On X-Ray Channeling in mu- and n-capillaries
  In this work X-ray propagation in micro- and nano-size capillaries has been considered in the frame of a simple unified wave theory. It is shown that the diminishing of the channel sizes completely changes the mode of beam transportation, namely, we obtain the transformation of surface channeling in microcapillaries to bulk channeling in nanocapillaries (nanotubes). 
S. Bellucci and S.B. Dabagov