Boundary effects in large deviation problems

Projet MEVALWe get explicit formulas for large deviation problems in [??] with a discontinuity along an hyperplane and on [??] These quite unexpected results are obtained by using new simple probabilistic techniques

Random walks in two-dimensional complexes

Projet MEVA

Spallation reactions. A successful interplay between modeling and applications

The spallation reactions are a type of nuclear reaction which occur in space by interaction of the cosmic rays with interstellar bodies. The first spallation reactions induced with an accelerator took place in 1947 at the Berkeley cyclotron (University of California) with 200 MeV deuterons and 400 MeV alpha beams. They highlighted the multiple emission of neutrons and charged particles and the production of a large number of residual nuclei far different from the target nuclei. The same year R. Serber describes the reaction in two steps: a first and fast one with high-energy particle emission leading to an excited remnant nucleus, and a second one, much slower, the de-excitation of the remnant. In 2010 IAEA organized a worskhop to present the results of the most widely used spallation codes within a benchmark of spallation models. If one of the goals was to understand the deficiencies, if any, in each code, one remarkable outcome points out the overall high-quality level of some models and so the great improvements achieved since Serber. Particle transport codes can then rely on such spallation models to treat the reactions between a light particle and an atomic nucleus with energies spanning from few tens of MeV up to some GeV. An overview of the spallation reactions modeling is presented in order to point out the incomparable contribution of models based on basic physics to numerous applications where such reactions occur. Validations or benchmarks, which are necessary steps in the improvement process, are also addressed, as well as the potential future domains of development. Spallation reactions modeling is a representative case of continuous studies aiming at understanding a reaction mechanism and which end up in a powerful tool.Comment: 59 pages, 54 figures, Revie

Random walk in dynamic environment with mutual influence

AbstractWe study a discrete time random walk in Zv in a dynamic random environment, when the evolution of the environment depends on the random walk (mutual influence). We assume that the unperturbed environment evolves independently at each site, as an ergodic Markov chain, and that the interaction is strictly local. We prove that the central limit theorem for the position Xt of the random walk (particle) holds, whenever one of the following conditions is met: (i) the particle cancels the memory of the environment and the influence of the environment on the random walk is small; (ii) the exponential relaxation rate of the environment is large; (iii) the mutual interaction of the environment and the random walk is small. We also prove convergence of the distribution of the ‘environment as seen from the particle’. Proofs are obtained by cluster expansion techniques

Boundary effects in large deviation problems

Programme 1 : Architectures paralleles, bases de donnees, reseaux et systemes distribuesSIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : 14802 E, issue : a.1993 n.1999 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc