Study of dispersion by NMR: comparison between NMR measurements and stochastic simulation

Dispersion remains, today, a highly topical subject. Our group has been interested in characterizing this phenomenon by pulsed-field-gradient NMR technique. Direct measurement of the dispersion coefficient can be done with a Pulsed Gradient Spin Echo (PGSE) sequence by assuming that the asymptotic regime is reached. In unsteady state, the propagator formalism is used. To better understand these measurements, the NMR experiment is modeled using a stochastic simulation (random walks) and compared with experimental results. The comparison is made for the simple case of Poiseuille flow in a circular tube (Taylor-Aris dispersion)

Study of dispersion by NMR: comparison between NMR measurements and stochastic simulation

Dispersion remains, today, a highly topical subject. Our group has been interested in characterizing this phenomenon by pulsed-field-gradient NMR technique. Direct measurement of the dispersion coefficient can be done with a Pulsed Gradient Spin Echo (PGSE) sequence by assuming that the asymptotic regime is reached. In unsteady state, the propagator formalism is used. To better understand these measurements, the NMR experiment is modeled using a stochastic simulation (random walks) and compared with experimental results. The comparison is made for the simple case of Poiseuille flow in a circular tube (Taylor-Aris dispersion)

Rehabilitation and release of orphaned Eurasian lynx (Lynx lynx) in Europe: Implications for management and conservation.

Rehabilitation of injured or immature individuals has become an increasingly used conservation and management tool. However, scientific evaluation of rehabilitations is rare, raising concern about post-release welfare as well as the cost-effectiveness of spending scarce financial resources. Over the past 20 years, events of juvenile Eurasian lynx presumably orphaned have been observed in many European lynx populations. To guide the management of orphaned lynx, we documented survival, rehabilitation and fate after the release and evaluated the potential relevance of lynx orphan rehabilitation for population management and conservation implications. Data on 320 orphaned lynx was collected from 1975 to 2022 from 13 countries and nine populations. The majority of orphaned lynx (55%) were taken to rehabilitation centres or other enclosures. A total of 66 orphans were released back to nature. The portion of rehabilitated lynx who survived at least one year after release was 0.66. Release location was the best predictor for their survival. Of the 66 released lynx, ten have reproduced at least once (8 females and 2 males). Conservation implications of rehabilitation programmes include managing genetic diversity in small, isolated populations and reintroducing species to historical habitats. The lynx is a perfect model species as most reintroduced populations in Central Europe show significantly lower observed heterozygosity than most of the autochthonous populations, indicating that reintroduction bottlenecks, isolation and post-release management have long-term consequences on the genetic composition of populations. The release of translocated orphans could be a valuable contribution to Eurasian lynx conservation in Europe. It is recommended to release orphans at the distribution edge or in the frame of reintroduction projects instead of a release in the core area of a population where it is not necessary from a demographic and genetic point of view. Rehabilitation programmes can have conservation implications that extend far beyond individual welfare benefits

A multi-scale formulation of the overall rigidity of unsaturated expansive clays derived by micromechanical analyses

International audienc

ANALYSE EXPERIMENTALE DES MECANISMES D'INSTABILITE LORS DE L'EBULLITION D'UN MILIEU POREUX CHAUFFE A TEMPERATURE CONSTANTE

NANCY/VANDOEUVRE-INPL (545472102) / SudocSudocFranceF

A multi-scale approach to analyze the role of the disjoining pressure in the overall stiffness of expansive clays

International audienc

Transferts thermiques : cours et 55 exercices corrigés

International audienc

Transfert hydrique dans des sols argileux gonflants (influence du confinement)

La description des mécanismes d'humidification et de gonflement dans les sols argileux représente un enjeu important dans différentes disciplines scientifiques comme l'agronomie, la géotechnique ou l'industrie pétrolière. L'objectif du travail présenté ici est de montrer, au moins du point de vue qualitatif, les effets de couplage hydromécanique lors de l'imbibition de milieux argileux gonflants soumis à différentes conditions de confinement. Le matériau que nous avons utilisé est un mélange de bentonite et de limon de Xeuilley. Préparé à une certaine teneur en eau massique, ce mélange est ensuite compacté par une technique double-piston. Cela permet d'élaborer des éprouvettes de sols uniformes à la fois en humidité et en terme de masse volumique sèche. Des essais d'imbibition d'eau par le bas ont été réalisés pour trois types de confinements (libre, œdométrique, à volume constant). Au cours des expériences, la technique de gammamétrie double-source est utilisée afin de suivre localement, et de manière non-intrusive, l'évolution de la masse volumique sèche et de la teneur en eau. Une comparaison des trois cinétiques d'imbibition est enfin menée pour chaque essai à partir d'une caractérisation en terme de diffusivité hydrique, basée sur une description lagrangienne des transferts.NANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

Séchage des bétons réfractaires (expérimentation, modélisation et influence d'un ajout de fibres polymère)

Les matériaux réfractaires non façonnés dense (MRNF) prennent une part de plus en plus importante aussi bien en cimenterie, fonderie, sidérurgie, ... Principalement constitués d agrégats à base d alumine, de magnésie, de spinelle, ils constituent des matériaux de faible perméabilité contenant une teneur résiduelle en eau de 4 à 6 %. Leur séchage avant leur première utilisation est une opération critique qui conditionne leur durée de vie. D une part, mal conduit, il peut du fait des endommagements occasionnés, réduire considérablement la durée de vie des installations. D autre part, certaines conditions de séchage conduisent à une véritable destruction de nature explosive du matériau correspondant à une élévation brutale de la pression interne (accompagnant l élévation de la pression de vapeur saturante de l eau avec la température). Le travail a permis de se familiariser avec les matériaux réfractaires non-façonnés à l aide d une caractérisation thermomécanique complète menée entre la température ambiante et 500 C, de comprendre les mécanismes mis en jeu lors de leur séchage, d une part, par une expérimentation et, d autre part, en les reproduisant en s appuyant sur un transfert simultané de chaleur et de masse en milieu poreux. Et enfin, il a permis d étudier l impact d un ajout de fibres polymère sur une caractéristique qui gère l évacuation de l eau, la perméabilité, et plus généralement sur le séchageCastable refractories take a more and more important place in various industries: cement factory, casting, iron and steel making. They consist mainly of aggregates of high-alumina and ultra-low cement. Their permeability is very low and they contain before the first heat-up a residual water content of 4 to 6 % (dry basis). Drying during the first heat-up is a crucial step which sharply influence the refractory in-service performances. On one hand, damaging can occur, and as a consequence will reduce drastically the life time of the plants. On the other hand, particular drying conditions can lead to an explosive spalling of the refractory corresponding to an internal gas pressure steep raise linked to the water saturated vapour pressure raise with temperature. First, a complete thermomechanical characterization between ambient temperature and 500 C of the unshaped refractory materials has been conducted. Then the mechanisms involved during their drying, on one hand, by an experiment and, on the other hand, by using a simultaneous heat and mass transfer model in porous media have been studied. And last, the impact of adding polymer fibers has been analysed both on the concrete permeability as well as their influence on dryingNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF