3,270 research outputs found
On the Nonlinear Triggering of VLF Emissions by Power Line Harmonic Radiation
No full textVLF ground data from Porojarvi in N. Finland has been presented. Spectrograms reveal frequent occurrence of power line harmonic radiation (PLHR), originating from the Finnish power system and from heavy industrial plant. This radiation is seen to penetrate the magnetosphere since numerous occurrences of PLHR triggered emissions are seen. Risers predominate but fallers and hooks are also observed. A well established 1D Vlasov simulation code has been used to simulate these emissions, using plausible magnetospheric data for a range of L values from L=4 to L=5.5. The code is able to reproduce risers fallers and hooks in close agreement with observations. The results shed considerable insight into the generation region structure of both risers and fallers
From the Hartree dynamics to the Vlasov equation
No full textWe consider the evolution of quasi-free states describing fermions in the mean field limit, as governed by the nonlinear Hartree equation. In the limit of large , we study the convergence towards the classical Vlasov equation. For a class of regular interaction potentials, we establish precise bounds on the 0rate of convergence
Vlasov versus N-body: the Hénon sphere
No full textInternational audienceWe perform a detailed comparison of the phase-space density traced by the particle distribution in GADGET simulations to the result obtained with a spherical Vlasov solver using the splitting algorithm. The systems considered are apodized Hénon spheres with two values of the virial ratio, R ≃ 0.1 and 0.5. After checking that spherical symmetry is well preserved by the N-body simulations, visual and quantitative comparisons are performed. In particular, we introduce new statistics, correlators and entropic estimators, based on the likelihood of whether N-body simulations actually trace randomly the Vlasov phase-space density. When taking into account the limits of both the N-body and the Vlasov codes, namely collective effects due to the particle shot noise in the first case and diffusion and possible non-linear instabilities due to finite resolution of the phase-space grid in the second case, we find a spectacular agreement between both methods, even in regions of phase-space where non-trivial physical instabilities develop. However, in the colder case, R = 0.1, it was not possible to prove actual numerical convergence of the N-body results after a number of dynamical times, even with N = 108 particles
(Table 3) Major- and trace element composition of clinopyroxenes from peridotides at 13°N MAR
No full text(Table 3) Major- and trace element composition of clinopyroxenes from peridotides at 13°N MA
(Table 5) Composition of minerals in the assemblage orthopyroxene+spinel+olivine from peridotides at 13°N MAR
No full text(Table 5) Composition of minerals in the assemblage orthopyroxene+spinel+olivine from peridotides at 13°N MA
Flows of singular vector fields and applications to fluid and kinetic equations
No full textSeveral physical phenomena arising in fluid dynamics and kinetic equations can be modeled by nonlinear transport PDE. Such quantities are the vorticity of a fluid, or the density of a collection of particles advected by a velocity field which is highly irregular. The theory of characteristics provides a link between this PDE and the ODE dX/dt=b(t,X(t,x)), where b is the velocity field. When b has Sobolev or BV regularity and bounded divergence, the theory of DiPerna-Lions and Ambrosio gives a good notion of solution to the ordinary differential equation using the concept of regular Lagrangian flow. Extending the results of Crippa-DeLellis, and more recently Bouchut-Crippa, we study Lagrangian flows associated to velocity fields with anisotropic regularity: those with gradient given by the singular integral of an L^1 function in some directions, and the singular integral of a measure in others. We exploit an anisotropic version of the previous arguments and estimate the difference quotients in this context, thereby gaining quantitative estimates in terms of the given regularity bounds. One then recovers well-posedness for the ordinary differential equation. This answers positively the question of existence of Lagrangian solutions to the Vlasov Poisson and Euler equations with L^1 data
Vlasov and Drift Kinetic Simulation Methods Based on the Symplectic Integrator
No full textVlasov and drift kinetic simulation methods based on the symplectic integrators are benchmarked for test problems on the linear and nonlinear Landau dampings and the Kelvin-Helmholtz (K-H) instability. The explicit symplectic integrator for the separable Hamiltonian straightforwardly leads to generalization of the splitting scheme for the Vlasov-Poisson system. The Nth-order version improves the total energy conservation decreasing the error as propto Delta t^N where Deltat denotes the time step size. An Eulerian drift kinetic simulation scheme derived from the implicit symplectic integrator for the non-separable Hamiltonian exactly satisfies the conservation of the energy and the enstrophy in the K-H instability, and results in successful application to the plasma echo.research repor
From the N-Body Schrödinger Equation to the Vlasov Equation
No full textInternational audienceThis paper describes a method for obtaining an estimate of the convergence rate for the joint mean-field and semiclassical limit of the N-particle Schrödinger equation leading to the Vlasov equation. The interaction force is assumed to be Lipschitz continuous. This is an account of a recent work in collaboration with T. Paul [Arch. Ration. Mech. Anal. 223 (2017), 57-94]
(Table 4) Compositions of quenched glasses from peridotides at 13°N MAR
No full text(Table 4) Compositions of quenched glasses from peridotides at 13°N MA
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