Recent results from simulations of the magnetorotational instability

AbstractThe nonlinear saturation of the magnetorotational instability (MRI) is best studied through numerical MHD simulations. Recent results of simulations that adopt the local shearing box approximation, and fully global models that follow the entire disk, are described. Outstanding issues remain, such as a first-principles understanding of the dynamo processes that control saturation with no net magnetic flux. Important directions for future work include a better understanding of basic plasma processes, such as reconnection, dissipation, and particle acceleration, in the MHD turbulence driven by the MRI.

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HFQPOs and discoseismic mode excitation in eccentric, relativistic discs. II. Magnetohydrodynamic simulations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1898 ◽

2020 ◽

Vol 497 (1) ◽

pp. 451-465 ◽

Cited By ~ 1

Author(s):

Janosz W Dewberry ◽

Henrik N Latter ◽

Gordon I Ogilvie ◽

Sebastien Fromang

Keyword(s):

Binary Systems ◽

Wave Excitation ◽

Mhd Turbulence ◽

Magnetorotational Instability ◽

X Ray ◽

Mhd Simulations ◽

The Face ◽

Inertial Wave ◽

Net Flux ◽

Magnetohydrodynamic Simulations

ABSTRACT Trapped inertial oscillations (r modes) provide a promising explanation for high-frequency quasi-periodic oscillations (HFQPOs) observed in the emission from black hole X-ray binary systems. An eccentricity (or warp) can excite r modes to large amplitudes, but concurrently, the oscillations are likely damped by magnetohydrodynamic (MHD) turbulence driven by the magnetorotational instability (MRI). We force eccentricity in global, unstratified, zero-net-flux MHD simulations of relativistic accretion discs and find that a sufficiently strong disc distortion generates trapped inertial waves despite this damping. In our simulations, eccentricities above ∼0.03 in the inner disc excite trapped waves. In addition to the competition between r-mode damping and driving, we observe that larger amplitude eccentric structures modify and in some cases suppress MRI turbulence. Given the variety of distortions (warps as well as eccentricities) capable of amplifying r modes, the robustness of trapped inertial wave excitation in the face of MRI turbulence in our simulations provides support for a discoseismic explanation for HFQPOs.

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Magnetohydrodynamics in a cylindrical shearing box

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psz082 ◽

2019 ◽

Vol 71 (5) ◽

Cited By ~ 1

Author(s):

Takeru K Suzuki ◽

Tetsuo Taki ◽

Scott S Suriano

Keyword(s):

Mhd Equations ◽

Radial Dependence ◽

Mhd Turbulence ◽

Magnetorotational Instability ◽

Mhd Simulations ◽

Self Consistent ◽

Consistent Manner ◽

Set Up ◽

Isothermal Equation ◽

Physical Quantities

ABSTRACT We develop a framework for magnetohydrodynamical (MHD) simulations in a local cylindrical shearing box by extending the formulation of the Cartesian shearing box. We construct shearing-periodic conditions at the radial boundaries of a simulation box from the conservation relations of the basic MHD equations, taking into account the explicit radial dependence of physical quantities. We demonstrate quasi-steady mass accretion, which cannot be handled by the standard Cartesian shearing box model, with an ideal MHD simulation in a vertically unstratified cylindrical shearing box for up to 200 rotations. In this demonstrative run we set up (i) net vertical magnetic flux, (ii) a locally isothermal equation of state, and (iii) a sub-Keplerian equilibrium rotation, whereas the sound velocity and the initial Alfvén velocity have the same radial dependence as that of the Keplerian velocity. Inward mass accretion is induced to balance the outward angular momentum flux of the MHD turbulence triggered by the magnetorotational instability in a self-consistent manner. We discuss detailed physical properties of the saturated magnetic field, in comparison to the results of a Cartesian shearing box simulation.

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Investigating lack of accretion disk eccentricity growth in a global 3D MHD simulation of a superhump system

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab1212 ◽

2021 ◽

Author(s):

Bryance Oyang ◽

Yan-Fei Jiang ◽

Omer Blaes

Keyword(s):

First Principles ◽

Mode Coupling ◽

Spiral Wave ◽

Relative Mass ◽

Coupling Mechanism ◽

Mhd Turbulence ◽

Mhd Simulation ◽

Dominant Term ◽

Mhd Simulations ◽

3D Mhd Simulation

Abstract We present the results of a 3D global magnetohydrodynamic (MHD) simulation of an AM CVn system that was aimed at exploring eccentricity growth in the accretion disc self-consistently from a first principles treatment of the MHD turbulence. No significant eccentricity growth occurs in the simulation. In order to investigate the reasons why, we ran 2D alpha disc simulations with alpha values of 0.01, 0.1, and 0.2, and found that only the latter two exhibit significant eccentricity growth. We present an equation expressing global eccentricity evolution in terms of contributing forces and use it to analyse the simulations. As expected, we find that the dominant term contributing to the growth of eccentricity is the tidal gravity of the companion star. In the 2D simulations, the alpha viscosity directly contributes to eccentricity growth. In contrast, the overall magnetic forces in the 3D simulation damp eccentricity. We also analyzed the mode-coupling mechanism of Lubow, and confirmed that the spiral wave excited by the 3:1 resonance was the dominant contributor to eccentricity growth in the 2D α = 0.1 simulations, but other waves also contribute significantly. We found that the α = 0.1 and 0.2 simulations had more relative mass at larger radii compared to the α = 0.01 and 3D MHD simulation, which also had an effective α of 0.01. This suggests that in 3D MHD simulations without sufficient poloidal magnetic flux, MRI turbulence does not saturate at a high enough α to spread the disc to large enough radii to reproduce the superhumps observed in real systems.

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Strain Conditions for the Inverse Heusler Type Fully Compensated Spin-Gapless Semiconductor Ti2MnAl: A First-Principles Study

Materials ◽

10.3390/ma11112091 ◽

2018 ◽

Vol 11 (11) ◽

pp. 2091 ◽

Cited By ~ 13

Author(s):

Tie Yang ◽

Liyu Hao ◽

Rabah Khenata ◽

Xiaotian Wang

Keyword(s):

Thermodynamic Properties ◽

First Principles ◽

Density Functional ◽

Theoretical Study ◽

Debye Model ◽

Pressure Effects ◽

First Principles Calculation ◽

Strain Condition ◽

Functional Theory ◽

Future Work

In this work, we systematically studied the structural, electronic, magnetic, mechanical and thermodynamic properties of the fully compensated spin-gapless inverse Heusler Ti2MnAl compound under pressure strain condition by applying the first-principles calculation based on density functional theory and the quasi-harmonic Debye model. The obtained structural, electronic and magnetic behaviors without pressure are well consistent with previous studies. It is found that the spin-gapless characteristic is destroyed at 20 GPa and then restored with further increase in pressure. While, the fully compensated ferromagnetism shows a better resistance against the pressure up to 30 GPa and then becomes to non-magnetism at higher pressure. Tetragonal distortion has also been investigated and it is found the spin-gapless property is only destroyed when c/a is less than 1 at 95% volume. Three independent elastic constants and various moduli have been calculated and they all show increasing tendency with pressure increase. Additionally, the pressure effects on the thermodynamic properties under different temperature have been studied, including the normalized volume, thermal expansion coefficient, heat capacity at constant volume, Grüneisen constant and Debye temperature. Overall, this theoretical study presents a detailed analysis of the physical properties’ variation under strain condition from different aspects on Ti2MnAl and, thus, can provide a helpful reference for the future work and even inspire some new studies and lead to some insight on the application of this material.

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IC Project: Magnetic Reconnection versus Shocks: First-principles Kinetic Simulations of Major Particle Acceleration Mechanisms in the Universe

10.2172/1498007 ◽

2019 ◽

Author(s):

Fan Guo

Keyword(s):

Particle Acceleration ◽

Magnetic Reconnection ◽

First Principles ◽

The Universe

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MHD simulations of the magnetorotational instability in a shearing box with zero net flux

Astronomy and Astrophysics ◽

10.1051/0004-6361:20077942 ◽

2007 ◽

Vol 476 (3) ◽

pp. 1113-1122 ◽

Cited By ~ 183

Author(s):

S. Fromang ◽

J. Papaloizou

Keyword(s):

Magnetorotational Instability ◽

Mhd Simulations ◽

Net Flux

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An In-depth Investigation of Faraday Depth Spectrum Using Synthetic Observations of Turbulent MHD Simulations

Galaxies ◽

10.3390/galaxies7040089 ◽

2019 ◽

Vol 7 (4) ◽

pp. 89 ◽

Cited By ~ 1

Author(s):

Aritra Basu ◽

Andrew Fletcher ◽

Sui Ann Mao ◽

Blakesley Burkhart ◽

Rainer Beck ◽

...

Keyword(s):

Faraday Rotation ◽

Turbulent Medium ◽

Line Of Sight ◽

Synchrotron Emission ◽

Mhd Turbulence ◽

Broad Bandwidth ◽

Mhd Simulations ◽

Rotation Measure ◽

Spread Function ◽

Pass Through

In this paper, we present a detailed analysis of the Faraday depth (FD) spectrum and its clean components obtained through the application of the commonly used technique of Faraday rotation measure synthesis to analyze spectro-polarimetric data. To directly compare the Faraday depth spectrum with physical properties of a magneto-ionic medium, we generated synthetic broad-bandwidth spectro-polarimetric observations from magnetohydrodynamic (MHD) simulations of a transonic, isothermal, compressible turbulent medium. We find that correlated magnetic field structures give rise to a combination of spiky, localized peaks at certain FD values, and broad structures in the FD spectrum. Although most of these spiky FD structures appear narrow, giving an impression of a Faraday thin medium, we show that they arise from strong synchrotron emissivity at that FD. Strong emissivity at a FD can arise because of both strong spatially local polarized synchrotron emissivity at a FD or accumulation of weaker emissions along the distance through a medium that have Faraday depths within half the width of the rotation measure spread function. Such a complex Faraday depth spectrum is a natural consequence of MHD turbulence when the lines of sight pass through a few turbulent cells. This therefore complicates the convention of attributing narrow FD peaks to the presence of a Faraday-rotating medium along the line of sight. Our work shows that it is difficult to extract the FD along a line of sight from the Faraday depth spectrum using standard methods for a turbulent medium in which synchrotron emission and Faraday rotation occur simultaneously.

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Global Hall-MHD simulations of magnetorotational instability in a plasma Couette flow experiment

Physics of Plasmas ◽

10.1063/1.3598481 ◽

2011 ◽

Vol 18 (6) ◽

pp. 062904 ◽

Cited By ~ 13

Author(s):

F. Ebrahimi ◽

B. Lefebvre ◽

C. B. Forest ◽

A. Bhattacharjee

Keyword(s):

Couette Flow ◽

Magnetorotational Instability ◽

Mhd Simulations ◽

Flow Experiment ◽

Hall Mhd

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First-Principles Calculations of Elastic Properties of HoBi and ErBi

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.664.672 ◽

2013 ◽

Vol 664 ◽

pp. 672-676

Author(s):

De Ming Han ◽

Gang Zhang ◽

Li Hui Zhao

Keyword(s):

Shear Modulus ◽

Physical Properties ◽

Bulk Modulus ◽

Elastic Properties ◽

Lattice Constant ◽

Elastic Constants ◽

First Principles ◽

Energy Band ◽

First Principles Calculations ◽

Future Work

We present first-principles investigations on the elastic properties of XBi (X=Ho, Er) compounds. Basic physical properties, such as lattice constant, elastic constants (Cij), isotropic shear modulus (G), bulk modulus (B), Young’s modulus (Y), Poisson’s ratio (υ), and Anisotropy factor (A) are calculated. The calculated energy band structures show that the two compounds possess semi-metallic character. We hope that these results would be useful for future work on two compounds.

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