On the air permeability of Populus pit

Sap hydrodynamics in vascular cells of trees seems to be controlled by small membranes called pits. Understanding how the pit junctions regulate the sap flow and stop embolism by cavitation is today a challenging issue. The hypothesis that the pit porosity adjusts the flow under negative pressure and stops the air bubble diffusion need to be validated. In this talk, we will present the experimental results on Populus trees that support the idea that pits operate "passively" in a biological point of view. This work is based on atomic force microscope (AFM) experiments, which have been realised to measure quantitatively the mechanical properties of pits at the nanoscale

Enhancing Citizens' Participation in the Processes of Governance: Digital India and MyGOV

[extract] Digital India Program (DIP) is an ambitious umbrella programme of Government of India. It weaves together a large number of technologies with governance processes and services to empower Indian citizens around its three vision areas viz. “Digital Infrastructure as a Utility to Every Citizen”, “Governance and Services on Demand”, and “Digital Empowerment of Citizens”. These key areas of visions rest on nine pillars of Digital India ranging from provision of “Broadband for all” to its forty-four mission mode projects related to governance services under “e-Kranti” pillar to “IT for Jobs” and “Digital Literacy for All” and so on. DIP is not merely a great opportunity to develop the digital backbone of the country but also promises to deliver a real improvement in the quality of life of Indians by offering an on-demand easier access to governance and services using Internet, Mobile, Cloud based Digi-lockers, Common Service Centres-CSCs, Post offices, public Wi-Fi hotspots and much more. In fact majority of the activities and services delineated under government-to-government (G2G), government-to-businesses (G2B) and government-to-citizens (G2C) categories have been proposed to be delivered using technology through the aegis of DIP by means of innovative implementation models such as 4P model (Panchayat-Public-Private-Partnership). The proposed actions and services are further expected to be refined by all the stakeholders in an open and interactive manner using digital mechanisms such as portal of MYGOV. Further, DIP is also expected to bring all the digital activity to India by ushering in other related concepts such as Smart Cities and therefore lead to a ripple effect business opportunities in all the related sectors such as Software, Support, Hardware, Government Services and Information Technology Enabled Services (ITES). The ultimate mission of DIP is to transform India into a digitally empowered society and a knowledge economy by leveraging information technology (IT) as a growth engine of new India

Sand transport over a barchan dune

The present work investigates an important and yet unsolved issue: the relationship between the sand flux and the fluid shear stress over a spatially varying bed of particles. It is now recognized that over such a bed, the particle flux is not in equilibrium with the shear stress: there is some lag related to the particle inertia or particle settling. A confident modelling of this relaxation phenomena and the corresponding length scales, is still lacking (Charru, Andreotti and Claudin 2013). This question is investigated here from experiments on barchan dunes in a closed-conduit water flow. From visualizations with a high-speed camera and a tracking algorithm, the particle motion over the whole dune surface is determined: particle trajectories, local velocity and surface density of the moving particles, and local particle flux. The relationship between the local particle flux and local shear stress (estimated from previous analyses) is investigated. Surprisingly, the particle flux appears to be out-ofequilibrium over the whole dune surface, with saturation length much larger than expected

On the large difference between Benjamin's and Hanratty's formulations of perturbed flow over uneven terrain

Flow over an uneven terrain is a complex phenomenon that requires a chain of approximations in order to be studied. In addition to modelling the intricacies of turbulence if present, the problem is classically first linearized about a flat bottom and a locally parallel flow, and then asymptotically approximated into an interactive representation that couples a boundary layer and an irrotational region through an intermediate inviscid but rotational layer. The first of these steps produces a stationary Orr–Sommerfeld equation; since this is a one-dimensional problem comparatively easy for any computer, it would seem appropriate today to forgo the second sweep of approximation and solve the Orr–Sommerfeld problem numerically. However, the results are inconsistent! It appears that the asymptotic approximation tacitly restores some of the original problem’s non-parallelism. In order to provide consistent results, Benjamin’s version of the Orr–Sommerfeld equation needs to be modified into Hanratty’s. The large difference between Benjamin’s and Hanratty’s formulations, which arises in some wavenumber ranges but not in others, is here explained through an asymptotic analysis based on the concept of admittance and on the symmetry transformations of the boundary layer. A compact and accurate analytical formula is provided for the wavenumber range of maximum laminar shear-stress response. We highlight that the maximum turbulent shear-stress response occurs in the quasi-laminar regime at a Reynolds-independent wavenumber, contrary to the maximum laminar shear-stress response whose wavenumber scales with a power of the boundary-layer thickness. A numerical computation involving an eddy-viscosity model provides a warning against the inaccuracy of such a model. We emphasize that the range $k\unicode[STIX]{x1D708}/u_{\unicode[STIX]{x1D70F}} of the spectrum remains essentially unexplored, and that the question is still open whether a fully developed turbulent regime, similar to the one predicted by an eddy-viscosity model, ever exists for open flow even in the limit of infinite wavelength

Determination of the sand flux over a barchan dune under a water flow

The modelling of sand transport by uid ows is crucial in many environmental as well as industrial problems. The present work investigates an important and yet unsolved issue: the relationship between the particle ux and the shear stress exerted by the uid ow at the bed surface

Subaqueous Barchan dunes in turbulent shear flow. Part 2: Fluid flow.

We report an experimental study of the turbulent flow above a barchan dune in a channel, from particle image velocimetry measurements, for Reynolds numbers ranging from 9000, just below the threshold for particle motion, up to 24 000, where the dune moves. Two calculations of the speed-up over the dune are compared, the usual ‘same-elevation’ and the more relevant ‘Lagrangian’, showing that the latter is smaller by a factor of two. The two-layer structure of the flow disturbance – an essentially inviscid outer layer and a turbulent inner layer of thickness δi – is assessed. In the outer layer, streamline curvature is shown to be responsible for half of the Lagrangian speed-up, from the comparison of the velocity measurements with two Bernoulli calculations. In the inner layer, detailed measurements of the velocity and stresses are provided, down to γ+ ≈ 1, and the momentum budget is discussed. The Reynolds shear stress decreases monotonically towards the dune surface, according to the standard mixing-length closure, whereas the total shear stress increases strongly in the viscous sublayer. Along the dune surface, the shear stress increases up to the crest where it reaches twice its unperturbed value. A good estimate of the surface stress is provided by a parabolic fit of the inner velocity profile matching the outer flow at γd ≈ δi. Doubling the Reynolds number, the surface shear stress and the speed-up decrease by ∼30 %. The implications of these results on the dune motion, presented in Part 1 of this study (Franklin & Charru, J. Fluid Mech., vol. 675, 2011, pp. 199–222), are finally discussed

Droplet entrainment from a single wave propagating in a stratified air-water pipe flow

We investigate the distribution of sizes and velocities of droplets detached from a single roll wave propagating in a pipe. The wave is induced by a pulse in liquid flowrate in a stratified air-water flow. Due to the shear applied on the crest of the wave by the faster gas stream, droplets are formed and entrained by the gas. Detection and tracking of the droplets is performed by image processing. The distributions of sizes and velocities of the droplets are determined in the center of the pipe for various distances to the roll wave and compared to those measured for higher gas flowrate when droplets are produced from all the roll waves formed naturally at the gas-liquid interface without external forcing

Dust emission by powder handling: Comparison between numerical analysis and experimental results

The dust generation occurring during the handling of bulk materials in free falls or at the impact on a stockpile can be a source of danger for the operators health. Proper design of control systems of fugitive dust requires knowledge of the behavior of the free falling powder, the air it entrains, and the concentration of dust liberated. This paper presents first a simple model for a free falling column of bulk solids and compares it with relevant previous research. This two phase model predicts the particle and air velocities, and especially the volumetric flow of induced air in the column without dependence on any empirical constant like the entrainment constant used in the plume model. For small drop heights, the predictions of the theory appear to be in qualitative agreement with the available data for the quantity of air entrained, but the theory needs to be extended in the case of large drop heights, when the expansion of the jet of particles is large. In a second part, the description of an expanded jet of particles is experimentally studied with PIV measurements. The data obtained are well fitted by the model by Liu, when the entrainment constant is taken as the angle of expansion of the jet obtained from the velocity field

Une histoire de l'Institut de Mécanique des Fluides de Toulouse de 1913 à 1970

En 1913, Charles Camichel crée le laboratoire d'hydraulique de l'institut électrotechnique de l'université de Toulouse, institut qu'il avait lui-même fondé six ans plus tôt. Ce laboratoire acquiert rapidement une grande notoriété pour la qualité de sa recherche expérimentale et pour ses succès dans la transposition à l'hydraulique des concepts et méthodes de la physique et de la mécanique. En 1930, le ministère de l'Air lui associe un institut de mécanique des fluides, et finance une grande soufflerie. Un siècle plus tard, l'IMFT a diversifié son activité dans de nombreux domaines autour d'enjeux scientifiques et d'applications très variés. Il est l'un des plus grands laboratoires de sa discipline à l'échelle internationale. Cet article en retrace l'histoire jusqu'un 1970, en insistant plus particulièrement sur les remarquables contributions scientifiques des trois premières décennie