The last mode of heat transfer, radiation, can be modeled in one of two ways. The first method is good only for small temperature ranges and approxi- mates non-linear radiative heat transfer as a linear phenomenon. In this case, the source is modeled as a resistor and capacitor just as is done for conduction and radiation. For larger tempera- ture ranges, the non-linear nature of radiation must be accounted for. In PSPICE, this requires the use of Analog Behavioral Models (ABMs).