In this paper we classify the centers and the isochronous centers of certain polynomial differential systems in R2 of degree d ≥ 5 odd that in complex notation can be written as ż = (λ+ i)z + (zz̄) d−5 2 (Az +Bzz̄ + Czz̄ +Dzz̄ + Ezz̄ + F z̄), where λ ∈ R and A,B,C,D,E, F ∈ C. Note that if d = 5 we obtain the full class of polynomial differential systems of the form a linear system with homogeneous po...

The paper studies L∞(IR )-norm approximations from a space spanned by a discrete set of translates of a basis function φ. Attention here is restricted to functions φ whose Fourier transform is smooth on IR\0, and has a singularity at the origin. Examples of such basis functions are the thin-plate splines and the multiquadrics, as well as other types of radial basis functions that are employed i...