Scaling laws in spherical shell dynamos with free-slip boundaries

Numerical simulations of convection driven rotating spherical shell dynamos have often been performed with rigid boundary conditions, as is appropriate for the metallic cores of terrestrial planets. Free-slip boundaries are more appropriate for dynamos in other astrophysical objects, such as gas-giants or stars. Using a set of 57 direct numerical simulations, we investigate the effect of free-slip boundary conditions on the scaling properties of heat flow, flow velocity and magnetic field strength and compare it with earlier results for rigid boundaries. We find that the nature of the mechanical boundary condition has only a minor influence on the scaling laws. We also find that although dipolar and multipolar dynamos exhibit approximately the same scaling exponents, there is an offset in the scaling pre-factors for velocity and magnetic field strength. We argue that the offset can be attributed to the differences in the zonal flow contribution between dipolar and multipolar dynamos.Comment: 10 pages, 9 figures, 1 table. To appear in ICARU

Psophos, Sonus, and Klang: Towards a Genealogy of Sound Terminology

As we think about sound and its many competing meanings and uses for musicians over the past hundred years, it is worth keeping in mind that defining sound was also a contentious problem in earlier times. Indeed, since the ancient Greeks first invoked the term psophos as a general concept for sound, there has been a persistent question of how to draw boundaries between musical sounds (covered by such sub-terms as phthongos and phoné) and more general notions of noise (klázō). The Latin term sonus was perhaps even more confusing in this regard, with a numbing variety of meanings and applications that cannot be easily reconciled. Still, one persistent demarcation that we can find in the history of the term’s usage is that between sound as an acoustical (»external«) object, and sound as a perceptible (»internal«) phenomenon. Each of these usages implies a distinctly differing aesthetic stance towards sound that has telling resonance for compositional and analytical issues that are still very much alive today. Indeed, an acoustical turn in the seventeenth and eighteenth centuries prompted music theorists to confront the perception of musical sounds more thoroughly than before as exemplified by Johann Mattheson’s little known treatise Versuch einer systematischen Klang-Lehre (1748)