scholarly journals Turbulent magnetic pressure instability in stratified turbulence

2010 ◽  
Vol 6 (S274) ◽  
pp. 473-475 ◽  
Author(s):  
K. Kemel ◽  
A. Brandenburg ◽  
N. Kleeorin ◽  
I. Rogachevskii
Keyword(s):  
Large Scale ◽  
Mean Field ◽  
Magnetic Pressure ◽  
Stratified Turbulence ◽  
Measurable Effect ◽  
Apparent Discrepancy ◽  
Large Scale Structures ◽  
Turbulent Pressure ◽  
Scale Structures ◽  
Parameter Dependency

AbstractA reduction of total mean turbulent pressure due to the presence of magnetic fields was previously shown to be a measurable effect in direct numerical simulations. However, in the studied parameter regime the formation of large-scale structures, as anticipated from earlier mean-field simulations, was not found. An analysis of the relevant mean-field parameter dependency and the parameter domain of interest is conducted in order to clarify this apparent discrepancy.

scholarly journals Convection and Dynamo in Newly Born Neutron Stars

2022 ◽  
Vol 924 (2) ◽  
pp. 75
Author(s):  
Youhei Masada ◽  
Tomoya Takiwaki ◽  
Kei Kotake
Keyword(s):  
Spherical Shell ◽  
Neutron Stars ◽  
Large Scale ◽  
Convection Zone ◽  
Turbulent Transport ◽  
Mean Field ◽  
Magnetic Component ◽  
Large Scale Structures ◽  
Scale Structures ◽  
Convective Model

Abstract To study properties of magnetohydrodynamic (MHD) convection and resultant dynamo activities in proto-neutron stars (PNSs), we construct a “PNS in a box” simulation model and solve the compressible MHD equation coupled with a nuclear equation of state (EOS) and simplified leptonic transport. As a demonstration, we apply it to two types of PNS model with different internal structures: a fully convective model and a spherical-shell convection model. By varying the spin rate of the models, the rotational dependence of convection and the dynamo that operate inside the PNS is investigated. We find that, as a consequence of turbulent transport by rotating stratified convection, large-scale structures of flow and thermodynamic fields are developed in all models. Depending on the spin rate and the depth of the convection zone, various profiles of the large-scale structures are obtained, which can be physically understood as steady-state solutions to the “mean-field” equation of motion. Additionally to those hydrodynamic structures, a large-scale magnetic component of  ( 10 15 ) G is also spontaneously organized in disordered tangled magnetic fields in all models. The higher the spin rate, the stronger the large-scale magnetic component grows. Intriguingly, as an overall trend, the fully convective models have a stronger large-scale magnetic component than that in the spherical-shell convection models. The deeper the convection zone extends, the larger the size of the convective eddies becomes. As a result, rotationally constrained convection seems to be more easily achieved in the fully convective model, resulting in a higher efficiency of the large-scale dynamo there. To gain a better understanding of the origin of the diversity of a neutron star’s magnetic field, we need to study the PNS dynamo in a wider parameter range.

scholarly journals The negative magnetic pressure effect in stratified turbulence

2010 ◽  
Vol 6 (S273) ◽  
pp. 83-88
Author(s):  
K. Kemel ◽  
A. Brandenburg ◽  
N. Kleeorin ◽  
I. Rogachevskii
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Convection Zone ◽  
Mean Field ◽  
Magnetic Pressure ◽  
Stratified Turbulence ◽  
Negative Contribution ◽  
Magnetic Structures ◽  
Large Scale Magnetic Field ◽  
Forced Turbulence

AbstractWhile the rising flux tube paradigm is an elegant theory, its basic assumptions, thin flux tubes at the bottom of the convection zone with field strengths two orders of magnitude above equipartition, remain numerically unverified at best. As such, in recent years the idea of a formation of sunspots near the top of the convection zone has generated some interest. The presence of turbulence can strongly enhance diffusive transport mechanisms, leading to an effective transport coefficient formalism in the mean-field formulation. The question is what happens to these coefficients when the turbulence becomes anisotropic due to a strong large-scale mean magnetic field. It has been noted in the past that this anisotropy can also lead to highly non-diffusive behavior. In the present work we investigate the formation of large-scale magnetic structures as a result of a negative contribution of turbulence to the large-scale effective magnetic pressure in the presence of stratification. In direct numerical simulations of forced turbulence in a stratified box, we verify the existence of this effect. This phenomenon can cause formation of large-scale magnetic structures even from initially uniform large-scale magnetic field.

Some comments about observations and image processing of comet 29P/Schwassmann-Wachmann 1

1999 ◽  
Vol 173 ◽  
pp. 243-248
Author(s):  
D. Kubáček ◽  
A. Galád ◽  
A. Pravda
Keyword(s):  
Image Processing ◽  
Large Scale ◽  
Harvard College ◽  
Oak Ridge ◽  
Large Scale Structures ◽  
Short Period Comet ◽  
Short Period ◽  
Scale Structures ◽  
Harvard College Observatory ◽  
Period Comet

AbstractUnusual short-period comet 29P/Schwassmann-Wachmann 1 inspired many observers to explain its unpredictable outbursts. In this paper large scale structures and features from the inner part of the coma in time periods around outbursts are studied. CCD images were taken at Whipple Observatory, Mt. Hopkins, in 1989 and at Astronomical Observatory, Modra, from 1995 to 1998. Photographic plates of the comet were taken at Harvard College Observatory, Oak Ridge, from 1974 to 1982. The latter were digitized at first to apply the same techniques of image processing for optimizing the visibility of features in the coma during outbursts. Outbursts and coma structures show various shapes.

scholarly journals The organization and control of an evolving interdependent population

2015 ◽  
Vol 12 (108) ◽  
pp. 20150044 ◽  
Author(s):  
Dervis C. Vural ◽  
Alexander Isakov ◽  
L. Mahadevan
Keyword(s):  
Evolutionary Game Theory ◽  
Large Scale ◽  
Social Evolution ◽  
Evolutionary Game ◽  
Large Scale Structures ◽  
External Perturbations ◽  
Emergence Of Cooperation ◽  
Scale Structures ◽  
And Control ◽  
Evolutionarily Stable

Starting with Darwin, biologists have asked how populations evolve from a low fitness state that is evolutionarily stable to a high fitness state that is not. Specifically of interest is the emergence of cooperation and multicellularity where the fitness of individuals often appears in conflict with that of the population. Theories of social evolution and evolutionary game theory have produced a number of fruitful results employing two-state two-body frameworks. In this study, we depart from this tradition and instead consider a multi-player, multi-state evolutionary game, in which the fitness of an agent is determined by its relationship to an arbitrary number of other agents. We show that populations organize themselves in one of four distinct phases of interdependence depending on one parameter, selection strength. Some of these phases involve the formation of specialized large-scale structures. We then describe how the evolution of independence can be manipulated through various external perturbations.

scholarly journals Oscillating non-linear large-scale structures in growing neutrino quintessence

2011 ◽  
Vol 418 (1) ◽  
pp. 214-229 ◽  
Author(s):  
Marco Baldi ◽  
Valeria Pettorino ◽  
Luca Amendola ◽  
Christof Wetterich
Keyword(s):  
Large Scale ◽  
Large Scale Structures ◽  
Non Linear ◽  
Scale Structures
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