B and δ11B biogeochemical cycle in a beech forest developed on a calcareous soil: Pools, fluxes, and forcing parameters.

Rock weathering and biological cycling hold the development and sustainability of continental ecosystems, yet the interdependence of macro- and micro-nutrients biogeochemical cycles and their implications for ecosystem functioning remains unclear, despite being of particular importance in the context of global changes. This study focuses on the stocks, fluxes and processes constituting the biogeochemical cycle of boron. Vegetation, soils and solutions were monitored for a full year in a temperate beech forest developed on calcareous soil. Despite an overwhelmingly large B pool in soils, this study points to limited influence of weathering emphasizing the importance of vegetation cycling on this site. The biological imprint on the B cycle is marked by (1) a strong 11B enrichment of solutions compared to the mineral source and (2) systematic correlations observed between B and other strongly recycled elements in all water samples. B isotopes are fractionated within the beech stand with higher values in leaves (23.5‰) and lower in fine roots (-11.7‰), suggesting that the light 10B isotope is preferentially assimilated during plant growth. B isotopic data are consistent with a Rayleigh-like behaviour during xylem transfer leading to an 11B enrichment in the higher parts of the trees, putting internal B transfer as the main driver of the large range of isotopic compositions between plant tissues. B apparent isotopic fractionations are observed in the annually produced biomass and total beech stand, albeit with different values: αxylem-biomass = 0.980 ± 0.009 and 0.990 ± 0.002, respectively, suggesting 11B transfer from old to new tissue. The developed model also points to an isotopic fractionation factor during B uptake much higher than previously evaluated (0.979 < αuptake < 0.994). Overall, this study demonstrates that B isotopes appear as a promising tracer of soil-plant interactions with particular emphasis on tree adaptation to B bioavailability in soil.

Modelling the precipitation of nanoparticles in a closed medium in the presence of seeds: Application to amorphous silica synthesis.

Seed-mediated methods are widely used in industrial or academic laboratories for the synthesis of nanoparticles of controlled shape and size. In the natural medium, precipitation of secondary minerals also often take place on seeds. In this context, we have devised a formalism which accounts for the competition between seed growth and nucleation and growth of secondary particles in an initially over-saturated aqueous solution. Based on the classical nucleation theory, it involves a size-dependent growth law which accounts for Ostwald ripening effects, unlike most water-rock interaction codes. We find that, in such closed system, seed growth and nucleation/growth of secondary particles are strongly coupled. In the multi-dimensional parameter space, regions where one or the other process prevails are well-separated by a rather abrupt transition. In general, the value of the initial seed total surface area is insufficient to fully orientate the synthesis. Relying on this approach, we propose an alternative interpretation of recent experimental results on amorphous silica nanoparticle synthesis. Besides fundamental understanding of the kinetics of precipitation, the interest of the present approach is to serve as a guideline to experimentalists or industrialists working in seed-mediated syntheses and warn on the undesired formation of secondary particles when monodispersed distributions of nano- or micro-particles are searched.

Influence of structural parameters on magnetoresistive properties of CuFeNi melt spun ribbons.

The microstructure of Cu(80)Fe(10)Ni(10) (at%) granular ribbon was investigated by means of atom probe tomography (APT). A granular system is composed of magnetic precipitates embedded in a non-magnetic matrix. In this ribbon, the magnetic precipitates have a diameter smaller than 5nm in the as-spun state, and their crystallographic structure is very similar to the one of the matrix, which makes it difficult to characterize them using conventional techniques. Those data are of great importance to understand the magnetic and the transport behaviour of these ribbons. Using atom probe tomography, a 3D reconstruction of the microstructure of the as-spun and annealed ribbons was achieved and a precise characterization of the compositions of the two phases and of the composition profile at interfaces was carried out. In the as-spun state the composition of the matrix is Cu(89)Fe(3)Ni(8), the one of the precipitates is Cu(30)Fe(40)Ni(30). Upon annealing, the precipitates get enriched in iron. After annealing at 600 degrees C for 24h, the measured compositions are close to the one predicted by Thermocalc, with Cu(94)Fe(1)Ni(5) for the matrix and Cu(5)Fe(64)Ni(31) for the precipitates.

Influence of ageing, grinding and preheating on the thermal behaviour of alpha-lactose monohydrate.

It is shown that the onset temperature and the magnitude of thermal events observed during DSC analyses of alpha-lactose monohydrate can be strongly affected by various treatments such as ageing, manual grinding and preheating (cycle of preliminary dehydration and rehydration). In the case of grinding and preheating, the change of dehydration pathways was further investigated by using a suitable combination of characterization techniques, including X-ray powder diffraction (XRPD) performed with a synchrotron source (allowing an accurate Rietveld analysis), scanning electron microscopy (SEM), laser particle size measurements, FTIR spectroscopy and (1)H NMR for the determination of beta-lactose contents in samples. It appeared that the dehydration mechanism is affected not only by a smaller particle size distribution, but also by residual anisotropic lattice distortions and by the formation of surface defects or high energy surfaces. The fusion-recrystallization process occurring between anhydrous forms of alpha-lactose at ca. 170 degrees C is not significantly affected by grinding, whereas a preheating treatment induces an unexpected large increase of the enthalpy associated with this transition. Our observations and interpretations confirm the important role of water molecules in the crystal cohesion of the title compound and illustrate the necessity to consider the history of each sample for a satisfactory understanding of the physical properties and the behaviour of this important pharmaceutical excipient.

The influence of rivers on marine boron isotopes and implications for reconstructing past ocean pH.

Ocean pH is particularly sensitive to atmospheric carbon dioxide content. Records of ocean pH can therefore be used to estimate past atmospheric carbon dioxide concentrations. The isotopic composition of boron (delta11B) contained in the carbonate shells of marine organisms varies according to pH, from which ocean pH can be reconstructed. This requires independent estimates of the delta11B of dissolved boron in sea water through time. The marine delta11B budget, however, is still largely unconstrained. Here we show that, by incorporating the global flux of riverine boron (as estimated from delta11B measurements in 22 of the world's main rivers), the marine boron isotope budget can be balanced. We also derive ocean delta11B budgets for the past 120 Myr. Estimated isotope compositions of boron in sea water show a remarkable consistency with records of delta11B in foraminiferal carbonates, suggesting that foraminifera delta11B records may in part reflect changes in the marine boron isotope budget rather than changes in ocean pH over the Cenozoic era.