Variable surface resistors

Rote et al. (1993, 1994) used a carotid thrombosis model in dogs. A calibrated electromagnetic flow meter was placed on each common carotid artery proximal to both the point of insertion of an intravascular electrode and a mechanical constrictor. The external constrictor was adjusted with a screw until the pulsatile flow pattern decreased by 25 % without altering the mean blood flow. Electrolytic injury to the intimal surface was accomplished with the use of an intravascular electrode composed of a Teflon-insulated silver-coated copper wire connected to the positive pole of a 9-V nickel-cadmium battery in series with a 250000 ohm variable resistor. The cathode was connected to a subcutaneous site. Injury was initiated in the right carotid artery by application of a 150 xA continuous pulse anodal direct current to the intimal surface of the vessel for a maximum duration of 3 h or for 30 min beyond the time of complete vessel occlusion as determined by the blood flow recording. Upon completion of the study on the right carotid, the procedure for induction of vessel wall injury was repeated on the left carotid artery after administration of the test drug. 

The experimental details have been reported elsewhere (X, X) Briefly, matrices are formed by codeposition of excess argon with atomic potassium on a sapphire plate mounted inside an ESR cavity which is itself attached to a variable temperature liquid helium dewar. Cluster formation occurs during deposition and is accomplished by warming the sapphire surface above a nominal deposition temperature of 4.2 K. For spectra shown here, temperature measurements were made with a calibrated carbon resistor and are judged accurate to within 5%. 

In variable resistors the resistance value can be modified at wiU, but after adjustment this value must remain constant. The usual way to obtain this is a sliding contact that can move over the surface of the resistive element. The variable resistance can be used as such. In this case two connections are used, one at the start of the resistive element and one connected with the sliding contact. 

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