scholarly journals Non-linear evolution of the angular momentum of protostructures from tidal torques

1996 ◽  
Vol 282 (2) ◽  
pp. 455-469 ◽  
Author(s):  
P. Catelan ◽  
T. Theuns
Keyword(s):  
Angular Momentum ◽  
Linear Evolution ◽  
Non Linear ◽  
Tidal Torques

scholarly journals Angular momentum transport, layering, and zonal jet formation by the GSF instability: non-linear simulations at a general latitude

2020 ◽  
Vol 495 (1) ◽  
pp. 1468-1490
Author(s):  
A J Barker ◽  
C A Jones ◽  
S M Tobias
Keyword(s):  
Angular Momentum ◽  
Linear Instability ◽  
Momentum Transport ◽  
Boussinesq Model ◽  
Angular Momentum Transport ◽  
Hot Jupiters ◽  
Linear Evolution ◽  
Non Linear ◽  
Red Giant ◽  
Subgiant Stars

ABSTRACT We continue our investigation into the non-linear evolution of the Goldreich–Schubert–Fricke (GSF) instability in differentially rotating radiation zones. This instability may be a key player in transporting angular momentum in stars and giant planets, but its non-linear evolution remains mostly unexplored. In a previous paper we considered the equatorial instability, whereas here we simulate the instability at a general latitude for the first time. We adopt a local Cartesian Boussinesq model in a modified shearing box for most of our simulations, but we also perform some simulations with stress-free, impenetrable, radial boundaries. We first revisit the linear instability and derive some new results, before studying its non-linear evolution. The instability is found to behave very differently compared with its behaviour at the equator. In particular, here we observe the development of strong zonal jets (‘layering’ in the angular momentum), which can considerably enhance angular momentum transport, particularly in axisymmetric simulations. The jets are, in general, tilted with respect to the local gravity by an angle that corresponds initially with that of the linear modes, but which evolves with time and depends on the strength of the flow. The instability transports angular momentum much more efficiently (by several orders of magnitude) than it does at the equator, and we estimate that the GSF instability could contribute to the missing angular momentum transport required in both red giant and subgiant stars. It could also play a role in the long-term evolution of the solar tachocline and the atmospheric dynamics of hot Jupiters.

scholarly journals Non-linear evolution of step meander during growth of a vicinal surface with no desorption

2000 ◽  
Vol 18 (3) ◽  
pp. 519-534 ◽  
Author(s):  
F. Gillet ◽  
O. Pierre-Louis ◽  
C. Misbah
Keyword(s):  
Vicinal Surface ◽  
Linear Evolution ◽  
Non Linear

Linguaggio e antropogenesi in G.H. Mead

PARADIGMI ◽  
2009 ◽  
pp. 145-156
Author(s):  
Emanuela Fadda
Keyword(s):  
Morphological Change ◽  
Joint Action ◽  
Social Relation ◽  
Adaptive Skills ◽  
Social Thinking ◽  
Linear Evolution ◽  
Non Linear ◽  
Great Relevance

- Language phylogenesis is often presented as a matter of controversy between followers of continuity vs discontinuity theories of development. Both kinds of theory may be described as projects for mind naturalization. However, the latter seems better to agree with recent paleo-anthropological data, which hint at a non-linear evolution, with no sudden morphological change. The paper presents an account of G. H. Mead's theory which is surprisingly modern and of great relevance for present debates, as it describes the emergence of language as the joint action of adaptive skills already present in nature. Taking sociality as a biological universal, operating in different forms and degrees, Mead can trace the path from more elementary forms of social relation to the most complex and abstract tools of social thinking, typical of human communities.Keywords: Phylogeny of language, Mind, Society, Biology, Subject, Communication.Parole chiave: Filogenesi del linguaggio, Mente, Socialitŕ, Biologia, Soggettivitŕ, Comunicazione

scholarly journals Non-linear evolution of the resonant drag instability in magnetized gas

2019 ◽  
Vol 485 (3) ◽  
pp. 3991-3998 ◽  
Author(s):  
Darryl Seligman ◽  
Philip F Hopkins ◽  
Jonathan Squire
Keyword(s):  
Linear Theory ◽  
Coherent Structures ◽  
Magnetic Energy ◽  
Density Fluctuations ◽  
Linear Evolution ◽  
Drag Forces ◽  
Non Linear ◽  
Magnetohydrodynamic Simulations ◽  
First Time ◽  
Different Parts

Abstract We investigate, for the first time, the non-linear evolution of the magnetized ‘resonant drag instabilities’ (RDIs). We explore magnetohydrodynamic simulations of gas mixed with (uniform) dust grains subject to Lorentz and drag forces, using the gizmo code. The magnetized RDIs exhibit fundamentally different behaviour than purely acoustic RDIs. The dust organizes into coherent structures and the system exhibits strong dust–gas separation. In the linear and early non-linear regime, the growth rates agree with linear theory and the dust self-organizes into 2D planes or ‘sheets.’ Eventually the gas develops fully non-linear, saturated Alfvénic, and compressible fast-mode turbulence, which fills the underdense regions with a small amount of dust, and drives a dynamo that saturates at equipartition of kinetic and magnetic energy. The dust density fluctuations exhibit significant non-Gaussianity, and the power spectrum is strongly weighted towards the largest (box scale) modes. The saturation level can be understood via quasi-linear theory, as the forcing and energy input via the instabilities become comparable to saturated tension forces and dissipation in turbulence. The magnetized simulation presented here is just one case; it is likely that the magnetic RDIs can take many forms in different parts of parameter space.

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