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Now showing items 21-28 of 28

#### Boundedness and compactness of a class of Hardy type operators

(Journal article; Tidsskriftartikkel; Peer reviewed, 2016-12-13)

We establish characterizations of both boundedness and of compactness of a general
class of fractional integral operators involving the Riemann-Liouville, Hadamard, and
Erdelyi-Kober operators. In particular, these results imply new results in the theory of
Hardy type inequalities. As applications both new and well-known results are pointed
out.

#### Two-sided estimates of the Lebesgue constants with respect to Vilenkin systems and applications

(Journal article; Peer reviewed; Tidsskriftartikkel, 2017-03-13)

In this paper, we derive two-sided estimates of the Lebesgue constants for bounded Vilenkin systems, we also present some applications of importance, e.g., we obtain a characterization for the boundedness of a subsequence of partial sums with respect to Vilenkin–Fourier series of H 1 martingales in terms of n's variation. The conditions given in this paper are in a sense necessary and sufficient.

#### Multi-dimensional Hardy type inequalities in Hölder spaces

(Journal article; Tidsskriftartikkel; Peer reviewed, 2018)

Most Hardy type inequalities concern boundedness of the Hardy type operators in Lebesgue spaces. In this paper we prove some new multi-dimensional Hardy type inequalities in Hölder spaces.

#### Potential type operators in PDEs and their applications

(Journal article; Peer reviewed; Tidsskriftartikkel, 2017-01)

We prove the boundedness of Potential operator in weighted generalized Morrey space in terms of Matuszewska-Orlicz indices of weights and apply this result to the Hemholtz equation in ℝ<sup>3</sup> with a free term in such a space. We also give a short overview of some typical situations when Potential type operators arise when solving PDEs.

#### Hardy-type inequalities in fractional h-discrete calculus

(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-04-04)

The first power weighted version of Hardy’s inequality can be rewritten as [<i>mathematical formula</i>] where the constant <i>C</i> =[<i>p</i> / <i>p</i> - <i><b>a</b></i> - 1]<sup><i>p</i></sup> is sharp. This inequality holds in the reversed direction when<math xmlns="http://www.w3.org/1998/Math/MathML">
<mn>0</mn>
<mo>≤<!-- ≤ --></mo>
<mi><i>p</i></mi>
<mo><</mo>
<mn>1</mn>
...

#### A sharp boundedness result for restricted maximal operators of Vilenkin-Fourier series on martingale Hardy spaces

(Journal article; Peer reviewed, 2018-09-20)

The restricted maximal operators of partial sums with respect to bounded Vilenkin systems are investigated. We derive the maximal subspace of positive numbers, for which this operator is bounded from the Hardy space
H
p
to the Lebesgue space
L
p
for all
0<p≤1
. We also prove that the result is sharp in a particular sense.

#### On geometric construction of some power means

(Journal article; Peer reviewed, 2018-11-27)

In the homogenization theory, there are many examples where the effective conductivities of composite structures are power means of the local conductivities. The main aim of this paper is to initiate research concerning geometric construction of some power means of three or more variables. We contribute by giving methods for the geometric construction of the harmonic mean $ P_{-1} $ and the arithmetic ...

#### Some Fourier inequalities for orthogonal systems in Lorentz–Zygmund spaces

(Journal article; Peer reviewed, 2019-06-13)

A number of classical inequalities and convergence results related to Fourier coefficients with respect to unbounded orthogonal systems are generalized and complemented. All results are given in the case of Lorentz–Zygmund spaces.