text: where G(X) is the Landauer conductance of the pristine CNT 
  with a single metal dopant occupied by molecule X and 
  1/(2G0) is the contact resistance of a (6,6) CNT. 
  
  We may now obtain the total resistance per dopant site rel- 
  ative to the reference background signal as a function of the 
  target molecule concentration 
  
  FIG. 3: Fractional coverage Θ in thermal equilibrium of Ni in a (a) 
  monovacancy, (b) divacancy I, (c) divacancy II and (d) change in 
  resistance ∆R per dopant site as a function of CO concentration in 
  a background of air at room temperature and 1 bar of pressure. The 
  reference concentration of CO is taken to be C0 =0.1 ppm. Note the 
  change from linear to log scale on the y-axis at ∆R =10 Ω. 
  
  (7) 
  
  where N is the number of dopants, Θ[X, C] is the fractional 
  coverage of species X at concentration C of the target and C0 
  is the reference concentration. Notice that the contact resis- 
  tance drops out as we evaluate a change in resistance. 