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Some remarks on quasi-Cohen sets

Pascal Lefèvre, Daniel Li (2001)

Colloquium Mathematicae

We are interested in Banach space geometry characterizations of quasi-Cohen sets. For example, it turns out that they are exactly the subsets E of the dual of an abelian compact group G such that the canonical injection C ( G ) / C E c ( G ) L ² E ( G ) is a 2-summing operator. This easily yields an extension of a result due to S. Kwapień and A. Pełczyński. We also investigate some properties of translation invariant quotients of L¹ which are isomorphic to subspaces of L¹.

Some results about the Henstock-Kurzweil Fourier transform

Francisco J. Mendoza Torres, Juan A. Escamilla Reyna, Salvador Sánchez Perales (2009)

Mathematica Bohemica

We consider the Fourier transform in the space of Henstock-Kurzweil integrable functions. We prove that the classical results related to the Riemann-Lebesgue lemma, existence and continuity are true in appropriate subspaces.

Spectra of elements in the group ring of SU(2)

Alex Gamburd, Dmitry Jakobson, Peter Sarnak (1999)

Journal of the European Mathematical Society

We present a new method for establishing the ‘‘gap” property for finitely generated subgroups of SU ( 2 ) , providing an elementary solution of Ruziewicz problem on S 2 as well as giving many new examples of finitely generated subgroups of SU ( 2 ) with an explicit gap. The distribution of the eigenvalues of the elements of the group ring 𝐑 [ SU ( 2 ) ] in the N -th irreducible representation of SU ( 2 ) is also studied. Numerical experiments indicate that for a generic (in measure) element of 𝐑 [ SU ( 2 ) ] , the “unfolded” consecutive spacings...

Spectral decompositions and harmonic analysis on UMD spaces

Earl Berkson, T. Gillespie (1994)

Studia Mathematica

We develop a spectral-theoretic harmonic analysis for an arbitrary UMD space X. Our approach utilizes the spectral decomposability of X and the multiplier theory for L X p to provide on the space X itself analogues of the classical themes embodied in the Littlewood-Paley Theorem, the Strong Marcinkiewicz Multiplier Theorem, and the M. Riesz Property. In particular, it is shown by spectral integration that classical Marcinkiewicz multipliers have associated transforms acting on X.

Spectral decompositions, ergodic averages, and the Hilbert transform

Earl Berkson, T. A. Gillespie (2001)

Studia Mathematica

Let U be a trigonometrically well-bounded operator on a Banach space , and denote by ( U ) n = 1 the sequence of (C,2) weighted discrete ergodic averages of U, that is, ( U ) = 1 / n 0 < | k | n ( 1 - | k | / ( n + 1 ) ) U k . We show that this sequence ( U ) n = 1 of weighted ergodic averages converges in the strong operator topology to an idempotent operator whose range is x ∈ : Ux = x, and whose null space is the closure of (I - U). This result expands the scope of the traditional Ergodic Theorem, and thereby serves as a link between Banach space spectral theory and...

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