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We expose analogies between turbulence in a fluid heated from below (Rayleigh-Bénard (RB) flow) and shear flows: The unifying theory for RB flow (S.Grossmann and D.Lohse, J.Fluid Mech. 407, 27-56 (2000) and subsequent refinements) can be extended to the flow between rotating cylinders (Taylor-Couette flow) and pipe flow. We identify wind dissipation rates and momentum fluxes that are analogous to the dissipation rate and heat flux in RB flow. The proposed unifying description for the three cases is consistent with the experimental data.
Aside from the increasing, impressive evidence on chemical identification of graded molecules involved, it is the capability of axons for approaching the target position from different aspects in a two-dimensional field which is per se a strong indication for the involvement of gradients. Targeting requires, in the target field, counter-graded effects, either by antagonistic gradients, or by a single gradient in each dimension exerting attractive effects at low, reverting to inhibitory (repulsive) effects at high concentrations. A further requirement for mapping is the modulation of the counter-graded effects by components of the growth cone itself which depends on the origin of the corresponding axon.Transduction and processing of graded signals in the navigating growth cones are proposed to be strongly enhanced by intra-growth-cone pattern formation. The concept also encompasses regulatory and branching processes including the formation of the terminal arbors.
Alexander von Humboldt’s descriptions of volcanic mountains in his travel journals (Reise auf dem Río Magdalena, durch die Anden und Mexico) show both his reliance on and impatience with literary conventions and travel narratives. Using Goethe’s Italienische Reise and Bürger’s Münchhausen as points of comparison for literary treatments of the volcano ascent, Humboldt’s process of writing is examined. Humboldt shows the failure of the existing discourse and begins to experiment with narratives which fragment and recombine personal and historical modes of writing with, in this case, images from new technical inventions which visualize landscape according to fundamental scientific principles. While the inclusion of scientific prose is relevant, Humboldt’s link to modernity is based on experimental narrative techniques which draw upon changing sets of discourse practices to describe complex realities.