Hybrid Simulation of Cosmic Ray Air Showers
  Air shower simulations are essential for interpreting data from cosmic ray experiments. At highest energies though, a microscopic treatment of a whole shower is not possible any more, since it would require a huge amount of CPU-time. We review hybrid approaches of air shower simulation which try to overcome this problem without giving rise to artificial fluctuations as generated by the thinning algorithm. 
H.J. Drescher