Granular Flows in a Rotating Drum: the Scaling Law between Velocity and Thickness of the Flow

The flow of dry granular material in a half-filled rotating drum is studied. The thickness of the flowing zone is measured for several rotation speeds, drum sizes and beads sizes (size ratio between drum and beads ranging from 47 to 7400). Varying the rotation speed, a scaling law linking mean velocity vs thickness of the flow, $v\sim h^m$, is deduced for each couple (beads, drum). The obtained exponent $m$ is not always equal to 1, value previously reported in a drum, but varies with the geometry of the system. For small size ratios, exponents higher than 1 are obtained due to a saturation of the flowing zone thickness. The exponent of the power law decreases with the size ratio, leading to exponents lower than 1 for high size ratios. These exponents imply that the velocity gradient of a dry granular flow in a rotating drum is not constant. More fundamentally, these results show that the flow of a granular material in a rotating drum is very sensible to the geometry, and that the deduction of the ``rheology'' of a granular medium flowing in such a geometry is not obvious

A Cross-Sectional Study of Treatments for Behavioral Disorders Following Traumatic Brain Injury: Comparison With French Recommendations

OBJECTIVE: To give a cross-sectional overview of ongoing management of behavioral disorders following traumatic brain injury (TBI) in a region of France, to compare this with recent recommendations from the French Society of Physical Medicine and Rehabilitation (SOFMER), and to evaluate associations between treatments and participant characteristics. SETTING: Outpatients referred to medical or community-based facilities in a region of France. PARTICIPANTS: One hundred twenty-nine adults with moderate to severe TBI, in the postacute period (over 3 months postinjury). DESIGN: Cross-sectional cohort study. MAIN MEASURES: Sociodemographic data, ongoing interventions including psychotherapy and medication, behavioral disorders assessed by the Behavioral Dysexecutive Syndrome Inventory (BDSI). RESULTS: Thirty-three percent of participants received ongoing psychotherapy and 43% were on medication. The most prescribed medications were antidepressants (21%), neuroleptics (18%), anxiolytics (16%), and mood stabilizers (14%). Eighty-five participants (71%) presented a current Behavioral Dysexecutive Syndrome (BDS) according to the BDSI. These participants more frequently received treatment (P = .004), psychotherapy (P = .048), medications (often 2 or more) (P = .007), and particularly antiepileptic mood stabilizers (P = .037) compared with those without BDS. CONCLUSION: Although recommended as first-line treatment, few participants with BDS received psychotherapy. Medications were overused, especially neuroleptics in view of their potential adverse effects. In contrast, recommended medications, such as mood stabilizers and β-blockers, did not appear to be highly prescribed whatever the evolution. Compliance with recommendations seemed insufficient

Signatures of granular microstructure in dense shear flows

Granular materials react to shear stresses differently than do ordinary fluids. Rather than deforming uniformly, materials such as dry sand or cohesionless powders develop shear bands: narrow zones containing large relative particle motion leaving adjacent regions essentially rigid[1,2,3,4,5]. Since shear bands mark areas of flow, material failure and energy dissipation, they play a crucial role for many industrial, civil engineering and geophysical processes[6]. They also appear in related contexts, such as in lubricating fluids confined to ultra-thin molecular layers[7]. Detailed information on motion within a shear band in a three-dimensional geometry, including the degree of particle rotation and inter-particle slip, is lacking. Similarly, only little is known about how properties of the individual grains - their microstructure - affect movement in densely packed material[5]. Combining magnetic resonance imaging, x-ray tomography, and high-speed video particle tracking, we obtain the local steady-state particle velocity, rotation and packing density for shear flow in a three-dimensional Couette geometry. We find that key characteristics of the granular microstructure determine the shape of the velocity profile.Comment: 5 pages, incl. 4 figure

Post-acute assessment programme for patients with traumatic brain injury: measuring the gap between patients' expectations on entering and end of programme recommendations

Objective: To compare the expectations of patients with brain injury (TBI) entering a post-acute programme to the recommendations made at the end. Design: Retrospective study (1997 and 2009). Intervention: This 12-week post-acute programme included ecological multidisciplinary assessment of physical and cognitive disabilities, independence in activities of daily living and work abilities. Recommendations made at the conclusion of the programme included advice regarding the ability to work in an unsheltered or a sheltered environment and possible social activities. Results: Two hundred and forty patients participated. The main objective of 95.8% was return-to-work: 93.7% expected a normal work environment, 2.1% considered a sheltered environment and 4% entered the programme with the aim of improving social abilities and integration in the community. The recommendations included return-to-work in 68.3% of cases, in an unsheltered environment in 44.2% and in a sheltered environment in 24.1% and advice for contact with social services in order to achieve better social integration in 31.7%. There was a discrepancy between expectations and recommendations in half of the cases. Conclusion: The discrepancy between patients’ expectations and recommendations is in part due to the cognitive disorders; long-term rehabilitation programmes should focus on this issue

Velocity and density profiles of granular flow in channels using lattice gas automaton

We have performed two-dimensional lattice-gas-automaton simulations of granular flow between two parallel planes. We find that the velocity profiles have non-parabolic distributions while simultaneously the density profiles are non-uniform. Under non-slip boundary conditions, deviation of velocity profiles from the parabolic form of newtonian fluids is found to be characterized solely by ratio of maximal velocity at the center to the average velocity, though the ratio depends on the model parameters in a complex manner. We also find that the maximal velocity ($u_{max}$) at the center is a linear function of the driving force (g) as $u_{max} = \alpha g - \delta$ with non-zero $\delta$ in contrast with newtonian fluids. Regarding density profiles, we observe that densities near the boundaries are higher than those in the center. The width of higher densities (above the average density) relative to the channel width is a decreasing function of a variable which scales with the driving force (g), energy dissipation parameter ($\epsilon$) and the width of the system (L) as $g^{\mu} L^{\nu}/\epsilon$ with exponents $\mu = 1.4 \pm 0.1$ and $\nu = 0.5 \pm 0.1$. A phenomenological theory based on a scaling argument is presented to interpret these findings.Comment: Latex, 15 figures, to appear in PR

Quantitative imaging of concentrated suspensions under flow

We review recent advances in imaging the flow of concentrated suspensions, focussing on the use of confocal microscopy to obtain time-resolved information on the single-particle level in these systems. After motivating the need for quantitative (confocal) imaging in suspension rheology, we briefly describe the particles, sample environments, microscopy tools and analysis algorithms needed to perform this kind of experiments. The second part of the review focusses on microscopic aspects of the flow of concentrated model hard-sphere-like suspensions, and the relation to non-linear rheological phenomena such as yielding, shear localization, wall slip and shear-induced ordering. Both Brownian and non-Brownian systems will be described. We show how quantitative imaging can improve our understanding of the connection between microscopic dynamics and bulk flow.Comment: Review on imaging hard-sphere suspensions, incl summary of methodology. Submitted for special volume 'High Solid Dispersions' ed. M. Cloitre, Vol. xx of 'Advances and Polymer Science' (Springer, Berlin, 2009); 22 pages, 16 fig

Le flux lacrymal precorneen: sa relation avec l'epithelium corneen et les biomateriaux utilisables comme lentille de contact

SIGLECNRS-CDST / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc