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DOI: 10.1039/c6sm00710d
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The structure of model gluten protein gels prepared in ethanol/water is investigated by small angle X-ray (SAXS) and neutrons (SANS) scattering. We show that gluten gels display radically different SAXS and SANS profiles when the solvent is (at least partially) deuterated. The detailed analysis of the SANS signal as a function of the solvent deuteration demonstrates heterogeneities of sample deuteration at different length scales. The progressive exchange between the protons (H) of the proteins and the deuteriums (D) of the solvent is inhomogeneous and 60 nm large zones that are enriched in H are evidenced. In addition, at low protein concentration, in the sol state, solvent deuteration induces a liquid/liquid phase separation. Complementary biochemical and structure analyses show that the denser protein phase is more protonated and specifically enriched in glutenin, the polymeric fraction of gluten proteins. These findings suggest that the presence of H-rich zones in gluten gels would arise from the preferential interaction of glutenin polymers through a tight network of non-exchangeable intermolecular hydrogen bonds.

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DOI: 10.1103/PhysRevB.93.144117
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none

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One of the major environmental issues related to spraying of pesticides on cultivated crops is the drift phenomenon. Because of the wind, small droplets may drift away from the targeted crop and cause contamination. One way to reduce the drift is to control the spray drop size distribution and reduce the proportion of small drops. In this context, anti-drift additives have been developed, including dilute oil-in-water emulsions. Although being documented, the effects of oil-in-water emulsions on spray drop size distribution are not yet understood. The objective of this work is to determine the mechanisms at the origin of the changes of the spray drop size distribution for emulsion-based sprays. Agricultural spraying involves atomizing a liquid stream through a hydraulic nozzle. At the exit of the nozzle, a free liquid sheet is formed, which is subsequently destabilized into droplets.In order to elucidate the mechanisms causing the changes of the spray drop size distribution, we investigate the influence of emulsions on the destabilization mechanisms of liquid sheets. Model single-tear experiments based on the collision of one tear of liquid on a small solid target are used to produce and visualize liquid sheets with a fast camera. Upon impact, the tear flattens into a sheet radially expanding in the air bounded by a thicker rim. Different destabilization mechanisms of the sheet are observed depending on the fluid properties. A pure water sheet spreads out radially and then retracts due to the effect of surface tension. Simultaneously, the rim corrugates forming radial ligaments, which are subsequently destabilized into droplets. The destabilization mechanism is drastically modified when a dilute oil-in-water emulsion is used. Emulsion-based liquid sheets are destabilized through the nucleation of holes within the sheet that perforate the sheet during its expansion. The holes grow until they merge together and form a web of ligaments, which are then destabilized into drops.The physical-chemical parameters of the emulsion, such as emulsion concentration and emulsion droplet size distribution, are modified to rationalize their influence on the perforation mechanism. We correlate the size distribution of drops issued from conventional agricultural spray with the amount of perforation events in single-tear experiments, demonstrating that the single-tear experiment is an appropriate model experiment to investigate the physical mechanisms governing the spray drop size distribution of anti-drift formulations. We show that the relevant mechanism causing the increase of drops size in the emulsion-based spray is a perforation mechanism.To gain an understanding of the physical mechanisms at the origin of the perforation events, we develop an optical technique that allows the determination of the time and space-resolved thickness of the sheet. We find that the formation of a hole in the sheet is systematically preceded by a localized thinning of the liquid film. We show that the thinning results from the entering and Marangoni-driven spreading of emulsion oil droplet at the air/water interface. The localized thinning of the liquid film ultimately leads to the rupture of the film. We propose the perforation mechanism as a sequence of two necessary steps: the emulsion oil droplets (i) enter the air/water interface, and (ii) spread at the interface. We show that the formulation of the emulsion is a critical parameter to control the perforation. The addition of salt or amphiphilic copolymers can trigger or completely inhibit the perforation mechanism. We show that the entering of oil droplets at the air/water interface is the limiting step of the mechanism. Thin-film forces such as electrostatic or steric repulsion forces stabilize the thin film formed between the interface and the approaching oil droplets preventing the entering of oil droplets at the interface and so inhibit the perforation process.

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Ref Arxiv: 1511.06182
DOI: 10.1103/PhysRevLett.116.238002
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We implement and optimize a particle-swap Monte-Carlo algorithm that allows us to thermalize a polydisperse system of hard spheres up to unprecedentedly-large volume fractions, where \revise{previous} algorithms and experiments fail to equilibrate. We show that no glass singularity intervenes before the jamming density, which we independently determine through two distinct non-equilibrium protocols. We demonstrate that equilibrium fluid and non-equilibrium jammed states can have the same density, showing that the jamming transition cannot be the end-point of the fluid branch.

Commentaires: 5 pages, 3 figs; To be published in Phys. Rev. Lett. Réf Journal: Phys. Rev. Lett. 116, 238002 (2016)

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I'll discuss the modular properties of D3-brane instantons appearing in Calabi-Yau string compactifications. I'll show that the D3-instanton contribution to a certain geometric potential on the hypermultiplet moduli space can be related to the elliptic genus of (0,4) SCFT. The modular properties of the potential imply that the elliptic genus associated with non-primitive divisors of Calabi-Yau is only mock modular. I'll show how to construct its modular completion and prove the modular invariance of the twistorial construction of D-instanton corrected hypermultiplet moduli space.

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Ref Arxiv: 1508.06914
DOI: 10.1103/PhysRevLett.116.043603
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12 Citations
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Coherent control of quantum systems has far-reaching implications in quantum engineering. In this context, coherent population trapping (CPT) involving dark resonances 1,2 has played a prominent role, leading to a wealth of major applications including laser cooling of atoms 3 and molecules 4 , optical magnetometry 5 , light storage 6–8 and highly precise atomic clocks 9. Extending CPT methods to individual solid-state quantum systems has been only achieved in cryogenic environments for electron spin impurities 10–17 and superconducting circuits 18–21. Here, we demonstrate efficient CPT of a single nuclear spin in a room temperature solid. To this end, we make use of a three-level system with a Λ-configuration in the microwave domain, which consists of nuclear spin states addressed through their hyperfine coupling to the electron spin of a single nitrogen-vacancy defect in diamond. Dark state pumping requires a relaxation mechanism which, in atomic systems, is simply provided by spontaneous emission. In this work, the relaxation process is externally controlled through incoherent optical pumping and separated in time from consecutive coherent microwave excitations of the nuclear spin Λ-system. Such a pumping scheme with controlled relaxation allows us (i) to monitor the sequential accumulation of population into the dark state and (ii) to reach a new regime of CPT dynamics for which periodic arrays of dark resonances can be observed, owing to multiple constructive interferences. This work offers new prospects for quantum state preparation, information storage in hybrid quantum systems 22,23 and metrology. Nuclear spins in solids have attracted considerable interest over the last years owing to their high level of isolation from the environment, leading to very long coherence times 24–26. The detection and control of individual nuclear spins is usually achieved by exploiting their hy-perfine coupling to an ancillary electronic spin. This can be performed by using a nitrogen-vacancy (NV) defect in diamond 27,28 whose spin triplet ground state (S = 1) can be optically initialized, coherently manipulated with microwave fields and read-out by optical means through its spin-dependent photoluminescence (PL) intensity 29. Experiments making use of the hyperfine coupling between the NV defect and nearby long-lived nuclear spins are now reaching a level of control allowing to realize elaborate quantum information protocols 30–32. Here, we make use of electron spin transitions of a single NV defect to achieve coherent control of a single nuclear spin through CPT under ambient conditions. The spin system considered in this study is depicted in Fig. 1a. The electronic spin of a single NV defect is coupled by hyperfine interaction with a nearby 13 C nuclear spin (I = 1/2). In the m s = 0 (|0 e) electron spin mani-fold, the nuclear spin eigenstates are denoted |↑ and |↓ , corresponding to the nuclear spin projections along the NV defect quantization axis. In the m s = −1 (|−1 e) electron spin manifold, efficient nuclear spin mixing can be obtained by exploiting the anisotropic component of the hyperfine interaction in combination with a magnetic field applied along the NV defect axis 34. The nuclear spin