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A Mangeney

Publications and source records attributed to A Mangeney.

6 recordsLinked to original sources
PubMed2005

Memory of the unjamming transition during cyclic tiltings of a granular pile.

Discrete numerical simulations are performed to study the evolution of the microstructure and the response of a granular packing during successive loading-unloading cycles, consisting of quasistatic rotations in the gravity field between opposite inclination angles. We show that internal variables--e.g., stress and fabric of the pile--exhibit hysteresis during these cycles due to the exploration of different metastable configurations. Interestingly, the hysteretic behavior of the pile strongly depends on the maximal inclination of the cycles, giving evidence of the irreversible modifications of the pile state occurring close to the unjamming transition. More specifically, we show that for cycles with maximal inclination larger than the repose angle, the weak-contact network carries the memory of the unjamming transition. These results demonstrate the relevance of a two-phase description--strong- and weak-contact networks--for a granular system, as soon as it has approached the unjamming transition.

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PubMed2005

Magnetic-field effects on nonlinear electrostatic-wave Landau damping.

A numerical code, which solves the Vlasov-Poisson system of equations for an electron magnetized plasma with motionless ions, is presented. The numerical integration of the Vlasov equation has been performed using the "splitting method" and the cylindric geometry in the velocity space is used to describe the motion of the particles around the external field. The time evolution of an electrostatic wave, propagating perpendicularly to the background magnetic field, is numerically studied in both the linear and nonlinear regimes, for different values of the ratio gamma between the electron oscillation time in a sinusoidal potential well and the electron cyclotron period. It is shown that the external magnetic field plays very different roles, depending on the values of the initial wave amplitude. When the initial amplitude is less than some threshold, the magnetic field prevents the Landau damping of the electrostatic wave (Bernstein-Landau paradox). When the wave amplitude is above the threshold, for intermediate values of gamma the presence of a background magnetic field allows for the electric energy dissipation at variance with the behavior of electrostatic wave in unmagnetized plasma, while for high gamma values once again the magnetic field prevents the damping.

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PubMed2001

Formation of double layers and electron holes in a current-driven space plasma.

Kinetic 1D simulations reveal that a weak density depression in a current-carrying plasma can lead to the formation of a strong potential ramp (double layer). The ramp and plasma turbulence it creates share many features with recent particle and field measurements in the auroral ionosphere. An electron beam accelerated by the ramp produces a series of propagating electron phase-space holes via a spatial two-stream instability. Electron heating associated with the formation and merging of these holes is found to influence the subsequent evolution of the potential ramp.

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