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- Andrushchenko, Zhanna N., et al.
(författare)
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Self-consistent model of electron drift mode turbulence
- 2008
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 74:1, s. 21-33
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Tidskriftsartikel (refereegranskat)abstract
- 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 quasilinear 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.
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- Jucker, Martin, et al.
(författare)
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Large scale magnetic fields and coherent structures in nonuniform unmagnetized plasma
- 2006
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 13:7, s. 072308-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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- Ohlson, Martin, et al.
(författare)
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Explicit Estimators under m-Dependence for a Multivariate Normal Distribution
- 2011
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Ingår i: Annals of the Institute of Statistical Mathematics. - : Springer. - 0020-3157 .- 1572-9052. ; 63:1, s. 29-42
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Tidskriftsartikel (refereegranskat)abstract
- The problemof estimating parameters of amultivariate normal p-dimensional random vector is considered for a banded covariance structure reflecting mdependence. A simple non-iterative estimation procedure is suggested which gives an explicit, unbiased and consistent estimator of the mean and an explicit and consistent estimator of the covariance matrix for arbitrary p and m.
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- Zucca, Constanza, et al.
(författare)
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Nonlinear dynamics of flute modes and self-organization phenomena in turbulent magnetized plasma
- 2007
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Ingår i: Plasma Physics and Controlled Fusion. - 0741-3335 .- 1361-6587. ; 49:5A, s. A249-A258
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Tidskriftsartikel (refereegranskat)abstract
- A two-fields model that self-consistently describes the coupled, spectral dynamics of flute mode large-scale flows turbulence is presented. This model has a characteristic form of a 'predator–prey' system, in which the populations of flute mode quanta (prey), growing via linear instability, generate large-scale flows (predators) through Reynolds stress. Concurrently, the mean flow growth regulates the prey population. To understand the long term nonlinear evolution of this one-prey two-predator system, a low-dimensional prototype of the model was constructed, assuming that the dynamics of such a complex system can be described within a phenomenological zero-dimensional approach. It is shown in the frame of this model that the dynamic outcome of interactions between the three system components may lead, depending on the system parameters, to their coexistence in the form of oscillatory solutions corresponding to quasi-periodic bursting of turbulence intensity level. These solutions are consistent with the time dependent behaviour of flute mode turbulence recently observed in numerical simulations.
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