1. Jones, D.L. and Evans, F.J., ‘A Classification of physical Variables and its Application in variational Methods’, J. Frank. Inst., 291, 449, 1971.
2. Callen, H.B., Thermodynamics, Wiley, New York, 1960.
3. Prigogine, I., Introduction to the Thermodynamics of irreversible Processes, Charles C. Thomas, 1955.
4. Cherry, C., Some general Theorems for Non-linear Networks possessing Reactance, Phil. Mag., 42, 1161, 1951.
5. Brayton, R.K. and Moser, J.K., A Theory of Non-linear Networks, Quart, AppZ. Maths., 22, 1, 1964.