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Sur le caractere gaussien de la convergence presque partout

Michel Weber — 2001

Fundamenta Mathematicae

We establish functional type inequalities linking the regularity properties of sequences of operators S = (Sₙ) acting on L²-spaces with those of the canonical Gaussian process on the associated subsets of L² defined by (Sₙ(f)), f ∈ L². These inequalities allow us to easily deduce as corollaries Bourgain's famous entropy criteria in the theory of almost everywhere convergence. They also provide a better understanding of the role of the Gaussian processes in the study of almost everywhere convergence....

Borel matrix

Michel Weber — 1995

Commentationes Mathematicae Universitatis Carolinae

We study the Borel summation method. We obtain a general sufficient condition for a given matrix A to have the Borel property. We deduce as corollaries, earlier results obtained by G. M“uller and J.D. Hill. Our result is expressed in terms belonging to the theory of Gaussian processes. We show that this result cannot be extended to the study of the Borel summation method on arbitrary dynamical systems. However, in the L p -setting, we establish necessary conditions of the same kind by using Bourgain’s...

On the convergence of moments in the CLT for triangular arrays with an application to random polynomials

Christophe CunyMichel Weber — 2006

Colloquium Mathematicae

We give a proof of convergence of moments in the Central Limit Theorem (under the Lyapunov-Lindeberg condition) for triangular arrays, yielding a new estimate of the speed of convergence expressed in terms of νth moments. We also give an application to the convergence in the mean of the pth moments of certain random trigonometric polynomials built from triangular arrays of independent random variables, thereby extending some recent work of Borwein and Lockhart.

On the supremum of random Dirichlet polynomials

Mikhail LifshitsMichel Weber — 2007

Studia Mathematica

We study the supremum of some random Dirichlet polynomials D N ( t ) = n = 2 N ε d n - σ - i t , where (εₙ) is a sequence of independent Rademacher random variables, the weights (dₙ) are multiplicative and 0 ≤ σ < 1/2. Particular attention is given to the polynomials n τ ε n - σ - i t , τ = 2 n N : P ( n ) p τ , P⁺(n) being the largest prime divisor of n. We obtain sharp upper and lower bounds for the supremum expectation that extend the optimal estimate of Halász-Queffélec, s u p t | n = 2 N ε n - σ - i t | ( N 1 - σ ) / ( l o g N ) . The proofs are entirely based on methods of stochastic processes, in particular the metric...

Convergence of series of dilated functions and spectral norms of GCD matrices

Christoph AistleitnerIstván BerkesKristian SeipMichel Weber — 2015

Acta Arithmetica

We establish a connection between the L² norm of sums of dilated functions whose jth Fourier coefficients are ( j - α ) for some α ∈ (1/2,1), and the spectral norms of certain greatest common divisor (GCD) matrices. Utilizing recent bounds for these spectral norms, we obtain sharp conditions for the convergence in L² and for the almost everywhere convergence of series of dilated functions.

On small deviations of Gaussian processes using majorizing measures

Michel J. G. Weber — 2012

Colloquium Mathematicae

We give two examples of periodic Gaussian processes, having entropy numbers of exactly the same order but radically different small deviations. Our construction is based on Knopp's classical result yielding existence of continuous nowhere differentiable functions, and more precisely on Loud's functions. We also obtain a general lower bound for small deviations using the majorizing measure method. We show by examples that our bound is sharp. We also apply it to Gaussian independent sequences and...

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