Grain kinematics during stress relaxation in sand: Not a problem for x-ray imaging

X-ray tomography is a very valuable tool for studying the full-field 3D deformation of granular materials. The requirement to stop loading and scan a given state (assumed to be stationary) used in most approaches implies unavoidable stress relaxation during scanning. Since scanning times on laboratory tomographs are normally in the order of 1 hour, the strength of the assumption of a stationary state cannot be tested, which introduces some potential weakness in the interpretation of the rich micro-mechanics observed. This paper presents the kinematics of relaxation of a dry natural sand in a typical oedometric cell used for X-ray scanning, using a synchrotron X-ray source to provide scanning times of around 3 minutes, at two different magnifications. This allows the relaxation of the cell & sand system for the first time to be quantified. Advanced image correlation tools are used to quantify the rearrangements of the soil skeleton during loading and the subsequent relaxation. The results indicate that the magnitude of grain displacements during relaxation, associated to ≈4% reduction in externally measured axial stress under oedometric loading, falls below 0.01 D50. It can, therefore, be concluded that the relaxation step required prior to an X-ray scan during an in-situ geomechanical experiment on dry sand does not lead to appreciable uncertainties

Étude numérique des pieux d'éolienne offshore soumis à la traction en milieu sableux

International audienceL'étude numérique d'une fondation offshore en sol sableux de type pieu soumise à un effort vertical en traction est présentée. La méthode des éléments finit est utilisée. Les résultats numériques sont comparés aux résultats expérimentaux obtenus en centrifugeuse géotechnique (des pieux battus à 1xg ont été testés à 100xg). La fondation est représentée à travers un modèle en deux-dimensions axisymétrique, des outils et des hypothèses du domaine de l'ingénierie sont utilisés. Deux conditions d'état de contrainte initiale dans le sol sont analysées. Le premier cas, simulant un pieu moulé, considère une distribution géostatique des contraintes initiales. Le second cas prend en compte la modification de l'état des contraintes initiales dues au fonçage du pieu, au travers de la méthode CPT ICP-05. La comparaison de ces résultats met en valeur l'importance de la prise en compte de l'état des contraintes initiales après la mise en place d'un pieu pour la détermination de sa capacité portante

Géométrie et propriétés élastiques des matériaux granulaires

Nous étudions par simulation numérique (de type « éléments discrets») les propriétés géométriques et élastiques d'assemblages de grains sphériques obtenus par différents protocoles de préparation : compression isotrope de « gaz granulaires », vibration de configurations denses, dépôt sous gravité. Nous montrons que le nombre de coor- dination des contacts portant les forces, inaccessible à l'expérience, peut varier indépendamment de la compacité et constitue le paramètre déterminant pour les propriétés élastiques qui, elles, sont mesurables en laboratoire. La comparaison de valeurs numériques et expérimentales pour les modules élastiques des billes de verre, encore partielle, donne un bon accord

Étude numérique des pieux d'éolienne offshore soumis à la traction en milieu sableux

National audienceThe response of an offshore pile embedded in sand under tension loading is studied. An axisymmetric two-dimensional finite element model is built using common engineering tools. Results are compared to experimental data obtained through geotechnical centrifuge tests (during the tests piles were driven at 1×g and tested at 100×g). Two models with different initial state of stresses in the soil are analysed. First, a geostatic case where radial stresses around the pile are a linear function of the soil weight, this hypotheses is used to represent a cast-in-place pile. Second, an initial state of stress is calculated and introduced in the model. In this case, stresses are calculated using the CPT method ICP-05, this method allows to take into account the effects in the stress field due to a driven pile. Comparing the results from both cases with the experimental data allows to emphasize the role of the initial state of stress to calculate the load carrying capacity of a pile foundation. MOTS-CLÉS : Pieu, offshore , traction, capacité portante, CPT, ICP-05.L'étude numérique d'une fondation offshore en sol sableux de type pieu soumise à un effort vertical en traction est présentée. La méthode des éléments finit est utilisée. Les résultats numériques sont comparés aux résultats expérimentaux obtenus en centrifugeuse géotechnique (des pieux battus à 1×g ont été testés à 100×g). La fondation est représentée à travers un modèle en deux-dimensions axisymétrique, des outils et des hypothèses du domaine de l'ingénierie sont utilisés. Deux conditions d'état de contrainte initiale dans le sol sont analysées. Le premier cas, simulant un pieu moulé, considère une distribution géostatique des contraintes initiales. Le second cas prend en compte la modification de l'état des contraintes initiales dues au fonçage du pieu, au travers de la méthode CPT ICP-05. La comparaison de ces résultats met en valeur l'importance de la prise en compte de l'état des contraintes initiales après la mise en place d'un pieu pour la détermination de sa capacité portante

Characterization of Botulinum Neurotoxin Type A Neutralizing Monoclonal Antibodies and Influence of Their Half-Lives on Therapeutic Activity

Botulinum toxins, i.e. BoNT/A to/G, include the most toxic substances known. Since botulism is a potentially fatal neuroparalytic disease with possible use as a biowarfare weapon (Centers for Disease Control and Prevention category A bioterrorism agent), intensive efforts are being made to develop vaccines or neutralizing antibodies. The use of active fragments from non-human immunoglobulins (F(ab')2, Fab', scFv), chemically modified or not, may avoid side effects, but also largely modify the in vivo half-life and effectiveness of these reagents. We evaluated the neutralizing activity of several monoclonal anti-BoNT/A antibodies (mAbs). F(ab')2 fragments, native or treated with polyethyleneglycol (PEG), were prepared from selected mAbs to determine their half-life and neutralizing activity as compared with the initial mAbs. We compared the protective efficiency of the different biochemical forms of anti-toxin mAbs providing the same neutralizing activity. Among fourteen tested mAbs, twelve exhibited neutralizing activity. Fragments from two of the best mAbs (TA12 and TA17), recognizing different epitopes, were produced. These two mAbs neutralized the A1 subtype of the toxin more efficiently than the A2 or A3 subtypes. Since mAb TA12 and its fragments both exhibited the greatest neutralizing activity, they were further evaluated in the therapeutic experiments. These showed that, in a mouse model, a 2- to 4-h interval between toxin and antitoxin injection allows the treatment to remain effective, but also suggested an absence of correlation between the half-life of the antitoxins and the length of time before treatment after botulinum toxin A contamination. These experiments demonstrate that PEG treatment has a strong impact on the half-life of the fragments, without affecting the effectiveness of neutralization, which was maintained after preparation of the fragments. These reagents may be useful for rapid treatment after botulinum toxin A contamination

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements