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The destabilization of a dielectric film flow due to an electrostatic surface force is investigated. A weighted residuals integral boundary-layer (WIBL) model is derived and validated against full numerical simulations. The equations of the WIBL model indicate that the electrostatic surface force contributes to the evolution equations in a similar mathematical way as the volumetric gravitational force. Contrary to gravity, an additional electrostatic contribution (, Taylor-cone waves occur prior to finite-time blow-up, leading to jetting. Finally, the transition from stable to unstable waves is investigated in terms of the two dimensionless electric parameters, the Reynolds, and viscous dissipation numbers. Imposing the most amplified wavelength, a transition border between stable solutions and jetting is identified.

This research presents an experimental study on the Faraday instability in one-dimensional cells filled with a mixture of water and glycerol, and for a range forcing frequency between 10 and 60 Hz. It showed that for a particular forcing frequency, whose value depends on the width of the cell, an anomalous surface oscillation arises, that appears as a large wavelength mode oscillating subharmonically with respect to the normal modes predicted by the linear stability analysis. Since all others studied forcing frequency, the observed modes are in agreement with the ones theoretically predicted. Key words: Faraday Instability, non-linear dynamics PACS: 47.20.Dr, 47.20.Gv, 47.35.+i, 47.54.+r

International audience; Inherent to time-domain method that use space-time discretization, the model dispersion produces field propagation velocity error. In methods such as finite-differences or TLM in time domain, it is customary to choose a maximum mesh size of one tenth of the minimum operating wavelength. If this criterion is easily applicable for normal ordinary media, it is more ambiguous to give interpretation of the wavelength when dealing with complex media such as anisotropic and/or dispersive (frequency dependent) media. After describing the procedure to evaluate dispersion in such media, the paper shows examples for which the simple rule underestimates the maximum mesh size and, consequently, increases the computing expenditure.

Elastic wave propagation is a complex physical phenomenon whose modelling in heterogeneous media requires well adapted numerical solvers. However, when the wavefield’s minimum wavelength is large toward the variations of the medium’s elastic properties, the numerical cost may become too important. In this case, homogenization techniques allow to compute a simpler effective medium in which computing the full waveform is much less expensive with very little and controlled precision loss. Moreover, homogenization techniques allow to understand physically better the effects of small heterogeneities on the wavefield. The objective of the present work is to develop extensions of the deterministic non periodic homogenization method allowing to improve both the numerical efficiency in modelling the wavefield and our understanding of wave propagation in complex media. In a first section, we present the basics of both the spectral element method as our numerical solver for the wave equations, and the deterministic homogenization method for non periodic media. In the second section, we derive the homogenization method for acoustic waves and use it to understand the differences between elastic P-wave propagation and acoustic wave propagation. In the third section, we develop an optimization of the homogenization method in the case of strong spatial variations for the main wavefield’s wavelength. In the last section, we present a variant allowing to homogenize the difference between two models, the residual homogenization, and two of its applications.; La propagation des ondes élastiques est un phénomène physique complexe dont la modélisation dans les milieux hétérogènes nécessite l’utilisation de solveurs numériques adaptés. Lorsque la longueur d’onde minimale du champ d’onde est grande devant les variations des propriétés élastiques du milieu de propagation, le coût calcul devient disproportionné. Dans ce cadre, la méthode d’homogénéisation permet de simplifier le milieu de propagation tout en contrôlant l’erreur commise sur les solutions calculées par le solveur. De plus, cette méthode permet de mieux comprendre physiquement l’effet des petites hétérogénéités sur les champs d’onde. L’objectif de cette thèse est de développer des extensions de la méthode d’homogénéisation visant à améliorer tant l’efficacité du calcul numérique que notre compréhension de la propagation des ondes en milieux complexes. Au premier chapitre nous rappelons les principes de la méthode des éléments spectraux, servant ici de solveur numérique pour l’équa tion des ondes, ainsi que ceux de la méthode d’homogénéisation déterministe pour les milieux non périodiques. Dans le second chapitre, nous développons l’homogénéisation pour les milieux purement acoustiques que nous utilisons ensuite pour interpréter les différences entre la propagation des ondes P élastiques et celle des ondes acoustiques. Dans le troisième chapitre, nous nous intéressons à une optimisation de l’homogénéisation lorsque la longueur d’onde dominante varie fortement spatialement. Enfin, dans le quatrième chapitre, nous exposons une extension permettant d’homogénéiser la différence entre deux modèles élastiques, l’homogénéisation résiduelle, et deux de ses applications.

Elastic wave propagation is a complex physical phenomenon whose modelling in heterogeneous media requires well adapted numerical solvers. However, when the wavefield’s minimum wavelength is large toward the variations of the medium’s elastic properties, the numerical cost may become too important. In this case, homogenization techniques allow to compute a simpler effective medium in which computing the full waveform is much less expensive with very little and controlled precision loss. Moreover, homogenization techniques allow to understand physically better the effects of small heterogeneities on the wavefield. The objective of the present work is to develop extensions of the deterministic non periodic homogenization method allowing to improve both the numerical efficiency in modelling the wavefield and our understanding of wave propagation in complex media. In a first section, we present the basics of both the spectral element method as our numerical solver for the wave equations, and the deterministic homogenization method for non periodic media. In the second section, we derive the homogenization method for acoustic waves and use it to understand the differences between elastic P-wave propagation and acoustic wave propagation. In the third section, we develop an optimization of the homogenization method in the case of strong spatial variations for the main wavefield’s wavelength. In the last section, we present a variant allowing to homogenize the difference between two models, the residual homogenization, and two of its applications.; La propagation des ondes élastiques est un phénomène physique complexe dont la modélisation dans les milieux hétérogènes nécessite l’utilisation de solveurs numériques adaptés. Lorsque la longueur d’onde minimale du champ d’onde est grande devant les variations des propriétés élastiques du milieu de propagation, le coût calcul devient disproportionné. Dans ce cadre, la méthode d’homogénéisation permet de simplifier le milieu de propagation tout en contrôlant l’erreur commise sur les solutions calculées par le solveur. De plus, cette méthode permet de mieux comprendre physiquement l’effet des petites hétérogénéités sur les champs d’onde. L’objectif de cette thèse est de développer des extensions de la méthode d’homogénéisation visant à améliorer tant l’efficacité du calcul numérique que notre compréhension de la propagation des ondes en milieux complexes. Au premier chapitre nous rappelons les principes de la méthode des éléments spectraux, servant ici de solveur numérique pour l’équa tion des ondes, ainsi que ceux de la méthode d’homogénéisation déterministe pour les milieux non périodiques. Dans le second chapitre, nous développons l’homogénéisation pour les milieux purement acoustiques que nous utilisons ensuite pour interpréter les différences entre la propagation des ondes P élastiques et celle des ondes acoustiques. Dans le troisième chapitre, nous nous intéressons à une optimisation de l’homogénéisation lorsque la longueur d’onde dominante varie fortement spatialement. Enfin, dans le quatrième chapitre, nous exposons une extension permettant d’homogénéiser la différence entre deux modèles élastiques, l’homogénéisation résiduelle, et deux de ses applications.

Publisher: ACS , ISSN 1520-6106; International audience; Under UV irradiation, poly(vinyl cinnamate) (PVCi) films undergo cross-linking due to [2 + 2] photocycloaddition between cinnamoyl groups. Consequently, electronic configuration of lateral polymer groups changes and also leads to the drop of the refractive index in the visible range. This mechanism is studied with regards to the level of the electronic absorption of cinnamate centered at 278 nm. It acts on refractive index by shifting the absorption UV band. Most of the time, this influence vanishes in the near infrared region (NIR). It is due to antagonist phenomena acting at the expense of the index lowering. The causes analysis leads us to optimize the irradiation spectrum, providing higher index contrasts between irradiated and nonirradiated area. We show that strong index changes can be achieved in PVCi film, up to 2.5 × 10-2 even in the NIR, enabling us, for example, to perform optical photoprinting waveguides for telecommunication wavelengths (1300-1550 nm).

International audience; Diffractive microlens arrays with up to 16 phase levels and 0.75 or 1.5 mm pitch have been fabricated to interconnect single mode fiber arrays (including extended mode fibers) in free-space switches. The fiber-to-fiber insertion loss can be in the 2 to 3 dB range at distances up to one meter, with only small (0.2 dB) inter-channel dispersion for one-dimension links. For two-dimension interconnections, the use of extended mode fibers could relax the packaging constraints and reduce the wavelength sensitivity, providing a bandwidth of several tens of nanometers, suited to optical cross-connects.

Planar stripe gain-guided laser diodes have been prepared from Ga 0.77 In 0.23 As 0.20 Sb 0.80 /Ga 0.53 Al 0.47 As 0.04 Sb 0.96 double-heterostructures grown by liquid phase epitaxy on GaSb (100) oriented. The emission wavelength is 2.1 μm at 80 K (in continuous mode) and 2.37 μm at 292 K (in pulsed mode) with threshold current ≃265 mA at 80 K and 4 A at room temperature. The analysis of the spontaneous emitted power versus the injection current allowed us at 292 K to determine, in the case of low injection, the non radiative lifetime that accounts for non radiative recombination via levels in the bulk of the active region and at the interfaces τ nr ≃4-5 ns, and for higher injection the Auger recombination coefficient C≃1.1×10 -28 cm 6 /s. A study of the optical gain from the emitted wavelength spectra gave us the linewidth enhancement factor of the laser diode α≃3.8±1.3 at the lasing wavelength at 80 K

2014 The variation of photoconductivity with various parameters (wavelength, light intensity, electric field and temperature) was studied on amorphous selenium thin films. The experimental results are enable us to suggest that the films are predominantly composed of Ses rings. At low temperatures the photoconduction is controlled by the hopping in the mobility edge, whereas at room temperature the photogeneration is field-assisted. Lastly, the comparison between our experimental data and Davis’ theories [15] permits us to calculate the band gap Eg = 2.238 eV. REVUE DE PHYSIQUE APPLIQUEE TOME 12, MAI 1977, PAGE

— New measurements of the solar flux in the wavelength bands 196-230 nm and 284-354 nm have been made in the stratosphere with an Ebert-Fastie spectrometer of focal length 25 cm with a pass-band of 0.6 nm. The instrument was on a stabilized stratospheric gondola and was directed towards the sun. The ultra-violet solar spectra obtained with various solar zenith angles lead, by extrapolation to zero air-mass, to the determination of the magnitude of the extraterrestrial solar flux. Below 225 nm the newly measured values are lower than those generally adopted, the apparent temperature of the sun being of the order of 4700 K at 200 nm. Between 225 nm and 310 nm they are in good agreement with Broadfoot (1971) and for wavelengths greater than 310 nm they agree with Arvesen et al. (1969)., Simon P. C. Nouvelles mesures de l'ultraviolet solaire dans la stratosphère. In: Bulletin de la Classe des sciences, tome 61, 1975. pp. 399-409.

We present here a numerical method for the calculation of the surface impedance Z s of metals, based on the semiclassical equations of the anomalous skin effect theory by Reuter and Sondheimer. This method allows the calculation of Z s for any value of the scattering parameter p of conduction electrons hitting the surface and could easily account for a possible anisotropy of p. The electromagnetic wave in the metal is considered as the sum of a finite number N of partial waves associated to discrete directions of the conduction electron momentum. For wavelengths inferior to 200 μm, it is sufficient to take N as low as N=4 to obtain results in very good agreement with exact results calculated by using Dingle series in both cases p=0 and p=1 Mise au point d'une methode de calcul numerique de l'impedance de surface reposant sur les equations semi-classiques de la theorie de l'effet de peau anormal de Reuter et Sondheimer dans le domaine infra-rouge. Cette methode permet de calculer l'impedance de surface pour toute valeur du parametre p de diffusion (0

The wavelength distribution and relative intensity of stray radiation due to double dispersions have been calculated for single-pass in-plane Ebert-Fastie grating monochromators in order to correct previous spectroscopic results., Marette G. Lumière parasite dans les spectromètres Ebert-Fastie à simple passage. In: Bulletin de la Classe des sciences, tome 56, 1970. pp. 310-321.