Plutonium in the environment: key factors related to impact assessment in case of an accidental atmospheric release

International audienceThis paper deals with plutonium and key factors related to impact assessment. It is based on recent work performed by CEA which summarize the main features of plutonium behaviour from sources inside installations to the environment and man, and to report current knowledge on the different parameters used in models for environmental and radiological impact assessment. These key factors are illustrated through a case study based on an accidental atmospheric release of Pu in a nuclear facility

Conference of Microelectronic Research 1990

https://scholarworks.rit.edu/meec_archive/1003/thumbnail.jp

Multiscale characterization of the organization of triglycerides and phospholipids in Emmental cheese: From the microscopic to the molecular level

Multiscale characterization of the organization of triglycerides and phospholipids in Emmental cheese: From the microscopic to the molecular leve

Kinetics of hydrogen adsorption and mobility on Ru nanoparticles supported on alumina: effects on the catalytic mechanism of ammonia synthesis

Relevant findings on hydrogen adsorption and mobility are provided in this work to elucidate the mechanism of low-temperature ammonia synthesis, catalyzed by polydispersed Ru nanoparticles supported on alumina. H/D isotopic exchange technique, complemented by DRIFTS analysis, was applied to study the kinetics of hydrogen adsorption/desorption on metallic Ru and hydrogen diffusivity on alumina, for catalysts presenting different size distributions of Ru nanoparticles. H atoms adsorbed on large Ru nanoparticles present higher mobility and they migrate on alumina via exchange with OH groups. A broad size distribution of Ru nanoparticles leads to synergy in the rate of ammonia synthesis, and also in hydrogen mobility. The mechanism of catalytic cooperation involves transfer of H atoms from large to small nanoparticles, where the reaction rate is promoted. Considering dynamic catalytic processes in the formulation of kinetic models is crucial for a more accurate description of processes and the development of large-scale processes

Disclosing the synergistic mechanism in the catalytic activity of different-sized Ru nanoparticles for ammonia synthesis at mild reaction conditions

According to our previous results, a broad size distribution of Ru-supported nanoparticles is required for a high activity in ammonia synthesis under mild reaction conditions, since a synergy in the catalytic activity was observed between particles of different sizes. In this work we reach a more controlled heterogeneity of sizes by mixing different ruthenia colloidal suspensions, before impregnation on alumina, which improves the catalytic activity. Kinetic studies, ‘in situ’ characterizations and H/D isotopic exchange experiments were separately performed on catalysts containing small Ru nanoparticles and catalysts containing larger particles, in order to elucidate the mechanism of catalytic cooperation. Clear evidence is presented of a mechanism involving the migration of H atoms from large to small Ru nanoparticles, which is expected to improve the catalytic performance by promoting the hydrogenation of adsorbed NHx species and the release of active sites

Investigation of the speciation of uranium(VI) in concentrated phosphoric acid and in synergistic extraction systems by time-resolved laser-induced fluorescence spectroscopy (TRLFS)

International audienceno abstrac

Fat globules selected from whole milk according to their size: Different compositions and structure of the biomembrane, revealing sphingomyelin-rich domains

 Milk fat globules are unique delivery systems for biologically active molecules in the gastrointestinal tract. However, their properties have not yet been fully investigated. In this study, we performed a comparative analysis of the polar lipid and fatty acid compositions of milk fat globules as a function of their size and investigated the structure of the milk fat globule membrane (MFGM). An optimised process of microfiltration was used to select the small milk fat globule (SMFG; 1.6 lm) fractions and the large milk fat globule (LMFG; 6.6 lm) fractions from the same initial whole milks (4.2 lm). The SMFG-fractions contained significantly (i) higher amounts of polar lipids, 8.9 ± 0.9 vs 2.7 ± 0.3 mg/g fat for LMFG-fractions and 6.3 ± 0.5 mg/g fat for whole milks, (ii) lower relative proportions of phosphatidylcholine and sphingomyelin in the MFGM, (iii) higher amounts of C12:0, C14:0, C16:0, C18:1 trans, C18:2 c9 tr11, and lower amounts of C18:0 and C18:1 c9 than did LMFG-fractions and whole milks. Whatever the size of native milk fat globules, the biophysical characterisation performed in-situ, using confocal laser scanning microscopy, showed heterogeneities in the MFGM. The lateral segregation of sphingomyelin in rigid liquid-ordered domains, surrounded by the fluid matrix of glycerophospholipids in the liquid-disordered phase, was revealed. The heterogeneous distribution of glycolipids and glycoproteins was also observed in the MFGM. A new model for the structure of the MFGM is proposed and discussed. The physical, chemical and biological consequences, (i) of the differences in milk fat globule compositions according to their size and (ii) of the specific structure of the MFGM due to sphingomyelin remain to be elucidated