Le retour d'expérience de la gestion des crises : d'octobre 1986 à septembre 2001

National audienceRappelez-vous Bhopal (3/12/1984), Challenger (28/1/1986), Tchernobyl (26/4/1986). Il faut de très cruelles séries noires pour rappeler aux terriens de se remettre à l'étude du Danger. En octobre 1986, ce sont Les Annales des Mines qui consacraient aux Risques Technologiques Majeurs un numéro spécial, motivé par la grande émotion suscitée par cette effroyable série. Les événements tragiques de la fin 2001, “11 septembre” et AZF à Toulouse, renforcent, si cela était nécessaire, le besoin d'analyser les accidents et les crises et d'en tirer des enseignements

Characterization of biochars by nuclear magnetic resonance

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Indirect detection of infinite-speed MAS solid-state NMR spectra

Heavy spin-1/2 nuclides are known to possess very large chemical shift anisotropies that can challenge even the most advanced magic-angle-spinning (MAS) techniques. Wide manifolds of overlapping spinning sidebands and insufficient excitation bandwidths often obfuscate meaningful spectral information and force the use of static, low-resolution solid-state (SS)NMR methods for the characterization of materials. To address these issues, we have merged fast-magic-angle-turning (MAT) and dipolar heteronuclear multiple-quantum coherence (D-HMQC) experiments to obtain D-HMQC-MAT pulse sequences which enable the rapid acquisition of 2D SSNMR spectra that correlate isotropic 1H chemical shifts to the indirectly detected isotropic “infinite-MAS” spectra of heavy spin-1/2 nuclides. For these nuclides, the combination of fast MAS and 1H detection provides a high sensitivity, which rivals the DNP-enhanced ultra-wideline SSNMR. The new pulse sequences were used to determine the Pt coordination environments in a complex mixture of decomposition products of transplatin and in a metal-organic framework with Pt ions coordinated to the linker ligands

Can dissonance engineering improve risk analysis of human–machine systems?

The paper discusses dissonance engineering and its application to risk analysis of human–machine systems. Dissonance engineering relates to sciences and technologies relevant to dissonances, defined as conflicts between knowledge. The richness of the concept of dissonance is illustrated by a taxonomy that covers a variety of cognitive and organisational dissonances based on different conflict modes and baselines of their analysis. Knowledge control is discussed and related to strategies for accepting or rejecting dissonances. This acceptability process can be justified by a risk analysis of dissonances which takes into account their positive and negative impacts and several assessment criteria. A risk analysis method is presented and discussed along with practical examples of application. The paper then provides key points to motivate the development of risk analysis methods dedicated to dissonances in order to identify the balance between the positive and negative impacts and to improve the design and use of future human–machine system by reinforcing knowledge

NMR-Based Structural Modeling of Graphite Oxide Using Multidimensional 13C Solid-State NMR and ab Initio Chemical Shift Calculations

Chemically modified graphenes and other graphite-based materials have attracted growing interest for their unique potential as lightweight electronic and structural nanomaterials. It is an important challenge to construct structural models of noncrystalline graphite-based materials on the basis of NMR or other spectroscopic data. To address this challenge, a solid-state NMR (SSNMR)-based structural modeling approach is presented on graphite oxide (GO), which is a prominent precursor and interesting benchmark system of modified graphene. An experimental 2D C-13 double-quantum/single-quantum correlation SSNMR spectrum of C-13-labeled GO was compared with spectra simulated for different structural models using ab initio geometry optimization and chemical shift calculations. The results show that the spectral features of the GO sample are best reproduced by a geometry-optimized structural model that is based on the Lerf-Klinowski model (Lerf, A. et al. Phys. Chem. B 1998, 102, 4477); this model is composed of interconnected sp(2), 1,2-epoxide, and COH carbons. This study also convincingly excludes the possibility of other previously proposed models, including the highly oxidized structures involving 1,3-epoxide carbons (Szabo, I. et al. Chem. Mater. 2006, 18, 2740). C-13 chemical shift anisotropy (CSA) patterns measured by a 2D C-13 CSA/isotropic shift correlation SSNMR were well reproduced by the chemical shift tensor obtained by the ab initio calculation for the former model. The approach presented here is likely to be applicable to other chemically modified graphenes and graphite-based systems

Polymorphism and magnetic properties of Li2MSiO4 (M 5 Fe, Mn) cathode materials

Transition metal-based lithium orthosilicates (Li2MSiO4,M=Fe, Ni, Co, Mn) are gaining a wide interest as cathode materials for lithium-ion batteries. These materials present a very complex polymorphism that could affect their physical properties. In this work, we synthesized the Li2FeSiO4 and Li2MnSiO4 compounds by a sol-gel method at different temperatures. The samples were investigated by XRPD, TEM, 7Li MAS NMR, and magnetization measurements, in order to characterize the relationships between crystal structure and magnetic properties. High-quality 7Li MAS NMR spectra were used to determine the silicate structure, which can otherwise be hard to study due to possible mixtures of different polymorphs. The magnetization study revealed that the Neel temperature does not depend on the polymorph structure for both iron and manganese lithium orthosilicates

Applying physical acoustics to near-seafloor object echo-structure estimation

In HF sonars (50kHz-500kHz), the assumption of a perfect rigid body for targets of interest is often admitted and the ratio "wave-length/object-length" leads to use physical acoustics theory to describe target-wave interactions. This has been done extensively for the determination of target strengths, especially for targets isolated in the water volume. However, it is experimentally well-known that echoes of near-seafloor objects are different in amplitude and shape from echoes of the same objects in free water. Despite the presence of such boundaries (seasurface or seafloor), physical acoustics theory can still be used in this case as a first approximation. In this paper, we propose a general method to rapidly evaluate strengths and structures of echoes from simple objects located near the seafloor and we present the validation of this target echo model by means of a specific experiment : a small scale experiment (1/5 scale) made around 200 kHz in a large water test tank and using the sea surface as reflecting interface. The results obtained during this experiment well square with the envisaged target-wave interaction mechanism

Utilisation des noyaux actifs en RMN comme sonde de la structure chimique et magnétique locale dans les solides

NMR of paramagnetic solids is a rapidly expanding research subject since 20 years. The simultaneous upcoming of ultra-fast magic angle spinning (UF-MAS) and broadband methods in solid-state NMR (SHAP and S3AP) has made the acquisition of solid-state NMR data on paramagnetic systems much easier. Parallel to these developments, ab-initio calculation on such systems were developped in order to give clear interpretation on these newly made measurements. It may come as a nonsense to try and develop new method for local magnetic structure in a context where many efficient techniques already exist. However, when we consider the complementarity of EPR and NMR, or the necessity of heavy equipment required for polarized neutron diffraction or muon spin-rotation, it might be interesting to add a new tool in the state-of-the-art in local magnetic structure determination. That is why this project aims to rationalize the solid-state NMR methods developped in the past 20 years for paramagnetic systems and set clear borders for approximate but fast calculation on such systems in order to facilitate the interpretation of NMR data in various situations that are accessible to solid-state NMR of paramagnetic systems.La RMN dans les solides paramagnétiques est un sujet de recherches en rapide expansion depuis une vingtaine d’années. L’avènement concomitant de technologies de très hautes vitesses de rotation à l’angle magique (UF-MAS) et de méthodes à large bandes dans les solides (SHAP et S3AP) a permis de faciliter l’obtention de données RMN dans des solides qui étaient réputés pour les difficultés qu’ils posaient pour l’acquisition et l’interprétation.Si l’acquisition de données a été facilitée par ces développements technologiques, on a vu en parallèle se développer des méthodes de calcul pour interpréter ces mesures en termes de structure magnétique locale.Dans un contexte où de nombreuses techniques sont à l’œuvre pour caractériser ces propriétés magnétiques locales, il peut paraître anachronique de développer de nouvelles méthodes de mesure. Cependant, si l’on fait état de la complémentarité de la RPE et de la RMN, de la nécessité d’équipement lourd pour la diffraction de neutrons polarisés ou la spin-rotation de muons, il peut-être intéressant d’ajouter de nouvelles techniques à l’état de l’art en détermination de structure magnétique.Ainsi le projet proposé ici consiste à systématiser les méthodes développées au cours des 20 dernières années et poser des bornes à l’utilisation de méthodes de calculs approchées mais rapides pour faciliter l’interprétation dans des contextes variés et accessibles à la RMN des solides paramagnétiques