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On definitions of superharmonic functions

Seizô Itô (1975)

Annales de l'institut Fourier

Let A be an elliptic differential operator of second order with variable coefficients. In this paper it is proved that any A -superharmonic function in the Riesz-Brelot sense is locally summable and satisfies the A -superharmonicity in the sense of Schwartz distribution.

On discrepancy theorems with applications to approximation theory

Hans-Peter Blatt (1995)

Banach Center Publications

We give an overview on discrepancy theorems based on bounds of the logarithmic potential of signed measures. The results generalize well-known results of P. Erdős and P. Turán on the distribution of zeros of polynomials. Besides of new estimates for the zeros of orthogonal polynomials, we give further applications to approximation theory concerning the distribution of Fekete points, extreme points and zeros of polynomials of best uniform approximation.

On essential norm of the Neumann operator

Dagmar Medková (1992)

Mathematica Bohemica

One of the classical methods of solving the Dirichlet problem and the Neumann problem in 𝐑 m is the method of integral equations. If we wish to use the Fredholm-Radon theory to solve the problem, it is useful to estimate the essential norm of the Neumann operator with respect to a norm on the space of continuous functions on the boundary of the domain investigated, where this norm is equivalent to the maximum norm. It is shown in the paper that under a deformation of the domain investigated by a diffeomorphism,...

On exit laws for semigroups in weak duality

Imed Bachar (2001)

Commentationes Mathematicae Universitatis Carolinae

Let : = ( P t ) t > 0 be a measurable semigroup and m a σ -finite positive measure on a Lusin space X . An m -exit law for is a family ( f t ) t > 0 of nonnegative measurable functions on X which are finite m -a.e. and satisfy for each s , t > 0 P s ...

On exit laws for subordinated semigroups by means of 𝒞 1 -subordinators

Mohamed Hmissi, Ezzedine Mliki (2010)

Commentationes Mathematicae Universitatis Carolinae

We study the integral representation of potentials by exit laws in the framework of sub-Markovian semigroups of bounded operators acting on L 2 ( m ) . We mainly investigate subordinated semigroups in the Bochner sense by means of 𝒞 1 -subordinators. By considering the one-sided stable subordinators, we deduce an integral representation for the original semigroup.

On extensions of the Mittag-Leffler theorem

Ewa Ligocka (1998)

Annales Polonici Mathematici

The classical Mittag-Leffler theorem on meromorphic functions is extended to the case of functions and hyperfunctions belonging to the kernels of linear partial differential operators with constant coefficients.

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