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Browsing by Author "Queffélec, Hervé"
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A criterion of weak compactness for operators on subspaces of Orlicz spaces [Article]
Lefèvre, Pascal; Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (Hindawi, 2008)We give a criterion of weak compactness for the operators on the MorseTransue space MΨ , the subspace of the Orlicz space LΨ generated by L∞. 
A spectral radius type formula for approximation numbers of composition operators [Article]
Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (Elsevier, 20141215)For approximation numbers an(Cφ) of composition operators Cφ on weighted analytic Hilbert spaces, including the Hardy, Bergman and Dirichlet cases, with symbol φ of uniform norm <1, we prove that limn→∞[an(Cφ)]1/n=e−1 ... 
Approximation numbers of composition operators on Hp [Article]
Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (De Gruyter Open, 201501)We give estimates for the approximation numbers of composition operators on the Hp spaces, 1 ≤ p < ∞. 
Approximation numbers of composition operators on the Dirichlet space [Article]
Lefèvre, Pascal; Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (Springer, 201504)We study the decay of approximation numbers of compact composition operators on the Dirichlet space. We give upper and lower bounds for these numbers. In particular, we improve on a result of O. ElFallah, K. Kellay, M. ... 
Approximation numbers of composition operators on the Hardy space of the infinite polydisk [Article]
Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (Springer, 201712)We study the composition operators of the Hardy space on D∞ ∩ℓ1, the ℓ1 part of the infinite polydisk, and the behavior of their approximation numbers. 
Approximation numbers of weighted composition operators [Article]
Lechner, Gandalf; Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (Elsevier, 2018)We study the approximation numbers of weighted composition operators f 7→ w · (f ◦ ϕ) on the Hardy space H2 on the unit disc. For general classes of such operators, upper and lower bounds on their approximation numbers ... 
Compact composition operators on HardyOrlicz and BergmanOrlicz spaces [Article]
Lefèvre, Pascal; Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (Springer, 201109)We construct an analytic selfmap ϕ of the unit disk and an Orlicz function Ψ for which the composition operator of symbol ϕ is compact on the HardyOrlicz space HΨ, but not on the BergmanOrlicz space BΨ. For that, we first ... 
Compact composition operators on the Dirichlet space and capacity of sets of contact points [Article]
Lefèvre, Pascal; Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (Elsevier, 20130215)We prove several results about composition operators on the Dirichlet space D⁎. For every compact set K⊆∂D of logarithmic capacity , there exists a Schur function φ both in the disk algebra A(D) and in D⁎ such that the ... 
Composition operators on HardyOrlicz spaces [Article]
Lefèvre, Pascal; Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (American Mathematical Society, 2010)We investigate composition operators on HardyOrlicz spaces when the Orlicz function Ψ grows rapidly: compactness, weak compactness, to be psumming, order bounded,..., and show how these notions behave according to the ... 
Estimates for approximation numbers of some classes of composition operators on the Hardy space [Article]
Rodríguez Piazza, Luis; Li, Daniel; Queffélec, Hervé (2013) 
Infinitesimal Carleson property for weighted measures induced by analytic selfmaps of the unit disk [Article]
Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (Springer, 201308)We prove that, for every α>−1, the pullback measure φ(Aα) of the measure dAα(z)=(α+1)(1−z2)αdA(z), where A is the normalized area measure on the unit disk D, by every analytic selfmap φ:D→D is not only an (α+2)Carleson ... 
Nevanlinna counting function and Carleson function of analytic maps [Article]
Lefèvre, Pascal; Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (Springer, 201110)We show that the maximal Nevanlinna counting function and the Carleson function of analytic selfmaps of the unit disk are equivalent, up to constants. 
On approximation numbers of composition operators [Article]
Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (Elsevier, 201204)We show that the approximation numbers of a compact composition operator on the weighted Bergman spaces Bα of the unit disk can tend to 0 arbitrarily slowly, but that they never tend quickly to 0: they grow at ... 
On some random thin sets of integers [Article]
Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (American Mathematical Society, 200801)We show how different random thin sets of integers may have different behaviour. First, using a recent deviation inequality of Boucheron, Lugosi and Massart, we give a simpler proof of one of our results in Some new thin ... 
Some examples of compact composition operators on H2 [Article]
Lefèvre, Pascal; Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (Elsevier, 20081201)We construct, in an essentially explicit way, various composition operators on H2 and study their compactness or their membership in the Schatten classes. We construct: noncompact composition operators on H2 whose symbols ... 
Some new properties of composition operators associated with lens maps [Article]
Lefèvre, Pascal; Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (Springer, 201305)We give examples of results on composition operators connected with lens maps. The first two concern the approximation numbers of those operators acting on the usual Hardy space H2. The last ones are connected with ... 
Some new thin sets of integers in harmonic analysis [Article]
Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (Springer, 200212)We randomly construct various subsets A of the integers which have both smallness and largeness properties. They are small since they are very close, in various senses, to Sidon sets: the continuous functions with spectrum ... 
Some revisited results about composition operators on Hardy spaces [Article]
Lefèvre, Pascal; Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (European Mathematical Society, 2012)We generalize, on one hand, some results known for composition operators on Hardy spaces to the case of HardyOrlicz spaces HΨ: construction of a “slow” Blaschke product giving a noncompact composition operator on ... 
Some translationinvariant Banach function spaces which contain C0 [Article]
Lefèvre, Pascal; Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (Polish Academy of Sciences, Institute of Mathematics, 2004)We produce several situations where some natural subspaces of classical Banach spaces of functions over a compact abelian group contain the space c0. 
The canonical injection of the HardyOrlicz space HΨ into the Bergman–Orlicz space BΨ [Article]
Lefèvre, Pascal; Li, Daniel; Queffélec, Hervé; Rodríguez Piazza, Luis (Polish Academy of Sciences, Institute of Mathematics, 2011)We study the canonical injection from the HardyOrlicz space HΨ into the Bergman–Orlicz space BΨ..