Activating Equations

How to activate equations (used in heat source) for particular temperature? And how to intepret them into the heat source (Q)

1. 400[K] 500[K] Q_sei*exp(a_sei/T[K])
2. 500[K] 530[K] Q_n*exp(a_n/T[K])
3. 530[K] 600[K] Q_sei*exp(a_sei/T[K])
4. 600[K] 620[K] Q_n*exp(a_n/T[K])