Rheology of a 2D granular film.

We study experimentally the rheology of a macroscopic particle-laden soap film, designated as a "Granular Film", in the simple shear configuration. Macroscopic particles are dispersed in a soap film, while being large enough that they bridge both fluid interfaces. We simultaneously perform macroscopic rheological measurements with a classical rheometer and investigate interactions at the particle scale with a camera underneath the film. The determination of the velocity field of the grains reveals the presence of an inhomogeneous shear within the granular film. Trying to correlate both measurements unveils the non-locality of the rheology of the granular film: similar to what has been observed in a dry granular material, we find an highly-sheared zone close to the moving wall contrasting with a large quasistatic area. This behavior can be accounted for through extended kinetic theory and correlated with a transition in the dominant component of the stress.

Pedestrians in static crowds are not grains, but game players.

The local navigation of pedestrians is assumed to involve no anticipation beyond the most imminent collisions, in most models. These typically fail to reproduce some key features experimentally evidenced in dense crowds crossed by an intruder, namely, transverse displacements toward regions of higher density due to the anticipation of the intruder's crossing. We introduce a minimal model based on mean-field games, emulating agents planning out a global strategy that minimizes their overall discomfort. By solving the problem in the permanent regime thanks to an elegant analogy with the nonlinear Schrödinger's equation, we are able to identify the two main variables governing the model's behavior and to exhaustively investigate its phase diagram. We find that, compared to some prominent microscopic approaches, the model is remarkably successful in replicating the experimental observations associated with the intruder experiment. In addition, the model can capture other daily-life situations such as partial metro boarding.

Penetrating a granular medium by successive impacts.

We consider the penetration dynamics of a vertical cylinder into a dry granular medium subjected to successive impacts. The depth of the impactor below the free surface z_{N} first evolves linearly with the impact number N and then follows a power-law evolution z_{N}∝N^{1/3}. The depth reached by the cylinder after a given number of impacts is observed to increase with the impact energy, but to decrease with its diameter and the density of the granular medium. We develop a model that accounts for the quasistatic and inertial granular forces applying on the cylinder to rationalize our observations. This approach reveals the existence of two intrusion regimes for large and small impact numbers, allowing all data to be rescaled on a master curve. Then, we extend the study to the effect of sidewalls on the dynamics of the impactor. We show that lateral confinement changes the dependence of the impactor depth on the impact number z_{N}(N). This effect is accounted for by considering the increase of the granular drag with the lateral confinement.

Twist-Controlled Force Amplification and Spinning Tension Transition in Yarn.

Combining experiments and numerical simulations with a mechanical-statistical model of twisted yarns, we discuss the spinning transition between a cohesionless assembly of fibers into a yarn. We show that this transition is continuous but very sharp due to a giant amplification of frictional forces which scales as expθ^{2}, where θ is the twist angle. We demonstrate that this transition is controlled solely by a nondimensional number H involving twist, friction coefficient, and geometric lengths. A critical value of this number H_{c}≃30 can be linked to a locking of the fibers together as the tensile strength is reached. This critical value imposes that yarns must be very slender structures with a given pitch. It also induces the existence of an optimal yarn radius. Predictions of our theory are successfully compared to yarns made from natural cotton fibers.

Quality Improvement of Services for Inpatients After Implementation of a Pediatric Nurse Coordinator and Porter.

BACKGROUND: Delays in finding inpatient beds and transferring patients lead to overcrowding in the Emergency Department (ED). LOCAL PROBLEM: The emergency nurse coordinator role was implemented in the general or adult ED to optimize patient flow, but few studies are available for pediatric hospitals. OBJECTIVE: The aim was to assess the impact of a pediatric emergency nurse coordinator and an ED porter on the ED length of stay for inpatients. METHODS: A retrospective before-after study was conducted in a pediatric hospital. ED inpatient length of stay was compared between December 2015 and December 2016. The probability to get an ED length of stay below the median was modeled in multivariate analysis. INTERVENTION: A pediatric emergency nurse coordinator and ED porter were implemented in 2016. RESULTS: 1086 hospitalized children were included. The ED length of stay was significantly longer in 2016 (median: 5.5 h, IQR: 3 h and 49 min, 7 h and 22 min) than in 2015 (median: 4.8 h, IQR: 3 h and 19 min, 6 h and 18 min). The year 2015 (OR 1.56, 95% CI [1.1, 2.2]), the absence of imaging, the absence of aerosol and IV drug administration, the number of hospitalizations on the day below the median, type of hospitalization unit, and the age of children younger than 1 years old were associated with a shorter ED length of stay (below the median) in the multivariate analysis. CONCLUSION: Our study did not confirm the advantages of these two professionals in our pediatric ED.

Influence of confinement on granular penetration by impact.

We study experimentally the influence of confinement on the penetration depth of impacting spheres into a granular medium contained in a finite cylindrical vessel. The presence of close lateral walls reduces the penetration depth, and the characteristic distance for these lateral wall effects is found to be of the order of one sphere diameter. The influence of the bottom wall is found to have a much shorter range.