Truncating the Fourier transform averaged by means of a generalized Hausdorff operator, we approximate functions and the adjoint to that Hausdorff operator of the given function. We find estimates for the rate of approximation in various metrics in terms of the parameter of truncation and the components of the Hausdorff operator. Explicit rates of approximation of functions and comparison with approximate identities are given in the case of continuous functions from the class $\text {Lip }\alpha $ .

Let {W(t), t ≥ 0} be a standard Brownian motion. For a positive integer m, define a Gaussian process Watanabe and Lachal gave some asymptotic properties of the process Xm(·), m ≥ 1. In this paper, we study the bounds of its moduli of continuity and large increments by establishing large deviation results.

We prove a Jackson type theorem for rational functions with prescribed numerator degree: For continuous functions f: [—1,1] —> ℝ with ℓ sign changes in (—1,1), there exists a real rational function Rℓ,n(x) with numerator degree ℓ and denominator degree at most n, that changes sign exactly where f does, and such that

Here C is independent of f, n and ℓ, and ωφ is the Ditzian-Totik modulus of continuity. For special functions such as f(x) = sign(x)|x|α we consider improvements of the Jackson rate.

We establish exact randomized moduli of continuity for ℓ2-norm squared independent Ornstein–Uhlenbeck processes.