A couple of things I made quickly. The waveforms look nice, and the circuits may have some use if you can compensate for variations in transistor gain, perhaps by a potentiometer diving the gate voltage. Very approximately, the upper circuit calculates a logarithm and the lower one calculates a power, but they don't behave as if 1V = 1, and I don't suppose I'm entirely working within the linear range of the transistors.
Both circuits make use of the virtual ground which exists at the inverting input of an op-amp in invertng amplifier configuration.
