IPG Photonics

About: IPG Photonics is a based out in . It is known for research contribution in the topics: Laser & Fiber laser. The organization has 903 authors who have published 1241 publications receiving 63339 citations.

Mineralogical gradients associated with alvinellids at deep-sea hydrothermal vents

Abstract: Alvinella pompejana and Alvinella caudata live in organic tubes on active sulphide chimney walls at deep-sea hydrothermal vents. These polychaete annelids are exposed to extreme thermal and chemical gradients and to intense mineral precipitation. This work points out that mineral particles associated with Pompeii worm (A. pompejana and A. caudata) tubes constitute useful markers for evaluating the chemical characteristics of their micro-environment. The minerals associated with these worm tubes were analysed on samples recovered from an experimental alvinellid colony, at different locations in the vent fluid–seawater interface. Inhabited tubes from the most upper and lower parts of the colony were analysed by light and electron microscopies, X-ray microanalysis and X-ray diffraction. A change was observed from a Fe–Zn–S mineral assemblage to a Zn–S assemblage at the millimeter scale from the outer to the inner face of a tube. A similar gradient in proportions of minerals was observed at a decimeter scale from the lower to the upper part of the colony. The marcasite/pyrite ratio of iron disulphides also displays a steep decrease along the few millimeters adjacent to the external tube surface. The occurrence of these gradients indicates that the micro-environment within the tube differs from that outside the tube, and suggests that the tube wall acts as an efficient barrier to the external environment.

The aperiodic states of zircon: an ab initio molecular dynamics study

Abstract: We theoretically investigated the local structure of the aperiodic states of zircon (ZrSiO 4 ) using ab initio quantum mechanical calculations. The low and high density liquid and solid glassy phases were obtained by constant volume Car-Parrinello molecular dynamics simulations, using the molar volume of metamict and crystalline zircon, respectively. As in naturally metamict zircons, the polymerization of Si units, the segregation of Zr atoms, and an overall decrease of the Zr coordination were observed. However, the local ordering of our theoretical glasses differs from that of the natural amorphous samples. In the theoretical glasses, the Zr-O distances in the first coordination polyhedra are significantly more distributed and five- and six-coordinated Si species were observed. The relaxation of the glass structure on a time scale exceeding the possibility of molecular modeling is a possible explanation for these discrepancies. The dielectric and 2 9 Si NMR responses of the glassy phases were computed, providing new constraints for the analysis of experimental data recorded from metamict zircons. The calculated NMR spectra are in good agreement with the experimental NMR spectra in the four-coordinated Si region. Our results show that the usual regular systematic decrease of the 2 9 Si chemical shift as a function of the polymerization of Si units (Q n species) cannot be used to interpret the 2 9 Si NMR spectrum of amorphous zircon. In particular, whereas the empirical scale would indicate an average polymerization of Q 3 , the average polymerization of Q 1 . 5 observed in the low density zircon glass can account for the experimental data. In a non-uniform model of the structure of metamict zircon, this lower average polymerization is consistent with a clustering of cations limited to few coordination polyhedra.

Phytoavailability of zirconium in relation to its initial added form and soil characteristics

Abstract: The various uses of zirconium (Zr) in chemical and nuclear industries generate a potential risk of environmental contamination by this element. This study was performed on two agricultural soils, an acidic soil (A) and a clayey calcareous soil (B), collected in the Meuse/Haute Marne experimental site of the French National Agency for radioactive waste management (Andra). Distribution coefficients (K d), defined as the ratio of Zr concentration in the solid phase (mol/kg) to Zr concentration in the solution (mol/l), were obtained for both soils. Their high values (6,000 < K d < 30,000 l/kg) suggest a rapid and strong retention of Zr on the soil constituents. Chemical extractions (0.01 M CaCl2, Calcium chloride, 0.005 M DTPA, Diethylene Triamine Penta Acetic acid, and 0.1 M NaPP, Sodium Pyrophosphate) showed that organic matter had a high affinity for the added Zr. Soil–plant transfer experiments showed low plant uptake. A significant absorption of Zr was, however, observed for the two studied plants, tomato (Lycopersicon esculentum L. cv. St. Pierre) and pea (Pisum sativum L. cv. “express”). For the most available forms of Zr (acetate and oxychloride), concentrations reached from 8 to 57 mg Zr/kg dry weight of roots. Zr is mainly accumulated in plant roots and is more absorbed by tomato than by pea. Zr bound to root cell walls (i.e. apoplastic Zr) concentrations, determined by HCl extraction, are significantly much lower than root absorbed Zr concentrations. Transfer to roots seemed to be more effective in the acidic soil and was strongly dependant on Zr added form.