The concept of transport capacity in geomorphology

The notion of sediment-transport capacity has been engrained in geomorphological and related literature for over 50 years, although its earliest roots date back explicitly to Gilbert in fluvial geomorphology in the 1870s and implicitly to eighteenth to nineteenth century developments in engineering. Despite cross fertilization between different process domains, there seem to have been independent inventions of the idea in aeolian geomorphology by Bagnold in the 1930s and in hillslope studies by Ellison in the 1940s. Here we review the invention and development of the idea of transport capacity in the fluvial, aeolian, coastal, hillslope, débris flow, and glacial process domains. As these various developments have occurred, different definitions have been used, which makes it both a difficult concept to test, and one that may lead to poor communications between those working in different domains of geomorphology. We argue that the original relation between the power of a flow and its ability to transport sediment can be challenged for three reasons. First, as sediment becomes entrained in a flow, the nature of the flow changes and so it is unreasonable to link the capacity of the water or wind only to the ability of the fluid to move sediment. Secondly, environmental sediment transport is complicated, and the range of processes involved in most movements means that simple relationships are unlikely to hold, not least because the movement of sediment often changes the substrate, which in turn affects the flow conditions. Thirdly, the inherently stochastic nature of sediment transport means that any capacity relationships do not scale either in time or in space. Consequently, new theories of sediment transport are needed to improve understanding and prediction and to guide measurement and management of all geomorphic systems

Construction de la matrice de l'élément fini triangulaire à déformation constante pour l'étude des problèmes à potentiel à partir de critères de consistance

International audienceCe papier court démontre comment la matrice d'un élément fini triangulaire à trois nœuds peut être construite de façon très simple, pour l'étude des problèmes à potentiels, à partir des conditions de consistance de « mouvement de solide rigide » et de symétrie, sans aucune référence aux fonctions d'interpolation, aux conditions de compatibilité, ou toute autre méthodologie conventionnelle en éléments finis. Cette démarche démontre également que la matrice de l'élément triangulaire à trois nœuds est unique

Lineage specific differentiation of pluripotent cells in vitro: a role for extraembryonic cell types

The controlled differentiation of pluripotent cells will be a prerequisite for many cell therapies. We have previously reported homogeneous conversion of embryonic stem (ES) cells in vitro to early primitive ectoderm-like (EPL) cells, equivalent to early primitive ectoderm, an obligatory differentiation intermediate between ES cells and somatic cell populations. Early primitive ectoderm-like cells differentiated within aggregates form mesodermal lineages at the expense of ectoderm. In this work we demonstrate that the failure of EPL cells to form ectodermal cell types does not reflect an inherent restriction in developmental potential. Early primitive ectoderm-like cells form ectodermal derivatives such as neurons in response to neural inducers such as retinoic acid, or when differentiated in the environment provided by ES cell embryoid bodies. This could be explained by signals from the extraembryonic cell type visceral endoderm which forms in differentiating ES cell but not EPL cell aggregates. Consistent with this possibility, culture of EPL cell aggregates in the presence of visceral endoderm-like signals did not prevent differentiation of the pluripotent cells, but resulted in suppression of mesoderm formation. These results suggest a role for visceral endoderm in regulation of germ layer specification from pluripotent cells, and can be integrated into a model for cell differentiation in vitro and in vivo

Developmental complexity of early mammalian pluripotent cell populations in vivo and in vitro

Copyright © CSIRO 1998T. A. Pelton, M. D. Bettess, J. Lake, J. Rathjen and P. D. Rathje