Micromechanics of root development in soil

International audienc

Structure and Magnetism of well-defined cobalt nanoparticles embedded in a niobium matrix

Our recent studies on Co-clusters embedded in various matrices reveal that the co-deposition technique (simultaneous deposition of two beams : one for the pre-formed clusters and one for the matrix atoms) is a powerful tool to prepare magnetic nanostructures with any couple of materials even though they are miscible. We study, both sharply related, structure and magnetism of the Co/Nb system. Because such a heterogeneous system needs to be described at different scales, we used microscopic and macroscopic techniques but also local selective absorption ones. We conclude that our clusters are 3 nm diameter f.c.c truncated octahedrons with a pure cobalt core and a solid solution between Co and Nb located at the interface which could be responsible for the magnetically inactive monolayers we found. The use of a very diluted Co/Nb film, further lithographed, would allow us to achieve a pattern of microsquid devices in view to study the magnetic dynamics of a single-Co cluster.Comment: 7 TeX pages, 9 Postscript figures, detailed heading adde

X-Ray Absorption Study of Ti, Cu and Fe Implanted AlN

Sintered AlN ceramics were implanted by Ti, Fe and Cu ions up to 1.9 × 10$\text{}^{17}$ atoms/cm$\text{}^{2}$ at mean energies of 70-110 keV in order to investigate the role of the chemical properties of the implanted species. on the phase formed during the implantation process. X-ray absorption studies were performed at room and at liquid nitrogen temperature to give information on the resulting systems and local environments of the Ti, Fe and Cu atoms. We observe the formation of TiN even for as-implanted samples, while the Cu ions aggregate to clusters. The Fe implanted samples show an intermediate behavior with both nitride formation and Fe clustering. In conclusion, the heat of formation is found to be a key parameter for the final system

Structure of Mn films grown on (111) and (001) fcc Ir determined by EXAFS and multiple-scattering approach

International audienc

Novel form of collective movement by soil bacteria

Although migrations are essential for soil microorganisms to exploit scarce and heterogeneously distributed resources, bacterial mobility in soil remains poorly studied due to experimental limitations. In this study, time-lapse images collected using live microscopy techniques captured collective and coordinated groups of B. subtilis cells exhibiting “crowd movement”. Groups of B. subtilis cells moved through transparent soil (nafion polymer with particle size resembling sand) toward plant roots and re-arranged dynamically around root tips in the form of elongating and retracting “flocks” resembling collective behaviour usually associated with higher organisms (e.g., bird flocks or fish schools). Genetic analysis reveals B. subtilis flocks are likely driven by the diffusion of extracellular signalling molecules (e.g., chemotaxis, quorum sensing) and may be impacted by the physical obstacles and hydrodynamics encountered in the soil like environment. Our findings advance understanding of bacterial migration through soil matrices and expand known behaviours for coordinated bacterial movement