University of Rennes

About: University of Rennes is a education organization based out in Rennes, France. It is known for research contribution in the topics: Population & Catalysis. The organization has 18404 authors who have published 40374 publications receiving 995327 citations.

Achieving few-femtosecond time-sorting at hard X-ray free-electron lasers

Abstract: Recently, few-femtosecond pulses have become available at hard X-ray free-electron lasers Coupled with the available sub-10 fs optical pulses, investigations into few-femtosecond dynamics are not far off However, achieving sufficient synchronization between optical lasers and X-ray pulses continues to be challenging We report a 'measure-and-sort' approach, which achieves sub-10 fs root-mean-squared (rms) error measurement at hard X-ray FELs, far beyond the 100-200 fs rms jitter limitations This timing diagnostic, now routinely available at the Linac Coherent Light Source (LCLS), is based on ultrafast free-carrier generation in optically transparent materials Correlation between two independent measurements enables unambiguous demonstration of ~6 fs rms error in reporting the optical/X-ray delay, with single shot error suggesting the possibility of reaching few-femtosecond resolution

The Role of Biodiversity in the Functioning of Freshwater and Marine Benthic Ecosystems

Abstract: Empirical studies investigating the role of species diversity in sustaining ecosystem processes have focused primarily on terrestrial plant and soil communities. Eighteen representative studies drawn from post-1999 literature specifically examined how changes in biodiversity affect benthic ecosystem processes. Results from these small-scale, low-diversity manipulative studies indicate that the effects of changes in biodiversity (mostly synonymous with local species richness) are highly variable over space and time and frequently depend on specific biological traits or functional roles of individual species. Future studies of freshwater and marine ecosystems will require the development of new experimental designs at larger spatial and temporal scales. Furthermore, to successfully integrate field and laboratory studies, the derivation of realistic models and appropriate experiments will require approaches different from those already used in terrestrial systems.

In search of a real definition of the biological invasion phenomenon itself

Abstract: The many qualifying terms attributed to invasive species reveal the lack of precision surrounding the notion of biological invasion itself. In spite of several proposed definitions, some basic disagreements persist concerning characterization of the phenomenon. These primarily arise from the lack of pertinence of both of the main current criteria—the geographic (or biogeographic) criterion and the impact criterion—to what is really intended by “invasion.” Faced with this situation, it seems preferable to adopt an ontological approach allowing a return to the basic principles of the elaboration of a definition. Starting with the nature of the phenomenon itself (i.e., its essence), we try to elucidate the notion of biological invasion and we suggest a general definition compatible with most of the ideas already expressed.