Minkowski's inequality for two variable difference means

We study Minkowski's inequality

and its reverse where is the difference mean introduced by Stolarsky. We give necessary and sufficient conditions (concerning the parameters ) for the inequality above (and for its reverse) to hold.

     

Spherical maximal operator on symmetric spaces of constant curvature

We prove an endpoint weak-type maximal inequality for the spherical maximal operator applied to radial funcions on symmetric spaces of constant curvature and dimension . More explicitly, in the Lorentz space associated with the natural isometry-invariant measure, we show that, for every radial function ,

The proof uses only geometric arguments and volume estimates, and applies uniformly in every dimension.

     

A strengthening of the Carleman-Hardy-Pólya inequality

As a consequence of a more general statement proved in the paper, it is deduced that, if , and , then

with equality if and only if . This is a new refinement of Carleman's classic inequality.

     

On the Bochner-Riesz means of critical order

Stein's well-known logarithmic asymptotics of the Lebesgue constants of the Bochner-Riesz means of critical order is extended to Lebesgue constants of more general linear means of multiple Fourier series. These means are generated by certain class of functions supported in convex domains with boundaries of non-vanishing Gaussian curvature.

     

Integral means and Pólya factorizations

Integral means of functions and their derivatives are studied. We find a relation between integral means and the Pólya factorization of ordinary linear differential operators.

     

Sundual characterizations of the translation group of

We characterize the first three sundual spaces of , with respect to the translation group of .

     

Lower estimate for the integral means spectrum for

In this paper we show that there exists a function bounded and univalent in the unit disk, such that ,

     

Defending the negated Kaplansky conjecture

To answer in the negative a conjecture of Kaplansky, four recent papers independently constructed four families of Hopf algebras of fixed finite dimension, each of which consisted of infinitely many isomorphism classes. We defend nevertheless the negated conjecture by proving that the Hopf algebras in each family are cocycle deformations of each other.

     

Schwarzian derivative, integral means, and the affine and linear invariant families of biharmonic mappings

In this paper we discuss the properties of the Schwarzian derivative, integral means and the affine and linear invariant families of biharmonic mappings. First, we introduce the Schwarzian derivative S(F) for biharmonic mappings F = ∣z∣²G + H, and obtain several necessary and sufficient conditions for S(F) to be analytic. Second, we introduce the subordination of biharmonic mappings and obtain inequalities for integral means of subordinate biharmonic mappings. Finally, we introduce the affine and linear invariant families of biharmonic mappings and prove several estimates related to the Jacobian of functions in these invariant families.     

Infinite families of solutions of the equation

We give explicit formulas providing two new infinite families of couples of binomial coefficients whose ratio is 2.