scholarly journals On Cross-Phase and the Quenching of the Turbulent Diffusion of Magnetic Fields in Two Dimensions

2008 ◽  
Vol 678 (2) ◽  
pp. L137-L140 ◽  
Author(s):  
Shane R. Keating ◽  
L. J. Silvers ◽  
P. H. Diamond
Keyword(s):  
Magnetic Fields ◽  
Turbulent Diffusion ◽  
Two Dimensions

scholarly journals The role of magnetic fields for planetary formation

2008 ◽  
Vol 4 (S259) ◽  
pp. 249-258 ◽  
Author(s):  
Anders Johansen
Keyword(s):  
Magnetic Fields ◽  
Turbulent Diffusion ◽  
Planet Formation ◽  
High Pressures ◽  
Mixing Time ◽  
Zonal Flow ◽  
Coherence Time ◽  
Maxwell Stress ◽  
Turbulent Diffusion Coefficient

AbstractThe role of magnetic fields for the formation of planets is reviewed. Protoplanetary disc turbulence driven by the magnetorotational instability has a huge influence on the early stages of planet formation. Small dust grains are transported both vertically and radially in the disc by turbulent diffusion, counteracting sedimentation to the mid-plane and transporting crystalline material from the hot inner disc to the outer parts. The conclusion from recent efforts to measure the turbulent diffusion coefficient of magnetorotational turbulence is that turbulent diffusion of small particles is much stronger than naively thought. Larger particles – pebbles, rocks and boulders – get trapped in long-lived high pressure regions that arise spontaneously at large scales in the turbulent flow. These gas high pressures, in geostrophic balance with a sub-Keplerian/super-Keplerian zonal flow envelope, are excited by radial fluctuations in the Maxwell stress. The coherence time of the Maxwell stress is only a few orbits, where as the correlation time of the pressure bumps is comparable to the turbulent mixing time-scale, many tens or orbits on scales much greater than one scale height. The particle overdensities contract under the combined gravity of all the particles and condense into gravitationally bound clusters of rocks and boulders. These planetesimals have masses comparable to the dwarf planet Ceres. I conclude with thoughts on future priorities in the field of planet formation in turbulent discs.

Diffusion of electrons in two dimensions in arbitrarily strong magnetic fields

1982 ◽  
Vol 25 (10) ◽  
pp. 6468-6471 ◽  
Author(s):  
A. Houghton ◽  
J. R. Senna ◽  
S. C. Ying
Keyword(s):  
Magnetic Fields ◽  
Two Dimensions ◽  
Strong Magnetic Fields

Turbulent diffusion of magnetic fields

1978 ◽  
Vol 225 ◽  
pp. 1050 ◽  
Author(s):  
E. Knobloch
Keyword(s):  
Magnetic Fields ◽  
Turbulent Diffusion

Whistler modes in highly nonuniform magnetic fields. I. Propagation in two-dimensions

2018 ◽  
Vol 25 (8) ◽  
pp. 082108 ◽  
Author(s):  
J. M. Urrutia ◽  
R. L. Stenzel
Keyword(s):  
Magnetic Fields ◽  
Two Dimensions

EFFECTS OF PARALLEL MAGNETIC FIELDS ON THE UNUSUAL METALLIC BEHAVIOR IN TWO DIMENSIONS

2002 ◽  
Vol 16 (20n22) ◽  
pp. 3279-3279
Author(s):  
D. POPOVIC
Keyword(s):  
Magnetic Fields ◽  
Electron Density ◽  
Electron System ◽  
Metallic Phase ◽  
Two Dimensions ◽  
Metallic Behavior ◽  
Temperature Conductivity ◽  
Temperature Dependence Of Conductivity ◽  
Interacting Systems ◽  
Parallel Magnetic Fields

The fate of the metallic phase in parallel magnetic fields represents one of the major open issues in the studies of dilute, strongly interacting systems in two dimensions (2D). In this experiment, the temperature dependence of conductivity σ(T) of a 2D electron system in silicon has been studied in parallel magnetic fields B. At B = 0, the system displays a new and unexpected kind of metallic behavior with dσ/dT > 0, and a novel type of a metal-insulator transition,1 which occurs at a critical electron density nc(0). At low fields (B ≤ 2 T ), nc increases as nc(B) - nc(0) ∝ Bβ(β ≈ 0.9), and the zero-temperature conductivity scales as σ(ns, B, 0)/σ (ns, 0, 0) = f(Bβ/δn) (where δn = (ns - nc(0))/nc(0), and ns is electron density) as expected for a quantum phase transition. The metallic phase persists in fields up to 18 T, consistent with the saturation of nc at high fields. These results strongly suggest that the 2D metal may exist even for spinless electrons.

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