Propagation of extragalactic ultra-high energy cosmic-ray nuclei : implications for the observed spectrum and composition

In this paper, we study the propagation of cosmic-ray nuclei and protons. We emphasize the influence of the source composition on the expected spectrum and composition on Earth as well as on the phenomenology of the transition from Galactic to extragalactic cosmic-rays and the interpretation of the ankle. We point out that the different source composition models cannot be distinguished on the sole basis of the cosmic-ray spectrum but that the the energy evolution of $<X_{\max }>$ should remove this degeneracy. Finally, we compare the predictions for the different source composition models with the available data and discuss the implications of our results.