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Motivated by recent observational searches of sub-structure in starless molecular cloud cores, we investigate the evolution of density perturbations on scales smaller than the Jeans length embedded in contracting isothermal clouds, adopting…

Solar and Stellar Astrophysics · Physics 2017-12-20 C. Toci , D. Galli , A. Verdini , L. Del Zanna , S. Landi

Here we investigate the contribution of surface Alfven wave damping to the heating of the solar wind in minima conditions. These waves are present in regions of strong inhomogeneities in density or magnetic field (e. g., the border between…

Solar and Stellar Astrophysics · Physics 2015-05-14 R. M. Evans , M. Opher , V. Jatenco-Pereira , T. I. Gombosi

Aims: This paper presents 2.5D numerical experiments of Alfv\'en wave phase mixing and aims to assess the effects of nonlinearities on wave behaviour and dissipation. In addition, this paper aims to quantify how effective the model…

Solar and Stellar Astrophysics · Physics 2019-04-17 Alexander Prokopyszyn , Alan Hood , Ineke De Moortel

Stars form inside molecular cloud filaments from the competition of gravitational forces with turbulence and magnetic fields. The exact orientation of these filaments with the magnetic fields depends on the strength of these fields, the…

This is a brief review of the main results of our recent studies of the nonlinear evolution of the small-scale MHD dynamo in the high-Prandtl-number regime and of the structure of the resulting saturated state of the isotropic homogeneous…

Astrophysics · Physics 2007-05-23 A. A. Schekochihin , S. C. Cowley , G. W. Hammett , J. L. Maron , J. C. McWilliams

A pair of nonlinear diffusion equations in Fourier space} is used to study the dynamics of strong Alfv\'en-wave turbulence, from MHD to electron scales. Special attention is paid to the regime of imbalance between the energies of…

Plasma Physics · Physics 2019-12-12 George Miloshevich , Thierry Passot , Pierre-Louis Sulem

We employ the first fully three-dimensional simulation to study the role of magnetic fields and ion-neutral friction in regulating gravitationally-driven fragmentation of molecular clouds. The cores in an initially subcritical cloud develop…

Astrophysics · Physics 2008-11-26 Takahiro Kudoh , Shantanu Basu , Youichi Ogata , Takashi Yabe

Hydrodynamic stability has been a longstanding issue for the cloud model of the broad line region in active galactic nuclei. We argue that the clouds may be gravitationally bound to the supermassive black hole. If true, stabilisation by…

Astrophysics of Galaxies · Physics 2015-06-05 Martin Krause , Marc Schartmann , Andreas Burkert

The modulation of the intensity of microwave emission from a plasma slab caused by a standing linear kink fast magnetoacoustic wave is considered. The slab is stretched along a straight magnetic field, and can represent, for example, a…

Solar and Stellar Astrophysics · Physics 2023-02-22 T. I. Kaltman , E. G. Kupriyanova

Using two-dimensional hybrid-kinetic simulations, we explore the nonlinear "interruption" of standing and traveling shear-Alfv\'en waves in collisionless plasmas. Interruption involves a self-generated pressure anisotropy removing the…

Plasma Physics · Physics 2017-12-14 J. Squire , M. W. Kunz , E. Quataert , A. A. Schekochihin

In this work, we consider the electromechanical density pulse as a coupled solitary waves represented by a longitudinal compression wave and an out-of-plane transversal wave (i.e., perpendicular to the membrane surface). We analyzed using,…

Pattern Formation and Solitons · Physics 2019-11-15 G. Fongang Achu , F. M. Moukam Kakmeni

It is well established now that the solar atmosphere, from photosphere to the corona and the solar wind is a highly structured medium. Satellite observations have confirmed the presence of steady flows. Here, we investigate the parallel…

Solar and Stellar Astrophysics · Physics 2015-05-13 I. Zhelyazkov

The shear Alfv\'en wave (SAW) continuum plays a critical role in the stability of energetic particle-driven Alfv\'{e}n eigenmodes. We develop a theoretical framework to analyze the SAW continuum in three-dimensional quasisymmetric magnetic…

The properties of amplitude modulated broadband Alfven waves is investigated. In particular, the dynamics of circularly polarized dispersive Alfven waves, governed by a derivative nonlinear Schroedinger equation, is analyzed using the…

Plasma Physics · Physics 2007-05-23 M. Marklund , P. K. Shukla

We examine the linear stability of a filamentary cloud permeated by a perpendicular magnetic field. The initial magnetic field is assumed to be uniform and perpendicular to the cloud axis. The model cloud is assumed to have a Plummer-like…

Astrophysics of Galaxies · Physics 2019-09-04 Tomoyuki Hanawa , Takahiro Kudoh , Kohji Tomisaka

We study the spontaneous generation and evolution of bending waves in $N$-body simulations of two isolated Milky Way-like galaxy models. The models differ by their disc-to-halo mass ratios, and hence by their susceptibility to the formation…

Astrophysics of Galaxies · Physics 2017-10-11 Matthew H. Chequers , Lawrence M. Widrow

The dense molecular cloud cores that form stars, like other self-gravitating objects, undergo bulk oscillations. Just at the point of gravitational instability, their fundamental oscillation mode has zero frequency. We study, using…

Solar and Stellar Astrophysics · Physics 2009-11-13 Steven W. Stahler , Jeffrey J. Yen

Recent measurements of the Zeeman effect in dark-cloud cores provide important tests for theories of cloud dynamics and prestellar core formation. In this Letter we report results of simulated Zeeman measurements, based on radiative…

Astrophysics of Galaxies · Physics 2016-08-14 Tuomas Lunttila , Paolo Padoan , Mika Juvela , Åke Nordlund

We review our recent results of Alfven wave-driven winds. First, we present the result of a self-consistent 1D MHD simulations for solar winds from the photosphere to interplanetary region. Here, we emphasize the importance of the…

Solar and Stellar Astrophysics · Physics 2015-05-18 Takeru K. Suzuki

We present numerical simulations of reduced magnetohydrodynamic (RMHD) turbulence in a magnetic flux tube at the center of a polar coronal hole. The model for the background atmosphere is a solution of the momentum equation, and includes…

Solar and Stellar Astrophysics · Physics 2016-04-27 A. A. van Ballegooijen , M. Asgari-Targhi