192 research outputs found
Scattering below critical energy for the radial 4D Yang-Mills equation and for the 2D corotational wave map system
We describe the asymptotic behavior as time goes to infinity of solutions of
the 2 dimensional corotational wave map system and of solutions to the 4
dimensional, radially symmetric Yang-Mills equation, in the critical energy
space, with data of energy smaller than or equal to a harmonic map of minimal
energy. An alternative holds: either the data is the harmonic map and the
soltuion is constant in time, or the solution scatters in infinite time
Nonlinear targeted energy transfer of two coupled cantilever beams coupled to a bistable light attachment
International audienceIn order to control the sound radiation by a structure, one aims to control vibration of radiating modes of vibration using " Energy Pumping " also named " Targeted Energy Transfer ". This principle is here applied to a simplified model of a double leaf panel. This model is made of two beams coupled by a spring. One of the beams is connected to a nonlinear absorber. This nonlinear absorber is made of a 3D-printed support on which is clamped a buckled thin small beam with a small mass fixed at its center having two equilibrium positions. The experiments showed that, once attached onto a vibrating system to be controlled, under forced excitation of the primary system, the light bistable oscillator allows a reduction of structural vibration up to 10 dB for significant amplitude and frequency range around the first two vibration modes of the system
Comparaison de techniques d'absorptions vibro-acoustiques
National audienceThis study presents the design of a test-rig built to caracterize a vibro-acoustical absorber. This experimental system is based on the properties of a short Kundt tube allowing low frequencies studies (below the first natural frequency of the tube). A precise measure method (surdetermined two-microphones method) is proposed in order to obtain the desired acoustical parameters of the absorber. Finally, we propose an energy balance of the obtanied frequency response (excitation frequency and its harmonics).Cette étude propose la conception d'un banc d'essai servant à la caractérisation d'absorbeurs vibro-acoustiques. Ce banc est conç u sur la propriété d'un tube de Kundt court permettant le travail en basses fréquences (en-dessous de la première fréquence de résonance du tube). Une méthode de me-sure fine (méthode à deux microphones surdéterminée) est mise en place afin d'extraire les paramètres acoustiques souhaités de l'absorbeur et in fine proposer un bilan énergétique résultant et sa répartition spectrale (fréquence d'excitation et ses harmoniques)
Stable self-similar blow-up dynamics for slightly -supercritical generalized KdV equations
In this paper we consider the slightly -supercritical gKdV equations
, with the nonlinearity
and . We will prove the existence and
stability of a blow-up dynamic with self-similar blow-up rate in the energy
space and give a specific description of the formation of the singularity
near the blow-up time.Comment: 38 page
Strong Correlation to Weak Correlation Phase Transition in Bilayer Quantum Hall Systems
At small layer separations, the ground state of a nu=1 bilayer quantum Hall
system exhibits spontaneous interlayer phase coherence and has a
charged-excitation gap E_g. The evolution of this state with increasing layer
separation d has been a matter of controversy. In this letter we report on
small system exact diagonalization calculations which suggest that a single
phase transition, likely of first order, separates coherent incompressible (E_g
>0) states with strong interlayer correlations from incoherent compressible
states with weak interlayer correlations. We find a dependence of the phase
boundary on d and interlayer tunneling amplitude that is in very good agreement
with recent experiments.Comment: 4 pages, 4 figures included, version to appear in Phys. Rev. Let
Skyrmion Dynamics and NMR Line Shapes in QHE Ferromagnets
The low energy charged excitations in quantum Hall ferromagnets are
topological defects in the spin orientation known as skyrmions. Recent
experimental studies on nuclear magnetic resonance spectral line shapes in
quantum well heterostructures show a transition from a motionally narrowed to a
broader `frozen' line shape as the temperature is lowered at fixed filling
factor. We present a skyrmion diffusion model that describes the experimental
observations qualitatively and shows a time scale of for
the transport relaxation time of the skyrmions. The transition is characterized
by an intermediate time regime that we demonstrate is weakly sensitive to the
dynamics of the charged spin texture excitations and the sub-band electronic
wave functions within our model. We also show that the spectral line shape is
very sensitive to the nuclear polarization profile along the z-axis obtained
through the optical pumping technique.Comment: 6 pages, 4 figure
Model study on the photoassociation of a pair of trapped atoms into an ultralong-range molecule
Using the method of quantum-defect theory, we calculate the ultralong-range
molecular vibrational states near the dissociation threshold of a diatomic
molecular potential which asymptotically varies as . The properties of
these states are of considerable interest as they can be formed by
photoassociation (PA) of two ground state atoms. The Franck-Condon overlap
integrals between the harmonically trapped atom-pair states and the
ultralong-range molecular vibrational states are estimated and compared with
their values for a pair of untrapped free atoms in the low-energy scattering
state. We find that the binding between a pair of ground-state atoms by a
harmonic trap has significant effect on the Franck-Condon integrals and thus
can be used to influence PA. Trap-induced binding between two ground-state
atoms may facilitate coherent PA dynamics between the two atoms and the
photoassociated diatomic molecule.Comment: 11 pages, 4 figures, to appear in Phys. Rev. A (September, 2003
Kinematics of globular cluster systems and the formation of early-type galaxies
We numerically investigate the kinematic properties of globular cluster
systems (GCSs) in E/S0 galaxies formed from dissipationless merging of spiral
galaxies. The metal-poor globular clusters (MPCs) and metal-rich clusters
(MRCs) in the merger progenitors are initially assumed to have spatial
distributions consistent with the Milky Way GC system. Our principal results,
which can be tested against observations, are as follows. Both MPCs and MRCs in
elliptical galaxies formed from major mergers can exhibit significant rotation
at large radii (20 kpc) due to the conversion of initial orbital angular
momentum into intrinsic angular momentum of the remnant. MPCs show higher
central velocity dispersions than MRCs for most major merger models. (where and , are the GCS maximum
rotational velocity and central velocity dispersion of respectively) ranges
from 0.2--1.0 and 0.1--0.9 for the MPCs and MRCs respectively, within for the remnant elliptical. For most merger remnant ellipticals, of GCSs within is greater than that of the field
stars within . The radial profiles of rotational velocities and
velocity dispersions of the GCSs depend upon the orbital configuration of the
merger progenitors, their mass-ratios, and the viewing angle. For example, more
flattened early-type galaxies, formed through mergers with small mass ratios
( 0.1), show little rotation in the outer MRCs. Two-dimensional (2D)
velocity dispersion distributions of the GCSs of merger remnant ellipticals are
generally flattened for both MPCs and MRCs, reflecting the fact that the GCSs
have anisotropic velocity dispersions (abridged).Comment: 14 pages, 16 figures, accepted by MNRA
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