[en] We analyze the role of soliton solutions and Hamiltonian singularities in the dynamics of counterpropagating waves in a medium of finite spatial extension. The soliton solution can become unstable due to the finite extension of the system. We show that the spatiotemporal dynamics then relaxes toward a Hamiltonian singular state of a nature different than that of the soliton state. This phenomenon can be explained through a geometrical analysis of the singularities of the stationary Hamiltonian system.

[en] We discuss symmetry properties of a quantum system comprised of 4 identical atoms in different large-distance molecular configurations and derive general selection rules with possible nuclei exchange after a four-atom collision, e.g. a molecular reaction. We focus on the following important collisional processes: (1) two bound diatomic molecules, (2) a bound triatomic molecule and a free atom, and (3) a bound diatomic molecule and two free atoms. The approach employed to treat this problem is based on analyzing Eigen spaces of the large-distance Hamiltonians and the corresponding constants of motion. The symmetry is then studied by decomposing a given Eigen space of the large-distance Hamiltonian in irreducible representations of the complete nuclear permutation inversion group G_4_8 of 4 identical nuclei appropriate for short distances using appropriate symmetry subgroups. The final results provide selection rules for collisions of four identical atom. (authors)

[en] We analyze the simultaneous time-optimal control of two-spin systems. The two noncoupled spins, which differ in the value of their chemical offsets, are controlled by the same magnetic fields. Using an appropriate rotating frame, we restrict the study to the case of opposite shifts. We then show that the optimal solution of the inversion problem in a rotating frame is composed of a pulse sequence of maximum intensity and is similar to the optimal solution for inverting only one spin by using a nonresonant control field in the laboratory frame. An example is implemented experimentally using nuclear magnetic resonance techniques.

[en] Prevention of possible noxious effects in relation with the exposure to one or several chemical, physical or biological agents present in our domestic or professional environment is one of today's big public health stakes. Another stake is the better assessment of the risks linked with the use of health-care products. The efficacy and predictiveness of toxicology studies are directly related to the combination of alternate complementary methods and animal experiments (obtaining data from different species and with different models: in vitro, ex vivo and in vivo). Despite important efforts, the toxicological evaluation remains perfectible. The proceedings of this 2010 congress of the French Society of cell pharmaco-toxicology deal with recent advances, both scientific and technological, in 'predictive toxicology'. Four main topics are approached: cell and organ models, 'omics', in silico modeling, and new technologies (imaging, cell ships, high-speed processing). Among the different presentations, 3 abstracts present some recent advances in imaging techniques applied to toxicology studies. These are: 1 - first uses in toxicology of TOF-SIMS mass spectroscopy imaging (O. Laprevote, Paris-Descartes Univ. (FR)); 2 - Small animal imaging, a tool for predictive toxicology (A. Le Pape, CNRS Orleans (FR)); 3 - uranium localization at cell level using SIMS imaging technique (C. Rouas et al., IRSN Fontenay-aux-Roses (FR)). (J.S.)