Strain in the mesoscale kinetic Monte Carlo model for sintering

Shrinkage strains measured from microstructural simulations using the mesoscale kinetic Monte Carlo (kMC) model for solid state sintering are discussed. This model represents the microstructure using digitized discrete sites that are either grain or pore sites. The algorithm used to simulate densification by vacancy annihilation removes an isolated pore site at a grain boundary and collapses a column of sites extending from the vacancy to the surface of sintering compact, through the center of mass of the nearest grain. Using this algorithm, the existing published kMC models are shown to produce anisotropic strains for homogeneous powder compacts with aspect ratios different from unity. It is shown that the line direction biases shrinkage strains in proportion the compact dimension aspect ratios. A new algorithm that corrects this bias in strains is proposed; the direction for collapsing the column is determined by choosing a random sample face and subsequently a random point on that face as the end point for an annihilation path with equal probabilities. This algorithm is mathematically and experimentally shown to result in isotropic strains for all samples regardless of their dimensions. Finally, the microstructural evolution is shown to be similar for the new and old annihilation algorithms.Comment: 6 pages, 6 figure

An original growth mode of MWCNTs on alumina supported iron catalysts

Multi-walled carbon nanotubes (MWCNTs) have been produced from ethylene by Fluidized Bed Catalytic Chemical Vapor Deposition (FB-CCVD) on alumina supported iron catalyst powders. Both catalysts and MWCNTs-catalyst composites have been characterized by XRD, SEM-EDX, TEM, Mössbauer Spectroscopy, TGA and nitrogen adsorption measurements at different stages of the process. The fresh catalyst is composed of amorphous iron (III) oxide nanoparticles located inside the porosity of the support and of a micrometric crystalline &-iron (III) oxide surface film. The beginning of the CVD process provokes a brutal reconstruction and simultaneous carburization of the surface film that allows MWCNT nucleation and growth. These MWCNTs grow aligned between the support and the surface catalytic film, leading to a uniform consumption and uprising of the film. When the catalytic film has been consumed, the catalytic particles located inside the alumina porosity are slowly reduced and activated leading to a secondary MWCNT growth regime, which produces a generalized grain explosion and entangled MWCNT growth. Based on experimental observations and characterizations, this original two-stage growth mode is discussed and a general growth mechanism is proposed

Biomimetic nanocrystalline apatites: Emerging perspectives in cancer diagnosis and treatment

Nanocrystalline calcium phosphate apatites constitute the mineral part of hard tissues, and the synthesis of biomimetic analogs is now wellmastered at the labscale. Recent advances in the fine physicochemical characterization of these phases enable one to envision original applications in the medical field along with a better understanding of the underlying chemistry and related pharmacological features. In this contribution, we specifically focused on applications of biomimetic apatites in the field of cancer diagnosis or treatment. We first report on the production and first biological evaluations (cytotoxicity, proinflammatory potential, internalization by ZR751 breast cancer cells) of individualized luminescent nanoparticles based on Eudoped apatites, eventually associated with folic acid, for medical imaging purposes. We then detail, in a first approach, the preparation of tridimensional constructs associating nanocrystalline apatite aqueous gels and drugloaded pectin microspheres. Sustained releases of a fluorescein analog (erythrosin) used as model molecule were obtained over 7 days, in comparison with the ceramic or microsphere reference compounds. Such systems could constitute original bonefilling materials for in situ delivery of anticancer drug

A unifying model for fluid flow and elastic solid deformation : a novel approach for fluid-structure interaction and wave propagation

Le modèle compressible multiphasique proposé, permettant de gérer dans un même système des phases fluides (compressibles) et solides (élastiques), est basé sur les équations classiques de conservation de masse, de quantité de mouvement et de flux de chaleur. Sa spécificité réside dans la prise en compte dans l’équation de Cauchy, définie sous sa forme Lagrangienne, de la pression p à l’instant t, explicitement définie à partir de la pression p0 à l’instant t0=t-dt, des coefficients thermodynamiques et des divergences de vitesse et de flux de chaleur de l’instant t. De façon similaire, la température T est explicitement définie dans l’équation de conservation des flux de chaleur. Les champs de vitesses et de flux de chaleur alors obtenus par la résolution du système d’équations de conservation permettent le calcul explicite de la pression p et de la température T contribuant à la fermeture du système. Notons que dans ce modèle, la masse volumique n’est plus déduite d’une équation d’état, mais est directement déterminée du calcul de la divergence de la vitesse. C’est dans une étape ultérieure que les différents champs scalaires et vectoriels sont advectés à partir de leur dérivée totale pour une résolution Eulérienne. Ce modèle compressible est dans un premier temps validé par plusieurs cas test comme : 1) la compression de systèmes monophasés fluide ou solides ; 2) la compression d’un système diphasé fluide/solide à interface plane ; 3) la propagation d’ondes de compression et de cisaillement dans un solide élastique pour le calcul de la vitesse des ondes sonores. Dans un second temps, est abordée l’étude d’un cas complexe 3D consistant en l’injection d’un fluide sur un solide élastique. La déformation de l’interface fluide/solide ainsi que l’évolution de la pression en des points caractéristiques des deux phases de l’instant initial à l’état stationnaire sont analysées

La justice algorithmique : analyse comparée (France/Québec) d'un phénomène doctrinal

The launch of the “open data des decisions de justice” in 2016 triggered the development of tools of what we call algorithmic justice. These tools have, themselves, gathered a concentration of legal literature about them in the form of a dense and reactive corpus organized around the idea of a core incompatibility between French law and algorithmic justice tools. While the passing years didn’t alter this crux of questioning, the development of the open data and the tools based on it never stopped. This study aims at reconciling these two contrary movements through the analysis of the French legal literature spanning from 2016 to 2022. This literature-based, empirical and comparative study is built on the three incompatibilities identified by that discourse: a juridical incompatibility, a systemic incompatibility and a cultural incompatibility. Each of the possible incompatibilities serves as a hypothesis and is studied using both quantitative and qualitative data extracted from the French as well as the Quebec legal literature, which serves as a contrast agent of what is specific to the French way of dealing with algorithmic justice tools. After admitting that the first two hypothesizes are false leads, we show that the incompatibility that explains the French concentration around those tools is cultural. This discourse thus appears as the realization of the ever-expanding gap between the law as it is understood and the law as it actually exists, meaning that algorithmic justice tools are just the medium of this realization. More generally, this study empirically confirms how much legal literature is both constructed and constructive itself. This analysis thus highlights the fundamental need to incorporate a literature-based approach to any analysis of positive law as to take charge of the representations and discursive strategies that precedes and towers above legal literature.Le lancement du mouvement de l’open data des décisions de justice en 2016 a enclenché le développement d’outils dits de justice algorithmique qui ont, à leur tour, agrégé autour d’eux une véritable concentration doctrinale sous la forme d’un discours fourni et réactif dont le pivot demeure une idée d’incompatibilité entre le droit français et ces outils de justice algorithmique. Si le passage des années n’a pas altéré ce nœud discursif, le développement progressif de l’open data et des outils construits sur son fondement ne s’est pas stoppé. La présente étude cherche à réconcilier ces deux mouvements a priori contraires en s’attachant à analyser le discours doctrinal français relatif aux outils de justice algorithmique de 2016 à 2022. Cette analyse métadoctrinale, empirique et comparée est construite sur les trois temps du discours français, correspondant eux-mêmes à trois incompatibilités potentielles : une incompatibilité d’ordre juridique, une incompatibilité d’ordre systémique et une incompatibilité d’ordre culturel. Chacune de ces hypothèses est analysée en convoquant à la fois les données quantitatives et qualitatives extraites du discours français et l’expérience québécoise comme produit de contraste de la réception française des outils de justice algorithmique. Une fois avoir admis que les deux premières hypothèses constituent autant de fausses pistes, il apparaît que l’incompatibilité susceptible d’expliquer la concentration doctrinale française autour de ces outils est une incompatibilité d’ordre culturel mais plus encore d’ordre doctrinal. Ce discours apparaît alors bien plus comme une prise de conscience de l’espace grandissant qui sépare la compréhension doctrinale du droit français et l’état dans lequel il se trouve véritablement. Plus largement, cette étude confirme de manière empirique la nature construite et constructive de tout discours doctrinal. La présente analyse souligne alors l’importance fondamentale d’intégrer à toute analyse de droit positif une démarche métadoctrinale de prise en charge des représentations et des stratégies discursives qui précèdent tout discours doctrinal

The impact of fluctuations on the sintering kinetics of two particles demonstrated through Monte Carlo simulation

In the field of particle sintering involving viscous bulk flow, this paper shows, using Monte Carlo modelling, that energy fluctuations influence particles sintering kinetics. These fluctuations are considered to be responsible for the non-linear mass transport behaviour during the sintering of two cylinders. In the case where these fluctuations are considered negligible, the Newtonian viscous flow regime is shown to be the main mechanism

Numerical modeling of diffusion-controlled phase transformation using the Darken method: Application to the dissolution/precipitation processes in materials

Many material phase transformations are controlled by mass transport induced by diffusion. To better understand such transformations, numerous modeling strategies at the scale of the moving interfaces exist, with their strengths and weaknesses. Phase-field approaches are based on diffuse interfaces that do not require any interface tracking, as opposed to those based on fixed-grid sharp interface tracking. In the case of binary two-phase systems, in this paper we address the key point of the mass balance equation at the interface involving a concentration jump, which determines the interface moving velocity. We propose a unique diffusion equation for both phases and their interface, based on the component’s chemical potentials which are continuous through the interface and a smooth volume-of-fluid phase representation. This model is achieved in the framework of the Darken method, which involves intrinsic diffusion of components and a drift velocity to which all compounds are subjected. This drift velocity is shown to be that of the interface displacement as well. This methodology is verified for 1D and 3D dissolution/precipitation problems and has a first-order spatial convergence. The 3D simulations of precipitation and dissolution processes of more complex microstructures clearly show a bifurcation of the particle morphology from the initial spherical shape when the diffusion edges of each particle interact with each other. An extension of the diffusion potential to mechanical driving forces should make it possible to deal with mechano-chemical coupling of mass transport

Numerical study of a hard sphere wetted by a spherical viscoelastic particle

The wetting process of a hard sphere by a fluid particle is numerically studied using a Monte Carlo approach. A methodology different to that based on the Potts model is being developed in the framework of an energetic potential, which explicitly accounts for the interfacial energies as well as a cohesive energy of the fluid particle. The minimisation of the potential through random changes of the particle configuration enables the quantification of stress gradients within the particle induced by the surface curvature gradients as well as the induced mass fluxes. The physical constants considered for the calculation of the energetic potential correspond to a wetting angle equal to 30°, and ensure that the rheological behaviour, which is implicitly generated during the Monte Carlo procedure, is viscoelastic. An insight into the stress gradients and mass fluxes within the fluid particle at different stages of the wetting process is presented. The wetting kinetics are analysed and compared to the kinetics of the co-sintering process of two fluid particles

3D original modelling of phase transformation/mechanics coupling : Effects of internal and external applied stresses on particle growth

The elastic effects on particle growth were studied from a developed 3D original model that couples explicitly phase transformations and mechanical fields. This model is shown to be able to describe the time-evolution of both chemical and mechanical fields and their interactions in diffusive mass transport. In order to isolate and to analyse some generic effects of elastic fields, the model developed was applied to the growth of an initially single spherical precipitate into a supersaturated matrix in a finite media. We account for both internal and external applied stresses effects on the growth process including both thermo-kinetics and morphological aspects. In all cases studied, the elastic effects are shown to affect the transformation kinetics and equilibrium state. It is also demonstrated that the applied uniaxial compression loading induces an anisotropy of growth that affects both the morphological evolution and hence the equilibrium shape of the particle. This is shown to result to complex interactions between local pressure gradients and local composition gradients

3D original modelling of phase transformation/mechanics coupling : Effects of internal and external applied stresses on particle growth

The elastic effects on particle growth were studied from a developed 3D original model that couples explicitly phase transformations and mechanical fields. This model is shown to be able to describe the time-evolution of both chemical and mechanical fields and their interactions in diffusive mass transport. In order to isolate and to analyse some generic effects of elastic fields, the model developed was applied to the growth of an initially single spherical precipitate into a supersaturated matrix in a finite media. We account for both internal and external applied stresses effects on the growth process including both thermo-kinetics and morphological aspects. In all cases studied, the elastic effects are shown to affect the transformation kinetics and equilibrium state. It is also demonstrated that the applied uniaxial compression loading induces an anisotropy of growth that affects both the morphological evolution and hence the equilibrium shape of the particle. This is shown to result to complex interactions between local pressure gradients and local composition gradients