Plan d'expériences | EPFL Graph Search

On nomme plan d'expériences (en anglais, design of experiments ou DOE) la suite ordonnée d'essais d'une expérimentation, chacun permettant d'acquérir de nouvelles connaissances en maîtrisant un ou plusieurs paramètres d'entrée pour obtenir des résultats validant un modèle avec une bonne économie de moyens (nombre d'essais le plus faible possible, par exemple). Un exemple classique est le « plan en étoile » où en partant d'un jeu de valeurs choisi pour les paramètres d'un essai central, on complète celui-ci par des essais où chaque fois un seul des facteurs varie « toutes choses égales par ailleurs ». Un type de plan plus exhaustif est le plan factoriel consistant à choisir des valeurs pour chacun des facteurs en faisant varier simultanément tous les facteurs (de façon exhaustive ou non). Le nombre d'essais peut alors devenir très grand (explosion combinatoire). Problématique Supposons que nous désirions savoir si la proportion de boules noires d'une urne est supérieure

A numerical model to reproduce an experimental design to detect strain in cement

Christina Maria Bauer

An experimental set-up consisting of a loading device inserted in a μCT scanner was numerically simulated to predict the strain at the bone-implant interface of the scapula after applying various loading conditions. The aim of the project was to determine which applied force is required to induce strain measurable by the μCT scanner. First, a 3D model of the bone was obtained by scanning a cadaveric scapula using CT scanner. Second, cortical and trabecular bone were segmented according to Hounsfield Units using Amira software. Extracted 3D scapula was assembled with a glenoid implant and cement and was cut to fit into the loading device. Final, a finite element model was created using Abaqus software. A mesh convergence study was undertaken to set the local element size to 2 mm around the peri-implant area. Strain – volume distribution in the cement was investigated. For an axial loading of 2.4 kN, 60% of the volume achieved a maximum principal strain value lying between 0.15% - 0.29% strain. Previous studies on DVC approach showed strain errors of 6 to 8 με. Such a low error percentage would be suitable for this study and hence the strain level should be detectable.

2016

Rapid screening of nanopore candidates in nanoporous single-layer graphene for selective separations using molecular visualization and interatomic potentials

Luc Sébastien Bondaz, Rohit Karnik

Nanoporous single-layer graphene is promising as an ideal membrane because of its extreme thinness, chemical resistance, and mechanical strength, provided that selective nanopores are successfully incorporated. However, screening and understanding the transport characteristics of the large number of possible pores in graphene are limited by the high computational requirements of molecular dynamics (MD) simulations and the difficulty in experimentally characterizing pores of known structures. MD simulations cannot readily simulate the large number of pores that are encountered in actual membranes to predict transport, and given the huge variety of possible pores, it is hard to narrow down which pores to simulate. Here, we report alternative routes to rapidly screen molecules and nanopores with negligible computational requirement to shortlist selective nanopore candidates. Through the 3D representation and visualization of the pores' and molecules' atoms with their van der Waals radii using open-source software, we could identify suitable C-passivated nanopores for both gas- and liquid-phase separation while accounting for the pore and molecule shapes. The method was validated by simulations reported in the literature and was applied to study the mass transport behavior across a given distribution of nanopores. We also designed a second method that accounts for Lennard-Jones and electrostatic interactions between atoms to screen selective non-C-passivated nanopores for gas separations. Overall, these visualization methods can reduce the computational requirements for pore screening and speed up selective pore identification for subsequent detailed MD simulations and guide the experimental design and interpretation of transport measurements in nanoporous atomically thin membranes.

AIP Publishing2021

Long Spin Lifetime in Rare-Earth Single-Atom Magnets at Surfaces

Boris Sorokin

Further miniaturisation of magnetic storage devices requires an advent of new types of magnets, since classical ferromagnetic materials show lack of remanence at nano- and subnanoscale. A single atom can represent the smallest possible bit of information. Even though the isolated single atoms are paramagnetic, the interaction of surface adsorbed atoms with a substrate can result in high magnetic anisotropy energy and long magnetisation lifetime. In this thesis the magnetic properties of surface supported rare-earth single atoms are investigated with X-ray absorption spectroscopy, X-ray magnetic circular dichroism and multiplet simulations. The first goal of the project was to find new adatom/substrate combinations that exhibit a long adatom magnetic lifetime, possibly extending the current limits of the atomic magnetic moment stability to higher temperatures and longer spin relaxation times. The second objective was to implement the external electric field control of the adatom magnetic properties.Firstly, we present the experimental and theoretical research on Dy and Ho single atoms deposited on BaO. A comparison of our results with similar studies sheds light on the impact of the substrate crystal field, in particular Dy-O bond covalency, on the magnetic stability of the rare-earth adatoms. Next, the detailed experimental investigation of Dy single atoms on ZnO is presented. This adatom/substrate pair is used as first attempt to implement the electric field control of the adatom magnetic properties. Lastly, we study the Dy adatoms on graphene layers grown on various metals. The vibrational modes of the metallic substrates are shown to strongly affect the Dy spin lifetime, while addition of a second graphene layer does not allow to significantly improve the adatom magnetic stability.

EPFL2022

Rapid screening of nanopore candidates in nanoporous single-layer graphene for selective separations using molecular visualization and interatomic potentials

Luc Sébastien Bondaz, Rohit Karnik

AIP Publishing2021