Institut Jean Le Rond d'Alembert

Arterial stiffening is influenced by the organization of focal adhesions in vascular smooth muscle cells (VSMCs). We investigated the contribution of αv integrins to both arterial wall stiffness (Young's modulus measured by echography) and VSMC stiffness (assessed by atomic force microscopy). Mice with VSMC-specific deletion of αv integrins (αvSMKO) were compared with controls at baseline and following angiotensin II infusion. Unstimulated cultured αv-deficient (αv-KD) VSMCs exhibited higher stiffness than controls, with a further increase after angiotensin II. To interpret AFM measurements performed at shallow indentation depths, we developed a computational model of VSMC nanoindentation. Simulations showed that higher apparent Young's moduli at shallow indentation fall within the experimental range of αv-KD cells. These cells also displayed enhanced actin polymerization, further amplified by angiotensin II through the formation of cortical F-actin. In vivo, arterial pressure and wall elastic modulus were similar between αvSMKO and control mice at baseline and after angiotensin II, despite αvSMKO mice exhibiting lower elastin and higher collagen content under angiotensin II. Together, these findings indicate that the comparable increase in arterial stiffness observed in αvSMKO mice under angiotensin II is driven primarily by elevated VSMC stiffness resulting from cortical actin redistribution, which outweighs extracellular matrix changes.

A bstract Protein filaments play fundamental functions in the cell, ranging from scaffolding like in the cytoskeleton to sensing and transmitting forces and torques. Here we address the case of the nucleoprotein filaments (NPFs) of homologous recombination (HR) formed by the polymerization of the RecA protein on DNA. In contrast to the cytoskeleton filaments, the HR filaments are not known to exert or sense forces. However the stress in the stretched and unwound DNA bound to those filaments was shown to play a role in promoting DNA strand exchange during the early stage of the HR mechanism. Here we use molecular dynamics simulations to examine whether the strain in the nucleoprotein filament upon strand exchange progression and D-loop formation may influence subsequent steps of the HR process. Our results indicate that the filament mechanical properties are sensitive to the length of DNA incorporated in the D-loop. The response we observe upon increasing the D-loop length is first elastic, up to a threshold that we estimate to be 27 incorporated base pairs, after which the NPF enters a new stage where the protein-DNA connectivities are reorganized. Notably, the DNA displaced strand locally switches from site II to site III, a newly characterized binding site. We discuss the possible consequence of this mechanical response of the NPFs for the course of the HR process.

Energy functionals produced by second-order homogenization of periodic elastic structures commonly feature negative gradient moduli. We show that this undesirable property is caused by the truncation of the energy expansion in powers of the small scale separation parameter. By revisiting Cholesky's LDLT decomposition, we propose an alternative truncation method that restores positivity while preserving the order of accuracy. We illustrate this method on a variety of periodic structures, both continuous and discrete, and derive compact analytical expressions of the homogenized energy that are positive and accurate to second order. The method can also cure the energy functionals produced by second-order dimension reduction, which suffer similar non-positivity issues. It naturally extends beyond second order.

Discrete two-dimensional simulations of cohesive granular collapse are carried out with a focus on the failure process. The existence of a reliable criterion to characterize the failure orientation is discussed. A criterion based on the distribution of the grains' cumulative displacement over the duration of the failure is selected. Questioning its reliability, it appears that a criterion based on grain displacement is fragile in the face of variations of system geometry and stability. Nevertheless, the measure of failure plane orientation appears fairly robust against moderate variations of the displacement criterion and against fluctuations of cohesive states close to the stability limit. This suggests that the measure of the failure orientation at the stability limit is reliable information. However, this work stresses the elusive nature of cohesive granular failure and the important role of fluctuations in granular matter in general.

This paper investigates the prerequisites to creating auralisations that preserve auditory cues used by blind individuals during indoor navigation. It is part of a research project on the design of assistive technologies for exploring places prior to navigation. The investigation starts by listing the type of information used by blind individuals during navigation (room size, distance to walls, etc.) and by discussing the auditory cues they rely on to access those information. It then proceeds to characterise how various auralisation workflows can be used to capture or simulate and then present these cues to users. The listing is based on a literature review complemented with interviews with seven early and late blind participants. The characterisation is based on informal evaluations with those participants exploring various small and large-scale auralisation scenarios.

We consider a generalized SEIS (susceptible, exposed, infectious, and susceptible) model where individuals are divided into three compartments: S (healthy and susceptible), E (infected but not just infectious, or exposed), and I (infectious). Finite waiting times in the compartments yield a system of delay-differential or memory equations and may exhibit oscillatory (Hopf) instabilities of the otherwise stationary endemic state, leading normally to regular oscillations in the form of an attractive limit cycle in the phase space spanned by the compartment rates. In the present paper, our aim is to demonstrate that in the dynamics of delayed SEIS models, persistent chaotic attractors can bifurcate from these limit cycles and become accessible if the nonlinear interaction terms fulfill certain basic requirements, which to our knowledge were not addressed in the literature so far. Computing the largest Lyapunov exponent, we show that chaotic behavior exists in a wide parameter range. Finally, we discuss a more general system and show that a sudden falloff of the infection rate with respect to increasing infection number may be responsible for the emergence of chaotic time evolution. Such a falloff can describe mitigation measures, such as wearing masques, individual isolation, or vaccination. The model may have a wide range of interdisciplinary applications beyond epidemic spreading, for instance, in the kinetics of certain chemical reactions.

In this study, we aim to improve the volume conservation of the interface advection method and the behavior of the triple point at small contact angles on arbitrary solid surfaces in a framework where volume-of-fluid methods and embedded solid representations are used to describe fluid and solid domains. We present a method with improved volume-conservation properties allowing for general solid boundaries. The method calculates the exact advected volume while accounting for the solid presence. In cases without solids, the existing method already maintains very good conservation. For configurations involving small contact angles, the solution focuses on accurately locating the triple point by identifying the intersection of the solid surface with the gas–liquid interface. To validate our approach, we tested the method with a relaxing sessile drop on both flat and cylindrical surfaces. Results demonstrate a significant improvement in accuracy, with a relative mass error reduced from 14% to 0.02%, and precise contact angles successfully achieved in the range of 5° to 165°.

We simulate cohesive granular flows over an inclined plane using the 2 D Contact Dynamics algorithm. The plug thickness is measured from numerical simulations considering various adhesive contact strengths. Flow surface roughness is investigated by calculating the fluctuation of surface topography. The distribution of fluctuation intensity across di↵erent adhesive strengths is also discussed. Roughness correlation on flow surface is studied using a pair correlation function applied to the positions of surface grains. A characteristic length is defined from the correlation results, considering both cohesive and non-cohesive cases. A quantitative comparison is conducted with a recent experimental study that relates the characteristic length to the agglomeration size in cohesive granular flows.