A high gain amplifier circuit includes two differential transistor pairs and a current generator coupled to each differential pair to control tail current. The method in one embodiment of the invention consists of determining the desired increase in main chamber neutral particle density to be contributed by the secondary chamber for a given main chamber ion density range, and then to maintain the main chamber source power below a level beneath which the secondary chamber is capable of supplying the desired main chamber neutral density contribution. The physiological sensor also includes a multiplexor configured select and output a signal from the photodetector array. In another aspect, the disclosure relates to a method of cooling a first friction brake system and a second friction brake system including diverting a flow of brake cooling fluid to the systems based on the use of the systems. Two or more of the transistor circuits have different threshold voltages with respect to each other. This material fills the entire volume of said panel shell, at the same time as it includes therein reinforcement means provided with points directly accessible from the outside of the concealed face of the panel.