1. Aliev, I.A., Gadjiev, A.D., Aral, A.: On approximation properties of a family of linear operators at critical value of parameter. J. Approx. Theory 138, 242–253 (2006)
2. Beatson, R.K.: Bell-shape preserving convolution operators. Technical Report, Department of Mathematics, University of Otago, Dunedin, New Zealand, 1978
3. DeVore, R.A., Lorentz, G.G.: Constructive Approximation: Polynomials and Splines Approximation, vol. 303. Springer, Berlin, Heidelberg (1993)
4. Flett, T.M.: Temperatures, Bessel potentials and Lipschitz space. Proc. Lond. Math. Soc. 22(3), 385–451 (1971)
5. Gadjiev, A.D., Aral, A., Aliev, I.A.: On behaviour of Riesz and generalized Riesz potentials as order tends to zero. Math. Inequalities Appl. 4, 875–888 (2007)