Existence of global strong solutions to a beam-fluid interaction system

We study an unsteady non linear fluid-structure interaction problem which is a simplified model to describe blood flow through viscoleastic arteries. We consider a Newtonian incompressible two-dimensional flow described by the Navier-Stokes equations set in an unknown domain depending on the displacement of a structure, which itself satisfies a linear viscoelastic beam equation. The fluid and the structure are fully coupled via interface conditions prescribing the continuity of the velocities at the fluid-structure interface and the action-reaction principle. We prove that strong solutions to this problem are global-in-time. We obtain in particular that contact between the viscoleastic wall and the bottom of the fluid cavity does not occur in finite time. To our knowledge, this is the first occurrence of a no-contact result, but also of existence of strong solutions globally in time, in the frame of interactions between a viscous fluid and a deformable structure

Mechanosensing of stem bending and its interspecific variability in five neotropical rainforest species

International audienceBackground and Aims: In rain forests, sapling survival is highly dependent on the regulation of trunk slenderness (height/diameter ratio): shade-intolerant species have to grow in height as fast as possible to reach the canopy but also have to withstand mechanical loadings (wind and their own weight) to avoid buckling. Recent studies suggest that mechanosensing is essential to control tree dimensions and stability-related morphogenesis. Differences in species slenderness have been observed among rainforest trees; the present study thus investigates whether species with different slenderness and growth habits exhibit differences in mechanosensitivity. Methods: Recent studies have led to a model of mechanosensing (sum-of-strains model) that predicts a quantitative relationship between the applied sum of longitudinal strains and the plant's responses in the case of a single bending. Saplings of five different neotropical species (Eperua falcata, E. grandiflora, Tachigali melinonii, Symphonia globulifera and Bauhinia guianensis) were subjected to a regimen of controlled mechanical loading phases (bending) alternating with still phases over a period of 2 months. Mechanical loading was controlled in terms of strains and the five species were subjected to the same range of sum of strains. The application of the sum-of-strain model led to a dose-response curve for each species. Dose-response curves were then compared between tested species. Key Results: The model of mechanosensing (sum-of-strain model) applied in the case of multiple bending as long as the bending frequency was low. A comparison of dose-response curves for each species demonstrated differences in the stimulus threshold, suggesting two groups of responses among the species. Interestingly, the liana species B. guianensis exhibited a higher threshold than other Leguminosae species tested. Conclusions: This study provides a conceptual framework to study variability in plant mechanosensing and demonstrated interspecific variability in mechanosensing

Vertical axis rotations across the Puna plateau (Northwestern Argentina) from paleomagnetic analysis of Cretaceous and Cenozoic rocks

Between 10°S and 30°S, the Central Andes are marked by both a major topographic anomaly, the Altiplano-Puna plateau, and a westward concave geometry whose origin remains controversial. The accurate shape is accompanied by a remarkable pattern of rotations about vertical axes. Indeed, in the Central Andes paleomagnetic studies have demonstrated counterclockwise rotations on the northern limb of the arc (throughout Peru, northernmost Chile, and Northern Bolivia) and clockwise rotations on the southern limb (throughout Southern Bolivia, Northwestern Argentina, and Northern Chile). To fill a gap in data from Northern Argentina and to contribute to the ongoing debate on the orgin of rotations in the Central Andes, we have undertaken a paleomagnetic study of 373 cores, taken at 29 sites (grouped into seven localities). The samples are from sediments and lava flows of Cretacous to Tertiary age located in intermontane basins of the Puna plateau in Northwestern Argentina. Vertical axis rotations calculated from paleomagnetic declinations, are clockwise for all localities and confirm the pattern of clockwise rotations associated with the Southern Central Andes. However, significant variations in the amount of local tectonics occur from one locality to another, suggesting that they are, at least in part, influenced by local tectonics. As most faults in the Puna plateau have reverse dip-slip components, we infer that the observed differential rotations between blocks are due to scissoring motions on thrust faults. Whether or not this mechanism has operated across the entire area of thickened crust in the Central Andes remains to be demonstrated. Even if such faulting has locally influenced rotations, Cenzoic oroclinal bending is a likely cause of the remarkable pattern of vertical axis rotations across the Central Andes. (Résumé d'auteur

Vertical axis rotations across the Puna plateau (Northwestern Argentina) from paleomagnetic analysis of Cretaceous and Cenozoic rocks

Between 10°S and 30°S, the Central Andes are marked by both a major topographic anomaly, the Altiplano-Puna plateau, and a westward concave geometry whose origin remains controversial. The accurate shape is accompanied by a remarkable pattern of rotations about vertical axes. Indeed, in the Central Andes paleomagnetic studies have demonstrated counterclockwise rotations on the northern limb of the arc (throughout Peru, northernmost Chile, and Northern Bolivia) and clockwise rotations on the southern limb (throughout Southern Bolivia, Northwestern Argentina, and Northern Chile). To fill a gap in data from Northern Argentina and to contribute to the ongoing debate on the orgin of rotations in the Central Andes, we have undertaken a paleomagnetic study of 373 cores, taken at 29 sites (grouped into seven localities). The samples are from sediments and lava flows of Cretacous to Tertiary age located in intermontane basins of the Puna plateau in Northwestern Argentina. Vertical axis rotations calculated from paleomagnetic declinations, are clockwise for all localities and confirm the pattern of clockwise rotations associated with the Southern Central Andes. However, significant variations in the amount of local tectonics occur from one locality to another, suggesting that they are, at least in part, influenced by local tectonics. As most faults in the Puna plateau have reverse dip-slip components, we infer that the observed differential rotations between blocks are due to scissoring motions on thrust faults. Whether or not this mechanism has operated across the entire area of thickened crust in the Central Andes remains to be demonstrated. Even if such faulting has locally influenced rotations, Cenzoic oroclinal bending is a likely cause of the remarkable pattern of vertical axis rotations across the Central Andes. (Résumé d'auteur

Géodynamique andine : résumés étendus = Andean geodynamics : extended abstracts

A 49° 30' S, le piémont des Andes patagoniennes est constitué d'une ceinture plissée et chevauchée. A l'ouest, des failles inverses de haut angle font remonter en surface un socle anté-crétacé, dont l'intrusion granitique miocène du Monte Fitzroy. A l'est, la présence de plis de croissance dans les arénites du Crétacé moyen et supérieur permet de conclure à un âge précoce pour le début de la déformation. D'autres structures témoignent de la présence de décrochements dextres parallèles à la chaîne. Nous attribuons cette cinématique à la collision oblique des plaques Nazca et Amérique du Sud. (Résumé d'auteur

Formation of a Rain Shadow:O and H Stable Isotope Records in Authigenic Clays From the Siwalik Group in Eastern Bhutan

We measure the oxygen and hydrogen stable isotope composition of authigenic clays from Himalayan foreland sediments (Siwalik Group), and from present day small stream waters in eastern Bhutan to explore the impact of uplift of the Shillong Plateau on rain shadow formation over the Himalayan foothills. Stable isotope data from authigenic clay minerals (<2 μm) suggest the presence of three paleoclimatic periods during deposition of the Siwalik Group, between ∼7 and ∼1 Ma. The mean δ18O value in paleometeoric waters, which were in equilibrium with clay minerals, is ∼2.5‰ lower than in modern meteoric and stream waters at the elevation of the foreland basin. We discuss the factors that could have changed the isotopic composition of water over time and we conclude that (a) the most likely and significant cause for the increase in meteoric water δ18O values over time is the “amount effect,” specifically, a decrease in mean annual precipitation. (b) The change in mean annual precipitation over the foreland basin and foothills of the Himalaya is the result of orographic effect caused by the Shillong Plateau's uplift. The critical elevation of the Shillong Plateau required to induce significant orographic precipitation was attained after ∼1.2 Ma. (c) By applying scale analysis, we estimate that the mean annual precipitation over the foreland basin of the eastern Bhutan Himalayas has decreased by a factor of 1.7–2.5 over the last 1–3 million years. ©2018. American Geophysical Union. All Rights Reserved

Tectonic Evolution of the Chos Malal Fold-and-Thrust Belt (Neuquén Basin, Argentina) From (U-Th)/He and Fission Track Thermochronometry

In the southern central Andes at 37–38°S latitude, the Chos Malal fold-and-thrust belt (FTB), which results from the Late Cretaceous closure of the Neuquén Basin, has generated increasing interest because of its potential for hydrocarbon exploration. Using detailed field mapping, seismic reflection, and well data analysis, we have produced balanced cross sections, which combined with apatite and zircon (U-Th)/He, and fission track thermochronology from samples distributed along the FTB, bring new constraints on the chronology of the structural development of the Chos Malal FTB. Fully reset samples obtained from the Early Jurassic rocks at the bottom of the sedimentary sequence exposed in the Cordillera del Viento, a major basement-involved hinterland structure, permit to quantify its cooling rate from 5.4 ± 4.1 and 3.8 ± 3.2 °C/Ma between 70 and 55 Ma down to between 2.0 ± 1.3 and 1.3 ± 0.9 °C/Ma after 55 Ma until the present. Detrital apatite fission track ages from Late Jurassic and Early Cretaceous sandstones reveal that tectonically driven exhumation through basement-involved thrusting has occurred at ~15–7 Ma in both the inner and outer sectors of the FTB. Finally, the cooling and exhumation of the Las Yeseras-Pampa Tril basement-involved anticlines at the mountain front at ~9–7 Ma, slightly younger than previously assumed, suggests a normal sequence of faulting propagation. Our proposed thermostructural model of the Chos Malal FTB contributes to a better understanding of the tectonic evolution of this segment of the Andes.Fil: Sánchez, Natalia Paola. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Coutand, I.. Dalhousie University Halifax; CanadáFil: Turienzo, Martin Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Lebinson, Fernando Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Araujo, Vanesa Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Dimieri, Luis Vicente. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; Argentin