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- BMO-VMO results for fractional integrals in variable exponent Morrey spacesPublication . Rafeiro, Humberto; Samko, StefanWe prove the boundedness of the fractional integration operator of variable order alpha(x) in the limiting Sobolev case alpha(x)p(x) = n - lambda(x) from variable exponent Morrey spaces L-p(.),L-lambda(.) (Omega) into BMO (Omega), where Omega is a bounded open set. In the case alpha(x) (math) const, we also show the boundedness from variable exponent vanishing Morrey spaces VLp(.),lambda (.) (Omega) into VMO (Omega). The results seem to be new even when p and A are constant. (C) 2019 Elsevier Ltd. All rights reserved.
- Characterization of the variable exponent Bessel potential spaces via the Poisson semigroupPublication . Rafeiro, Humberto; Samko, StefanUnder the standard assumptions on the variable exponent p(x) (log- and decay conditions), we give a characterization of the variable exponent Bessel potential space B(alpha)[L(p(-))(R(n))] in terms of the rate of convergence of the Poisson semigroup P(t). We show that the existence of the Riesz fractional derivative D(alpha) f in the space L(p(-))(R(n)) is equivalent to the existence of the limit 1/epsilon(alpha)(I - P(epsilon))(alpha) f. In the pre-limiting case sup(x) p(x) < n/alpha we show that the Bessel potential space is characterized by the condition parallel to(I - P(epsilon))(alpha) f parallel to p((.)) <= C epsilon(alpha). (C) 2009 Elsevier Inc. All rights reserved.
- Boundedness of the Bergman projection and some properties of Bergman type spacesPublication . Karapetyants, Alexey; Rafeiro, Humberto; Samko, StefanWe give a simple proof of the boundedness of Bergman projection in various Banach spaces of functions on the unit disc in the complex plain. The approach of the paper is based on the idea of Zaharyuta and Yudovich (Uspekhi Mat Nauk 19(2):139-142, 1964) where the boundedness of the Bergman projection in Lebesgue spaces was proved using Calderon-Zygmund operators. We exploit this approach and treat the cases of variable exponent Lebesgue space, Orlicz space and variable exponent generalized Morrey spaces. In the case of variable exponent Lebesgue space the boundedness result is known, so in that case we provide a simpler proof, whereas the other cases are new. The major idea of this paper is to show that the approach can be applied to a wide range of function spaces. We also study the rate of growth of functions near the boundary in spaces under consideration and their approximation by mollified dilations.
- Hardy type inequalityin variable lebesgue spacesPublication . Rafeiro, Humberto; Samko, StefanWe prove that in variable exponent spaces where L-p(.)(Omega), where p(.) satisfies the log-condition and Omega is a bounded domain in R-n with the property that R-n\(Omega) over bar has the cone property, the validity of the Hardy type inequality parallel to 1/delta(x)(alpha)integral(Omega)phi(y)/vertical bar x-y vertical bar(n-alpha)dy parallel to(p(.)) <= C parallel to phi parallel to(p(.)), 0 < alpha < min (1, n/p(+)), where delta(x) is approximately equal to dist(x, partial derivative Omega), is equivalent to a certain property of the domain Omega expressed in terms of alpha and chi(Omega).