Approximation theorems for certain positive linear operators

In this work we prove approximation theorems for certain positive linear operators via Ditzian–Totik moduli ω2,ϕ(f,⋅)ω2,ϕ(f,⋅) of second order where the step-weights are functions whose squares are concave. The results obtained are applied to the qq-Lupaş–Bernstein operators, the ω,qω,q-Bernstein operators and the convergence of the iterates of theqq-Bernstein polynomials.