A new fractional model for the dynamics of the hepatitis B virus using the Caputo-Fabrizio derivative Saif Ullah, Muhammad Altaf Khan and Muhammad Farooq Eur. Phys. J. Plus, 133 6 (2018) 237 Published online: 26 June 2018 DOI: 10.1140/epjp/i2018-12072-4