Electron cooling and Debye-Waller effect in photoexcited bismuth

By means of first principles calculations, we computed the effective electron-phonon coupling constant $G_0$ governing the electron cooling in photoexcited bismuth. $G_0$ strongly increases as a function of electron temperature, which can be traced back to the semi-metallic nature of bismuth. We also used a thermodynamical model to compute the time evolution of both electron and lattice temperatures following laser excitation. Thereby, we simulated the time evolution of (1 -1 0), (-2 1 1) and (2 -2 0) Bragg peak intensities measured by Sciaini et al [Nature 458, 56 (2009)] in femtosecond electron diffraction experiments. The effect of the electron temperature on the Debye-Waller factors through the softening of all optical modes across the whole Brillouin zone turns out to be crucial to reproduce the time evolution of these Bragg peak intensities

Entropy Driven Atomic Motion in Laser-Excited Bismuth

We introduce a thermodynamical model based on the two-temperature approach in order to fully understand the dynamics of the coherent A(1g) phonon in laser-excited bismuth. Using this model, we simulate the time evolution of (111) Bragg peak intensities measured by Fritz et al. [Science 315, 633 (2007)] in femtosecond x-ray diffraction experiments performed on a bismuth film for different laser fluences. The agreement between theoretical and experimental results is striking not only because we use fluences very close to the experimental ones but also because most of the model parameters are obtained from ab initio calculations performed for different electron temperatures

Generation of coherent phonons in photoexcited bismuth

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Time-resolved X-ray diffraction in laser excited bismuth from first principles

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De la dynamique adiabatique d'un piston aux mécanismes de génération de phonons cohérents dans le bismuth photoexcité

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Influences of the Climatic Cycles on the Crustal Deformation and Seismicity - Part 2

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Experimental soft-sediment deformation caused by fluidization and intrusive ice melt in sand

(IF 3.41; Q1)International audienceIdentifying the driving mechanisms of soft‐sediment deformation in the geological record is the subject of debate. Thawing of ice‐rich clayey silt above permafrost was proved experimentally to be among the processes capable of triggering deformation. However, previous work failed so far to reproduce similar structures in sand. This study investigates fluidization and intrusive ice formation from soil models in the laboratory. Experimental conditions reproduce the growth of ice‐cored mounds caused by pore water pressure increase during freeze‐back of sand in permafrost context. Excess pore water pressure causes hydraulic fracturing and the development of water lenses beneath the freezing front. Later freezing of the water lenses generates intrusive ice. The main structures consist of sand dykes and sills formed when the increase in pore water pressure exceeds a critical threshold, and soft‐sediment deformations induced by subsidence during ice melt. The combination of processes has resulted in diapir‐like structures. The experimental structures are similar to those described in Pleistocene sites from France. These processes constitute a credible alternative to the seismic hypothesis evoked to explain soft‐sediment deformation structures in other European regions subjected to Pleistocene cold climates

Features caused by ground ice growth and decay in Late Pleistocene fluvial deposits

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Jeunesse(s) et transitions vers l'âge adulte : quelles permanences, quelles évolutions depuis 30 ans ? XXIVèmes journées du Longitudinal, Marseille, 7 et 8 juin 2018

International audienceLes XXIVèmes Journées du longitudinal (JDL) proposent de questionner les évolutions de la jeunesse et des conditions qui lui sont faites pour cheminer vers l'âge adulte. Qu'elles concernent la relation formation-emploi et l'entrée dans la vie active, l'émancipation familiale, l'acquisition d'une autonomie résidentielle et sociale, la mise en couple ou la constitution d'une famille, les transitions vers l'âge adulte se prêtent particulièrement, par leur caractère processuel, à l'analyse longitudinale. Les profondes transformations opérées depuis une trentaine d'années dans ces processus de transition, s'inscrivant à la fois dans des logiques d'allongement et de désynchronisation croissante entre leurs différentes dimensions, invitent à revisiter les diagnostics établis