Elastic behavior in Contact Dynamics of rigid particles

The systematic errors due to the practical implementation of the Contact Dynamics method for simulation of dense granular media are examined. It is shown that, using the usual iterative solver to simulate a chain of rigid particles, effective elasticity and sound propagation with a finite velocity occur. The characteristics of these phenomena are investigated analytically and numerically in order to assess the limits of applicability of this simulation method and to compare it with soft particle molecular dynamics.Comment: submitted to PRE, 7 pages, 6 figure

Effect of Grain Size and Shape on Undrained Behaviour of Sands

The stress–strain and stress path characteristics of sands are influenced by their grain size, shape, and packing. Morphological characteristics and size of particles play important role on the undrained shear strength of sands. Often, effects of these parameters are complex and cannot be easily distinguished. This study advances the knowledge of the role of particle size and shape on the undrained shear strength of sands. To eliminate the consequence of morphological characteristics, two sands with different particle sizes but similar angularity, and another sand with different roundness were selected for the study. These morphological characteristics for all three sands were determined from the analysis of scanning electron microscope images. F131 sand with higher median grain size and lower shape factors (rᵣ and rₛ) had highest undrained peak shear strength and phase transformation value. Undrained strength (qₚₜ) and effective principal stress (P′ₚₜ) in phase transformation point had direct relationship with grain median grain size (D₅₀) and inversely effect of shape factor (rᵣ and rₛ). F131 and F161 sands represented highest peak and ultimate steady-state strengths, respectively. Flow potential appeared to be directly proportional with (rᵣ and rₛ) and inversely with D₅₀. The peak index decreased with increasing shape factors (rᵣ and rₛ)

Human dentin characteristics of patients with osteogenesis imperfecta: insights into collagen-based biomaterials

International audienceOsteogenesis imperfecta (OI), also known as "brittle bone disease", is a rare genetic disorder of the skeleton, whose most benign form I corresponds to autosomal dominant mutations in the genes encoding type I collagen (COLA1, COLA2). Several associated skeletal manifestations are often observed but, surprisingly, while dentin defects often reflect genetic bone disorders, about half of OI patients have no obvious oral manifestations. Here, we investigated the collagen, mineral and mechanical properties of dentin from deciduous teeth collected from patients with mild form of OI and displaying no obvious clinical signs of dentinogenesis imperfecta. For the first time, an increase in the hardness of OI dentin associated with an increase in mineral content compared to healthy patients was reported. In addition, OI altered the tissue characteristics of the dentin-enamel junction but the interfacial gradient was preserved. The impact of changes in molecular structure due to mutations in OI was assessed by Raman microspectroscopy. Our results highlighted a change in the hydroxyproline-proline ratio in direct association with collagen mineralization. Our findings suggest that the evaluation of teeth could be an important aid for mild types of OI that are often difficult to diagnose clinically and provide experimental evidence that hydroxyproline content should be considered in future studies on collagen-based biomaterials

ESA EE-9 SKIM airborne demonstrator: first results

International audienceSKIM is an ESA Earth Explorer-9 candidate mission designed to measure directly and simultaneously, for the first time, directional ocean surface current vector (OSCV) and ocean wave spectra. SKIM will measure at 6° and 12° incidence angle using the pulse-pair radar Doppler technique to observe the sea surface Doppler signal and then derive the ocean surface current. The concept has been first demonstrated using opportunity data from the Ka-band AirSWOT instrument showing unambiguous estimations of the wave spectrum and surface current [Nouguier et al., 2016, IEEE TGRSL].The DRIFT4SKIM campaign is a dedicated airborne campaign to validate the SKIM concept. In order to assess this capability, airborne Doppler measurement will be compared with a wide range of observations that cover all instruments generally used as reference for the measurement of both currents and the driving forces of currents (wind, temperature gradient, waves). The DRIFT4SKIM campaign, takes place in the Iroise sea (4 to 6°W, 48 to 49°N) end of November 2018 (after the deadline for the abstract).Observations will be performed in two 4-km side squares located in the field-of-view of a shore-based HF radar system (measuring surface current vectors):one where currents are spatially homogeneous; and one where strong horizontal current gradients are present. Two microwave radars will observed the sea surface: KuROS is a near nadir Ku-band conical scanning fan-beam real aperture pulse-coherent radar (Caudal et al., 2014, JAOT)KaRADOC is a near nadir Ka-band narrow-beam real aperture pulse-coherent radar. Additional observations will be carried out from optical cameras with an additional airborne platform in order to confirm the homogeneity of the experiment based on the sea surface temperature, and provide additional observations of wave spectrum and current. Ocean surface processes will be characterized using in situ instrumentation with a large number (100) of surface drifters (current in the top meter); drogue drifters (10 for each drogue depth) at 15, 5, 2 and 1 m; 10 drifting wave measuring buoys; wind measurement and a buoy carrying current profiler.The paper will present a first analysis of the microwave radar Doppler measurements and assessed these measurements against the geophysical conditions which will be well monitored during the campaign with comparison with in situ measurements