Behavior of nanoparticle clouds around a magnetized microsphere under magnetic and flow fields

When a micron-sized magnetizable particle is introduced into a suspension of nanosized magnetic particles, the nanoparticles accumulate around the microparticle and form thick anisotropic clouds extended in the direction of the applied magnetic field. This phenomenon promotes colloidal stabilization of bimodal magnetic suspensions and allows efficient magnetic separation of nanoparticles used in bioanalysis and water purification. In the present work, size and shape of nanoparticle clouds under the simultaneous action of an external uniform magnetic field and the flow have been studied in details. In experiments, dilute suspension of iron oxide nanoclusters (of a mean diameter of 60 nm) was pushed through a thin slit channel with the nickel microspheres (of a mean diameter of 50$\mu$m) attached to the channel wall. The behavior of nanocluster clouds was observed in the steady state using an optical microscope. In the presence of strong enough flow, the size of the clouds monotonically decreases with increasing flow speed in both longitudinal and transverse magnetic fields. This is qualitatively explained by enhancement of hydrodynamic forces washing the nanoclusters away from the clouds. In the longitudinal field, the flow induces asymmetry of the front and the back clouds. To explain the flow and the field effects on the clouds, we have developed a simple model based on the balance of the stresses and particle fluxes on the cloud surface. This model, applied to the case of the magnetic field parallel to the flow, captures reasonably well the flow effect on the size and shape of the cloud and reveals that the only dimensionless parameter governing the cloud size is the ratio of hydrodynamic-to-magnetic forces - the Mason number. At strong magnetic interactions considered in the present work (dipolar coupling parameter $\alpha \geq 2$), the Brownian motion seems not to affect the cloud behavior

A modelling exercise on the importance of ternary alkaline earth carbonate species of uranium(VI) in the inorganic speciation of natural waters

International audiencePredictive modelling of uranium speciation in natural waters can be achieved using equilibrium thermodynamic data and adequate speciation software. The reliability of such calculations is highly dependent on the equilibrium reactions that are considered as entry data, and the values chosen for the equilibrium constants. The working group " Speciation " of the CETAMA (Analytical methods establishment committee of the French Atomic Energy commission, CEA) has organized a modelling exercise, including four participants, in order to compare modellers' selections of data and test thermodynamic data bases regarding the calculation of U(VI) inorganic speciation. Six different compositions of model waters were chosen so that to check the importance of ternary alkaline earth carbonate species of U(VI) on the aqueous speciation, and the possible uranium solid phases as solubility-limiting phases. The comparison of the results from the participants suggests i) that it would be highly valuable for end-users to review thermodynamic constants of ternary carbonate species of U(VI) in a consistent way and implement them in available speciation data bases, and ii) stresses the necessary care when using data bases to avoid biases and possible erroneous calculations

Les ambassadeurs suisses à Paris en 1663. Usages protocolaires : entre tradition et politique

Louis XIV invite les ambassadeurs des cantons suisses à jurer le renouvellement d’alliance le 18 novembre 1663 à Paris. L’étude du protocole en vigueur lors de cette cérémonie permettra une meilleure compréhension du rôle des ambassadeurs du Corps helvétique dans une mise en scène savamment orchestrée

Etude mécanistique de l'interaction des ions uranyle avec l'oxyde et le silicate de zirconium

Ce travail de thèse porte sur l'étude structurale et thermodynamique de l'adsorption des ions uranyle sur le silicate et l'oxyde de zirconium. La démarche adoptée a consiste à coupler à une approche macroscopique classique, une approche structurale microscopique de l'interface, permettant une définition expérimentale des équilibres de sorption, utilisée pour contraindre le code de calcul lors de la simulation des données thermodynamiques. Après la caractérisation de la surface des matériaux, l'étude thermodynamique a été réalisée pour différentes concentrations initiales des ions uranyle, différents sels de fond (NaClO4 et KNO3) et différentes forces ioniques. L'identification structurale des complexes de surface et des sites de sorption a été menée grâce à différentes spectroscopies complémentaires. Alors que les mesures de temps de vie par spectrofluorimétrie ont donné le nombre d'entités présentes en surface, la spectroscopie XPS a permis une détermination de la nature des sites de sorption, de type =Zr-O- sur la zircone et =Si-O- sur le zircon. L'usage combiné des différentes spectroscopies a rendu possible une détermination de la nature des espèces sorbées en fonction du sel de fond et du pH de sorption; en particulier, la spectroscopie DRIFT a été un outil remarquable pour la détermination de la présence de complexes uranyle nitrate sorbés sur la zircone. Les résultats des expériences de spectroscopie EXAFS indiquent clairement la nature sphère interne et polydentate du complexe de surface. Des expériences EXAFS ont également été menées à la fois sur des échantillons secs et in situ: la similarité des spectres obtenus confirme la validité de l'ensemble de l'étude structurale. Les données thermodynamiques ont ensuite été simulées à l'aide d'un modèle de complexation de surface (modèle à deux pK et à capacité constante), les résultats de l'étude structurale étant alors utilisées comme contraintes lors de la simulation.This work deals with structural and thermodynamic studies of the sorption of uranyl species on zircon and zirconia. After determination of the specific areas, of the pH of the isoelectric points, and of the sorption site numbers, thermodynamic data were obtained using alpha spectrometry, for different uranyl concentrations, different background electrolytes (NaClO4 or KNO3) and different ionic strengths. The structural identification of the different surface complexes and sorption sites was carried out using several different spectroscopies: XPS spectroscopy allowed a determination of the nature of the sorption sites (=Zr-O- on zirconia and =Si-O- on zircon). Whereas fluorescence decay measurements gave the number of surface species, the combinated use of XPS spectroscopy and laser spectrofluorimetry enabled us to correlate differences in bonding energies and emission wavelengths with differences in the nature of the background electrolyte or in the pH of sorption; DRIFT spectroscopy was a powerful tool for the determination of the presence of sorbed uranyl nitrate species. EXAFS results clearly showed a splitting of the equatorial oxygen atoms in two shells, corresponding to a polydentate, inner-sphere complex. EXAFS results also indicated strong similarities between dry samples and in situ experiments, which confirms the validity of all the spectroscopic measurements. Macroscopic thermodynamic data were then modelised using a surface complexation model (2 pK and constant capacitance models), the results of the structural study being used as constraints for the simulation code FITEQL.STRASBOURG-Bib.Central Recherche (674822133) / SudocORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Sorption of silicates on goethite, hematite, and magnetite: Experiments and modelling

International audienceSorption of H4SiO4 (including experiments as a function of time, Kd measurement with different m/v ratios and sorption edges) onto different iron (hydro)oxides as goethite (α-FeOOH), hematite (α-Fe2O3), and magnetite (Fe3O4) has been studied with concentration of silicates under solubility limit. A surface complexation model has been used to account for sorption edge of silicates onto these iron oxide surfaces. It reveals that two types of surface complex namely FeH3SiO4 and FeH2SiO−4, are needed to describe properly the experimental observations

High gellan gum concentration and secondary somatic embryogenesis: two key factors to improve somatic embryo development in Pseudotsuga menziesii [Mirb.]

Douglas-fir is a conifer species of major economic importance worldwide, including Western Europe and New Zealand. Herein we describe some characterization and significant refinement of somatic embryogenesis in Douglas-fir, with focus on maturation. The most typical structures observed in the embryonal masses were large polyembryogenic centres (up to 800-1500 μm) with a broad meristem, creating a compact ce ll “package” with suspensor cells. Singulated somatic embryos composed of both a embryonal head (300-400 μm) and long, tightly arranged suspensor were also frequent. Embryo development was enhanced following embryonal mass dispersion on filter paper discs at low density (50-100 mg fresh mass). Moreover, increasing gellan gum concentration in maturation medium (up to 10 g L-1) improved both the quantity and quality of cotyledonary somatic embryos (SEs), which were subsequently able to germinate and develop into plantlets at high frequency. Embryogenic yield was highly variable among the seven embryogenic lines tested (27-1544 SE g-1 fresh mass). Interestingly secondary somatic embryogenesis could be induced from cotyledonary SEs of both low- and highly-productive lines with some useful practical outcomes: secondary lines from low-performance lines (30-39 478 SE g-1) displayed significantly higher embryogenic yield (148-1343 SE g-1). In our best conditions, the total protein content in cotyledonary SEs increased significantly with maturation 41 duration (up to 150 μg mg-1 fresh mass after 7 weeks) but remained below that of mature zygotic embryos (300 μg mg-1). The protein pattern was similar in both somatic and zygotic embryos, with major storage proteins identified as 7S-vicilin- and legumin-like proteins

Le diplomate en question (XVe-XVIIIe siècles)

Ambassadeurs, envoyés, négociateurs, messagers, chevaucheurs… autant de vocables rencontrés pour désigner les acteurs de la diplomatie du Moyen Age aux Temps modernes. Si l’histoire des relations extérieures connaît un regain d’intérêt depuis une décennie, l’attention des chercheurs se porte encore trop souvent sur l’art de la négociation et les grands traités. On s’est, de fait, encore peu intéressé aux hommes sur qui reposaient les ambassades. Dans le but de saisir les évolutions et les pratiques de ce personnel diplomatique, le présent volume embrasse la longue durée, du XVe au XVIIIe siècle, et retient l’espace helvétique, au sens large, comme cadre spatial. La Suisse, par son importance politique, militaire et économique vis-à-vis de ses voisins, offre un espace propice au questionnement. Ce volume collectif apporte des éléments novateurs pour mettre en lumière les modalités de recrutement et les compétences des acteurs de la négociation étrangère auprès des cantons, qu’il s’agisse des ambassadeurs ou des membres du personnel secondaire. Fort de douze contributions réunissant des chercheurs de huit universités suisses et étrangères, cet ouvrage présente les résultats du colloque international qui s’est tenu à l’Université de Lausanne les 11 et 12 décembre 2009 sur «Le diplomate en question»

Repetitive somatic embryogenesis induced cytological and proteomic changes in embryogenic lines of Pseudotsuga menziesii

International audienc