Rheological behaviour and spectroscopic investigations of cerium-modified AlO(OH)colloidal suspensions

The rheological behaviour of aqueous suspensions of boehmite (AlO(OH)) modified with different Ce-salts (Ce(NO3)3, CeCl3, Ce(CH3COO)3 and Ce2(SO4)3) was investigated at a fixed Ce/Al molar ratio (0.05). Freshly prepared boehmite suspensions were near-Newtonian and time-independent. A shear-sensitive thixotropic network developed when Ce-salts with monovalent anions were introduced in the nanoparticle sols. The extent of particle aggregation dramatically increased with ageing for Ce(NO3)3 and CeCl3 whereas an equilibrium value was reached with Ce(CH3COO)3. The addition of Ce2(SO4)3 with divalent anions involved no thixotropy but rather a sudden phase separation. The combined data set of IRTF and DRIFT spectra indicated that free View the MathML source anions of peptized boehmite adsorb on the nanoparticle surface by H-bond. The introduction of Ce-salts in the boehmite sol led to the coordination between Ce3+ ions and View the MathML source anions adsorbed on boehmite i.e. to [Ce(NO3)4(H2O)x]− complex. Such coordination led to a thixotropic behaviour which was lower with Ce(NO3)3 compared to CeCl3 and Ce(CH3COO)3. In contrast, Ce2(SO4)3 formed insoluble complexes with dissolved aluminium species. The formation of H-bonded surface nitrate complexes was found to play a decisive role on the particle–particle interactions and consequently on the rheological behaviour of the sols

Revêtements hybrides multifonctionneles élaborés par voie sol-gel pour la protection d'alliages d'aluminium pour l'aéronautique (AA2024-T3)

Les travaux de cette thèse portent sur l'élaboration de revêtements hybrides, exempts de Cr(VI), multifonctionnels innovants pour la protection contre la corrosion de l'alliage d'aluminium AA2024-T3. Le choix s'est porté sur une matrice sol-gel à base d'organoalkoxysilane, d'alkoxyde d'aluminium et d'un inhibiteur de corrosion. L'effet de la concentration de chaque précurseur a été étudié en estimant les performances anticorrosion des revêtements obtenus à l'aide du test du brouillard salin neutre (BSN) et de la spectroscopie d'impédance électrochimique (SIE). Ces résultats ont été ensuite complétés par des analyses RMN de xérogels pour corréler les performances anticorrosion à la structure chimique des revêtements. Ensuite des travaux sur la synthèse et la caractérisation de nanoparticules de boehmite préparées selon la méthode de Yoldas ont été discutés. Ces nanoparticules ont été modifiées par physisorption de l'inhibiteur de corrosion. La SIE a permis de démontrer que les nanoparticules ainsi modifiées sont bien des nanoréservoirs d'inhibiteur de corrosion. Dans la dernière partie de ce travail, l'élaboration de revêtements multifonctionnels est abordée de deux façons : tout d'abord en proposant une architecture originale pour de nouveaux revêtements présentant à la fois des nanoréservoirs d'inhibiteur de corrosion et une surface hydrophobe, puis enfin en obtenant des revêtements anticorrosion colorés. Ainsi des revêtements présentant une architecture originale et innovante ont été mis au point permettant de relever le défi du cahier des charges établi par les partenaires industriels.This thesis focuses on the development of innovative multifunctional hybrid coatings, free of Cr(VI), for protecting aluminum alloy AA2024-T3 against corrosion. The sol-gel innovative matrix is based on organoalkoxysilane, aluminum alkoxide and a corrosion inhibitor. The effect of the concentration of each precursor has been studied by measuring the anticorrosion performances of the coatings with the neutral salt spray test (NSS) and electrochemical impedance spectroscopy (EIS). Afterwards these results were corroborated by NMR analysis of xerogels to correlate corrosion performance with the chemical structure. The synthesis and characterization of boehmite nanoparticles were prepared according to the Yoldas method. These nanoparticles were modified by physisorption of the corrosion inhibitor. By EIS we have demonstrated that modified nanoparticles act as nanocontainers of corrosion inhibitor. In the last part of this work, the development of multifunctional coatings is approched in two ways: firstly, by providing an original architecture for new coatings displaying both corrosion inhibitor nanocontainers and a hydrophobic surface. Secondly by getting colored anticorrosion coatings. In conclusion coatings with an optimal and innovative original architecture have been engineered to satisfy the requirements established by the industrial partners

Magnetic Resonance Fingerprinting with Total Nuclear Variation Regularisation

Magnetic Resonance Fingerprinting (MRF) accelerates quantitative magnetic resonance imaging. The reconstruction can be separated into two problems: reconstruction of a set of multi-contrast images from k-space signals, and estimation of parametric maps from the set of multi-contrast images. In this study we focus on the former problem, while leveraging dictionary matching for the estimation of parametric maps. Two different sparsity promoting regularisation strategies were investigated: contrast-wise Total Variation (TV) which encourages image sparsity separately; and Total Nuclear Variation (TNV) which promotes a measure of joint edge sparsity. We found improved results using joint sparsity

HyperSLICE: HyperBand optimized spiral for low-latency interactive cardiac examination

PURPOSE: Interactive cardiac MRI is used for fast scan planning and MR-guided interventions. However, the requirement for real-time acquisition and near-real-time visualization constrains the achievable spatio-temporal resolution. This study aims to improve interactive imaging resolution through optimization of undersampled spiral sampling and leveraging of deep learning for low-latency reconstruction (deep artifact suppression). METHODS: A variable density spiral trajectory was parametrized and optimized via HyperBand to provide the best candidate trajectory for rapid deep artifact suppression. Training data consisted of 692 breath-held CINEs. The developed interactive sequence was tested in simulations and prospectively in 13 subjects (10 for image evaluation, 2 during catheterization, 1 during exercise). In the prospective study, the optimized framework-HyperSLICE- was compared with conventional Cartesian real-time and breath-hold CINE imaging in terms quantitative and qualitative image metrics. Statistical differences were tested using Friedman chi-squared tests with post hoc Nemenyi test (p < 0.05). RESULTS: In simulations the normalized RMS error, peak SNR, structural similarity, and Laplacian energy were all statistically significantly higher using optimized spiral compared to radial and uniform spiral sampling, particularly after scan plan changes (structural similarity: 0.71 vs. 0.45 and 0.43). Prospectively, HyperSLICE enabled a higher spatial and temporal resolution than conventional Cartesian real-time imaging. The pipeline was demonstrated in patients during catheter pull back, showing sufficiently fast reconstruction for interactive imaging. CONCLUSION: HyperSLICE enables high spatial and temporal resolution interactive imaging. Optimizing the spiral sampling enabled better overall image quality and superior handling of image transitions compared with radial and uniform spiral trajectories

Identification of plastic and creep properties of plasma-sprayed coatings by means of macro-indentation and a Levenberg-Marquardt method

Plasma-sprayed coatings are widely used for thermal protection and wear stability of structural components. These coatings feature an anisotropic porous structure as a result of the thermal spraying process. To our knowledge little research is dedicated to describing the temperature-dependent plastic behavior of these coatings, let alone to identifying the coating's properties when subjected to macro-scale contacts encountered in industrial applications. In this work we present a novel inverse method for the identification of plastic properties of thick plasma-sprayed coatings over a wide temperature range by means of macro-indentation and finite element simulations coupled to a Levenberg-Marquardt optimization. For the description of the coatings' plastic behavior we made use of the Gurson-Tvergaard plasticity criterion coupled to a linear isotropic work hardening of the matrix. The constitutive parameters to be identified include the yield strength ?y0(T) and the work hardening coefficient K(T) of the solid matrix as function of temperature as well as two dimensionless fitting parameters q1 and q2 and the initial void fraction f0 that are proper to the Gurson plasticity criterion. We could show that the proposed method is capable of identifying these parameters after as little as three iterations

FReSCO: Flow Reconstruction and Segmentation for low-latency Cardiac Output monitoring using deep artifact suppression and segmentation

Purpose: Real-time monitoring of cardiac output (CO) requires low-latency reconstruction and segmentation of real-time phase-contrast MR, which has previously been difficult to perform. Here we propose a deep learning framework for “FReSCO” (Flow Reconstruction and Segmentation for low latency Cardiac Output monitoring). Methods: Deep artifact suppression and segmentation U-Nets were independently trained. Breath-hold spiral phase-contrast MR data (N = 516) were synthetically undersampled using a variable-density spiral sampling pattern and gridded to create aliased data for training of the artifact suppression U-net. A subset of the data (N = 96) was segmented and used to train the segmentation U-net. Real-time spiral phase-contrast MR was prospectively acquired and then reconstructed and segmented using the trained models (FReSCO) at low latency at the scanner in 10 healthy subjects during rest, exercise, and recovery periods. Cardiac output obtained via FReSCO was compared with a reference rest CO and rest and exercise compressed-sensing CO. Results: The FReSCO framework was demonstrated prospectively at the scanner. Beat-to-beat heartrate, stroke volume, and CO could be visualized with a mean latency of 622 ms. No significant differences were noted when compared with reference at rest (bias = −0.21 ± 0.50 L/min, p = 0.246) or compressed sensing at peak exercise (bias = 0.12 ± 0.48 L/min, p = 0.458). Conclusions: The FReSCO framework was successfully demonstrated for real-time monitoring of CO during exercise and could provide a convenient tool for assessment of the hemodynamic response to a range of stressors

Ce(III) corrosion inhibitor release from silica and boehmite nanocontainers

Electrochemical impedance spectroscopy clearly appeared as a suitable technique to investigate the releasing properties of cerium (III) loaded on silica and boehmite nanocontainers. In this way the electrochemical behavior of the AA2024-T3 was evaluated by electrochemical impedance spectroscopy in a 0.045 mol L−1 NaCl solution with nanocontainers containing the inhibitor. Results show that the inhibitor release is influenced by both the chemical nature and the morphology of the nanocontainers. The lower loading and release phenomena were observed for the mesoporous silica nanocontainers, whereas the inhibitor is liberated until 168 h from dense silica nanocontainers. Boehmite nanocontainers combine a good loading ratio with a longer release until the second week of immersion

Light-driven processes: key players of the functional biodiversity in microalgae

International audienc

A chemical survey of exoplanets with ARIEL

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10–100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio