A functional limit theorem for the position of a particle in a Lorentz   type model
  Consider a particle moving through a random medium, which consists of spherical obstacles, randomly distributed in R^d. The particle is accelerated by a constant external field; when colliding with an obstacle, the particle inelastically reflects. We study the asymptotics of X(t), which denotes the position of the particle at time t, as t tends to infinity. The result is a functional limit theorem for X(t). 
Vladislav Vysotsky