Biomedical subjects

E Clément

Publications and source records attributed to E Clément.

At least 19 recordsLinked to original sources

PubMed2005

From the stress response function (back) to the sand pile "dip".

We relate the pressure "dip" observed at the bottom of a sand pile prepared by successive avalanches to the stress profile obtained on sheared granular layers in response to a localized vertical overload. We show that, within a simple anisotropic elastic analysis, the skewness and the tilt of the response profile caused by shearing provide a qualitative agreement with the sand pile dip effect. We conclude that the texture anisotropy produced by the avalanches is in essence similar to that induced by a simple shearing --albeit tilted by the angle of repose of the pile. This work also shows that this response function technique could be very well adapted to probe the texture of static granular packing.

Journal Article↗

PubMed2004

[Range of motion of the scoliotic spine in adults].

OBJECTIVE: To describe the movement of the trunk in adults with untreated adolescent idiopathic scoliosis (AIS) and to evaluate their relationship with the age of the patients, the location and angle of the curve, and the number of involved intervertebral segments. MATERIALS AND METHODS: Two hundred adult subjects with untreated AIS, without associated signs, were analyzed with rachimetry. The flexion, extension, bending, and rotation of the trunk were determined for each patient. The results were compared with a different sample: healthy subjects without spinal disease/other groups with more severe scoliosis (treated). RESULTS: In the absence of discopathy, regardless of the angle, location of the curve, or age of the patient, adults with untreated AIS demonstrated a 24% increase in truncal flexion, and a 30% decrease in hip flexion. The other movements studied with rachimetry were comparable to normal subjects. Lesions of the intervertebral segments increased in number and severity with age. These lesions progressively limited the mobility of the spine, initially in extension; and then in bending and flexion. CONCLUSIONS: The measurement of the mobility of the spine and the pelvis is part of the systematic examination of patients with adult scoliosis. This information can be used to improve the patients' health and spinal function; independent of their age and degree of spinal deformity.

Adolescent↗

PubMed2003

Slow dynamics and aging of a confined granular flow.

We present experimental results on slow flow properties of a granular assembly confined in a vertical column and driven upwards at a constant velocity V. The wall roughness is much lower than the typical grain size. For monodisperse assemblies this study evidences at low velocities (1<V<100 microm/s) a stiffening behavior, i.e., the stress necessary to obtain a steady-state velocity increases roughly logarithmically with velocity. On the other hand, at very low driving velocity (V<1 microm/s), we evidence a discontinuous and hysteretic transition to a stick-slip regime characterized by a strong divergence of the maximal blockage force when the velocity goes to zero. We show that all this phenomenology is strongly influenced by surrounding humidity. We also present an attempt to establish a link between the granular rheology and the solid friction forces between the wall and the grains. We base our discussions on a simple theoretical model and independent grain/wall tribology measurements. We also use finite element numerical simulations to compare experimental results with isotropic elasticity. A second system made of polydisperse assemblies of glass beads is investigated. We emphasize the onset of a new dynamical behavior, i.e., the large distribution of blockage forces evidenced in the stick-slip regime.

Journal Article↗

PubMed2003

Overshoot effect in the Janssen granular column: a crucial test for granular mechanics.

We present experimental results on the mechanical behavior of static granular assemblies confined in a vertical column. Our measurements confirm the universal Janssen scaling for the stress saturation curve. We show consequently, in the context of isotropic elasticity, a relation between the Poisson ratio and the granular packing fraction. Moreover, using a systematic study of the overshoot effect created by a top mass equal to the saturation mass, we show behaviors that are reproduced qualitatively by isotropic elastic materials but of a spectacular amplitude in the case of a granular assembly. These experimental results are strong tests for any theory of granular matter.

Journal Article↗

PubMed2001

Rheology of a confined granular material.

We study the rheology of a granular material slowly driven in a confined geometry. The motion is characterized by a steady sliding with a resistance force increasing with the driving velocity and the surrounding relative humidity. For lower driving velocities a transition to stick-slip motion occurs, exhibiting a blocking enhancement with decreasing velocity. We propose a model to explain this behavior pointing out the leading role of friction properties between the grains and the container's boundary.

Journal Article↗

PubMed2001

Footprints in sand: the response of a granular material to local perturbations.

We experimentally determine ensemble-averaged responses of granular packings to point forces, and we compare these results to recent models for force propagation in a granular material. We use 2D granular arrays consisting of photoelastic particles: either disks or pentagons, thus spanning the range from ordered to disordered packings. A key finding is that spatial ordering of the particles is a key factor in the force response. Ordered packings have a propagative component that does not occur in disordered packings.

Journal Article↗

PubMed2001

Green's function probe of a static granular piling.

We present an experiment which aims to investigate the mechanical properties of a static granular assembly. The piling is a horizontal 3D granular layer confined in a box. We apply a localized extra force at the surface and the spatial distribution of stresses at the bottom is obtained (the mechanical Green's function). For different types of granular media, we observe a linear pressure response whose profile shows one peak centered at the vertical of the point of application. The peak's width increases linearly with increasing depth. This Green's function seems to be in at least qualitative agreement with predictions of elastic theory.

Journal Article↗

PubMed2001

Influence of auto-organization and fluctuations on the kinetics of a monomer-monomer catalytic scheme.

We study analytically the kinetics of an elementary bimolecular reaction scheme of the Langmuir-Hinshelwood type taking place on a d-dimensional catalytic substrate. We propose a general approach that takes into account explicitly the influence of spatial correlations on the time evolution of the mean particle density. With this approach, we recover some known results concerning the time evolution of the mean particle density and establish others.

Journal Article↗

PubMed1999

Memories in sand: experimental tests of construction history on stress distributions under sandpiles.

We report experiments on piles of cohesionless granular materials showing the effect of construction history on static stress distributions. Stresses under piles are monitored by sensitive capacitive techniques. The piles are formed either by pouring granular material from a funnel with a small outlet (localized source), or from a large sieve (homogeneous rain). Localized sources yield stress profiles with a clear stress dip near the center of the pile; the homogeneous rain profiles have no stress dip. We show that the stress profiles scale linearly with the pile height. Experiments on wedge-shaped piles show similar but weaker effects.

Journal Article↗

PubMed1996

Amino-terminal maturation of the Bordetella pertussis filamentous haemagglutinin.

The 220 kDa filamentous haemagglutinin (FHA) is a major adhesin of Bordetella pertussis and is produced from a large precursor designated FhaB. Although partly surface associated, it is also very efficiently secreted into the extracellular milieu. Its secretion depends on the outer membrane accessory protein FhaC. An 80 kDa N-terminal derivative of FHA, named Fha44, can also be very efficiently secreted in a FhaC-dependent manner, indicating that all necessary secretion signals are localized in the N-terminal region of FhaB. A comparison of predicted and apparent sizes of FHA derivatives, in addition to immunoblot analyses of cell-associated and secreted FHA polypeptides, indicated that FhaB undergoes N-terminal maturation by the cleavage of an 8-9 kDa segment. However, phenotypic analyses of translational lacZ and phoA fusions showed that this segment does not function as a typical signal peptide. Co-expression of the Fha44-encoding gene with fhaC also did not allow for secretion of Fha44 in Escherichia coli. High levels of secretion could, however, be observed when the OmpA signal peptide was fused to the N-terminal end of Fha44. Regardless of the OmpA signal peptide-Fha44 fusion point, the E. coli-secreted Fha44 had the same M(r) as that secreted by B. pertussis, indicating that the N-terminal proteolytic maturation does not require a B. pertussis-specific factor. Similar to FHA, the B. pertussis-secreted Fha44 contains an as yet uncharacterized modification at its N-terminus. This modification did not occur in E. coli and is therefore not required for secretion. The N-terminus of Fha44 secreted by E. coli was determined and found to correspond to the 72nd residue after the first in-frame methionine of FhaB. The N-terminal modification was also found not to be required for haemagglutination or interaction with sulphated glycoconjugates.

Alkaline Phosphatase↗

PubMed1996