Etude morpho-pédologique des Iles Wallis, Futuna et Alofi : cartes à l'échelle de 1:40000

Cette étude comporte les cartes morpho-pédologiques des îles Wallis, Futuna et Alofi et une notice explicative. Dans ce texte sont présentées les principales caractéristiques géographiques ainsi que les principaux aspects des sols et des paysages morpho-pédologiques

An experimental study of turbulent flow in vertical slot fishways

The vertical slot fishways are hydraulic structures that allow the upstream migration of fishes through engineering constructions or natural obstructions in rivers. This type of pool fish pass is generally very effective in ensuring passage of the target species, particularly diadromous species. However, visual observations have shown that certain small species may be trapped in the large recirculation zones and seem to have difficulty in rapidly passing through very large pools. An experimental study was undertaken to characterize the turbulent flow for various configurations of vertical slot fishways and to determine how their characteristics might be modified in order to facilitate the passage of small species. The characteristics of mean flow and turbulence were studied by PIV and visualizations for several different slopes, flow discharges and pool widths. The results showed that the flow pattern always takes one of two topology models depending on the ratio length/width of the pool. In order to study the extent to which the dimensions of recirculation zones can be reduced, the effect of the insertion of vertical cylinders within the pools was visualized

Melhoria da qualidade ambiental de terras agricultáveis por meio da silvopastagem no sudeste dos Estados Unidos

Nossa hipótese é de que devido à habilidade das árvores seqüestrarem carbono (C) no perfil profundo do solo e remover o excesso de nutrientes dos solos, o sistema de silvopastagem agroflorestal poderia melhorar a qualidade ambiental de terras agricultáveis. Para testar esta hipótese, dois grupos de experimentos foram conduzidos em duas ordens de solos na Florida, Espodossolos e Ultissolos, com dois objetivos principais: i) determinar a acumulação de C do solo e investigar as fontes de C para as plantas nas frações dos solos, e ii) quantificar o fósforo solúvel em água (FSA) e estimar a capacidade de armazenamento de fósforo no solo (CAFS). O C total em ambos os solos foi maior sob o sistema de silvopastagem do que sob pastagens com menos árvores, particularmente nas profundidades mais baixas. A análise por assinatura de isótopo estável sugeriu que as plantas C3 (neste caso, slash pine, Pinis elliotti) contribuíram mais para a fração estável do carbono do que plantas C4 (neste caso, bahiagrass, Paspalum notatum) nas profundidades dos solos acima de 1 m. O FSA foi consistentemente maior em pastagens com poucas árvores, enquanto que a CAFS foi mais baixa neste sistema, sugerindo a grande probabilidade do fósforo ser mais facilmente movido do solo sob pastagens com poucas árvores do que nos sob silvopastagem. Deste modo, a presença de árvores em pastagens contribuiu para C mais estável nos perfis dos solos e o mais baixo FSA e a maior CAFS indicaram os grandes benefícios ambientais fornecidos pelos sistemas de silvopastagem comparados com as pastagens com poucas árvores em condições ecológicas similares.We hypothesized that, because of the ability of trees to sequester carbon (C) in the deep soil profile and remove excess nutrients from soils, the silvopastoral agroforestry system could enhance the environmental quality of the agricultural lands. To test this hypothesis, two sets of experiments were conducted in two soil orders in Florida, Spodosols and Ultisols, with two major objectives: i) determining the soil C accumulation and tracing the plant sources of C in soil fractions, and ii) quantifying water soluble phosphorus (WSP) and estimating the Soil P Storage Capacity (SPSC). Total C in both soil orders was greater under silvopasture than in treeless pastures, particularly at lower depths. Stable-isotope signature analysis suggested that C3 plants (in this case, slash pine, Pinus elliotii) contributed to a more stable C fraction than C4 plants (in this case, bahiagrass, Paspalum notatum) at soil depths up to 1 m. WSP was consistently higher in treeless pastures, while the remaining SPSC was lower in this land-use system, suggesting the greater likelihood of P moving out of the soil under treeless pasture than in silvopasture. Thus, the presence of trees in pastures contributed to more stable C within the soil profiles, lower WSP, and greater SPSC, indicating more environmental benefits provided by silvopastoral systems as compared to treeless pastures under similar ecological settings

Modeling the mean interaction forces between powder particles. Application to silica gel-magnesium stearate mixtures.

International audienceDry coating experiments were performed by using the Hybridizer (Nara). Large host silica gel (SG) particles (d50 = 55 μm) were coated with fine invited particles of magnesium stearate (MS, d50 = 4.6 μm) for different contents of MS in the mixture. The real MS mass fraction wI obtained after mechanical treatment has been determined thanks to calibration from TGA measurements. The surface structure and morphology of MS coatings were observed using Environmental Scanning Electron Microscopy (ESEM) and Atomic Force Microscopy (AFM) [26, 27]. AFM has been also used to measure the adhesion forces between particles. Interaction forces between the material attached to the cantilever (Magnesium Stearate MS) and the surface of the composite material (Silica Gel SG or Magnesium Stearate MS) have been determined at different surface locations. For different compositions wI of the mixture MS-SG, the numeric distribution and the mean value f of the forces fH obtained for MS-SG interactions or fI for MS-MS interactions have been established and the experimental curve showing the evolution of f versus wI has been derived. Models of ordered structures have been developed, implying morphological hypotheses concerning large spherical or cylindrical host particles H and small invited spherical I. Different types of distribution of I materials onto the surface of H have been considered: for examples a discrete monolayer –or multilayers- of monosized particles I on the H surface. The coordinence of MS particles around SG particles has been estimated to calculate the free SG surface fraction through different modelling and to obtain the mean force f versus composition wI. The theoretical force values have been compared to experimental ones. The deviations have been discussed in terms of guest particle distributions on the surface of the large host particles and morphological hypotheses

Experiment and simulation of dry particle coating

Issu de : 5th International granulation Workshop, 20-22 June 2011, Lausanne, SWITZERLANDInternational audienceThe objective of this study is to get a better understanding of dry powder coating process using experiments and numerical methods. Materials chosen as host particles are SUGLETS® (granules mainly consisting of sugar) and as invited particles, magnesium stearate (MgSt). These two materials are introduced into a high shear mixer (Cyclomix). Operations were performed at various mixing time and rotation speed of the Cyclomix. The surface morphology analysis has confirmed that Suglet particles are coated with MgSt. The product properties such as flowability, wettability and particle size distributions were also characterized. The particle motion in the Cyclomix has been simulated by using Discrete Element Method (DEM). Both number of collisions and the collision force frequency are calculated. The simulation shows an increase of the collision number with the rotational speeds. This result indicates that choosing higher rotation speeds should be better for the dry coating process as long as the particles are not broken down

Production de particules composites par enrobage en voie sèche dans un mélangeur cyclomix et modélisation DEM

National audienceUne modélisation de l'enrobage en voie sèche selon la méthode par éléments discrets (DEM) a été développée afin de mieux comprendre les phénomènes mis en jeu. Dans ce procédé, des poudres de taille relativement grande (dites " hôtes ") sont recouvertes de particules fines (dites " invitées ") par l'application de forces mécaniques sans l'aide de solvants ni de liants hydrauliques. Dans ce travail, les matériaux choisis comme particules hôtes sont les Suglets® (des granules sphériques constituées principalement de sucre) et les particules invitées sont constituées de stéarate de magnésium (MgSt). Ces deux éléments sont introduits sous forme de poudre dans un mélangeur à fort cisaillement appelé Cyclomix. Les propriétés du produit final comme la coulabilité et la fraction massique ont été caractérisées. La variation de l'indice de coulabilité en fonction de la durée de traitement par Cyclomix pour 4 vitesses de rotation et 3 taux de remplissage différents. La coulabilité des produits a été améliorée avec une augmentation de la durée d'opération et de la vitesse de rotation. Mais le taux de remplissage ne semble pas influer sur l' amélioration de la coulabilité. Le rendement en produit, estimé par sa fraction massique, est analysé. La constante de taux d'enrobage est corrélée avec la distance de rotation obtenue par DEM. Il a été montré que l'efficacité d'enrobage peut être prévue par la simulation