text: FIG. 2: Calculated (a) adsorption energy Eads in eV and (b) change in 
  conductance ∆G in units of G0 =2e2/h for N2, O2, H2O, CO, NH3, 
  and H2S on 3d transition metals occupying a monovacancy (top), 
  divacancy I (middle), and divacancy II (bottom) in a (6,6) carbon 
  nanotube. 
  FIG. 1: Structural schematics and formation energy for a 3d tran- 
  sition metal occupied monovacancy (black), divacancy I (gray), or 
  divacancy II (white) in a (6,6) carbon nanotube. Formation energies 
  of the empty vacancies are indicated by dashed lines. 