Activated aging dynamics and negative fluctuation-dissipation ratios

In glassy materials aging proceeds at large times via thermal activation. We show that this can lead to negative dynamical response functions and novel and well-defined violations of the fluctuation-dissipation theorem, in particular, negative fluctuation-dissipation ratios. Our analysis is based on detailed theoretical and numerical results for the activated aging regime of simple kinetically constrained models. The results are relevant to a variety of physical situations such as aging in glass-formers, thermally activated domain growth and granular compaction.Comment: 4 pages, 4 figs; v2 final version (minor modifs) published in Phys. Rev. Let

Lifetime of dynamic heterogeneity in strong and fragile kinetically constrained spin models

Kinetically constrained spin models are schematic coarse-grained models for the glass transition which represent an efficient theoretical tool to study detailed spatio-temporal aspects of dynamic heterogeneity in supercooled liquids. Here, we study how spatially correlated dynamic domains evolve with time and compare our results to various experimental and numerical investigations. We find that strong and fragile models yield different results. In particular, the lifetime of dynamic heterogeneity remains constant and roughly equal to the alpha relaxation time in strong models, while it increases more rapidly in fragile models when the glass transition is approached.Comment: Submitted to the proceedings of the 6th EPS Liquid Matter Conference, Utrecht 2-6 July 200

Vibrated polar disks: spontaneous motion, binary collisions, and collective dynamics

We study the spontaneous motion, binary collisions, and collective dynamics of "polar disks", i.e. purpose-built particles which, when vibrated between two horizontal plates, move coherently along a direction strongly correlated to their intrinsic polarity. The motion of our particles, although nominally three-dimensional and complicated, is well accounted for by a two-dimensional persistent random walk. Their binary collisions are spatiotemporally extended events during which multiple actual collisions happen, yielding a weak average effective alignment. We show that this well-controlled, "dry active matter" system can display collective motion with orientationally-ordered regions of the order of the system size. We provide evidence of strong number density in the most ordered regimes observed. These results are discussed in the light of the limitations of our system, notably those due to the inevitable presence of walls.Comment: 13 pages, 10 figures, 4 movie

Multimodal Plane Wave Imaging for Non-destructive Testing

International audienceUltrasonic imaging with high frame rates is of great interest in Non-Destructive Testing (NDT) to perform fast inspections. In this communication, we propose a new fast imaging method for NDT which is derived from the medical Plane Wave Imaging (PWI). The PWI method is applied to immersion-testing configurations (plane or complex water/steel interface between the probe and the image area) and to different imaging modes (imaging with direct or half-skip wave paths) according to the type of defects (point-like or extended crack-types defects)

Plane Wave Imaging for ultrasonic non-destructive testing: Generalization to multimodal imaging

Pre-printInternational audienceThis paper describes a new ultrasonic array imaging method for Non-Destructive Testing (NDT) which is derived from the medical Plane Wave Imaging (PWI) technique. The objective is to perform fast ultrasound imaging with high image quality. The approach is to transmit plane waves at several angles and to record the back-scattered signals with all the array elements. Focusing in receive is then achieved by coherent summations of the signals in every point of a region of interest. The medical PWI is generalized to immersion setups where water acts as a coupling medium and to multimodal (direct, half-skip modes) imaging in order to detect different types of defects (inclusions, porosities, cracks). This method is compared to the Total Focusing Method (TFM) which is the reference imaging technique in NDT. First, the two post-processing algorithms are described. Then experimental results with the array probe either in contact or in immersion are presented. A good agreement between the TFM and the PWI is observed, with three to ten times less transmissions required for the PWI

Quand les fleurs sont des déchets

Dans le cadre d’un vaste projet d’aménagement de territoire autour d’un fleuve, une équipe de chercheurs en sciences sociales a été engagée pour traiter de la présence des déchets flottant sur l’eau parmi lesquels se trouvent des végétaux et notamment des fleurs. L’analyse ethnographique de la participation des anthropologues, celle du contexte de leur engagement, et celle des réponses qu’ils ont pu apporter en fonction de leurs savoirs disciplinaires, permet de découvrir qu’ils ont été sollicités pour œuvrer au « ré-ensauvagement » de la nature. Cette enquête sur le travail des anthropologues dans le domaine de l’environnement montre que c’est le maintien d’une coupure nature-société qui permet à une anthropologie s’appuyant sur ses compétences empiriques de s’engager avec pertinence dans les politiques de la nature.In the context of a large-scale development project focusing on the territory surrounding a river, a team of social scientists was hired to address the presence of waste floating on the water, including plants and notably flowers. The ethnographic analysis of the anthropologists’ participation, in the context of their involvement, and the responses that they were able to make based on their disciplinary knowledge, shows that they were called upon to work towards a "re‑feralisation (ré-ensauvagement)" of nature. This study of the work of anthropologists in the field of the environment shows that it is the maintenance of a break between nature and society that allows an anthropology based on its empirical skills to engage in a relevant way with the politics of nature

A Phase Field Approach to Limited-angle Tomographic Reconstruction

The tomography of an object with limited angle can be addressed through Iterative Reconstruction Reprojection (IRR) procedure, wherein a standard reconstruction procedure is used together with a “filtering” of the image at each iteration. It is here proposed to use as a filter a phase-field—or Cahn-Hilliard—regularization interlaced with a filtered back-projection reconstruction. This reconstruction procedure is tested on a cone-beam tomography of a 3D woven ceramic composite material, and is shown to retrieve a reconstructed volume with very low artifacts in spite of a large missing angle interval (up to 28%)

Repetitive transcranial magnetic stimulation alone and in combination with motor control exercise for the treatment of individuals with chronic non-s­pecific ­low­ back­ pain­ (ExTraStim­ trial): study protocol for a randomised controlled trial

Introduction While multiple pharmacological and non-pharmacological interventions treating chronic non-specific low back pain (CLBP) are available, they have been shown to produce at best modest effects. Interventions such as repetitive transcranial magnetic stimulation (rTMS), a form of non-invasive brain stimulation, have exhibited promising results to alleviate chronic pain. However, evidence on the effectiveness of rTMS for CLBP is scarce due to limited rigorous clinical trials. Combining rTMS with motor control exercises (MCE) may help to address both central and nociceptive factors contributing to the persistence of LBP. The primary aim of this randomised controlled trial is to compare the effectiveness of a combination of rTMS and MCE to repeated rTMS sessions alone, sham rTMS and a combination of sham rTMS and MCE on pain intensity. Methods and analysis One hundred and forty participants (35/group) with CLBP will be randomised into four groups (active rTMS+MCE, sham rTMS+MCE, active rTMS and sham rTMS) to receive 10 sessions of their allocated intervention. The primary outcome will be the pain intensity, assessed at baseline, 4, 8, 12 and 24 weeks. Secondary outcomes will include disability, fear of movement, quality of life and patient global rating of change. Ethics and dissemination Ethics approval was obtained from the Comité d’éthique de la recherche sectoriel en réadaptation et intégration sociale, CIUSS de la Capitale Nationale in June 2019 (#2020–1844 – CER CIUSSS-CN). The results of the study will be submitted to a peer- reviewed journal and scientific meetings. Trial registration number NCT04555278