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Tengiz Kopaliani

Publications and source records attributed to Tengiz Kopaliani.

14 recordsLinked to original sources
arXiv2026

Double phase meets Muckenhoupt

In this paper we generalize the famous result of [FKS] to the double phase model. In particular, we work with minimal assumptions on the modulating coefficient by introducing a Muckenhoupt-type condition on generalized Orlicz spaces. We develop a complete theory equivalent to that of classical Muckenhoupt weights, including the boundedness of the maximal operator and Sobolev-Poincare estimates. We combine this with the De~Giorgi technique to show Hölder continuity of the solutions.

math.AP↗
arXiv2025

Vilenkin-Fourier series in variable Lebesgue spaces

Let $S_{n}f$ denote the $n$th partial sum of the Vilenkin-Fourier series of a function $f \in L^{1}(G)$. For $1 < p_{-} \leq p_{+} < \infty$, we characterize all exponents $p(\cdot)$ for which the convergence of $S_{n}f$ to $f$ in $L^{p(\cdot)}(G)$ holds whenever $f \in L^{p(\cdot)}(G)$.

math.FA↗
arXiv2025

Maximal operator on variable exponent spaces

We explore the boundedness of the Hardy-Littlewood maximal operator $M$ on variable exponent spaces. Our findings demonstrate that the Muckenhoupt condition, in conjunction with Nekvinda's decay condition, implies the boundedness of $M$ even for unbounded exponents. This extends the results of Lerner, Cruz-Uribe and Fiorenza for bounded exponents. We also introduce a novel argument that allows approximate unbounded exponents by bounded ones while preserving the Muckenhoupt and Nekvinda conditions.

math.FA↗
arXiv2024

On the embedding between the variable Lebesgue space $L^{p(\cdot)}(Ω)$ and the Orlicz space $L(\log L)^α(Ω)$

We give a sharp sufficient condition on the distribution function, $|\{x\in Ω:\,p(x)\leq 1+λ\}|$, $λ>0$, of the exponent function $p(\cdot): Ω\to [1,\infty)$ that implies the embedding of the variable Lebesgue space $L^{p(\cdot)}(Ω)$ into the Orlicz space $L(\log L)^α(Ω)$, $α>0$, where $Ω$ is an open set with finite Lebesgue measure. As applications of our results, we first give conditions that imply the strong differentiation of integrals of functions in $L^{p(\cdot)}((0,1)^{n})$, $n>1$. We then consider the integrability of the maximal function on variable Lebesgue spaces, where the exponent function $p(\cdot)$ approaches $1$ in value on some part of the domain. This result is an improvement of the result in~\cite{CUF2}.

math.CA↗
arXiv2020

On singular extensions of continuous functionals from C([0,1]) to variable Lebesgue spaces

Valadier and Hensgen proved independently that the restriction of functional $ϕ(x)=\int_{0}^{1}x(t)dt,\,\,x\in L^{\infty}([0,1])$ on the space of continuous functions $C([0,1])$ admits a singular extension back to the whole space $L^{\infty}([0,1]).$ Some general results in this direction for the Banach lattices were obtained by Abramovich and Wickstead. In present note we investigate analogous problem for variable exponent Lebesgue spaces, namely we prove that if the space of continuous functions $C([0,1])$ is closed subspace in $L^{p(\cdot)}([0,1]),$ then every bounded linear functional on $C([0,1])$ is the restriction of a singular linear functional on $L^{p(\cdot)}([0,1])$.

math.FA↗
arXiv2020

divergent Fourier series in function spaces near $L^1[0;1]$

In this paper we generalize Bochkariev's theorem, which states that for any uniformly bounded orthonormal system $Φ$, there exists a Lebesgue integrable function such that the Fourier series of it with respect to system $Φ$ diverge on the set of positive measure. We characterize the class of variable exponent Lebesgue spaces $L^{p(\cdot)}[0;1]$, $1<p(x)<\infty$ a.e. on [0;1], such that above mentioned Bochkarev's theorem is valid.

math.FA↗
arXiv2017

Construction of function spaces close to $L^\infty$ with associate space close to $L^1$

The paper introduces a variable exponent space $X$ which has in common with $L^{\infty}([0,1])$ the property that the space $C([0,1])$ of continuous functions on $[0,1]$ is a closed linear subspace in it. The associate space of $X$ contains both the Kolmogorov and the Marcinkiewicz examples of functions in $L^{1}$ with a.e. divergent Fourier series.

math.FA↗
arXiv2017

Characterization of interpolation between Grand, small or classical Lebesgue spaces

In this paper, we show that the interpolation spaces between Grand, small or classical Lebesgue are so called Lorentz-Zygmund spaces or more generally $GΓ$-spaces. As a direct consequence of our results any Lorentz-Zygmund space $L^{a,r}({\rm Log}\, L)^β$, is an interpolation space in the sense of Peetre between either two Grand Lebesgue spaces or between two small spaces provided that $ 1<a<\infty, β\not= 0$. The method consists in computing the so called K-functional of the interpolation space and in identifying the associated norm.

math.FA↗
arXiv2014

Hardy-Littlewood Maximal Operator And $BLO^{1/\log}$ Class of Exponents

It is well known that if Hardy-Littlewood maximal operator is bounded in space $L^{p(\cdot)}[0;1]$ then $1/p(\cdot)\in BMO^{1/\log}$. On the other hand if $p(\cdot)\in BMO^{1/\log},$ ($1 0$ such that Hardy-Littlewood maximal operator is bounded in $L^{p(\cdot)+c}[0;1].$ Also There exists exponent $p(\cdot)\in BMO^{1/\log},$ ($1<p_{-}\leq p_{+}<\infty$) such that Hardy-Littlewood maximal operator is not bounded in $L^{p(\cdot)}[0;1]$. In the present paper we construct exponent $p(\cdot),$ $(1<p_{-}\leq p_{+}<\infty)$, $1/p(\cdot)\in BLO^{1/\log}$ such that Hardy-Littlewood maximal operator is not bounded in $L^{p(\cdot)}[0;1]$.

math.CA↗
arXiv2014

On the upper and lower estimates of norms in variable exponent spaces

In the present paper we investigate some geometrical properties of the norms in Banach function spaces. Particularly there is shown that if exponent $1/p(\cdot)$ belongs to $BLO^{1/\log}$ then for the norm of corresponding variable exponent Lebesgue space we have the following lower estimate $$\left\|\sum χ_{Q}\|fχ_{Q}\|_{p(\cdot)}/\|χ_{Q}\|_{p(\cdot)}\right\|_{p(\cdot)}\leq C\|f\|_{p(\cdot)}$$ where $\{Q\}$ defines disjoint partition of $[0;1]$. Also we have constructed variable exponent Lebesgue space with above property which does not possess following upper estimation $$\|f\|_{p(\cdot)}\leq C\left\|\sum χ_{Q}\|fχ_{Q}\|_{p(\cdot)}/\|χ_{Q}\|_{p(\cdot)}\right\|_{p(\cdot)}. $$

math.FA↗
arXiv2013

Some estimates for imaginary powers of the Laplace operator in variable Lebesgue spaces and applications

In this paper we study some estimates of norms in variable exponent Lebesgue spaces for a singular integral operators that are imaginary powers of the Laplace operator in $\R^n$. Using Mellin transform argument, from this estimates we obtain boundedness for a family of maximal operators in variable exponent Lebesgue spaces, which are closely related to the (weak) solution of the wave equation.42B25, 42B20, 46E30, 44A10, 42B10, 35L05

math.AP↗
arXiv2013

Local Hardy-Littlewood maximal opeator in variable Lebesgue spaces

We investigate the class $\mathcal{B}^{loc}(\mathbb{R}^{n})$ of exponents $p(\cdot)$ for with local Hardy-Littlewood maximal operator is bounded in $L^{p(\cdot)}(\mathbb{R}^{n})$ space. Littlewood-Paley square-function characterization of $L^{p(\cdot)}(\mathbb{R}^{n})$ spaces with the above class of exponent are also obtained.

math.FA↗