Burst Dynamics Research Articles

Dynamics of ponderomotive self-focusing and periodic bursts of stimulated Brillouin backscattering in plasmas

The space–time evolution of ponderomotive self-focusing of electromagnetic beams in a plasma is investigated. The quasineutral, hydrodynamic plasma response to the ponderomotive force is considered. The set of coupled quasioptic and acoustic equations is solved both analytically and numerically for slab and cylindrical beams. It is shown that the transient process of self-focusing has the form of a nonlinear wave propagating along the beam axis from boundary into the interior of a plasma with velocity considerably higher than the ion-sound velocity. Mutual dynamics of self-focusing and stimulated Brillouin backscattering (SBBS) is computed. It is shown that self-focusing results in the high intensity periodical bursts of SBBS. However, the time average level of scattered radiation is quite low.

Computer model of ethosuximide's effect on a thalamic neuron.

Ethosuximide appears to have a specific effect on the low-threshold calcium current in thalamic cells. This may be related to its efficacy in the treatment of absence epilepsy. We used a computer model of an individual thalamocortical neuron to better understand the alteration in the low-threshold calcium current under voltage clamp and to predict response to current injection in the presence of ethosuximide. The full model included nine voltage-sensitive ionic channels and a realistic dendritic morphology. The model reproduced the two major responses seen in tissue slices: repetitive spiking with depolarization and the low-threshold calcium spike elicited on release from hyperpolarization. The alteration in low-threshold calcium current with ethosuximide can be explained by a 10-mV depolarizing shift in the steady-state activation curve for this channel with a 10% reduction in maximum channel permeability. Simulations of current injection showed that ethosuximide diminished the low-threshold calcium spike while leaving the tonic firing pattern unaffected. Our results support the hypothesis that ethosuximide's effects on low-threshold calcium current might selectively alter the dynamics of slow bursting in thalamic cells.

Breakdown of Chaos Symmetry and Intermittency in Band-Splitting Phenomena

A band·splitting phenomenon is studied from the viewpoint of the breakdown of the chaos symmetry and the development of the intermittency. The analyses are carried out for two kinds of coarse·grained variables relevant to the symmetry argument and the burst dynamics, mainly by utilizing similarity exponents introduced for analyzing one·dimensional time series. The develop· ment of the intermittency near the band·splitting point is shown to be chan.cterized as the scaling laws for the similarity exponents.

The dynamics of the energetic proton bursts in the course of the magnetic field topology reconstruction in the earth‘s magnetotail

The paper considers the energy spectrum of particles accelerated near X-point of the magnetic field in the course of the tearing instability development in the current layer. The time dynamics of the spectrum at the linear and nonlinear stages of the instability is studied. The contribution of the particles inflowing into the vicinity of the magnetic X-point due to drift in the crossed electrical and magnetic fields was also taken into account. The dynamics of particle acceleration is numerically simulated and the results of the simulation are compared with the theoretical model. The analytical and numerical calculations are in reasonable agreement with the results of IMP satellites 7 and 8 energetic proton measurements in a wide energy interval.