A process and apparatus for refining iron from high-phosphorus content iron ores. The systems include a test module configured to operate between automated testing equipment and an integrated circuit to be tested. The transconductance control circuit provides a feedback control arrangement in which, for example, the comparison circuitry output is utilized to adjust one or more of the current sources such that a difference signal Vg between voltages at the respective terminals of the first and second field effect devices converges to a reference signal VR. An integral, simple and convenient means is provided to vary the intensity and pattern of the heat output, thereby controlling the cooking performance of the stove. Compounds of the present invention are useful for the treatment of cancers.