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Laboratoire de physique (Lyon)

Works: 107 works in 115 publications in 2 languages and 116 library holdings
Roles: Other
Publication Timeline
Most widely held works by Laboratoire de physique (Lyon)
Estimation de la structure d'indépendance conditionnelle d'un réseau de capteurs : application à l'imagerie médicale by Aude Costard( )

2 editions published in 2014 in French and held by 3 WorldCat member libraries worldwide

This thesis is motivated by the study of sensors networks. The goal is to compare networks using their conditional independence structures. This structure illustrates the relations between two sensors according to the information recorded by the others sensors in the network. We made the hypothesis that the studied networks are multivariate Gaussian processes. Under this assumption, estimating the conditional independence structure of a process is equivalent to estimate its Gaussian graphical model.First, we propose a new method for Gaussian graphical model estimation : it uses a score proportional to the probability of a graph to represent the conditional independence structure of the studied process and it is initialized by Graphical lasso. To compare our method to existing ones, we developed a procedure to evaluate the performances of Gaussian graphical models estimation methods. One part of this procedure is an algorithm to simulated multivariate Gaussian processes with known conditional independence structure.Then, we conduct a classification over processes thanks to their conditional independence structure estimates. To do so, we introduce a new metric : the symmetrized Kullback-Leibler divergence over normalized cross-profiles of studied processes. We use this approach to find sets of brain regions that are relevant to study comatose patients from functional MRI data
Localized Surface Plasmon Imaging : a non intrusive optical tool to cover nanometer to micrometer scales in biological systems by Thibault Roland( Book )

2 editions published in 2009 in English and held by 2 WorldCat member libraries worldwide

Most of the microscopy techniques used to study biological samples or processes relies on the use of markers or physical probes, which may modify artificially the phenomena considered.So as to propose an alternate to these techniques, a high resolution Scanning Surface Plasmon Microscope (SSPM) has been developed. Plasmons consist in collective oscillations of the free electrons at the surface of a metal. A high numerical aperture objective focuses the incident light on a small area of the metal/observation medium interface, which leads to the localization and the structuring of these waves here. Finally, the local variations of the sample dielectric index are detected while scanning the sample surface. First of all, we present the experimental principle of the SSPM, as well as a modelization of its response thanks to a 3D resolution of the Maxwell's equations. In chapter two, we study the structure of the thin gold films used during the SSPM experiments, after being deposited onto glass substrates by thermal evaporation. We address in the third chapter the problem of imaging in air and in water isolated nanoparticles of different sizes (from 10 to 200 nm of diameter). We show that this method is well suited to visualize such objects and also to discriminate them from their size or the material they are made of (depending on their dielectric index). Finally, we apply in the last chapter the SSPM to the visualization of unlabelled biological samples, such as nucleosomes (nucleoproteic complexes of about 10 nm of diameter) as well as human fibroblasts in which we resolve several subcellular structures (nucleus, nucleolus, cytoskeleton structures)
Mechanics and Dynamics of Cell Adhesion : Experimental Study of the Osteoclasts by Shiqiong Hu( Book )

2 editions published in 2010 in English and held by 2 WorldCat member libraries worldwide

Osteoclasts are large, multinucleated cells, which resorb mineralized bone. When an osteoclast encounters a substrate, dot-like actin-rich structures, the podosomes, appear and assemble into clusters, rings or a belt. We experimentally investigate, from a cell population to a single podosome, their function and dynamics. Over a cell population, kinetic measurements show that the cell surface area A scales as A ~ K2, where K is the number of nuclei, indicating a flat morphology. By defining quantities that account for the spatial distribution of the actin within the cell, we demonstrate that the podosomes organization only depends on the time after differentiation, and not on K. In a single osteoclast, the observation of a strong coupling between cell spreading and podosomes formation lead us to propose that podosomes play an important role in osteoclast motility. Analysis of osteoclast migration, and the forces it applies on the substrate, demonstrates that the internal dynamics of the actin within the cell does not only correlate with cell migration, but drives it. Finally, in order to understand the internal dynamics of a single podosome, we improved the model of Biben et al. (2005) by considering on the one hand, actin polymerization, and on the other hand, diffusion and attachment kinetics of the gelsolin, an actin severing protein. We find that podosomes are mainly governed by the actin dynamics, regardless of gelsolin concentration
Physique statistique du repliement et de la dénturation des acides nucléiques by Daniel Jost( Book )

2 editions published in 2010 in French and held by 2 WorldCat member libraries worldwide

A quantitative understanding of the folding and opening of nucleic acids is relevant for many biological and nanotechnological processes. The main goal of my PhD thesis is to understand these mechanisms by using and developping thermodynamics-based models. In a first part, we develop a unified Poland-Scheraga model of DNA thermal denaturation. Our description covers the entire crossover from oligo- to polynucleotide melting behavior and is applicable in the full experimental range of DNA strand and salt concentrations. We use our model to discuss generic aspects of DNA melting. In particular, we emphasize that the observable features are particularly sensitive to the remaining parameterization uncertainty for long oligomers. Then, we reconsider the Zimm-Bragg model, an approximation of the previous model. This allows us to perform a statistical and systematic genome wide comparison between biologically coding domains and thermodynamically stable regions. In a second part, we investigate the RNA folding by developping a lattice model parameterized with a unified and reduced version of the Turner model. The use of advanced Monte-Carlo techniques allows us to show that the lattice model quantitatively describe the folding of complex structures. We also evaluate the impact of steric interactions. In particular, we estimate mean-field corrections that can be used in standard programs working at the secondary structure level. Finally, the tridimensional definition of the model is exploited to study the effect of a geometrical confinement
Exemples d'invariance d'échelle dans la fracture des matériaux fragiles désordonnés by Nicolas Mallick( Book )

2 editions published in 2010 in French and held by 2 WorldCat member libraries worldwide

The aim of this thesis is to characterize and understand the scale invariances in the fracture of brittle disordered materials, exhibited by both earthquakes series and fracture experiments in laboratory. In this thesis, two differents experimental situations are studied, the statical indentation of glass and the sub-critical rupture of paper in a creep experiment. In the first situation, the indentation crack dynamic is followed by acoustic emissions, and the statistical distributions of physical quantities associated with the microcracks are found to be power laws, wich indicates scale invariances. In particular, the dynamic follows an Omori law, as shown in a recent study in sapphire at 10mK. The influence of temperature is also shown. A modelisation, based on disordered fiber bundle is proposed and explains qualitatively the observations, with a thermal activation mechanism. In the second situation, the scaling laws wich characterize the morphology of the crack fronts in paper are analysed. We show experimentaly that the growth regime influences the roughness exponent and that the fronts can be considered as multifractal structures. In both situations, recent signal processing tools are implemented. This allows to improve the detection of acoustic emissions and to precisely and rigorously characterize the scaling laws
Supergravités jaugées et symétrie locale d'échelle by Arnaud Le Diffon( Book )

2 editions published in 2010 in English and held by 2 WorldCat member libraries worldwide

To address the problem of the unification of the four fundamental interactions, numerous works have been proposed. String theory could be a good answer. Compared to quantum field theory (QFT), describing annihilation and creation of point-particles, string theory describes the dynamics of one-dimensional strings. It has also been found that local supersymmetric field theories, known as supergravities, are low-energy limit of string theories. The use of supersymmetry, which relates bosons and fermions in the same framework, improves the quantum behaviour of field theories, and is necessary to string theory for mathematical consistency reasons. The edification of the standard model of particle physics is based on QFTs with non-abelian gauge symmetries, known as Yang- Mills theories. In the perspective of the unification of the four interactions, supergravities with nonabelian gauge interactions are relevant effective field theories. Using a systematic method to generate non-abelian gauged supergravities, this thesis completes the classification of gauged supergravities by including a local scaling symmetry. The formalism of the embedding tensor is used to build a local gauge group from the global symmetries of supergravity theory. These particular theories including a local scaling symmetry are submitted to new constraints and they do no longer possess an action. Consequently, we are led to build the gauged theory at the level of the equations of motion. An interesting consequence of gauged supergravities with local scaling symmetry is the presence of a positive contribution to the scalar potential in Einstein equations, which could lead to de Sitter vacuum solutions
Décompositions Modales Empiriques : Contributions à la théorie, l'algorithmie et l'analyse de performances by Gabriel Rilling( Book )

2 editions published in 2007 in French and held by 2 WorldCat member libraries worldwide

The Empirical Mode Decomposition (EMD) is a novel signal processing tool dedicated to the analysis of nonstationary and/or nonlinear signals. The EMD provides for any signal a data-driven multi-scale decomposition. The components are oscillatory signals, not necessarily harmonic, whose characteristics, waveform, amplitude and frequency may be time-varying. The EMD being rather recent, it is only defined as the output of an unusual algorithm, with many degrees of freedom and no sound theoretical basis. We firstfocus on the algorithm of the EMD. The questions raised by the possibilities for the degrees of freedom are studied in order to propose an implementation. We also propose some slight variations on the original algorithm and an extension to process bivariate signals. Motivated by the fact that the algorithm is initially presented in a continuous time framework, but systematically applied to sampled signals, we study the effect of sampling on the decomposition. A model of sampling effects is proposed for the simple case of a sinusoidal input signal and a bound on the magnitude of these effects is derived for arbitrary input signals. Finally the mechanism underlying the decomposition is studied by means of the analysis of two complementary situations, the decomposition of sums of two sinusoids and that of broadband noise signals. The first case allows the derivation of a simple model explaining the behavior of the EMD for a vast majority of the possibilities of sums of sinusoids. This model remains valid for slightly amplitude and frequency modulated sinusoids and also for some cases of sums of non harmonic periodic waveforms. As for broadband noise signals, we observe that the behavior of the EMD is close to that of an autosimilar filter bank, analogous to those corresponding to discrete wavelet transforms. The properties of the equivalent filter bank are studied in detail as a function of the key parameters of the EMD algorithm. A link is also established between this filter bank behavior and the model developed for the sums of sinusoids
Transcriptional activity, chromatin state and replication timing in domains of compositional skew in the human genome by Lamia Zaghloul( Book )

2 editions published in 2009 in English and held by 2 WorldCat member libraries worldwide

We analysed the large-scale organisation of the human genome in terms of transcriptional activity, chromatin state and replication timing, focusing on a segmentation of the genome based on strand composition asymmetry. The large-scale variations of compositional skew along the human genome define Mbp scale skew domains that are bordered by large upward jumps. These upward jumps in the skew profile were proposed to be a subset of replication origins active in the germline that have been conserved throughout mammalian evolution. This first described skew domains were named N-Domains because their skew profile is shaped like an 'N', and they were shown to be strongly linked both to the organisation of transcription and replication. Indeed, the borders of N-Domains colocalize with promoters of genes oriented divergently from the border and often with an early-replicating locus. Here, we described a novel kind of skew domains, Split-N-Domains, similar at their borders to N-Domains but larger (>3Mbp) and presenting a gene desert with a null and constant skew at their heart. Central regions of Split-N-Domains constitute an evidence of the link between absence of genes, heterochromatin and late replication timing, and we proposed that the initiation of replication in these regions could be random. We found that genes close to skew domains borders have in general a CpG island promoter, thus suggesting a link between skew domains borders and DNA hypomethylation and gene expression in the germline. Using both experimental and sequence-derived markers of chromatin state, we showed that the region a few 100 kbp large around skew domains borders is also often characterized by an open chromatin state, particularly when it is early-replicating. We discuss how this open chromatin region can relate to the organisation of genes and to the replication program. In addition, we asked how did the distribution of evolutionary breakpoints relate to genome organisation. We found, contrarily to the expectation, that breakpoint regions are over-represented in small intergenes. In fact, breakpoint density is higher in regions hypomethylated and with a higher sensitivity to DNase I. We proposed that the heterogeneous distribution of breakpoints in mammalian genomes could be due to a mutation bias in relation to chromatin state
Propriétés de transport électronique des isolants topologiques by Pierre Adroguer( )

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

The works presented in this thesis intend to contribute to condensed matter physics in the understanding of the electronic properties of a recently discovered class of materials : the topological insulators.The first part of this memoir is an introduction to topological insulators, focusing on their specifities compared to "trivial" insulators : helical edge states (in the two dimensional quantum spin Hall effect) or relativistic surface states (for three dimensional topological insulators) both robust agiant disorder.The second part proposes a new way to probe the unique properties of the helical edge states of quantum spin Hall effect via the injection of Cooper pair from a superconductor.The third part deals with the diffusion of the three dimensional topological insulator surface states, in the phase coherent regime. The diffusion, the quantum correction to conductivity, and the amplitude of the universal conductance fluctuations are studied. This study is also led in the experimentally relevant case where the Fermi surface presents a hexagonal deformation
Écoulements et écrasements de fluides : effet du mouillage et de la rhéologie by Jérémy Ferrand( )

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

The draining of a tank through an orifice was described by Torricelli almost 400 years ago. His model does not provide for any wetting effect of the flowing fluid on the drilled plate. This thesis shows experimentally that the effect of wetting on the flow rate is important for Newtonian fluids with low viscosity in the case of an orifice the size of which is comparable to the capillary length. A model calculating the kinetic energy variation within the meniscus at the outlet of the hole allows us to account for experimental observations. Unknown jet instability also appears at the outlet of the hole; this is the oscillation of the meniscus triple line that is causing it. The relations of dispersion of the excitation frequency as well as that of the secondary frequencies appearing along the jet have been established.This investigation was supplemented by flows of both viscous and viscoelastic fluids. For viscous fluids, the perfect fluid model is corrected based on our experiments. For viscoelastic fluids, experiments show that there is competition between viscous dissipations and elastic effects throughout the flow. The prediction of both effects is challenging. We show situations where elastic effects dominate, allowing a polymer solution to flow faster than water.Finally, a second experimental set-up was build for compressing complex fluids between two parallel glass plates. Visualization, both position and normal force measurements, allow a better understanding of the behavior under normal stress of systems such as foams, emulsions, gels
Transitions de phase en turbulence bidimensionnelle et géophysique by Marianne Corvellec( )

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

Prédire la statistique des grandes échelles des écoulements turbulents constitue un enjeu important. Pour l'équation d'Euler 2D et des modèles analogues d'écoulements géophysiques, une auto-organisation est observée (formation de cyclones/anticyclones, jets intenses). La mécanique statistique d'équilibre des écoulements bidimensionnels s'est avérée fondamentale et pertinente même en présence de forçage et dissipation, dans la limite inertielle. La thèse est motivée par le phénomène de transitions aléatoires entre deux topologies différentes, lié à une bistabilité. Il s'agit de prédire la multiplicité des équilibres d'un écoulement (quasi) bidimensionnel. On développe une classification des transitions de phase, pour des équilibres (statistiques et/ou dynamiques) d'un tel écoulement. Les diagrammes de phase font apparaître la présence générique de points critiques et tricritiques, et des domaines d'inéquivalence d'ensembles statistiques. Dans le cas d'une géométrie annulaire, on décrit les effets de la topographie et de la conservation de deux circulations. Des analogies avec la bistabilité du courant océanique Kuroshio sont proposées à partir de cette étude académique. Enfin, pour le système Euler 2D, on détaille un résultat de mécanique statistique dans l'ensemble énergie-enstrophie : la distribution microcanonique, construite à partir du théorème de Liouville en dimension finie, correspond à la maximisation d'une entropie de mélange de la vorticité
Approches innovantes en convection thermique turbulente. Influence des rugosités et étude Lagrangienne. by Olivier Liot( )

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

In this work, turbulent thermal convection is studied. Undestanding the mechanisms of induced thermal flux is still a challenge. In this context we used two innovative approaches.The first one consists in a Lagrangian approach. An instrumented particle, designed for temperature measurements, is immersed in the flow. The simultaneous measurement of the temperature view from the particle and its velocity allowsto obtain local Lagrangian heat flux. By comparing these measurements with numerical simulation and Eulerian investigations we can assert the relevance of this method. Then we seeded the flow with particles whose diameter is smaller than the dissipative scale of the system. We performed 3D tracking to access to turbulent statistics and pair dipersion.On the other hand we study a configuration with controlled roughness on the bottom plate. It is well-known that it leads to thermal flux enhancement higher than the one linked to the surface increasing. We bring out possible mechanisms to explain this phenomenon. Thermometric measurements in water-filled cell and anemometric measurements in a six-time larger air-filled cell point out a dramatic change of the boundary layers structure close to roughness. Particularly a turbulent viscous boundary layer appears. Theses investigations are supplemented by velocity measurements of the global flow and reveal a large increase of velocity fluctuations and the appearance of a new turbulence regime
Relativistic phases in condensed matter by Eric Brillaux( )

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

This thesis focuses on the electronic properties of crystalline materials knownas relativistic semimetals, where the energy bands touch linearly at discrete points of the Brillouin zone. A historical example of such material is graphene, whose elementary excitations behave as two-dimensional massless Dirac fermions, even though they propagate at sublight speed. Massless relativistic fermions also appear in the spectrum of three-dimensional materials: Weyl and Dirac semimetals. In this thesis, we analyse the stabilityof the band crossing points with respect to perturbations, either disorder or interactions.The first part addresses the disorder-driven continuous phase transition of a Weyl semimetalto a metallic phase. In this semimetal-metal transition, which differs from Anderson's localisation, the disorder-averaged density of states acts as an order parameter. As an alternative way to characterise the transition, we study a continuous set of exponents,the multifractal spectrum, which encodes the geometrical properties of the critical wavefunctions. These multifractality exponents, which we determine within a renormalisation group approach, govern the scaling law of the typical density of states. We also investigatethe fate of surface states in disordered Weyl and Dirac semimetals using a self-consistent approximation, and show that the Dirac surface states undergo a similar disorder-inducedtransition. The second part addresses twisted bilayer graphene, a system where the interplay between interlayer tunnelling and the moiré geometry of the bilayer leads to anunusual 'magic' angle physics. The Fermi velocity vanishes at a discrete set of so-calledmagic angles, which enable many-body effects to dominate the electronic properties. Weclassify all contact interactions allowed by symmetry, and develop a renormalisation group approach to study the competition between the relevant instabilities. We explain the emergence of a gapped phase at charge neutrality that breaks the three-fold rotational symmetry, which we call a nematic insulator
Estimation régularisée d'attributs fractals par minimisation convexe pour la segmentation de textures : formulations variationnelles conjointes, algorithmes proximaux rapides et sélection non supervisée des paramètres de régularisation; Applications à l'étude du frottement solide et de la microfluidique des écoulements multiphasiques by Barbara Pascal( )

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

In this doctoral thesis several scale-free texture segmentation procedures based on two fractal attributes, the Hölder exponent, measuring the local regularity of a texture, and local variance, are proposed.A piecewise homogeneous fractal texture model is built, along with a synthesis procedure, providing images composed of the aggregation of fractal texture patches with known attributes and segmentation. This synthesis procedure is used to evaluate the proposed methods performance.A first method, based on the Total Variation regularization of a noisy estimate of local regularity, is illustrated and refined thanks to a post-processing step consisting in an iterative thresholding and resulting in a segmentation.After evidencing the limitations of this first approach, deux segmentation methods, with either "free" or "co-located" contours, are built, taking in account jointly the local regularity and the local variance.These two procedures are formulated as convex nonsmooth functional minimization problems.We show that the two functionals, with "free" and "co-located" penalizations, are both strongly-convex. and compute their respective strong convexity moduli.Several minimization schemes are derived, and their convergence speed are compared.The segmentation performance of the different methods are evaluated over a large amount of synthetic data in configurations of increasing difficulty, as well as on real world images, and compared to state-of-the-art procedures, including convolutional neural networks.An application for the segmentation of multiphasic flow through a porous medium experiment images is presented.Finally, a strategy for automated selection of the hyperparameters of the "free" and "co-located" functionals is built, inspired from the SURE estimator of the quadratic risk
Renormalization and Coarse-graining of Loop Quantum Gravity by Christoph Charles( )

1 edition published in 2016 in English and held by 1 WorldCat member library worldwide

The continuum limit of loop quantum gravity is still an open problem. Indeed, no proper dynamics in known to start with and we still lack the mathematical tools to study its would-be continuum limit. In the present PhD dissertation, we will investigate some coarse-graining methods that should become helpful in this enterprise. We concentrate on two aspects of the theory's coarse-graining: finding natural large scale observables on one hand and studying how the dynamics of varying graphs could be cast onto fixed graphs on the other hand.To determine large scale observables, we study the case of hyperbolic tetrahedra and their natural description in a language close to loop quantum gravity. The surface holonomies in particular play an important role. This highlights the structure of double spin networks, which consist in a graph and its dual, which seems to also appear in works from Freidel et al. To solve the problem of varying graphs, we consider and define loopy spin networks. They encode the local curvature with loops around an effective vertex and allow to describe different graphs by hidding them in a coarse-graining process. Moreover, their definition gives a natural procedure for coarse-graining allowing to relate different scales.Together, these two results constitute the foundation of a coarse-graining programme for diffeomorphism invariant theories
Measurement and control of electronic coherences by Clément Cabart( )

1 edition published in 2018 in English and held by 1 WorldCat member library worldwide

Over the last few years, extensive experimental efforts have been devoted to thedevelopment of quantum nanoelectronics tools aiming at controlling electronic trans-port down to the single electron level. These advances led to a paradigm shift inthe domain of coherent electronic transport, giving birth to electron quantum optics,which is the domain of this work.This manuscript is devoted to two problems. The first of these is the one ofCoulomb interactions between electrons, which lead to a decoherence phenomenonthat must be characterized and predicted in order to be controlled. Using an analyt-ical and numerical approach, it became possible to predict the effect of interactionson an experimentally relevant system, a prediction that was then confirmed in the ex-periment. After this result, this manuscript displays some ideas aiming at controllinginteractions and proposes some ways to test them experimentally.In this work, I also took on the problem of characterizing complex quantum states.In particular, following the experimental demonstration of a tomography protocol forfirst order coherences, I tried to extend this protocol to more complex states thatcould exhibit two-electron coherences, or more. These states being also sensitive to Coulomb interactions, an extension of the tools used to treat interactions to thismulti-electronic state is also presented in this work
New Avenues for Einstein's Gravity : from Penrose's Twistors to Hitchin's Three-Forms by Yannick Herfray( )

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

In this thesis we take Einstein theory in dimension four seriously, and explore the special aspects of gravity in this number of dimension.Among the many surprising features in dimension four, one of them is the possibility of `Chiral formulations of gravity' - they are surprising as they typically do not rely on a metric. Another is the existence of the Twistor correspondence. The Chiral and Twistor formulations might seems different in nature. In the first part of this thesis we demonstrate that they are in fact closely related. In particular we give a new proof for Penrose's `non-linear graviton theorem' that relies on the geometry of SU(2)-connections only (rather than on metric).In the second part of this thesis we describe partial results towards encoding the full GR in the total space of some fibre bundle over space-time. We indeed show that gravity theory in three and four dimensions can be related to theories of a completely different nature in six and seven dimension respectively. This theories, first advertised by Hitchin, are diffeomorphism invariant theories of differential three-forms.Starting with seven dimensions, we are only partially succesfull: the resulting theory is some deformed version of gravity. We however found that solutions to a particular gravity theory in four dimension have a seven dimensional interpretation as G2 holonomy manifold. On the other hand by going from six to three dimension we do recover three dimensional gravity. As a bonus, we describe new diffeomorphism invariant functionnals for differential forms in six dimension and prove that two of them are topological
Instrumentation for Thermal Noise Spectroscopy by Richard Pedurand( )

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

The resolution limit of gravitational wave interferometers is set by their mirrors' Brownian motion - or thermal noise - in the central part of their detection band, from 10Hz to 1kHz. This thermal noise frequency distribution is given by the mechanical energy dissipation mechanisms it originates from, in agreement with the fluctuation-dissipation theorem. This dissipation mainly derives from the optical coatings deposited on the mirrors to give them their reflectivity. To reduce this thermal noise, a new generation of gravitational wave detectors employing mirrors cooled to cryogenic temperature has been suggested. The development of new optical thin-film materials with low mechanical dissipation, operating at both room and cryogenic temperatures, therefore requires new experimental tools. The main object of this thesis is the construction of a new instrument, the CryoQPDI, which is an association between a high-resolution interferometer and a cryostat based on a pulse tube cooler. It can directly measure the Brownian motion of a microcantilever between 300 K and 7 K. By combining measurements made on a microcantilever before and after the deposition of a thin film, it is possible to characterize the internal mechanical dissipation of this thin film. This instrument will eventually contribute to the optimisation of optical coatings of future gravitational wave detectors, aiming at minimizing the limitations due to thermal noise
Modèles intégrables avec fonction twist et modèles de Gaudin affines by Sylvain Lacroix( )

1 edition published in 2018 in English and held by 1 WorldCat member library worldwide

Cette thèse a pour sujet une classe de théories des champs intégrables appelées modèles avec fonction twist. Les principaux exemples de tels modèles sont les modèles sigma non-linéaires intégrables, tel le Modèle Principal Chiral, et leurs déformations. Un premier résultat obtenu est la preuve que le modèle dit de Bi-Yang-Baxter, qui est une déformation à deux paramètres du Modèle Principal Chiral, est lui aussi un modèle avec fonction twist. Il est ensuite montré que les déformations de type Yang-Baxter modifient certaines symétries globales du modèle non déformé en symétries de Poisson-Lie. Un autre chapitre concerne la construction d'une infinité de charges locales en involution pour tous les modèles sigma intégrables et leurs déformations : ce résultat repose sur le formalisme général partagé par tous ces modèles en tant que théories des champs avec fonction twist.La seconde partie de la thèse a pour sujet les modèles de Gaudin. Ceux-ci sont des modèles intégrables associés à des algèbres de Lie. En particulier, les théories des champs avec fonction twist sont liées aux modèles de Gaudin associés à des algèbres de Lie affines. Une approche standard pour l'étude du spectre des modèles de Gaudin quantiques sur des algèbres finies est celle de Feigin-Frenkel-Reshetikhin. Dans cette thèse, des généralisations de cette approche sont conjecturées, motivées et testées. L'une d'elles concerne les modèles de Gaudin finis dits cyclotomiques. La seconde porte sur les modèles de Gaudin associés à des algèbres affines
Energy and Buoyancy Transport by Inertia-Gravity Waves in Non-Linear Stratifications. Application to the Ocean by Samuel Boury( )

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

Inertia-gravity waves contribute to the worldwide transport of energy and momentum in the oceans, and theyplay a crucial role in stratified mixing through non-linear processes transferring energy from scales to scalessuch as super-harmonic generation or triadic resonant instability.Of primary relevance are these waves to the Arctic Ocean, and more particularly energy transport by internalwaves created by storms at the surface of the ocean. Due to increasing ice melting in the last decades, thesurface of the Arctic Ocean is more exposed to winds and storms than ever and for a longer durationthroughout the year. The very stratified layers of the ocean can now be disturbed by atmospheric events and,in return, the modified dynamics of energy transport plays a crucial role in climate changes. A betterunderstanding of how storm energy can be transferred to the ocean, and of how it can propagate through, isa very relevant issue.Based on these considerations, this thesis explores the impact of the geometry on internal wave propagationin stratified and rotating media, both in the linear and non-linear theory. Different phenomena such as modes,wave resonator, transmission though buoyancy interface, tunnelling effect, super-harmonic generation andtriadic resonant instability, wave attractors, are discussed. Theory is validated by experiments, through the useof a storm-like axisymmetric wave generator creating inertia-gravity waves in stratified and rotating fluids, inconfined and unconfined cylindrical geometries. Applications to in-situ measurements are also proposed withcomparisons to internal waves in real world stratifications
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ENS de Lyon. Laboratoire de physique

English (17)

French (11)