Physical interpretation of initial conditions for fractional   differential equations with Riemann-Liouville fractional derivatives
  On a series of examples from the field of viscoelasticity we demonstrate that it is possible to attribute physical meaning to initial conditions expressed in terms of Riemann-Liouville fractional derivatives, and that it is possible to obtain initial values for such initial conditions by appropriate measurements or observations. 
Nicole Heymans and Igor Podlubny