Effective Long-Distance Pollen Dispersal in Centaurea jacea

BACKGROUND: Agri-environment schemes play an increasingly important role for the conservation of rare plants in intensively managed agricultural landscapes. However, little is known about their effects on gene flow via pollen dispersal between populations of these species. METHODOLOGY/PRINCIPAL FINDINGS: In a 2-year experiment, we observed effective pollen dispersal from source populations of Centaurea jacea in restored meadows, the most widespread Swiss agri-environment scheme, to potted plants in adjacent intensively managed meadows without other individuals of this species. Potted plants were put in replicated source populations at 25, 50, 100 m and where possible 200 m distance from these source populations. Pollen transfer among isolated plants was prevented by temporary bagging, such that only one isolated plant was accessible for flower visitors at any one time. Because C. jacea is self-incompatible, seed set in single-plant isolates indicated insect mediated effective pollen dispersal from the source population. Seed set was higher in source populations (35.7+/-4.4) than in isolates (4.8+/-1.0). Seed set declined from 18.9% of that in source populations at a distance of 25 m to 7.4% at 200 m. At a distance of 200 m seed set was still significantly higher in selfed plants, indicating long-distance effective pollen dispersal up to 200 m. Analyses of covariance suggested that bees contributed more than flies to this long-distance pollen dispersal. We found evidence that pollen dispersal to single-plant isolates was positively affected by the diversity and flower abundance of neighboring plant species in the intensively managed meadow. Furthermore, the decline of the dispersal was less steep when the source population of C. jacea was large. CONCLUSIONS: We conclude that insect pollinators can effectively transfer pollen from source populations of C. jacea over at least 200 m, even when "recipient populations" consisted of single-plant isolates, suggesting that gene flow by pollen over this distance is very likely. Source population size and flowering environment surrounding recipient plants appear to be important factors affecting pollen dispersal in C. jacea. It is conceivable that most insect-pollinated plants in a network of restored sites within intensively managed grassland can form metapopulations, if distances between sites are of similar magnitude as tested here

Dynamic behaviour of dry and water-satured sand under planar shock conditions

International audiencePlane shock-wave experiments were performed on dry and partially water-saturated sand, using three water contents, in order to validate predictive models of material behaviour at stress levels between 1 and 10 GPa. Gas and powder guns were used to load the sample under uni-axial strain conditions at low and high stress levels, respectively. Wave motions were detected by piezoelectric pins in the samples and a VISAR (Velocity Interferometer System for Any Reflector) recorded the free-surface velocity on the back target. This study presents both experimental and simulated results. Experimental data are used to determine shock Hugoniot states. Significant differences are observed in the dynamic response of the materials under various water-saturated conditions, and are reproduced with good agreement by numerical simulations using the ARMORS (A Rheological MOdel of Rocks Saturated) model

Relations sols-plantes en milieu pollue par les metaux lourds Caracteristiques phytosociologiques, chimiques, genetiques et biochimiques de quelques plantes resistantes sur sites pollues par l'antimoine

Titre de l'appel d'offres : Evaluation du risque lie a la presence de metaux lourdsAvailable from INIST (FR), Document Supply Service, under shelf-number : RP 185 (4294) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEMinistere de l'Amenagement du Territoire et de l'Environnement, 75 - Paris (France). Service de la Recherche et des Affaires Economiques (SRAE)FRFranc

APD photodetectors in the Geiger photon counter mode.

International audienceGeiger APD technology, which has been used for a few years now, is evolving towards better performances, including integration in multifunctional Microsystems; one such achievement is today the so-called SiPM [ref 1]. The present work has been conducted by a consortium of researchers from CESR and LAAS/CNRS and the manufacturing of components was achieved in the clean room of LAAS/CNRS. We present here an original N/P technology of photodiode, designed so as to offer a very good homogeneity in the electrical operating characteristics. For this, we have chosen a design and technological process which defines the breakdown voltage from the substrate doping. We present the technological process which we developed, in which we took a special care to maintain, by low transit temperature processes, at the highest quality level the initial characteristics of the materials. We will also present the performances of the diodes produced, with sizes ranging from 10 to 100µm, as a function of many parameters (gain, dark current, etc). We also produced SiPM, and also 8X8 arrays of SiPM. Typical characteristics for a single diode are a Vbr between 43V and 44V, and a dark current below 1 pA at ambient temperature. But the most important feature seems to be the high homogeneity of these performances all over the wafer surface. This gives us a great confidence in the next step of our work, which is the manufacturing of very high sensitivity imaging devices