Browsing by Author "Sparber, Christof"

Now showing 1 - 3 of 3
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    High-frequency averaging in semi-classical Hartree-type equations
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2009) Giannoulis, Johannes; Mielke, Alexander; Sparber, Christof
    We investigate the asymptotic behavior of solutions to semi-classical Schröodinger equations with nonlinearities of Hartree type. For a weakly nonlinear scaling, we show the validity of an asymptotic superposition principle for slowly modulated highly oscillatory pulses. The result is based on a high-frequency averaging effect due to the nonlocal nature of the Hartree potential, which inhibits the creation of new resonant waves. In the proof we make use of the framework of Wiener algebras.
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    Interaction of modulated pulses in the nonlinear Schrödinger equation with periodic potential
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2007) Giannoulis, Johannes; Mielke, Alexander; Sparber, Christof
    We consider a cubic nonlinear Schrödinger equation with periodic potential. In a semiclassical scaling the nonlinear interaction of modulated pulses concentrated in one or several Bloch bands is studied. The notion of closed mode systems is introduced which allows for the rigorous derivation of a finite system of amplitude equations describing the macroscopic dynamics of these pulses.
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    Thermal effects in gravitational Hartree systems
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2010) Aki, Gonca L.; Dolbeault, Jean; Sparber, Christof
    We consider the non-relativistic Hartree model in the gravitational case, i.e. with attractive Coulomb-Newton interaction. For a given mass $M>0$, we construct stationary states with non-zero temperature T by minimizing the corresponding free energy functional. It is proved that minimizers exist if and only if the temperature of the system is below a certain threshold T^*>0 (possibly infinite), which itself depends on the specific choice of the entropy functional. We also investigate whether the corresponding minimizers are mixed or pure quantum states and characterize a critical temperature T_c in (0, T^*) above which mixed states appear.