@Misc{ 
  Olb21,
  author = { Olbermann, Heiner },
  title = { Godunov variables and convex entropy for relativistic fluid dynamics
  with bulk viscosity },
  journal = {  },
  year = { 2021 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/6694/ },
  note = { cvgmt preprint}
}