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Úterý, 06.02.2018 15:00

Apostolos Apostolakis (Department of Condensed Matter Theory, Institute of Physics, Czech Acad. of Sci.)

Abstract: We study the nonlinear dynamics and band transport in a semiconductor superlattice driven by a high-frequency acoustic plane wave. The transport characteristics of the system are investigated by using exact path-integral solutions of the Boltzmann transport equation. We show that electron drift and averaged velocities have strongly non-monotonic behavior induced by changing the amplitude of the acoustic wave. These nontrivial kinetic features are associated to some global bifurcations arising in connection with the variation of the control parameter. They cause...

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Pondělí, 12.02.2018 14:00

Roberto Oliveri (Université Libre de Bruxelles)

We define multipole moments for an arbitrary theory of gravity in terms of canonical Noether charges associated with specific residual transformations in canonical harmonic gauge, which we call multipole symmetries. We show that our definition exactly matches Thorne's mass and current multipole moments in Einstein gravity. For radiative configurations, the total multipole charges -- including the contributions from the source and the radiation -- are given by surface charges at spatial infinity. The conservation of total multipole charges is used to derive the variation of source multipole...

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