Monte Carlo simulation of subsurface ordering kinetics in an fcc-alloy model

Within the atom-vacancy exchange mechanism in a nearest-neighbor interaction model we investigate the kinetics of surface-induced ordering processes close to the (001) surface of an fcc A_3B-alloy. After a sudden quench into the ordered phase with a final temperature above the ordering spinodal, T_f > T_sp, the early time kinetics is dominated by a segregation front which propagates into the bulk with nearly constant velocity. Below the spinodal, T_f < T_sp, motion of the segregation wave reflects a coarsening process which appears to be slower than predicted by the Lifschitz-Allen-Cahn law. In addition, in the front-penetrated region lateral growth differs distinctly from perpendicular growth, as a result of the special structure of antiphase boundaries near the surface. Our results are compared with recent experiments on the subsurface ordering kinetics at Cu_3Au (001).Comment: 10 pages, 9 figures, submitted to Phys. Rev. B, in prin

Glycans in Sera of Amyotrophic Lateral Sclerosis Patients and Their Role in Killing Neuronal Cells

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease caused by degeneration of upper and lower motor neurons. To date, glycosylation patterns of glycoproteins in fluids of ALS patients have not been described. Moreover, the aberrant glycosylation related to the pathogenesis of other neurodegenerative diseases encouraged us to explore the glycome of ALS patient sera. We found high levels of sialylated glycans and low levels of core fucosylated glycans in serum-derived N-glycans of patients with ALS, compared to healthy volunteer sera. Based on these results, we analyzed the IgG Fc N297-glycans, as IgG are major serum glycoproteins affected by sialylation or core fucosylation and are found in the motor cortex of ALS patients. The analyses revealed a distinct glycan, A2BG2, in IgG derived from ALS patient sera (ALS-IgG). This glycan increases the affinity of IgG to CD16 on effector cells, consequently enhancing Antibody-Dependent Cellular Cytotoxicity (ADCC). Therefore, we explore whether the Fc-N297-glycans of IgG may be involved in ALS disease. Immunostaining of brain and spinal cord tissues revealed over-expression of CD16 and co-localization of intact ALS-IgG with CD16 and in brain with activated microglia of G93A-SOD1 mice. Intact ALS-IgG enhanced effector cell activation and ADCC reaction in comparison to sugar-depleted or control IgG. ALS-IgG were localized in the synapse between brain microglia and neurons of G93A-SOD1 mice, manifesting a promising in vivo ADCC reaction. Therefore, glycans of ALS-IgG may serve as a biomarker for the disease and may be involved in neuronal damage

La tradition manuscrite des œuvres de Moïse de Narbonne (1300-1362)

Like Gersonides (ob. 1344) Moshe Narboni (1300-1362) is the most important Jewish thinker of the XIVth century. But till the past few years most of his works had not yet been edited. We have started an important plan which consists in publishing critically some of his important writings. In the following one can read a study on this manuscript material. This is an important step on the way to editing the whole works of this author who was considered as the most important Maimonides interpreter in the Middle Ages. Besides, the Guide of the perplexed who draws heavily on al-farabo-avicennian philosophy was commented by him in a rather averroistic way ; this was an attitude that was to bring him into trouble in the eyes of the other school of maimonidean interpretation.Moïse de Narbonne (1300-1362) est avec Gersonide (Ob. 1344) la plus grande figure de la philosophie juive du XIVe siècle. Son œuvre n'en est pas moins demeurée à l'état de manuscrits jusqu'à nos jours. Ayant entamé depuis quelques années un large travail d'édition critique de l'œuvre de ce grand averroïste nous donnons dans les pages qui suivent un aperçu sur tous les manuscrits que nous avons consultés ou édités. Ceci est une étape importante dans la connaissance d'un penseur qui fut le lecteur le plus pénétrant de Maïmonide au Moyen Age. Il en fut aussi l'admirateur quoi qu'il infléchisse la pensée alfarabo-avicennienne de l'auteur du Guide des Égarés dans un sens nettement averroïste, ce qui n'est pas sans poser quelques problèmes avec l'autre école de l'interprétation de Maïmonide au Moyen Age.Hayoun Maurice R. La tradition manuscrite des œuvres de Moïse de Narbonne (1300-1362). In: Revue d'histoire des textes, bulletin n°14-15 (1984-1985), 1986. pp. 337-357

Moshe Narboni.

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La méthode dʻinterprétation allegorique dans la pensée juive du Moyen-Age.

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Thermostat quantique pour la méthode de dynamique moléculaire utilisant les intégrales de chemin

International audienceThe quantum thermal bath (QTB) method has been recently developed to account for the quantum nature of the nuclei by using standard molecular dynamics (MD) simulation. QTB-MD is an efficient but approximate method for dealing with strongly anharmonic systems, while path integral molecular dynamics (PIMD) gives exact results in a huge amount of computation time. The QTB and PIMD methods have been combined in order to improve the PIMD convergence or correct the failures of the QTB-MD technique. A new power spectral density of the random force within the QTB has therefore been developed. A modified centroid-virial estimator of the kinetic energy, especially adapted to QTB-PIMD, has also been proposed. The method is applied to selected systems: a one-dimensional double well system, a ferroelectric phase transition, and the position distribution of an hydrogen atom in a fuel cell material. The advantage of the QTB-PIMD method is its ability to give exact results with a more reasonable computation time for strongly anharmonic systems.

Fragmentation of displacement cascades into subcascades: A molecular dynamics study

International audienceThe fragmentation of displacement cascades into subcascades in copper and iron has been investigated through the molecular dynamics technique. A two-point density correlation function has been used to analyze the cascades as a function of the primary knock-on (PKA) energy. This approach is used as a tool for detecting subcascade formation. The fragmentation can already be identified at the end of the ballistic phase. Its resulting evolution in the peak damage state discriminates between unconnected and connected subcascades. The damage zone at the end of the ballistic phase is the precursor of the extended regions that contain the surviving defects. A fractal analysis of the cascade exhibits a dependence on both the stage of the cascade development and the PKA energy. This type of analysis enables the minimum and maximum displacement spike energies together with the subcascade formation threshold energy to be determined