Role of the unstable directions in the equilibrium and aging dynamics of   supercooled liquids
  The connectivity of the potential energy landscape in supercooled atomic liquids is investigated through the calculation of the instantaneous normal modes spectrum and a detailed analysis of the unstable directions in configuration space. We confirm the hypothesis that the mode-coupling critical temperature is the $T$ at which the dynamics crosses over from free to activated exploration of configuration space. We also report the observed changes in the local connectivity of configuration space sampled during aging, following a temperature jump from a liquid to a glassy state. 
Claudio Donati, Francesco Sciortino and Piero Tartaglia