717 research outputs found
Formation et évolution des patrons de coloration / Formation and evolution of color patterns
No full text Responsable : Marie Manceau Publications Friocourt F., Lafont A.-G., Kress C., Pain B., Manceau M., Dufour S. et Chédotal A., « Recurrent DCC gene losses during bird evolution », Scientific Reports, vol. 7, 2017, p. 37569, DOI : 10.1038/srep37569. Mallarino R., Henegar C., Mirasierra M., Manceau M., Schradin C., Vallejo M., Beronja S., Barsh G.S. et Hoekstra H.E., « Developmental mechanisms of stripe patterns in rodents », Nature, vol. 539, n° 7630, 2016, p. 518-523, DOI : 10.1038/nature2..
Mid-infrared intersubband polaritons in dispersive metal-insulator-metal resonators
No full textWe demonstrate room-temperature strong coupling between a mid-infrared (lambda = 9.9 lm) intersubband transition and the fundamental cavity mode of a metal-insulator-metal resonator. Patterning of the resonator surface enables surface-coupling of the radiation and introduces an energy dispersion which can be probed with angle-resolved reflectivity. In particular, the polaritonic dispersion presents an accessible energy minimum at k = 0 where-potentially-polaritons can accumulate. We also show that it is possible to maximize the coupling of photons into the polaritonic states and-simultaneously-to engineer the position of the minimum Rabi splitting at a desired value of the in-plane wavevector. This can be precisely accomplished via a simple post-processing technique. The results are confirmed using the temporal coupled mode theory formalism and their significance in the context of the strong critical coupling concept is highlighted
Mid-infrared intersubband polaritons in dispersive metal-insulator-metal resonators
No full textWe demonstrate room-temperature strong coupling between a mid-infrared (lambda = 9.9 lm) intersubband transition and the fundamental cavity mode of a metal-insulator-metal resonator. Patterning of the resonator surface enables surface-coupling of the radiation and introduces an energy dispersion which can be probed with angle-resolved reflectivity. In particular, the polaritonic dispersion presents an accessible energy minimum at k = 0 where-potentially-polaritons can accumulate. We also show that it is possible to maximize the coupling of photons into the polaritonic states and-simultaneously-to engineer the position of the minimum Rabi splitting at a desired value of the in-plane wavevector. This can be precisely accomplished via a simple post-processing technique. The results are confirmed using the temporal coupled mode theory formalism and their significance in the context of the strong critical coupling concept is highlighted
Resonant intersubband polariton-LO phonon scattering in an optically pumped polaritonic device
No full textWe report experimental evidence of longitudinal optical (LO) phonon-intersubband polariton scattering processes under resonant injection of light. The scattering process is resonant with both the initial (upper polariton) and final (lower polariton) states and is induced by the interaction of confined electrons with longitudinal optical phonons. The system is optically pumped with a mid-IR laser tuned between 1094 cm−1 and 1134 cm−1 (λ = 9.14 μm and λ = 8.82 μm). The demonstration is provided for both GaAs/AlGaAs and InGaAs/AlInAs doped quantum well systems whose intersubband plasmon lies at a wavelength of ≈10 μm. In addition to elucidating the microscopic mechanism of the polariton-phonon scattering, it is found to differ substantially from the standard single particle electron-LO phonon scattering mechanism, and this work constitutes an important step towards the hopefully forthcoming demonstration of an intersubband polariton laser
Mechanisms of photo-induced degradation of polythiophene derivatives: re-examination of the role of singlet oxygen
No full textRoles of singlet oxygen (1O2) in photo-induced degradation of poly(3-hexylthiophene) (P3HT) and poly(3-hexyloxythiophene) (P3HOT) were examined. The results indicate that 1O2 has a considerable role in the degradation of P3HT and P3HOT. Photo-irradiation of P3HT in air resulted in the reduction of the pi-conjugation. The photo-induced reduction also occurred for P3HOT, and it was much faster than that of P3HT. Manceau et al. have reported that 1O2 was generated by photo-irradiation of P3HT in the presence of oxygen and, nevertheless, 1O2 is not the principal photo-oxidative degradation intermediate of P3HT (Manceau et al., Macromol Rapid Commun 29:1823-1827, 2008). However, exposures of solid P3HT and P3HOT to chemically generated 1O2 provided decreases in the pi pi*absorption in our study. The decrease for P3HOT was much larger than that for P3HT. The exposure of P3HOT showed the formation of polarons. The difference in P3HT and P3HOT for the effects of the photo-irradiation and of 1O2 will be ascribed to the difference in their ionization potentials
Elliptic blending model: A new near-wall Reynolds-stress turbulence closure
No full textA new approach to modeling the effects of a solid wall in one-point second-moment (Reynolds-stress) turbulence closures is presented. The model is based on the relaxation of an inhomogeneous (near-wall) formulation of the pressure–strain tensor towards the chosen conventional homogeneous (far-from-a-wall) form using the blending function ?, for which an elliptic equation is solved. The approach preserves the main features of Durbin’s Reynolds-stress model, but instead of six elliptic equations (for each stress component), it involves only one, scalar elliptic equation. The model, called “the elliptic blending model,” offers significant simplification, while still complying with the basic physical rationale for the elliptic relaxation concept. In addition to model validation against direct numerical simulation in a plane channel for Re? = 590, the model was applied in the computation of the channel flow at a “real-life” Reynolds number of 106, showing a good prediction of the logarithmic profile of the mean velocity.Multi-Scale PhysicsApplied Science
Comportement du chrome dans les minéraux d'altération du gisement de Campo Formoso (Bahia, Brésil)
No full textChromiferous ultramafic rocks from Campo Formoso (Bahia State, Brazil) exhibit various stages of hydrothermal alteration and weathering, each being characterized by distinct chromiferous parageneses. These Cr-bearing minerals are mainly phyllosilicates, but other phases are also present as chromiferous opal and hydroxycarbonates. Optical absorption spectra and K-edge fine structure allow a better knowledge of chromium crystal chemistry in these minerals. The first stages of chromite oxidation have been precised, and particularly the influence of structural factors was pointed out : the inversion grade of these spinels controls the evolution from a mainly direct chromite to the inverse forms (ferritchromit). Chromium ions inserted in mineral structures do not exhibit any change in the oxidation state during alteration processes. In contrast, crystal field stabilization energy (CFSE) of Cr3+ ions exhibits important variations among the studied minerals. Study of EXAFS spectra demonstrated that Cr-O distances do not change significandy among the investigated minerals, the effective oxygen charge playing the main role in the observed CFSE variations. This latter parameter explains the concentration of chromium in these minerals and contributes to the stability of some phases like clinochlores and hydroxycarbonates, where trivalent chromium has the highest CFSE.Les ultrabasites chromifères de Campo Formoso (Etat de Bahia, Brésil) montrent plusieurs stades successifs d'altération hydrothermale puis superficielle qui s'accompagnent de paragenèses chromifères variées. Les minéraux caractéristiques de ces dernières sont essentiellement des phyllosilicates, mais on note aussi d'autres phases comme la stichtite et l'opale chromifère. Les spectres d'absorption X ont permis de caractériser la cristallochimie du chrome dans ces minéraux. Les premiers stades d'oxydation des chromites ont été précisés, en particulier l'influence de la structure réelle du spinelle (degré d'inversion) qui contrôle les conditions d'évolution de la chromite. Le degré d'oxydation +3 du chrome est conservé lors des processus d'altération et seule l'énergie de stabilisation liée au champ cristallin montre des changements importants. L'étude des spectres EXAFS (Extended X-ray Absorption Fine Structure) a montré que, les distances Cr-O ne changeant pas entre les minéraux étudiés, seule la nature des ligandes a une influence sur la valeur de l'énergie de champ cristallin. Ceci explique la forte concentration en chrome de ces minéraux d'altération et contribue à la stabilité des phases comme les clinochlores ou les hydroxycarbonates où les ions Cr3+ ont la plus forte énergie de stabilisation.Calas Georges, Manceau Alain, Novikoff André, Boukili Hassan. Comportement du chrome dans les minéraux d'altération du gisement de chromite de Campo Formoso (Bahia, Brésil). In: Bulletin de Minéralogie, volume 107, 6, 1984. pp. 755-766
Acoustic manipulation of droplets
No full textInternational audienceAcoustic manipulation of droplets<br&g
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