  The evolution of the aging process of glassy materials quenched from
temperatures above their glass transition temperature $T_g$, when plotting the
relaxed enthalpy versus the decrease in volume, leads to a slope comparable to
the isothermal compressibility close to $T_g$. This empirical result was
explained in an earlier publication (V. Katsika-Tsigourakou, G. E. Zardas J.
Non-Cryst. Solids 356 (2010) 179-180) by means of a thermodynamical model.
Here, we show that the same model enables the explanation of the rare cases of
negative defect activation in solids.
