18 research outputs found
Spatial repartition of local plastic processes in different creep regimes in a granular material
Granular packings under constant shear stress display below the Coulomb
limit, a logarithmic creep dynamics. However the addition of small stress
modulations induces a linear creep regime characterized by an effective viscous
response. Using Diffusing Wave Spectroscopy, we investigate the relation
between creep and local plastic events spatial distribution ("hot-spots")
contributing to the plastic yield. The study is done in the two regimes, i.e.
with and without mechanical activation. The hot-spot dynamics is related to the
material effective fluidity. We show that far from the threshold, a local
visco-elastic rheology coupled to an ageing of the fluidity parameter, is able
to render the essential spatio-temporal features of the observed creep
dynamics
Intruder mobility in a vibrated granular packing
We study experimentally the dynamics of a dense intruder sinking under
gravity inside a vibrated 2D granular packing. The surrounding flow patterns
are characterized and the falling trajectories are interpreted in terms of an
effectivive friction coefficient related to the intruder mean descent velocity
(flow rules). At higher confining pressures i.e. close to jamming, a transition
to intermittent dynamics is evidenced and displays anomalous "on-off" blockade
statistics. A systematic analysis of the flow rules, obtained for different
intruder sizes, either in the flowing regime or averaged over the flowing and
blockade regimes, strongly suggest the existence of non-local properties for
the vibrated packing rheology.
Oscillatory surface rheotaxis of swimming E. coli bacteria
Bacterial contamination of biological conducts, catheters or water resources
is a major threat to public health and can be amplified by the ability of
bacteria to swim upstream. The mechanisms of this rheotaxis, the reorientation
with respect to flow gradients, often in complex and confined environments, are
still poorly understood. Here, we follow individual E. coli bacteria swimming
at surfaces under shear flow with two complementary experimental assays, based
on 3D Lagrangian tracking and fluorescent flagellar labelling and we develop a
theoretical model for their rheotactic motion. Three transitions are identified
with increasing shear rate: Above a first critical shear rate, bacteria shift
to swimming upstream. After a second threshold, we report the discovery of an
oscillatory rheotaxis. Beyond a third transition, we further observe
coexistence of rheotaxis along the positive and negative vorticity directions.
A full theoretical analysis explains these regimes and predicts the
corresponding critical shear rates. The predicted transitions as well as the
oscillation dynamics are in good agreement with experimental observations. Our
results shed new light on bacterial transport and reveal new strategies for
contamination prevention.Comment: 12 pages, 5 figure
Membrane vesicles, current state-of-the-art: emerging role of extracellular vesicles
Release of membrane vesicles, a process conserved in both prokaryotes and eukaryotes, represents an evolutionary link, and suggests essential functions of a dynamic extracellular vesicular compartment (including exosomes, microparticles or microvesicles and apoptotic bodies). Compelling evidence supports the significance of this compartment in a broad range of physiological and pathological processes. However, classification of membrane vesicles, protocols of their isolation and detection, molecular details of vesicular release, clearance and biological functions are still under intense investigation. Here, we give a comprehensive overview of extracellular vesicles. After discussing the technical pitfalls and potential artifacts of the rapidly emerging field, we compare results from meta-analyses of published proteomic studies on membrane vesicles. We also summarize clinical implications of membrane vesicles. Lessons from this compartment challenge current paradigms concerning the mechanisms of intercellular communication and immune regulation. Furthermore, its clinical implementation may open new perspectives in translational medicine both in diagnostics and therapy
Mechanical fluctuations suppress the threshold of soft-glassy solids: The secular drift scenario
Modalités du traitement de la maladie veineuse thromboembolique du patient VIH par les anticoagulants oraux directs
International audienc
Management of bleeding in acquired hemophilia A: results from the European Acquired Haemophilia (EACH2) Registry
Acquired hemophilia A is a rare bleeding disorder caused by autoantibodies to coagulation FVIII. Bleeding episodes at presentation are spontaneous and severe in most cases. Optimal hemostatic therapy is controversial, and available data are from observational and retrospective studies only. The EACH2 registry, a multicenter, pan-European, Web-based database, reports current patient management. The aim was to assess the control of first bleeding episodes treated with a bypassing agent (rFVIIa or aPCC), FVIII, or DDAVP among 501 registered patients. Of 482 patients with one or more bleeding episodes, 144 (30%) received no treatment for bleeding; 31 were treated with symptomatic therapy only. Among 307 patients treated with a first-line hemostatic agent, 174 (56.7%) received rFVIIa, 63 (20.5%) aPCC, 56 (18.2%) FVIII, and 14 (4.6%) DDAVP. Bleeding was controlled in 269 of 338 (79.6%) patients treated with a first-line hemostatic agent or ancillary therapy alone. Propensity score matching was applied to allow unbiased comparison between treatment groups. Bleeding control was significantly higher in patients treated with bypassing agents versus FVIII/DDAVP (93.3% vs 68.3%; P = .003). Bleeding control was similar between rFVIIa and aPCC (93.0%; P = 1). Thrombotic events were reported in 3.6% of treated patients with a similar incidence between rFVIIa (2.9%) and aPCC (4.8%). (Blood. 2012;120(1):39-46
Demographic and clinical data in acquired hemophilia A:results from the European Acquired Haemophilia Registry (EACH2)
Background: Acquired hemophilia A (AHA) is a rare autoimmune disease caused by autoantibodies against coagulation factor VIII and characterized by spontaneous hemorrhage in patients with no previous family or personal history of bleeding. Although data on several AHA cohorts have been collected, limited information is available on the optimal management of AHA. Objectives: The European Acquired Hemophilia Registry (EACH2) was established to generate a prospective, large-scale, pan-European database on demographics, diagnosis, underlying disorders, bleeding characteristics, treatment and outcome of AHA patients. Results: Five hundred and one (266 male, 235 female) patients from 117 centers and 13 European countries were included in the registry between 2003 and 2008. In 467 cases, hemostasis investigations and AHA diagnosis were triggered by a bleeding event. At diagnosis, patients were a median of 73.9 years. AHA was idiopathic in 51.9%; malignancy or autoimmune diseases were associated with 11.8% and 11.6% of cases. Fifty-seven per cent of the non-pregnancy-related cases were male. Four hundred and seventy-four bleeding episodes were reported at presentation, and hemostatic therapy initiated in 70.5% of patients. Delayed diagnosis significantly impacted treatment initiation in 33.5%. Four hundred and seventy-seven patients underwent immunosuppression, and 72.6% achieved complete remission. Conclusions: Representing the largest collection of consecutive AHA cases to date, EACH2 facilitates the analysis of a variety of open questions in AHA