1,721,004 research outputs found
Quasi periodicità e uniforme continuità di semigruppi e funzioni coseno: criteri spettrali
No full textWe present some original results, concerning the relationship between the the asymptotic behavior of a semigroup of linear operators and the spectral properties of the infinitesimal generator of the semigroup, contained in the author's PhD thesis
Almost automorphic groups and semigroups
No full textIn this paper we establish that a strongly continuous group of bounded linear operators on a Banach space is weakly almost periodic if and only if it is weakly almost automorphic. The result is extended to Stepanov-type almost automorphism groups and semigroups of bounded linear
operators, suitably defined
Equicontinuous families of operators generating mean periodic maps
No full textThe existence of mean periodic functions in the sense of L. Schwartz, generated, in various ways, by an equicontinuous group U or an equicontinuous cosine function C forces the spectral structure of the infinitesimal generator of U or C. In particular, it is proved under fairly general hypotheses that the spectrum has no accumulation point and that the continuous spectrum is empty
Two-parameter estimates for joint spectral projections on complexspheres
No full textWe prove sharp two-parameter estimates for the L(p)-L(2) norm, 1 <= p <= 2, of the joint spectral projectors associated to the Laplace-Beltrami operator and to the Kohn Laplacian on the unit sphere S(2n-1) in C(n). Then, by using the notion of contraction of Lie groups, we deduce the estimates recently obtained by H. Koch and F. Ricci for joint spectral projections on the reduced Heisenberg group h(1)
Spectral properties of weakly asymptotically almost periodic semigroups in the sense of Stepanov
No full textThe spectral structure of the infinitesimal generator of strongly measurable, asymptotically S^p almost periodic semigroups is investigated
Spectral properties of weakly almost periodic cosine functions
No full textThe spectral structure of the infinitesimal generator of a strongly continuous cosine function of linear bounded operators is investigated, under assumptions on the almost periodic behaviour of applications generated, in various ways, by C. Moreover, a first approach is presented to the analysis of connection between cosine functions and dynamical systems
NORMS OF COMPLEX HARMONIC PROJECTION OPERATORS,
No full textIn this paper we estimate the (L(P) - L(2))-norm of the complex harmonic projectors pi_(ll'), for p between 1 and 2, uniformly with respect to the indexes l, l'. We provide sharp estimates both for the projectors pi_(ll'), when l, l' belong to a proper angular sector in N x N, and for the projectors pi_(l0) and pi_(0l). The proof is based on an extension of a complex interpolation argument by C. Sogge. In the appendix, we prove in a direct way the uniform boundedness; of a particular zonal kernel in the L(1) norm on the unit sphere of R(2n)
Some remarks on harmonic projection operators on spheres
Full text linkWe give a survey of recent works concerning the mapping properties of joint harmonic projection operators, mapping the space of square integrable functions on complex and quaternionic spheres onto the eigenspaces of the Laplace-Beltrami operator and of a suitably defined subLaplacian. In particular, we discuss similarities and differences between the real, the complex and the quaternionic framework
Semigroups and asymptotic mean periodicity
No full textWe investigate the spectral structure of the infinitesimal generator of an equicontinuous semigroup, giving rise to asymptotically mean periodic functions
A restriction Theorem for Métivier groups
Full text linkIn the spirit of an earlier result of D. Mueller on the Heisenberg group we prove a restriction theorem on a certain class of two step nilpotent Lie groups. Our result extends that of Mueller also in the framework of the Heisenberg group
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