The coefficients , , , and , as well as and for the Roberts flow, calculated in the second-order correlation approximation, as functions of k _⊥ /k_f, where is the effective wavenumber of the flow. Results obtained with k_x = k_y and or are represented by open squares and dotted lines or by open diamonds and dashed lines, respectively. Results with k_x/k_y = 0.75 [k _⊥  = (3,4,0)k₁] or k_x/k_y = 5 [k _⊥  = (5,1,0)k₁] and k_∥/k _⊥  = 0.2 are indicated by open or filled circles, respectively. Orange and black symbols correspond to the first and second expressions for and in (21) or for in (26).