This invention is a variable orifice for controlling the mass flow rate of nitrous oxide used as an engine oxidizer, this orifice having an effective size, or area, which changes with changes in the nitrous oxide pressure applied to it. A column selector circuit selects a part of the columns in response to a column address, and a plurality of sense amplifier groups are connected with the selected columns by the column selector circuit. The metallic layer is attached to the layer of fiber-based material with its first surface facing towards the layer of fiber-based material. The feature vector set is divided into a desired number of initial clusters and a seed determined from each initial cluster. The method including: providing a heat source with an output of radiation in a predetermined spectrum; generating a first portion of the power from the absorption of the radiation; and generating a second portion of the power from a temperature difference between a first element heated by the heat source and a second element at least partially thermally insulated from the first element.