Non-parallel effects which are due to the growing boundary layer are investigated by direct numerical integration of the complete Navier-Stokes equations for incompressible flows. The problem formulation is spatial, i.e. disturbances may grow or decay in the downstream direction as in the physical experiments. In the past various non-parallel theories were published that differ considerably from each other in both approach and interpretation of the results. In this paper a detailed comparison of the Navier-Stokes calculation with the various non-parallel theories is provided. It is shown, that the good agreement of some of the theories with experiments is fortuitous and that the difference between experiments and theories concerning the branch I neutral location cannot be explained by non-parallel effects.
The dephasing of optically prepared k:::::Q triplet excitons in crystalline (1,4)-dibromonaphlhalene (DBN) has been investigated by measurement of the temperature dependence of the absorption line shape. At temperatures below 10 K the dephasing is due to scattering of the exciton by impurities or lattice defects. We show that the naturally occurring l3C containing DBN molecules can make a significant contribution to this linewidth. Above 10 K the excitons are scattered by optical phonons. The most likely exciton-phonon scattering process is shown to involve a single phonon scattering of the exciton between the two crystallographically inequivalent sites.
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