The geometry of canal surfaces and the length of curves in de Sitter   space
  We find the minimal value of the length in de Sitter space of closed space-like curves with non-vanishing non-space-like geodesic curvature vector. These curves are in correspondence with closed almost-regular canal surfaces, and their length is a natural magnitude in conformal geometry. As an application, we get a lower bound for the total conformal torsion of closed space curves. 
R\'emi Langevin and Gil Solanes
math.DG