Glass elasticity from particle trajectories
  Using positional data from video-microscopy of a two-dimensional colloidal system and from simulations of hard discs we determine the wave-vector-dependent normal mode spring constants in the supercooled fluid and glassy state, respectively. The emergence of rigidity and the existence of a displacement field in amorphous solids is clarified. Continuum elastic theory is used in the limit of long wavelengths to analyze the bulk and shear modulus of this amorphous system as a function of temperature. The onset of a finite static shear modulus upon cooling marks the fluid/solid transition. This provides an opportunity to determine the glass transition temperature $T_g$ in an intuitive and precise way. 
Christian L. Klix, Florian Ebert, Fabian Weysser, Matthias Fuchs,   Georg Maret, Peter Keim
cond-mat.soft