Long-term denudation rates from the Central Andes (Chile) estimated from a digital elevation model using the black top hat function and inverse distance weighting : implications for the neogene climate of the Atacama Desert

A methodology for determining long-term denudation rates from morphologic markers in a Digital Elevation Model (DEM) is checked by a comparative study of two drainage basins in the Precordillera of the Central Andes. In both cases the initial configuration of an incised pediment surface has been restored by using two different methods: the Black Top Hat (BTH) function and the Inverse Distance Weighting (IDW) interpolation. Where vertical incision and hillslope erosion are recorded, the 1DW appears to be the most adequate to reconstitute the pediment surfaces. Conversely, where only vertical incision is observed, the BTH describes more precisely the former pediment surfaces and it is easier to solve. By subtracting the DEM from the reconstructed marker we calculated an eroded volume, and estimated its uncertainty by considering Root Mean Square Error (RMSE) and DEM grid error. For the last similar to 10 Myr we obtained long-term denudation rates of 7.33 +/- 1.6 m/Myr in the San Andres drainage basin and 13.59 +/- 1.9 m/Myr in the El Salado drainage basin. These estimations are largely in agreement with other reported estimates of long-term denudation rates in the Atacama Desert. Comparison with long-term denudation rates reported in a wide range of climatic regimes suggests that our estimates cannot be explained by the current rainfall in the Precordillera. However they could be explained by a rainfall similar to that reported 40 km to the east in the Puna. This suggests that during the time span concerned the geomorphologic evolution of the study area, this evolution is dominated by an orographically controlled rainfall pattern. The preserved pediment surface and the small long term denudation rates determined in this study also indicate that the Precordillera was never reached by humid tropical air masses and precipitation as currently observed in the Altiplano during the summer months

Conception d'hypermédias en médecine : l'expérience du projet FORUM

L'activité médicale est directement concernée par les technologies de l'information aussi bien dans les phases d'apprentissage que dans la pratique quotidienne. Mais une des erreurs serait de se focaliser sur les outils et de minimiser l'importance des aspects organisationnels, sociaux, voire culturels dans l'intégration de ces technologies. La conception d'hypermédias, trop souvent abordée en Médecine uniquement sur le plan technologique, n'échappe pas à cette règle. Cette communication fait le point sur une expérience de développements d'hypermédias en Médecine dans le cadre du projet FORUM. Elle aborde les aspects techniques, méthodologiques et organisationnels qui se veulent contribuer à dynamiser l'implication des enseignants hospitalo-universitaires dans le développement de ce type d'applications

Serum Apolipoproteins A-I, A-II and B in Hepatic Metastases Comparison with other Liver Diseases: Hepatomas and Cirrhosis

Peer Reviewe

Hypermédias et apprentissage en médecine : le projet FORUM

We describe the FORUM hypermedia authoring system used to make educative medical applications. The lack of conceptual model for hypertext application makes it difficult to represent the mental model of the author and for the user to navigate. Handling information and knowledge is a way to reduce this risk. We present an approach to separate the levels of information and knowledge. In the first part, we describe the structure of FORUM. Medical applications of the system are presented in the second part.Cet article présente le générateur d'hypermédias FORUM utilisé pour développer des applications éducatives en Médecine. Les hypertextes et hypermédias sont souvent proposés en Médecine comme une solution pour venir en complément des modes d'apprentissages classiques. Pourtant, l'absence de modèles conceptuels rend difficile le développement d'applications concrètes et qui satisfassent l'enseignant et l'apprenant. Considérer les hypertextes en termes d'informations et de connaissances est une façon de limiter ces difficultés. La première partie de cet article décrit la structure de FORUM en mettant en évidence la séparation entre l'information et la connaissance. Cette séparation est une approche pour faciliter la représentation du modèle mental de l'auteur et la navigation de l'apprenant. Des expériences concrètes de réalisations médicales sont abordées dans la seconde partie.Soula Gérard, Bartoli Jean-Michel, Fieschi Mario. Hypermédias et apprentissage en médecine : le projet FORUM. In: Sciences et techniques éducatives, volume 1 n°4, 1994. pp. 521-538

Long-term denudation rates from the Central Andes (Chile) estimated from a digital elevation model using the black top hat function and inverse distance weighting: implications for the neogene climate of the Atacama Desert

International audienceA methodology for determining long-term denudation rates from morphologic markers in a Digital Elevation Model (DEM) is checked by a comparative study of two drainage basins in the Precordillera of the Central Andes. In both cases the initial configuration of an incised pediment surface has been restored by using two different methods: the Black Top Hat (BTH) function and the Inverse Distance Weighting (IDW) interpolation. Where vertical incision and hillslope erosion are recorded, the 1DW appears to be the most adequate to reconstitute the pediment surfaces. Conversely, where only vertical incision is observed, the BTH describes more precisely the former pediment surfaces and it is easier to solve. By subtracting the DEM from the reconstructed marker we calculated an eroded volume, and estimated its uncertainty by considering Root Mean Square Error (RMSE) and DEM grid error. For the last similar to 10 Myr we obtained long-term denudation rates of 7.33 +/- 1.6 m/Myr in the San Andres drainage basin and 13.59 +/- 1.9 m/Myr in the El Salado drainage basin. These estimations are largely in agreement with other reported estimates of long-term denudation rates in the Atacama Desert. Comparison with long-term denudation rates reported in a wide range of climatic regimes suggests that our estimates cannot be explained by the current rainfall in the Precordillera. However they could be explained by a rainfall similar to that reported 40 km to the east in the Puna. This suggests that during the time span concerned the geomorphologic evolution of the study area, this evolution is dominated by an orographically controlled rainfall pattern. The preserved pediment surface and the small long term denudation rates determined in this study also indicate that the Precordillera was never reached by humid tropical air masses and precipitation as currently observed in the Altiplano during the summer months