12,426 research outputs found
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 phoneÌ) and more general notions of noise (klaÌzoÌ). 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 termâs 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 Matthesonâs little known treatise Versuch einer systematischen Klang-Lehre (1748)
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