Compensation magnétique de pesanteur dans des fluides : synthèse des performances et contraintes

La communication présente les principauxrésultats théoriques et expérimentaux obtenus depuis unequinzaine d'années dans le domaine de la compensationmagnétique de pesanteur. Cette technique, destinéeprincipalement à des études de comportement de fluides enenvironnement spatial, utilise des sources de champ magnétiquegénéralement élevé. Les avantages et les limites de la lévitationsont présentés ; son application à des problèmes decomportement de fluides sous forme diphasique est décrite.</p

Multilevel Modular Mesocrystalline Organization in Red Coral

International audienceBiominerals can achieve complex shapes as aggregates of crystalline building blocks. In the red coral skeleton, we observe that these building blocks are arranged into eight hierarchical levels of similarly (but not identically) oriented modules. The modules in each hierarchical level assemble into larger units that comprise the next higher level of the hierarchy, and consist themselves of smaller, oriented modules. EBSD and TEM studies show that the degree of crystallographic misorientation between the building blocks decreases with decreasing module size. We observe this organization down to a few nm. Thus, the transition from imperfect crystallographic order at mm scale to nearly perfect single crystalline domains at nm scale is progressive. The concept of 'mesocrystal' involves the three-dimensional crystallographic organization of nanoparticles into a highly ordered mesostructure. We add to this concept the notion of 'multilevel modularity'. This modularity has potential implications for the origin of complex biomineral shapes in nature. A multilevel modular organization with small intermodular misorientations combines a simple construction scheme, ruled by crystallographic laws, with the possibility of complex shapes. If the observations we have made on red coral extend to other biominerals, long-range crystallographic order and interfaces at all scales may be key to how some biominerals achieve complex shapes adapted to the environment in which they grow

Interfaces between Pb grains and Cu surfaces

International audienc

L'épreuve du tri sur site des déchets de la construction

ÉpisciencesLa transformation du secteur de la construction, plus gros producteur de déchets dans de nombreux pays, représente un enjeu majeur pour une diminution de l'empreinte matérielle de nos sociétés. Cependant, les déchets sont souvent mélangés sur les chantiers de construction, triés seulement a posteriori dans des unités centralisées, diminuant fortement la recyclabilité de certains matériaux. La mise en place de tri directement sur les chantiers de construction est ainsi un enjeu d'importance, dont la diffusion demeure décorrélée des bénéfices environnementaux qui lui sont associés. Cette faible diffusion du tri sur site révèle une faible connaissance des pratiques réelles de tri, qui reste une boîte noire opérationnelle comme académique. Cet article, via une recherche en partenariat avec une entreprise de la construction francilienne, permet de documenter la réalité des faibles pratiques de tri sur les chantiers de construction. Celle-ci est notamment associée à des doutes sur la viabilité économique de ce type de démarche. L'article propose une simulation simple pour tester l'intérêt économique du tri sur chantier, montrant une baisse des coûts de gestion des déchets pour les constructeurs jusqu'à 48%. Celle-ci est mise à l'épreuve de la mise en place dans deux chantiers, montrant les défis que celle-ci ouvrent pour confirmer à la fois l'intérêt économique et la soutenabilité de la démarche de tri sur site des déchets de la construction. Mots-clés : déchets-construction-tri sur site-pratiques professionnelles-Ile de Franc

Multilevel modular mesocrystalline organization in red coral

Biominerals can achieve complex shapes as aggregates of crystalline building blocks. In the red coral skeleton, we observe that these building blocks are arranged into eight hierarchical levels of similarly (but not identically) oriented modules. The modules in each hierarchical level assemble into larger units that comprise the next higher level of the hierarchy, and consist themselves of smaller, oriented modules. EBSD and TEM studies show that the degree of crystallographic misorientation between the building blocks decreases with decreasing module size. We observe this organization down to a few nanometers. Thus, the transition from imperfect crystallographic order at millimeter scale to nearly perfect single crystalline domains at nanometer scale is progressive. The concept of >mesocrystal> involves the three-dimensional crystallographic organization of nanoparticles into a highly ordered mesostructure. We add to this concept the notion of >multilevel modularity.> This modularity has potential implications for the origin of complex biomineral shapes in nature. A multi-level modular organization with small intermodular misorientations combines a simple construction scheme, ruled by crystallographic laws, with the possibility of complex shapes. If the observations we have made on red coral extend to other biominerals, long-range crystallographic order and interfaces at all scales may be key to how some biominerals achieve complex shapes adapted to the environment in which they growThis work has been supported by Centre National de la Recherche Scientifique (CNRS), Institut National des Sciences de l’Univers (INSU) through grants ECLIPSE 2005, INTERRVIE 2009, and by Centre Interdisciplinaire de Nanoscience de Marseille (CINaM) through internal grants to D.V.Peer Reviewe

Determining the experimental leachability of copper, lead, and zinc in a harbor sediment and modeling

International audienceThe potential leaching of pollutants present in harbor sediments has to be evaluated in order to choose the best practices for managing them. Little is known about the speciation and mobility of heavy metals in these specific solid materials. The objective of this paper is to determine and model the leachability of copper, lead, and zinc present in harbor sediments in order to obtain essential new data. The mobility of inorganic contaminants in a polluted harbor sediment collected in France was investigated as a function of physicochemical conditions. The investigation relied mainly on the use of leaching tests performed in combina- tion with mineralogical analysis and thermodynamic mod- eling using PHREEQC. The modeling phase was dedicated to both confirm the hypothesis formulated to explain the experimental results and improve the determination of the main physico-chemical parameters governing mobility. The experimental results and modeling showed that the release of copper, lead, and zinc is very low with deionized water which is due to the stability of the associated solid phases (organic matter, carbonate minerals, and/or iron sulfides) at natural slightly basic conditions. However, increased mobilization is observed under pH values below 6.0 and above 10.0. This methodology helped to consistently obtain the geochemical parameters governing the mobility of the contaminants studied

Nucleation and growth of a bubble pattern under vibrations in weightlessness

Liquid-vapor phase transition of hydrogen was investigated during vibrations of "high" frequency = [10\hbox 25.4] s-1 and "low" amplitude [0.3\hbox0.47] mm in a weightless environment. Gravity effects were compensated in a strong magnetic-field gradient. The experiments were performed near the liquid-vapor critical point and at liquid, slightly off-critical density. Vapor bubbles nucleate and grow in the liquid phase. During the initial stage, the mean bubble diameter, D, is lower than the viscous boundary layer thickness, $\delta$, and bubble growth is unaffected by vibrations, i.e. D ~ (time)1/3. When D > $\delta$, the bubbles and the liquid phase have different velocities and the bubble pattern orders in rows perpendicular to vibration under the influence of forces of hydrodynamic origin. An analysis in terms of Levy flight and superdiffusion gives a bubble evolution of D ~ (time)1/2, a result that compares reasonably well with the experimental data

Contribution à l’étude des propriétés électriques de la fluorine

Nous présentons dans cet article les résultats obtenus sur la fluorine par différentes méthodes. La méthode TCI a permis de séparer des processus de relaxation voisins qui avaient été mis en évidence par une méthode pendulaire sans contact d’électrodes et par l’étude du déphasage courant-tension. Des informations sur la conduction ont été déduites de l’étude comparative de mesures de pertes diélectriques, de répartitions de potentiel et des thermocourants de dépolarisation observés au-dessus de la température ambiante

Phase transition under forced vibrations in critical CO₂

Phase separation is investigated in CO2 under linear harmonic vibrations. The study is performed under weightlessness in a sounding rocket. The fluid is at critical density near its critical point to get benefit from universal behavior. Without vibration, phase separation is characterized by an interconnected pattern of vapor and liquid domains and a near linear growth law. Under vibration, three time regions have been identified. i) When the liquid-vapor domains are smaller than a few viscous boundary layer thickness, growth is unaffected by vibration. ii) Then the Bernoulli pressure across the interfaces makes the domains grow exponentially perpendicularly to the vibration direction while growth parallel to the vibration direction is unaffected. iii) When the domains reach the sample size, the pattern looks as periodic stripes perpendicular to the vibration direction and keep on growing parallel to the vibration direction. A theoretical approach of these phenomena is proposed