Etude de l'interaction entre l'hydroxosulfure de cobalt et l'hydrogène

National audienceLes effluents liquides générés lors du traitement du combustible nucléaire usé sont enrobés dans une matrice de bitume. L'hydroxosulfure de cobalt, CoSOH, est utilisé pour piéger l'hydrogène formé lors de la radiolyse de ces enrobés bitumineux. Des expériences de piégeage d'hydrogène ont été réalisées à température ambiante selon deux techniques (la gravimétrie et la manométrie) afin de comprendre le mode d'action de ce solide vis-à-vis de l'hydrogène. Les expériences de gravimétrie et de manométrie ont montré que la capacité maximale de piégeage d'hydrogène est égale à 0,59 ± 0,18 mole d'hydrogène par mole de cobalt. L'analyse des phases présentes après interaction avec l'hydrogène a permis de conclure à la réaction suivante : 9 CoSOH + 11/2 H2 = Co9S8 + 9 H2O + H2S. Du fait de la présence d'une phase minoritaire Co(OH)2 dans le solide initial, une deuxième réaction en parallèle, entre H2S produit et Co(OH)2 est envisagée, en accord avec les caractérisations effectuées et les bilans de masse mesurés

Non-local numerical treatment of non-linear behavior by means of Helmholtz equation, with variable coefficients. Application to reinforced concrete structures.

Numerous work has been done with the aim of modeling the cracking of reinforced concrete (RC) structures. Among the recent methods proposed in the literature, the combination of reinforcement-concrete equilibrium combined with the linear behavior of the interface leads to a Helmholtz equation which takes account of the slip between the homogenized reinforcements and the concrete in presence of localized cracks [1][2]. In the case of large cracks openings, it is necessary to consider the non-linear behaviors of material and interfaces, such as the plasticity of reinforcements or the damage of the matrix-reinforcement interface. These phenomena induce variations of the coefficients in the Helmholtz equation, which leads to two levels of iterative procedures: one at a global level considering equilibrium of homogenized RC, and another one at a non-local level taking account of equilibrium between reinforcement and concrete. The implementation of a convergence criterion is then needed at each level. The goal of this paper is to describe the developments implemented in the Finite Element code Cast3m to perform non-local Helmholtz type calculations with non-constant coefficients. This method, using an acceleration method [3] is illustrated by the cases of reinforced concrete tie and beam, with homogenized reinforcements. References : [1] A. Sellier and A. Millard, “A homogenized formulation to account for sliding of non-meshed reinforcements during the cracking of brittle matrix composites: Application to reinforced concrete,” Eng. Fract. Mech., vol. 213, pp. 182–196, May 2019, doi: 10.1016/j.engfracmech.2019.04.008. [2] A. Sellier and A. Millard, “Traitement numérique non local de phénomènes physiques par l’équation d’Helmholtz : les effets d’échelle et le glissement renfort-matrice,” in Club Cast3M 2018, Paris, 2018, vol. 1, no. 1, pp. 12–18. Available: http://www-cast3m.cea.fr/html/ClubCast3m/club2018/Presentation_Sellier.pdf. [3] A. C. Aitken, “On the iterative solution of a system of linear equations.,” Proc. Roy. Sot. Edinburgh, pp. 52–60, 1950

Path-following methods for unstable structural responses induced by strain softening: a critical review

Path-following methods for describing unstable structural responses induced by strain-softening are discussed. The main ingredients of the formalisms introduced by Riks and Crisfield for arc-length methods for geometrical non-linearities are presented. A link between two ways (monolithic and partitioned) of solving the resulting augmented equilibrium problem is discussed based on the Sherman–Morrison formula. The original monolithic approach assumes that the path-following constraint equation is differentiable with respect to the unknown displacement field and load factor. However, when dealing with material non-linearities, it is often preferred to consider constraint equations controlling the maximum of a field defined on the computational domain (e.g., a scalar strain measure, the rate of variation of an internal variable of the constitutive model). In that case, differentiability cannot be guaranteed due to the presence of the maximum operator. This makes only the partitioned formulation usable. Several path-following constraint equations from the literature are presented, and the corresponding implementations in the finite element method are discussed. The different formulations are compared based on a simple two-dimensional test case of damage localization in a beam submitted to tension. A test case involving multiple snap-backs is illustrated, finally, to show the robustness of the considered formulations

Une nouvelle loi constitutive pour la description du comportement cyclique des matériaux quasi-fragiles : effet unilatéral régularisé et effets hystérétiques

Une nouvelle loi de comportement visant à étudier le comportement du béton sous chargement cyclique est proposée. La formulation de la loi repose en partie sur une approche par expérimentation numérique à l'aide d'un modèle de type lattice. Ainsi, une prise en compte de l'effet unilatéral régularisé est proposée afin de décrire le phénomène de refermeture progressif des fissures. La loi de comportement développée a été validée à l'échelle de la structure sur le cas d'un voile en béton armé sous chargement cyclique

Severe Asthma Standard-of-Care Background Medication Reduction With Benralizumab: ANDHI in Practice Substudy

Background: The phase IIIb, randomized, parallel-group, placebo-controlled ANDHI double-blind (DB) study extended understanding of the efficacy of benralizumab for patients with severe eosinophilic asthma. Patients from ANDHI DB could join the 56-week ANDHI in Practice (IP) single-arm, open-label extension substudy. Objective: Assess potential for standard-of-care background medication reductions while maintaining asthma control with benralizumab. Methods: Following ANDHI DB completion, eligible adults were enrolled in ANDHI IP. After an 8-week run-in with benralizumab, there were 5 visits to potentially reduce background asthma medications for patients achieving and maintaining protocol-defined asthma control with benralizumab. Main outcome measures for non-oral corticosteroid (OCS)-dependent patients were the proportions with at least 1 background medication reduction (ie, lower inhaled corticosteroid dose, background medication discontinuation) and the number of adapted Global Initiative for Asthma (GINA) step reductions at end of treatment (EOT). Main outcomes for OCS-dependent patients were reductions in daily OCS dosage and proportion achieving OCS dosage of 5 mg or lower at EOT. Results: For non-OCS-dependent patients, 53.3% (n = 208 of 390) achieved at least 1 background medication reduction, increasing to 72.6% (n = 130 of 179) for patients who maintained protocol-defined asthma control at EOT. A total of 41.9% (n = 163 of 389) achieved at least 1 adapted GINA step reduction, increasing to 61.8% (n = 110 of 178) for patients with protocol-defined EOT asthma control. At ANDHI IP baseline, OCS dosages were 5 mg or lower for 40.4% (n = 40 of 99) of OCS-dependent patients. Of OCS-dependent patients, 50.5% (n = 50 of 99) eliminated OCS and 74.7% (n = 74 of 99) achieved dosages of 5 mg or lower at EOT. Conclusions: These findings demonstrate benralizumab's ability to improve asthma control, thereby allowing background medication reduction

The 2021 WHO catalogue of Mycobacterium tuberculosis complex mutations associated with drug resistance: a genotypic analysis.

Background: Molecular diagnostics are considered the most promising route to achievement of rapid, universal drug susceptibility testing for Mycobacterium tuberculosis complex (MTBC). We aimed to generate a WHO-endorsed catalogue of mutations to serve as a global standard for interpreting molecular information for drug resistance prediction. Methods: In this systematic analysis, we used a candidate gene approach to identify mutations associated with resistance or consistent with susceptibility for 13 WHO-endorsed antituberculosis drugs. We collected existing worldwide MTBC whole-genome sequencing data and phenotypic data from academic groups and consortia, reference laboratories, public health organisations, and published literature. We categorised phenotypes as follows: methods and critical concentrations currently endorsed by WHO (category 1); critical concentrations previously endorsed by WHO for those methods (category 2); methods or critical concentrations not currently endorsed by WHO (category 3). For each mutation, we used a contingency table of binary phenotypes and presence or absence of the mutation to compute positive predictive value, and we used Fisher's exact tests to generate odds ratios and Benjamini-Hochberg corrected p values. Mutations were graded as associated with resistance if present in at least five isolates, if the odds ratio was more than 1 with a statistically significant corrected p value, and if the lower bound of the 95% CI on the positive predictive value for phenotypic resistance was greater than 25%. A series of expert rules were applied for final confidence grading of each mutation. Findings: We analysed 41 137 MTBC isolates with phenotypic and whole-genome sequencing data from 45 countries. 38 215 MTBC isolates passed quality control steps and were included in the final analysis. 15 667 associations were computed for 13 211 unique mutations linked to one or more drugs. 1149 (7·3%) of 15 667 mutations were classified as associated with phenotypic resistance and 107 (0·7%) were deemed consistent with susceptibility. For rifampicin, isoniazid, ethambutol, fluoroquinolones, and streptomycin, the mutations' pooled sensitivity was more than 80%. Specificity was over 95% for all drugs except ethionamide (91·4%), moxifloxacin (91·6%) and ethambutol (93·3%). Only two resistance mutations were identified for bedaquiline, delamanid, clofazimine, and linezolid as prevalence of phenotypic resistance was low for these drugs. Interpretation: We present the first WHO-endorsed catalogue of molecular targets for MTBC drug susceptibility testing, which is intended to provide a global standard for resistance interpretation. The existence of this catalogue should encourage the implementation of molecular diagnostics by national tuberculosis programmes. Funding: Unitaid, Wellcome Trust, UK Medical Research Council, and Bill and Melinda Gates Foundation

Thermo-hydro-mechanical couplings in radioactive waste disposal

International audienceThis chapter presents some of the main issues related to the thermo-hydro-mechanical couplings which can be encountered in the framework of radioactive waste disposal problems and their modeling. First, the different kinds of radioactive wastes are briefly reviewed, and the deep underground disposal solution, based on a multi-barrier concept, is detailed. With regards to the rock mechanics issue, the main processes which can occur at short and long term are explained. Then, the theoretical formulation underlying the thermo-hydro-mechanical studies are fully detailed and some indications on numerical implementation are given. In addition, a specific hydro-mechanical formulation related to a well identified fracture is exposed. Finally, in order to appraise the influence of the various thermo-hydro-mechanical couplings, the study of the short term behavior of a generic high level wastes repository is proposed as an illustration of the previous developments

Weakest link and localisation WL2: a method to conciliate probabilistic and energetic scale effects in numerical models

WOS:000343606400009International audienceThe random nature of geomaterial tensile strength, combined with a softening behaviour, leads to a strong and systematic dependency of the first crack stress value on the loaded volume. This problem is so important that the predictive capability of efficient damage models can be occulted by the phenomenon. The method proposed here allows this aspect to be efficiently considered in a non-linear finite element context thanks to a variant of the Weibull theory, in which the classical weakest link theory is rearranged in a non-local form permitting a second gradient implementation