We have investigated the slow dynamics of ultrasoft particles in crystalline cluster phases, where point particles interact through the generalized exponential potential u(r) = ǫ exp[−(r/σ) n ], focusing on the cluster fcc phase of this model with n = 4. In an effort to elucidate how the mechanisms of mass transport depend on the microscopic dynamics and in order to mimic a realistic scenario in a related experiment we have performed molecular dynamics, Brownian dynamics, and Monte Carlo simulations. In molecular dynamics simulations the diffusion of particles proceeds through long-range jumps, guided by strong correlations in the momentum direction. In Monte Carlo and Brownian dynamics simulations jump events are short-ranged, reflecting the purely configurational nature of the dynamics. In contrast to what was found in models of glass-forming liquids, the effect of Newtonian and stochastic microscopic dynamics on the long-time relaxation cannot be accounted for by a temperature-independent rescaling of the time units. From the obvious qualitative discrepancies in the short time behavior between the three simulation methods and the non-trivial difference in jump length distributions, long time relaxation, and dynamic heterogeneity, we learn that a more complex modeling of the dynamics in realistic systems of ultrasoft colloids is required.

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The conceptual model of an atmospheric rotor is reexamined in the context of a valley, using data from the Terrain-Induced Rotor Experiment (T-REX) conducted in 2006 in the southern Sierra Nevada and Owens Valley, California. All T-REX cases with strong mountain-wave activity have been investigated, and four of them (IOPs 1, 4, 6, and 13) are presented in detail. Their analysis reveals a rich variety of rotorlike turbulent flow structures that may form in the valley during periods of strong cross-mountain winds. Typical flow scenarios in the valley include elevated turbulence zones, downslope flow separation at a valley inversion, turbulent interaction of in-valley westerlies and along-valley flows, and highly transient mountain waves and rotors. The scenarios can be related to different stages of the passage of midlatitude frontal systems across the region. The observations from Owens Valley show that the elements of the classic rotor concept are modulated and, at times, almost completely offset by dynamically and thermally driven processes in the valley. Strong lee-side pressure perturbations induced by large-amplitude waves, commonly regarded as the prerequisite for flow separation, are found to be only one of the factors controlling rotor formation and severe turbulence generation in the valley. Buoyancy perturbations in the thermally layered valley atmosphere appear to play a role in many of the observed cases. Based on observational evidence from T-REX, extensions to the classic rotor concept, appropriate for a long deep valley, are proposed.

To mitigate the risk of wake vortex encounters during final approach, so-called plate lines have been developed. Wake vortices generated by landing aircraft induce secondary vortices at the plates' surfaces that approach the primary vortices and trigger premature wake vortex decay. Each plate line consists of several upright plates being installed underneath the approach slope. While the plate line extends perpendicular to the flight direction, its individual plates are oriented in parallel to the runway centerline. To obtain the approval of the authorities for the installation of the plate lines at runway 16 of Vienna International Airport, the plate design had to comply with airport requirements like obstacle clearance, stability, and frangibility. During a six-month campaign, wake vortex behavior of about 9500 landings with and without plates was measured simultaneously by three lidars complemented by a comprehensive suite of meteorological instrumentation. The analysis of over 1000 measured wake vortex evolutions indicates that the plate lines reduce the lifetimes of the vortices in a safety corridor along the final approach by 22-37% depending on the aircraft type. This corresponds to a reduction of vortex circulation by about 50% for the most relevant International Civil Aviation Organization separation (Medium behind Heavy).