[en] Published in summary form only

No abstract available

No abstract available

No abstract available

[en] Short communication

[en] For a certain order of frequencies defined here we give the derivation and general solution of the 4th order differential equation obeyed by the radial MHD displacement of a cylindrical, resistive and incompressible plasma column. By means of a flux function the expressions of the elctromagnetic field and the current density in the resistive layer are obtained the power dissipated in this layer by an external wave and its limit when the resistivity disappears are then discussed

[en] A general method for studying the ideal and resistive MHD stability of plasma configurations with line-tying is presented, and applied to the case of the m=1 kink mode in coronal loops. The method consists in a truncated Fourier series approach applied to the linearized equations of motion, and is found to converge rapidly with the order of the truncation. Different models of the boundary conditions at the corona-photosphere interface are discussed, and the growth rates of unstable modes are calculated for equilibrium profiles both with and without a reversal in the field component connecting to the photosphere. The relevance of these modes to compace loop flares is assessed. (author). 9 refs.; 3 figs

[en] The ideal MHD model is inadequate to fully account for the physical effects relevant for a relatively weak instability as the internal kink mode. In particular, perpendicular compressibility of the thermal trapped and barely circulating particles can produce a significant stabilizing effect which can determine, in situation of practical interest, the actual stability of the internal kink mode. It has been shown that the effect of compressibility has a strong stabilizing influence on the internal kink mode

[en] The ubiquitous relativistic jet phenomena associated with black holes play a major role in high and very-high-energy (VHE) astrophysics. In particular, observations have demonstrated that blazars show VHE emission with time variability from days to minutes (in the gigaelectronvolt and teraelectronvolt bands), implying very compact emission regions. The real mechanism of the particle acceleration process responsible for this emission is still being debated, but magnetic reconnection has lately been discussed as a strong potential candidate. In this work, we present the results of three-dimensional special relativistic magnetohydrodynamic simulations of the development of reconnection events driven by turbulence induced by current-driven kink instability along a relativistic jet. We have performed a systematic identification of all reconnection regions in the system, characterizing their local magnetic field topology and quantifying the reconnection rates. We obtained average rates of 0.051 ± 0.026 (in units of Alfvén speed), which are comparable to the predictions of the theory of turbulence-induced fast reconnection. A detailed statistical analysis also demonstrated that the fast reconnection events follow a log-normal distribution, which is a signature of its turbulent origin. To probe the robustness of our method, we have applied our results to the blazar Mrk 421. Building a synthetic light curve from the integrated magnetic reconnection power, we evaluated the time variability from a power spectral density analysis, obtaining good agreement with observations in the gigaelectronvolt band. This suggests that turbulent fast magnetic reconnection can be a possible process behind the high-energy emission variability phenomena observed in blazars.

[en] The pursuit of steady-state economic production of thermonuclear fusion energy has led to research on the stabilization of the external kink and the resistive wall mode. Advances in both experiment and theory, together with improvements in diagnostics, heating and feedback methods have led to substantial and steady progress in the understanding and stabilization of these instabilities. Many of the theory and experimental techniques and results that have been developed are useful not only for the stabilization of the resistive wall mode. They can also be used to improve the general performance of fusion confinement devices. The conceptual foundations and experimental results on the stabilization of the external kink and the resistive wall mode are reviewed. (topical review)