ED Sciences Chimiques
Thermal-gradient CVI to increase CMC density
by Natacha BESSOUET (Laboratoire des Composites ThermoStructuraux)
The defense will take place at 14h00 - Amphithéâtre - LCTS LCTS – 3, Allée La Boétie – Domaine Universitaire – 33600 PESSAC – France
in front of the jury composed of
- Sylvain JACQUES - Chargé de recherche - Laboratoire des Composites Thermostructuraux - Directeur de these
- Gérard-Louis VIGNOLES - Professeur des universités - Laboratoire des Composites Thermostructuraux - CoDirecteur de these
- Frédéric SANCHETTE - Professeur des universités - Université de Technologie de Troyes - Rapporteur
- Gabriel FERRO - Directeur de recherche - Laboratoire des Multimatériaux et Interfaces, CNRS - Rapporteur
- Didier CHAUSSENDE - Directeur de recherche - Laboratoire Science et Ingénierie des Matériaux et Procédés - Examinateur
- René FOURNET - Professeur des universités - Laboratoire Réactions et Génie des Procédés - Examinateur
In the current economic and ecological context, the aeronautics and space sector has been interested for several years in alternatives to nickel or cobalt-based superalloys, which constitute the most mechanically stressed engine parts under high temperatures and oxidizing environments. SiC/SiC ceramic matrix composites are promising materials to meet the requirements of applications with temperatures above 1480 °C (2700F material range) in aircraft engines. The gas route allows control of the matrix purity during its synthesis. However, the reference process under isothermal/isobaric conditions (I-CVI) currently does not allow obtaining materials with porosity below 10-15 %. This work therefore focuses on an alternative process involving a temperature gradient (TG-CVI) in a next-generation reactor in order to control the localization of chemical reactions. This process theoretically allows the appearance of a densification front phenomenon and results in a dense and homogeneous matrix. The chemistry of the silicon carbide precursor, MethylTrichloroSilane (MTS), was studied on various model substrates (1D model pores, 3D isotropic woven preforms, and industrial woven preforms) in TG-CVI. The composition and microstructure of the deposits were studied using various analytical techniques (SEM, TEM, Raman Spectroscopy). Extended densification tests experimentally demonstrated the progression of a densification front and defined its characteristics. These results were compared with analytical models and used to inform numerical simulations.
ED Droit
A paradoxical re-enchantment of salvation in a doomed world? The post-secular dimensions of the conversion trajectories of ecological virtuosos.
by Gauthier SIMON (INSTITUT DE RECHERCHE MONTESQUIEU)
The defense will take place at 14h00 - 1K Pôle Juridique et Judiciaire 35, place Pey Berland Bordeaux 33000
in front of the jury composed of
- Yann RAISON DU CLEUZIOU - Professeur des universités - Université de Bordeaux - Directeur de these
- Sylvie OLLITRAULT - Directrice de recherche - École des hautes études en santé publique - Rapporteur
- Bruno VILLALBA - Professeur des universités - AgroParisTech - Rapporteur
- Jean-Michel EYMERI-DOUZANS - Professeur des universités - Sciences Po Toulouse - Examinateur
- Camille MAZé-LAMBRECHTS - Directrice de recherche - Sciences Po Paris - Examinateur
- Xabier ITçAINA - Directeur de recherche - Sciences Po Bordeaux - Examinateur
This thesis aims to demonstrate that, to analyse the trajectories of ecological conversion, the sociology of religion is heuristic, complementing traditional approaches in political science. Dramatized by the category of the Anthropocene, which confronts humanity with the prospect of its own demise, the ecological emergency demands conversion, with individual and collective salvation at stake. The ecological question is reconfiguring politics, restoring eschatological, even apocalyptic dimensions that had disappeared with the advent of liberal democracy. Analysing the conversion trajectories of ecological virtuosos allows us to study this reconfiguration. To this end, it is heuristic to give central importance to the categories of analysis used in the sociology of religion, which are often marginalised in the sociology of mobilisation. The thesis is that, to think about ecological conversion, the reference to religion must not remain a mere metaphorical register but must be honoured as a strong epistemological proposition. Drawing on Weberian sociology of religion, this work sets out to reveal the post-secular dimensions of the practical and ethical problems raised by conversion. Empirically, it is based on non-directive interviews with ‘virtuosos' of ecology (elected officials, association members, senior civil servants, civil disobedience activists). Their world is structured by dynamics and conflicts that were long those of the Churches. Conversion thus stems from an urgency of existence, which must be constantly reactivated against the erosion of everyday life. Its intensity depends on the depth of awareness of anthropogenic ‘evil,' from which liberation is a struggle with personal and collective horizons. Ecology appears as a regime of truth from which soteriology and ascetic paths are organised. The transformation of one's relationship with oneself can only succeed through the transformation of society by proselytism, the modalities of which remain problematic insofar as the social image of the convert may be compromised. Finally, the world of converts is caught between elitist necessities and democratic aspirations, which replay the rivalry between sect and Church described by Troeltsch. The analytical contribution of the sociology of religion to the political science of ecology is not to reduce ecology to religion, but to highlight the post-secular dimensions involved in the praxis of conversion, which can only be identified through analogy. Through its post-secular dimensions, the ecological conversion of these virtuosos contributes to a paradoxical re-enchantment of a world threatened by the end.
ED Sciences Physiques et de l'Ingénieur
Diffusion properties of carbon nanotubes within tortuous and biological environments
by Quentin GRESIL (Laboratoire Photonique, Numérique & Nanosciences)
The defense will take place at 14h00 - Amphithéâtre Ducasse Institut d'Optique d'Aquitaine Rue François Mitterrand – FR 33400 Talence
in front of the jury composed of
- Laurent COGNET - Directeur de recherche - Université de Bordeaux - Directeur de these
- Sebastian KRUSS - Professeur - Ruhr-University Bochum - Rapporteur
- Raphaël VOITURIEZ - Directeur de recherche - CNRS - Laboratoire Jean Perrin - Rapporteur
- Aleksandra RADENOVIC - Professeure - EPFL - Laboratory of Nanoscale Biology - Examinateur
- Thomas SALEZ - Directeur de recherche - CNRS - Laboratoire Ondes et Matière d'Aquitaine (LOMA) - Examinateur
The brain's extracellular space (ECS) is a network of narrow clefts between neurons, glia, and blood vessels, accounting for about one-fifth of brain volume in healthy tissue. This fluid-filled compartment is essential for molecular transport, signalling, and homeostasis. It contains interstitial fluid (ISF) and a structural scaffold provided by the extracellular matrix (ECM). Despite decades of study, a full quantitative description remains elusive. Ensemble measurements of small-ion diffusion have shown that transport in the ECS is slowed two- to threefold compared to free solution. Yet such bulk approaches cannot pinpoint whether this hindrance arises from cellular geometry, ECM organisation, or transient molecular interactions. Single-particle tracking (SPT) offers a way to bridge this gap. By following fluorescent nanoparticles with nanometric precision and video-rate resolution, SPT exposes local heterogeneities invisible to ensemble averaging. A landmark study by Godin et al. introduced single-walled carbon nanotubes (SWCNTs) as near-infrared, photostable probes for SPT in brain tissue, showing that nanoscale trajectories could be recorded deep within scattering tissue. Later studies extended SPT to other tracers and experimental conditions, often contrasting control and pathology. While these provided valuable insights, they remained self-contained, leaving a patchwork of results—sometimes at odds with ensemble measurements and difficult to reconcile across probes. This thesis is motivated by filling this gap. By using novel ultra-short carbon nanotubes (uCCNTs) as tracers better matched to ECS dimensions, and combining them with three-dimensional tracking, it develops an experimental platform tailored to the nanoscale geometry of the ECS. Analytically, it adopts statistical tools from anomalous diffusion studies in membranes and cytoplasm, offering a more rigorous characterisation than conventional MSD fits. These methods allow the contributions of confinement, ECM organisation, and transient interactions to be disentangled. The results show that ECS diffusion is heterogeneous and often anomalous. At short timescales tracer motion is Brownian, but over longer intervals cellular boundaries drive a crossover to non-linear dynamics. Within this landscape, hyaluronan emerges as a key regulator: its depletion tightens local widths and hinders transport, underscoring its role as a buffer that preserves typical ECS dimensions. By integrating these insights, the thesis advances a unified view of extracellular transport that links single-trajectory statistics with structural determinants of the ECS. Beyond local transport, a key question is whether clearance from the ECS relies solely on diffusion or also involves active pathways. This distinction is central to understanding how the brain eliminates metabolites, aggregates, and therapeutic agents, with direct implications for the glymphatic system. To address this, we implemented gradient-index (GRIN) lens–based imaging for in-vivo single-particle tracking, extending nanoscale diffusion measurements from slices into the intact brain. This approach enables visualisation of tracer motion under conditions closer to physiology and provides a first step toward disentangling which mechanisms can drive clearance in the brain ECS.
theoretical modelling of infinite-layer nickelates
by Alpesh Rasikbhai SHETH (Laboratoire Ondes et Matière d'Aquitaine)
The defense will take place at 14h00 - Amphi C Bâtiment A29 University of Bordeaux - Talence Campus 33400 Talence, France
in front of the jury composed of
- Sébastien BURDIN - Professor - Université de Bordeaux - Directeur de these
- Alain PAUTRAT - Directeur de recherche - CRISMAT,Caen - Rapporteur
- Luca DE'MEDICI - Professeur - ESPCI,Paris - Rapporteur
- Lucia IGLESIAS - Chargée de recherche - Unité Mixte de Physique CNRS/Thales Laboratory,Palaiseau - Examinateur
- Gertrud ZWICKNAGL - Professeure - T.U.Braunschweig, Braunschweig, Germany - Examinateur
This thesis provides a comprehensive theoretical investigation into the electronic properties of infinite-layer nickelates (RNiO2), with a focus on understanding their similarities to and differences from high-Tc Cuprates and perovskite Nickelates. In the first part, we developed a multi-orbital theoretical framework to model the transition from perovskite RNiO3 to infinite-layer RNiO2. Our analysis confirms that the low-energy physics of infinite-layer nickelates is dominated by the Ni-3dx2−y2 and Ni-3dz2 orbitals, along with a significant contribution from the extended rare-earth 5d orbitals. We show that, unlike Cuprates, infinite-layer nickelates possess a tunable, rare-earth-derived Fermi surface pocket that acts as an electron reservoir. This self-doping band hybridizes with the NiO2 planes, thereby screening Ni magnetic moments and altering localization tendencies. By downfolding this framework into an effective two-orbital model, we calculated the Lindhard susceptibility and found strong electronic fluctuations with a peak at the antiferromagnetic wave vector q=(π,π). This indicates that nesting effects, similar to those in Cuprates, drive robust antiferromagnetic and charge-order tendencies. In the second part, we explored the effects of extrinsic impurities, such as remnant apical Oxygens and alkaline-earth dopants, on the electronic structure. Using a T-matrix scattering formalism, we demonstrated that these defects can serve as intrinsic probes of the multi-band structure. Our real-space calculations of impurity-induced Friedel oscillations reveal distinct spatial patterns that depend on the underlying Fermi surface geometry. We show that an apical-Oxygen defect generates oscillations whose patterns can be used to unambiguously detect the presence of the secondary rare-earth pocket. In contrast, alkaline-earth substitution, which primarily affects the Ni-derived band, produces patterns from a single pocket. This demonstrates that impurity scattering can be tuned to selectively probe different Fermi surface features, providing experimentalists with a powerful diagnostic tool for mapping the complex electronic landscape of infinite-layer nickelates. Keywords: Infinite-layer Nickelates (RNiO2), Fermi-surface, Instabilities, Friedel oscillations.