Experimental study of particle impact on cohesive granular packing.

We investigate experimentally the impact process of sand particles onto a cohesive granular packing made of similar particles. We use a sand-oil mixture with varying liquid content to tune the cohesive strength of the packing. The outcome of the impact is analyzed in terms of the production of ejected particles from the packing.

Particle impact on a cohesive granular media.

We investigate numerically the impact process of a particle of diameter d and velocity V_{i} onto a cohesive granular packing made of similar particles via two-dimensional discrete element method simulations. The cohesion is ensured by liquid bridges between neighboring particles and described by short range attraction force based on capillary modeling. The outcome of the impact is analyzed through the production of ejected particles from the packing, referred to as the splash process.

Experimental assessment of the effective friction at the base of granular chute flows on a smooth incline.

We report on direct measurements of the basal force components for granular material flowing down a smooth incline. We investigate granular flows for a large range of inclination angles from θ=13.4^{∘} to 83.

Transition from Saltation to Collisional Regime in Windblown Sand.

We report experiments on windblown sand that highlight a transition from saltation to collisional regime above a critical dimensionless mass flux or Shields number. The transition is first seen through the mass flow rate Q, which deviates from a linear trend with the Shields number and seems to follow a quadratic law. Other physical evidences confirm the change of the transport properties.

Spreading of a granular droplet under horizontal vibrations.

By means of three-dimensional discrete element simulations, we study the spreading of a granular droplet on a horizontally vibrated plate. Apart from a short transient with a parabolic shape, the droplet adopts a triangular profile during the spreading. The dynamics of the spreading is governed by two distinct regimes: a superdiffusive regime in the early stages driven by surface flow followed by a second one which is subdiffusive and governed by bulk flow.

Potentially inappropriate prescribing in elderly patient: analyze before/after hospitalization.

Unlabelled: In the context of improved medication management in the elderly patient, we were interested in the reevaluation of drug prescription during hospitalization. The aim of this study is to assess the prevalence of inappropriate prescribing in the elderly patient before and after hospitalization.

Patients And Methods: This is a descriptive and retrospective study of drug prescriptions in a non-geriatric unit.

Erosion and deposition processes in surface granular flows.

We report on experiments aiming at characterizing erosion and deposition processes on a tilted granular bed. We investigate the existence of the neutral angle, that is, the critical angle at which erosion exactly balances accretion after the passage of a granular avalanche of a finite mass. Experiments show in particular that the neutral angle depends on both avalanche mass and shape but is rather insensitive to the bed length.

Grain-scale modeling and splash parametrization for aeolian sand transport.

The collision of a spherical grain with a granular bed is commonly parametrized by the splash function, which provides the velocity of the rebounding grain and the velocity distribution and number of ejected grains. Starting from elementary geometric considerations and physical principles, like momentum conservation and energy dissipation in inelastic pair collisions, we derive a rebound parametrization for the collision of a spherical grain with a granular bed. Combined with a recently proposed energy-splitting model [Ho et al.

Granular flows on a dissipative base.

We study inclined channel flows of sand over a sensor-enabled composite geotextile fabric base that dissipates granular fluctuation energy. We record strain of the fabric along the flow direction with imbedded fiber-optic Bragg gratings, flow velocity on the surface by correlating grain position in successive images, flow thickness with the streamwise shift of an oblique laser light sheet, velocity depth profile through a transparent side wall using a high-speed camera, and overall discharge rate. These independent measurements at inclinations between 33∘ and 37∘ above the angle of repose at 32.

Sand dunes as migrating strings.

We develop a reduced complexity model for three-dimensional sand dunes, based on a simplified description of the longitudinal and lateral sand transport. The spatiotemporal evolution of a dune migrating over a nonerodible bed under unidirectional wind is reduced to the dynamics of its crest line, providing a simple framework for the investigation of three-dimensional dunes, such as barchan and transverse dunes. Within this model, we derive analytical solutions for barchan dunes and investigate the stability of a rectilinear transverse dune against lateral fluctuations.

Particle velocity distribution in saltation transport.

We report on wind-tunnel measurements of particle velocity distribution in aeolian transport. By performing extended statistics, we show that for saltation occurring over an erodible bed the vertical lift-off velocity distributions deviate significantly from a Gaussian law and exhibit a long tail accurately described by a lognormal law. In contrast, saltation over a rigid bed produces Gaussian velocity distributions.

Nonlinear sand bedform dynamics in a viscous flow.

We investigate theoretically the nonlinear evolution of a sand bedform sheared by a laminar viscous flow. On the basis of the hydrodynamic equations coupled with a sediment transport law, we derive a closed nonlinear and nonlocal equation for the spatiotemporal evolution of the bedform profile in the case of an unbounded flow. The numerical resolution of this equation shows that the bedform coarsens indefinitely in the course of time.

Scaling laws in aeolian sand transport.

We report on wind tunnel measurements on saltating particles in a turbulent boundary layer and provide evidence that over an erodible bed the particle velocity in the saltation layer and the saltation length are almost invariant with the wind strength, whereas over a nonerodible bed these quantities vary significantly with the air friction speed. It results that the particle transport rate over an erodible bed does not exhibit a cubic dependence with the air friction speed, as predicted by Bagnold, but a quadratic one. This contrasts with saltation over a nonerodible bed where the cubic Bagnold scaling holds.

Continuum model for steady, fully developed saltation above a horizontal particle bed.

We propose a continuum model for steady, fully developed saltation above a horizontal particle bed that provides local, analytical expressions for the particle pressure and shear stress. This analytical approach contrasts with discrete numerical simulations in which the trajectories of individual particles are computed as they interact with gravity, the wind, and the bed. The continuum model has the advantage that it can easily be extended to nonuniform and unsteady situations.

Granular medium impacted by a projectile: experiment and model.

We present a minimal discrete model for the propagation of energy through a 3D granular medium impacted by a particulate projectile. In this model, energy is transferred from grain to grain via binary collision events. This description can be successfully applied to the analysis of the collision process of a single spherical particle (of diameter donto a half space of granular medium composed of similarly sized particles.

Three-dimensional analysis of the collision process of a bead on a granular packing.

We present results of the collision process of a bead onto a static granular packing. We provide, in particular, a three-dimensional (3D) extensive characterization of this process from a model experiment that allows us to propel a spherical bead onto a granular packing with a well-controlled velocity and impact angle. A collision typically produces a high-energy particle (rebound particle) and several low-energy grains (ejected particles).

Rheology of confined granular flows: scale invariance, glass transition, and friction weakening.

We study fully developed, steady granular flows confined between parallel flat frictional sidewalls using numerical simulations and experiments. Above a critical rate, sidewall friction stabilizes the underlying heap at an inclination larger than the angle of repose. The shear rate is constant and independent of inclination over much of the flowing layer.

Impact of a projectile on a granular medium described by a collision model.

We propose a model for the propagation of energy due to the impact of a granular projectile on a dense granular medium. Energy is transferred from grain to grain during binary collision events. The transport of energy may then be viewed as a random walk with a split of energy during successive collisions.

Collision process between an incident bead and a three-dimensional granular packing.

We report on experimental studies of the collision process between an incident bead and a three-dimensional granular packing (made of particles identical to the impacting one). The understanding of such a process and the resulting ejection of particles is, in particular, crucial to describe eolian sand transport. We present here an extensive experimental analysis of the collision and ejection process.

Initiation and evolution of current ripples on a flat sand bed under turbulent water flow.

We investigate the formation and dynamics of sand ripples under a turbulent water flow. Our experiments were conducted in an open flume with spherical glass beads between 100 and 500 microm in diameter. The flow Reynolds number is of the order of 10,000 and the particle Reynolds number of the order of 1 to 10.

Towards a theoretical picture of dense granular flows down inclines.

Unlike most fluids, granular materials include coexisting solid, liquid or gaseous regions, which produce a rich variety of complex flows. Dense flows down inclines preserve this complexity but remain simple enough for detailed analysis. In this review we survey recent advances in this rapidly evolving area of granular flow, with the aim of providing an organized, synthetic review of phenomena and a characterization of the state of understanding.

Discrete Element Method studies of the collision of one rapid sphere on 2D and 3D packings.

We performed numerical simulations of one-bead collision on the surface of a static granular medium. The simulations have been done for two- and three-dimensional packings of beads. The effect of the incident bead velocity, the shot angle, the mechanical parameters and the packing structure are analyzed for ordered and disordered 2D packings and only disordered 3D packings.

Defibrillation shock success estimation by a set of six parameters derived from the electrocardiogram.

It is well known that in some cases defibrillator shocks cannot terminate ventricular fibrillation (VF). Repeated failed shocks often may worsen subsequent response to therapy. This study assesses the ability of six parameters derived from the surface electrocardiogram (ECG) to predict defibrillation shock outcome.

Sand ripple dynamics in the case of out-of-equilibrium aeolian regimes.

From a phenomenological hydrodynamical model, we analyze the aeolian sand ripple evolution in an out-of-equilibrium aeolian regime where erosion exceeds accretion (and vice versa). We find, in particular, that the ripple structure can be destroyed in favor of a flat sand bed. In the ripple regime we report on a new class of generic dynamics described by the Benney equation.

Superstable granular heap in a thin channel.

We observed experimentally a new regime for granular flows in an inclined channel with a flow-rate-controlled system. For high flow rates, the flow occurs atop a static granular heap whose angle is considerably higher than those usually exhibited by granular heaps. The properties of such superstable heaps (SSH) are drastically affected by a change in the channel width W.