The development of the passé composé in lower-intermediate learners of French as a second language

In this study we tracked the development of the passe compose in second-language learners of French whose first language is English. Although the passe compose is a highly used tense among native speakers of French and it appears to present particular difficulty for first-language English speakers, its second-language development has been surprisingly under-researched. In order to trace developmental patterns of the passe compose we obtained a corpus of obligatory context use of this tense by 30 Year-12 (lower-intermediate) students at two time points six months apart and analysed the data both quantitatively and qualitatively. Our findings suggest that these students used remarkably few memorized formulas, that they passed through five distinct stages in their acquisition of the passe compose, that those early stages were characterized by transfer errors, and that the presence of the auxiliary, whether correct or incorrect, formed a crucial stage in the development of the tense. Theoretical explanations for the findings are presented together with some tentative pedagogical implications

Volume interdiffusion coeffcient and uncertainty assessment for polycrystalline materials

A method has been developed in order to assess small volume interdiffusion coeffcients from experimental Electron Probe MicroAnalysis concentration profiles of polycrystalline materials by means of Boltzmann-Matano or den Broeder methods and their complementary Hall method. These methods have been used as tools for the investigation of the quasi-binary UO2/U(1-y)PuyO(2-z) interdiffusion, for which obtaining a solid solution in the bulk of grains is of major interest. In this paper uncertainties on the interdiffusion coefficient as a function of concentration have been computed for each method. Small volume cofficient measurements were enhanced by means of a small angle acquisition profile line with respect to the interdiffusion interface

Influence of the oxygen potential on the sintering of UO2–45% PuO2

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Towards Measuring the Pu Self-Diffusion Coefficient in Polycrystalline U0.55Pu0.45O2±x

International audienceThis paper describes an original method to measure the plutonium self-diffusion coefficient in the mixed oxide U0.55Pu0.45O2±x. This method is based on using 242Pu as a tracer atom. A thin film of the tracer was deposited on the well-polished surface of the samples and then diffusion annealings were performed from 1500°C to 1700°C, in an Ar-H2 5% atmosphere. The oxygen potential was fixed at-395 kJ.mol-1. After annealing, the 242Pu self-diffusion profiles were established by means of secondary ion mass spectrometry (SIMS). The 242Pu concentration profiles were determined by assessing the relative U, Am and Pu ionisation yields according to the experimental parameters. The choice of favourable experimental conditions and the relevance of the resulting concentration profiles are discussed at lengt

Highly transparent Nd:Lu2O3 ceramics obtained by coupling slip-casting and spark plasma sintering

International audienceA ceramic process coupling slip-casting of nanopowder suspensions and spark plasma sintering was used to prepare highly transparent Nd:Lu2O3 ceramic without any sintering aids. The influence of shaping by slip-casting on residual microstructural defects after sintering was investigated. Green compacts of nanopowders with homogeneous and submicron pore size promotes the elaboration of highly transparent ceramics with near-to-theoretical inline transmittance of 81.3% at 1060 nm. Spectroscopic properties of Nd:Lu2O3 ceramics were investigated at room temperature and 77 K