61 research outputs found
Data-Driven Statistical Reduced-Order Modeling and Quantification of Polycrystal Mechanics Leading to Porosity-Based Ductile Damage
Predicting the process of porosity-based ductile damage in polycrystalline
metallic materials is an essential practical topic. Ductile damage and its
precursors are represented by extreme values in stress and material state
quantities, the spatial PDF of which are highly non-Gaussian with strong fat
tails. Traditional deterministic forecasts using physical models often fail to
capture the statistics of structural evolution during material deformation.
This study proposes a data-driven statistical reduced-order modeling framework
to provide a probabilistic forecast of the deformation process leading to
porosity-based ductile damage, with uncertainty quantification. The framework
starts with computing the time evolution of the leading moments of specific
state variables from full-field polycrystal simulations. Then a sparse model
identification algorithm based on causation entropy, including essential
physical constraints, is used to discover the governing equations of these
moments. An approximate solution of the time evolution of the PDF is obtained
from the predicted moments exploiting the maximum entropy principle. Numerical
experiments based on polycrystal realizations show that the model can
characterize the time evolution of the non-Gaussian PDF of the von Mises stress
and quantify the probability of extreme events. The learning process also
reveals that the mean stress interacts with higher-order moments and extreme
events in a strongly nonlinear and multiplicative fashion. In addition, the
calibrated moment equations provide a reasonably accurate forecast when applied
to the realizations outside the training data set, indicating the robustness of
the model and the skill for extrapolation. Finally, an information-based
measurement shows that the leading four moments are sufficient to characterize
the crucial non-Gaussian features throughout the entire deformation history
GPS-derived strain rate field within the boundary zones of the Eurasian, African, and Arabian Plates
Adjoint-based estimation of plate coupling in a non-linear mantle flow model: theory and examples
Reduced methane emissions in former permafrost soils driven by vegetation and microbial changes following drainage
International audienceIn Arctic regions, thawing permafrost soils are projected to release 50 to 250 Gt of carbon by 2100. This data is mostly derived from carbon-rich wetlands, although 71% of this carbon pool is stored in faster-thawing mineral soils, where ecosystems close to the outer boundaries of permafrost regions are especially vulnerable. Although extensive data exists from currently thawing sites and short-term thawing experiments, investigations of the long-term changes following final thaw and co-occurring drainage are scarce. Here we show ecosystem changes at two comparable tussocktundra sites with distinct permafrost thaw histories, representing 15 and 25 years of natural drainage, that resulted in a 10-fold decrease in CH4 emissions (3.2 ± 2.2 vs. 0.3 ± 0.4 mg C-CH4 m−2 day−1), while CO2 emissions were comparable. These data extend the time perspective from earlier studies based on short-term experimental drainage. The overall microbial community structures did not differ significantly between sites, although the drier top soils at the most advanced site led to a loss of methanogens and their syntrophic partners in surface layers while the abundance of methanotrophs remained unchanged. The resulting deeper aeration zones likely increased CH4 oxidation due to the longer residence time of CH4 in the oxidation zone, while the observed loss of aerenchyma plants reduced CH4 diffusion from deeper soil layers directly to the atmosphere. Our findings highlight the importance of including hydrological, vegetation and microbial specific responses when studying long-termeffects of climate change on CH4 emissions and underscores the need for data from different soil types and thaw histories
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Investigation of associations between Piezo1 mechanoreceptor gain-of-function variants and glaucoma-related phenotypes in humans and mice.
Glaucoma disproportionately affects individuals of African descent. Prior studies of the PIEZO1 mechanoreceptor have suggested a possible role in glaucoma pathophysiology. Here, we investigated associations between a Piezo1 gain-of-function variant common in individuals of African descent with glaucoma-related phenotypes. We analyzed whole genome sequences to identify Piezo1 variants and their frequencies among 1565 human participants. For the most common variant (e756del), we compared phenotypes between heterozygotes, homozygotes, and wildtypes. Longitudinal mixed effects models of visual field mean deviation (MD) and retinal nerve fiber layer (RNFL) thickness were used to evaluate progression. Based on trends in the models, further investigation was conducted using Piezo1 gain-of-function mice. About 30% of African descent individuals had at least one e756del allele. There were trends suggesting e756del was associated with higher IOPs, thinner RNFLs, lower optic nerve head capillary densities, and greater decreases in MD and RNFL thickness over time, but these did not reach statistical significance. Among mice, increased Piezo1 activity was not significantly associated with IOP or retinal ganglion cell density. Our study confirms that the Piezo1 e756del gain-of-function variant is a frequent polymorphism present in African descent individuals but is unrelated to examined differences in glaucoma phenotypes. Ongoing work is needed to elucidate the role of Piezo1-mediated mechanotransduction in glaucoma
Abrupt along-strike change in tectonic style: San Andreas fault zone, San Francisco Peninsula
Seismicity and high-resolution aeromagnetic data are used to define an abrupt change from compressional to extensional tectonism within a 10- to 15-km-wide zone along the San Andreas fault on the San Francisco Peninsula and offshore from the Golden Gate. This 100-km-long section of the San Andreas fault includes the hypocenter of the Mw= 7.8 1906 San Francisco earthquake as well as the highest level of persistent microseismicity along that ~470-km-long rupture. We define two distinct zones of deformation along this stretch of the fault using well-constrained relocations of all post- 1969 earthquakes based a joint one-dimensional velocity/hypocenter inversion and a redetermination of focal mechanisms. The southern zone is characterized by thrust- and reverse-faulting focal mechanisms with NE trending P axes that indicate fault-normal compression in 7- to 10-km-wide zones of deformation on both sides of the San Andreas fault. A 1- to 2-km-wide vertical zone beneath the surface trace of the San Andreas is characterized by its almost complete lack of seismicity. The compressional deformation is consistent with the young, high topography of the Santa Cruz Mountains/Coast Ranges as the San Andreas fault makes a broad restraining left bend (~10 °) through the southernmost peninsula. A zone of seismic quiescence ~15 km long separates this compressional zone to the south from a zone of combined normal-faulting and strike-slipfaulting focal mechanisms (including a ML= 5.3 earthquake in 1957) on the northernmost peninsula and offshore on the Golden Gate platform. Both linear pseudogravity gradients, calculated from the aeromagnetic data, and seismic reflection data indicate that the San Andreas fault makes an abrupt ~3-km right step less than 5 km offshore in this northern zone. A similar right-stepping (dilatational) geometry is also observed for the subparallel San Gregorio fault offshore. Persistent seismicity and extensional tectonism occur within the San Andreas right stepover region and at least 15 km along-strike both to the SE and NW. The 1906 San Francisco earthquake may have nucleated within the San Andreas right stepover, which may help explain the bilateral nature of rupture of this event. Our analysis suggests two seismic hazards for the San Francisco Peninsula in addition to the hazard associated with a M = 7 to 8 strike-slip earthquake along the San Andreas fault: the potential for a M ≈ 6 normal-faulting earthquake just 5-8 km west of San Francisco and a M ≈ 6+ thrust faulting event in the southern peninsula
Neotectonic Deformation in Central Eurasia: A Geodynamic Model Approach
Central Eurasia hosts wide orogenic belts of collision between India and Arabia with Eurasia, with diffuse or localized deformation occurring up to hundreds of kilometers from the primary plate boundaries. Although numerous studies have investigated the neotectonic deformation in central Eurasia, most of them have focused on limited segments of the orogenic systems. Here we explore the neotectonic deformation of all of central Eurasia, including both collision zones and the links between them. We use a thin-spherical sheet approach in which lithosphere strength is calculated from lithosphere structure and its thermal regime. We investigate the contributions of variations in lithospheric structure, rheology, boundary conditions, and fault friction coefficients on the predicted velocity and stress fields. Results (deformation pattern, surface velocities, tectonic stresses, and slip rates on faults) are constrained by independent observations of tectonic regime, GPS, and stress data. Our model predictions reproduce the counterclockwise rotation of Arabia and Iran, the westward escape of Anatolia, and the eastward extrusion of the northern Tibetan Plateau. To simulate the observed extensional faults in the Tibetan Plateau, a weaker lithosphere is required, provided by a change in the rheological parameters. The southward movement of the SE Tibetan Plateau can be explained by the combined effects of the Sumatra trench retreat, a thinner lithospheric mantle, and strik-slip faults in the region. This study offers a comprehensive model for regions with little or no data coverage, like the Arabia-India intercollision zone, where the surface velocity is northward showing no deflection related to Arabia and India indentations. ©2017. American Geophysical Union.Funding was granted by the Spanish Government through the project MITE (CGL2014-59516-P) and ALPIMED (PIECSIC-201530E082).Peer reviewe
Performance of real-world functional vision tasks by blind subjects improves after implantation with the Argus® II retinal prosthesis system
The main objective of this study was to test Argus II subjects on three real-world functional vision tasks
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