Displaying similar documents to “Uniformly convex operators and martingale type.”

A quantitative version of Krein's theorem.

M. Fabian, P. Hájek, V. Montesinos, V. Zizler (2005)

Revista Matemática Iberoamericana

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A quantitative version of Krein's Theorem on convex hulls of weak compact sets is proved. Some applications to weakly compactly generated Banach spaces are given.

A generalized sharp Whitney theorem for jets.

Charles Fefferman (2005)

Revista Matemática Iberoamericana

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Suppose that, for each point x in a given subset E ⊂ R, we are given an m-jet f(x) and a convex, symmetric set σ(x) of m-jets at x. We ask whether there exist a function F ∈ C(R) and a finite constant M, such that the m-jet of F at x belongs to f(x) + Mσ(x) for all x ∈ E. We give a necessary and sufficient condition for the existence of such F, M, provided each σ(x) satisfies a condition that we call "Whitnet w-convexity".

SAK principle for a class of Grushin-type operators.

Lidia Maniccia, Marco Mughetti (2006)

Revista Matemática Iberoamericana

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We prove Fefferman's SAK Principle for a class of hypoelliptic operators on R whose nonnegative symbol vanishes anisotropically on the characteristic manifold.

Time-frequency analysis of Sjöstrand's class.

Karlheinz Gröchenig (2006)

Revista Matemática Iberoamericana

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We investigate the properties an exotic symbol class of pseudodifferential operators, Sjöstrand's class, with methods of time-frequency analysis (phase space analysis). Compared to the classical treatment, the time-frequency approach leads to striklingly simple proofs of Sjöstrand's fundamental results and to far-reaching generalizations.

Superposition operators and functions of bounded p-variation.

Gérard Bourdaud, Massimo Lanza de Cristoforis, Winfried Sickel (2006)

Revista Matemática Iberoamericana

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We characterize the set of all functions f of R to itself such that the associated superposition operator T: g → f º g maps the class BV (R) into itself. Here BV (R), 1 ≤ p < ∞, denotes the set of primitives of functions of bounded p-variation, endowed with a suitable norm. It turns out that such an operator is always bounded and sublinear. Also, consequences for the boundedness of superposition operators defined on Besov spaces B ...

Multi-parameter paraproducts.

Camil Muscalu, Jill Pipher, Terence Tao, Christoph Thiele (2006)

Revista Matemática Iberoamericana

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We prove that classical Coifman-Meyer theorem holds on any polidisc T or arbitrary dimension d ≥ 1.