Keli de Barros
2009-01-01

Resumo em inglês This works proposes a homemade construction of a lead(II) ISE of solid membrane (Ag2S/PbS) to determine Pb2+ ions in potentiometric titrations, using damaged combined glass electrodes. This electrode can be constructed in teaching laboratories, using it as a learning tool related to the theoretical principle of ISE. The analytical curve obtained (y = 27.056x + 337.58; R = 0.996) was linear on the range of 1 x 10-5 to 1 mol L-1 and has presented a very close behavior of th (mais) e Nernstian. The homemade ISE has presented a similar selectivity to the commercial electrodes, showing to be a good alternative to the experimental activities on teaching laboratories.

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Otimização da preparação de eletrodo de pasta de carbono contendo riboflavina imobilizada em suporte inorgânico/ Optimization of the carbon paste electrode preparation containing riboflavin immobilized on an inorganic support

Pereira, Arnaldo César; Kubota, Lauro Tatsuo
2004-10-01

Resumo em inglês The aim of this work was to optimize the preparation of electrodes with riboflavin (RF) immobilized on a silica surface modified with niobium oxide and carbon paste. Electrode preparation was optimized employing a factorial design consisting of two levels and three factors. The electrochemical properties of immobilized RF were investigated by cyclic voltammetry. The factorial analysis was carried out analysing the current intensity (Ipa). It was possible to optimize the e (mais) lectrode to get the best reversibility in the redox process, i. e. the lowest separation between anodic and cathodic peak potentials and a current ratio close to unity. The concentration of supporting electrolyte has a small effect. The proportion has the highest effect and the interaction factor between proportion and mixture has also a significant effect on the current intensity.

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Desenvolvimento de processo de produção de conjuntos eletrodo-membrana-eletrodo para células a combustível baseadas no uso de membrana polimérica condutora de prótons (PEMFC) por impressão a tela/ Development of a sieve printing process for the production of membrane electrode assembly for proton exchange membrane fuel cell

Bonifácio, Rafael Nogueira; Linardi, Marcelo; Cuenca, Ricardo
2011-01-01

Resumo em inglês Proton exchange membrane fuel cell (PEMFC) requires membrane electrode assemblies (MEA) to generate electrical energy from hydrogen and oxygen. In this study a MEA production process by sieve printing and an ink composition were developed to produce catalyst layers of MEAs. The deposition of the exact catalyst content was possible on cathodes and anodes with only one print step. The optimal ink developed shown viscosity of 2.75 Pa s, density 1.27 g cm-3, total solid conte (mais) nt of 33.76 % and tack of 92 U.T. The electrodes prepared in only one printing step showed higher performance than those prepared in several steps.

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Determinação voltamétrica de 4-clorofenol sobre o eletrodo de diamante dopado com boro utilizando a voltametria de onda quadrada/ Electroanalytical determination of 4-chilorophenol by square wave voltammetry on boron-doped diamond electrodes

Pedrosa, Valber de Albuquerque; Codognoto, Lúcia; Avaca, Luis Alberto
2003-12-01

Resumo em inglês The anodic voltammetric behavior of 4-chlorophenol (4-CF) in aqueous solution has been studied on a Boron-doped diamond electrode using square wave voltammetry (SWV). After optimization of the experimental conditions, 4-CF was analyzed in pure and natural waters using a Britton-Robinson buffer with pH = 6.0 as the supporting electrolyte. Oxidation occurs at 0.80 V vs Ag/AgCl in a two-electron process controlled by adsorption of the species. The detection limits obtained w (mais) ere 6.4 µg L-1 in pure water and 21.5 µg L-1 for polluted water taken from a local creek, respectively. The combination of square wave voltammetry and diamond electrodes is an interesting and desirable alternative for analytical determinations.

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Influência de M/C (M = Mo, Cu, Fe e W) incorporado à camada difusora do eletrodo de difusão de gás frente à reação de oxidação de hidrogênio na presença de CO/ The effect of M/C (M = Mo, Cu, Fe and W) in the diffusion layer of gas diffusion electrodes on the hydrogen oxidation reaction in the presence of carbon monoxide

Pereira, Luis Gustavo da Silva; Pereira, Maristela Elisabete; Ticianelli, Edson Antonio
2007-01-01

Resumo em inglês The performance of proton exchange membrane fuel cells (PEMFC) with Pt-based anodes is drastically lowered when CO-containing hydrogen is used to feed the system, because of the strong adsorption of CO on platinum. In the present work the effects of the presence of a conversion layer of CO to CO2 composed by several M/C materials (where M = Mo, Cu, Fe and W) in gas diffusion anodes formed by Pt catalysts were investigated. The diffusion layers formed by Mo/C e W/C show go (mais) od CO-tolerance, and this was attributed to the CO removal by parallel occurrence of the water-gas shift reaction and the so-called bifunctional mechanism.

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Determinação voltamétrica de Cd e Pb usando eletrodo modificado com polianilina sulfonada/ Voltammetric determination of Cd and Pb using sulfonated polyaniline modified electrode

Fungaro, D. A.
2004-01-01

Resumo em português A co-polimerização eletroquímica de misturas de anilina e ácido 3-aminobenzenosulfônico foi realizada por voltametria cíclica em solução de ácido sulfúrico.O grau de polimerização aumentou com o crescimento da acidez e da concentração de anilina em solução. Os eletrodos cobertos com filme de mercúrio e polianilina sulfonada foram avaliados para a análise de metais traço por voltametria de redissolução anódica. Os limites de detecção para o chumbo e (mais) cádmio foram 6,96 e 15,3 nmol L-1, respectivamente. O eletrodo modificado foi usado para determinar os metais em amostras ambientais reais. Resumo em inglês The electrochemical copolymerization of mixtures of aniline and 3-aminobenzenesulfonic acid monomers has been carried out by cyclic potencial sweep in sulfuric acid solution. The degree of polymerization increased with increasing acidity and aniline concentration in solution. Sulfonated polyaniline - mercury film coated electrodes have been evaluated for the analysis of trace metals by anodic stripping voltammetry. The detection limits for lead and cadmium were 6.96 and 1 (mais) 5.3 nmol L-1, respectively. The modified electrode was used to determine metals in real environmental samples.

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Estudo do comportamento eletroquímico de substâncias complexantes utilizando eletrodo de cobre/ Study of electrochemical behavior of complexing compounds using copper electrode

Coutinho, Cláudia F. B.; Coutinho, Lincoln F. M.; Mazo, Luiz H.
2009-01-01

Resumo em inglês Copper electrode can be used for determination of complexing compounds through complexation reactions between Cu(II) and the analites. In this work some studies with three compounds were performed: glycine (precursor of glyphosate synthesis), herbicide glyphosate and aminomethylphosphonic acid (main metabolite of glyphosate). These compounds are complexing agents for Cu electrodes. Through simple experiments (cyclic voltammetry and corrosion studies) the applicability of (mais) the copper electrode as electrochemical sensor for complexing compounds in flow systems was presented.

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Telemetria de resposta neural intra-operatória em usuários de implante coclear/ Neural response telemetry measures in patients implanted with Nucleus 24®

Guedes, Mariana Cardoso; Brito Neto, Rubens V.; Goffi Gomez, Maria Valéria S.; Sant'Anna, Sandra B. Giorgi; Peralta, Cristina G. Ornelas; Castilho, Arthur Menino; Bento, Ricardo Ferreira
2005-10-01

Resumo em português A possibilidade de realizar o implante coclear em crianças pequenas torna necessário o uso de medidas objetivas para auxiliar a programação do processador de fala. Telemetria é a propriedade que permite, no Nucleus 24®, a obtenção do potencial de ação composto evocado do VIII par (EAP) utilizando o implante como instrumento de estimulação e gravação para o estudo das propriedades neurais remanescentes. OBJETIVO: Descrever a utilização do sistema de telemet (mais) ria para a gravação do EAP, caracterizando as respostas obtidas e a sua prevalência na condição intraoperatória. FORMA DE ESTUDO: clínico com coorte transversal. MATERIAL E MÉTODO: Medidas das impedâncias dos eletrodos e do EAP em um grupo de 17 indivíduos usuários do implante Nucleus 24® durante a cirurgia. Análise das respostas de acordo com a etiologia, o tempo de duração da surdez e a posição dos eletrodos dentro da cóclea. RESULTADOS: Maior prevalência nos eletrodos apicais e limiares mais elevados nos casos de meningite e otosclerose. CONCLUSÃO: A telemetria é eficiente para a verificação da integridade dos eletrodos na condição intraoperatória e para a gravação do EAP, apresentando alta prevalência na população estudada. Resumo em inglês Cochlear implantation has been recommended for children under 24 months of age. The use of objective measures is needed to help speech processor programming. The electrically evoked compound potential (EAP), which can be assessed by neural response telemetry (NRT), is one of those objective measures. AIM: to determine how often the EAP can be recorded by NRT system during surgery and to describe the responses. STUDY DESIGN: clinical with transversal cohort. MATERIAL AND M (mais) ETHOD: the impedances and NRT were measured in a group of 17 Nucleus 24 ® implant users. The responses were analyzed and compared to the etiology, hearing loss duration and electrode array position. RESULTS: The EAP was easily recorded in the apical electrodes and, in otosclerosis and meningitis cases the EAP threshold was higher than in the other etiology cases. CONCLUSIONS: The NRT can be found in 82% of the cases during surgery. The responses obtained may vary according to etiology and the position of electrodes along the cochlea.

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Eletrencefalograma quatitativo em crianças com epilepsia benigna da infância com pontas centrotemporais: análise de freqüências/ Quantitative electroencephalography in children with bening childhood epilepsy with centrotemporal spikes: analysis of band power

Fonseca, Lineu C.; Tedrus, Glória M.A.S.; Chiodi, Marcelo G.; Cerqueira, Jaciara Näf; Duran, Marcos Henrique Coelho
2004-06-01

Resumo em português Abordaram-se parâmetros quantitativos do eletrencefalograma em crianças com epilepsia benigna da infância com pontas centrotemporais (EBICT). Foram estudadas 27 crianças com diagnósticos de EBICT. Foi realizado o eletrecenfalograma durante vigília, em repouso, e selecionadas cerca de 20 janelas com 2,56 s. Foram calculados os valores de potência absoluta e relativa nas faixas delta, teta, alfa e beta. Os resultados foram comparados aos de 27 crianças sadias paread (mais) as quanto a idade e escolaridade materna. A potência absoluta foi significativamente maior no grupo EBICT nas nas bandas delta e teta para a quase totalidade dos eletrodos e para alguns eletrodos nas faixas alfa e beta. A potência relativa teta foi também maior no grupo EBICT na maioria dos eletrodos. Esses achados sugerem que na EBICT, embora a atividade epileptiforme seja focal. Ocorrem modificações funcionais difusas que incluem alterações do perfil da distribuição das faixas de frequência, com maior potência relativa teta. Resumo em inglês Quantitative EEG aspects are studied in children with benign childhood epilepsy with centrotempral spikes (BCET). A total of 27 children, from 7 to 11 years neurologically and intellectually normal was studied and compared to a control group of normal children. They were submitted to anamnesis, neurological examination, Raven test, digital electroencephalogram and quantitative eletroencephalogram analysis. There was a higher delta, theta, alpha and beta absolute power in (mais) most of the electrodes and of alpha and beta for some electrodes in the BCET group. Relative theta power was also higher for the BECT group in most of the electrodes. These findings suggest that in BECT there are diffuse differences form age-matched normal children including a difference in relative spectrum of electrical cerebral activity and that this may be related to a functional immaturity.

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Avaliação longitudinal do ECAP registrado em crianças usuárias de implante coclear/ Longitudinal study of the ecap measured in children with cochlear implants

Tanamati, Liege Franzini; Bevilacqua, Maria Cecília; Costa, Orozimbo Alves
2009-02-01

Resumo em português Em crianças usuárias de Implante Coclear (IC), o registro do potencial de ação composto do nervo auditivo evocado eletricamente (ECAP) representa uma maneira de avaliar as modificações nas respostas neurais e entre o feixe de eletrodos e o tecido neural ao longo do tempo. OBJETIVO: Estudar o ECAP em crianças ao longo do primeiro ano de uso do IC. MATERIAL E MÉTODO: As características do ECAP foram analisadas em 13 crianças, implantadas com idades inferiores a tr (mais) ês anos de idade. Estudo de série. RESULTADOS: Houve aumento estatisticamente significante na amplitude do pico N1, nos eletrodos basais, entre o segundo e o terceiro retorno. Não foram obtidas diferenças significantes para: a latência do pico N1, o slope, o p-NRT e o período de recuperação entre os retornos. Nos três retornos, a maioria dos sujeitos apresentou tempo de recuperação entre 1000 e 2000µs. CONCLUSÃO: Ao longo do primeiro ano de uso do IC, a estimulação elétrica liberada pelos eletrodos intracocleares não causou alterações significativas às características do ECAP, exceto pelo aumento da amplitude do pico N1. Resumo em inglês In children with cochlear implant (CI), the recording of the electrically evoked compound action potential (ECAP) of the auditory nerve represents an option to assess changes in auditory nerve responses and the interaction between the electrode bundle and the neural tissue over time. AIM: To study ECAP in children during the first year of CI use. MATERIALS AND METHODS: The ECAP characteristics have been analyzed in 13 children implanted younger than three years of age. Se (mais) ries study. RESULTS: During the first year of CI use there was a significant statistical raise in the N1 peak amplitude, in basal electrodes, between the second and third return visits. There were not any significant differences obtained for N1 peak, latency, slope, p-NRT or recovery time, in the return visits. CONCLUSION: During the first year of CI use, the electrical stimulation provided by the intracochlear electrodes did not cause significant changes to ECAP characteristics, except for an increase in N1 peak amplitude.

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Avaliação da limpeza de CDtrodo construídos a partir de CD de ouro gravável/fita adesiva de galvanoplastia/ Evaluation of the CDtrode cleaning constructed from gold recordable CD/galvanoplasty tape

Foguel, M. V.; Uliana, C. V.; Tomaz, P. R. U.; Marques, P. R. B. Oliveira; Yamanaka, H.; Ferreira, A. A. Pupim
2009-01-01

Resumo em português Os eletrodos de ouro são largamente utilizados em estudos eletroquímicos e eletroanalíticos, devido à sua elevada pureza, ampla faixa de potencial de trabalho, bem como a possibilidade de controle e modificação da superfície eletródica. Neste trabalho são descritos procedimentos para construção e limpeza de eletrodos a partir de CDs de ouro graváveis, denominados CDtrodos. Inicialmente, os CDs foram submetidos à ação de HNO3 concentrado para retirada da cam (mais) ada polimérica protetora e exposição da camada metálica, posteriormente, para a construção dos CDtrodos, delimitou-se a área eletródica com fita de galvanoplastia. Diversos métodos para a limpeza da superfície do ouro foram empregados, após ataque do HNO3, tais como, aplicação de potencial fixo em solução de NaCl, ciclagens sucessivas em H2SO4 e aplicação de ultra-som, sendo que os melhores resultados foram obtidos por tratamento com H2SO4. A literatura tem registrado vários trabalhos empregando CDtrodo no entanto são focados na aplicação e pouco se descreve sobre a limpeza do eletrodo; nenhum trabalho foi registrado empregando a fita de galvanoplastia para delimitar a área do eletrodo. A utilização desse tipo alternativo de eletrodo é de suma importância, uma vez que o mesmo apresenta desempenho eletroquímico comparável aos eletrodos comerciais, além de grande versatilidade e baixo custo. Resumo em inglês Gold electrodes are widely used in electrochemistry and electroanalytical chemistry, due to the high purity, broad range of work potential as well as the possibility to control and modify the surface. On this work construction and cleaning of electrodes from gold recordables compact discs (CD-Rs), namely CDtrodes, are described. The CDs was submitted to the action of concentrated HNO3 in order to remove the protection layer and to expose the metallic layer; the electrode (mais) area was delimited by using galvanoplasty tape. The literature has been published many articles on CDtrode focused on the application but not on the cleaning; there is no register on galvanoplasty tape to define electrode area. Several methods for gold surface cleaning after attack of HNO3 were investigated, such as application of fixed potential in NaCl solution, successive scans in H2SO4 and ultrasound application, and best results were obtained in H2SO4 solution. This electrode material is interesting due to the performance comparable to the commercial electrodes, besides great versatility and low cost.

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Potencial evocado auditivo de longa latência-P300 em indivíduos normais: valor do registro simultâneo em Fz e Cz/ P300-long-latency auditory evoked potential in normal hearing subjects: simultaneous recording value in Fz and Cz

Duarte, Josilene Luciene; Alvarenga, Kátia de Freitas; Banhara, Marcos Roberto; Melo, Ana Dolores Passarelli de; Sás, Roberta Moreno; Costa Filho, Orozimbo Alves
2009-04-01

Resumo em português O P300 é um Potencial Evocado Auditivo denominado potencial endógeno por refletir o uso funcional que o indivíduo faz do estímulo auditivo, sendo altamente dependente das habilidades cognitivas, entre elas atenção e discriminação auditiva. É um procedimento de avaliação objetiva, mas que depende da experiência do avaliador em detectar os picos das ondas, sendo importante a utilização de métodos de registro que facilitem a análise da presença de resposta e (mais) a interpretação dos resultados. OBJETIVO: Analisar o Potencial Evocado Auditivo de Longa Latência-P300 obtido com a utilização de dois eletrodos ativos posicionados em Fz e Cz. MATERIAIS E MÉTODOS: Participaram deste estudo 33 indivíduos de ambos os gêneros com idade entre 7 e 34 anos, audição normal e sem fator de risco para problemas mentais. RESULTADOS: Os resultados demonstraram que não houve diferença estatisticamente significante para a latência de N2 e P3 e amplitude do P3 quando analisado o gênero e nem correlação com a idade dos indivíduos. Houve forte correlação destas medidas com o posicionamento dos eletrodos em Fz e Cz. CONCLUSÃO: O posicionamento dos eletrodos ativos em Fz e Cz pode ser considerado um recurso a mais para auxiliar na análise clínica do P300. Resumo em inglês The P300 is and auditory Evoked Potential, called endogenous potential because it reflects the functional use the individual makes of the auditory stimulus, being highly dependent on cognitive skills; among them we list attention and auditory discrimination. It is a procedure of objective evaluation; however, one that depends on the examiner's experience to detect wave peaks, and it is important to use recording methods that facilitate the response presence analysis and r (mais) esult interpretation. AIM: to analyze the P300 Long Latency Auditory Evoked Potential obtained through the use of two active electrodes positioned on Fz and Cz. MATERIALS AND METHODS: 330 individuals from both genders and age ranging between 7 and 34 years participated in this study, they all had normal hearing and did not have any risk factor for mental problems. RESULTS: Results show that there was no statistically significant difference for N2 and P3 latency and P3 amplitude as far as gender is concerned, nor correlation with the individual's age. There was a strong correlation of these measures with Fz and Cz electrode positioning. CONCLUSION: Fz and Cz active electrodes positioning can be considered one more resource to help in the P300 clinical analysis.

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Estudo da obtenção através de síntese eletroquímica de poliaminonaftalenos e poliaminoantracenos/ Preparation of polyaminonaphthalenes and polyaminoanthracenes by electrochemical synthesis

Amado, Franco D. R.; Silveira, Christian C.; Rodrigues Jr., Luiz F.; Ferreira, Carlos A.; Meneguzzi, Alvaro
2008-09-01

Resumo em português Os poliaromáticos são um grupo de polímeros condutores composto por poliaminonaftalenos, poliaminoantracenos, poliaminonaftóis e polinaftoquinonas com a presença de dois ou três anéis aromáticos. Neste trabalho, filmes de poliaminoantraceno (PAA) e 1,5 polidiaminonaftaleno (1,5-PDAN) foram obtidos por eletropolimerização sobre eletrodos de platina, utilizando uma célula de três eletrodos e um único compartimento. Espectroscopia de infravermelho com transforma (mais) da de Fourier (FTIR) e espectroscopia RAMAN foram usadas para investigar a estrutura do PAA e foi determinada que ela é similar àquela encontrada na polianilina (PAni) e nos poliaminonaftalenos. Estudos do comportamento eletroquímico por voltametria cíclica mostraram que tanto o PAA como o 1,5-PDAN apresentam somente um par redox e que o PAA não tem boa estabilidade à ciclagem repetitiva, ao contrário do 1,5-PDAN. Micrografias obtidas por Microscopia Eletrônica de Varredura mostraram filmes compactos e homogêneos, com estrutura globular para ambos os polímeros. Resumo em inglês The polyaromatics are a group of polymers composed by polyaminonaphthalenes, polyaminoanthracenes and polynaphthoquinones that have aromatic systems with two or three rings. In this work, films of polyaminoanthracene (PAA) and 1,5 polydiaminonaphthalene (PDAN-1,5) have been electropolymerized on Pt electrodes in a single compartment cell with three electrodes. Fourier transform infra-red (FTIR) and Raman spectroscopies have been used to confirm that the PAA structure is s (mais) imilar to that of polyaniline (PAni). Electrochemical studies have shown that the PAA and the PDAN-1,5 present only one redox pair. However, the PAA did not show a good electrochemical stability, in contrast to PDAN-1,5. The micrographs showed homogeneous and compact films, with globular structure and for both polymers, although PAA showed cracks produced during drying with cold air flow.

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Estudo da coerência do eletrencefalograma na banda de frequência alfa em indivíduos adultos normais: resultados preliminares em 10 casos/ EEG alpha band coherence analysis in healthy adults: preliminary results

Anghinah, Renato; Caramelli, Paulo; Takahashi, Daniel Yassumasa; Nitrini, Ricardo; Sameshima, Koichi
2005-03-01

Resumo em português A coerência espectral inter-hemisférica do eletrencefalograma da região occipital do escalpo (eletrodos O1 e O2) foi estimada usando a transformada rápida de Fourier. As médias de coerências na banda de freqüência alfa (alfa1 - 8,0 a 10,0 Hz e alfa2 -10,1 a 12,5 Hz) em indivíduos normais com mais de 50 anos foram comparadas com as obtidas em adultos jovens com idade inferior a 50 anos. Nossos resultados mostraram que não há diferença significativa dos níveis de coerência na banda alfa entre indivíduos em faixas etárias mais avançadas comparados aos adultos jovens. Resumo em inglês We studied the occipital inter-hemispheric coherence of Electroencephalogram (electrodes O1-O2) for alpha band (alpha1 - 8,0 to 10,0 Hz and alpha2 - 10,1 to 12,5 Hz) in two groups of healthy individuals (young adults and subjects older than 50 years-old), to assess if there is significant difference between this two age groups. No significant difference in alpha band coherences was found between these two age groups.

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Determinação do limiar de percepção de corrente elétrica em uma amostra de voluntários normais/ Determination of electric current perception threshold in a sample of normal volunteers

Galvão, Maria de Lourdes de Souza; Manzano, Gilberto Mastrocola; Braga, Nadia Iandoli de Oliveira; Nóbrega, João Antonio Maciel
2005-06-01

Resumo em português Determinaram valores de referência para limiares de percepção de corrente elétrica senoidal em indivíduos normais, utilizando-se o instrumento Neurometer®; contrastaram-se os resultados com os fornecidos pelo fabricante; analisaram-se os limiares em diferentes segmentos corporais e avaliou-se o efeito da idade, sexo, grau de escolaridade e reutilização dos eletrodos. Estudou-se uma amostra de 101 voluntários normais (68 mulheres), com idades entre 17 e 87 anos. O (mais) procedimento foi completamente automatizado utilizando o método de límites e o de escolha forçada. Houve diferença significante entre os limiares obtidos no dedo indicador e no hálux nas três freqüências. Não houve diferenças significantes em relação ao sexo e grau de escolaridade; a idade apresentou discreta relação em algumas medidas. A reutilização dos eletrodos por três vezes nos dedos indicadores não comprometeu a confiabilidade, porém no hálux direito a reutilização por mais de duas vezes comprometeu a determinação do limiar para 2000Hz. Os valores obtidos diferiram das referências fornecidas pelo fabricante, nas freqüências 250Hz e 5Hz. Resumo em inglês Reference values using the instrument Neurometer® were determined and compared with those suggested by the manufacturer; the sensory thresholds for the different frequencies in different body segments were determined; the influence of age, level of education, gender and the reutilization of the electrodes in the different sites were also evaluated. Sensory threshold was determined in 101 normal volunteers (68 women), ages ranged from 17 to 87 years old. The procedure was (mais) fully automated with the sensory threshold being determined by the method of limits followed by the forced choice method. Analysis of the results revealed that: there was a significant difference between the values obtained for the index fingers and the halux; no difference was detected between both index fingers; gender and level of instruction had no effect on the results, age had a small influence after stimulation with 2000Hz and 250Hz; three reutilizations of the electrodes did not affect the results on the index fingers, however at the halux, the third utilization deteriorated the results from the 2000Hz stimulation. Except for the 2000Hz stimulation, significant differences were suggested between the values reported here and those provided by the manufacturer.

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Anastomose do nervo facial de coelhos com cola de fibrina: estudo da velocidade de condução nervosa/ Rabbit facial nerve anastomosis with fibrin glue: nerve conduction velocity evaluation

Sandrini, Francisco Aurelio Lucchesi; Pereira-Júnior, Edwaldo Dourado; Gay-Escoda, Cosme
2007-04-01

Resumo em português OBJETIVO: Este estudo tem o objetivo de avaliar através da velocidade de condução nervosa com eletrodos de superfície a utilização da cola de fibrina na anastomose nervosa. MÉTODOS: Neste experimento, foram avaliadas as diferenças entre as velocidades de condução nervosa pré e pós-operatória do nervo facial esquerdo de 12 coelhos. Foi verificada a existência de correlação entre a velocidade de condução nervosa e o número de axônios regenerados no pós- (mais) operatório. Os nervos transeccionados foram unidos com cola de fibrina. O potencial de ação motora foi obtido com o uso de eletrodos de superfície. O eletrodo de estimulação foi colocado imediatamente à frente do pavilhão auditivo (tronco do nervo facial) e o eletrodo de gravação foi colocado no músculo quadrado do lábio inferior. RESULTADOS: A média normal da velocidade de condução nervosa foi de 36,53 m/seg. Ao final do período, a velocidade de condução nervosa atingiu um valor de aproximadamente 81% do valor normal. Não foi observada correlação significativa entre a velocidade de condução nervosa pós-operatória e o número de axônios regenerados (p=0,146). CONCLUSÃO: A anastomose com cola de fibrina pode ser utilizada para anastomose nervosa no modelo animal e nervo estudados. Resumo em inglês AIM: The aim of this study was to evaluate the use of fibrin glue on nerve anastomosis, and study conduction velocity obtained by surface electrodes. METHODS: In this experimental model we evaluated nerve conduction velocity differences in the preoperative and postoperative periods, for the left facial nerve of 12 rabbits. Then, we evaluated whether there were correlations between conduction velocity and the number of postoperative regenerated axons. The sectioned nerves (mais) were anastomosed with fibrin glue. The muscle action potentials were obtained from surface electrodes. The stimulation electrode was placed immediately before the ear pinna (facial nerve trunk) and the recording surface electrode was placed on the quadratus labii inferioris muscle. RESULTS: The facial nerve normal conduction velocity mean value was of 36.53 m/sec. On the postoperative period, the mean conduction velocity was approximately 81% of the normal mean value. A significant correlation was not observed between the postoperative conduction velocity and the number of regenerated axons (p=0.146). CONCLUSION: The fibrin glue can be used on nerve anastomosis in this animal model and nerve.

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Mapeamento epicárdico da taquicardia ventricular sustentada em cardiopatias não isquêmicas/ Epicardial mapping of sustained ventricular tachycardia in nonischemic heart disease

Silva, Geórgia Guedes da; Veloso, Henrique Horta; Leite, Luiz Roberto; Farias, Roberto Lima; Paola, Angelo Amato Vincenzo de
2011-01-01

Resumo em português FUNDAMENTO: A complexidade dos circuitos reentrantes relacionados às taquicardias ventriculares diminui os índices de sucesso dos procedimentos de ablação por radiofrequência. OBJETIVO: Avaliar se o mapeamento epicárdico com múltiplos eletrodos realizado simultaneamente com o mapeamento endocárdico auxilia na ablação da taquicardia ventricular (TV) sustentada em pacientes com cardiopatia não isquêmica. MÉTODOS: Vinte e seis pacientes com TV sustentada recorre (mais) nte, sendo 22 (84,6%) com cardiopatia chagásica crônica, dois (7,7%) com cardiomiopatia dilatada idiopática e dois (7,7%) portadores de displasia arritmogênica do ventrículo direito, foram submetidos a mapeamento epicárdico com dois ou três microcateteres, com 8 eletrodos cada, simultaneamente ao mapeamento endocárdico convencional. Utilizou-se cateter com ponta de 4 mm para ablação com radiofrequência (RF) realizada durante a TV induzida. RESULTADOS: Das 33 TVs induzidas, 25 foram mapeadas e 20 tiveram sua origem definida. Onze com origem epicárdica e 9 endocárdica. A estimulação ventricular programada não induziu TV sustentada em 11 (42,0%) dos 26 pacientes após a ablação. Eventos como recorrência da TV e morte ocorreram em 10,0% dos pacientes submetidos à ablação com sucesso, e em 59,0% dos insucessos, em seguimento ambulatorial médio de 357 ± 208 dias. CONCLUSÃO: Circuitos subepicárdicos são frequentes em pacientes com cardiopatia não isquêmica. O mapeamento epicárdico com múltiplos cateteres realizado simultaneamente com o mapeamento endocárdico contribui para a identificação destes circuitos em um mesmo procedimento. Resumo em inglês BACKGROUND: The complexity of reentrant circuits related to ventricular tachycardias decreases the success rate of radiofrequency ablation procedures. OBJECTIVE: To evaluate whether the epicardial mapping with multiple electrodes carried out simultaneously with the endocardial mapping helps in ablation procedures of sustained ventricular tachycardia (VT) in patients with nonischemic heart disease. METHODS: Twenty-six patients with recurrent sustained VT, of which 22 (84.6 (mais) %) presenting chronic chagasic cardiomyopathy, 2 (7.7%) with idiopathic dilated cardiomyopathy and 2 with right ventricular arrhythmogenic dysplasia (RVAD), were submitted to epicardial mapping with two or three microcatheters, with 8 electrodes each, simultaneously to the conventional endocardial mapping. A catheter with a 4-mm tip was used for the ablation by radiofrequency (RF) carried out during the induced VT. RESULTS: Of the 33 induced VT, 25 were mapped and 20 had their origin defined. Eleven had epicardial and 9 had endocardial origin. The programmed ventricular stimulation did not induce sustained VT in 11 (42.0%) of the 26 patients after the ablation. Events such as VT recurrence and death occurred in 10.0% of the patients submitted to successful ablation and in 59.0% of the unsuccessful cases, during a mean ambulatory follow-up of 357 ± 208 days. CONCLUSION: Subepicardial circuits are frequent in patients with nonischemic heart disease. The epicardial mapping with multiple catheters carried out simultaneously with the endocardial mapping contributes to the identification of these circuits in a same procedure.

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Maturação do sistema auditivo central em crianças ouvintes normais/ Central hearing system maturation in normally hearing children

Ventura, Luzia Maria Pozzobom; Costa Filho, Orozimbo Alves; Alvarenga, Kátia de Freitas
2009-06-01

Resumo em português TEMA: os potenciais evocados auditivos de longa latência (PEALLs) fornecem dados objetivos sobre a funcionalidade das estruturas centrais auditivas. OBJETIVO: caracterizar a maturação do sistema auditivo central em crianças com audição normal. MÉTODO: registro dos PEALLs de 56 indivíduos ouvintes normais, de ambos os sexos, sendo 46 crianças e 10 adultos. Com a disponibilidade de dois canais de registro, um foi destinado à captação dos PEALLs e outro, ao regis (mais) tro do artefato gerado pelo movimento ocular, visando ao seu controle. Os potenciais foram registrados com os indivíduos em estado de alerta, por meio de eletrodos posicionados em Cz (ativo) e A2 (referência) e os movimentos oculares, por eletrodos em posição supra e infra-orbital esquerda; o eletrodo terra foi colocado em A1. Foram analisados a morfologia e os valores de latência e amplitude dos componentes P1, N1 e P2, de acordo com a idade. Para verificar a reprodutibilidade dos registros, foi realizado um estudo duplo-cego com a introdução da análise de outra avaliadora. RESULTADOS: o estudo duplo-cego não mostrou diferenças estatisticamente significantes entre as análises. Com o avanço da idade, houve melhora na morfologia e diminuição nos valores de latência dos componentes P1, N1 e P2. O componente P1 teve sua amplitude diminuída e não foi observada variação nos valores de amplitude dos componentes N1 e P2. Não foi observada diferença estatisticamente significante entre os sexos. CONCLUSÃO: o processo maturacional do sistema auditivo central acontece de maneira gradativa, sendo as maiores modificações observadas ao se comparar crianças e adultos. Resumo em inglês BACKGROUND: the long latency auditory evoked potentials (LLAEP) provide objective data about the function of hearing cortical structures. AIM: to characterize the maturation of the central hearing system in normally hearing children. METHOD: record of LLAEP of fifty-six subjects with hearing tresholds within normal limits, of both genders, being 46 children and 10 adults. With the availability of two recording channels, one was directed to register the LLAEP and the other (mais) , to record the artifact generated by ocular movement, aiming at its control. The potentials were recorded with subjects in an alert state, through electrodes positioned in Cz (active) and A2 (reference), and the ocular movements, through electrodes in the left supra and infra-orbital positions; the ground electrode was placed in A1. The morphology and the values of latency and of amplitude for components P1, N1 and P2, according to age, were analyzed. In order to verify the reproducibility of the recorded potentials, a double blind study was carried out, by introducing the analysis of another evaluator. RESULTS: the double blind study did not present statistically significant differences between the analyses. With the increase in age there was an improvement in the morphology and a decrease in the latency values of components P1, N1 and P2. Also there was a decrease in the amplitude of component P1 and no variation in the amplitude values was observed for components N1 and P2. No statistically significant difference was observed between genders. CONCLUSION: the maturational process of the central hearing system occurs gradually, being the greatest changes observed when comparing children and adults.

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Efeitos da estimulação com corrente elétrica contínua pulsátil sobre as propriedades eletrofisiológicas atriais: estudo experimental da fibrilação atrial em cães/ Effects of stimulation with pulsatile continuous electrical current on atrial electrophysiological properties: experimental study of atrial fibrillation in dogs

Moreira, Dalmo Antonio Ribeiro; Sousa, Amanda Guerra Moraes Rego; Valente, Paulo; Leone, Elizabete Hosri
2004-12-01

Resumo em português OBJETIVO: Avaliar se a estimulação atrial com corrente elétrica contínua pulsátil induz fibrilação atrial e os seus efeitos sobre as propriedades eletrofisiológicas atriais e as alterações histológicas atriais. MÉTODOS: Foram submetidos à toracotomia lateral direita 22 cães e implantados eletrodos de marcapasso no sulcus terminalis (ST), apêndice atrial direito (ADb) e na região póstero-inferior do átrio esquerdo (AE); um par de eletrodos foi suturado na (mais) auriculeta direita para estimulação com bateria alcalina de 9 Volts conectada a uma sistema (LM 555) que transforma a energia contínua linear da bateria em corrente contínua pulsátil, durante 60 min. A biópsia epicárdica atrial foi realizada antes e após a estimulação atrial. RESULTADOS: Não foram observadas diferenças nas durações dos períodos refratários efetivos atriais. Os tempos de condução intra-atrial, interatrial, bem como dos extra-estímulos atriais também prolongaram-se. A duração dos eletrogramas atriais prolongou-se durante ritmo sinusal e estimulação atrial programada; em 68% dos cães a fibrilação atrial foi induzida e sustentou-se. Foram observados edema intersticial e bandas de contração celular no subepicárdio à microscopia óptica, e intensa desorganização miofibrilar e aumento do tamanho das mitocôndrias à microscopia eletrônica. CONCLUSÃO: Esta técnica de estimulação atrial induz fibrilação atrial e provoca modificações atriais que aumentam sua vulnerabilidade para o surgimento de fibrilação atrial. Resumo em inglês OBJECTIVE: To assess whether atrial stimulation with pulsatile continuous electrical current induces atrial fibrillation and to evaluate its effects on atrial electrophysiological properties as well as the atrial histological alterations. METHODS: Twenty-two dogs underwent right lateral thoracotomy and implantation of pacemaker electrodes in the sulcus terminalis (ST), in the right atrial appendix (RAb), and in the posteroinferior region of the left atrium (LA). A pair of (mais) electrodes was sutured to the right atrial appendix for stimulation with a 9-volt alkaline battery connected to a system (LM 555) that transforms the linear continuous energy of the battery into a pulsatile continuous current for 60 minutes. Atrial epicardial biopsy was performed before and after atrial stimulation. RESULTS: No differences were observed in the durations of the effective atrial refractory periods. The times of intra-atrial and interatrial conduction, as well as that of atrial extrastimuli, were prolonged. The duration of atrial electrograms was prolonged during sinus rhythm and programmed atrial stimulation; in 68% of the dogs, atrial fibrillation was induced and was sustained. Interstitial edema and bands of cellular contraction were observed in the subepicardium on optical microscopy, as were intense myofibrillar disorganization and an increase in the size of the mitochondria on electron microscopy. CONCLUSION: That technique of atrial stimulation induces atrial fibrillation and causes atrial changes that increase atrial vulnerability to the appearance of atrial fibrillation.

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Influência da distância intereletrodos e da cadência de movimento no domínio da frequência do sinal de EMG de superfície/ Influence of the inter-electrodes distance and cadence of movement in the surface EMG signal frequency domain

Tank, Flávia Fernandes; Silva, Gustavo Telles da; Oliveira, Carlos Gomes de; Garcia, Marco Antonio Cavalcanti
2009-08-01

Resumo em português A eletromiografia de superfície (sEMG), apesar de amplamente utilizada em investigações biomecânicas, ainda apresenta inúmeros questionamentos sobre a influência das distâncias intereletrodos (DIE) na morfologia do sinal, principalmente em contrações isotônicas. Logo, muitos dos trabalhos desenvolvidos ainda se limitam ao âmbito do laboratório de pesquisa, onde é possível estabelecer maior controle nos protocolos de registro e análise, o que não é comumen (mais) te observado na prática clínico-desportiva. Dessa forma, o objetivo do estudo foi examinar os efeitos de dois protocolos de colocação de eletrodos e a realização de contrações isotônicas no domínio da frequência do sinal de sEMG. Quinze sujeitos do sexo masculino (idade: 22,8 ± 3,5 anos), todos destros, realizaram contrações dinâmicas do bíceps braquial direito com carga estimada em 20% da contração voluntária máxima em três diferentes cadências (30, 45, 60bpm). Os sinais de sEMG foram registrados por meio de dois canais, cujas DIEs foram de 4,2 e 13cm, respectivamente. A avaliação dos sinais de sEMG foi baseada na frequência mediana do espectro de potencial do sinal, calculado via transformada rápida de Fourier. A DIE e a cadência foram definidas como fatores (ANOVA two-way; α = 0,05). Não foram observadas diferenças estatísticas e qualquer interação entre ambos os fatores nas três cadências (P > 0,05). Sugere-se que, independentemente da distância utilizada entre os eletrodos, uma investigação no domínio da frequência do sinal de sEMG em tarefas dinâmicas seja evitada, mesmo a partir de DIEs reduzidas, como é sugerido pela literatura, dado que variações no torque e no comprimento muscular podem corromper o sinal e, portanto, sua interpretação. Resumo em inglês Surface electromyography (SEMG), despite being widely used in biomechanical investigations, still presents massive questioning about the influence of the distance of the inter-electrodes (DIE) in the signal morphology, especially in isotonic contractions. Thus, much of the research developed is still limited to the laboratory, where it is possible to establish better control over the recording and analysis protocols, which is not commonly observed in the clinical-sportive (mais) practice. Therefore, the aim of this study was to examine the effects of two electrodes placement protocols and the performance of isotonic contractions in the SEMG sign frequency domain. Fifteen right-handed male subjects (aged 22.8 ± 3.5 years) performed dynamic contractions of the right brachial biceps with load estimated in 20% of the maximum voluntary contraction in three different cadences (30, 45 and 60 bpm). The SEMG signals were registered by two channels with DIEs of 4.2 and 13 cm, respectively. The SEMG signals assessment was based on the median frequency of the potential spectrum of the signal, calculated via fast Fourier transform. DIE and cadence were defined as factors (two-way ANOVA; α = 0.05). No statistical differences or any interaction between both factors were observed in the three cadences (P> 0.05). Regardless of the distance used between electrodes, an investigation in the SEMG signal frequency domain in dynamic tasks should be avoided, even from reduced DIEs, as suggested in the literature, since variations in the torque and muscular length may disrupt the signal and hence its interpretation.

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Influência da estimulação biatrial temporária externa na prevenção da fibrilação atrial no pós-operatório de revascularização miocárdica sem circulação extracorpórea/ Influence of external temporary biatrial pacing on the prevention of atrial fibrillation after coronary artery bypass without extracorporeal circulation

Silva, Francisco Maia da; Milani, Rodrigo; Précoma, Dalton; Guimarães, Maximiliano; Moutinho, Jose Augusto; Barboza, Laura; Sartori, Alexandre; Brofman, Paulo
2008-02-01

Resumo em português FUNDAMENTO: A fibrilação atrial é a mais comum complicação no pós-operatório de revascularização miocárdica, aumentando a incidência de morbi-mortalidade. OBJETIVO: O propósito deste estudo prospectivo e randomizado foi testar a hipótese de que a estimulação cardíaca temporária biatrial reduz a incidência da fibrilação atrial no pós-operatório de revascularização miocárdica. MÉTODOS: Em uma casuística de 98 pacientes não-consecutivos, submetido (mais) s a revascularização miocárdica sem circulação extracorpórea, foram implantados respectivamente dois eletrodos temporários em átrio direito e em átrio esquerdo e conectados a cada par de saída atrial do marcapasso, além dos eletrodos implantados no ventrículo direito. Foram randomizados dois grupos (controle: 49 pacientes sem a estimulação biatrial; terapêutico: 49 pacientes com a estimulação biatrial). As variáveis de interesse foram: fibrilação atrial (presença ou não), tempo de hospitalização. RESULTADOS: A incidência de fibrilação atrial foi de 36,73% no grupo controle e 14,29% no grupo terapêutico (p=0,0194). O tempo de hospitalização foi de 7,00±2,82 dias nos pacientes sem fibrilação atrial (n=73), e de 9,20±2,87 dias nos pacientes com fibrilação atrial (n=25) (p=0,0001). A idade foi importante preditor da arritmia, variou de 62,34±9,00 anos no grupo sem fibrilação atrial, e de 67,20±7,42 anos no grupo com fibrilação atrial (p=0,0170). CONCLUSÃO: A estimulação temporária biatrial profilática é efetiva na prevenção da fibrilação atrial, quando comparada ao grupo controle. Permanência hospitalar foi maior nos pacientes que apresentaram fibrilação atrial no pós-operatório e a idade foi importante preditor para o desenvolvimento da arritmia. Resumo em inglês BACKGROUND: Atrial fibrillation is the most common complication after myocardial revascularization, and it increases morbidity/mortality. OBJECTIVE: The purpose of this prospective randomized study was to test the hypothesis that temporary biatrial pacing is effective in reducing the incidence of postoperative atrial fibrillation after myocardial revascularization. METHODS: Ninety-eight non-consecutive patients who had undergone off-pump myocardial revascularization recei (mais) ved two temporary electrodes attached to the right and left atria, which were connected to either pair of atrial pacemaker electrodes, in addition to the leads implanted in the right ventricle. Two groups of patients were randomized (control: 49 patients with no biatrial pacing; therapeutic: 49 patients with biatrial pacing). The variables of interest were atrial fibrillation (present or absent) and length of hospital stay. RESULTS: The incidence of atrial fibrillation was 36.73% in the control group and 14.29% in the therapeutic group (p=0.0194). Length of hospital stay was 7.00 ± 2.82 days for patients with no atrial fibrillation (n=73) and 9.20 ± 2.87 days for patients with atrial fibrillation (n=25) (p=0.0001). Age was an important predictor of arrhythmia and ranged between 62.34 ± 9.00 years in the group with no atrial fibrillation and 67.20 ± 7.42 years in the group with atrial fibrillation (p=0.0170). CONCLUSION: Compared to controls, prophylactic temporary biatrial pacing is effective in preventing atrial fibrillation. Hospital stay was longer for patients who developed postoperative atrial fibrillation, and age was an important predictor for the development of arrhythmia.

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Atividades de fala e não-fala em gagueira: estudo preliminar/ Speech and non-speech activities in stuttering: a preliminary study

Andrade, Claudia Regina Furquim de; Sassi, Fernanda Chiarion; Juste, Fabiola Staróbole; Meira, Maria Isis Marinho
2008-03-01

Resumo em português TEMA: gagueira. OBJETIVO: comparar a ativação muscular em indivíduos fluentes e gagos durante tarefas de fala e não-fala. MÉTODO: seis adultos foram divididos em dois grupos: G1 - três indivíduos fluentes; G2 - três indivíduos com gagueira. A atividade muscular (eletromiografia de superfície) foi captada por eletrodos fixados em quatro regiões. Situações testadas: tensão muscular de repouso, tempo de reação da fala; atividade não verbal e atividade verbal (mais) . RESULTADOS: não houve significância estatística entre os grupos para a tensão de repouso; G2 apresentou tempo de reação de fala mais longo; G2 apresentou atividade muscular durante a tarefa não verbal semelhante a observada durante o repouso; a atividade muscular de G1 e G2 durante a tarefa verbal foi similar. CONCLUSÃO: estes resultados sugerem que G2 apresenta um pobre controle temporal para a coordenação dos processos motores. Resumo em inglês BACKGROUND: stuttering. AIM: to compare muscle activation in fluent and stuttering individuals during speech and non-speech tasks. METHOD: six adults divided in two groups: G1 - three fluent individuals; G2 - three stuttering individuals. Muscle activity (surface electromyography) was captured by disposable electrodes fixed in four regions. Testing situations: muscle rest tension, speech reaction time, non-verbal activity, verbal activity. RESULTS: There was no significan (mais) t statistical difference between the groups for the rest tension; G2 present longer speech reaction times; G2 presented muscle activity during the non-verbal task similar to that observed during rest; Muscle activity of G1 and G2 during the verbal task demonstrated to be similar. CONCLUSION: these results suggests that for G2 there is a poor control of timing for the coordination of motor processes.

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Estimulação transcraniana por corrente direta: uma alternativa promissora para o tratamento da depressão maior?/ Transcranial direct current stimulation: a promising alternative for the treatment of major depression?

Berlim, Marcelo T.; Dias Neto, Vitor; Turecki, Gustavo
2009-05-01

Resumo em português OBJETIVO: Nos últimos anos, uma série de novos tratamentos somáticos não-farmacológicos vem sendo desenvolvida para o tratamento da depressão maior e de outros transtornos neuropsiquiátricos. Dentre esses, um dos mais promissores é a estimulação transcraniana por corrente direta. MÉTODO: Para a presente revisão da literatura consultou-se o PubMed entre janeiro de 1985 e fevereiro de 2009. Os artigos deveriam ser publicados em língua inglesa e deveriam abordar (mais) princípios gerais da estimulação transcraniana por corrente direta e sua utilização na depressão maior. DISCUSSÃO: Os protocolos atuais de estimulação transcraniana por corrente direta para o tratamento da depressão maior envolvem a aplicação de dois eletrodos-esponja no escalpo. Em geral, o eletrodo positivo é aplicado na região sobrejacente ao córtex pré-frontal dorsolateral esquerdo (região F3 do Sistema Internacional 10/20 para eletroencefalograma) e o eletrodo negativo é aplicado na região sobrejacente à área supra-orbital direita. Uma corrente elétrica direta de 1-2 mA é então aplicada entre os dois eletrodos por cerca 20 minutos, sendo as sessões de estimulação transcraniana por corrente direta realizadas diariamente durante uma a duas semanas. Estudos iniciais (incluindo um ensaio clínico randomizado, duplo-cego e controlado por placebo) demonstraram que a estimulação transcraniana por corrente direta é efetiva no tratamento da depressão maior não-complicada e que essa técnica, quando utilizada em pacientes deprimidos, está associada com melhoras na performance cognitiva (incluindo na memória de trabalho). Por fim, a estimulação transcraniana por corrente direta é segura e bem tolerada. CONCLUSÃO: Investigações recentes demonstram que a estimulação transcraniana por corrente direta é um importante método neuromodulatório que pode ser útil no tratamento de pacientes deprimidos. Contudo, novos estudos são necessários para esclarecer seu real papel no manejo dos transtornos depressivos. Resumo em inglês OBJECTIVE: In recent years, a number of new somatic (non-pharmacological treatments) have been developed for the treatment of major depression and other neuropsychiatric disorders. Among these, one of the most promising is transcranial direct current stimulation. Method: For the present literature review we searched the PubMed between January 1985 and February 2009. To be included, articles should have been published in English and should address general principles of tra (mais) nscranial direct current stimulation and its use in major depression. DISCUSSION: Current protocols for the treatment of major depression with transcranial direct current stimulation usually involve the application of two sponge-electrodes in the scalp. In general, the positive electrode is applied in the region above the left dorsolateral prefrontal cortex (i.e., F3 region of the 10/20 International System for EEG) and the negative electrode is applied in the region above the right supra-orbital area. A direct electrical current of 1-2 mA is then applied between the electrodes for about 20 minutes, with sessions being daily performed for one to two weeks. Initial studies (including a randomized, double-blind, placebo-controlled clinical trial) showed that transcranial direct current stimulation is effective for the treatment of non-complicated major depression and that this technique, when used in depressed patients, is associated with improvement in cognitive performance (including working memory). Finally, transcranial direct current stimulation is safe and well tolerated. CONCLUSION: Recent studies show that transcranial direct current stimulation is an important neuromodulatory method that may be useful for the treatment of depressed patients. However, further studies are needed to better clarify its precise role in the management of depressive disorders.

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Padronização do eletrorretinograma de campo total em cães/ Full field electrorretinogram standartization in dogs

Safatle, Angélica M.V.; Hvenegaard, Ana Paula; Kahvegian, Márcia; Martins, Teresinha L.; Shimamura, Graziele M.; Fantoni, Denise T.; Barros, Paulo S.M.
2010-09-01

Resumo em português Eletrorretinograma (ERG) é o meio diagnóstico objetivo e não-invasivo para avaliar a função retiniana e detectar precocemente, em várias espécies, lesões nas suas camadas mais externas. As indicações mais comuns para ERG em cães são: avaliação pré-cirúrgica de pacientes com catarata, caracterização de distúrbios que causam cegueira, além de servir como importante modelo para o estudo da distrofia retiniana que acomete o homem. Vários são os fatores q (mais) ue podem alterar o ERG tais como: eletrorretinógrafo, fonte de estimulação luminosa, tipo do eletrodo, tempo de adaptação ao escuro, tamanho pupilar, opacidade de meios e protocolo de sedação ou anestesia; além da espécie, raça e idade. Objetivou-se com este estudo padronizar o ERG para cães submetidos à sedação, seguindo o protocolo da International Society for Clinical Electrophysiology of Vision (ISCEV), utilizando Ganzfeld e eletrodos Burian Allen. Foram realizados 233 eletrorretinogramas em cães, 147 fêmeas e 86 machos, com idades entre um e 14 anos. Dos 233 cães examinados, 100 apresentavam catarata em diferentes estágios de maturação, 72 eram diabéticos e apresentavam catarata madura ou hipermadura, 26 apresentaram eletrorretinograma compatível com degeneração retiniana progressiva, três apresentaram eletrorretinograma compatível com síndrome da degeneração retiniana adquirida subitamente e 32 não apresentaram lesão retiniana capaz de atenuar as respostas do ERG, sendo considerados normais quanto à função retiniana. A sedação foi capaz de produzir boa imobilização do paciente sem rotacionar o bulbo ocular, permitindo adequada estimulação retiniana bilateralmente, com auxílio do Ganzfeld. O sistema eletrodiagnóstico Veris registrou com sucesso e simultaneamente de ambos os olhos, as cinco respostas preconizadas pela ISCEV. Como o ERG de campo total tornou-se exame fundamental na rotina oftalmológica, sua padronização é indispensável quando se objetiva comparar resultados de laboratórios distintos. A confiabilidade e reprodutibilidade deste protocolo foi demonstrada com a obtenção de registros de ótima qualidade utilizando protocolo padrão da ISCEV, eletrorretinógrafo Veris, Ganzfeld e eletrodos Burian Allen nos cães submetidos à sedação. Resumo em inglês Electroretinogram (ERG) is an objective non invasive diagnostic method to evaluate retinal function which permits the early detection of lesions at retinal external layers, even before the appearance of clinical signs. In dogs, ERG is mostly utilized for preoperative evaluation in patients presenting cataracts; characterization of disturbances causing blindness, among the utilization of dogs as animal models in scientific research. Several factors interfere in ERG respons (mais) es, such as the ERG machine, light stimulation, electrode, time spent on dark adaptation, pupil size, means opacity, sedation or anesthetization, species, breed and age. The purpose of this study was to standardize the full field ERG in sedated dogs, according to the International Society for Clinical Electrophysiology of Vision (ISCEV) protocol, using Ganzfeld and bipolar electrodes. Two hundred thirty threes ERGs were performed in 147 female and 86 male with ages from 1 to 14 years old. Among those 233 dogs, 100 presented cataracts in different stages of maturation, 72 were diabetic and presented mature or hypermature cataracts, 26 presented ERG compatible to progressive retinal degeneration, 3 presented ERG compatible to sudden acquired retinal degeneration syndrome; for 32 dogs no abnormal ERG was registered and they were considered as having normal retinal function. Sedation was capable to induce a good immobilization with no bulb rotation, resulting uniform retinal stimulation, using Ganzfeld. Veris system successfully registered all 5 ISCEV responses, simultaneously from both eyes, at the same time. Full field ERG became a fundamental ophthalmic exam, then, its standardization is mandatory to allow comparison between ERGs from different laboratories. The reliability and reproducibility of this protocol has shown very good responses, using ISCEV protocol, Veris system, Ganzfeld and Burian Allen electrodes in sedated dogs.

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Eletrocirurgia: sistemas mono e bipolar em cirurgia videolaparoscópica

Trindade, Manoel Roberto Maciel; Grazziotin, Rodrigo Ughini; Grazziotin, Rossano Ughini
1998-07-01

Resumo em português O conhecimento das leis físicas e dos mecanismos de funcionamento da eletrocirurgia são de grande importância para o cirurgião. Lesões por eletrocirurgia em laparoscopia têm sido observadas, e estão associadas ao uso do eletrodo monopolar, com freqüência de 1 a 2 lesões a cada 1000 procedimentos.Com relação ao desenvolvimento de lesão, existem vários fatores que influenciam: densidade da corrente; o tipo de onda e de coagulação usadas, com suas respectivas (mais) voltagens; as condições de isolamento dos dispositivos; a ocorrência do fenômeno de capacitância; e os riscos oferecidos pelo uso em pacientes com marcapasso. No sistema bipolar, a densidade de corrente encontrada ao redor de seus eletrodos é bem menor, levando a menos lesões e, ainda, elimina vários dos outros mecanismos lesivos, como a placa de retorno e os citados acima. Vários estudos demonstram, em colecistectomias, apendicectomias, polipectomias e outros, que o índice de complicações com o eletrodo bipolar é significativamente menor. Resumo em inglês the knowledge of the physical laws and of the mechanisms of functioning of electrosurgery are of great importance for the surgeon. Lesions caused by electrosurgery in laparoscopic procedures have been observed, and are associated with the use of monopolar electrode, with the frequency of 1 to 2 lesions in every 1000 procedures. Concerning the development of the lesions, several factors are involved; current density, the waveform and the type of coagulation used, with its (mais) respective voltages; the insulation condition of the devices; the occurrence of the phenomenon of capacitance and the risks involved with the use in patients with pacemakers. In bipolar electrosurgery, the current density produced around the electrodes is much lower, causing less tissue damage and, still, eliminating several of the other mechanims of injury, such as the dispersive electrode and those quoted above. Several studies reveal that the incidence of complications with the use of bipolar electrodes in cholecystectomies, appendicectomies, polypectomies and other procedures is significantly lower.

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Implante auditivo de tronco cerebral: técnica cirúrgica e resultados auditivos precoces em pacientes com neurofibromatose tipo 2/ Auditory Brainstem Implant: surgical technique and early audiological results in patients with neurofibromatosis type 2

Bento, Ricardo Ferreira; Brito Neto, Rubens Vuono; Tsuji, Robinson Koji; Gomes, Marcos Queiroz Telas; Goffi-Gomez, Maria Valéria Schmidt
2008-10-01

Resumo em português O implante auditivo de tronco cerebral foi desenvolvido para restaurar alguma audição útil em pacientes que apresentam ausência de nervo coclear bilateralmente. OBJETIVOS: Discutir a indicação, cirurgia e resultados em quatro pacientes submetidos à cirurgia para colocação de implante auditivo de tronco cerebral. CASUÍSTICA E MÉTODOS: Quatro pacientes com diagnóstico de schwannomas vestibulares bilaterais foram submetidos à cirurgia para colocação de Implant (mais) e Auditivo de Tronco Cerebral durante o mesmo ato cirúrgico utilizado para a exérese de um dos tumores. Aspectos clínicos e técnicos e as referências anatômicas da cirurgia e os resultados auditivos foram analisados. RESULTADOS: Em todos os casos foram identificados as referências anatômicas ao forame de Luschka. As complicações cirúrgicas se resumiram à fístula liquórica em dois pacientes. Os eletrodos foram bem posicionados e a sensação auditiva foi suficiente para reconhecimento de sons e auxílio à leitura labial. CONCLUSÃO: Os resultados auditivos de nossos pacientes abrem uma perspectiva importante aos pacientes com surdez profunda bilateral sem integridade anatômica das vias auditivas centrais. Resumo em inglês Auditory Brainstem Implants were developed to partially restore the hearing capabilities of patients without cochlear nerves bilaterally. AIM: this paper aims to discuss the clinical and surgical findings of four ABI patients. MATERIALS AND METHOD: four patients diagnosed with bilateral schwannomas received auditory brainstem implants (ABI) and had one of their tumors resected in the same surgical procedure. Clinical aspects, surgical technique, anatomic landmarks, and ou (mais) tcomes were analyzed. RESULTS: the anatomic landmarks were identified in all four patients in relation to the foramina of Luschka. Two patients had CSF leaks. The electrodes were well positioned and hearing sensation was good enough to allow for sound recognition and assist patients perform lip reading. CONCLUSION: the outcomes observed in our patients were quite encouraging and offer great perspectives for those suffering from deep bilateral deafness and impaired central auditory pathways.

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Estudo do comportamento eletroquímico da enzima peroxidase na presença de peróxido de hidrogênio e ácido 5-aminossalicílico/ Investigation on electrochemical behavior of peroxidase enzyme in the presence of hydrogen peroxide and 5-aminosalicylic acid

Uliana, C. V.; Riccardi, C. S; Yamanaka, H.
2008-01-01

Resumo em português O comportamento eletroquímico da enzima peroxidase (HRP) foi estudado utilizando o peróxido de hidrogênio como substrato enzimático e o ácido 5-aminossalicílico (5-ASA) como mediador de elétrons sobre eletrodo de grafite. Diversos parâmetros foram otimizados, tais como, o potencial aplicado à técnica amperométrica fixado em -0,125V, a solução tampão fosfato-citrato 0,1 mol L-1 pH 5,0 como eletrólito suporte e a proporção entre o 5-ASA e H2O2 em 1:7, entre (mais) outros. Foi observada a catálise da reação de oxidação do peróxido de hidrogênio na presença da enzima HRP e do mediador 5-ASA. O produto dessa oxidação foi reduzido na superfície do eletrodo, evidenciando um significativo aumento na intensidade da corrente catódica. Resumo em inglês The electrochemical behavior of the enzyme peroxidase (HRP) was investigated using the hydrogen peroxide as enzymatic substrate and the 5-aminosalicylic acid (5-ASA) as mediator of electrons on graphite electrodes. Several parameters were optimized, namely, the applied potential to the amperometric technique fixed in -0.125V, the 0.1 mol L-1 phosphate-citrate buffer at pH 5.0 as supporting electrolyte and the proportion between the 5-ASA and H2O2 in 1:7, among others. It (mais) was observed the catalysis of the oxidation reaction of the H2O2 in the presence of the enzyme HRP and 5-ASA. The oxidation product was reduced in the electrode surface, evidencing a significant increase in the intensity of the cathodic current.

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Estimulação cerebral contínua (DBS) talâmica para controle do tremor/ Deep brain stimulation of VIM thalamic nucleus for tremor control

Nasser, José Augusto; Falavigna, Asdrubal; Alaminos, Armando; Bonatelli, Antônio de Pádua; Ferraz, Fernando
2002-06-01

Resumo em português OBJETIVO: Apresentamos resultados da estimulação contínua do núcleo ventral intermédio (VIM) talâmico para o controle do tremor. MÉTODO: Quatro pacientes foram selecionados no período de outubro de 1999 a janeiro de 2001 com tremor incapacitante refratário à farmacoterapia. Dois pacientes apresentavam tremor essencial (TE) bilateral e 2 pacientes tremor de repouso por doença de Parkinson (DP), um à direita e outro à esquerda. Após avaliação sistemática, f (mais) oram submetidos ao implante de eletrodo talâmico, modelo DBS 3387(Medtronic), para estimulação cerebral profunda (ECP) com alta frequência, sendo este bilateral nos casos de TE e unilateral nos casos com tremor por DP. RESULTADOS: Os pacientes tiveram seu seguimente clínico até o presente, com média de 12 meses, sendo observada a eficácia da estimulação do núcleo VIM no controle dos disparos das células do tremor. As complicações temporárias do tipo parestesias, disartrias e discreto aumento do tônus foram revertidas após o ajuste dos parâmetros de estimulação. CONCLUSÃO: Os resultados confirmam os achados da literatura, de que a estimulação talâmica é excelente opção terapêutica no tratamento do tremor, havendo possibilidade de estimulação talâmica bilateral simultânea com segurança. Resumo em inglês PURPOSE: We present our results in 4 patients with tremor, in whom electrodes (uni and bilateral) for Deep Brain Stimulation (DBS) were implanted in the ventral intermediate nucleus (VIM) of the thalamus. METHOD: Four patients with disabling tremor, with drug-resistant spite of optimum therapeutic trials with poor response were referred to do surgery. Two patients had bilateral essential tremor. These patients were implanted with electrodes for DBS 3387 (Medtronic). Two p (mais) atients had unilateral parkinsonian tremor and they received unilateral implantation of model 3387 DBS. RESULTS: All four patients showed relieve of the tremor symptoms with significant tremor control seen at the scores. There were no definite adverse events after the electrodes implants for DBS; adverse events were transient and promptly reversed after the adjustment of the parameters. CONCLUSIONS: The results the authors found in this study indicate that VIM-stimulation is effective for tremor control either parkinsonian or essential tremor. The results correlate with the data in the literature.

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Voltametria de onda quadrada. Segunda parte: aplicações/ Square wave voltammetry. Second part: applications

Souza, Djenaine de; Codognoto, Lúcia; Malagutti, Andréa R.; Toledo, Renata A.; Pedrosa, Valber A.; Oliveira, Robson T. S.; Mazo, Luiz H.; Avaca, Luis A.; Machado, Sergio A. S.
2004-10-01

Resumo em inglês The aim of this work is to discuss some selected applications of square wave voltammetry published in the last five years. The applications focused here cover several electroanalytical fields such as: determination of pesticides; molecules with biological activity; metals and other environmental pollutants. Special attention is given to the work developed in the Grupo de Materiais Eletroquímicos e Métodos Eletroanalíticos - IQSC - USP concerning the utilization of squa (mais) re wave voltammetry, with different kinds of electrodes, for the determination of pesticides in natural waters and active principles in pharmaceutical formulations. The new methodology is simple, fast and sensitive when compared with the traditional ones such as chromatography and spectrophotometry. The satisfactory results obtained provide alternative procedures for the quality control of drugs and the monitoring of pesticides in natural environments.

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Utilização de técnicas eletroanalíticas na determinação de pesticidas em alimentos/ Electroanalytical techniques for the determination of pesticides in foods

Galli, Andressa; De Souza, Djenaine; Garbellini, Gustavo S.; Coutinho, Cláudia F. B.; Mazo, Luiz H.; Avaca, Luis A.; Machado, Sergio A. S.
2006-02-01

Resumo em inglês The aim of this work is to discuss selected applications of electroanalytical techniques for the detection of pesticides in foods and beverages, published in the last ten years. The applications involved different working electrodes for the electroanalytical determination of pesticides, namely amperometric biosensors, cholinesterase-based biosensors, polymer-modified electrodes, ultramicroelectrodes and hanging mercury drop electrodes. They were used for several voltammet (mais) ric and amperometric techniques in different analytical procedures for the detection and quantification of different classes of pesticides in different food matrices.

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Uso de espectrometria de massas em medidas eletroquímicas - a técnica de DEMS/ The use of mass spectrometry in electrochemical measurements - the DEMS technique

Souza, José Pio I. de; Queiroz, Salete Linhares; Nart, Francisco Carlos
2000-06-01

Resumo em inglês The combination of cyclic voltammetry and on line mass spectrometry, called differential electrochemical mass spectrometry (DEMS), is already a well established method for on line identification and quantitative detection of the products and intermediates of electrochemical reactions. This article aims to show the principles of the method and how this technique have been used to study electrochemical problems such the electrocatalytic oxidation of organic molecules, as methanol and ethanol, at noble metal electrodes.

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Tratamento de efluente da indústria de processamento de coco utilizando eletroflotação/ Brazilian industrial coconut wastewater treatment by electroflotation

Crespilho, Frank Nelson; Santana, Claudemir Gomes; Rezende, Maria Olímpia Oliveira
2004-06-01

Resumo em inglês Electroflotation (EF) with aluminum electrodes was applied in the treatment of Brazilian industrial coconut wastewater. The results show that EF with polarity inversion is a very good treatment when compared to others. The removal of pollutants in the wastewater after EF with polarity inversion was 96.3% of oils and grease, 99% of color and 66% of total organic carbon. Also, metal concentrations, turbidity and total solids were reduced.

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Síntese de nanotubos de carbono de parede simples por sublimação de grafite em atmosfera de hélio/ Synthesis of single-wall nanotubes by pyrolysis of graphite in helium atmosphere

Romero, José Gino Venegas; Luengo, Carlos Alberto; Huber, John G; Rosolen, José Maurício
2002-02-01

Resumo em inglês Macroscopic samples of fullerene nanostructures are obtained in a modified arc furnace using the electric arc method with a Helium atmosphere at low pressures. High purity graphite rods are used as electrodes but, when drilled and the orifices filled with powders of transition metals (Fe, Co, Ni) acting as catalysts, the resulting particles are carbon nanostructures of the fullerene family, known as Single Wall Nanotubes (SWNTs). They have typical diameters of 1.4 nm, len (mais) gths up to tenths of microns and they are arranged together in bundles containing several SWNTs. Those samples are observed and analyzed using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques.

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Sistema com atmosfera controlada para a caracterização de sensores a gases/ Controlled atmosphere system for gas sensors characterization

Andrade, Ricardo L. T.; Lindino, Cleber A.; Bulhões, Luis Otavio de Sousa
1998-06-01

Resumo em inglês This paper describes a sample holder for the electrical measurement of oxides or conducting polymers in the form of pellets or films which are used as gas sensors. The system makes it possible to control the sample temperature, the gas pressure and composition. The temperature in the sample can be changed from 25ºC to 450ºC, and the gas pressure in the chamber is controlled between 5 ¥ 10-4 and 1000 mbar. The performance of the system in resistance measurements of doped tin oxide pellets and polyaniline films deposited on platinum electrodes for methane is analyzed.

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Sensores eletroquímicos: considerações sobre mecanismos de funcionamento e aplicações no monitoramento de espécies químicas em ambientes microscópicos/ Electrochemical sensors: fundamentals and applications in microenvironments

Lowinsohn, Denise; Bertotti, Mauro
2006-12-01

Resumo em inglês Electrochemical sensors have attracted considerable attention in recent years because they provide data about the chemical state of our surroundings and the dynamics of the chemical transformations in the form a spatially resolved image. Particular interest has been directed to measurements in restricted-volume samples as new technologies enable the fabrication of miniaturized versions of sensors with reproducible characteristics. Taking these aspects into consideration, (mais) this review focuses on the use of electrodes of micrometer dimensions to acquire chemical information in microdomains in which concentrations may not be spatially homogeneous. This is possible because microelectrodes allow fast-response measurements with micrometer resolution to be performed. On the other hand, the use of microelectrodes as amperometric sensors presents an inherent drawback owing to the insufficient specificity toward the substrate of interest. Hence, some comments on strategies to enhance the selectivity of amperometric sensors are also made. Finally, recent applications of structurally microscopic electrodes as in vivo sensors are shown, as well as a prospect of the future trend in this field.

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Projeto de aterramento para sistema monofilar com retorno pelo terra/ Grounding project for single wire earth return system

Bertolo, Humberto C; Oliveira Filho, Delly; Pizziolo, Tarcísio A; Rodrigues, Denilson E; Monteiro, Paulo M. B; Xavier, Gustavo A
2011-02-01

Resumo em português Este trabalho apresenta o projeto de aterramento elétrico para Sistema Monofilar com Retorno pela Terra (MRT), em solicitações de baixas frequências, utilizando-se o método das imagens e considerando a simplificação do método dos potenciais constantes. Simulou-se o comportamento de três diferentes configurações de aterramento: hastes em triângulo, em quadrado vazio e para nove hastes, formando uma malha com quatro quadrados. A partir da simulação obtiveram-s (mais) e o valor da resistência de aterramento para cada configuração e os potenciais gerados na superfície do solo. Com base nesses resultados foi possível comparar os valores tabelados para resistências mínimas, em função da potência do transformador, aplicados para diferentes concessionárias de energia que utilizam o Sistema MRT, com os valores calculados que mantêm os potenciais no solo em níveis seguros para seres humanos e animais. Os resultados mostraram que é possível utilizar aterramentos mais simples e mais baratos, pois os gradientes de tensões no solo se mantiveram em níveis seguros. Resumo em inglês This work presents a grounding project for a Single Wire Earth Return (SWER) system in low frequency applications, through the use of the image method, a simplification of the constant potential method. The responses of three different grounding configurations were simulated: electrodes in triangular format, electrodes placed in the corners of a square and nine electrodes placed in the corners of a grid with four squares. With the mentioned simulation it was possible to c (mais) alculate the ground resistance and the surface voltage of each configuration. Based on these results, it was possible to compare the values for minimal resistance, depending on the power of the transformer, applied to various power utilities that use the SWER system with the values that hold the potential in the soil at safe levels for human beings and animals. Results showed that it is possible to use simpler and cheaper grounding configurations due to the fact that the surface voltages were maintained at safe levels.

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71

Produção de Biobaterias a partir de Membranas obtidas pela Técnica de Electrofiação

Baptista, A.C.; Borges, J.P.; Ferreira, I.
2010-06-01

Resumo em português O presente trabalho visa a produção de biobaterias a partir de membranas obtidas pela técnica de electrofiação. Com este trabalho pretendeu-se desenvolver um dispositivo electroquímico (biobateria) capaz de gerar energia eléctrica a partir de biofluidos, como a transpiração e o sangue, e com capacidade de satisfazer as necessidades de dispositivos electrónicos de baixo consumo. Para o desenvolvimento das biobaterias, começou-se por produzir as membranas de acet (mais) ato de celulose por electrofiação. Estas membranas são utilizadas como suporte físico (substrato) e separador, sendo os eléctrodos depositados sob a forma de filme fino, em ambas as faces da membrana, formando o dispositivo electroquímico. O comportamento electroquímico da membrana foi analisado por voltametria cíclica, pretendendo-se averiguar a existência de possíveis reacções electroquímicas. De um modo geral, verificou-se que a produção de energia depende não só dos materiais que formam o ânodo e o cátodo, como também da espessura da membrana. Com o intuito de demonstrar as potencialidades, para a aplicação em causa, estes dispositivos foram testados sobre a pele suada, apresentado valores de tensão e corrente bastante promissores. Resumo em inglês This research work envisages the production of bio-batteries based on electrospun membranes.The present work aims at the development of an electrochemical device (bio-battery) able to generate electrical power from body fluids, like sweat or blood, to supply small power consumption electronic devices.To the development of these bio-batteries, cellulose acetate membranes were made with a matrix of nanofibers produced by electrospinning. The cellulose acetate membrane works (mais) both as support and as a separator. Thin films were deposited on both surfaces of the membrane to form the electrodes of the electrochemical device.The electrochemical behavior of membranes was analysed by cyclic voltammetry in order to evaluate the electrochemical reactions. The power generated by these devices depends not only on the materials used as electrodes, but also on the membrane thickness. In order to demonstrate the great potential of these electrochemical devices, bio-batteries prototypes were tested in sweated skin, demonstrating promising voltage and current values.

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72

Princípio e utilização da técnica de efeito miragem de concentração/ Principles and use of the mirage effect technique - mirage effect of concentration

Trigueiro, João Paulo Campos; Matencio, Tulio; Moraga, Gastón Alvial; Lopez, Christian
2006-10-01

Resumo em inglês The aim of this work is to present the theoretical and experimental aspects of the mirage effect technique. We are especially interested in the concentration mirage effect, which is a powerful tool in the study of electrochemical reactions that produce ionic movements close to electrodes and to get some fundamental information on mass transport and charge transfer during electrochemical processes. Limitations of this technique are discussed as well as the recent attempts to overcome them.

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73

Pitting Corrosion and Passivation of Zr/HCl 1.0 M Electrodes: The Effect of the Pre-Immersion in Molibdate Solutions

Giannetti, B.F.; Quintino, M.S.M.; Rabóczkay, T.
2003-01-01

Resumo em inglês The aim of this paper is to evaluate the use of molibdate solutions for pre-treatments of zirconiun surfaces. Zirconium electrodes were held immersed in molibdate solutions for predetermined time intervals. With the subsequent determination of the pitting nucleation potential and the analysis of the surface morphology, it was possible to evaluate the effect of the molibdate concentration and of the solution pH on the pitting corrosion processes. Among the most important r (mais) esults, two are worthy of attention: (i) for all pH values, the immersion of zirconium electrodes in molibdate solutions hinders the pitting corrosion process of the metal, shifting the pitting nucleation potential to more positive values, (ii) the more pronounced shifts of the pitting nucleation potential were observed in alkaline solutions with high molibdate concentration and in acid solutions with low molibdate concentration; this effect was attributed to the adsorption of different species formed at different pH values.

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74

Oxidações catalíticas e eletrocatalíticas de substratos orgânicos. O cério como oxidante/ Catalytic and electrocatalytic oxidation of organic substrates. Cerium as oxidant

Carrijo, Rosa Maria C.; Romero, José Ricardo
2000-06-01

Resumo em inglês This paper reviews the catalytic and electrocatalytic oxidation of organic compounds using cerium (IV) salts. Direct and indirect methods and those using modified electrodes are described.

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75

Métodos para fabricação de microeletrodos visando a detecção em microambientes/ Methods for fabrication of microelectrodes towards detection in microenvironments

Paixão, Thiago R. L. C.; Bertotti, Mauro
2009-01-01

Resumo em inglês Analysis at microenvironments, like single cells or in minute volumes (nL), is an area of great interest for analytical and biological sciences. Measurements at these experimental conditions demand analytical tools (microelectrodes) capable of monitoring with rapid response, good resolution and minimal perturbation of the system. The major drawbacks in producing these microscopic electrodes have been largely overcome, principally due to the development of new fabrication (mais) methods. In this review, these procedures are described with emphasis to those devoted to the construction of microelectrodes for application in microenvironments. Examples of our efforts to use these devices as effective electrochemical sensors are also addressed.

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76

Montagem de um sistema para medidas galvanostáticas simultâneas em mais de uma célula/ The constrution of a multi-cell galvanostatic equipament for accelerated stability electrode test

Solymossy, Victor; Pereira, Ernesto Chaves; Terezo, Ailton José
2007-10-01

Resumo em inglês The present work deals with the design and construction of an equipment for muti-cell accelerated stability test measurements (AST) of dimensionally stable anodes (DSA). The equipment was built using only components that were available in the laboratory. Measurements of three electrochemical cells can be performed using the developed software. The acquisition time interval and the cut-off potencial can be set by the user. Experimental data for RuO2 electrodes obtained with the built equipment are in agreement with the literature.

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77

Hidróxido de níquel suportado em carbono: um catalisador de baixo custo para a eletro-oxidação de alcoóis em meio alcalino/ Carbon supported nickel hydroxide: a low cost catalyst for alcohol electro-oxidation in alkaline medium

Silva, Marcelo Rodrigues da; Ângelo, Antonio Carlos Dias; Dall'Antonia, Luiz Henrrique
2010-01-01

Resumo em inglês The present manuscript shows the synthesis of nickel hydroxide supported in carbon (Ni(OH)2/C) as a alternative material for catalytic alcohol oxidation in alkaline medium. The Ni(OH)2/C was synthesized in different percentage using a sonic bath. No current densities variation during successive cyclic voltammetry experiments was observed. The Ni(OH)2/C electrodes exhibit a potent and persistent electrocatalytic activity towards the oxidation of different alcohols. In addi (mais) tion, alcohols electooxidation occurs in less positive potential compared with noble metal catalyst.

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78

Filmes de nanodiamantes para aplicações em sistemas eletroquímicos e tecnologia aeroespacial/ Nanodiamond films for applications in electrochemical systems and aeronautics and space technology

Azevedo, Adriana Faria; Ferreira, Neidenêi Gomes
2006-02-01

Resumo em inglês The goal of this work is to show the use of undoped nanodiamond films as a new material for electrochemical and aerospace applications. Correlation between the applications and physico-chemical features of nano and conventional CVD polycrystalline diamond films are presented. An important and innovative application of these nanodiamonds is organic electrosynthesis, including pharmaceutical and water disinfection products, as well as electroanalytical applications, for exa (mais) mple, development of biosensors for detection of glucose, glutamate and dopamine. In aeronautics and space developments, these nanodiamonds could be used as electrodes in rechargable batteries and in tribological investigations.

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79

Filmes de metal-hexacianoferrato: uma ferramenta em química analítica/ Metal-hexacyanoferrate films: a tool in analytical Chemistry

Mattos, Ivanildo Luiz de; Gorton, Lo
2001-04-01

Resumo em inglês Chemically modified electrodes based on hexacyanometalate films are presented as a tool in analytical chemistry. Use of amperometric sensors and/or biosensors based on the metal-hexacyanoferrate films is a tendency. This article reviews some applications of these films for analytical determination of both inorganic (e.g. As3+, S2O3(2-)) and organic (e.g. cysteine, hydrazine, ascorbic acid, gluthatione, glucose, etc.) compounds.

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80

Filmes de diamante CVD dopado com boro. Parte I . Histórico, produção e caracterização/ Boron-doped CVD diamond films. Part I. History, production and characterization

Barros, Rita de Cássia Mendes de; Ribeiro, Mauro Celso; An-Sumodjo, Paulo Teng; Julião, Murilo Sérgio da Silva; Serrano, Sílvia Helena Pires; Ferreira, Neidenêi Gomes
2005-03-01

Resumo em inglês This review presents a brief account concerning the production, characterization and evolution of the knowledge in the area of diamond and boron-doped diamond films. The most important methods used for the growth of these films, such as chemical vapor deposition and high pressure/high temperature systems, as well as the several kinds of reactors which can be employed are reviewed. However, larger emphasis is given to the CVD method. Morphological, structural and electric (mais) properties of these films, as well as their role in the performance of voltammetric electrodes for electrochemistry and electroanalytical chemistry are also discussed.

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81

Fatores de risco para mortalidade em octogenários submetidos a cirurgia de revascularização miocárdica/ Risk factors for mortality in octogenarians undergoing myocardial revascularization surgery

Guimarães, Isaac Newton; Moraes, Fernando; Segundo, João Paulo; Silva, Igor; Andrade, Tamyris Guimarães; Moraes, Carlos R.
2011-01-01

Resumo em português FUNDAMENTO: Idade maior a 80 anos não é, por si só, o único fator de risco para a mortalidade em revascularização miocárdica. OBJETIVO: Identificar fatores de risco para a mortalidade em pacientes octogenários submetidos a revascularização miocárdica. MÉTODOS: Estudamos 164 pacientes, com idade igual ou maior a 80 anos. As variáveis estudadas foram: sexo, idade (em anos), fração de ejeção do ventrículo esquerdo (FEVE), reoperação, cirurgia de emergênc (mais) ia, número de artérias revascularizadas, uso da artéria torácica interna esquerda (ATIE), uso de circulação extracorpórea (CEC), cirurgia associada, revascularização da artéria interventricular anterior (AIVA) e uso de balão intra-aórtico (BIA). A análise estatística foi feita por meio de análises descritiva, univariada e multivariada por regressão logística. Foram considerados significância estatística os valores de p Resumo em inglês BACKGROUND: The complexity of reentrant circuits related to ventricular tachycardias decreases the success rate of radiofrequency ablation procedures. OBJECTIVE: To evaluate whether the epicardial mapping with multiple electrodes carried out simultaneously with the endocardial mapping helps in ablation procedures of sustained ventricular tachycardia (VT) in patients with nonischemic heart disease. METHODS: Twenty-six patients with recurrent sustained VT, of which 22 (84.6 (mais) %) presenting chronic chagasic cardiomyopathy, 2 (7.7%) with idiopathic dilated cardiomyopathy and 2 with right ventricular arrhythmogenic dysplasia (RVAD), were submitted to epicardial mapping with two or three microcatheters, with 8 electrodes each, simultaneously to the conventional endocardial mapping. A catheter with a 4-mm tip was used for the ablation by radiofrequency (RF) carried out during the induced VT. RESULTS: Of the 33 induced VT, 25 were mapped and 20 had their origin defined. Eleven had epicardial and 9 had endocardial origin. The programmed ventricular stimulation did not induce sustained VT in 11 (42.0%) of the 26 patients after the ablation. Events such as VT recurrence and death occurred in 10.0% of the patients submitted to successful ablation and in 59.0% of the unsuccessful cases, during a mean ambulatory follow-up of 357 ± 208 days. CONCLUSION: Subepicardial circuits are frequent in patients with nonischemic heart disease. The epicardial mapping with multiple catheters carried out simultaneously with the endocardial mapping contributes to the identification of these circuits in a same procedure.

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82

Estudos da deposição em subtensão de cádmio sobre ouro policristalino na presença de diferentes ânions co-adsorvidos/ Voltammetric and microgravimetric studies of the anions influence in the underpotential deposition of cadmium on policrystalline gold electrodes

Santos, Mauro C.; Miwa, Douglas W.; Machado, Sérgio A. S.; Avaca, Luis A.
2001-08-01

Resumo em inglês Cadmium UPD on Au was studied by voltammetric and microgravimetric measurements. In the oxide formation/reduction potential region, a mass increasing/decreasing of 32 ng cm-2 was associated to incorporation/elimination of one oxygen per active site. The modifications promoted in the voltammetric and mass profiles by 10-5 M Cd(ClO4)2 are restricted to potentials more negative than 0.4 V. After a 120 s potential delay at 0.05 V, the positive sweep reveals an anodic peak wit (mais) h charge of 40 muC cm-2 and mass decrease of 22 ng cm-2, associated to Cd ads dissolution. Sulphate or chloride was added to the solution without significant influence, due to the low coverage with Cd or anions.

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83

Estudo da capacidade de complexação e sua relação com algumas variáveis ambientais em cinco represas do Rio Tietê/Brasil/ Study of complexation capacity and its relationship with some environmental variables in five reservoirs of the Tietê River system

Borges, Elisangela C. L.; Mozeto, Antonio Aparecido; Neves, Eduardo F. Almeida; Borges Neto, Waldomiro; Bezerra, José Mauro
2007-01-01

Resumo em inglês The copper and cadmium complexation properties in natural sediment suspensions of reservoirs of the Tietê River were studied using the solid membrane copper and cadmium ion-selective electrodes. The complexation and the average conditional stability constants were determined under equilibrium conditions at pH=6.00 ± 0.05 in a medium of 1.0 mol L-1 sodium nitrate, using the Scatchard method. The copper and cadmium electrodes presented Nernstian behavior from 1x10-6 (mais) to 1x10-3 mol L-1 of total metal concentration. Scatchard graphs suggest two classes of binding sites for both metals. A multivariate study was done to correlate the reservoirs and the variables: complexation properties, size, total organic carbon, volatile acid sulfide, E II and pH.

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84

Espectroscopia de impedância eletroquímica aplicada ao estudo das reações heterogêneas em ânodos dimensionalmente estáveis/ Electrochemical impedance spectroscopy applied in the study of heterogeneous reactions at dimensionally stable anodes

Carvalho, Liliane A. de; Andrade, Adalgisa R. de; Bueno, Paulo R.
2006-07-01

Resumo em inglês This paper discusses different aspects related to the application of electrochemical impedance spectroscopy (EIS) in the study of heterogeneous electrochemical reactions occurring on Dimensionally Stable anodes (DSA®). The most relevant aspects of the semiconductor/electrolyte interface, the application of the EIS classical equivalent circuit approach and the ac porous model in DSA are presented. The paper shows that DSA type electrodes can be consistently investigated b (mais) y using the ac porous model and an analysis is presented showing the advantage of applying this kind of approach to study heterogeneous reactions on DSA electrodes. Furthermore, some preliminary results on Ti/Ru0,3Ti(0,7-x)Sn x O2 based electrodes are presented to exemplify the use of the ac porous model analysis.

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85

Emprego de monocamadas auto-organizadas no desenvolvimento de sensores eletroquímicos/ Self-assembled monolayers applications for the development of electrochemical sensors

Freire, Renato S.; Pessoa, Christiana A.; Kubota, Lauro T.
2003-05-01

Resumo em inglês Self-assembled monolayers (SAMs) modified electrodes exhibit unique behavior that can greatly benefit electrochemical sensing. This brief review highlights the applications of SAM modified electrodes in electroanalytical chemistry. After a general introduction, which includes the approaches for SAM development, different electrochemical systems for detecting inorganic and organic species are described and discussed. Special attention to the coupling of biological sensing (mais) element to the SAM is given, which can selectively recognize the analyte. Future prospects are also evaluated.

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86

Eletrólise de resíduos poluidores: I - Efluente de uma indústria liofilizadora de condimentos/ Electrolysis of polluting wastes: I - Wastewater from a seasoning freeze-drying industry

Angelis, Dejanira F. de; Corso, Carlos R.; Bidoia, Ederio D.; Moraes, Peterson B.; Domingos, Roberto N.; Rocha-Filho, Romeu C.
1998-02-01

Resumo em inglês Wastewater from a seasoning freeze-drying industry was electrolysed to increase its biodegradability. Stainless-steel electrodes were used at 9.09 A/m², for up to 80 min. Conductivity, pH, biochemical (BOD) and chemical (COD) oxygen demands, Daphnia similis acute toxicity bioassays, and bacteria counting through the plate count agar method were determined after different times of electrolysis. The results (e.g. higher BOD and lower COD) showed that the biodegradability o (mais) f the wastewater was significantly increased; furthermore, Fe2+ ions liberated by the electrodes cause microorganisms to die and, when oxidised to Fe3+, contribute for the flocculation and sedimentation of solid residues.

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87

Eletrocatálise das reações de oxidação de hidrogênio e de redução de oxigênio/ Electrocatalysis of the hydrogen oxidation and oxygen reduction reactions

Ticianelli, Edson A.; Camara, Giuseppe A.; Santos, Luís G. R. A.
2005-08-01

Resumo em inglês This work discusses the electrocatalytic processes taking place in the polymer electrolyte fuel cell electrodes, specifically the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR), because these are clear examples of electrochemical reactions favored by the use of electrocatalysts. Since the gaseous reactants are very little soluble in the electrolyte, the use of special electrodes, named gas diffusion electrodes, is required to promote easy and co (mais) ntinuous access of reactant gases to the electrocatalytic sites. Besides this, other important aspects such as the use of spectroscopic techniques and of theoretical models to improve the knowledge of the electrocatalytic systems are shortly discussed.

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88

Dinâmica complexa no sistema bromato/hipofosfito/acetona/manganês e ferroína/ Complex Dynamics in the bromate/hypophosphite/acetone/manganese and ferroin system

Tokoro, Gustavo; Oliveira, Hyrla C. L.; Varela, Hamilton
2007-01-01

Resumo em inglês New chemical systems have been recently designed for the study of complex phenomena such as oscillatory dynamics in the temporal domain and spatiotemporal pattern formation. Systems derived from oscillators based on the chemistry of bromate are the most extensively studied, with the celebrated Belousov-Zhabotinsky (BZ) reaction being the most popular example. Problems such as the formation of bubbles (CO2) and solid precipitate in the course of the reaction and the occurr (mais) ence of simply short-lived oscillations under batch conditions are very common and, in some cases, compromise the use of some of these systems. It is investigated in this paper the dynamic behavior of the bromate/hypophosphite/acetone/dual catalyst system, which has been sugested as an interesting alternative to circumvent those inconvenients. In this work, manganese and ferroin are employed as catalysts and the complete system (BrO3-/H2PO2-/acetone/Mn(II)-ferroin) is studied under batch conditions. Temporal symmetry breaking was studied in a reactor under agitation by means of simultaneous records of the potential changes of platinum and Ag/AgBr electrodes, both measured versus a reversible hydrogen electrode. Additionally, spatio-temporal formation of target patterns and spiral waves were obtained when the oscillating mixture was placed in a quasi two-dimensional reactor.

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89

Determinação potenciométrica da concentração micelar crítica de surfactantes: uma nova aplicação metodológica no ensino de Química/ Potenciometric determination of the critical micellar concentration of the surfactants: a new methodological application in the Chemical learning

Rizzatti, Ivanise Mª; Zanette, Dilson R.; Mello, Ligia C.
2009-01-01

Resumo em inglês The participation of the students in the planning, execution and discussion of experimental results is important for the valuation of the role of them in the construction of the chemical knowledge implicited in the approach between education and research. This work relates either the construction of selective membrane electrodes for surfactants and its application in the potenciometric determination of the critical micellar concentration of the sodium dodecyl sulfate (SDS (mais) ) and dodecyltrimethylammonium bromide (DTAB) surfactants. In adition it´s possible to discuss the potenciometric results in matching with the data valued for the tensiometric and condutimetric traditionally used in the physical-chemistry lessons.

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90

Detecção eletroquímica em eletroforese capilar/ Electrochemical detection in capillary electrophoresis

Silva, José Alberto Fracassi da
2003-01-01

Resumo em inglês This review focuses the development of electrochemical detection systems coupled to capillary electrophoresis. Conductometric, amperometric, voltametric, and potentiometric modes of detection are reviewed. The positioning of the electrodes, interferences of high electric field, and the materials employed in the fabrication and modification of the electrodes are discussed. The advantages of the use of electrochemical detection with capillary electrophoresis, regarding to t (mais) he sensitivity and selectivity, is exemplified with a large number of applications. Also, the use of electrochemical detection systems in microchip technology is addressed.

Scientific Electronic Library Online (Portuguese)

91

Detectores potenciométricos para sistemas de análise por injecção em fluxo, evolução e aplicação/ Potentiometric detectors for flow injection analysis systems, evolution and application

Couto, Cristina M. C. M.; Montenegro, M. Conceição B. S. M.
2000-12-01

Resumo em inglês The field of flow injection potentiometry (FIP) is reviewed and its current status assessed. The research development and application of electrodes in flow injection systems are presented and discussed.

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92

Desenvolvimento, caracterização e aplicação eletroanalítica de um compósito fluido de adesivo epóxi, grafite e ciclo-hexanona/ Development, characterization and electroanalytical application of a fluid composite made of epoxy adhesive, graphite, and ciclohexanone

Silva, Rodrigo Amorim Bezerra da; Rabelo, Adriano César; Bottecchia, Otávio Luiz; Muñoz, Rodrigo Alejandro Abarza; Richter, Eduardo Mathias
2010-01-01

Resumo em inglês A fluid conducting composite material prepared from graphite powder, commercial epoxy resin Araldite®, and cyclohexanone has been developed. The composition was optimized considering the mechanical properties as conductivity and adhesiveness using response surface methodology. This work employed cyclic voltammetry and amperometry to investigate the characteristics of such composite electrodes without and with the insertion of Prussian blue in the electrode body (bulk mod (mais) ified electrode). The composite electrodes were also successfully used for the amperometric detection of hydrogen peroxide at 0.0V vs Ag/AgCl.

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93

Desenvolvimento de um procedimento biamperométrico para determinação de sacarina em produtos dietéticos/ Development of a biamperometric procedure for the determination of saccharin in dietary products

Assumpção, Mônica H. M. T.; Medeiros, Roberta Antigo; Madi, Alexandro; Fatibello-Filho, Orlando
2008-01-01

Resumo em inglês In this work was developed a method for the determination of saccharin in dietary products by a biamperometric titration, using two silver electrodes as working electrodes and silver nitrate as titrant. It were used products as juices (light) and sweeteners with saccharin in concentrations ranged from 8.73 x 10-5 mol L-1 to 1.0 x 10-2 mol L-1, and the results were in close agreement with those data found using a HPLC method at a confidence level of 95%. The main advantages of the proposed method are its simplicity, rapid and low cost.

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94

Degradação fotoeletroquímica de corantes dispersos em efluente têxtil utilizando fotoanodos de Ti/TiO2/ Photoeletrochemical degradation of disperse dyes in textile effluent on photoanodes of Ti/TiO2

Brunelli, Tamara F. T.; Guaraldo, Thaís T.; Paschoal, Fabiana M. M.; Zanoni, Maria Valnice B.
2009-01-01

Resumo em inglês The degradation of disperses dyes in aqueous solution and in effluents from textile industry has been investigated by photoelectrocatalytic oxidation using nanoporous thin films electrodes of Ti/TiO2. Samples of dispersil black dye and dispersil blue dye after 300 min of photoelectrolyzed at applied potential of +1.0 V and UV irradiation exhibited 100% of discoloration and 90% and 64% reduction total organic carbon, respectively. The proposed method was applied with succe (mais) ss in a textile industry effluent containing residues of these dyes, which after 300 min of treatment leads to reduction of 60% of COD and 64% removal of TOC.

Scientific Electronic Library Online (Portuguese)

95

Construção e caracterização de um detector eletroquímico para análises em fluxo/ Construction and characterization of an electrochemical detector for flow analysis

Santos, Wallans Torres P. dos; Azevedo, Eduardo F.; Richter, Eduardo M.; Albuquerque, Yaico D. Tanimoto de
2009-01-01

Resumo em inglês The present work describes a low-cost electrochemical "wall-jet" detector for flow analysis. The electrolytic solution enters into the cell through a tube of stainless steel (200 to 300 µm i.d), reaching to the center of the working electrode perpendicularly and then being mixed to the remaining solution in the cell, which flows under atmospheric pressure into a waste reservoir. The proposed electrochemical detector can be used with any type of working electrode, from co (mais) mmercial to home-made, such as glassy carbon and metallic electrodes (modified or unmodified), which enlarge the applications of the electrochemical detector.

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96

Construção de célula eletroquímica para observação de amostras in situ em estereomicroscópio/ Construction of an electrochemical cell to visualize samples in situ in stereomicroscope

Alencar, Mônica Alessandra Silva; Benedetti, Assis Vicente; Fugivara, Cecílio Sadao; Messaddeq, Younès
2010-01-01

Resumo em inglês The electrochemical study of glass like tungsten oxide derivatives requires the construction of special electrodes due to the fact that these glasses are not conductive. Electrodes modified with WO3 change their color when submitted to some potential perturbation. The color change of the electrochromic materials was observed in situ by coupling an electrochemical cell to a stereomicroscope. The constructed cell is versatile and may represent a great contribution to the el (mais) ectrochemical studies of materials, especially in the systems where it is interest to observe the working electrode surface during the electrochemical experiment.

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97

Biossensor enzimático para detecção de fungicidas ditiocarbamatos: estudo cinético da enzima aldeído desidrogenase e otimização do biossensor/ Enzymatic biosensor for the detection of dithiocarbamate fungicides: kinetic study of aldehyde dehydrogenase enzyme and biosensor optimization

Lima, Roberval Soares; Nunes, Gilvanda Silva; Noguer, Thierry; Marty, Jean-Louis
2007-02-01

Resumo em inglês Initially, all major factors that affect the rate of the AldH-catalyzed reaction (enzyme concentration, substrate concentration, temperature and pH) were investigated. Optimal activity was observed between pH values of 7.5 and 9.5 in the temperature range of 25 to 50 ºC. Kinetic parameters, such as Km (2.92 µmol L-1) and Vmax (1.33 10-2 µmol min-1) demonstrate a strong enzyme-substrate affinity. The sensors were based on screen-printed electrodes modified with the Meld (mais) ola Blue-Reinecke salt (MBRS) combination. Operational conditions (NAD+ and substrate contents, enzyme loading and response time) were optimized. Also, two enzyme immobilization procedures were tested: entrapment in poly(vinyl alcohol) bearing styrylpyridinium groups (PVA-SbQ) and crosslinking with glutaraldehyde. Chronoamperometry was employed to observe the biosensor responses during enzymatic hydrolysis of propionaldehyde and also to construct inhibition curves with maneb and zineb fungicides. Best results were found with the following conditions: [NAD+] = 0.25 mmol L-1; [propionaldehyde] = 80 µmol L-1; enzyme loading = 0.8 U per electrode; response time = 10 min, and inhibition time = 10 min. Current intensities around 103 ± 13 nA with the sensors and good stability was obtained for both immobilization procedures. Detection limits, calculated using 10% inhibition were 31.5 µg L-1 and 35 µg L-1 for maneb and zineb, respectively. Results obtained with other MBRS-modified electrodes consisting of mono and bi-enzymic sensors were compared. The ability to catalyze NADH oxidation by MB was also highlighted.

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98

Avaliação em escala laboratorial da utilização do processo eletrolítico no tratamento de águas/ Laboratory scale assessment of an electrolytic process for water treatment

Otenio, Marcelo Henrique; Panchoni, Luciana Cadioli; Cruz, Gabriela Correia Araújo da; Ravanhani, Clézio; Bidóia, Ederio Dino
2008-01-01

Resumo em inglês Water treatment uses chlorine for disinfection causing formation of trihalomethanes. In this work, an electrolytic water pre-treatment was studied and applied to the water from a fountainhead. The action against microorganisms was evaluated using cast-iron and aluminum electrodes. Assays were made in laboratory using the electrolytic treatment. After 5 min of electrolysis the heterotrophic bacteria count was below 500 cfu/mL and complete elimination of total and fecal col (mais) iforms was observed. Using electrolytic treatment as a pretreatment of conventional tap water treatment is proposed.

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99

Avaliação do processo eletrolítico em corrente alternada no tratamento de água de produção/ Evaluation electrolytic process in alternate current in treatment of water production

Cerqueira, Alexandre Andrade; Marques, Monica Regina da Costa; Russo, Carlos
2011-01-01

Resumo em inglês The main objective was to study the treatment of wastewater generated by the oil industry. This work consisted of tests of electroflocculation with alternate current (AC), and chemical coagulation. The removal efficiencies of organic load were evaluated by the removal of oils and greases, color and turbidity. The parameters investigated were the change in alternate current frequency, the initial pH, the distance between electrodes, the applied potential and time lapse. Fr (mais) om the results, one may conclude that the electroflocculation process is potential applicability to the effluent studied, while chemical coagulation was not successful.

Scientific Electronic Library Online (Portuguese)

100

Aplicação do ultra-som em sistemas eletroquímicos: considerações teóricas e experimentais/ Ultrasound applications in electrochemical systems: theoretical and experimental aspects

Garbellini, Gustavo S.; Salazar-Banda, Giancarlo R.; Avaca, Luis A.
2008-01-01

Resumo em inglês The aim of this review is to present and discuss the applications of ultrasound in electrochemical systems such as in sonoelectroanalysis and sonoelectrolysis for the electrochemical combustion of organic compounds. Initially, theoretical and experimental aspects are discussed, particularly those related to the enhancement of mass transport and the surface cleaning effects. Some results are included to illustrate alternative geometries for the experimental measurements an (mais) d the working electrodes used in these systems. In the sequence, the available publications are presented and discussed to demonstrate that ultrasound combined with electrochemical techniques is a powerful set-up for the detection of analytes such as metals and/or organic compounds in hostile media and for the effective destruction of toxic organic substances. At the end, a table summarizes the results already published in the literature.

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