Flow law, stress exponent, homologous temperature কী?

A flow law gives the strain rate of a rock deforming by one mechanism as a function of the differential stress $\sigma$, the grain size $d$, the temperature $T$ and the pressure $P$:

with $A$, $n$, $m$, the activation energy $E$ and the activation volume $V$ measured in the laboratory. The stress exponent is $n$, the grain-size exponent $m$. The homologous temperature of a mineral is $T/T_m$, its absolute temperature over its absolute melting temperature.