First order Fermi acceleration at multiple oblique shocks
  Numerical results for particle acceleration at multiple oblique shocks are presented. We calculate the steady state spectral slope of test particles accelerated by the first order Fermi process. The results are compared to analytical treatments, for parameters, where the diffusion approximation does apply. Effects of injection and finite shock extend are included phenomenologically. We find the spectrum of accelerated particles to harden substantially at multiple oblique shocks and discuss the influence of the number of shocks compared to the obliquity itself. 
U.D.J. Gieseler, T.W. Jones, (University of Minnesota, Department of   Astronomy, U.S.A.)