123 research outputs found
Faults Self-Organized by Repeated Earthquakes in a Quasi-Static Antiplane Crack Model
We study a 2D quasi-static discrete {\it crack} anti-plane model of a
tectonic plate with long range elastic forces and quenched disorder. The plate
is driven at its border and the load is transfered to all elements through
elastic forces. This model can be considered as belonging to the class of
self-organized models which may exhibit spontaneous criticality, with four
additional ingredients compared to sandpile models, namely quenched disorder,
boundary driving, long range forces and fast time crack rules. In this
''crack'' model, as in the ''dislocation'' version previously studied, we find
that the occurrence of repeated earthquakes organizes the activity on
well-defined fault-like structures. In contrast with the ''dislocation'' model,
after a transient, the time evolution becomes periodic with run-aways ending
each cycle. This stems from the ''crack'' stress transfer rule preventing
criticality to organize in favor of cyclic behavior. For sufficiently large
disorder and weak stress drop, these large events are preceded by a complex
space-time history of foreshock activity, characterized by a Gutenberg-Richter
power law distribution with universal exponent . This is similar
to a power law distribution of small nucleating droplets before the nucleation
of the macroscopic phase in a first-order phase transition. For large disorder
and large stress drop, and for certain specific initial disorder
configurations, the stress field becomes frustrated in fast time : out-of-plane
deformations (thrust and normal faulting) and/or a genuine dynamics must be
introduced to resolve this frustration
Linear and Non-linear Rabi Oscillations of a Two-Level System Resonantly Coupled to an Anderson-Localized Mode
We use time-domain numerical simulations of a two-dimensional (2D) scattering
system to study the interaction of a collection of emitters resonantly coupled
to an Anderson-localized mode. For a small electric field intensity, we observe
the strong coupling between the emitters and the mode, which is characterized
by linear Rabi oscillations. Remarkably, a larger intensity induces non-linear
interaction between the emitters and the mode, referred to as the dynamical
Stark effect, resulting in non-linear Rabi oscillations. The transition between
both regimes is observed and an analytical model is proposed which accurately
describes our numerical observations.Comment: 11 pages, 6 figure
Rapport supplémentaire sur le projet de loi relatif au droit d\u27auteur et aux droits voisins dans la société de l\u27information
Assemblée nationale - Rapport fait au nom de la commission des Lois constitutionnelles, de la Législation et de l\u27Administration générale de la République sur l\u27article 7 du projet de loi (n° 1206) relatif au droit d\u27auteur et aux droits voisins dans la société de l\u27information, faisant l\u27objet d\u27une seconde délibération, en application de l\u27article 101 du Règlement
Localized Modes in a Finite-Size Open Disordered Microwave Cavity
We present measurements of the spatial intensity distribution of localized
modes in a two-dimensional open microwave cavity randomly filled with
cylindrical dielectric scatterers. We show that each of these modes displays a
range of localization lengths and successfully relate the largest value to the
measured leakage rate at the boundary. These results constitute unambiguous
signatures of the existence of strongly localized electromagnetic modes in
two-dimensionnal open random media
Approximate equivalence between guided modes in a low-contrast photonic bandgap fiber and Maxwell TM modes of a high-contrast two-dimensional photonic structure
We present a formal analogy between the eigenvalue problem for guided scalar
modes in a low-contrast photonic bandgap fiber and quasi-stationary TM modes of
a two-dimensional (2D) photonic structure. Using this analogy, we numerically
study the confinement losses of disordered microstructured fibers through the
leakage rate of an open 2D system with high refractive index inclusions. Our
results show that for large values of the disorder, the confinement losses
increase. However, they also suggest that losses might be improved in strongly
disordered fibers by exploring ranges of physical parameters where Anderson
localization sets in
Modes of Random Lasers
In conventional lasers, the optical cavity that confines the photons also
determines essential characteristics of the lasing modes such as wavelength,
emission pattern, ... In random lasers, which do not have mirrors or a
well-defined cavity, light is confined within the gain medium by means of
multiple scattering. The sharp peaks in the emission spectra of semiconductor
powders, first observed in 1999, has therefore lead to an intense debate about
the nature of the lasing modes in these so-called lasers with resonant
feedback. In this paper, we review numerical and theoretical studies aimed at
clarifying the nature of the lasing modes in disordered scattering systems with
gain. We will discuss in particular the link between random laser modes near
threshold (TLM) and the resonances or quasi-bound (QB) states of the passive
system without gain. For random lasers in the localized regime, QB states and
threshold lasing modes were found to be nearly identical within the scattering
medium. These studies were later extended to the case of more lossy systems
such as random systems in the diffusive regime where differences between
quasi-bound states and lasing modes were measured. Very recently, a theory able
to treat lasers with arbitrarily complex and open cavities such as random
lasers established that the TLM are better described in terms of the so-called
constant-flux states.Comment: Review paper submitted to Advances in Optics and Photonic
Effects of Spatially Nonuniform Gain on Lasing Modes in Weakly Scattering Random Systems
A study on the effects of optical gain nonuniformly distributed in
one-dimensional random systems is presented. It is demonstrated numerically
that even without gain saturation and mode competition, the spatial
nonuniformity of gain can cause dramatic and complicated changes to lasing
modes. Lasing modes are decomposed in terms of the quasi modes of the passive
system to monitor the changes. As the gain distribution changes gradually from
uniform to nonuniform, the amount of mode mixing increases. Furthermore, we
investigate new lasing modes created by nonuniform gain distributions. We find
that new lasing modes may disappear together with existing lasing modes,
thereby causing fluctuations in the local density of lasing states.Comment: 26 pages, 10 figures (quality reduced for arXiv
Enabling the control of a new degree of freedom by using anisotropic material on a 6-DOF parallel soft robot
International audienceIn this paper, we design in simulation and build a parallel soft robot with a 6 degrees of freedom (DOF) endeffector. We show that by using a 3D-printed meso-structured material which displays an anisotropic behaviour, we can modify the kinematics of the structure in order to control one additional DOF which is not possible to achieve using a standard isotropic and homogeneous material like silicone. The behaviour of the robot is simulated using numerical homogenization and the finite element method (FEM), which runs in real-time and can be used for control. We finally show that the parallel soft robot we have built is controllable in open loop thanks to the use of inverse simulation. We demonstrate its maneuverability by guiding a marble in a maze game
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