Zhanna Andrushchenko

Generation of large-scale magnetic flows in turbulent plasma

Nonlinear dynamics of the magnetic electron drift mode turbulence is outlined and generation of large-scale magnetic structures in a nonuniform unmagnetized plasma by turbulent Reynolds stress is demonstrated. A two-component turbulent system consisting of magnetic fluctuations and generated secondary flows is considered. The evolution equations for mean magnetic flow generation are obtained by averaging the two-field model equations over fast small scales. It is found, in turn, that the pattern of the flow modulates and regulates the turbulence dynamics. The main features of the flows are controlled by the structure of the nonlinear coupling to the small-scale magnetic fluctuations as well as by the spectral properties of the turbulence and its anisotropy. Thus, the parent waves and secondary magnetic flows form a self-regulating system. It is shown that the presence of large-scale structures leads to shearing of turbulence. The k-space diffusion coefficient for the magnetic zonal flows and streamers are...

Self-consistent model of electron drift mode turbulence

The nonlinear dynamics of magnetic electron drift mode turbulence are outlined and the generation of large-scale magnetic structures in a non-uniform magnetized plasma by turbulent Reynolds stress is demonstrated. The loop-back of large-scale flows on the microturbulence is elucidated and the modulation of the electron drift mode turbulence spectrum in a medium with slowly varying parameters is presented. The wave kinetic equation in the presence of large-scale flows is derived and it can be seen that the small-scale turbulence and the large-scale structures form a self-regulating system. Finally, it is shown by the use of quasi-linear theory that the shearing of microturbulence by the flows can be described by a diffusion equation in k-space and the corresponding diffusion coefficients are calculated.

Large scale magnetic fields and coherent structures in nonuniform unmagnetized plasma

The properties of streamers and zonal magnetic structures in magnetic electron drift mode turbulence are investigated. The stability of such large scale structures is investigated in the kinetic and the hydrodynamic regime, for which an instability criterion similar to the Lighthill criterion for modulational instability is found. Furthermore, these large scale flows can undergo further nonlinear evolution after initial linear growth, which can lead to the formation of long-lived coherent structures consisting of self-bound wave packets between the surfaces of two different flow velocities with an expected modification of the anomalous electron transport properties.

Towards the Optimal Feature Selection in High-Dimensional

We focus on Bayesian network (BN) classifiers and formalize the feature selection from a perspective of improving classification accuracy. To exploring the effect of high-dimensionality we apply the growing dimension asymptotics. We modify the weighted BN by introducing inclusion-exclusion factors which eliminate the features whose separation score do not exceed a given threshold. We establish the asymptotic optimal threshold and demonstrate that the proposed selection technique carries improvements over classification accuracy.