Bou Grara (mer de)

La mer de Bou Grara, qui couvre une superficie d’environ 450 km2 est située dans le Sud tunisien, à proximité de l’île de Jerba qu’elle sépare du continent. Elle communique avec le golfe de Gabès par deux passages. Le premier, au nord-est, est celui d’El Kantara qui est large d’environ 6 km et profond de moins de 2 m. Dans l’antiquité, il a été barré par une chaussée romaine et, par la suite, des caravanes l’ont franchi à gué en suivant le trik el jemel. L’autre passage, au nord-ouest, corres..

Bou Grara (mer de)

La mer de Bou Grara, qui couvre une superficie d’environ 450 km2 est située dans le Sud tunisien, à proximité de l’île de Jerba qu’elle sépare du continent. Elle communique avec le golfe de Gabès par deux passages. Le premier, au nord-est, est celui d’El Kantara qui est large d’environ 6 km et profond de moins de 2 m. Dans l’antiquité, il a été barré par une chaussée romaine et, par la suite, des caravanes l’ont franchi à gué en suivant le trik el jemel. L’autre passage, au nord-ouest, corres..

Biban (Les Portes)

Ce nom arabe entre fréquemment dans la toponymie du Maghreb. Il s’applique principalement à l’ensemble montagneux que les géographes ont appelé ainsi en raison des deux défilés des « Portes de Fer ». Il entre également dans la dénomination d’une importante lagune du Sud tunisien, la Bahiret el Biban. Il sert aussi à désigner de petits hypogées creusés à flanc de rocher, particulièrement nombreux dans le nord de la Tunisie. Les monts des Biban (E.B.) Le nom donné à cette chaîne montagneuse de ..

Biban (Les Portes)

Ce nom arabe entre fréquemment dans la toponymie du Maghreb. Il s’applique principalement à l’ensemble montagneux que les géographes ont appelé ainsi en raison des deux défilés des « Portes de Fer ». Il entre également dans la dénomination d’une importante lagune du Sud tunisien, la Bahiret el Biban. Il sert aussi à désigner de petits hypogées creusés à flanc de rocher, particulièrement nombreux dans le nord de la Tunisie. Les monts des Biban (E.B.) Le nom donné à cette chaîne montagneuse de ..

Influence of bone microstructure on the mechanical properties of skull cortical bone – A combined experimental and computational approach

The strength and compliance of the dense cortical layers of the human skull have been examined since the beginning of the 20th century with the wide range in the observed mechanical properties attributed to natural biological variance. Since this variance may be explained by the difference in structural arrangement of bone tissue, micro-computed tomography (μCT) was used in conjunction with mechanical testing to study the relationship between the microstructure of human skull cortical coupons and their mechanical response. Ninety-seven bone samples were machined from the cortical tables of the calvaria of ten fresh post mortem human surrogates and tested in dynamic tension until failure. A linear response between stress and strain was observed until close to failure, which occurred at 0.6% strain on average. The effective modulus of elasticity for the coupons was 12.01 ± 3.28 GPa. Porosity of the test specimens, determined from μCT, could explain only 51% of the variation of their effective elastic modulus. Finite element (FE) models of the tested specimens built from μCT images indicated that modeling the microstructural arrangement of the bone, in addition to the porosity, led to a marginal improvement of the coefficient of determination to 54%. Modulus for skull cortical bone for an element size of 50 μm was estimated to be 19 GPa at an average. Unlike the load bearing bones of the body, almost half of the variance in the mechanical properties of cortical bone from the skull may be attributed to differences at the sub-osteon ( < 50 μm) level. ANOVA tests indicated that effective failure stress and strain varied significantly between the frontal and parietal bones, while the bone phase modulus was different for the superior and inferior aspects of the calvarium. The micro FE models did not indicate any anisotropy attributable to the pores observable under μCT.This research was sponsored by contract no. N00421-11-C-0004 from the U.S. Naval Air Warfare Center, Aircraft Division, Patuxent River, MD

Surface velocity fields of active rock glaciers and ice-debris complexes in the Central Andes of Argentina

Rock glaciers and transitional ice-debris complexes predominate the Central Andean landform assemblage, yet regional studies on their state of activity and their kinematics remain sparse. Here we utilize the national glacier inventory of Argentina to quantify surface velocity fields of 244 rock glaciers and 51 ice-debris complexes, located in the Cordón del Plata range, Argentina. Applying a feature-tracking approach to repeated RapidEye satellite imagery acquired between 2010 and 2017/18, we find mean displacement rates between 0.37 and 2.61 m year−1 for 149 landforms, while for the remaining 146 features, surface movement remains below our level of detection. We compare our satellite-derived velocity fields with ground-truth data from two local field sites and find closely matching results in magnitude and spatial distribution. With average displacement of one-third of the active rock glaciers and ice-debris complexes exceeding 1 m year−1, the region hosts an exceptional number of fast-flowing periglacial landforms, compared to other mountain belts. Using a random forest model, we test the predictive power of 25 morphometric and topoclimatic candidate predictors for modelling the state of activity of rock glaciers and ice-debris complexes on two different scales. For entire landforms and individual landform segments, constructed along displacement centrelines, we can predict the state of activity with overall accuracies of 70.08% (mean AUROC = 0.785) and 74.86% (mean AUROC = 0.753), respectively. While topoclimatic parameters such as solar radiation and elevation are most important for entire landforms, geometric parameters become more important at the scale of landform segments. Despite tentative correlations between local slope and surface kinematics, our results point to factors integrating slope and distance to the source to govern local deformation. We conclude that feature tracking in optical imagery is feasible for regional studies in remote regions and provides valuable insight into the current state of the Andean cryosphere.Fil: Blöthe, Jan Henrik. Universitat Bonn; AlemaniaFil: Halla, Christian. Universitat Bonn; AlemaniaFil: Schwalbe, Ellen. Technische Universität Dresden; AlemaniaFil: Bottegal, Estefania Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Trombotto, Dario Tomas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Schrott, Lothar. Universitat Bonn; Alemani

Level- and Region-Specific Properties of Young Human Lumbar Annulus

ABSTRACT The objective of this study was to determine the material properties of the human lumbar intervertebral disc annulus as a function of anatomical region and spinal level. Samples from minimally or nondegenerated spines were extracted from young post mortem human subjects and tested in tension. Statistically significant differences were found based on anatomical region. Trends appear to indicate spinal level dependency, although additional samples are required to attain statistical significance. It is possible to use finite element models incorporating these region-and level-specific properties to quantify internal load-sharing and delineate the mechanism of disorders such as herniation