Local yield stress statistics in model amorphous solids

We develop and extend a method presented in [S. Patinet, D. Vandembroucq, and M. L. Falk, Phys. Rev. Lett., 117, 045501 (2016)] to compute the local yield stresses at the atomic scale in model two-dimensional Lennard-Jones glasses produced via differing quench protocols. This technique allows us to sample the plastic rearrangements in a non-perturbative manner for different loading directions on a well-controlled length scale. Plastic activity upon shearing correlates strongly with the locations of low yield stresses in the quenched states. This correlation is higher in more structurally relaxed systems. The distribution of local yield stresses is also shown to strongly depend on the quench protocol: the more relaxed the glass, the higher the local plastic thresholds. Analysis of the magnitude of local plastic relaxations reveals that stress drops follow exponential distributions, justifying the hypothesis of an average characteristic amplitude often conjectured in mesoscopic or continuum models. The amplitude of the local plastic rearrangements increases on average with the yield stress, regardless of the system preparation. The local yield stress varies with the shear orientation tested and strongly correlates with the plastic rearrangement locations when the system is sheared correspondingly. It is thus argued that plastic rearrangements are the consequence of shear transformation zones encoded in the glass structure that possess weak slip planes along different orientations. Finally, we justify the length scale employed in this work and extract the yield threshold statistics as a function of the size of the probing zones. This method makes it possible to derive physically grounded models of plasticity for amorphous materials by directly revealing the relevant details of the shear transformation zones that mediate this process

SIMUS: an open-source simulator for ultrasound imaging. Part II: comparison with three popular simulators

Computational ultrasound imaging has become a well-established methodology in the ultrasound community. In the accompanying paper (part I), we described a new ultrasound simulator (SIMUS) for Matlab, which belongs to the Matlab UltraSound Toolbox (MUST). SIMUS can generate pressure fields and radiofrequency RF signals for simulations in medical ultrasound imaging. It works in a harmonic domain and uses linear equations derived from far-field and paraxial approximations. In this article (part II), we illustrate how SIMUS compares with three popular ultrasound simulators (Field II, k-Wave, and Verasonics) for a homogeneous medium. We designed different transmit sequences (focused, planar, and diverging wavefronts) and calculated the corresponding 2-D and 3-D (with elevation focusing) RMS pressure fields. SIMUS produced pressure fields similar to those of Field II and k-Wave. The acoustic fields provided by the Verasonics simulator were significantly different from those of SIMUS and k-Wave, although the overall appearance remained consistent. Our simulations tend to demonstrate that SIMUS is reliable and can be used on a par with Field II and k-Wave for realistic ultrasound simulations.Comment: to be submitte

Application du concept de perte de charge au diagnostic échocardiographique des sténoses aortiques

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal

Greedy optimization for growing spatially embedded oscillatory networks

The coupling of some types of oscillators requires the mediation of a physical link between them, rendering the distance between oscillators a critical factor to achieve synchronization. In this paper we propose and explore a greedy algorithm to grow spatially embedded oscillator networks. The algorithm is constructed in such a way that nodes are sequentially added seeking to minimize the cost of the added links' length and optimize the linear stability of the growing network. We show that, for appropriate parameters, the stability of the resulting network, measured in terms of the dynamics of small perturbations and the correlation length of the disturbances, can be significantly improved with a minimal added length cost. In addition, we analyze numerically the topological properties of the resulting networks and find that, while being more stable, their degree distribution is approximately exponential and independent of the algorithm parameters. Moreover, we find that other topological parameters related with network resilience and efficiency are also affected by the proposed algorithm. Finally, we extend our findings to more general classes of networks with different sources of heterogeneity. Our results are a first step in the development of algorithms for the directed growth of oscillatory networks with desirable stability, dynamical and topological properties.Comment: 13 pages, 9 figure

Real time 3D US-tagging combined with 3D phase-based motion estimation

International audienceBy contrast with 2D imaging, quantitative analysis of 3D motion from ultrasound images can provide improved information in several applications, such as arterial mechanical assessment, heart motion and blood flow. Unfortunately, it remains difficult to obtain a high definition of the motion estimate in the lateral and elevation directions (i.e. perpendicular to the beam axis). To increase the definition in both these directions, this paper presents a 3D extension of a the transverse oscillations method that enables one to obtain ultrasound fields featuring oscillations along the 3 spatial dimensions, using a single apodization function. The 3D motion method is estimated using the phases of the images. Simulation results show that a 3D trajectory can be followed with a relative mean error smaller than 8%

Création d'une nouvelle filiale de la holding NAVINANCE en plomberie chauffage

Aquestes són les quatre missions del màster fetes a l'EMN (Ecole de Management de Normandie)Notre mission création d’entreprise consiste à aider M. Droinet dans la création d’une nouvelle filiale en synergie avec ses deux autres entreprises. L’idée principale consiste à créer un showroom où serait exposée une gamme complète de solutions de chauffage et de plomberie dans la région Caennaise. De plus, cette proposition serait complétée par l’apport de conseils et de formations faites par des équipes de professionnels

Role of frozen lubricant film on tribological behaviour and wear mechanisms in grinding

International audienceIn this paper the friction conditions of Minimum Coolant Grinding (MCG) technology are deeply characterized. The MCG is a successful cooling/lubricating system that combines the application of Minimum Quantity of Lubrication (MQL) and CO2 at low temperatures to create a frozen layer of oil able to reach the contact zone. This technique has previously shown promising results to reduce heat generation in grinding process and improve the workpiece finish. A comparison of the energy consumption, forces and wear patterns have been performed between MCG and dry grinding by means of the On-Machine Test Bench. In the work authors have identified that MCG favours the shearing of the material reducing the energy consumption and wear of the abrasive. Differences are highlighted on the size of wear flats, the shape of the debris and the various types of wear mechanisms