Soil calcium availability influences shell ecophenotype formation in the sub-antarctic land snail, Notodiscus hookeri.

Ecophenotypes reflect local matches between organisms and their environment, and show plasticity across generations in response to current living conditions. Plastic responses in shell morphology and shell growth have been widely studied in gastropods and are often related to environmental calcium availability, which influences shell biomineralisation. To date, all of these studies have overlooked micro-scale structure of the shell, in addition to how it is related to species responses in the context of environmental pressure. This study is the first to demonstrate that environmental factors induce a bi-modal variation in the shell micro-scale structure of a land gastropod. Notodiscus hookeri is the only native land snail present in the Crozet Archipelago (sub-Antarctic region). The adults have evolved into two ecophenotypes, which are referred to here as MS (mineral shell) and OS (organic shell). The MS-ecophenotype is characterised by a thick mineralised shell. It is primarily distributed along the coastline, and could be associated to the presence of exchangeable calcium in the clay minerals of the soils. The Os-ecophenotype is characterised by a thin organic shell. It is primarily distributed at high altitudes in the mesic and xeric fell-fields in soils with large particles that lack clay and exchangeable calcium. Snails of the Os-ecophenotype are characterised by thinner and larger shell sizes compared to snails of the MS-ecophenotype, indicating a trade-off between mineral thickness and shell size. This pattern increased along a temporal scale; whereby, older adult snails were more clearly separated into two clusters compared to the younger adult snails. The prevalence of glycine-rich proteins in the organic shell layer of N. hookeri, along with the absence of chitin, differs to the organic scaffolds of molluscan biominerals. The present study provides new insights for testing the adaptive value of phenotypic plasticity in response to spatial and temporal environmental variations.

Selective spectral modulation of strongly coupled spins with an echo top refocusing pulse in PRESS sequences.

The double spin echo is the basis of the point resolved spectroscopy (PRESS) sequence. In this study we sought to investigate the effects of a broadband 180° pulse - incorporated in the PRESS sequence at the location of the first echo (gPRESS) - on the citrate resonances, chosen as a model of strongly coupled spin system. A significant signal modulation generated by the additional 180° pulse was predicted with simulations and observed experimentally in the citrate resonances. No effects were observed on the singlet resonance of glycine and the weakly coupled resonances of lactate. The phenomenon observed in gPRESS was attributed to the off-diagonal Hamiltonian elements responsible for a coherence transfer occurring throughout the evolution periods. The results of this study show that it is necessary to assess the effects of broadband 180° pulses on strongly coupled spin systems, since these pulses can selectively modify the spectral shape of strongly coupled resonances.

Structural investigations of glass ceramics in the Ga(2)S(3)-GeS(2)-CsCl system.

Transparent glass ceramics have been prepared in the Ga(2)S(3)-GeS(2)-CsCl pseudoternary system using appropriate heat treatment time and temperature. In situ X-ray diffraction at the heat treatment temperature and (133)Cs and (71)Ga solid-state nuclear magnetic resonance have been performed in function of annealing time to understand the crystallization process. Both techniques have evidenced the nucleating agent role played by gallium with the formation of Ga(2)S(3) nanocrystals. On the other hand, cesium is incorporated very much later into the crystallites during the ceramization. Moreover, the addition of CsCl, which is readily integrated into the glassy network, permits us to shift the optical band gap toward shorter wavelength. Thus, new glass ceramics transmitting in the whole visible range up to 11.5 mum have been successfully synthesized from the (Ga(2)S(3))(35)-(GeS(2))(25)-CsCl(40) base glass composition.

Synthesis, electronic and crystal structures, and physical studies of the superconductor Cs(~1)Mo12S14, final step of the condensation of the Mo6L8(i)L6(a) unit.

The ternary reduced molybdenum sulphide Cs(~1)Mo12S14 has been synthesized by solid-state reaction at 1400 degrees C for 96 h in sealed molybdenum crucibles. The compound crystallizes in the trigonal space group P31c with the following lattice parameters: a = 9.9793 (2) A, c = 6.3730 (2) A, Z = 1. Its crystal structure was determined from single crystal X-ray diffraction data and consists of interconnected Mo6S8(i)S6(a) units forming an original three-dimensional framework in which large tunnels are occupied randomly by the Cs+ ions. 133Cs static NMR studies are in favor of a static cesium disorder. Unlike Ba4Mo12S18 where some Mo6S8(i)S6(a) units are also connected through S(i-i) ligands, this connection mode does not lead to significant interactions in the title compound. Single-crystal resistivity measurements show that Cs(~1)Mo12S14 presents a metallic behavior with a superconducting transition at 7.7 K as confirmed by magnetic measurements.