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Search Results: 1 - 10 of 149813 matches for " H. Leblond "
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Higher order terms in multiscale expansions: a linearized KdV hierarchy
H. Leblond
Physics , 2003,
Abstract: We consider a wide class of model equations, able to describe wave propagation in dispersive nonlinear media. The Korteweg-de Vries (KdV) equation is derived in this general frame under some conditions, the physical meanings of which are clarified. It is obtained as usual at leading order in some multiscale expansion. The higher order terms in this expansion are studied making use of a multi-time formalism and imposing the condition that the main term satisfies the whole KdV hierarchy. The evolution of the higher order terms with respect to the higher order time variables can be described through the introduction of a linearized KdV hierarchy. This allows one to give an expression of the higher order time derivatives that appear in the right hand member of the perturbative expansion equations, to show that overall the higher order terms do not produce any secularity and to prove that the formal expansion contains only bounded terms.
Stability of D1-Strings Inside a D3-Brane
Louis Leblond,S. -H. Henry Tye
Physics , 2004, DOI: 10.1088/1126-6708/2004/03/055
Abstract: Within the tachyon condensation approach, we find that a D(p-2)-brane is stable inside Dp-branes when the bulk is compactified. It is a codimension-2 soliton of the Dp-brane action with coupling to the bulk (p-1)-form RR field. We discuss the properties of such solitons. They may appear as detectable cosmic strings in our universe.
Spatiotemporal vortex solitons in hexagonal arrays of waveguides
H. Leblond,B. A. Malomed,D. Mihalache
Physics , 2011, DOI: 10.1103/PhysRevA.83.063825
Abstract: By means of a systematic numerical analysis, we demonstrate that hexagonal lattices of parallel linearly-coupled waveguides, with the intrinsic cubic self-focusing nonlinearity, give rise to three species of stable semi-discrete complexes (which are continuous in the longitudinal direction), with embedded vorticity S: triangular modes with S=1, hexagonal ones with S=2, both centered around an empty central core, and compact triangles with S=1, which do not not include the empty site. Collisions between stable triangular vortices are studied too. These waveguiding lattices can be realized in optics and BEC.
An integrable evolution equation for surface waves in deep water
R. Kraenkel,H. Leblond,M. A. Manna
Physics , 2011,
Abstract: In order to describe the dynamics of monochromatic surface waves in deep water, we derive a nonlinear and dispersive system of equations for the free surface elevation and the free surface velocity from the Euler equations in infinite depth. From it, and using a multiscale perturbative methods, an asymptotic model for small-aspect-ratio waves is derived. The model is shown to be completely integrable. The Lax pair, the first conserved quantities as well as the symmetries are exhibited. Theoretical and numerical studies reveal that it supports periodic progressive Stokes waves which peak and break in finite time. Comparison between the limiting wave solution of the asymptotic model and classical irrotational results is performed.
Motivational State and Reward Content Determine Choice Behavior under Risk in Mice
Mona Leblond, David Fan, Julia K. Brynildsen, Henry H. Yin
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0025342
Abstract: Risk is a ubiquitous feature of the environment for most organisms, who must often choose between a small and certain reward and a larger but less certain reward. To study choice behavior under risk in a genetically well characterized species, we trained mice (C57BL/6) on a discrete trial, concurrent-choice task in which they must choose between two levers. Pressing one lever (safe choice) is always followed by a small reward. Pressing the other lever (risky choice) is followed by a larger reward, but only on some of the trials. The overall payoff is the same on both levers. When mice were not food deprived, they were indifferent to risk, choosing both levers with equal probability regardless of the level of risk. In contrast, following food or water deprivation, mice earning 10% sucrose solution were risk-averse, though the addition of alcohol to the sucrose solution dose-dependently reduced risk aversion, even before the mice became intoxicated. Our results falsify the budget rule in optimal foraging theory often used to explain behavior under risk. Instead, they suggest that the overall demand or desired amount for a particular reward determines risk preference. Changes in motivational state or reward identity affect risk preference by changing demand. Any manipulation that increases the demand for a reward also increases risk aversion, by selectively increasing the frequency of safe choices without affecting frequency of risky choices.
Jean-Luc Gréau, La trahison des économistes.
Patrick Leblond
The Canadian Journal of Sociology , 2009,
Mixed perturbative expansion: the validity of a model for the cascading
Herve Leblond
Physics , 2002, DOI: 10.2991/jnmp.2002.9.2.1
Abstract: A new type of perturbative expansion is built in order to give a rigorous derivation and to clarify the range of validity of some commonly used model equations. This model describes the evolution of the modulation of two short and localized pulses, fundamental and second harmonic, propagating together in a bulk uniaxial crystal with non-vanishing second order susceptibility $\chi^(2)$ and interacting through the nonlinear effect known as ``cascading'' in nonlinear optics. The perturbative method mixes a multi-scale expansion with a power series expansion of the susceptibility, and must be carefully adapted to the physical situation. It allows the determination of the physical conditions under which the model is valid: the order of magnitude of the walk-off, phase-mismatch,and anisotropy must have determined values.
A new criterion for the existence of KdV solitons in ferromagnets
Herve Leblond
Physics , 2004,
Abstract: The long-time evolution of the KdV-type solitons propagating in ferromagnetic materials is considered trough a multi-time formalism, it is governed by all equations of the KdV Hierarchy. The scaling coefficients of the higher order time variables are explicitly computed in terms of the physical parameters, showing that the KdV asymptotic is valid only when the angle between the propagation direction and the external magnetic field is large enough. The one-soliton solution of the KdV hierarchy is written down in terms of the physical parameters. A maximum value of the soliton parameter is determined, above which the perturbative approach is not valid. Below this value, the KdV soliton conserves its properties during an infinite propagation time.
Geometry of Large Extra Dimensions versus Graviton Emission
Frederic Leblond
Physics , 2001, DOI: 10.1103/PhysRevD.64.045016
Abstract: We study how the geometry of the large extra dimensions may affect field theory results on a three-brane. More specifically, we compare cross sections for graviton emission from a brane when the internal space is a N-torus and a N-sphere for N=2 to 6. The method we present can be used for other smooth compact geometries. We find that the ability of high energy colliders to determine the geometry of the extra dimensions is limited but there is an enhancement when both the quantum gravity scale and N are large. Our field theory results are compared with the low energy corrections to the gravitational inverse square law due to large dimensions compactified on other spaces such as Calabi-Yau manifolds.
Spontaneous formation of optically induced surface relief gratings
H. Leblond,R. Barille,S. Ahamadi-kandjani,J. -M. Nunzi,E. Ortyl,S. Kucharski
Physics , 2009, DOI: 10.1088/0953-4075/42/20/205401
Abstract: A model based on Fick's law of diffusion as a phenomenological description of the molecular motion, and on the coupled mode theory, is developped to describe single-beam surface relief grating formation in azopolymers thin films. It allows to explain the mechanism of spontaneous patterning, and self-organization. It allows also to compute the surface relief profile and its evolution in time with good agreement with experiments.
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