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1.
In this paper we study the boundedness of composition operators on the weighted Bergman spaces and the Hardy space over the polydisc Dn. Studying the volume of sublevel sets we show for which n the necessary conditions obtained by Bayart are sufficient. For arbitrary polydisc we prove the rank sufficiency theorem which, in particular, provides us with a simple criterion describing boundedness of composition operators on the spaces over the bidisc. Such a consistent characterization is obtained for the classical Bergman space over the tridisc.  相似文献   

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We study multivariate approximation of periodic functions in the worst case setting with the error measured in the L norm. We consider algorithms that use standard information Λstd consisting of function values or general linear information Λall consisting of arbitrary continuous linear functionals. We investigate equivalences of various notions of algebraic and exponential tractability for Λstd and Λall under the absolute or normalized error criterion, and show that the power of Λstd is the same as the one of Λall for various notions of algebraic and exponential tractability. Our results can be applied to weighted Korobov spaces and Korobov spaces with exponential weights. This gives a special solution to Open Problem 145 as posed by Novak and Woźniakowski (2012) [40].  相似文献   

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We extend Feichtinger's minimality property on the smallest non-trivial time-frequency shift invariant Banach space, to the quasi-Banach case. Analogous properties are deduced for certain matrix spaces.We use these results to prove that the pseudo-differential operator Op(a) is a Schatten-q operator from M to Mp and r-nuclear operator from M to Mr when aMr for suitable p, q and r in (0,].  相似文献   

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We extend the notions of p-convexity and p-concavity for Banach ideals of measurable functions following an asymptotic procedure. We prove a representation theorem for the spaces satisfying both properties as the one that works for the classical case: each almost p-convex and almost p-concave space is order isomorphic to an almost-Lp-space. The class of almost-Lp-spaces contains, in particular, direct sums of (infinitely many) Lp-spaces with different norms, that are not in general p-convex – nor p-concave –. We also analyze in this context the extension of the Maurey–Rosenthal factorization theorem that works for p-concave operators acting in p-convex spaces. In this way we provide factorization results that allow to deal with more general factorization spaces than Lp-spaces.  相似文献   

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Given a commutative ring A and a finitely generated ideal I, we prove that I-torsion A-modules that are also I-adically complete (or merely derived I-complete) must have bounded I-torsion, i.e., they are killed by In for some n0.  相似文献   

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For a closed symplectic manifold (M,ω) with compatible Riemannian metric g we study the Sobolev H1 geometry of the group of all Hs diffeomorphisms on M which preserve the symplectic structure. We show that, for sufficiently large s, the H1 metric admits globally defined geodesics and the corresponding exponential map is a non-linear Fredholm map of index zero. Finally, we show that the H1 metric carries conjugate points via some simple examples.  相似文献   

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We prove that any weak* continuous semigroup (Tt)t?0 of factorizable Markov maps acting on a von Neumann algebra M equipped with a normal faithful state can be dilated by a group of Markov ?-automorphisms analogous to the case of a single factorizable Markov operator, which is an optimal result. We also give a version of this result for strongly continuous semigroups of operators acting on noncommutative Lp-spaces and examples of semigroups to which the results of this paper can be applied. Our results imply the boundedness of the McIntosh's H functional calculus of the generators of these semigroups on the associated noncommutative Lp-spaces generalising some previous work from Junge, Le Merdy and Xu. Finally, we also give concrete dilations for Poisson semigroups which are even new in the case of Rn.  相似文献   

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In this paper, we introduce the Fock space on C and obtain an isomorphism between the Fock space on C and Bose-Fock space. Based on this isomorphism, we obtain representations of some operators on the Bose-Fock space and answer a question in [2]. As a physical application, we study the Gibbs state.  相似文献   

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This paper is twofold. The first part aims to study the long-time asymptotic behavior of solutions to the heat equation on Riemannian symmetric spaces G/K of noncompact type and of general rank. We show that any solution to the heat equation with bi-K-invariant L1 initial data behaves asymptotically as the mass times the fundamental solution, and provide a counterexample in the non bi-K-invariant case. These answer problems recently raised by J.L. Vázquez. In the second part, we investigate the long-time asymptotic behavior of solutions to the heat equation associated with the so-called distinguished Laplacian on G/K. Interestingly, we observe in this case phenomena which are similar to the Euclidean setting, namely L1 asymptotic convergence with no bi-K-invariance condition and strong L convergence.  相似文献   

17.
In this paper, we construct new families of flag-transitive linear spaces with q2n points and q2 points on each line that admit a one-dimensional affine automorphism group. We achieve this by building a natural connection with permutation polynomials of Fq2 of a particular form and following the scheme of Pauley and Bamberg in (2008) [14].  相似文献   

18.
Let p be an odd prime, and λ be a nonzero element of the finite field Fpm. The λ-constacyclic codes of length 2ps over Fpm are classified as the ideals of quotient ring Fpm[x]x2ps?λ in terms of their generator polynomials. Based on these generator polynomials, the symbol-pair distances of all such λ-constacyclic codes of length 2ps are obtained in this paper. As an application, all MDS symbol-pair constacyclic codes of length 2ps over Fpm are established, which produce many new MDS symbol-pair codes with good parameters.  相似文献   

19.
A new a priori estimate for solutions to Navier–Stokes equations is derived. Uniqueness and existence of these solutions in R3 for all t>0 is proved in a class of solutions locally differentiable in time with values in H1(R3), where H1(R3) is the Sobolev space. By the solution a solution to an integral equation is understood. No smallness restrictions on the data are imposed.  相似文献   

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