897 research outputs found
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
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