Agricultural spraying involves atomizing a liquid stream through a hydraulic nozzle forming a liquid sheet, which is subsequently destabilized into droplets. Standard solution adjuvants as dilute oil-in-water emulsions are known to influence the spray drop size distribution. To elucidate the mechanisms causing the changes on the drop size distribution, we investigate the influence of dilute emulsions on the destabilization mechanisms of liquid sheets. Model laboratory experiments based on the collision of a liquid drop on a small solid target are used to produce and visualize liquid sheets. With dilute oil-in-water emulsions, the liquid sheet is destabilized by the nucleation of holes in the sheet that perforate it during its expansion. The emulsion concentration is varied to rationalize its influence on the sheet destabilization mechanisms. The results obtained with the drop impact experiments are compared to the measurement of the spray drop size distribution. The very good correlation between the number of nucleation events and the volume fraction of small drops in the spray suggests (i) that the model experiment on liquid sheet is appropriate to investigate and gain an understanding of the physical mechanisms governing the spray drop size distribution and (ii) that the perforation destabilization mechanism of liquid sheets occurring for dilute emulsions is at the origin of the increase of size of the spray drops.

Silica ionogels were synthesized from tetramethoxysilane (T MOS ),methyltrimethoxysilane (MT MS ) and 1-ethyl- 2-methylimidazolium Acetate (EMI MAc: Ionic Liquid) in different proportions .The textural characterizations showed an effect of these concentrations on the corresponding aerogels: pore size distributions and effective surfaces. The structure of the aerogels was measured with a SAXS (Small- Angle XRay Scattering) apparatus and was typical of acid catalyzed aerogels. Conductivity voltage measurements, operated on the ionogels, were carried out using an electrical 4 wire-electrodes set up. The electrical voltage temporal response of the EMIMAc silica ionogel was modelled by a RLC series circuit which characteristics depended on the synthesis.

Pesticide spraying in agriculture involves atomizing a liquid stream through a hydraulic nozzle. The spray droplets results from the destabilization of a liquid sheet formed by the nozzle. Standard pesticide solution adjuvants as dilute solution of long polymer chains or dilute emulsions are known to influence the spray drop size distribution. Although being documented, these effects are not understood yet. In order to elucidate the physical mechanisms at the origin of the change on the drop size distribution, we investigate the influence of different complex fluids on the destabilization mechanisms of liquid sheets. We here form liquid sheets by the collision of a liquid drop on a small solid target. Upon impact, the drop flattens into a radial sheet expanding in the air bounded by a thicker rim. Different destabilization mechanisms of the sheet are observed depending on the fluid nature. A pure water sheet spreads out radially until it reaches a maximum diameter and then retracts due to the effect of surface tension. The destabilization mechanism is drastically modified when a dilute oil in water emulsion is used. The liquid sheet spreads out radially but holes perforate the sheet before the retraction, as already observed for some surfactant solutions [1]. The holes grow until they merge together and form a web of ligaments, which are then destabilized into droplets. To investigate the different sheet destabilization mechanisms, we use a fast camera imaging coupled to an original technique recently developed to access the time and space-resolved sheet thickness. Physico-chemical parameters of the dilute emulsion are modified to rationalize their influence on the perforation mechanism as for instance the influence of the emulsion concentration. We show in particular that the number of hole nucleation events per liquid sheet is directly governed by the emulsion concentration. In striking concordance, we find that the emulsion concentration directly controls the drop size distributions of a spray, as measured with a diffraction-based size analyzer, suggesting that experiments on liquid sheets are appropriate model experiments to gain an understanding on the physical mechanisms governing the spray drop size distribution. [1] A. Rozhkov, B. Prunet-Foch, M. Vignes-Adler, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 466, 2897-2916 (2010).

In cells and in vitro assays the number of motor proteins involved in biological transport processes is far from being unlimited. The cytoskeletal binding sites are in contact with the same finite reservoir of motors (either the cytosol or the flow chamber) and hence compete for recruiting the available motors, potentially depleting the reservoir and affecting cytoskeletal transport. In this work we provide a theoretical framework to study, analytically and numerically, how motor density profiles and crowding along cytoskeletal filaments depend on the competition of motors for their binding sites. We propose two models in which finite processive motor proteins actively advance along cytoskeletal filaments and are continuously exchanged with the motor pool. We first look at homogeneous reservoirs and then examine the effects of free motor diffusion in the surrounding medium. We consider as a reference situation recent in vitro experimental setups of kinesin-8 motors binding and moving along microtubule filaments in a flow chamber. We investigate how the crowding of linear motor proteins moving on a filament can be regulated by the balance between supply (concentration of motor proteins in the flow chamber) and demand (total number of polymerised tubulin heterodimers). We present analytical results for the density profiles of bound motors, the reservoir depletion, and propose novel phase diagrams that present the formation of jams of motor proteins on the filament as a function of two tuneable experimental parameters: the motor protein concentration and the concentration of tubulins polymerized into cytoskeletal filaments. Extensive numerical simulations corroborate the analytical results for parameters in the experimental range and also address the effects of diffusion of motor proteins in the reservoir.

Optical properties of GaN/Al0.2Ga0.8N multiple quantum wells grown with semi-polar (10-11) orientation on patterned 7°-off Si (001) substrates have been investigated. Studies performed at 8 K reveal the in-plane anisotropic behavior of the QW photoluminescence (PL) intensity for this semi-polar orientation. The time resolved PL measurements were carried out in the temperature range from 8 to 295 K to deduce the effective recombination decay times, with respective radiative and non-radiative contributions. The non-radiative component remains relatively weak with increasing temperature, indicative of high crystalline quality. The radiative decay time is a consequence of contribution from both localized and free excitons. We report an effective density of interfacial defects of 2.3 × 1012 cm−2 and a radiative recombination time of τloc = 355 ps for the localized excitons. This latter value is significantly larger than those reported for the non-polar structures, which we attribute to the presence of a weak residual electric field in the semi-polar QW layers.