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Full-Text Articles in Physics
Low Magnetic Prandtl Number Dynamos With Helical Forcing, Pablo D. Mininni, David C. Montgomery
Low Magnetic Prandtl Number Dynamos With Helical Forcing, Pablo D. Mininni, David C. Montgomery
Dartmouth Scholarship
We present direct numerical simulations of dynamo action in a forced Roberts flow. The behavior of the dynamo is followed as the mechanical Reynolds number is increased, starting from the laminar case until a turbulent regime is reached. The critical magnetic Reynolds for dynamo action is found, and in the turbulent flow it is observed to be nearly independent on the magnetic Prandtl number in the range from ∼0.3 to ∼0.1. Also the dependence of this threshold with the amount of mechanical helicity in the flow is studied. For the different regimes found, the configuration of the magnetic and velocity …
Steady States Of A Nonequilibrium Lattice Gas, Edward Lyman, Beate Schmittmann
Steady States Of A Nonequilibrium Lattice Gas, Edward Lyman, Beate Schmittmann
Beate Schmittmann
We present a Monte Carlo study of a lattice gas driven out of equilibrium by a local hopping bias. Sites can be empty or occupied by one of two types of particles, which are distinguished by their response to the hopping bias. All particles interact via excluded volume and a nearest-neighbor attractive force. The main result is a phase diagram with three phases: a homogeneous phase and two distinct ordered phases. Continuous boundaries separate the homogeneous phase from the ordered phases, and a first-order line separates the two ordered phases. The three lines merge in a nonequilibrium bicritical point.
Exact Dynamics Of A Reaction-Diffusion Model With Spatially Alternating Rates, M. Mobilia, Beate Schmittmann, R. K. P. Zia
Exact Dynamics Of A Reaction-Diffusion Model With Spatially Alternating Rates, M. Mobilia, Beate Schmittmann, R. K. P. Zia
Beate Schmittmann
We present the exact solution for the full dynamics of a nonequilibrium spin chain and its dual reaction-diffusion model, for arbitrary initial conditions. The spin chain is driven out of equilibrium by coupling alternating spins to two thermal baths at different temperatures. In the reaction-diffusion model, this translates into spatially alternating rates for particle creation and annihilation, and even negative “temperatures” have a perfectly natural interpretation. Observables of interest include the magnetization, the particle density, and all correlation functions for both models. Two generic types of time dependence are found: if both temperatures are positive, the magnetization, density, and correlation …
Numerical Solutions Of The Three-Dimensional Magnetohydrodynamic Α Model, Pablo D. Mininni, David C. Montgomery, Annick Pouquet
Numerical Solutions Of The Three-Dimensional Magnetohydrodynamic Α Model, Pablo D. Mininni, David C. Montgomery, Annick Pouquet
Dartmouth Scholarship
We present direct numerical simulations and α-model simulations of four familiar three-dimensional magnetohydrodynamic (MHD) turbulence effects: selective decay, dynamic alignment, inverse cascade of magnetic helicity, and the helical dynamo effect. The MHD α model is shown to capture the long-wavelength spectra in all these problems, allowing for a significant reduction of computer time and memory at the same kinetic and magnetic Reynolds numbers. In the helical dynamo, not only does the α model correctly reproduce the growth rate of magnetic energy during the kinematic regime, it also captures the nonlinear saturation level and the late generation of a large scale …
Anomalous Nucleation Far From Equilibrium, I. T. Georgiev, Beate Schmittmann, R. K. P. Zia
Anomalous Nucleation Far From Equilibrium, I. T. Georgiev, Beate Schmittmann, R. K. P. Zia
Beate Schmittmann
We present precision Monte Carlo data and analytic arguments for an asymmetric exclusion process, involving two species of particles driven in opposite directions on a 2×L lattice. To resolve a stark discrepancy between earlier simulation data and an analytic conjecture, we argue that the presence of a single macroscopic cluster is an intermediate stage of a complex nucleation process: in smaller systems, this cluster is destabilized while larger systems form multiple clusters. Both limits lead to exponential cluster size distributions, controlled by very different length scales.