Migration und Schulpolitik in Preußen-Deutschland. Ein Überblick

Migration ist in Preußen-Deutschland über Jahrhunderte kein Gegenstand von Schulpolitik gewesen. Schulpflicht gilt für die jeweiligen Staatsangehörigen bzw. für ethnisch Deutsche – Migranten galten als Störfaktor bei der Schaffung der ethnisch homogenen Nation. Erst im Kontext von EWG/EU wird Migration in der zweiten Hälfte des 20. Jahrhunderts sowohl als unvermeidbare Realität akzeptiert, als auch in schulpolitische Konzepte aufgenommen. (DIPF/Orig.)Migration has not been a topic of educational policies in Prussia-Germany for centuries. National subjects or ethnical Germans had to be schooled - migrants were considered as disturbing the building of an ethnically homogenous nation. Only the creation of the EEC/EU made migration an accepted reality and an inevitable fact for the conceptualization of educational policies in the second half of 20th century. (DIPF/Orig.

Self-induced neutrino flavor conversion without flavor mixing

Neutrino-neutrino refraction in dense media can cause self-induced flavor conversion triggered by collective run-away modes of the interacting flavor oscillators. The growth rates were usually found to be of order a typical vacuum oscillation frequency $\Delta m^2/2E$. However, even in the simple case of a $\nu_e$ beam interacting with an opposite-moving $\bar\nu_e$ beam, and allowing for spatial inhomogeneities, the growth rate of the fastest-growing Fourier mode is of order $\mu=\sqrt{2} G_{\rm F} n_{\nu}$, a typical $\nu$--$\nu$ interaction energy. This growth rate is much larger than the vacuum oscillation frequency and gives rise to flavor conversion on a much shorter time scale. This phenomenon of "fast flavor conversion" occurs even for vanishing $\Delta m^2/2E$ and thus does not depend on energy, but only on the angle distributions. Moreover, it does not require neutrinos to mix or to have masses, except perhaps for providing seed disturbances. We also construct a simple homogeneous example consisting of intersecting beams and study a schematic supernova model proposed by Ray Sawyer, where $\nu_e$ and $\bar\nu_e$ emerge with different zenith-angle distributions, the key ingredient for fast flavor conversion. What happens in realistic astrophysical scenarios remains to be understood.Comment: 17 pages, 6 figures. Minor changes and updated references. Content matches published versio

Collective neutrino flavor conversion: Recent developments

Neutrino flavor evolution in core-collapse supernovae, neutron-star mergers, or the early universe is dominated by neutrino-neutrino refraction, often spawning "self-induced flavor conversion", i.e., shuffling of flavor among momentum modes. This effect is driven by collective run-away modes of the coupled "flavor oscillators" and can spontaneously break the initial symmetries such as axial symmetry, homogeneity, isotropy, and even stationarity. Moreover, the growth rates of unstable modes can be of the order of the neutrino-neutrino interaction energy instead of the much smaller vacuum oscillation frequency: self-induced flavor conversion does not always require neutrino masses. We illustrate these newly found phenomena in terms of simple toy models. What happens in realistic astrophysical settings is up to speculation at present.Comment: 16 pages, 3 figure

Fundamental aeroelastic properties of a bend–twist coupled blade section

AbstractThe effects of bend–twist coupling on the aeroelastic modal properties and stability limits of a two-dimensional blade section in attached flow are investigated. Bend–twist coupling is introduced in the stiffness matrix of the structural blade section model. The structural model is coupled with an unsteady aerodynamic model in a linearised state–space formulation. A numerical study is performed using structural and aerodynamic parameters representative for wind turbine blades. It is shown that damping of the edgewise mode is primarily influenced by the work of the lift which is close to antiphase, making the stability of the mode sensitive to changes in the stiffness matrix. The aerodynamic forces increase the stiffness of the flapwise mode for flap–twist coupling to feather for downwind deflections. The stiffness reduces and damping increases for flap–twist to stall. Edge–twist coupling is prone to an edgetwist flutter instability at much lower inflow speeds than the uncoupled blade section. Flap–twist coupling results in a moderate reduction of the flutter speed for twist to feather and divergence for twist to stall