Radial Electrode Research Articles

Spatial selectivity in a rotationally symmetric model of the electrically stimulated cochlea

A rotationally symmetric model of electrical stimulation of the guinea pig cochlea with active neural elements is used to study the influence of temporal stimulus parameters and electrode configurations on the spatial selectivity of electrical stimulation by cochlear implants. The width of the excitation patterns is determined with respect to the position of the stimulating electrode pairs in the cochlea. Computed Q 10db values are compared against single fibre data from the cat cochlear nerve as measured by Van den Honert and Stypulkowsky (1987). It turns out that the use of charge-balanced asymmetric rather than symmetric biphasic pulses approximately doubles the number of independent channels that can be applied in a cochlear implant with longitudinal bipolar electrodes, like a configuration with radial electrode pairs using symmetric biphasic pulse stimulation will also do. Finally, the influence on selectivity of the physiological variation in diameter of the cochlear nerve fibres and of a possible loss of their peripheral processes is studied.

Spatial variations in the charge density of argon discharges in the Gaseous Electronics Conference reference reactor

The spatially dependent ion and electron concentrations of argon discharges in the gaseous electronics conference reference reactor reach a saddle point maximum in the center of the glow. The concentrations were measured using a Langmuir probe. The charge density decreases in the axial direction from the glow center to the electrode sheath edges as expected. In contrast, the charge density increases in the radial direction from the glow center to the radial electrode edge. The maximum occurs approximately 1 cm inside of the actual electrode edge. The most plausible explanation for this increase is enhanced ionization at the electrode edges due to field enhancement there. The electric field is enhanced by the close proximity of the ground shield and driven electrode at the radial edge of the electrode. We estimate that the ionization rate in the plasma near the electrode edge must be almost double of that in the glow center.

Influence of the rf excitation on the low energy broad ion beam characteristics

Influence of the rf excitation in a capacitively coupled filamentless broad ion beam source with radial electrode configuration on the ion beam properties has been examined. Ion energy distribution was measured by use of a retarding field energy analyzer connected to a computer controlled data acquisition system. Influence of working conditions on the average ion energy and on the ion energy spread in the beam is described. Energy spread has typical values between 8 and 25 eV. Average ion energy can change due to variations of ion source working conditions (at constant extraction voltages) up to 60 eV. Increase of both the average ion energy and ion energy spread is observed with increasing rf power coupled to the plasma (20–100 W). This correlates to the increasing amplitude of plasma floating potential oscillation. Average ion energy decreases with increasing magnetic induction (0–75 mT) and with increasing pressure in the vacuum chamber (2×10−4–1.8×10−3 mbar) due to decreasing cathode oscillation amplitudes. Average ion energy decreases with increasing distance from the broad beam axis because of chromatical and spherical aberrations of the source extraction optics. Multiple peaks in the ion energy spectrum are observed. Their occurrence can be explained by charge exchange effects in the rf oscillating plasma sheath.

Influence of the rf excitation on the low energy broad ion beam characteristics (abstract)a)

Influence of the rf excitation in a capacitively coupled filamentless broad ion beam source with radial electrode configuration on the ion beam properties has been examined. Ion energy distribution was measured by use of a retarding field energy analyzer connected to a computer controlled data acquisition system. Influence of working conditions on the average ion energy and on the ion energy spread in the beam is described. Energy spread has typical values between 8 and 25 eV. Average ion energy can change due to variations of ion source working conditions (at constant extraction voltages) up to 60 eV. Increase of both the average ion energy and ion energy spread is observed with increasing rf power coupled to the plasma (20–100 W). This correlates to the increasing amplitude of plasma floating potential oscillation. Average ion energy decreases with increasing magnetic induction (0–75 mT) and with increasing pressure in the vacuum chamber (2×10−4–1.8×10−3 mbar) due to decreasing cathode oscillation amplitudes. Average ion energy decreases with increasing distance from the broad beam axis because of chromatical and spherical aberrations of the source extraction optics. Multiple peaks in the ion energy spectrum are observed. Their occurrence can be explained by charge exchange effects in the rf oscillating plasma sheath.

Power spectra of single infinite fibre extracellular potentials recorded by a bipolar electrode

The power spectra of bipolarly recorded extracellular action potentials (EAPs) generated by an infinite, homogeneous, excitable fibre in an infinite, resistive, isotropic and homogeneous volume conductor were theoretically analysed. The changes in the power spectrum of EAP, which occurred as a result of alterations in the propagation velocity v and duration Tin of the intracellular action potential IAP, were analytically determined for bipolar parallel and radial electrodes with a small interpole distance. It was found that the sensitivity of the spectral characteristics to alterations in v, Tin and/or the IAP asymmetry substantially depends on the fibre-electrode distance; information on the IAP fast changes, that seems to be lost in unipolar recording as a result of the filtering effect of the fibre-electrode distance, can be restored. The orientation of the recording electrode need not be taken into account when a qualitative analysis is carried out, but when a quantitative analysis has to be performed, then the electrode orientation has a significant influence. A method is suggested for determination of the fibres' orientation by means of the spectrum of EAPs recorded bipolarly. The selectivity of the bipolar electrodes is analysed.

Effects of Particle Shape and Size Distribution on Sorption and Flow Performance in Electrically Stabilized Expanded Beds

Use of the electrically stabilized expanded bed is an approach to the improvement of the performance of processes in beds of solid sorbents. Particle motion in a fluidized bed of nonconducting particles such as molecular sieves is halted when the bed is frozen by a strong electric field imposed across the bed. This allows sorption performance to approach that of fixed beds while maintaining the low pressure drops which are characteristic of fluidized beds. Beds with axial and radial electrode geometries function equally well in the sorption of carbon dioxide (CO/sub 2/) from nitrogen (N/sub 2/). The effects of particle shape and particle size distribution on bed stabilization are presented. Particle shape was varied from spherical to the irregular forms that are characteristic of crushed particles. The sorption performance was not appreciably different with particles having various shapes. Particles with a size range from 200 to approximately 1200 ..mu..m were blended from individual spherical fractions to create mixtures with peak distributions at both ends of this range. To a first approximation, the distribution of particle sizes did not affect sorption performance. These results demonstrate that both irregularly shaped particles and multiple-sized particles can be stabilized in electric fields, and themore » stabilized beds behave much like fixed beds of the same materials except that the pressure drops across the beds can be significantly less than those for fixed beds. However, the rate of adsorption in the system used for this study is controlled by diffusion within the particles (actually within the micropores of crystals); so the study did not address the effects of electric stabilization on the gas-film resistance.« less

Proposal for an Extra RF System Dedicated to Bunch Length Control and Synchrotron Movement Stabilization

A gain limitation for the F.E.L. installed in ACO appears as the charge density decreases in connection with the anomalous lengthening and the synchrotron movement instabilities which are affecting high current operation of the storage ring. An extra RF system is designed to cure both these effects. The basic component of the system is an extra cavity driven through a power RF amplifier by a signal whose spectrum is composed by the even harmonics of the revolution frequency and the nfo - fs side bands. The proper input is achieved from the signal induced by the beam on a radial pick-up electrode by means of a pulsed window amplifier. The amplifier equalizes the two components of the picked-up signal, one due to energy oscillation and the other to phase oscillation and thus realizes the suitable spectrum for the input. A feedback loop ensures the normalization of that signal. Synchrotron movement stabilization and bunch length control are expected to work for stored currents up to 100 mA.

Application of volumetric electrodes to the recuperation of metals in industrial effluents—III. Potential distributions and design of radial field electrodes

An experimental and theoretical study is described of a fixed bed electrochemical reactor with perpendicular current and electrolyte flows. A two-dimensional model with different sets of boundary conditions has been developed for limiting current conditions. The influence on the potential distribution in the solution phase of different parameters, namely solution velocity, particles, diameter, axial and radial thickness of the bed, has been studied. The test reaction chosen was copper recovery from dilute solution in sulphuric acid supporting electrolyte. Using the proposed model, a design diagram has been set up to build an optimal industrial reactor.

Phase lock of electrical slow waves and spike bursts in cat duodenum.

The phase relationship between slow waves and spike bursts was studied in vitro in the cat duodenum. Electrodes were arranged radially about the duodenum. Records were read for T1, the time between the slow-wave "valley" and the first spike, and T2, the time between successive valleys. The distributions of the ratio T1/T2 showed very small differences, not uniquely attributable to radial electrode position. The distribution of T1/T2 indicated that spike bursts began 58.8% of the way through a slow-wave cycle, measured from the valley. Also, electrodes were arranged longitudinally and records were read to determine deltaSW, the slow-wave delay time between adjacent electrode positions, and deltaS, the spike burst delay time between adjacent electrode positions. The correlation of deltaS and deltaSW suggested a linear relation, and a regression resulted in a good linear description. These results are consistent with an assumed phase lock of spike bursts to slow waves.

A Fast Technique of Measuring Equilibrium Orbit Warps in the Zero Gradient Synchrotron (ZGS) at Injection

The difference signals from radial pi induction electrodes located in the eight straight section boxes of the ZGS are used to determine equilibrium orbit warps. A 1 ?s, debunched linac beam is injected in the ZGS ring and the eight coasting beam signals are analyzed. Since the effective electrode centers and inflector magnet positions are known, one can obtain orbit positions around the ZGS ring. The zero crossing times of all eight coasting beam bow-tie patterns are entered into our CDC-924A computer. The computer graphically displays orbit warps via CRT terminal. An additional feature to be described is that betatron tunes at injection can be very easily obtained from the coasting beam patterns.

Mass Transfer to Point Electrodes on the Surface of a Rotating Disk

A zeroth order perturbation solution is presented for the rate of laminar mass transfer to three types of point electrodes embedded in the surface of an insulating rotating disk—those sensitive to radial, tangential, and local velocity components. It is shown that the diffusion current density on the point electrode increases with decreasing geometrical parameter defined as the ratio of the electrode size to the radial location of the electrode on the disk surface. With a properly chosen geometrical parameter, it is possible to obtain a current density ten times greater than that on the disk electrode at a given rotational speed. From the electroanalytical point of view, this offers experimental advantages in the study of fast surface reactions.An experimental setup for studying the transfer characteristics of such electrodes is described. A diffusion‐controlled redox reaction is used for the measurement. The results indicate that the “local” and the “tangential” electrodes give reasonable agreement with the theory prediction. However, data from the “radial” electrode scatter randomly around the predicted values. This failure of the radial electrode to behave properly appears to be consistent with thin‐ring experiments reported in the literature.

Transorbital hypophysectomy in primates.

Radio-frequency thermal hypophysectomy of rhesus monkeys can be achieved using a simple transorbital puncture of the pituitary. Both the superior orbital fissure and the lateral orbital wall are in line with the pituitary; it is thus possible to direct an electrodealong this axis through the fissure into the sella turcica. Using a radial electrode, radio-frequency thermal destruction of the gland can be carried out. This approach also permits pituitary blood sampling and electrical recording. (Endocrinology 85: 949, 1969)

Radiofrequency thermal hypophysectomy. Technical note.

N a recent report, a technique for transsphenoidal stereotaxic destruction of the hypophysis was described. 1 The ablatory agent was radiofrequency (rf) current applied via a stainless steel radial electrode. Temperature monitoring of the heat lesions was provided by a thermistor bead inserted at the base of the spring. This procedure brought about panhypopituitarism in 39 of 40 cases. The temperature monitoring system proved unsatisfactory, however, since the thermistor bead used to monitor temperature at the electrode tip was easily damaged and required frequent replacement at considerable expense. The procedure described below permits rf coagulation of the pituitary with or without monitoring of temperature. To attempt rf destruction of the pituitary without monitoring temperature, it is only necessary to prove that boiling has begun at the electrode tip, thus indicating that temperature has in fact risen to destructive levels. This is easily ascertained since a rise in the tissue resistance occurs as steam formation begins. Thus, at any adequate rf generator output, voltage and current remain steady until the boiling point is reached; then, a slow rise in voltage and fall in current occur. When temperature is monitored while such lesions are in progress, a sharp rise in temperature to 70~176 occurs within 30 seconds, followed by a slow rise to 95~ or higher. These observations confirm the reliability and practicality of producing lesions without temperature recording.

Électrocorticogramme et activités unitaires lors de processus expansifs chez l'homme

1. 1. Recordings from the cerebral cortex have been made in man with radial transcortical electrodes (TC) and with micro-electrodes during neurosurgical operations for expanding lesions. 2. 2. Three types of abnormal electrical activity can be recognized in the case of tumours involving the cerebral cortex. In the involved cortex there is neither electrocorticographic (ECoG) activity nor cellular discharge. Immediately around this area in which the tumour comes to the surface the ECoG consists of bursts separated by periods of silence; the slow discharges are grouped during the periods of ECoG activity. Outside this zone the record is composed of slow waves; unitary activity occurs here also in bursts. When the tumour is subcortical, but superficial, only the 2 last zones exist. If the tumour is deep the overlying cortex is the site of slow waves. 3. 3. Precise agreements have been shown between cortical waves and unitary activities: cellular discharges simultaneous with the positive waves at the surface; absence of discharges with negative waves. These relationships are only clear in the transcortical ECoG, as monopolar recording does not show agreement between the pathological slow waves and cellular discharges. 4. 4. The probable role of deafferentiation in the mechanism of the electrical abnormalities is emphasized.

X-Ray Pinhole Photographic Evidence of Multiple Field-Emission Sources

An investigation was carried out to exhibit the existence of localized field-emitting areas on nickel electrode surfaces. To this end, a system consisting of concentric cylindrical electrodes, whose radial electrode spacing and inner radius were 7.75 and 16 mm, respectively, and which had an effective length of 12 cm and a cathode area of 130 sq cm, was used as a source to expose x-ray films through a pinhole setup. The resultant images clearly show the existence of discrete electron beams bombarding the anode. There were an average of 3.5 spots per square centimeter at a gross field of 157 kV/cm. A number of Fowler-Nordheim plots were taken, and the usual result was a straight line. The x-ray sources from the anode were also found to be smaller than 0.1 mm.

Measurement of Betatron Oscillation Frequencies in the Cosmotron

Coherent betatron oscillations are excited by an impulse magnetic field in one straight section of the cosmotron. The resulting oscillations can be observed using a communications receiver connected to the radial position induction electrodes.