Comparison between classical potentials and ab initio for silicon under large shear

The homogeneous shear of the {111} planes along the <110> direction of bulk silicon has been investigated using ab initio techniques, to better understand the strain properties of both shuffle and glide set planes. Similar calculations have been done with three empirical potentials, Stillinger-Weber, Tersoff and EDIP, in order to find the one giving the best results under large shear strains. The generalized stacking fault energies have also been calculated with these potentials to complement this study. It turns out that the Stillinger-Weber potential better reproduces the ab initio results, for the smoothness and the amplitude of the energy variation as well as the localization of shear in the shuffle set

Dislocation formation from a surface step in semiconductors: an ab initio study

The role of a simple surface defect, such as a step, for relaxing the stress applied to a semiconductor, has been investigated by means of large scale first principles calculations. Our results indicate that the step is the privileged site for initiating plasticity, with the formation and glide of 60$^\circ$ dislocations for both tensile and compressive deformations. We have also examined the effect of surface and step termination on the plastic mechanisms

Lithiation-delithiation cycles of amorphous Si nanowires investigated by molecular dynamics simulations

The atomistic mechanisms during lithiation and delithiation of amorphous Si nanowires ($a$-SiNW) have been investigated over cycles by molecular dynamics simulations. First, the Modified Embedded Atom Method (MEAM) potential from Cui et al. [J. Power Sources. 2012, (207) 150] has been further optimized on static (Li$_x$Si alloy phases and point defect energies) and on dynamic properties (Li diffusion) to reproduce the lithiation of small crystalline Si nanowires calculated at the {\it ab initio} level. The lithiation of $a$-SiNW reveals a two-phase process of lithiation with a larger diffusion interface compared to crystalline Si lithiation. Compressive axial stresses are observed in the amorphous Si$_x$Li alloy outer shell. They are easily released thanks to the soft glassy behavior of the amorphous alloy. Conversely, in crystalline SiNW, the larger stress in the narrow crystalline lithiated interface is hardly released and requires a phase transformation to amorphous to operate, which delays the lithiation. The history of the charge-discharge cycles as well as the temperature appear as driving forces for phase transformation from amorphous Li$_x$Si alloy to the more stable crystalline phase counterpart. Our work suggest that a full delithiation could heal the SiNWs to improve the life cycles of Li-ion batteries with Si anode.Comment: 11 pages, 8 figures

A fully molecular dynamics-based method for modeling nanoporous gold

International audienceModels that can be used to describe nanoporous gold are often generated either by phase-field or Monte-Carlo methods. It is not ascertained that these models are closely matching experimental systems, and there is a need for other variants. Here is proposed an original approach to generate alternative models, which is solely based on molecular dynamics simulations. Structures obtained with this method are structurally characterized by determining the ligaments diameter distributions, the scaled genus densities and the interfacial shape distributions. Selected mechanical characterizations are also done by deforming the structures in tension and in compression. Structural and mechanical properties are in good agreement with experimental and theoretical published results

Étude par simulations à l'échelle atomique de la déformation de nanofils de silicium

L'étude des nano-objets en matériau semi-conducteur a révélé des propriétés mécaniques exceptionnelles, différentes de celles observées dans le massif. Outre l'intérêt technologique majeur qu'ils représentent à travers la miniaturisation toujours plus poussée des systèmes électroniques, leurs caractéristiques intrinsèques en font des objets particulièrement bien adaptés pour des études fondamentales. Dans ce contexte, nous avons étudié le déclenchement de la plasticité dans les nano-fils de silicium, les premiers stades de la plasticité étant en effet déterminants pour l'évolution ultérieure du système. Le silicium est ici considéré comme un semi-conducteur modèle. Pour cette étude, nous avons utilisé des simulations atomistiques qui sont parfaitement appropriées à l'analyse détaillée de la structure atomique des nano-objets. Après avoir contextualisé notre étude tant du point de vue de l'expérience que de celui des simulations, nous présentons les techniques numériques que nous avons utilisées. Nous décrivons ensuite l'étude de la déformation de nano-fils monocristallins, révélant notamment le rôle majeur des surfaces et l'activation d'un système de glissement jamais observé dans le silicium massif. Ce système de glissement est analysé en détail, et son activation est expliquée notamment au moyen de calculs ab initio. Enfin, nous avons considéré la déformation de nano-fils coeur-coquille cristal-amorphe et mis en évidence un comportement différent de celui observé pour les nano-fils monocristallins. Ainsi, des défauts natifs à l'interface cristal-amorphe semblent agir comme des germes favorisant la nucléation de la première dislocation qui va initier la plasticité.The study of semiconductor nano-objets has revealed amazing mechanical properties, different from what is commonly observed in bulk. Besides the technological interest of these objects, due to the ever more pronounced miniaturization of electronic devices, their intrinsic specificities make them particularly well suited for fundamental studies. During this thesis, we have thus studied the onset of plasticity in silicon nanowires, the first stages of plasticity being indeed deciding for the subsequent evolution of the system. Silicon is here considered as a model semiconductor. For that study, we have used atomistic simulations, which are well appropriate for the detailed analysis of the nano-objects atomic structure. We first recall the context of that study, both from the experiments and simulations points of view. We then present the numerical methods used. Thestudy of the deformation of monocrystalline nanowires is then described; it reveals in particular the deciding role of surfaces, and the activation of one slip system never observed in bulk silicon. This slip system is analyzed in details, and its activation is explained notably thanks to ab initio calculations. Finally, crystalline-amorphous core-shell silicon nanowires are considered; and shownto exhibit a different behavior from that of monocrystalline nanowires. Indeed, native defects at the crystalline/amorphous interface seem to act as seeds, favoring the nucleation of the first dislocation which gives rise to the plasticity.POITIERS-SCD-Bib. électronique (861949901) / SudocSudocFranceF

The Combinatorial PP1-Binding Consensus Motif (R/K)x (0,1)V/IxFxx(R/K)x(R/K) Is a New Apoptotic Signature

BACKGROUND: Previous studies established that PP1 is a target for Bcl-2 proteins and an important regulator of apoptosis. The two distinct functional PP1 consensus docking motifs, R/Kx((0,1))V/IxF and FxxR/KxR/K, involved in PP1 binding and cell death were previously characterized in the BH1 and BH3 domains of some Bcl-2 proteins. PRINCIPAL FINDINGS: In this study, we demonstrate that DPT-AIF(1), a peptide containing the AIF(562-571) sequence located in a c-terminal domain of AIF, is a new PP1 interacting and cell penetrating molecule. We also showed that DPT-AIF(1) provoked apoptosis in several human cell lines. Furthermore, DPT-APAF(1) a bi-partite cell penetrating peptide containing APAF-1(122-131), a non penetrating sequence from APAF-1 protein, linked to our previously described DPT-sh1 peptide shuttle, is also a PP1-interacting death molecule. Both AIF(562-571) and APAF-1(122-131) sequences contain a common R/Kx((0,1))V/IxFxxR/KxR/K motif, shared by several proteins involved in control of cell survival pathways. This motif combines the two distinct PP1c consensus docking motifs initially identified in some Bcl-2 proteins. Interestingly DPT-AIF(2) and DPT-APAF(2) that carry a F to A mutation within this combinatorial motif, no longer exhibited any PP1c binding or apoptotic effects. Moreover the F to A mutation in DPT-AIF(2) also suppressed cell penetration. CONCLUSION: These results indicate that the combinatorial PP1c docking motif R/Kx((0,1))V/IxFxxR/KxR/K, deduced from AIF(562-571) and APAF-1(122-131) sequences, is a new PP1c-dependent Apoptotic Signature. This motif is also a new tool for drug design that could be used to characterize potential anti-tumour molecules

Severe Occupational Asthma : Insights From a Multicenter European Cohort

BACKGROUND: Although sensitizer-induced occupational asthma (OA) accounts for an appreciable fraction of adult asthma, the severity of OA has received little attention. OBJECTIVE: The aim of this study was to characterize the burden and determinants of severe OA in a large multicenter cohort of subjects with OA. METHODS: This retrospective study included 997 subjects with OA ascertained by a positive specific inhalation challenge completed in 20 tertiary centers in 11 European countries during the period 2006 to 2015. Severe asthma was defined by a high level of treatment and any 1 of the following criteria: (1) daily need for a reliever medication, (2) 2 or more severe exacerbations in the previous year, or (3) airflow obstruction. RESULTS: Overall, 162 (16.2%; 95% CI, 14.0%-18.7%) subjects were classified as having severe OA. Multivariable logistic regression analysis revealed that severe OA was associated with persistent (vs reduced) exposure to the causal agent at work (odds ratio [OR], 2.78; 95% CI, 1.50-5.60); a longer duration of the disease (OR, 1.04; 95% CI, 1.00-1.07); a low level of education (OR, 2.69; 95% CI, 1.73-4.18); childhood asthma (OR, 2.92; 95% CI, 1.13-7.36); and sputum production (OR, 2.86; 95% CI, 1.87-4.38). In subjects removed from exposure, severe OA was associated only with sputum production (OR, 3.68; 95% CI, 1.87-7.40); a low education level (OR, 3.41; 95% CI, 1.72-6.80); and obesity (OR, 1.98; 95% CI, 0.97-3.97). CONCLUSIONS: This study indicates that a substantial proportion of subjects with OA experience severe asthma and identifies potentially modifiable risk factors for severe OA that should be targeted to reduce the adverse impacts of the disease. (C) 2019 Published by Elsevier Inc. on behalf of the American Academy of Allergy, Asthma & ImmunologyPeer reviewe

A Power Consumption Estimation Approach for Embedded Software Design using Trace Analysis

International audienceWith the explosion of advanced power control knobs such as dynamic voltage frequency scaling, mastering energy constraints in embedded systems is becoming challenging for software developers. Several power estimation techniques have been proposed over the past years, from electrical level to more abstract models such as SystemC/TLM. They offer various trade-offs between performance and accuracy, but suffer from a number of shortcomings. They are expensive and time-consuming, requiring intricate models of the architecture and finally, fail to be applied from the software developer perspective. In this paper, we propose a lightweight and cost-effective approach suitable for software developers. It relies on trace analysis and high-level modeling of architectures to perform quick and efficient power consumption estimations without loosing accuracy. This approach is fully supported by a tool and is validated using a simple thermal mitigation case study and checked against physical measurements. We show that, for our case study, the relative error between our tool and real values is 8% in average