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Laboratoire Ondes et Matière d'Aquitaine

Overview
Works: 56 works in 56 publications in 2 languages and 56 library holdings
Roles: Other
Publication Timeline
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Most widely held works by Laboratoire Ondes et Matière d'Aquitaine
Une évaluation des performances analytiques de la spectroscopie sur plasma induit par laser (LIBS) by Amina Ismaël( )

1 edition published in 2011 in French and held by 1 WorldCat member library worldwide

Laser-Induced Breakdown Spectroscopy (LIBS) is an elemental analytical technique which combines laser ablation with atomic emission spectroscopy. LIBS spectroscopy has many advantages but is not recognized as a fully quantitative method. Indeed, the problem of samples' heterogeneity, matrix effects, self-absorption of emission lines and the lack of repeatability deteriorate the analytical performances of LIBS. In order to improve this technique, the work presented in this thesis includes an example of analytical performances evaluation with the use of quality notions of a laboratory LIBS system. The method is here specially applied to the analysis of certified steel samples. A first study deals with the optimization of the LIBS system for the quantitative analysis. As the effect of the different experimental parameters on LIBS signal is complex, a methodical protocol is necessary. Here, a parametric study is proposed to determine the experimental conditions suitable for quantitative analysis. Once optimized, the LIBS method is then characterized with basics of method validation. The trueness and the precision of the method are evaluated in conditions of repeatability and intermediate precision. This study shows promising results for LIBS technique. The application of a control chart reveals however an instability of the laboratory system and enables to introduce corrective actions to improve its analytical performances
Transport and spectral properties of low-dimensional superconductors in the presence of spin-dependent fields by Julie Baumard( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

The interplay between superconductivity and spin-dependent fields is known to lead to striking phenomena, like critical field enhancement, magnetoelectric effects and the appearance of Yu-Shiba-Rusinov bound states at magnetic impurities. In this thesis, we investigate these effects in low dimensional systems.We first demonstrate that the combination of both spin-orbit and Zeeman fields in superconducting one-dimensional systems leads to the appearance of an inhomogeneous phase at low magnetic field and high critical temperature. We show that the ground state corresponds to a zero-current state where the current stemming from spin-orbit coupling, called anomalous charge current, is exactly compensated by the current coming from the wave-vector of the superconducting order parameter. We also discuss how it is possible to predict the appearance of the anomalous current from symmetry arguments based on the SU(2)-covariant formalism.In a second part, we consider a type-II superconducting thin film in contact with a Néel skyrmion. The skyrmion induces spontaneous currents in the superconducting layer, which under the right condition generate a superconducting vortex in the absence of external magnetic fields. We compute the magnetic field and current distributions in the superconducting layer in the presence of the Néel skyrmion.In the last part of this thesis, we focus on the appearance of Yu-Shiba-Rusinov states in the superconducting crystal beta-Bi2Pd. We propose effective models in order to explain recent experimental results showing a double spatial oscillation of the local density of states at Shiba energy. We demonstrate that the minimal condition to reproduce this double oscillation is the presence of two superconducting channels connected via a hopping term or via a magnetic impurity. These effective models can be easily generalized to describe the spectrum of multiband superconductors with magnetic impurities
Surface plasmons and hot electrons imaging with femtosecond pump-probe thermoreflectance by Olga Lozan( )

1 edition published in 2015 in English and held by 1 WorldCat member library worldwide

In this work we explored the ultrafast dynamics of photo-excited hot electrons in plasmonic structures. The particular interest of this field resides on the fact surface plasmons (SP), because of their unrivaled temporal and spatial characteristics, provide a technological route for ultrafast information processes at the nanoscale. In this context, this manuscript provides a comprehension and the harnessing of one of the major limitation of the SP-based technologies : absorption losses by Joule heating. We exploit the fact that the mechanism of plasmon absorption in metals is followed by generation of hot electrons at femtosecond time scale, thus losses can be seen as a plasmon-to-hot-electron energy conversion. This energy conversion is measured with femtosecond pump-probe technique. Femtosecond SP pulses are launched and probed over hundred femtoseconds through the permittivity variations induced by the hot-electron gas and which accompany the SP propagation. The measured electron temperature profile is therefore an image of plasmon power density distribution (absorption) not broadened spatially and temporally by energy carrier diffusion. As an important result we demonstrated the capability to link the electronic temperature measurement to the plasmonic absorption, revealing an anomalous light absorption for a sub- slit surroundings, in quantitative agreement with predictions of the power density distribution. In a second part we studied plasmon losses and their characteristics when they propagate on semi-infinite metal film. We determined the electronic thermal wave velocity and damping. In the last part we used a focusing taper-structure to adiabatically guide and focus the plasmon at the apex. Was demonstrated the generation of a nanoscale hot spot and put in evidence a delayed electron heating at the taper apex. Perspectives and the remaining open questions are also discussed
Vortex statics and dynamics in anisotropic and/or magnetic superconductors. by Anton Bespalov( )

1 edition published in 2014 in English and held by 1 WorldCat member library worldwide

Récemment, les études des propriétés de vortex Abrikosov dans des systèmes fortement anisotropes et magnétiques ont été stimulées par la découverte des supraconducteurs à base de fer et des supraconducteurs ferromagnétiques.Dans cette thèse nous étudions la statique et la dynamique de vortex dans ces systèmes. D'abord, le problème de l'interaction de vortex avec un petit défaut a été examiné dans le cadre de la théorie de Ginzburg-Landau. Le potentiel de pinning pour une cavité cylindrique elliptique a été calculé. D'autre part, la conductivité d'un supraconducteur anisotrope à l'état mixte a été analysée en détail dans le cadre de la théorie de Ginzburg-Landau dépendant du temps.Une partie significative de la thèse est consacrée à l'étude de l'interaction entre lesondes de spin (magnons) et vortex dans les supraconducteurs ferromagnétiques.Nous avons démontré que le spectre de magnon acquiert une structure de bande en présence d'un réseau de vortex idéal. En utilisant les équations phénoménologiques de London et de Landau-Lifshitz-Gilbert, nous avons étudié les réponses ac et dc de vortex dans les supraconducteurs ferromagnétiques. Enfin, nous avons examiné l'état de vortex dans des structures hybrides supraconducteur(S)-ferromagnétique(F)(par exemple, super-réseaux FS) avec une forte dispersion spatiale de la susceptibilité magnétique. Dans ces systèmes l'électrodynamique supraconductrice peut être fortement non locale, qui mène à l'attraction des vortex et à une transition de phase du premier ordre dans la phase de vortex
Caractérisation de métamatériaux pour applications millimétriques et submillimétriques by Riad Yahiaoui( )

1 edition published in 2011 in English and held by 1 WorldCat member library worldwide

This PhD dissertation is dedicated to the study, fabrication and characterization of metamaterials for millimeter and submillimeter applications. First of all we proposed to remind the extraordinary properties and physical processes involving within this new generation of materials. The manuscript contains results obtained from studies performed on different categories of metamaterials at microwave and terahertz frequencies: composite metamaterials, all dielectric metamaterials based on Mie resonances, subwavelength apertures based on the extraordinary transmission assisted by surface Plasmon polaritons. Our investigations have contributed to open the path to multiple potential applications in the field of sensors and telecommunications
Sensitivité de la méthode dite de mélange des courants pour la détection du déplacement nano-mécanique by Yue Wang( )

1 edition published in 2017 in English and held by 1 WorldCat member library worldwide

Detection of nanomechanical displacement by electronic transport techniques has reached a high level of sensitivity and versatility. In order to detect the amplitude of oscillation of a nanomechanical oscillator, a widely used technique consists of coupling this motion capacitively to a single-electron transistor or, more generally, to a transport device, and to detect the high-frequency modulation of the current through the nonlinear mixing with an electric signal at a slightly detuned frequency. This method, known as mixing-current technique, is employed in particular for the detection of suspended carbon nanotubes and has proven to be particularly successful leading to record sensitivities of mass and force detection. In this thesis we study theoretically the limiting conditions on the sensitivity of this method in different kind of transport devices. The sensitivity is a compromise between the noise, the back-action noise, and the response function. The latter is proportional to the electromechanical coupling. For these reasons in the thesis we study the response function, the effect of current and displacement (back-action) fluctuations for the following detection devices: (i) the metallic single electron transistor, (ii) the single-electronic level single electron transistor, and (iii) the coherent transport quantum dot. The optimal sensitivity is obtained, as usual, when the back-action of the detection device equals the intrinsic signal noise that, in our case, is the current noise. We found that the typical optimal values of the coupling are obtained in the strong coupling limit, where a strong renormalization of the resonating frequency is observed and a bistability of the mechanical oscillator is present [as discussed in G. Micchi, R. Avriller, F. Pistolesi, Phys. Rev. Lett. 115, 206802 (2015)]. We thus find upper bounds to the sensitivity of the mixing-current detection technique. We also consider how the mixing-current technique is modified in the limit where the tunneling rate becomes comparable to the resonating frequency of the mechanical oscillator
Microrhéomètre sur puce pour l'étude de l'écoulement d'un liquide proche d'une surface liquide by Ahmad Darwiche( )

1 edition published in 2012 in French and held by 1 WorldCat member library worldwide

Ce travail porte sur l'étude du comportement rhéologique de fluide en milieu confiné. Pour cela le levier d'un microscope à force atomique (AFM) est utilisé pour sonder les propriétés rhéologiques d'un fluide confiné entre deux surfaces : la surface d'une sphère collée à l'extrémité du levier et une surface plane sur lequel le fluide est déposé. Le dispositif expérimental est constitué du système de mesure d'un AFM et d'un piézoélectrique permettant d'approcher ou d'éloigner de la sphère la surface plane. Un modèle analytique permet d'extraire les propriétés rhéologiques du fluide confiné à partir de la déflexion du levier induite par le pincement du fluide. Cette méthode a été validée pour les fluides newtoniens. Par contre pour les fluides non-newtoniens comme par exemple la solution de polyacrylami de nous avons trouvé que la viscosité dépend de la distance D et que le cisaillement n'est pas le seul paramètre pertinent pour interpréter les propriétés rhéologiques
Investigations expérimentales du transport thermique et électronique dans des nanofils hétérostructurés 3C/2H by Aymen Ben amor( )

1 edition published in 2021 in French and held by 1 WorldCat member library worldwide

This research project presents an experimental exploration of thermal, electrical and thermoelectric properties of 3C/2H heterostructured Si and Ge nanowires. These studied nanowires are made by the Center for Nanosciences and Nanotechnologies of the University of Paris-Saclay, thanks to an original method which allows the creation of phase transformations in these nanowires. This results in a 3C/2H heterostructures along the nanowires with abrupt interfaces, giving hope for a significant reduction in their thermal conductivity without significantly altering their electronic properties. First, we showed the strong diameter dependence on thermal transport in such heterostructured nanowires. On the other hand, the annealing temperature during the phase transformation, which influences the size and the number of 2H domains, can constitute an effective parameter for reducing thermal conductivity. This study constitutes the first experimental evidence of reduced thermal conductivity in such types of nanowires. Then, with the aim of evaluation the electrical and thermoelectric properties of nanowires, an original prototype was developed during this thesis. This prototype allows simultaneous and real-time imaging of thermal and electrical conductivities and the Seebeck coefficient at the nanometric scale
Réorientation optique des cristaux liquides en présence de singularités matérielles ou lumineuses by Mohamed El Ketara( )

1 edition published in 2013 in French and held by 1 WorldCat member library worldwide

This thesis deals with a detailed study of the material an optical waves aspects of the lightinducedreorientation of a nematic liquid crystal film in a particular framework, called the optical“topological” reorientation. In practice, it corresponds to a situation where a laser beaminduces an orientational topological defect for the director field, whose nature depends on thecharacteristics of the excitation light field (polarization, phase, intensity). First, the concept oftopological optical reorientation is introduced and the experimental conditions for its appearanceare discussed and experimentally verified. Then, the role of the polarization state of a Gaussianlight beam excitation is investigated, followed with the more complex situation of singular lightbeams with structured phase or polarization. Finally, we report on self-induced nonlinear opticalmanifestations of the topological reorientation, which include the experimental identificationand discussion of novel singular phenomena such as nonlinear spin-orbit interaction of light andself-induced vortex beam precession
Etude des propriétés électroniques et vibrationnelles de nano-objets métalliques et hybrides par spectroscopie femtoseconde by Benoit Dacosta Fernandes( )

1 edition published in 2015 in French and held by 1 WorldCat member library worldwide

Electronic and vibrational dynamics have been studied in metallic and hybrid nano-object using femtosecond timeresolved spectroscopy. The study of electron-lattice energy exchanges in two-dimensional metallic systems showed an acceleration of the energy transfer between electrons and phonons due to confinement. This acceleration is governed by the smallest dimension of the nano-objects (2D-silver nano triangles ) when it becomes smaller than 10 nm. We also studied the vibrational dynamics of metallic nanoparticles, bimetallic and metal-dielectric. We investigated the longitudinal and radial modes of vibration of gold bipyramids which depend on their size, and studied their evolution under silver deposition. A high sensitivity of periods and amplitudes for small deposition were demonstrated. Our work on the evolution of acoustic vibrations of core-shell nano-objects (silver-silica and goldsilica) allowed us to obtain information on the quality of mechanical contact at the metal-dielectric interface. Finally, we studied the electronic interactions in hybrid metal / semiconductor (ZnO-Ag) nano-systems, and especially the charge transfer and energy exchanges between the two components. We showed a strong influence of the environment on the electron dynamics of ZnO and proved the existence of an electron transfer, photoinduced by an infrared pulse, from the metal particle to the semiconductor conduction band
Flower-like azimuthal instability of a divergent flow at the water/air interface by Goce Koleski( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

Un écoulement axisymétrique à une interface eau-air s'avère instable azimutalement. Durant cette thèse,nous avons mené deux expériences afin d'étudier ce point : (1) une petite fontaine subaquatique propulse un jet contre l'interface eau-air créant ainsi en surface un écoulement centrifuge radial; (2) une microbille chauffée par laser, en mouillage partiel à la surface de l'eau, engendre un écoulement thermocapillaire divergent. Lorsque la vitesse du jet ou la puissance du laser est suffisamment forte, il se produit une brisure de symétrie de l'écoulement torique initial en paires de vortex contrarotatifs entourant la source.Nous précisons les caractères morphologiques du tore ainsi que du dipôle par le biais d'expériences de tomographie laser et d'injection de colorant. Dans l'expérience du jet d'eau, nous montrons que la taille du tore est essentiellement déterminée par la distance séparant l'injecteur de la surface. Dans les deux expériences, un état "bloqué" de l'interface en régime toroïdal mais "débloqué" en régime dipolaire est mis en évidence par suivi de traceurs. Ce type de phénomène est piloté par l'élasticité de surface. Une preuve convaincante est la réponse élastique, à l'extinction du laser, de la couche de surfactants adsorbés à l'interface. Le principal intérêt de ce travail est de mettre en avant le rôle - clé que joue l'élasticité interfaciale dans le scénario de l'instabilité. D'un point de vue théorique, nous étudions la convection thermocapillaire induite par une source fixe ponctuelle à l'interface eau-air. Nous résolvons l'équation de Stokes incompressible au sein du demi - espace contenant le liquide et déterminons la solution exacte du problème advectif, non-linéaire, dans le régime axisymétrique en limite de champ lointain. Enfin, nous posons les bases sur lesquelles élaborer une théorie de l'instabilité. Ce travail de thèse devrait permettre de comprendre comment une petite sphère chaude à la surface de l'eau déclenche le type d'instabilité étudié ici, devenant de ce fait une "particule active" capable de s'autopropulser à grande vitesse
Controlling electron transport : quantum pumping and single-electron tunneling oscillations by Carlotta Negri( )

1 edition published in 2012 in English and held by 1 WorldCat member library worldwide

Exploiter des effets dépendants du temps pour induire et contrôler des courants à travers des conducteurs mésoscopiques et nanoscopiques est un enjeu majeur dans le domaine du transport quantique. Dans cette thèse, nous considérons deux systèmes de taille nanométrique pour lesquels un courant est induit grâce au couplage entre champs extérieurs dépendants du temps et le transport d'électrons. Nous étudions d'abord un problème de pompage quantique au sein d'un système à trois sites en configuration d'anneau, en considérant la possibilité d'induire un courant continu par modulation temporelle des paramètres de contrôle. Nous nous intéressons en particulier à la transition entre régime adiabatique et antiadiabatique en présence d'un mécanisme de dissipation modélisé par un couplage entre le système et un bain extérieur.Nous montrons que le modèle dissipatif admet une solution analytique complète valable pour la composante DC du courant à fréquence arbitraire. Ceci nous permet de bien comprendre comment le courant induit dépend de la fréquence de pompage. Nous nous concentrons ensuite sur un autre système de contrôle du courant exploitant le phénomène des oscillations tunnel à un électron (SETOs). Contrairement au cas précédent, ici la circulation d'un courant continu à travers un circuit comportant une jonction tunnel produit, pour le régime approprié, un courant quasi-périodique d'électrons. On étudie le spectre de bruit à température nulle d'une jonction tunnel dans différents environnements résistifs dans le but de déterminer les limites du régime des SETOs et de quantifier leur degré de périodicité. Nous généralisons par la suite les résultats à température finie et discutons des effets des fluctuations quantiques
Mise en forme topologique large-bande de la lumière by Mikaël Ghadimi nassiri( )

1 edition published in 2019 in French and held by 1 WorldCat member library worldwide

Today, several beam shaping tools are available, some of them commercially, but most of themare designed for only one working wavelength. This thesis aims to develop several experimentalapproaches for broadband topological beam shaping of light. After the presentation of the state ofthe art, our work focuses on vortex shaping of polychromatic beam exploiting the spin-orbitinteraction of light. Concretely, we report the development of four techniques to modulate the socalledgeometric phase of polychromatic light fields. First, we describe anisotropic reflection frominterfaces that involves at least one uniaxial crystal. We identify a refractive index matchingcriterion enabling highly pure broadband phase control. Then we discuss the use of circularBragg reflection phenomenon inherent to the optics of cholesteric liquid crystals. This propertyallows the selective reflection of circularly polarized light over a bandgap while the reflected fieldacquires a geometric phase. These properties are exploited to design, fabricate and characterizestructured mirrors reflecting Laguerre-Gauss optical modes to a good approximation. The last twosolutions consist of vortex beam shaping using inhomogeneous anisotropic planar opticalelements, namely, topological defects that spontaneously appear in homeotropic nematic liquidcrystal films characterized by negative dielectric anisotropy. The first option is based on using twodefects in series while the other is based of parallel processing using an array of independentlycontrolled topological defects, each of them being dedicated to process distinct spectralchannels. The latter approach can be viewed as a spatial light modulator whose pixels areinhomogeneous and potential applications are proposed in the field of super-resolution opticalimaging and spatio-temporal beam shaping of ultrashort pulses
Mechanical effects of light in presence of optical spin-orbit interaction by Hernando Magallanes González( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

Interactions between light and matter cause optomechanical phenomena, where a distinctive feature of light-matter interaction, namely, the spin-orbit interaction of light, takes place within an emerging research area dedicated to the study of optomechanical effects in the presence of the interplay between polarization and spatial degrees of freedom of light. In particular, this work aims to directly observe the manifestation of (i) lateral forces and (ii) left-handed torques, which are counterintuitive optomechanical effects, by using inhomogeneous and anisotropic media as a critical ingredient for the manufacture of spin-orbit optical elements. Hence, we report on their direct experimental observations attempts, starting from the preliminary results obtained in our group before this work, and then present our new proposals and further generalization to the case of lateral forces. Consequently, we report on a millimeter-scale direct observation of optical spin-dependent lateral forces and left-handed torques with a full study. From the analysis of both phenomena, it turns out that their speed can be increased by reducing the spin-orbit optical elements inertia or size, making the phenomena relevant at microscopic-scale and interesting for technological applications. Thus, we account for our experimental journey chronologically, to observe the left-handed torque at micrometer-scale with samples that correspond to miniaturized versions of previous ones. Since the last results were inconclusive, we finish by proposing new strategies of manipulation of such micro-elements with promising implementation
Cyclones dans une bulle de savon by Tinihau Meuel( )

1 edition published in 2014 in French and held by 1 WorldCat member library worldwide

This thesis aims at the characterisation of quasi two dimensionalvortices stemming from turbulent thermal convection in a half soap bubble heatedfrom below. The power law in time for their mean square displacement is also validfor Earth hurricanes. This law allows simple hurricane trajectory prediction with itstrack forecast cone wich compares very well to already available cones. In this way,track prediction uncertainty and track fluctuations around a mean track are linked.The intensity of the soap bubble vortices is also studied by the mean of particleimages velocimetry and shows that their velocity field profiles are well described by aLamb type model. The Lagrangian tracking of fluid praticles in a bubble vortex allowsus to follow its intensification and decline phases. We propose an intensification lawfor both soap bubble vortices and Earth hurricanes. Rotation influence on the vorticesnumber, on their life-time, on their trajectory and on the power law of their meansquared displacement is also gauged. The statistical properties of the temperaturefield fluctuations also seem to change with rotation. The exponent of the temperaturestructure functions present a scaling transition from n/3 to n/2
Structure des ondes de choc dans les gaz granulaires by Alexandre Vilquin( )

1 edition published in 2015 in French and held by 1 WorldCat member library worldwide

Dans des milieux tels que les gaz, les plasmas et les milieux granulaires, un objet se déplaçant à des vitessessupersoniques, compresse et chauffe le fluide devant lui, formant ainsi une onde de choc. La zone hors-équilibreappelée front d'onde, où ont lieu de brusques variations de température, pression et densité, présente unestructure particulière, avec notamment des distributions des vitesses des particules fortement non-gaussienneset difficiles à visualiser. Dans une avancée importante en 1951, Mott-Smith décrit le front d'onde comme lasuperposition des deux états que sont le gaz supersonique initial et le gaz subsonique compressé et chauffé,impliquant ainsi l'existence de distributions des vitesses bimodales. Des expériences à grands nombres de Machont confirmé cette structure globalement bimodale. Ce modèle n'explique cependant pas la présence d'un surplusde particules à des vitesses intermédiaires, entre le gaz supersonique et le gaz subsonique.Ce travail de thèse porte sur l'étude des ondes de choc dans les gaz granulaires, où les particules interagissentuniquement par des collisions binaires inélastiques. Dans ces gaz dissipatifs, la température granulaire, traduisantl'agitation des particules, permet de définir l'équivalent d'une vitesse du son par analogie aux gaz moléculaires.Les basses valeurs de ces vitesses du son dans les gaz granulaires, permettent de générer facilement des ondes dechoc dans lesquelles chaque particule peut être suivie, contrairement aux gaz moléculaires. La première partie decette étude porte sur l'effet de la dissipation d'énergie, due aux collisions inélastiques, sur la structure des ondesde choc dans les gaz granulaires. Les modifications induites sur la température, la densité et la vitesse moyennemesurées, sont interprétées à l'aide d'un modèle basé sur l'hypothèse bimodale de Mott-Smith et intégrant ladissipation d'énergie. La deuxième partie est consacrée à l'interprétation des distributions des vitesses dans lefront d'onde. À partir des expériences réalisées dans les gaz granulaires, une description trimodale, incluant unétat intermédiaire supplémentaire, est proposée et étendue avec succès aux distributions des vitesses dans lesgaz moléculaires
Confinement and driving effects on continuous and discrete model interfaces by Paul Gersberg( )

1 edition published in 2020 in English and held by 1 WorldCat member library worldwide

This thesis examines the properties of the interface between two phases in phase separated systems. We are interested in how finite size effects modify the statistical properties of these interfaces, in particular how the dependence of the free energy on the system size gives rise to long range critical Casimir forces close to thecritical point. Often the interfaces in phase separated systems are described by simplified or coarsegrained models whose only degrees of freedom are the interface height. We review how the statics and dynamics of these interface models can be derived from microscopic spin models and statistical field theories. We then examine finite size effects for continuous interface models such as the Edwards Wilkinson model and discrete models such as the Solid-On-Solid model and discuss their relevance to the critical Casimir effect. In the second part of the thesis we examine models of driven interfaces which have nonequilibrium steady states. We develop a model C type model of an interface which shows a nonequlibrium steady state even with constant driving. The resulting nonequlibrium steady state shows properties seen in experiments on sheared colloidal systems, notably the suppression of height fluctuations but an increase in the fluctuations'correlation length. Finally we propose a new model for one dimensional interfaces which is a modification of the solid on-solid model and containing an extra entropic term ,whose correspondance with physical systems is yet to be found
Étude de la photo-commutation de complexes du fer : comportements individuels et collectifs by Geoffrey Gallé( )

1 edition published in 2012 in French and held by 1 WorldCat member library worldwide

This work deals with the study of the optical properties of spin cross-over (SCO) compounds. More precisely, we have characterized the photo-induced transition leading iron(II) SCO complexes from their low-spin (LS) to their high-spin (HS) states and conversely. These molecules have been studied in the solid state and in solution.In the solid state, our compounds display a thermal hysteresis loop at room temperature. When the temperature of the compounds is set inside their hysteresis loop, it is possible to switch them optically from the LS state to the HS state. First, we have studied the parameters impacting on the efficiency of the photo-induced SCO. Then, we have built an experimental set-up that makes it possible to record the kinetics of this transition inside the hysteresis loop. This latter experiment has confirmed our hypothesis that this phase transition is induced by a laser heating of the sample.In solution, we have studied, by means of time-resolved UV-visible pump-probe experiments, the elementary mechanisms involved in the SCO phenomenon. We focused our attention on two complexes: [Fe(phen)3](BF4)2 and [Fe(2-CH3-phen)3](BF4)2. The first one is in the LS state at room temperature, whereas the other one is in the HS state. Thanks to these experiments, we have evidenced and measured the lifetimes of the energy levels involved in the SCO at the molecular level.Finally, we have studied the photo-isomerization of a Na2[Fe(CN)5NO].2H2O crystal. By means of transient absorption experiments combining visible and infrared femtosecond pulses, we have evidenced the levels involved in this phase transition
Propriétés de jets granulaires denses et mesure d'une tension de surface granulaire by Gaël Prado( )

1 edition published in 2012 in French and held by 1 WorldCat member library worldwide

Les milieux granulaires présentent une grande diversité de comportements physiques que l'on peut relier aux différents états "conventionnels" de la matière : solide, liquide ou gaz. Les travaux décrits dans ce manuscrit se concentrent sur les écoulements granulaires denses présentant de nombreuses analogies avec les liquides moléculaires. Les expériences présentées dans ce manuscrit sont réalisées en utilisant des jets granulaires s'écoulant d'un réservoir, dans l'air et sous l'effet de la gravité. Quelques propriétés de tels jets sont étudiées, notamment l'évolution du diamètre au cours de la propagation. L'évolution de cette grandeur permet une description des jets granulaires comme des fluides incompressibles dans une certaine gamme de diamètres de sortie D et de diamètres des particules d, résumés en une grandeur réduite : le rapport d'aspect D/d. Lorsque ce dernier est inférieur à une grandeur critique proche de 15, les jets granulaires cessent de se comporter comme des liquides incompressibles et sont alors décrits comme des gaz en expansion.La transition entre les deux régimes d'écoulements est expliquée par un modèle faisant intervenir l'équilibre entre la température granulaire et sa dissipation par l'inélasticité des collisions entre les billes constituant le milieu granulaire. En utilisant les mesures de la température granulaire accessibles à la paroi dans le réservoir, ce modèle permet d'obtenir les profils de température et de fraction volumique du milieu en fonction du rapport d'aspect ainsi que leurs valeurs moyennes, présentant un bon accord avec les mesures de la fraction volumique en sortie du réservoir.Dans le régime "liquide" des jets granulaires mis en évidence ici, une tension de surface effective est mesurée par l'étude d'une instabilité similaire à celle de Rayleigh-Plateau. En soumettant le jet à une oscillation verticale apparaît une modulation du diamètre du jet dont il est possible d'étudier l'évolution au cours du temps. La mesure des taux de croissance des modes instables excités permet d'établir la relation de dispersion et d'obtenir une tension de surface effective dans les jets granulaires. Il est montré que cette tension de surface effective décroit lorsque la taille des particules augmente, décroit lorsque la pression de l'air ambiant diminue et augmente avec la distance de propagation.Le mécanisme proposé pour expliquer l'origine de cette tension de surface effective est l'interaction entre le jet granulaire et l'air ambiant. Les profils de vitesse de l'air entraîné par le jet sont mesurés pour différentes diamètres de particules, différentes pression ambiantes et différentes distances de propagation. L'entraînement de l'air et les profils de vitesses sont utilisés pour définir certaines forces s'exerçant sur les billes et construire une tension de surface effective : l'ordre de grandeur de cette tension de surface est incompatible avec les mesures réalisées précédemment. Une mesure de la pression de l'air à l'intérieur du jet granulaire permet d'obtenir une force exercée par la perméation de l'air à travers les pores du jet dont l'ordre de grandeur est correct
Déformations et instabilités d'interfaces liquides pilotées par la diffusion d'une onde laser en milieux turbides by Julien Petit( )

1 edition published in 2011 in French and held by 1 WorldCat member library worldwide

This thesis work is dedicated to liquid interface deformations from a continuous laser wave. We demonstrate that elastic scattering of the incident wave in turbid medium induces a scattering force density giving birth to permanent bulk flows in the fluid. Near a soft interface, viscous stresses associated to these flows can deform the interface up to instability and produce a liquid jet. In this manuscript, we report an experimental study dedicated to this new light-fluid coupling in combination with numerical simulations. We also study interface deformations and instability induced by radiation pressure, due to refractive index contrast between the two liquid phases in coexistence, in transparent fluids. We finally analyzed the combination of both couplings in turbid media, scattering force and radiation pressure which differently operate for the interface deformation. To do this, we used different turbid and transparent fluids systems, which have the main particularity to present very low interfacial tension
 
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Audience level: 0.96 (from 0.96 for Vortex sta ... to 0.96 for Vortex sta ...)

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Alternative Names
LOMA

UMR 5798

Languages
French (11)

English (9)