The Composition of Cosmic Rays at the Knee
  The observation of a small change in spectral slope, or 'knee' in the fluxes of cosmic rays near energies 10^15 eV has caused much speculation since its discovery over 40 years ago. The origin of this feature remains unknown. A small workshop to review some modern experimental measurements of this region was held at the Adler Planetarium in Chicago, USA in June 2000. This paper summarizes the results presented at this workshop and the discussion of their interpretation in the context of hadronic models of atmospheric airshowers. 
S.P. Swordy, L.F. Fortson, J. Hinton, J. Horandel, J. Knapp, C.L.   Pryke, T. Shibata, S.P. Wakely, Z. Cao, M. L. Cherry, S....