Dual Darboux Frame of a Spacelike Ruled Surface and Darboux Approach to   Mannheim Offsets of Spacelike Ruled Surfaces
  In this paper, we define dual geodesic trihedron(dual Darboux frame) of a spacelike ruled surface. Then, we study Mannheim offsets of spacelike ruled surfaces in dual Lorentzian space by considering the E. Study Mapping. We represent spacelike ruled surfaces by dual Lorentzian unit spherical curves and define Mannheim offsets of the spacelike ruled surfaces by means of dual Darboux frame. We obtain relationships between the invariants of Mannheim spacelike offset surfaces and offset angle, offset distance. Furthermore, we give conditions for these surface offsets to be developable. 
Mehmet \"Onder, H. H\"useyin U\u{g}urlu
math.DG