Numerical simulations of self-gravitating magnetized disks

We present the first global simulations of self-gravitating magnetized tori. The simulations are performed with Zeus-2D and GLOBAL. We find the magnetorotational instability (MRI) to behave similarly in a self-gravitating environment as in previous simulations of non self-gravitating systems: enhancement of turbulent angular momentum transport follows the linear phase. The torus quickly develops a two component structure composed of an inner thick disk in Keplerian rotation and an outer massive disk. We compare this result with zero mass global simulations in 2D, and also present preliminary results of 3D simulations.Comment: 6 pages, 6 figures, kluwer.cls, To appear in the proceedings of "Magnetic fields and star formation: Theory versus observations", Madrid,April 21-25 200

Evolution of massive and magnetized protoplanetary disks

We present global 2D and 3D simulations of self-gravitating magnetized tori. We used the 2D calculations to demonstrate that the properties of the MRI are not affected by the presence of self-gravity: MHD turbulence and enhanced angular momentum transport follow the linear growth of the instability. In 3D, we have studied the interaction between an $m=2$ gravitational instability and MHD turbulence. We found its strength to be significantly decreased by the presence of the latter, showing that both instabilities strongly interact in their non-linear phases. We discuss the consequences of these results.Comment: 8 pages, 7 figures, to appear in the proceedings of the XIXth IAP colloquium "Extrasolar Planets: Today and Tomorrow" held in Paris, France, 2003, June 30 - July 4, ASP Conf. Serie

Evolution of self-gravitating magnetized disks. I- Axisymmetric simulations

In this paper and a companion work, we report on the first global numerical simulations of self-gravitating magnetized tori, subject in particular to the influence of the magnetorotational instability (MRI). In this work, paper I, we restrict our calculations to the study of the axisymmetric evolution of such tori. Our goals are twofold: (1) to investigate how self-gravity influences the global structure and evolution of the disks; and (2) to determine whether turbulent density inhomogeneities can be enhanced by self-gravity in this regime. As in non self-gravitating models, the linear growth of the MRI is followed by a turbulent phase during which angular momentum is transported outward. As a result, self-gravitating tori quickly develop a dual structure composed of an inner thin Keplerian disk fed by a thicker self-gravitating disk, whose rotation profile is close to a Mestel disk. Our results show that the effects of self-gravity enhance density fluctuations much less than they smooth the disk, and giving it more coherence. We discuss the expected changes that will occur in 3D simulations, the results of which are presented in a companion paper.Comment: 20 pages, 7 figures, accepted for publication in Ap

A cluster partitioning method: determination of density matrices of solids and comparison with X-ray experiments

In this paper we show that 1-electron properties such as Compton profiles and structure factors of crystals can be asymptotically retrieved through cluster-based calculations, followed by an appropriate partition of the 1-electron reduced density matrix (1RDM). This approach, conceptually simple, is checked with respects to both position and momentum spaces simultaneously for insulators and a covalent crystal. Restricting the calculations to small clusters further enables a fair description of local correlation effects in ionic compounds, which improves both Compton profiles and structure factors vs. their experimentally determined counterparts.Comment: 19 pages, 9 figures, 3 tables. Currently submitted to PR

Evolution of self-gravitating magnetized disks. II- Interaction between MHD turbulence and gravitational instabilities

We present 3D magnetohydrodynamic (MHD) numerical simulations of the evolution of self--gravitating and weakly magnetized disks with an adiabatic equation of state. Such disks are subject to the development of both the magnetorotational and gravitational instabilities, which transport angular momentum outward. As in previous studies, our hydrodynamical simulations show the growth of strong m=2 spiral structure. This spiral disturbance drives matter toward the central object and disappears when the Toomre parameter Q has increased well above unity. When a weak magnetic field is present as well, the magnetorotational instability grows and leads to turbulence. In that case, the strength of the gravitational stress tensor is lowered by a factor of about~2 compared to the hydrodynamical run and oscillates periodically, reaching very small values at its minimum. We attribute this behavior to the presence of a second spiral mode with higher pattern speed than the one which dominates in the hydrodynamical simulations. It is apparently excited by the high frequency motions associated with MHD turbulence. The nonlinear coupling between these two spiral modes gives rise to a stress tensor that oscillates with a frequency which is a combination of the frequencies of each of the modes. This interaction between MHD turbulence and gravitational instabilities therefore results in a smaller mass accretion rate onto the central object.Comment: 31 pages, 19 figures, accepted for publication in ApJ, animation avalaible at http://www2.iap.fr/users/fromang/simu3d/simu3d.htm

Observateur à mode glissant d'ordre 2 pour la machine asynchrone sans capteur mécanique

International audienceCet article présente un observateur à mode glissant du second ordre pour un moteur asynchrone sans capteur mécanique. Cet observateur converge en un temps fini et est robuste vis à vis des variations de paramètres. En utilisant Matlab/Simulink, les résultats de simulations montrent les performances de l'observateur proposé. De plus au travers d'une application industrielle, l'intérêt technologique de la méthode proposée ainsi que les difficultés liées aux calculs en temps réel sont mis en évidence

A Pressure Based Compressible Solver for Electric Arc-plasma Simulation

The electric arc discharge in a liquid medium is used in several applications such as the sterilization of the liquid by UV radiation, the fracturing of rocks by shock wave, the circuit breakers in oil bath or the forming of mechanical parts. Thus, describing the physics of the arc in a liquid and in particular its interaction with a liquid interface is an important issue to better characterize this type of configuration. However, such a challenging task requires to couple high-fidelity solver for compressible two-phase flows with liquid phase change and a plasma solver to describe the plasma and its interaction with the bubble. To study this type of medium, we use a compressible formulation of the fluid equations. For this purpose, a pressure based solver has been developed for the computation of the energy conservation equation. Moreover, our numerical model uses the immersed boundary method to simulate the solid electrodes. The numerical model is briefly described in this paper and the first results of the electric arc discharge in steam water are presented. To our knowledge this pressure based model has never been used to describe plasmas and electric arc discharge

Early life nutritional quality effects on adult memory retention in a parasitic wasp

Nutritional quality during early life can affect learning ability and memory retention of animals. Here we studied the effect of resource quality gained during larval development on the learning ability and memory retention of 2 sympatric strains of similar genetic background of the parasitoid Trichogramma brassicae: one uninfected and one infected by Wolbachia. Wolbachia is a common arthropod parasite/mutualistic symbiont with a range of known effects on host fitness. Here we studied, for the first time, the interaction between resource quality and Wolbachia infection on memory retention and resource acquisition. Memory retention of uninfected wasps was significantly longer when reared on high quality hosts when compared to low quality hosts. Furthermore, uninfected wasps emerging from high quality hosts showed higher values of protein and triglyceride than those emerging from low quality hosts. In contrast, the memory retention for infected wasps was the same irrespective of host quality, although retention was significantly lower than uninfected wasps. No significant effect of host quality on capital resource amount of infected wasps was observed, and infected wasps displayed a lower amount of protein and triglyceride than uninfected wasps when reared on high quality hosts. This study suggests that the nutritional quality of the embryonic period can affect memory retention of adult wasps not infected by Wolbachia. However, by manipulating the host’s obtained capital resource amount, Wolbachia could enable exploitation of the maximum available resources from a range of hosts to acquire suitable performance in complex environments