Experimental velocity fields and forces for a cylinder penetrating into a granular medium

We present here a detailed granular flow characterization together with force measurements for the quasi-bidimensional situation of a horizontal cylinder penetrating vertically at a constant velocity in dry granular matter between two parallel glass walls. In the velocity range studied here, the drag force on the cylinder does not depend on the velocity V_0 and is mainly proportional to the cylinder diameter d. Whereas the force on the cylinder increases with its penetration depth, the granular velocity profile around the cylinder is found stationary with fluctuations around a mean value leading to the granular temperature profile. Both mean velocity profile and temperature profile exhibit strong localization near the cylinder. The mean flow perturbation induced by the cylinder decreases exponentially away from the cylinder on a characteristic length \lambda, that is mainly governed by the cylinder diameter for large enough cylinder/grain size ratio d/d_g: \lambda ~ d/4 + 2d_g. The granular temperature exhibits a constant plateau value T_0 in a thin layer close to the cylinder of extension \delta_{T_0} ~ \lambda/2 and decays exponentially far away with a characteristic length \lambda_T of a few grain diameters (\lambda_T ~ 3d_g). The granular temperature plateau T_0 that scales as (V_0^2 d_g/d) is created by the flow itself from the balance between the "granular heat" production by the shear rate V_0/\lambda over \delta_{T_0} close to the cylinder and the granular dissipation far away

Influence of humidity on granular packings with moving walls

A significant dependence on the relative humidity H for the apparent mass (Mapp) measured at the bottom of a granular packing inside a vertical tube in relative motion is demonstrated experimentally. While the predictions of Janssen's model are verified for all values of H investigated (25%< H <80%), Mapp increases with time towards a limiting value at high relative humidities (H>60%) but remains constant at lower ones (H=25%). The corresponding Janssen length is nearly independent of the tube velocity for H>60% but decreases markedly for H=25%. Other differences are observed on the motion of individual beads in the packing. For H=25%, they are almost motionless while the mean particle fraction of the packing remains constant; for H>60% the bead motion is much more significant and the mean particle fraction decreases. The dependence of these results on the bead diameter and their interpretation in terms of the influence of capillary forces are discussed.Comment: 6 pages, 6 figure

Competitive dynamics of two erosion patterns around a cylinder

We investigate experimentally the local erosion of a granular bed near a fixed vertical cylinder that emerges from the bed. The onset of erosion arising at the base of the cylinder and usually ascribed to the wrapping horseshoe vortex is determined and rationalized by a flow contraction effect. We report a new erosion pattern visible downstream of the cylinder that consists of two side-by-side elongated holes. This pattern is observed for flow regimes close to the horseshoe scour onset, whose growth usually inhibits its spatiotemporal development.Comment: 6 pages, 6 figure

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. For monodisperse assemblies this study evidences at low velocities ($1<V<100 \mu m/s$) a stiffening behaviour i.e. the stress necessary to obtain a steady sate velocity increases roughly logarithmically with velocity. On the other hand, at very low driving velocity ($V<1 \mu m/s$), 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 a tentative 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 elements numerical simulations to confront experimental results to 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

Next-generation plasmids for transgenesis in zebrafish and beyond

Transgenesis is an essential technique for any genetic model. Tol2-based transgenesis paired with Gateway-compatible vector collections has transformed zebrafish transgenesis with an accessible, modular system. Here, we established several next-generation transgenesis tools for zebrafish and other species to expand and enhance transgenic applications. To facilitate gene-regulatory element testing, we generated Gateway middle entry vectors harboring the small mouse beta-globin minimal promoter coupled to several fluorophores, CreERT2, and Gal4. To extend the color spectrum for transgenic applications, we established middle entry vectors encoding the bright, blue-fluorescent protein mCerulean and mApple as an alternative red fluorophore. We present a series of p2A peptide-based 3' vectors with different fluorophores and subcellular localizations to co-label cells expressing proteins of interest. Lastly, we established Tol2 destination vectors carrying the zebrafish exorh promoter driving different fluorophores as a pineal gland-specific transgenesis marker active prior to hatching and through adulthood. exorh-based reporters and transgenesis markers also drive specific pineal gland expression in the eye-less cavefish (Astyanax). Together, our vectors provide versatile reagents for transgenesis applications in zebrafish, cavefish, and other models

Next-generation plasmids for transgenesis in zebrafish and beyond

Transgenesis is an essential technique for any genetic model. Tol2-based transgenesis paired with Gateway-compatible vector collections has transformed zebrafish transgenesis with an accessible, modular system. Here, we established several next-generation transgenesis tools for zebrafish and other species to expand and enhance transgenic applications. To facilitate gene-regulatory element testing, we generated Gateway middle entry vectors harboring the small mouse betaglobin minimal promoter coupled to several fluorophores, CreERT2, and Gal4. To extend the color spectrum for transgenic applications, we established middle entry vectors encoding the bright, blue-fluorescent protein Cerulean and mApple as an alternative red fluorophore. We present a series of p2A peptide-based 3' vectors with different fluorophores and subcellular localizations to co-label cells expressing proteins of interest. Lastly, we established Tol2 destination vectors carrying the zebrafish exorh promoter driving different fluorophores as a pineal gland-specific transgenesis marker active prior to hatching and through adulthood. exorh-based reporters and transgenesis markers also drive specific pineal gland expression in the eye-less cavefish (Astyanax). Together, our vectors provide versatile reagents for transgenesis applications in zebrafish, cavefish, and other models