WorldCat Identities

École doctorale Physique en Île-de-France (Paris / 2014-....).

Overview
Works: 585 works in 605 publications in 2 languages and 608 library holdings
Roles: Other, Degree grantor
Publication Timeline
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Most widely held works by École doctorale Physique en Île-de-France (Paris / 2014-....).
Numerical characterization of boson stars and Kerr Black holes = Caractérisations numériques d'étoiles bosoniques et de trous noirs by Claire Cochet Some( )

2 editions published in 2016 in English and held by 3 WorldCat member libraries worldwide

The Galactic Center is an interesting place to test possible effects of strong gravity regime. Whereas it is generally believed that the compact object located at the Galactic Center, named Sgr A*, is a rotating black hole, some alternative models can also explain the current observations. This work is centered on one of these other objects, which is the Boson Star. Rotating boson stars are numerical solutions of the coupled Einstein-Klein-Gordon system, so these equations are written within the 3+1 formalism and then a numerical code capable of solving them with the Kadath library has been developed. Several kinds of boson stars with different potentials are presented : free fields an self-interacting fields, with quartic and sextic potentials, and different values of the rotational quantum number. Then two different ways of comparing this spacetime to Kerr's are presented. One way was to compute timelike geodesics in this geometry and study them. For that the ray-tracing code Gyoto is used to integrate numerically the geodesic equations for several types of boson stars. A peculiar type of orbits has been identifyed: the zero-angular-momentum ones which is called pointy-petal orbits thanks to their shape. These orbits pass very close to the center and are qualitatively different from orbits around a Kerr black hole. Another way to compare Kerr to any stationary and asymptotically flat metric given in its 3+1 form was to us a the characterization of the Kerr spacetime given by the Simon-Mars tensor. This tensor has the property of being identically zero for a vacuum and asymptotically flat spacetime if and only if the latter is locally isometric to the Kerr spacetime. The idea was to build a scalar with this tensor, and a scalar which is an invariant quality factor. Then, write it in 3+1 form to be able to compute it with numerical codes such as Kadath. Computing this scalar provides a simple way of comparing locally a generic (even non vacuum and non analytic) stationary spacetime to Kerr, therefore measure its 'non-Kerness". As an illustration, this invariant quality factor is evaluated for numerical solutions of the Einstein equations generated by boson stars and neutron stars, and for analytic solutions of the Einstein equations such as Curzon Chazy spacetime
Modèles d'Univers inhomogènes à Big-Bang retardé by Marie-Noëlle Célérier( )

2 editions published between 1998 and 2019 in French and held by 3 WorldCat member libraries worldwide

The hot Big-Bang standard model for the evolution of the Universe, despite strong successes, lets unresolved a number of problems. The purpose of this thesis is to propose a class of inhomogeneous models of Universe, getting rid of some of the drawbacks of the standard model, while leaving unimpaired its main cornestones. It is shown, with the help, for this preliminary study, of very simplifying assumptions : 1. That the notion of inhomogeneous Big-Bang is worth being developed. The observable consequences of an inhomogeneous initial singularity, of “delayed” type, are studied, under some peculiar conditions. The horizon problem is thus solved without need for any inflationary phase. The flatness and cosmological constant problems disappear. Mechanisms able to explain the origin of structure formation are put forward. 2. That the parameters of the model can be tuned such as to reproduce the data obtained from observations. Such a tuning is thus performed to reproduce, with good approximation, the dipole and quadrupole moments of the temperature anisotropies of the cosmological micro-wave background radiation. Are also studied a number of special classes of Einstein's equations for a relativistic spherically symmetric perfect fluid, of which a reduced form, with separated variables, is proposed
Développement d'outils de modélisation et de méthodes pour le contrôle de pneumatiques par ultrasons by Blandine Dobigny( Book )

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

This thesis deals with ultrasonic non-destructive testing of tires. More precisely, this work aims to model ultrasonic wave interactions with wires collections that reinforce the tire. The tire is considered as an attenuating medium with several embedded gratings of cylinders. The orientation of each grating may be different but they ail constitute parallel plans. First, the calculation of the field scattered by a unidirectional grating is extended both to the case of an attenuating medium and a plane wave with an arbitrary angle of incidence. The model is used to compare the behaviors of infinite and large finite gratings. We also study a grating with a perturbation and the influence of the incidence angle. Each case is considered in a frequency range below and above the cutoff frequency where the wave field is written as a sum of several plane waves. This decomposition is then used to deal with stacks of gratings. After the decomposition into plane waves, with a shared basis, the fields calculated for each grating are joined to model the interaction between gratings. This approach is validated with a bidirectional array. Finally, experimental validations are conducted on simplified tire-like samples. Through-transmission experiments have shown the grating effects depending on the frequency and the incidence angle. The experimental transmission coefficients have finally been compared to those calculated with the model
Efficient artificial ordered vortex pinning in high-Tc supercondiuctors via masked ion irradiation = éseaux de défauts ordonnés fabriqués par irradiation ionique pour le piégeage efficace de vortex dans le supraconducteur à haut-Tc YBa₂Cu₃O₇ by Juan Trastoy Quintela( Book )

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

Superconducting flux quanta in nanostructured YBa₂Cu₃O₇-d films constitute a model to study the general problem of interacting particles in a potential-energy landscape. Using 0+ ion irradiation through a mask defined via electron-beam lithography, ordered nanometric regions with a depressed local critical temperature can be defined to precisely engineer the vortex energy landscape. A detailed characterization of this artificial pinning's strength with temperature and vortex velocity is given, as well as a study of the vortex phase diagram and the associated thermodynamic phase transition. Thanks to the ability to modulate the superconducting condensate at the nanoscale, a new mechanism to reversibly switch the vortex energy landscape's geometry using temperature as a control knob is developed. This is shown through the thermal switching of a geometrically frustrated array into a square periodic one. Finally, asymmetric vortex motion under a symmetric drive is studied using asymmetric pinning sites
Rôle de Myocardin-Related Transcription Factor dans la mécanotransduction de la cellule musculaire by Lorraine Montel( Book )

2 editions published in 2015 in French and held by 2 WorldCat member libraries worldwide

Our muscles show the most intuitive example of mechanotransduction : when trained they grow whereas immobilized they atrophy. To a mechanical signal, the cells give a biological response. The Sotiropoulos group showed that Serum Response Factor (SRF) and Myocardin-Related Transcription Factor (MRTF-A) play a central role in this phenomenon by regulating cytoskeletal genes and muscle development. The localization of MRTF-A in the cell is regulated by the state of the actin cytoskeleton : in the presence of monomeric actin, MRTF-A in confined to the cytoplasm and SRF inactive. Whereas ir case of monomeric actin scarcity, MRTF-A is accumulated in the nucleus, where it triggers SRF. Using magnetic tweezers and stretching experiments, we demonstrated that, when submitted tc mechanical cues, the actin cytoskeleton reorganizes and MRTF-A is relocated. In response to moderate cues, actin polymerizes and MRTF-A is transported to the nucleus. On the contrary, when the stress is too high, the cytoskeleton is damaged and MRTF-A is confined to the cytoplasm. Using a fluorescent MRTF-A and a panel of actin visualization techniques, we were able to observe the chronology of these events. Moreover, we showed that all the actin visualization techniques interfere with the actin cytoskeleton at a level detectable through MRTF-A localization. Finally we studied the changes in rheological properties of cells submitted to repeated steps of force
Combinaisons tensioactifs-polymères pour la Récupération Améliorée des Hydrocarbures (RAH) par voie chimique appliquée aux réservoirs de pétroles extra-lourds : propriétés de transport en milieux poreux et mécanismes de récupération = Surfactant-Polymer Combinations for Chemical Enhanced Oil Recovery (EOR) Applied to Extra-Heavy Oil Reservoirs : Transport Properties in Porous Media and Recovery Mechanisms by Fernancelys Del Carmen Rodriguez Manrique( Book )

2 editions published in 2016 in English and held by 2 WorldCat member libraries worldwide

Cette thèse consiste en une étude de l'injection de produits chimiques pour la Récupération Améliorée des Hydrocarbures (CRAH) en lien avec un cas de réservoir d'huile extra-lourde au Vénézuéla. En premier lieu, les propriétés de transport de solutions concentrées de polymères ont été étudiées dans les milieux poreux en conditions monophasiques. Les résultats obtenus ont montré une augmentation de rétention/adsorption avec la concentration du polymère. Ils ont également permis de valider la modélisation basée sur l'effet de couche de déplétion comme un outil pour expliquer les valeurs de réduction de mobilité. Deuxièmement l'huile, la saumure et la roche du réservoir vénézuélien ont été caractérisées et des tests de récupération d'huile extra-lourde en milieu poreux ont été réalisés. Ces tests avaient pour objectif de déterminer la saturation en huile ultime atteignable en CRAH. Les résultats obtenus à la fois sur grès de Bentheimer et sur roche réservoir ont montré que l'injection de tensioactif et de polymères (SP) dans des conditions secondaires est un procédé plus efficient que l'injection de polymère (P) ou de tensioactifs (S) seuls. La réduction des instabilités visqueuses et l'amélioration du contrôle de la mobilité après l'injection SP ont été constatées à partir d'analyses des roches par CT-scanner. Les résultats obtenus dans ce travail, à l'échelle du laboratoire, sont destinées à être utilisés comme données d'entrée pour la simulation des processus CRAH à l'échelle du réservoir. Ils ouvrent la voie à des évaluations économiques réalistes des procédés CRAH pour le pétrole extra-lourd Vénézuélien et, potentiellement, à des développements à grande échelle
Lire les lignes de la ville : méthodologie de caractérisation des graphes spatiaux by Claire Lagesse( )

1 edition published in 2015 in French and held by 2 WorldCat member libraries worldwide

La ville regroupe une grande diversité de composants et d'interactions. Parmi sa pluralité, nous choisissons un élément qui structure son développement et son usage : le réseau de ses rues. À partir de sa représentation sous forme de graphe, nous construisons un objet, la voie, qui se révèle être multi-échelle, rendant son analyse robuste au découpage du réseau. Nous étudions plusieurs indicateurs et nous établissons une grammaire de caractérisations non-redondantes des graphes spatiaux. La voie montre ainsi des propriétés spatiales particulières, rendant équivalentes certaines analyses globales à d'autres locales. L'application de cette méthodologie nous permet de mettre en évidence les propriétés particulières partagées par des graphes viaires de différents continents, et celles qui se retrouvent également dans d'autres réseaux spatiaux (biologiques, etc). Dans une approche diachronique, nous construisons une méthodologie de différentiation temporelle, permettant de quantifier les changements de proximité topologique entre les éléments du graphe. Cela nous permet d'avoir une première appréhension de la cinématique de croissance des réseaux étudiés. Cette recherche se termine par l'intégration de l'objet voie et de ses indicateurs dans une approche qualitative. Nous montrons ainsi comment l'analyse de villes, à travers les propriétés topologiques et topographiques de leurs réseaux viaires, permet de retrouver une partie des contextes historiques et géographiques de leur construction. La mise en perspective de ces travaux, par une synthèse des échanges pluridisciplinaires qui les ont entourés, révèle le potentiel de leurs applications et les pistes de recherches offertes
Applications de l'imagerie ultrasonore ultrarapide aux pathologies hépatiques diffuses de l'enfant by Stéphanie Franchi-Abella( Book )

2 editions published in 2015 in French and held by 2 WorldCat member libraries worldwide

Les travaux menés durant cette thèse portent sur les applications de l'imagerie ultrasonore ultrarapide aux pathologies du foie de l'enfant notamment l'élastographie (supersonic shearwave elastography sSWE) et le Doppler ultrarapide. Dans un premier temps nous avons évalué différents systèmes d'élastographie ultrasonore sur un fantôme et montré les limites des différentes techniques et les précautions nécessaires pour leur utilisation en clinique. Dans un deuxième temps une étude a permis de montrer la faisabilité de l'élastographie sSWE du foie chez l'enfant y compris le nouveau-né, et d'établir les valeurs normales et les premiers résultats de performances diagnostiques pour le diagnostic de la fibrose hépatique avec corrélation à la biopsie hépatique. La troisième partie du travail a concerné les applications du Doppler ultrarapide pour l'analyse morphologique et fonctionnelle de la vascularisation hépatique en condition physiologique et pathologique. Nous avons dans un premier temps adapté les séquences d'acquisition et le traitement du signal aux spécificités de la vascularisation hépatique. Dans un deuxième temps les acquisitions chez le nourrisson ont permis d'observer l'évolution de la vascularisation des régions sous-capsulaires du foie depuis la naissance et en condition pathologique. Le Doppler ultrarapide permet aussi une quantification précise des vitesses en tout point du champ de vue et d'établir des cartes paramétriques de paramètre Doppler. Cette approche a permis d'établir la preuve de concept des cartes de résistivité du foie
Ultrasound sensitive agents for transcranial functional imaging, super-resolution microscopy and drug delivery = Utilisation d'agents sensibles aux ultrasons pour l'imagerie fonctionnelle transcrânienne du cerveau, microscopie ultrasonore et délivrance ultrasonore de médicaments by Claudia Errico( Book )

2 editions published in 2016 in English and held by 2 WorldCat member libraries worldwide

This thesis focuses on two main branches of the application of ultrasound contrast agents: microbubbles-aided ultrafast ultrasound imaging of the brain and ultrasound-triggered drug delivery for cancer therapy. At first, gas-filled microbubbles have been used to retrieve the brain activation through the skull in large animais. With this approach we have been able to non-invasively reconstruct the cerebral network of the brain, as well as retrieve its hemodynamic response to specific evoked tasks with high spatiotemporal resolution. The validation of this novel functional ultrasound (fUS) imaging approach was facilitated by the high sensitivity of the ultrasensitive Doppler technique able to detect subtle hemodynamic changes due to the neurovascular coupling. These resuits suggested that combining microbubbles injections with ultrafast imaging may help to fully compensate for the attenuation from the skull. Indeed, by combining both, we preserved resolution and increased penetration depth. The injection of ultrasound contrast agents has also lead to outstanding resuits in ultrafast ultrasound imaging by breaking the diffraction barrier and move beyond the half-wavelength limit in resolution. We have demonstrated that cerebral microvessels of 9pm in diameter can me distinguished via ultrafast ultrasound localization microscopy (uULM). Millions of blinking sources were localized in space and in time in few seconds in a higher dimensional space, leading to super-resolved images (microbubble density map) of the whole rat brain with a spatial resolution of À/10. Moreover, a displacement vector allowed microbubbles-tracking within frames yielding to in-plane velocity measurements retrieving a large dynamic of cerebral blood velocities. Next, we have exploited how we can spatiotemporally control the vaporization of composite perfluorocarbon (PFC) microdroplets when their activation is triggered by short ultrasound pulses. The concept 'chemistry in-situ' is introduced as we have been able to control a spontaneous chemical reaction in-vitro. Moreover, a new microfluidic device in glass has been proposed to robustly produce monodisperse droplets for future in-vivo applications of the chemistry in situ. This new device presents 128-parallel generators with two pressurized rivers. Eventually, new ultrafast ultrasound monitoring sequences have been developed in order to control and monitor the release of composite droplets
Détection non destructive en cavité pour une horloge à réseau optique au strontium by Grégoire Vallet( Book )

2 editions published in 2018 in English and held by 2 WorldCat member libraries worldwide

Les travaux réalisés dans le cadre de cette thèse ont consisté en la réalisation d'un système de détection non destructif assisté par cavité d'atomes piégés sur réseau optique pour l'amélioration de la stabilité d'une horloge optique au strontium. La caractérisation de ce système dans son fonctionnement en régime classique, dans lequel les atomes piégés diffusent suffisamment peu de photons pour ne pas être expulsés du piège durant la détection, a mis en évidence des améliorations significatives en termes de rapport signal à bruit avec un gain d'un facteur cent en comparaison avec le système précédent de détection par fluorescence. Les gains en termes de stabilité par réduction de l'effet Dick restent cependant à concrétiser.Pour la réalisation du régime quantique, dans lequel moins d'un photon est diffusé par atome durant la détection, des idées nouvelles et des changements significatifs ont du être opérés sur le système et un travail théorique conséquent a été entrepris afin de déterminer la stratégie permettant une amélioration de la stabilité par réduction du bruit de projection quantique par mesure sans démolition de la cohérence de l'état interne atomique.J'y ai également aborder l'étude des effets des collisions chaudes des atomes de strontium piégés avec les particules du fond de vide résiduel, permettant une amélioration de l'exactitude de l'horloge. Cette thèse rapporte en particulier la première mesure expérimentale du déplacement de la fréquence de transition d'horloge due à ces collisions ainsi que son étude théorique
Biphoton Frequency-Correlations Engineering and Measurement with a Semiconductor Microcavity by Guillaume Boucher( Book )

2 editions published in 2016 in French and held by 2 WorldCat member libraries worldwide

This work is focused on the engineering and characterization of the frequency-time properties of photon pairs generated with a semiconductor source. This device emits photons propagating in opposite directions at telecom wavelengths using spontaneous parametric down-conversion at room temperature. A microcavity integrated in the source allows the resonance of the transverse pump beam, enhancing the efficiency of the nonlinear interaction. We give a theoretical description of the down-conversion process in the source and we show how the spatial and spectral properties of the pump beam impact the properties of the photons, in particular their degree of entanglement in frequency allowing a versatile engineering. The variety of states that can be produced is illustrated using the Joint Spectral Amplitude. Two techniques allowing the characterization of the Joint Spectral Intensity have been implemented. The first one is a single photon spectrograph. The second one, based on the stimulation of the down-conversion process showed a dramatic improvement in terms of resolution and integration time. Both techniques allowed the demonstration of the frequency correlation engineering by varying the waist and curvature radius of the pump beam. Examples of more exotic states and a technique to characterize their chronocyclic Wigner function are theoretically investigated. The relationship between time-frequency properties and degree of entanglement in polarization of the biphoton is also explored
Statistical physics of linear and bilinear inference problems = Physique statistique des problèmes d'inférence linéaire et bilinéaire by Christophe Schülke( Book )

2 editions published in 2016 in English and held by 2 WorldCat member libraries worldwide

The recent development of compressed sensing has led to spectacular advances in the under standing of sparse linear estimation problems as well as in algorithms to solve them. It has also triggered anew wave of developments in the related fields of generalized linear and bilinear inference problems. These problems have in common that they combine a linear mixing step and a nonlinear, probabilistic sensing step, producing indirect measurements of a signal of interest. Such a setting arises in problems such as medical or astronomical Imaging. The aim of this thesis is to propose efficient algorithms for this class of problems and to perform their theoretical analysis. To this end, it uses belief propagation, thanks to which high-dimensional distributions can be sampled efficiently, thus making a bayesian approach to inference tractable. The resulting algorithms undergo phase transitions that can be analyzed using the replica method, initially developed in statistical physics of disordered systems. The analysis reveals phases in which inference is easy, hard or impossible, corresponding to different energy landscapes of the problem. The main contributions of this thesis can be divided into three categories. First, the application of known algorithms to concrete problems : community detection, superposition codes and an innovative imaging system. Second, a new, efficient message-passing algorithm for blind sensor calibration, that could be used in signal processing for a large class of measurement systems. Third, a theoretical analysis of achievable performances in matrix compressed sensing and of instabilities in bayesian bilinear inference algorithms
Grandes déviations d'exposants de Lyapunov dans les systèmes étendus by Tanguy Laffargue( Book )

2 editions published in 2015 in French and held by 2 WorldCat member libraries worldwide

Lyapunov exponents are natural observables to quantify the chaoticity of a trajectory. They thus appear as good candidates to discriminate between different dynamical regimes, allowing to study phenomena such as the onset of turbulence which goes hand in hand with the emergence of chaotic trajectories in an otherwise regular flow--or the glass transition--which can be seen as a transition from diffusive dynamics to an arrested, frozen-in, and ergodicity-breaking regime. The present thesis strives to apply the thermodynamic formalism of Sinai, Ruelle and Bowen which transposes in trajectory space the language of equilibrium statistical physics--to fluctuations of Lyapunov exponents in spatially extended systems, for which only few results are available. We begin by presenting a numerical method to sample trajectories of atypical chaoticity in spatially extended systems, hence revealing their various dynamical structures. We also exhibit how this algorithm can be used to measure the dynamical free energy, opening the way for the study of dynamical phase transitions resulting from the possible coexistence of these structures. This method is in particular applied to the Fermi-Pasta-Ulam-Tsingou (FPU) chain of anharmonic oscillators. Next, we show how fluctuations of the largest Lyapunov exponent in systems of interacting particles with underlying diffusive dynamics can be analytically characterized. Carrying out this program allows us to establish interesting connections with damage spreading and reaction-diffusion processes
Strongly correlated photons in arrays of nonlinear cavities = Photons fortement corrélés dans des réseaux de cavités non-linéaires by Alexandre Le Boité( Book )

2 editions published in 2015 in English and held by 2 WorldCat member libraries worldwide

In recent years, the control of photon-photon interactions in optical nonlinear media has led to the realization of quantum fluids of light. One of the current challenges is to increase the strength of these interactions and enter the so-called strongly correlated regime. To achieve this goal, arrays of nonlinear cavities are a very promising candidate. In this thesis, theoretical results on arrays of nonlinear cavities described by a driven¬dissipative Bose-Hubbard model are presented. In particular, a general method to compute the mean-field phase diagram of this model is described. Due to the finite life time of photons, the system is intrinsically dissipative : cavity losses must be compensated by an external driving field. This nonequilibrium nature gives rise to interesting features, such as a transition between monostable and bistable phases induced by tunneling. In the limit of weak dissipation and weak driving, analytical results describing generalized Mott insulating phases are derived. These states survive up to a critical tunneling strength, above which a crossover to a classical coherent state takes place. Finally, the issue of how to go beyond the mean-field approximation is addressed by performing exact numerical simulations. Large arrays of cavities were simulated by implementing a new method specifically tailored for driven-dissipative systems
Ordres cachés et magnétisme étudiés par spectroscopie Raman en conditions extrêmes by Jonathan Buhot( Book )

2 editions published in 2015 in French and held by 2 WorldCat member libraries worldwide

Outre le magnétisme classique, de nouvelles phases électroniques, dites « exotiques », dont le paramètre d'ordre n'est pas clairement identifié, apparaissent parfois dans la matière à basse température et/ou sous pression. Cette thèse porte sur l'étude de ces ordres exotiques dans les matériaux URu2Si2 et PrRu4Sb12 et du magnétisme dans le composé multiférroïque BiFeO3 par spectroscopie Raman. Pour cela, nous avons développé un nouveau dispositif de spectroscopie Raman des excitations de très basses énergies (1meV) sous haute pression (20GPa) et à basse température (3K). Dans la skutterudite PrRu4P12, nous avons suivi l'évolution en pression des excitations de champ cristallin et des phonons jusqu'à 17 GPa. Nos résultats confirment le fait que la dynamique de réseau est un effet secondaire de la transition métal-isolant. En revanche, ils infirment les théories actuelles expliquant l'évolution de l'ordre électronique sous pression, basées sur un croisement de niveaux de champ cristallin. Ils pointent une possible présence de magnétisme sous pression. Le composé URu2Si2 a été étudié à pression ambiante et basse température. Nous observons de nouvelles signatures de la phase d'ordre caché, à savoir une excitation étroite et un gap de basse énergie, et ce, uniquement dans la symétrie A2g. L'étude de la réponse électronique et de la dynamique de réseau montre l'influence de l'anisotropie de la physique Kondo. Enfin, grâce à la combinaison de notre mesure Raman sous pression à température ambiante, d'une simulation numérique et d'un calcul théorique, nous proposons une compréhension globale du magnétisme de BiFeO3 à travers ses différentes phases structurales jusqu'à 12 GPa
Mécanique d'une cellule végétale isolée : contribution des éléments structuraux et comparaison avec une cellule animale by Pauline Durand( Book )

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

Les cellules végétales présentent une structure mécanique particulière : elles sont enchâssées dans une paroi rigide de cellulose et sont sous pression. Lorsqu'une cellule croît, la paroi doit se déformer et, en même temps, elle doit être assez rigide pour prévenir la cellule d'exploser sous l'effet de la pression. La capacité de la paroi à se déformer sans se rompre détermine le taux de croissance et donc le changement de forme chez les plantes. Lors de cette thèse, nous avons caractérisé les propriétés mécaniques de cellules végétales isolées. En particulier, nous avons étudié les contributions respectives de la pression et de la paroi dans la réponse mécanique des cellules. Il s'est avéré que la pression est principalement responsable des propriétés mécaniques à l'échelle globale d'une cellule végétale. Nous avons ensuite comparé ce résultat au comportement mécanique d'un ballon de football sous pression. La comparaison des résultats avec un modèle mécanique simple nous révélera que les cellules adaptent leur pression interne en fonction de celle de leur environnement. Ensuite, pour déterminer la réponse mécanique des cellules végétales indépendamment de la paroi cellulosique, nous avons réalisé des mesures sur des cellules privées de leur paroi (protoplastes). De façon surprenante, le comportement mécanique des protoplastes s'est avéré similaire à celui des cellules animales, malgré les différences structurales entre ces deux types de cellules. Ce comportement mécanique commun repose sur des éléments cytosquelettiques différents ce qui révèle une possible convergence évolutive
Études pour un résonateur optique à profil d'intensité plat et son application à l'interférométrie atomique by Nicolas Mielec( Book )

2 editions published in 2018 in French and held by 2 WorldCat member libraries worldwide

Inertials sensors based on atom interferometry use cold atom clouds cooled to micro-Kelvin temperatures and interrogation times of a few hundred of milliseconds.These conditions lead to an expansion of the atom clouds reaching centimetric sizes, which leads to difficulties when trying to adress them efficiently with gaussian laser beams.This work aims at developing different means to counteract the constraints brought by these gaussian beams and their limited intensity.Two main axes are explored.On the one hand, the intensity inhomogeneity of the interrogation beams has been adressed by the study, realisation and characterization of beamshaping solutions.One of these solutions has been adapted to an atom interferometry experiment, and its impact characterized.On the other hand, the current use of gaussian beams with centimetric sizes to interrogate as many atoms as possible brings constraints on the laser power.The idea of taking advantage of the optical gain of optical resonators rises in the field and constitutes the heart of this work.Different optical resonators concepts have been considered to allow the resonance of a large optical mode in a compact geometry.We built a degenerated optical resonator, with an intra-cavity lens, and studied the influence of misalignments and opticals defects on the resonance of large injected gaussian beams.These two devices and their combination open the way towards a generation of advanced atom interferometers, for precise experiments of fundamental physics or the development of compact cold atom inertial sensors
Spontaneous spin squeezing in a spinor Bose-Einstein condensate trapped on an atom chip by Théo Laudat( Book )

2 editions published in 2017 in French and held by 2 WorldCat member libraries worldwide

In this manuscript, we present an experimental study of spin squeezing in a spinor Bose-Einstein condensate of 87Rb, arising from a non-linear interaction originating from collisions between the two internal states |F = 1,mF = -1 > and |F = 2,mF = 1 > of the 5²S1/2 manifold. The atoms are cooled down in a magneto-optical trap and magnetically trapped thanks to our atom-chip which acts as a top wall for our vacuum cell. The chip is also used to emit the radio-frequency field that perform the evaporative cooling leading to Bose-Einstein condensation, and the microwave field used to coherently transfer the atoms from one internal state to another.The atomic ensemble in a coherent superposition is well described by the so-called textit{one-axis-twisting} Hamiltonian that contains a term quadratic in the z-component of the spin vector Sz. the strength of this non-linear interaction, initially very weak, depends on the intra- and inter-state s-wave scattering lengths, and can be greatly enhanced by reducing the wave-function spatial overlap between the two states. We therefore place the system in a configuration (high atom number and cigar-shaped trap) for which the two states experience spontaneous relative spatial separation and recombination phases. The impact of this spatial dynamics on the mean field interaction and coherence of the system is experimentally analyzed through the study of the contrast and central frequency of a Ramsey interferometer.Theoretically, when the two states are separated, the spin noise distribution evolves from a uniform circular distribution defined by the quantum projection noise, to an elliptic one whose small axis is smaller than the standard quantum limit, under the action of the Sz² interaction. This is verified experimentally by performing the tomography of the atomic state, when the two internal modes recombine. A squeezing parameter -1.3 dB is reached for 5000 atoms and a 90% contrast. The study of the different instability sources highlights the atomic-density-dependent losses as the main limitation for both the noise reduction and the contrast of the interferometer.This work has been initiated in the context of quantum metrology and represents a step towards the production of spin squeezed states enabling the realization of atom interferometers working below the standard quantum limit. It also addresses the fundamental question of coherence of spinor Bose-Einstein condensates undergoing many elastic and inelastic collisions
Etude expérimentale de gouttes nageuses : mécanismes physico-chimiques et hydrodynamiques = xperimental study of swimming droplets : physico-chemical and hydrodynamic mechanisms by Ziane Izri( Book )

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

The goal of this thesis work is to propose a propulsion mechanism that accounts for the swimming properties of water droplets with a diameter of tens of micrometers in a mixture of squalane and monoolein. As a matter of fact, with the right composition, these water droplets are able to swim along a distance much longer than their diameter, and for about two hours. Two main variants of this system have been studied in this work: one that hosts the Belouzov-Zhabotinsky reaction, another that is chemically passive. After stating the main notions and equations involved in the description of the motion of these droplets, the microfluidic experimental setup that satisfies very constraining specifications to produce these droplets will be presented. Then, for each of the two variants, the behavior of the swimming droplets will be described and confronted to a hydrodynamic model to account for their self-propulsion. The comparison of these two cases, and of their respective variants, will highlight the existence of two different mechanisms, both taking their roots in an inhomogeneity of surface energy, that is to say in the Marangoni effect
Optomécanique fibrée des disques GaAs : dissipation, amplification et non-linéarités by David Parrain( Book )

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

Cavity optomechanics is the field that studies reciprocal interactions between light and the mechanical degrees of freedom of an optical cavity. This optomechanical coupling allows us to precisely measure but also control a mechanical resonator displacement. This thesis work deals with the study of optomechanical effects in GaAs disks. These disks are both optical resonators supporting whispering gallery modes and mechanical resonators oscillating at frequencies as high as hundreds of MHz. Optomechanical interactions in these disks rest mainly on radiation pressure, electrostriction and photothermal effects. We formulate an analytical model describing the optomechanical coupling through those three vectors. We present the experimental setup used to probe optomechanical effects, highlighting the significant improvements brought during this thesis. Samples and tapered fiber fabrication techniques are described as well as Brownian motion measurements. In order to improve our device performance, we investigated optical and mechanical dissipation channels. These studies, by allowing a better understanding of the system, pave the way to further improvements. Finally, we present the self-oscillation regime of the optomechanical resonator, a regime achieved thanks to technical improvements in the setup. At high optical power, a new nonlinear phenomenon appears, called self-modulation of the self-oscillation, involving free carriers dynamics, created by two photon absorption
 
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Alternative Names
École doctorale 564

École doctorale Physique de l'Ile de France

École doctorale PIF

ED 564

ED Physique en Île-de-France

ED PIF

ED564

Physique en Île-de-France

PIF

Languages
French (25)

English (14)