Rhombohedral calcite precipitation from CO2-H2O-Ca(OH)2 slurry under supercritical and gas CO2 media

The formation of solid calcium carbonate (CaCO3) from aqueous solutions or slurries containing calcium and carbon dioxide (CO2) is a complex process of considerable importance in the ecological, geochemical and biological areas. Moreover, the demand for powdered CaCO3 has increased considerably recently in various fields of industry. The aim of this study was therefore to synthesize fine particles of calcite with controlled morphology by hydrothermal carbonation of calcium hydroxide at high CO2 pressure (initial PCO2=55 bar) and at moderate and high temperature (30 and 90 degrees C). The morphology of precipitated particles was identified by transmission electron microscopy (TEM/EDS) and scanning electron microscopy (SEM/EDS). In addition, an X-ray diffraction analysis was performed to investigate the carbonation efficiency and purity of the solid product. Carbonation of dispersed calcium hydroxide in the presence of supercritical (PT=90 bar, T=90 degrees C) or gaseous (PT=55 bar, T=30 degrees C) CO2 led to the precipitation of sub-micrometric isolated particles (<1$\mu$m) and micrometric agglomerates (<5$\mu$m) of calcite. For this study, the carbonation efficiency (Ca(OH)2-CaCO3 conversion) was not significantly affected by PT conditions after 24 h of reaction. In contrast, the initial rate of calcium carbonate precipitation increased from 4.3 mol/h in the "90bar-90 degrees C" system to 15.9 mol/h in the "55bar-30 degrees C" system. The use of high CO2 pressure may therefore be desirable for increasing the production rate of CaCO3, carbonation efficiency and purity, to approximately 48 kg/m3h, 95% and 96.3%, respectively in this study. The dissipated heat for this exothermic reaction was estimated by calorimetry to be -32 kJ/mol in the "90bar-90 degrees C" system and -42 kJ/mol in the "55bar-30 degrees C" system

Statics and dynamics of magnetocapillary bonds

When ferromagnetic particles are suspended at an interface under magnetic fields, dipole-dipole interactions compete with capillary attraction. This combination of forces has recently given promising results towards controllable self-assemblies, as well as low Reynolds swimming systems. The elementary unit of these assemblies is a pair of particles. Although equilibrium properties of this interaction are well described, dynamics remain unclear. In this letter, the properties of magnetocapillary bonds are determined by probing them with magnetic perturbations. Two deformation modes are evidenced and discussed. These modes exhibit resonances whose frequencies can be detuned to generate non-reciprocal motion. A model is proposed which can become the basis for elaborate collective behaviours

Remote control of self-assembled microswimmers

Physics governing the locomotion of microorganisms and other microsystems is dominated by viscous damping. An effective swimming strategy involves the non-reciprocal and periodic deformations of the considered body. Here, we show that a magnetocapillary-driven self-assembly, composed of three soft ferromagnetic beads, is able to swim along a liquid-air interface when powered by an external magnetic field. More importantly, we demonstrate that trajectories can be fully controlled, opening ways to explore low Reynolds number swimming. This magnetocapillary system spontaneously forms by self-assembly, allowing miniaturization and other possible applications such as cargo transport or solvent flows.Comment: 5 pages, 5 figures articl

Magnetocapillary self-assemblies: Swimming and micromanipulation

Floating magnetic particles can self-assemble into structures, by a combination of a magnetic dipole-dipole interaction and an attraction due to the interfacial deformation. These structures are periodically deformed in a non reciprocal way using magnetic fields, which leads to controllable low Reynolds number locomotion. Such microswimmers provide a basis for micromanipulation applications such as transport of micro-objects, local mixing of fluids or surface cleaning

Scattering from controlled defects in woodpile photonic crystals

Photonic crystals with a sufficiently high refractive index contrast display partial or full band gaps. However, imperfections in the metamaterial cause light scattering and extinction of the interfering propagating waves. Positive as well as negative defect volumes may contribute to this kind of optical perturbation. In this study, we fabricate and characterize three-dimensional woodpile photonic crystals, with a pseudo-bandgap for near-infrared optical wavelengths. By direct laser writing, we intentionally introduce random defects in the periodic structure. We show that we can model random defect scattering by considering the difference between the disordered and the regular structure. Our findings pave the way towards better control and understanding of the role of defects in photonic materials that will be crucial for their usability in potential applications.Comment: 8 pages, 7 figures + SI 5 pages, 6 figure

Ribbons of superparamagnetic colloids

While the aggregation process of superparamagnetic colloids in strong magnetic eld is well known on short time since a few decades, recent theoretical works predicted an equilibrium state reached after a long time. In this talk, we present experimental observations of this equilibrium state with a twodimensional system and we compare our data with the predictions of a pre-existing model. Above a critical aggregation size, a deviation between the model and the experimental data is observed. This deviation is explained by the formation of ribbon-shaped aggregates. The ribbons are formed due to lateral aggregation of chains. An estimation of the magnetic energy for chains and ribbons shows that ribbons are stable structures when the number of magnetic grains is higher than N=30

Topological and semantic Web based method for analyzing TGF-β signaling pathways

International audienceTargeting the deleterious effects of Transforming Growth Factor TGF-β without affecting its physiological role is the common goal of therapeutic strategies aiming at curing fibrosis, the final outcome of all chronic liver disease. The pleiotropic effects of TGF-β are linked to the complex nature of its activation and signaling net- works which understanding requires modeling approaches. Our group recently developed a model of TGF-beta signal propagation based on guarded transitions (ref, Andrieux et al, 2014). In this initial work, we explored the combinatorial complexity of cell signaling, developing a discrete formalism based on guarded transitions. We imported the whole database Pathway Interaction Database into a single unified model of signal transduction. We detected 16,000 chains of reactions linking TGF-β to at least one of 159 target genes in the nucleus. The size and complexity of this model place it beyond current understanding. Its analysis requires automated tools for identifying general patterns.Currently, we focus on designing one reasoning method based on Semantic Web technologies for the analysis of signaling pathways. Our method aims at leveraging external domain knowledge represented in biomedical ontologies and linked databases to rank these candidates. We consider a signaling pathway as a set of proteins involved in the respons of a cell to an external stimulus and influencing at least one gene. The underlying reasoning methods are based on graph topological analysis, formal concepts analysis (FCA) and semantic similarity and particularity measures. First, we determine the formal concepts, maximal bi-cliques, between proteins sets and genes. Then, to determine the biological relevance of theses gene clusters, we calculate a similarity score for each cluster based on Wang semantic similarity. Using such approaches, we identify groups of genes sharing signaling networks.Cibler les effets délétères du Transforming Growth Factor, TGF-β, sans affecter son rôle physiologique est l’objectif commun des stratégies thérapeutiques visant à guérir la fibrose, la conséquence finale de toutes les maladies chroniques du foie. Les effets pléiotropiques du TGF-β sont liés à la nature complexe de son activation et du réseaux de signalisation qu’il induit, et dont la compréhension nécessite des approches de modélisation. Notre équipe a développé un modèle de la propagation du signal induit par le TGF-β base ́ sur les transitions gardées. Le développement d’un formalisme discret base ́ sur les transitions gardées permet d’étudier la complexité combinatoire de la signalisation cellulaire. Nous avons formalise ́ l’intégralité de la base de données Pathway Interaction Database en un unique modèle de la propagation du signal. Nous avons détecté 16 000 chaines de réactions reliant le TGF-β à au moins l’un des 159 gènes cibles d’intérêt Pour identifier des propriétés au sein de ces résultats il est nécessaire d’utiliser des outils automatisés.Nous développons actuellement une méthode basée sur le Web sémantique pour l’analyse des voies de signalisation. Cette méthode vise à tirer parti des connaissances de domaine externe représentées dans les ontologies biomédicales et des bases de données pour classer ces candidats. Nous considérons qu’une voie de signalisation est un ensemble des protéines impliquées dans la réaction d’une cellule à un stimulus externe et qui influence au moins un gène. Les méthodes de raisonnement sous-jacentes sont basées sur l’analyse topologique, l’analyse formelle de concepts et les mesures de similarité et de particularité sémantique. Tout d’abord, nous déterminons les concepts formels, c’est-à-dire les bi-cliques maximales, entre les ensembles de protéines et les gènes. Puis, afin de déterminer la pertinence biologique de ces groupes de gènes, nous calculons un score de similarité pour chacun des groupes, base ́ sur la mesure de Wang. La finalité est d’identifier des groupes de gènes similaires influencés par un même ensemble de voies de signalisation

Memory System for a Dynamically Adaptable Pixel Stream Architecture

International audienceNowadays, embedded vision systems have to face new hard requirements involved by modern applications: realtime processing of high resolution images issued by multiple image sensors. Recently, a new adaptable ring-based interconnection network on chip has been proposed. Based on adaptive datapath, it allows handling of multiple parallel pixel streams. In this paper, we present a new hierarchical memory system proposed for this adaptable ring-based architecture. The design of its different levels is discussed and we show how the memory system adapts dynamically with respect to the datapath and data access management in the interconnection network. We also present the timing performance and area occupation measured on an FPGA prototype

Localization and speciation of Zn in mycorrihizd roots by μSXRF and μEXAFS.

Mycorrhizae are symbiotic associations between soil fungi and plant roots, which enhance mineral nutrition for the plant, and might play an important role in metals acquisition and accumulation. The processes allowing metals mobilization in the soil, absorption by the root and/or the fungus, transfer or bioaccumulation are still poorly understood. However, the properties of mycorrhizal fungi could be used for phytoremediation, a soft technique using plants for the clean-up of metal polluted soils. In this work, mycorrhized roots of tomato plants grown in a Zn-contaminated soil were investigated. The distribution of metals and the speciation of Zn were studied at the micron scale using micro synchrotron-based X-ray fluorescence (μSXRF) and micro X-ray absorption spectroscopy (μEXAFS). Zn associated to the root was Zn malate and/or Zn citrate, and Zn associated to the fungus was Zn phyllosilicate. This study illustrates the great potential of X-ray microbeams for the study of biological samples containing various amounts of metals