Transition from viscous to inertial regime in dense suspensions

Non-Brownian suspensions present a transition from Newtonian behavior in the zero-shear limit to a shear thickening behaviour at a large shear rate, none of which is clearly understood so far. Here, we carry out numerical simulations of such an athermal dense suspension under shear, at an imposed confining pressure. This set-up is conceptually identical to the recent experiments of Boyer and co-workers [Phys. Rev. Lett. 107,188301 (2011)]. Varying the interstitial fluid viscosities, we recover the Newtonian and Bagnoldian regimes and show that they correspond to a dissipation dominated by viscous and contact forces respectively. We show that the two rheological regimes can be unified as a function of a single dimensionless number, by adding the contributions to the dissipation at a given volume fraction.Comment: 4 pages, 3 figure

Adaptabilidade de linhagens e cultivares de feijao (Phaseolus vulgaris L.) em Rondonia e resistencia a "mela" (Thanatephorus cucumeris (Frank.) Donk).

bitstream/item/60390/1/PA-1588-0001.pd

Fluctuations and stratification in sedimentation of dilute suspensions of spheres

International audienceWe have tested in experiments and simulations whether stratification can control velocity fluctuations in suspensions of sedimenting spheres. The initial value and early decay of the velocity fluctuations are not affected by stratification. On the other hand, in the descending front where the stratification is strong and well defined, the velocity fluctuations are inhibited according to a previously proposed scaling. In between, after the initial decay and before the arrival of the front, the local value of the stratification does not always play a role

Spreading fronts in sedimentation of dilute suspension of spheres

International audienceThe thickness of the diffuse front between a sedimenting dilute suspension and the clear fluid above grows linearly in time due to polydispersity in the size of the particles and due to a hydrodynamic effect in which randomly heavy clusters fall out of the front leaving it depleted. Experiments and simplified point-particle numerical simulations agree that these two effects are not simply linearly additive

Gravity waves over topographical bottoms: Comparison with the experiment

In this paper, the propagation of water surface waves over one-dimensional periodic and random bottoms is investigated by the transfer matrix method. For the periodic bottoms, the band structure is calculated, and the results are compared to the transmission results. When the bottoms are randomized, the Anderson localization phenomenon is observed. The theory has been applied to an existing experiment (Belzons, et al., J. Fluid Mech. {\bf 186}, 530 (1988)). In general, the results are compared favorably with the experimental observation.Comment: 15 pages, 7 figure

Prolate and temperature-responsive self-assemblies of amphiphilic random copolymers with perfluoroalkyl and polyoxyethylene side chains in solution

Two amphiphilic random copolymers, PEGMAx-co-FAy (x = 90 and 70 mol%), were synthesized by ATRP and their solutions were investigated as a function of solvent, concentration and temperature by DLS and SANS analyses. Both copolymers self-assembled in nanostructures by single-chain folding in water solutions over a wide range of temperatures. The values of the DLS hydrodynamic radius and the SANS radius of gyration were found to be ~4 nm and ~3.4–3.7 nm, respectively. Moreover, SANS showed the self-folded nanoassemblies to be prolated spheroids with ratio of polar/equatorial axes ~5:1 for PEGMA90-co-FA10 and ~2:1 for PEGMA70-co-FA30. On heating above a critical temperature Tc, multi-chain microassemblies were formed that reverted back to nanoassemblies on cooling below Tc. This temperature-responsive transition was fully and sharply reversible

New Thermophilic α/β Class Epoxide Hydrolases Found in Metagenomes From Hot Environments

This is the final version. Available from Frontiers Media via the DOI in this record.Two novel epoxide hydrolases (EHs), Sibe-EH and CH65-EH, were identified in the metagenomes of samples collected in hot springs in Russia and China, respectively. The two α/β hydrolase superfamily fold enzymes were cloned, over-expressed in Escherichia coli, purified and characterized. The new EHs were active toward a broad range of substrates, and in particular, Sibe-EH was excellent in the desymmetrization of cis-2,3-epoxybutane producing the (2R,3R)-diol product with ee exceeding 99%. Interestingly these enzymes also hydrolyse (4R)-limonene-1,2-epoxide with Sibe-EH being specific for the trans isomer. The Sibe-EH is a monomer in solution whereas the CH65-EH is a dimer. Both enzymes showed high melting temperatures with the CH65-EH being the highest at 85°C retaining 80% of its initial activity after 3 h thermal treatment at 70°C making it the most thermal tolerant wild type epoxide hydrolase described. The Sibe-EH and CH65-EH have been crystallized and their structures determined to high resolution, 1.6 and 1.4 Å, respectively. The CH65-EH enzyme forms a dimer via its cap domains with different relative orientation of the monomers compared to previously described EHs. The entrance to the active site cavity is located in a different position in CH65-EH and Sibe-EH in relation to other known bacterial and mammalian EHs

On the Effect of the Reaction Medium on the HydroClaus Process: A Novel Sustainable H2S Valorization Strategy

Hydrogen sulfide (H2S) is becoming a critical issue to manage, due to the increasing sulfur content in the processed gas together with the stricter environmental regulations. Novel alternatives are being developed for the H2S abatement and conversion to valuable chemicals. Among them, the HydroClaus process, patented by Eni S.p.A., deserves attention. This technology aims at converting H2S and SO2 into a hydrophilic mixture of sulfur and sulfur-rich compounds, polythionates, to be used as a fertilizer. An improved configuration for an efficient water management is proposed in this work. The process operability has been demonstrated at the bench scale, through an ad hoc experimental campaign. For the technology scale-up, a flowsheet has been set up and its performances have been assessed in terms of heat and material balances and CO2 emissions. Results reveal that the modified HydroClaus process can be a valid solution for an effective H2S valorization, also considering that no direct CO2 emissions are released. Moreover, since only electric power is required, a further reduction of the indirect CO2 emissions is expected, if renewable sources can be exploited for this purpose