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Can lateral mobility be restored along a highly domesticated low-energy gravel-bed river?
No full textInternational audienc
Nanoscale characterization of collagen structural responses to in situ loading in rat Achilles tendons
No full textInternational audienceThe specific viscoelastic mechanical properties of Achilles tendons are highly dependent on the structural characteristics of collagen at and between all hierarchical levels. Research has been conducted on the deformation mechanisms of positional tendons and single fibrils, but knowledge about the coupling between the whole tendon and nanoscale deformation mechanisms of more commonly injured energy-storing tendons, such as Achilles tendons, remains sparse. By exploiting the highly periodic arrangement of tendons at the nanoscale, in situ loading of rat Achilles tendons during small-angle X-ray scattering acquisition was used to investigate the collagen structural response during load to rupture, cyclic loading and stress relaxation. The fibril strain was substantially lower than the applied tissue strain. The fibrils strained linearly in the elastic region of the tissue, but also exhibited viscoelastic properties, such as an increased stretchability and recovery during cyclic loading and fibril strain relaxation during tissue stress relaxation. We demonstrate that the changes in the width of the collagen reflections could be attributed to strain heterogeneity and not changes in size of the coherently diffracting domains. Fibril strain heterogeneity increased with applied loads and after the toe region, fibrils also became increasingly disordered. Additionally, a thorough evaluation of radiation damage was performed. In conclusion, this study clearly displays the simultaneous structural response and adaption of the collagen fibrils to the applied tissue loads and provide novel information about the transition of loads between length scales in the Achilles tendon
Can lateral mobility be restored along a highly domesticated low-energy gravel-bed river?
No full textInternational audienceFluvial engineering works such as weirs, rip-rap, groynes, and dykes have constrained for decades and more the lateral mobility of rivers, one of the key drivers of aquatic and riparian diversity. Preserving or restoring a sufficient space for river mobility has therefore become a major river management focus. Because the success and relevance of management actions are conditioned by the level of energy and sediment supply of rivers, such actions are generally considered unsuitable for low-energy rivers. However, some low-energy rivers have numerous ancient engineering works along their length, especially bank protections, suggesting a potential capacity for bed migration. In this context, it is essential to determine to what extent planform dynamics is disturbed, and if lateral mobility can be restored. Herein, a case study was done on a 146 km stretch of the lowenergy meandering gravel-bed Cher River (France). The goal of the study was to estimate the remnant shifting capacity, identify the factors controlling the location and intensity of lateral erosion, determine the potential for preserving and restoring lateral mobility, and examine management measures that could be implemented to this end. For that, field surveys, analysis of existing databases, aerial photographs, and laser imaging detection and ranging digital elevation model (LiDAR DEM) data were combined. The study revealed a strong longitudinal fragmentation of the river, with most of it laterally constrained due to the presence of anthropogenic structures such as bank protections, former gravel pits in the alluvial plain, bridges, and weirs. The river is now composed of a string of constrained and unconstrained reaches, and the space available for river shifting has been dramatically reduced. Due to these fluvial engineering works and anthropogenic legacies, the potential for lateral movement of the riverbed, and, therefore, diversification of riparian and aquatic habitats, is limited. Furthermore, lateral mobility could be preserved or restored only for very short sections of the river. It is therefore highly unlikely that good ecological status could be achieved on the entire river corridor through removal of bank protections. Nevertheless, a possible solution could be combining bank protection removals with a series of gravel augmentations close to each other
Force tuning through regulation of clathrin-dependent integrin endocytosis
No full textInternational audienceIntegrin endocytosis is essential for many fundamental cellular processes. Whether and how the internalization impacts cellular mechanics remains elusive. Whereas previous studies reported the contribution of the integrin activator, talin, in force development, the involvement of inhibitors is less documented. We identified ICAP-1 as an integrin inhibitor involved in mechanotransduction by co-working with NME2 to control clathrin-mediated endocytosis of integrins at the edge of focal adhesions (FA). Loss of ICAP-1 enables β3-integrin-mediated force generation independently of β1 integrin. β3-integrin-mediated forces were associated with a decrease in β3 integrin dynamics stemming from their reduced diffusion within adhesion sites and slow turnover of FA. The decrease in β3 integrin dynamics correlated with a defect in integrin endocytosis. ICAP-1 acts as an adaptor for clathrin-dependent endocytosis of integrins. ICAP-1 controls integrin endocytosis by interacting with NME2, a key regulator of dynamin-dependent clathrin-coated pits fission. Control of clathrin-mediated integrin endocytosis by an inhibitor is an unprecedented mechanism to tune forces at FA
Statistical deconvolution of the free Fokker-Planck equation at fixed time
No full textInternational audienceWe are interested in reconstructing the initial condition of a non-linear partial differential equation (PDE), namely the Fokker-Planck equation, from the observation of a Dyson Brownian motion at a given time t > 0. The Fokker-Planck equation describes the evolution of electrostatic repulsive particle systems, and can be seen as the large particle limit of correctly renormalized Dyson Brownian motions. The solution of the Fokker-Planck equation can be written as the free convolution of the initial condition and the semi-circular distribution. We propose a nonparametric estimator for the initial condition obtained by performing the free deconvolution via the subordination functions method. This statistical estimator is original as it involves the resolution of a fixed point equation, and a classical deconvolution by a Cauchy distribution. This is due to the fact that, in free probability, the analogue of the Fourier transform is the R-transform, related to the Cauchy transform. In past literature, there has been a focus on the estimation of the initial conditions of linear PDEs such as the heat equation, but to the best of our knowledge, this is the first time that the problem is tackled for a non-linear PDE. The convergence of the estimator is proved and the integrated mean square error is computed, providing rates of convergence similar to the ones known for non-parametric deconvolution methods. Finally, a simulation study illustrates the good performances of our estimator
Un modèle SIS en dimension infinie
No full textInternational audienceIn this article, we introduce an infinite-dimensional deterministic SIS model which takes into account the heterogeneity of the infections and the social network among a large population. We study the long-time behavior of the dynamic. We identify the basic reproduction number which determines whether there exists a stable endemic steady state (super-critical case: ) or if the only equilibrium is disease-free (critical and sub-critical case: ). As an application of this general study, we prove that the so-called ``leaky'' and ``all-or-nothing'' vaccination mechanism have the same effect on . This framework is also very natural and intuitive to model lockdown policies and study their impact
Convergence in total variation of the Euler-Maruyama scheme applied to diffusion processes with measurable drift coefficient and additive noise
No full text37 pages, 6 figuresInternational audienceWe are interested in the Euler-Maruyama discretization of a stochastic differential equation in dimension with constant diffusion coefficient and bounded measurable drift coefficient. In the scheme, a randomization of the time variable is used to get rid of any regularity assumption of the drift in this variable. We prove weak convergence with order in total variation distance. When the drift has a spatial divergence in the sense of distributions with -th power integrable with respect to the Lebesgue measure in space uniformly in time for some , the order of convergence at the terminal time improves to up to some logarithmic factor. In dimension , this result is preserved when the spatial derivative of the drift is a measure in space with total mass bounded uniformly in time. We confirm our theoretical analysis by numerical experiments
Global well-posedness for the derivative nonlinear Schr\"odinger equation
No full textInternational audienceThis paper is dedicated to the study of the derivative nonlinear Schrödinger equation on the real line. The local well-posedness of this equation in the Sobolev spaces H s (R) is well understood since a couple of decades, while the global well-posedness is not completely settled. For the latter issue, the best known results up-to-date concern either Cauchy data in H 2.3. Bäcklund transformation 17 3. Proof of the main theorem 18 3.1. Strategy of proof 18 3.2. Rigidity type results 18 3.3. End of the proof of Theorem 1 24 Appendix A. Regularized Determinants 29 Appendix B. Proof of the estimate (2.74) 31 References 3
Echocardiography Findings in COVID-19 Patients Admitted to Intensive Care Units: A Multi-National Observational Study (the ECHO-COVID Study).
No full textInternational audiencePURPOSE: Severely ill patients affected by coronavirus disease 2019 (COVID-19) develop circulatory failure. We aimed to report patterns of left and right ventricular dysfunction in the first echocardiography following admission to intensive care unit (ICU). METHODS: Retrospective, descriptive study that collected echocardiographic and clinical information from severely ill COVID-19 patients admitted to 14 ICUs in 8 countries. Patients admitted to ICU who received at least one echocardiography between 1st February 2020 and 30th June 2021 were included. Clinical and echocardiographic data were uploaded using a secured web-based electronic database (REDCap). RESULTS: Six hundred and seventy-seven patients were included and the first echo was performed 2 [1, 4] days after ICU admission. The median age was 65 [56, 73] years, and 71% were male. Left ventricle (LV) and/or right ventricle (RV) systolic dysfunction were found in 234 (34.5%) patients. 149 (22%) patients had LV systolic dysfunction (with or without RV dysfunction) without LV dilatation and no elevation in filling pressure. 152 (22.5%) had RV systolic dysfunction. In 517 patients with information on both paradoxical septal motion and quantitative RV size, 90 (17.4%) had acute cor pulmonale (ACP). ACP was associated with mechanical ventilation (OR\,>\,4), pulmonary embolism (OR\,>\,5) and increased PaCO(2). Exploratory analyses showed that patients with ACP and older age were more likely to die in hospital (including ICU). CONCLUSION: Almost one-third of this cohort of critically ill COVID-19 patients exhibited abnormal LV and/or RV systolic function in their first echocardiography assessment. While LV systolic dysfunction appears similar to septic cardiomyopathy, RV systolic dysfunction was related to pressure overload due to positive pressure ventilation, hypercapnia and pulmonary embolism. ACP and age seemed to be associated with mortality in this cohort