[en] classical particles diffuse inside the one dimensional interval [0,L]. There are reflecting walls at the edges of this interval. The diffusion constant of each particle is assumed independent of its energy and position. The particles interact through short range repulsive interaction that prevents them from exchanging positions - they stay ordered in there initial ordering on the line. The probability that at time t, all the particles are back at the points there were at t=0 (up to a distance less than a mean free path), and the configuration space average of this probability, are calculated. The interaction is dominating these quantities, even for times in which it is not expected to affect most of the dynamics of the system. Both results are exact, analytic, and have the form of the sum over terms that represents different kinds of many body processes - describing different ways of clustering of particles in the system. Connections to the Bethe Ansatz method, to quantum chaos and mesoscopic systems, and to random walks in nonequilibrium statistical mechanics, are pointed out

[en] Dynamics of magnetic flux tubes in the fast rotating stellar atmosphere is studied. We focus on the effects and signatures of the instability of the flux tube emergence influenced by the Coriolis force. We present the result from a linear stability analysis and discuss its possible signatures in the course of the evolution of G-type and M-type stars. We present a three dimensional magnetohydrodynamical simulation of local isolated magnetic flux tubes under a magnetic buoyancy instability in co-rotating Cartesian coordinates. We find that the combination of the buoyancy instability and the Coriolis effect gives rise to a mechanism, to twist the emerging magnetic flux tube into a helical structure. The tilt angle, east-west asymmetry and magnetic helicity of the Twisted flux tubes in the simulations are studied in detail. The linear and nonlinear analyses provide hints as to what kind of pattern of large spots in young M-type main-sequence stars might be observed. We find that young and old G-type stars may have different distributions of spots while M-type stars may always have low latitudes spots. The size of stellar spots may decrease when a star becomes older, due to the decreasing of magnetic field. A qualitative comparison with solar observations is also presented

[en] There has been significant progress in understanding substorm injections since the Third International Conference on Substorms in 1996. Progress has come from a combination of new theories, quantitative modeling, and observations--particularly multi-satellite observations. There is now mounting evidence that fast convective flows are the mechanism that directly couples substorm processes in the mid tail, where reconnection occurs, with substorm processes the inner magnetosphere where Pi2 pulsations, auroral breakups, and substorm injections occur. This paper presents evidence that those flows combined with an earthward-propagating compressional wave are responsible for substorm injections and discusses how that model can account for various substorm injection signatures

[en] The aim of this thesis is to study metallic sodium clusters by numerical simulation. We have developed two ab initio molecular dynamics programs within the formalism of density functional theory. The first is based on the semi-classical extended Thomas-Fermi approach. We use a real-space grid and a Car-Parrinello-like scheme. The computational cost is O(N), and we have built a pseudopotential that speeds up the calculations. By neglecting quantum shell effects, we are able to study a very large set of clusters. We show that sodium cluster energies fit well a liquid drop formula, by adjusting a few parameters. We have investigated breathing modes, surface oscillations and the net charge density. We have shown that the surface energy varies strongly with temperature, and that clusters have a lower melting point than bulk material. We have calculated fission barriers by a constraint method. The second program is based on the quantum Kohn-Sham approach. We use a real-space grid, and combine a generalized Broyden scheme for assuring self-consistency with an iterative Davidson-Lanczos algorithm for solving the Eigen-problem. The cost of the method is much higher. First of all, we have calculated some stable structures for small clusters and their energetics. We obtained very good agreement with previous works. Then, we have investigated highly charged cluster dynamics. We have identified a chaotic fission process. For high fissility systems, we observe a multi-fragmentation dynamics and we find preferential emission of monomers on a characteristic time scale less than a pico-second. This has been simulated for the first time, with the help of our adaptive grid method which follows each fragment as they move apart during the fragmentation. (author)

[en] In these lectures several approaches describing out of equilibrium systems are summarised. Using variational principle either for wave functions or for density matrices generalised mean-field approaches are derived as Erhenfest equations for a set of observables. With the help of projection methods these mean-field approaches are reinterpreted in order to justify the stochastic extensions of these theories. In this derivation the physical importance of the observables and the result of the measurement: the observation are emphasized. (author)

No abstract available

[en] In this paper I investigate the quantum noise reduction of a radiation field propagating, in a nonlinear medium due to the temporal changes of the refractive index. It is found that the squeezing properties of the radiation field varies in the prefocal and beyond focal region. (author)

[en] In many industrial applications, convection radiation and conduction participate simultaneously to the heat transfers. A numerical approach able to cope with such problems has been developed. The code SYRTHES is tackling conduction and radiation (limited to non participating medium) while the fluid part is solved by CFD codes like ESTET (Finite volumes) or N3S (Finite elements). SYRTHES relies on an explicit numerical scheme to couple all phenomena. No stability problems has been encountered. To provide further flexibility, the three phenomena are solved on independent grids. All data transfers being automatically taken care of by SYRTHES. Extending the development to multi-physics or multi-code problems it is fairly straightforward thanks to the explicit approach. Illustrating applications show how SYRTHES is managing problems for which several CFD codes are needed simultaneously with message passing tools like PVM and CALCIUM. (author)

[en] A model which incorporates all the characteristic features of the over all interactions in alkaline earth metals has been developed. The model makes use of minimum number of input data and it is utilized to compute the phonon-dispersion in fcc calcium and fcc barium with reasonable success. (author). 21 refs., 2 figs., 1 tab

[en] Roughening of a one-dimensional interface is studied under the assumption that the interface configurations are continuous, periodic random walks. The distribution of the square of the width of interface, w², is found to scale as P(w²)=left-angle w² right-angle ^-1Φ(w²/left-angle w² right-angle) where left-angle w² right-angle is the average of w². We calculate the scaling function Φ(x) exactly and compare it both to exact enumerations for a discrete-slope surface evolution model and to Φ's obtained in Monte Carlo simulations of equilibrium and driven interfaces of chemically reacting systems