Construction of rational surfaces of degree 12 in projective fourspace   (with an appendix by Kristian Ranestad)
  The aim of this paper is to present two different constructions of smooth rational surfaces in projective fourspace with degree 12 and sectional genus 13. In particular, we establish the existences of five different families of smooth rational surfaces in projective fourspace with the prescribed invariants. 
Hirotachi Abo