High-harmonic generation from few layer hexagonal boron nitride: evolution from the monolayer to the bulk response

Two-dimensional materials offer a versatile platform to study high-harmonic generation (HHG), encompassing as limiting cases bulk-like and atomic-like harmonic generation [Tancogne-Dejean and Rubio, Science Advance \textbf{4}, eaao5207 (2018)]. Understanding the high-harmonic response of few-layer semiconducting systems is important, and might open up possible technological applications. Using extensive first-principle calculations within a time-dependent density functional theory framework, we show how the in-plane and out-of-plane nonlinear non-perturbative response of two-dimensional materials evolve from the monolayer to the bulk. We illustrate this phenomenon for the case of multilayer hexagonal BN layered systems. Whereas the in-plane HHG is found not to be strongly altered by the stacking of the layers, we found that the out-of-plane response is strongly affected by the number of layers considered. This is explained by the interplay between the induced electric field by electron-electron interactions and the interlayer delocalization of the wave-functions contributing most to the HHG signal. The gliding of a bilayer is also found to affect the high-harmonic emission. Our results will have important ramifications for the experimental study of monolayer and few-layer two-dimensional materials beyond the case of hexagonal BN studied here as the result we found arew generic and applicable to all 2D semiconducting multilayer systems

A force model for superfinish turning of pure copper with rounded edge tools at low feed rate

International audienceThis paper presents a model for force prediction of superfinish turning operation on pure copper. The model is divided in two parts. The first part computes the forces acting on the rake face of the tool. The second part computes the forces on the clearance face that are much more important in superfinish machining than in conventional machining

From large-scale to micro machining: a review of force prediction models

International audienceIn this paper, a reviewof work performed in the area of force modelling in metal cutting processes is presented. Past and present trends are described and criticised to compare their relevance with current requirements. Several approaches are reviewed, such as empirical, mechanistic and analytical models. The models' ability to predict forces, from rough machining to finish machining, is analysed

Identification d'un modèle d'efforts de coupe mécanistique et application dans le cas d'un contournage de cuivre pur

L'obtention des caractéristiques des pièces usinées ainsi que la bonne maîtrise du procédé d'usinage sont liées aux efforts de coupe. De nombreux modèles d'efforts de coupe ont déjà été développés, mais ils sont souvent appliqués dans le cas d'opérations d'usinage élémentaires (coupe orthogonale ou oblique), ce qui limite leur utilisation à la communauté scientifique. La méthode de discrétisation d'arête permet de généraliser les applications de ces modèles à des géométries d'outils plus complexes. Néanmoins, les applications restent généralement limitées à des opérations d'usinage simples (chariotage, dressage, fraisage flanc...) plutôt éloignées des besoins industriels. D'autre part, les modèles mécanistiques sont généralement critiqués car nécessitant d'être calibrés à partir d'un trop grand nombre d'essais. La présente étude propose de minimiser le nombre d'essais nécessaires à l'identification. Pour cela, les coefficients d'un modèle mécanistique ont été estimés par identification inverse, à partir de différents nombres d'essais de chariotage. Le modèle ainsi identifié est comparé, pour chaque couple de coefficients, à des essais couvrant une large plage de conditions de coupe. Ce modèle est ensuite appliqué dans le cas d'une opération de contournage. Les résultats obtenus par modélisation à partir de la trajectoire théorique, mais aussi de la trajectoire mesurée à vide sur la machine, sont comparés avec les efforts mesurés lors de l'opération de contournage

Anatomically accurate modeling and rendering of the human eye

Recovering anatomical features of organic materials is a challenging issue. The human eye, as an important part of the non verbal communication, needs to be accurately modeled and rendered to increase the realism of virtual characters. The recent improvements of the graphics hardware offer the opportunity of rendering complex organic materials, following correct anatomical properties. We propose a novel method that allows to recover the iris structure and scattering features from a single eye photograph. In this aim, we developed a method to unrefract iris photographs. We model the iris using the Subsurface Texture Mapping representation which allows to describe the relieves of the human iris. Finally, we introduce a refraction function for accurate real-time rendering of the eye, accounting for the refraction of the light at the corneal interface

Preclinical evaluation of the atraumatic nature of a spring loaded blunt tip coaxial needle in a swine model

International audiencePurpose: To test in vivo in an animal model the inherent atraumatic characteristics of the spring loaded blunt tip of a coaxial needle (Gangi-SoftGuard®, Apriomed, Sweden) against a conventional sharp stylet coaxial needle.Material and Methods: The study was conducted on a 40 kg male swine that was its own control for a vascular trauma model. The procedure consisted of voluntary attempts to transfix and traverse the artery/aorta under continuous real-time angiogram. Test and control needles were positioned in the region of the intercostal, superior mesenteric and femoral/deep femoral arteries, and in the aorta. Computed tomography (CT) angiogram was performed post trauma to check for bleeding in the form of extravasation of contrast material. One attempt was performed per site and needle, except for the intercostal artery where a second attempt was done with the test needle, resulting in a total of 4 and 5 tests for the control and test needles, respectively.Results: With the spring loaded blunt tip, no vascular trauma or bleeding was noted in the intercostal, superior mesenteric and femoral arteries, nor in the aorta. Vascular spasm that recovered with time was noted during the second attempt to transfix the same intercostal artery. There were consistent vascular traumas and bleedings with the control needle in all three tested arteries and the aorta, confirmed on angiogram as well as CT angiogram.Conclusion: The atraumatic feature offered by the spring loaded blunt tip prevented vascular trauma during the 5 attempts made to transfix the artery/aorta in a swin

Impact of post-procedural glycemic variability on cardiovascular morbidity and mortality after transcatheter aortic valve implantation : a post hoc cohort analysis

International audienceBackground : Glycemic variability is associated with worse outcomes after cardiac surgery, but the prognosis value of early glycemic variability after transcatheter aortic valve implantation is not known. This study was therefore designed to analyze the prognosis significance of post-procedural glycemic variability within 30 days after transcatheter aortic valve implantation.Methods : A post hoc analysis of patients from our center included in the FRANCE and FRANCE-2 registries was conducted. Post-procedural glycemic variability was assessed by calculating the mean daily δ blood glucose during the first 2 days after transcatheter aortic valve implantation. Major complications within 30 days were death, stroke, myocardial infarction, acute heart failure, and life-threatening cardiac arrhythmias.Results : We analyzed 160 patients (age (median [interquartile] = 84 [80–88] years; diabetes mellitus (n) = 41 (26%) patients; logistic Euroscore = 20 [12–32]). The median value of mean daily δ blood glucose was 4.3 mmol l−1. The rate of major complications within 30 days after procedure among patients with the lowest quartile of glycemic variability was 12%, increasing from 12 to 26%, and 39% in the second, third, and fourth quartiles, respectively. In multivariate analysis, glycemic variability was independently associated with an increased risk of major complications within 30 days after the procedure (odds ratio [95% CI] = 1.83 [1.19–2.83]; p = 0.006).Conclusions : This study showed that post-procedural glycemic variability was associated with an increased risk of major complications within 30 days after transcatheter aortic valve implantation

A generalised geometrical model of turning operations for cutting force modelling using edge discretisation

The knowledge of cutting forces is of prime importance to ensure the success of cutting operations, the desired properties of the machined parts and therefore the functionality of the workpieces. Edge discretisation is one way to model cutting forces. Traditionally used in milling, this methodology enables local changes in uncut chip thickness or cutting geometry to be taken into account and then gives suitable results in the three directions. A key point of this method is the geometrical transformation that enables the description of various tool geometries. This study proposes a geometrical model based on homogeneous matrices, whose main interest is to decompose the transformations step-by-step. The method, generalisable to all machining operations, is detailed for turning operations. Inserted cutters are modelled considering both the positioning of the insert and the local geometry of the insert. The cutting geometry and the edge are described using the same model in the machine coordinates system, allowing forces and moments to be calculated easily