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Résumé:

Une introduction à la théorie du transfert radiatif et à quelques unes de ses applications est présentée. Ce cours simple et non exhaustif présente la théorie élémentaire, les domaines dans lesquels cette théorie est utile, et les méthodes les plus simples de résolution de l'équation du transfert radiatif (ETR). Des sujets peu abordés par les astrophysiciens y sont traités (sphère intégrante, correction de Giovanelli...). Ce cours correspond à l'enseignement de transfert radiatif du Master Physique Informatique de l'université de Montpellier 2.

Ref HAL: hal-00628026_v1
DOI: 10.1103/PhysRevA.83.043836
WoS: 000290107500016
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10 Citations
Résumé:

A method is proposed to generate and study the dynamics of spatial light solitons in a birefringent medium with quadratic nonlinearity. Although no analytical expression for propagating solitons has been obtained, our numerical simulations show the existence of stable localized spatial solitons in the frequency forbidden band gap of the medium. The dynamics of these objects is quite rich and manifests for instance elastic reflections, or inelastic collisions where two solitons merge and propagate as a single solitary wave. We derive the dynamics of the slowly varying envelopes of the three fields (second harmonic pump and two-component signal) and study this new system theoretically. We show that it does present a threshold for nonlinear supratransmission that can be calculated from a series expansion approach with a very high accuracy. Specific physical implications of our theoretical predictions are illustrated on LiGaTe2 (LGT) crystals. Once irradiated by a cw laser beam of 10 mu m wavelength, at an incidence beyond the extinction angle, such crystals will transmit light, in the form of spatial solitons generated in the nonlinear regime above the nonlinear supratransmission threshold.

Ref HAL: hal-00510988_v1
PMID 20868047
DOI: 10.1103/PhysRevLett.105.074101
WoS: 000280811700003
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23 Citations
Résumé:

A method is proposed to solve the challenging problem of determining the supratransmission threshold (onset of insability of harmonic boundary driving inside a band gap) in multicomponent non-integrable nonlinear systems. It is successfully applied to the degenerate three-wave resonant interaction in a birefrigent quadratic medium where the process generates spatial gap solitons. No analytic expression is known for such nonlinear solitary waves showing the broad applicability of the method to nonlinear systems.

Commentaires: http://arxiv.org/abs/1008.1920

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- apprendre à voir/regarder les couleurs de façon consciente : « s'éveiller au monde de la couleur ». Bien que cet aspect ne puisse pas s'enseigner au moyen des livres et des formules, c'est le point le plus important de ce cours : rien ne remplace l'œil d'un bon coloriste, et pour le former, il faut observer autour de soi. - Apprendre à reconnaître, trier et caractériser les couleurs. Ce point vient soutenir le précédent. - Apprendre à mesurer précisément une couleur au moyen d'appareils de mesure dont il faut comprendre le fonctionnement, afin de la contrôler et la reproduire à l'identique. - Dans le domaine de la colorimétrie, la couleur à reproduire s'appelle le « standard » et sa reproduction prend le nom de « contretype ». On parle donc de « contretyper un standard », et la production de contretypes acceptables pour un standard donné est un des problèmes récurent de la colorimétrie.

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Ref Arxiv: cond-mat/0305391
Ref. & Cit.: NASA ADS
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Résumé:

A nonlinear system possessing a natural forbidden band gap cantransmit energy of a signal with a frequency in the gap, as recently shown forthe nonlinear chain of coupled pendula [Phys Rev Lett 89 (2002) 134102]. Thisprocess of nonlinear supratransmission, occurring at a threshold exactlypredictable in many cases, is shown to have a simple experimental realizationwith a mechanical chain of pendula coupled by a coil spring. It is thenanalyzed in more detail by first going to different (non-integrable) systemswhich do sustain nonlinear supratransmission. Then a Josephson transmissionline (one dimensional array of short Josephson junctions coupled throughsuper-conducting wires), is shown to sustain also nonlinear supratransmission,though being related to a different class of boundary conditions, and despitethe presence of damping, finiteness and discreteness. Finally the mechanism atthe origin of nonlinear supratransmission is a nonlinear instability, and it isbriefly discussed here.

PMID 12225030
Ref Arxiv: nlin.PS/0209020
DOI: 10.1103/PhysRevLett.89.134102
WoS: 000178071800021
Ref. & Cit.: NASA ADS
173 Citations
Résumé:

A nonlinear chain driven by one end may propagate energy in the forbidden band gap by means of nonlinear modes. For harmonic driving at a given frequency, the process occurs at a threshold amplitude by sudden large energy flow that we call nonlinear supratransmission. The bifurcation of energy transmission is demonstrated numerically and experimentally on the chain of coupled pendula (sine-Gordon and nonlinear Klein-Gordon equations) and sustained by an extremely simple theory.