Shape functions and power corrections to the event shapes
  We show that the leading power corrections to the event shape distributions can be resummed into nonperturbative shape functions that do not depend on the center-of-mass energy and measure the energy flow in the final state. In the case of the thrust variable, the distribution is given by the convolution of the perturbative spectrum with the shape function. Choosing the simplest ansatz for the shape function we find that our predictions for the thrust distribution provide a good description of the data throughout a wide range of energies. 
G.P.Korchemsky