Simon Gagne

Prediction of Temperature Profiles in Tumors and Surrounding Normal Tissues During Magnetic Induction Heating

The development and preliminary verification of a simple two-compartment model describing the thermal response of adjacent normal and cancerous tissues subjected to magnetic induction heating is presented. Analytical expressions were found for estimating the spatial temperature distributions in the system composed of a spherical tumor mass imbedded in a cylindrical normal tissue as a function of the field intensity and the tissues physical, geometrical, and physiological characteristics. The conditions leading to preferential heating of the tumor are described.

Low resistance and tip potential of glass microelectrode: Improvement through a new filling method

The complete filling of a micropipette with an appropriate electrolytic solution remains a very delicate step in the fabrication of glass microelectrodes. Imperfectly filled microelectrodes result in large and unpredictable resistances and tip potentials. This note describes a new method for filling glass microele-ctrodes. The technique presents significant advantages in routine use: ease and rapidity of complete filling, low resistance and tip potential, better electrical stability,and high rate of success.

On the Influence of Diffusion, Double Layer, and Glass Conduction on the Electrical Resistance of Open Tip Glass Microelectrodes

A theoretical study of the electrical resistance of open tip glass microelectrodes based on the main physicochemical phenomena occurring at the microtip is described. An analytical expression for the total resistance of a microelectrode is derived from a model which assumes an electrically insulated glass wail. The model takes into account the diffusion process through the open tip, the ionic conduction in the bulk solutions, and the ionic conduction in the electrochemical double layers. These latter elements embody to some extent the conduction in a hydrated glass layer at the glass surface. A detailed study of the ionic flow through the microtip is also presented. The validity of this model is supported by experimental results presented at the end of this paper. Comparisons between these experimental results and their theoretical predictions are shown to be of electrophysiological interest. Practical comments involving an improved utilization of glass microelectrodes are also discussed throughout this paper.

Instantaneous Frequency Measurements of Neural Events: Application of Non-Uniformly Distributed RC Line

The display of instantaneous frequency as a function of real time (Frequencygram) is an efficient type of data presentation in studies of point processes such as neuronal events. This paper surveys and compares various methods for its analog implementation.

Open Tip Glass Microelectrodes: Conduction Through the Wall at the Tip

A theoretical and experimental study of the electrical resistance and the tip potential of open tip glass microelectrodes is presented. The main physico-chemica1l factors considered are the diffusion process of ions through the open tip, the ionic conduction in the bulk solutions, and the ionic conduction in the electrochemical double layers at the glass-electrolyte interface. In order to take into account possible conduction through the glass at the tip, a small part of the microtip is considered to be highly hydrated and its length is considered as an upper limit for the extent of hydration. Its longitudinal conduction is assumed to be much greater than in the remaining truncated cone. This lumped model, like a previous one which assumed a uniform distributed hydration, can be used to explain the electrical properties of open tip glass microelectrodes. It is concluded that end effects at the tip of a glass microelectrode are important and could explain in part their electrical properties.

Recordings of Bioelectric Potentials with Glass Microelectrodes: Limitations of Unity-Gain Follower with Buffer

It is possible to design amplifiers with virtually no input capacitance. As shown in the sequel, this feature, however, is not by itself sufficient to insure faithful recording of fast transmembrane potentials with glass microelectrodes.

Compensation of the differential floating capacitance between dual microelectrodes

A circuit for compensating the floating differential capacitance appearing between two recording microelectrodes is presented. It is shown how this floating capacitance can be neutralized so that current in any microelectrode can be injected without any significant crosstalk picked up by the other.

Studies on Electroosmotic Effects in Glass Microelectrodes - Improvement of Microelectrode Selection

Changes in the resistance and tip potential of open-tip glass microelectrodes as function of the polarity and intensity of an injected current are presented and analyzed. These experimental results are explained on the basis of a quantitative diffusion model which includes an electroosmotic effect through the microtip. This study also results in a practical method to improve microelectrode selection. The method, based on the change of resistance as a function of the polarity of the injected current, allows immediate rejection of incompletely filed microelectrodes.

Power Spectrum Density Analysis of Electrical Noise in Glass Microelectrodes

Experiments were performed on glass microelectrodes in order to obtain quantitative estimates of the power spectrum density of their current and voltage noises. The effects of current injection (under voltage or current clamp), and ion concentration gradients, were studied separately or concurrently. It was observed that the spectral distribution of the fluctuations is of the 1/f¿type, with ¿values close to unity. The excess noise values measured, relative to specific Nyquist levels, depend approximately on the square value of the current injected through the microtip and on the absolute value of the tip potential of the microelectrode. Dependence of these spontaneous fluctuations as a function of the nature of the external solution was also investigated.

Neural model for feature matching in stereo vision

The aim of this paper is to propose a neural network architecture as an approach to the feature matching problem in stereo vision. The model is based on the principle of shunting feedback competitive equations studied in depth by Grossberg and his colleagues. Psychophysical constraints utilized in the early computational models ofMarr-Poggio-Grimson Pollard-Mayhew- Frisby and Prazdny serve as basis for the architecture design of our network and for the selection of candidate matches. Competition and cooperation take place among the candidate matches and provide a strong and natural disambiguation power. 1.