Constru����o, caracteriza����o e aplica����o de eletrodos para descarga por arco de c��todo oco

The system built to characterize electrodes and, consequently, deposited fine films are constituted by a hollow cathode that works to discharges and low pressures (approximately 10-3 to 5 mbar), a source DC (0 to 1200 V), a cylindrical camera of closed borossilicato for flanges of stainless steel with an association of vacuum bombs mechanical and spread. In the upper flange it is connected the system of hollow cathode, which possesses an entrance of gas and two entrances for its refrigeration, the same is electrically isolated of the rest of the equipment and it is polarized negatively. In front of the system of hollow cathode there is a movable sample in stainless steel with possibility of moving in the horizontal and vertical. In the vertical, the sample can vary its distance between 0 and 70 mm and, in the horizontal, can leave completely from the front of the hollow cathode. The sample and also the cathode hollow are equipped with cromel-alumel termopares with simultaneous reading of the temperatures during the time of treatment. In this work copper electrodes, bronze, titanium, iron, stainless steel, powder of titanium, powder of titanium and sil��cio, glass and ceramic were used. The electrodes were investigated relating their geometry change and behavior of the plasma of the cavity of hollow cathode and channel of the gas. As the cavity of hollow cathode, the analyzed aspects were the diameter and depth. With the channel of the gas, we verified the diameter. In the two situations, we investigated parameters as flow of the gas, pressure, current and applied tension in the electrode, temperature, loss of mass of the electrode with relationship at the time of use. The flow of gas investigated in the electrodes it was fastened in a work strip from 15 to 6 sccm, the constant pressure of work was among 2.7 to 8 x 10-2 mbar. The applied current was among a strip of work from 0,8 to 0,4 A, and their respective tensions were in a strip from 400 to 220 V. Fixing the value of the current, it was possible to lift the curve of the behavior of the tension with the time of use. That curves esteem in that time of use of the electrode to its efficiency is maximum. The temperatures of the electrodes were in the dependence of that curves showing a maximum temperature when the tension was maximum, yet the measured temperatures in the samples showed to be sensitive the variation of the temperature in the electrodes. An accompaniment of the loss of mass of the electrode relating to its time of use showed that the electrodes that appeared the spherical cavities lost more mass in comparison with the electrodes in that didn't appear. That phenomenon is only seen for pressures of 10-2 mbar, in these conditions a plasma column is formed inside of the channel of the gas and in certain points it is concentrated in form of spheres. Those spherical cavities develop inside of the channel of the gas spreading during the whole extension of the channel of the gas. The used electrodes were cut after they could not be more used, however among those electrodes, films that were deposited in alternate times and the electrodes that were used to deposit films in same times, those films were deposited in the glass substrata, alumina, stainless steel 420, stainless steel 316, sil��cio and steel M2. As the eletros used to deposit films in alternate time as the ones that they were used to deposit in same times, the behavior of the thickness of the film obeyed the curve of the tension with relationship the time of use of the electrode, that is, when the tension was maximum, the thickness of the film was also maximum and when the tension was minimum, the thickness was minimum and in the case where the value of the tension was constant, the thickness of the film tends to be constant. The fine films that were produced they had applications with nano stick, bio-compatibility, cellular growth, inhibition of bacterias, cut tool, metallic leagues, brasagem, pineapple fiber and ornamental. In those films it was investigated the thickness, the adherence and the uniformity characterized by sweeping electronic microscopy. Another technique developed to assist the production and characterization of the films produced in that work was the caloteste. It uses a sphere and abrasive to mark the sample with a cap impression, with that cap form it is possible to calculate the thickness of the film. Through the time of life of the cathode, it was possible to evaluate the rate of waste of its material for the different work conditions. Values of waste rate up to 3,2 x 10-6 g/s were verified. For a distance of the substratum of 11 mm, the deposited film was limited to a circular area of 22 mm diameter mm for high pressures and a circular area of 75 mm for pressure strip. The obtained films presented thickness around 2,1 ��m, showing that the discharge of arch of hollow cathode in argon obeys a curve characteristic of the tension with the time of life of the eletrodo. The deposition rate obtained in this system it is of approximately 0,18 ��m/min

Constru����o, caracteriza����o e aplica����o de eletrodos para descarga por arco de c��todo oco

The system built to characterize electrodes and, consequently, deposited fine films are constituted by a hollow cathode that works to discharges and low pressures (approximately 10-3 to 5 mbar), a source DC (0 to 1200 V), a cylindrical camera of closed borossilicato for flanges of stainless steel with an association of vacuum bombs mechanical and spread. In the upper flange it is connected the system of hollow cathode, which possesses an entrance of gas and two entrances for its refrigeration, the same is electrically isolated of the rest of the equipment and it is polarized negatively. In front of the system of hollow cathode there is a movable sample in stainless steel with possibility of moving in the horizontal and vertical. In the vertical, the sample can vary its distance between 0 and 70 mm and, in the horizontal, can leave completely from the front of the hollow cathode. The sample and also the cathode hollow are equipped with cromel-alumel termopares with simultaneous reading of the temperatures during the time of treatment. In this work copper electrodes, bronze, titanium, iron, stainless steel, powder of titanium, powder of titanium and sil��cio, glass and ceramic were used. The electrodes were investigated relating their geometry change and behavior of the plasma of the cavity of hollow cathode and channel of the gas. As the cavity of hollow cathode, the analyzed aspects were the diameter and depth. With the channel of the gas, we verified the diameter. In the two situations, we investigated parameters as flow of the gas, pressure, current and applied tension in the electrode, temperature, loss of mass of the electrode with relationship at the time of use. The flow of gas investigated in the electrodes it was fastened in a work strip from 15 to 6 sccm, the constant pressure of work was among 2.7 to 8 x 10-2 mbar. The applied current was among a strip of work from 0,8 to 0,4 A, and their respective tensions were in a strip from 400 to 220 V. Fixing the value of the current, it was possible to lift the curve of the behavior of the tension with the time of use. That curves esteem in that time of use of the electrode to its efficiency is maximum. The temperatures of the electrodes were in the dependence of that curves showing a maximum temperature when the tension was maximum, yet the measured temperatures in the samples showed to be sensitive the variation of the temperature in the electrodes. An accompaniment of the loss of mass of the electrode relating to its time of use showed that the electrodes that appeared the spherical cavities lost more mass in comparison with the electrodes in that didn't appear. That phenomenon is only seen for pressures of 10-2 mbar, in these conditions a plasma column is formed inside of the channel of the gas and in certain points it is concentrated in form of spheres. Those spherical cavities develop inside of the channel of the gas spreading during the whole extension of the channel of the gas. The used electrodes were cut after they could not be more used, however among those electrodes, films that were deposited in alternate times and the electrodes that were used to deposit films in same times, those films were deposited in the glass substrata, alumina, stainless steel 420, stainless steel 316, sil��cio and steel M2. As the eletros used to deposit films in alternate time as the ones that they were used to deposit in same times, the behavior of the thickness of the film obeyed the curve of the tension with relationship the time of use of the electrode, that is, when the tension was maximum, the thickness of the film was also maximum and when the tension was minimum, the thickness was minimum and in the case where the value of the tension was constant, the thickness of the film tends to be constant. The fine films that were produced they had applications with nano stick, bio-compatibility, cellular growth, inhibition of bacterias, cut tool, metallic leagues, brasagem, pineapple fiber and ornamental. In those films it was investigated the thickness, the adherence and the uniformity characterized by sweeping electronic microscopy. Another technique developed to assist the production and characterization of the films produced in that work was the caloteste. It uses a sphere and abrasive to mark the sample with a cap impression, with that cap form it is possible to calculate the thickness of the film. Through the time of life of the cathode, it was possible to evaluate the rate of waste of its material for the different work conditions. Values of waste rate up to 3,2 x 10-6 g/s were verified. For a distance of the substratum of 11 mm, the deposited film was limited to a circular area of 22 mm diameter mm for high pressures and a circular area of 75 mm for pressure strip. The obtained films presented thickness around 2,1 ��m, showing that the discharge of arch of hollow cathode in argon obeys a curve characteristic of the tension with the time of life of the eletrodo. The deposition rate obtained in this system it is of approximately 0,18 ��m/min

Determina����o de Cd, Ni e Zn por espectrometria de emiss��o at��mica com plasma indutivamente acoplado, ap��s separa����o e pr��-concentra����o em coluna contendo p-dimetilaminobenzilidenorodanina adsorvida sobre s��lica gel

A column packed with 5-(4-dimethylaminobenzylidene)rhodanine adsorbed on silica gel was used for the preconcentration of Cd, Ni and Zn at different spiked solutions prior to their determination by inductively coupled plasma atomic emission spectrometry. This column allowed recoveries over than 98% for the above elements and accurate analyses of coastal sea-water certified reference material were also achieved.

Altera����es da curvatura da coluna vertebral: influ��ncia da fisioterapia, a n��vel neuromuscular

Mestrado em Fisioterapia

Met��stases da Coluna. Revis��o de uma Popula����o Hospitalar

As les��es metast��ticas extradurais s��o o tipo de tumor mais frequente a n��vel dos diferentes segmentos da coluna. Entre Janeiro de 1989 e Junho de 1996, foram observados a n��vel hospitalar 209 doentes com met��stases da coluna. Com base num protocolo de avalia����o individual, foi efectuado um estudo retrospectivo destes doentes, incidindo primordialmente sobre o respectivo quadro cl��nico e altera����es neuro-imagiol��gicas encontradas, bem como sobre o tipo de neoplasia prim��ria e a resposta �� terap��utica institu��da. Tivemos como objectivo fundamental o de tentar caracterizar a semiologia e evolu����o mais habituais deste tipo de les��es, no sentido da obten����o dum diagn��stico r��pido e da institui����o duma terap��utica em tempo ��til, permitindo um ��ndice de sobrevida com o m��nimo de qualidade.

Avalia����o da padroniza����o interna em espectrometria de absor����o at��mica utilizando gr��ficos de correla����o

The use of an internal standard (IS) in ET AAS can be considered a new trend after the commercial introduction of a simultaneous spectrometer. The evaluation of experimental data to choose the most appropriate IS can be done by comparing correlation graphs. They were used to verify the resemblance among the simultaneous measurements obtained for the analyte(s) and the IS by inductively coupled plasma optical emission spectrometry (ICPOES). The judicious selection of IS by using correlation graphs for determinations by ET AAS can be exploited to improve the precision and accuracy of the analytical results. Therefore, a new approach for studying the use of IS in ET AAS is presented.

Potencialidades anal��ticas do dietilditiofosfato de am��nio em espectrometria de massas com plasma indutivamente acoplado empregando extra����o em fase s��lida e sistemas de inje����o em fluxo

Um sistema de inje����o em fluxo envolvendo complexa����o com dietilditiofosfato de am��nio e sor����o de complexos met��licos em minicolunas de s��lica gel modificada por grupos octadecil C18 �� proposto para determina����es multielementares em espectrometria de massa com plasma indutivamente acoplado. Influ��ncia da concentra����o de reagentes, natureza do ��cido, tempo de rea����o, tempos de comuta����o, vaz��es e interfer��ncia de s��dio foram investigadas. ��gua ou solu����o 2% v/v HNO3 podem ser utilizadas para lavar a coluna antes da elui����o dos analitos com etanol. Amostras contendo 5000 mg Na L-1 e analisadas diretamente com o sistema proposto produzem uma concentra����o aparente de 63Cu de 0,45 ��g L-1; por outro lado n��o foi observada interfer��ncia para As, Pb, Bi, Se, In, Tl, Cd, Hg e 65Cu. Para 0,25 % w/v NH4DTP e 3 mL de solu����o de amostra, curvas anal��ticas para Bi, Cu, Pb, As, Se, In, Tl, Cd, Hg no intervalo de 0,10 a 2,00 ��g L-1 podem ser constru��das com boas correla����es (r2 > 0.998). A velocidade anal��tica e sensibilidade podem ser melhoradas pois dependem das condi����es de pr��-concentra����o e elui����o selecionadas. Com os par��metros acima fixados, limites de detec����o de 0.014 (Cu), 0.027 (As), 0.06 (Se), 0.02 (Cd), 0.029 (In), 0.043 (Hg), 0.02 (Tl), 0.06 (Pb) e 0.002 ��g L-1 (Bi) foram obtidos.

Desenvolvimento de um m��todo anal��tico r��pido e eficiente para a determina����o de corticoster��ides plasm��ticos por inje����o direta em coluna cromatogr��fica ISRP-C18 por CLAE

O presente trabalho teve como objetivo o desenvolvimento de um m��todo anal��tico simples, r��pido e eficiente para a determina����o de corticoster��ides (cortisona, corticosterona, acetato de hidrocortisona e acetato de dexametasona) em amostras sang����neas de ratos empregando um sistema isocr��tico de cromatografia l��quida de alta efici��ncia (CLAE) com detec����o ultravioleta. O m��todo envolveu a inje����o direta da amostra sang����nea em uma coluna cromatogr��fica com superf��cie interna de fase reversa (ISRP-C18), empregando a fase m��vel composta por tamp��o fosfato pH 4,0: acetonitrila (65:35 v/v). A detec����o dos analitos foi obtida, atrav��s de um detector de ultravioleta de comprimento de onda vari��vel (Varian Modelo 2550) ajustado em 240 nm e um integrador SP 4400 Chromaject (Varian Associates, Inc, Sunnyvale, CA, USA). A extra����o do analito resultou em valores de recupera����o entre 90% e 108%, e coeficiente de varia����o entre 1,1% a 2,5%. Os limites de detec����o e quantifica����o do m��todo foram de 0,02 e 0,04 ��g mL-1, respectivamente. Assim, o m��todo anal��tico proposto possibilitou a inje����o direta (on-line) da amostra sem tratamento pr��vio apresentando tamb��m v��rias vantagens, tais como: rapidez, exatid��o, precis��o e especificidade.

Potencialidades anal��ticas do dietilditiofosfato de am��nio em espectrometria de massas com plasma indutivamente acoplado empregando extra����o em fase s��lida e sistemas de inje����o em fluxo

Conselho Nacional de Desenvolvimento Cient��fico e Tecnol��gico (CNPq)

Desenvolvimento de um m��todo anal��tico r��pido e eficiente para a determina����o de corticoster��ides plasm��ticos por inje����o direta em coluna cromatogr��fica ISRP-C18 por CLAE

Coordena����o de Aperfei��oamento de Pessoal de N��vel Superior (CAPES)

T��cnica experimental para inser����o de parafuso no processo articular da coluna cervical inferior

P��s-gradua����o em Bases Gerais da Cirurgia - FMB

Efeito da aplica����o de filmes de carbono tipo diamante por plasma no destorque de pilares de implantes com conex��es c��nicas internas

P��s-gradua����o em Odontologia Restauradora - ICT

Plasma rico em plaquetas, medula ��ssea ou quitosana nas osteoss��nteses minimamente invasivas na t��bia de c��es

P��s-gradua����o em Cirurgia Veterin��ria - FCAV

Analysis of Magnetic Nozzles For Space Plasma Thrusters = An��lisis de Toberas Magn��ticas para Motores Espaciales de Plasma

Esta tesis presenta un an��lisis te��rico del funcionamiento de toberas magn��ticas para la propulsi��n espacial por plasmas. El estudio est�� basado en un modelo tridimensional y bi-fluido de la expansi��n supers��nica de un plasma caliente en un campo magn��tico divergente. El modelo b��sico es ampliado progresivamente con la inclusi��n de t��rminos convectivos dominantes de electrones, el campo magn��tico inducido por el plasma, poblaciones electr��nicas m��ltiples a distintas temperaturas, y la capacidad de integrar el flujo en la regi��n de expansi��n lejana. La respuesta hiperb��lica del plasma es integrada con alta precisi��n y eficiencia haciendo uso del m��todo de las l��neas caracter��sticas. Se realiza una caracterizaci��n param��trica de la expansi��n 2D del plasma en t��rminos del grado de magnetizaci��n de iones, la geometr��a del campo magn��tico, y el perfil inicial del plasma. Se investigan los mecanismos de aceleraci��n, mostrando que el campo ambipolar convierte la energ��a interna de electrones en energ��a dirigida de iones. Las corrientes diamagn��ticas de Hall, que pueden hallarse distribuidas en el volumen del plasma o localizadas en una delgada capa de corriente en el borde del chorro, son esenciales para la operaci��n de la tobera, ya que la fuerza magn��tica repulsiva sobre ellas es la encargada de confinar radialmente y acelerar axialmente el plasma. El empuje magn��tico es la reacci��n a esta fuerza sobre el motor. La respuesta del plasma muestra la separaci��n gradual hacia adentro de los tubos de iones respecto de los magn��ticos, lo cual produce la formaci��n de corrientes el��ctricas longitudinales y pone el plasma en rotaci��n. La ganancia de empuje obtenida y las p��rdidas radiales de la pluma de plasma se eval��an en funci��n de los par��metros de dise��o. Se analiza en detalle la separaci��n magn��tica del plasma aguas abajo respecto a las l��neas magn��ticas (cerradas sobre s�� mismas), necesaria para la aplicaci��n de la tobera magn��tica a fines propulsivos. Se demuestra que tres teor��as existentes sobre separaci��n, que se fundamentan en la resistividad del plasma, la inercia de electrones, y el campo magn��tico que induce el plasma, son inadecuadas para la tobera magn��tica propulsiva, ya que producen separaci��n hacia afuera en lugar de hacia adentro, aumentando la divergencia de la pluma. En su lugar, se muestra que la separaci��n del plasma tiene lugar gracias a la inercia de iones y la desmagnetizaci��n gradual del plasma que tiene lugar aguas abajo, que permiten la separaci��n ilimitada del flujo de iones respecto a las l��neas de campo en condiciones muy generales. Se eval��a la cantidad de plasma que permanece unida al campo magn��tico y retorna hacia el motor a lo largo de las l��neas cerradas de campo, mostrando que es marginal. Se muestra c��mo el campo magn��tico inducido por el plasma incrementa la divergencia de la tobera magn��tica y por ende de la pluma de plasma en el caso propulsivo, contrariamente a las predicciones existentes. Se muestra tambi��n c��mo el inducido favorece la desmagnetizaci��n del n��cleo del chorro, acelerando la separaci��n magn��tica. La hip��tesis de ambipolaridad de corriente local, com��n a varios modelos de tobera magn��tica existentes, es discutida cr��ticamente, mostrando que es inadecuada para el estudio de la separaci��n de plasma. Una inconsistencia grave en la derivaci��n matem��tica de uno de los modelos m��s aceptados es se��alada y comentada. Incluyendo una especie adicional de electrones suprat��rmicos en el modelo, se estudia la formaci��n y geometr��a de dobles capas el��ctricas en el interior del plasma. Cuando dicha capa se forma, su curvatura aumenta cuanto m��s perif��ricamente se inyecten los electrones suprat��rmicos, cuanto menor sea el campo magn��tico, y cuanto m��s divergente sea la tobera magn��tica. El plasma con dos temperaturas electr��nicas posee un mayor ratio de empuje magn��tico frente a total. A pesar de ello, no se encuentra ninguna ventaja propulsiva de las dobles capas, reforzando las cr��ticas existentes frente a las propuestas de estas formaciones como un mecanismo de empuje. Por ��ltimo, se presenta una formulaci��n general de modelos autosemejantes de la expansi��n 2D de una pluma no magnetizada en el vac��o. El error asociado a la hip��tesis de autosemejanza es calculado, mostrando que es peque��o para plumas hipers��nicas. Tres modelos de la literatura son particularizados a partir de la formulaci��n general y comparados. Abstract This Thesis presents a theoretical analysis of the operation of magnetic nozzles for plasma space propulsion. The study is based on a two-dimensional, two-fluid model of the supersonic expansion of a hot plasma in a divergent magnetic field. The basic model is extended progressively to include the dominant electron convective terms, the plasma-induced magnetic field, multi-temperature electron populations, and the capability to integrate the plasma flow in the far expansion region. The hyperbolic plasma response is integrated accurately and efficiently with the method of the characteristic lines. The 2D plasma expansion is characterized parametrically in terms of the ion magnetization strength, the magnetic field geometry, and the initial plasma profile. Acceleration mechanisms are investigated, showing that the ambipolar electric field converts the internal electron energy into directed ion energy. The diamagnetic electron Hall current, which can be distributed in the plasma volume or localized in a thin current sheet at the jet edge, is shown to be central for the operation of the magnetic nozzle. The repelling magnetic force on this current is responsible for the radial confinement and axial acceleration of the plasma, and magnetic thrust is the reaction to this force on the magnetic coils of the thruster. The plasma response exhibits a gradual inward separation of the ion streamtubes from the magnetic streamtubes, which focuses the jet about the nozzle axis, gives rise to the formation of longitudinal currents and sets the plasma into rotation. The obtained thrust gain in the magnetic nozzle and radial plasma losses are evaluated as a function of the design parameters. The downstream plasma detachment from the closed magnetic field lines, required for the propulsive application of the magnetic nozzle, is investigated in detail. Three prevailing detachment theories for magnetic nozzles, relying on plasma resistivity, electron inertia, and the plasma-induced magnetic field, are shown to be inadequate for the propulsive magnetic nozzle, as these mechanisms detach the plume outward, increasing its divergence, rather than focusing it as desired. Instead, plasma detachment is shown to occur essentially due to ion inertia and the gradual demagnetization that takes place downstream, which enable the unbounded inward ion separation from the magnetic lines beyond the turning point of the outermost plasma streamline under rather general conditions. The plasma fraction that remains attached to the field and turns around along the magnetic field back to the thruster is evaluated and shown to be marginal. The plasmainduced magnetic field is shown to increase the divergence of the nozzle and the resulting plasma plume in the propulsive case, and to enhance the demagnetization of the central part of the plasma jet, contrary to existing predictions. The increased demagnetization favors the earlier ion inward separation from the magnetic field. The local current ambipolarity assumption, common to many existing magnetic nozzle models, is critically discussed, showing that it is unsuitable for the study of plasma detachment. A grave mathematical inconsistency in a well-accepted model, related to the acceptance of this assumption, is found out and commented on. The formation and 2D shape of electric double layers in the plasma expansion is studied with the inclusion of an additional suprathermal electron population in the model. When a double layer forms, its curvature is shown to increase the more peripherally suprathermal electrons are injected, the lower the magnetic field strength, and the more divergent the magnetic nozzle is. The twoelectron- temperature plasma is seen to have a greater magnetic-to-total thrust ratio. Notwithstanding, no propulsive advantage of the double layer is found, supporting and reinforcing previous critiques to their proposal as a thrust mechanism. Finally, a general framework of self-similar models of a 2D unmagnetized plasma plume expansion into vacuum is presented and discussed. The error associated with the self-similarity assumption is calculated and shown to be small for hypersonic plasma plumes. Three models of the literature are recovered as particularizations from the general framework and compared.

Instabilidades MHD no Tokamak TCABR

Este trabalho descreve o estudo das instabilidades magneto-hidro-din��micas (MHD) comumente observadas nas descargas el��tricas de plasma no tokamak TCABR, do Instituto de F��sica da USP. Dois diagn��sticos principais foram empregados para observar essas instabilidades: um conjunto poloidal de 24 bobinas magn��ticas (bobinas de Mirnov) colocadas pr��ximas �� borda do plasma e um medidor de emiss��es na faixa do Ultra Violeta e de raios X moles com 20 canais (sistema SXR), cujo circuito de condicionamento de sinais foi aprimorado como parte deste trabalho. Esses diagn��sticos foram escolhidos porque fornecem informa����es complementares, uma vez que o sistema SXR observa a parte central da coluna de plasma, enquanto as bobinas de Mirnov detectam as instabilidades MHD na regi��o mais externa da coluna. As informa����es coletadas por esses diagn��sticos foram submetidas �� an��lise espectral com resolu����o temporal e espacial, possibilitando determinar a evolu����o das caracter��sticas espectrais e espaciais das instabilidades MHD observadas. Essas an��lises revelaram que durante a etapa inicial da forma����o do plasma (quando a corrente de plasma ainda est�� aumentando) ilhas magn��ticas com n��meros de onda decrescente, identificadas como sendo modos kink de borda, s��o detectadas nas bobinas de Mirnov. Ap��s a forma����o do plasma, quando os par��metros de equil��brio est��o relativamente est��veis (plat��), oscila����es s��o detectadas tanto nas bobinas de Mirnov quanto no sistema de SXR, indicando a presen��a de instabilidades MHD em toda a coluna de plasma. Em geral as oscila����es medidas nas bobinas de Mirnov tem baixa amplitude e correspondem a pequenas ilhas magn��ticas que foram identificadas como sendo modos de ruptura (modos tearing). Por outro lado, as instabilidades na regi��o central foram identificadas como dentes de serra, que correspondem a relaxa����es peri��dicas da regi��o interna �� superf��cie magn��tica com fator de seguran��a q=1 e que s��o acompanhadas de oscila����es precursoras, cuja amplitude depende da fase do ciclo de relaxa����o. Devido �� essa modula����o de amplitude, aparecem picos de frequ��ncia sat��lite nos espectrogramas dos sinais do SXR. Al��m disso, devido ao fato dos ciclos de relaxa����o n��o serem sinusoidais, os harm��nicos da frequ��ncia de relaxa����o tamb��m aparecem nesses espectrogramas. No entanto, em muitas descargas do TCABR, a intensidade das oscila����es medidas nas bobinas de Mirnov aumentam significativamente durante o plat��, com efeitos sobre a frequ��ncia de todas as instabilidades MHD, at�� mesmo sobre os dentes de serra localizados na regi��o central da coluna. Em todos os casos, observou-se que durante o plat�� a frequ��ncia das ilhas magn��ticas coincide com a frequ��ncia das oscila����es precursoras do dente de serra, apesar de serem duas instabilidades distintas, localizadas em posi����es radiais muito diferentes. Essa coincid��ncia de frequ��ncias possibilitou descrever a evolu����o em frequ��ncia de todas as oscila����es detectadas em diversos diagn��sticos com base em apenas duas frequ��ncias b��sicas: a dos ciclos de relaxa����o dente de serra e a das ilhas magn��ticas.