Diffraction with a coherent X-ray beam: dynamics and imaging

Techniques for coherent X-ray scattering measurements are detailed. Applications in the study of the dynamics of fluctuations and in lensless high-resolution imaging are described

Experimental clues of soft glassy rheology in strained filled elastomers

International audienceTensile stress-relaxation measurements have been performed on a series of cross-linked filled elastomers. The fillers are chosen in order to investigate the effect of the filler-filler and the filler-matrix interactions on the time dependence of the tensile relaxation modulus E(t) after UP and DOWN jumps. For the carbon black filled sample (strong filler-elastomer interaction) E(t) decreases as log(t) when the strain epsilon is strictly larger than 0.2 and reached by UP jumps. For the silica filled samples in the same conditions, and for all samples after a DOWN jump including epsilon = 0.2, the experimental data can be fitted with a power law equation characterized by the exponent m. Thus, in all cases, |dE(t)⁄dt| scales as t^(-α) with α=m+1. Pertinence of the Soft Glassy Rheology (SGR) model for interpreting the present results is examined. It is shown that α could be equivalent to the effective noise temperature x and related to the polymer chain mobility

Strain inhomogeneity in copper islands probed by coherent X-ray diffraction

International audienceThe strain field of individual epitaxial sub-micrometric copper islands is studied using coherent X-ray diffraction and finite element modelling. The strain inhomogeneity in each island is so large that the characteristic features of the island shape tend to disappear in the diffraction pattern, which is dominated by strain effects. The model confirms the tensile strain imposed to the island by the thermal mismatch occurring during the preparation of the samples. An evaluation of the residual strain is obtained by qualitatively fitting the diffraction data

Color Imaging with Multimodal Three-Photon Microscopy

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Monte Carlo static and dynamic simulations of a three-dimensional Ising critical model

International audienceThe critical dynamics of 'model A" of Hohenberg and Halperin has been studied by the Monte Carlo method. Simulations have been carried out in the three-dimensional (3d) simple cubic Ising model for lattices of sizes L = 16 to L = 512. Using Wolff's cluster algorithm, the critical temperature is precisely found as β c = 0.221 654 68(5). By Fourier transform of the lattice configurations, the critical scattering intensities I (q) can be obtained. After circular averaging, the static simulations with L = 256 and L = 512 provide an estimate of the critical exponent γ /ν = 2 − η = 1.9640(5). The | q |-dependent distribution of I (q) showed an exponential distribution, corresponding to a Gaussian distribution of the scattering amplitudes for a large q domain. The time-dependent intensities were then used for the study of the critical dynamics of 3d lattices at the critical point. To simulate results of an x-ray photon correlation spectroscopy experiment, the time-dependent correlation function of the intensities was studied for each | q |-value. In the q region where I (q) had an exponential distribution, the time correlations can be fit to a stretched exponential, where the exponent μ = γ /νz 0.975 provides an estimate of the dynamic exponent z. This corresponds to z = 2.0145, in agreement with the observed variations of the characteristic fluctuation time of the intensity: τ (q) ∝ q −z , which gives z = 2.015. These results agree with the expansion of field-theoretical methods (2.017). In this paper, the need to take account of the anomalous time behavior (μ < 1) in the dynamics is exemplified. This dynamics reflects a nonlinear time behavior of model A, and its large time extension is discussed in detail

Les êtres sociaux

Les êtres sociau

Optimizing Native Ion Mobility Q-TOF in Helium and Nitrogen for Very Fragile Noncovalent Structures

International audienceThe amount of internal energy imparted to the ions prior to the ion mobility cell influences the ion structure and thus the collision cross section. Non-covalent complexes with few internal degrees of freedom and/or high charge densities are particularly sensitive to collisional activation. Here, we investigated the effects of virtually all tuning parameters of the Agilent 6560 IM-Q-TOF on the arrival time distributions of ubiquitin7+ and found conditions in which the native state prevails. We discuss the effects of solvent evaporation conditions in the source, of the entire pre-IM DC voltage gradient, of the funnel RF amplitudes. We also report on ubiquitin7+ conformations in different solvents, including native supercharging conditions. Collision-induced unfolding (CIU) can be conveniently provoked either behind the source capillary or in the trapping funnel. The softness of the instrumental conditions behind the mobility cell was further optimized with the DNA G-quadruplex [(dG4T4G4)2·(NH4+)3-8H]5−, for which ion activation results in ammonia loss. To reduce the ion internal energy and obtain the intact 3-NH4+ complex, we reduce the post-IM voltage gradient, but this results in a lower IM resolving power due to increased diffusion behind the drift tube. The article describes the various trade-offs between ion activation, ion transmission, and ion mobility performance for native MS of very fragile structure