ED Sciences Physiques et de l'Ingénieur
Optically active 1D heterostructures based on organic molecules ordered inside dielectric nanotubes
by Jean-Baptiste MARCEAU (Laboratoire Photonique, Numérique & Nanosciences)
The defense will take place at 14h00 - Amphithéâtre Rue François Mitterrand, IOGS, 33400, Talence
in front of the jury composed of
- Etienne GAUFRES - Chargé de recherche - Université de Bordeaux - Directeur de these
- Laurent ALVAREZ - Professeur des universités - Laboratoire Charles Coulomb, CNRS, Université de Montpellier - Rapporteur
- Philippe PONCHARAL - Professeur des universités - Institut Lumière Matière, CNRS, Université Lyon I - Rapporteur
- Aloyse DEGIRON - Directeur de recherche - Laboratoire Matériaux et Phénomènes Quantiques, CNRS, Université Paris Cité - Examinateur
- Laëtitia MARTY - Chargée de recherche - Institut Néel, CNRS, Université Grenoble Alpes - Examinateur
Organic dyes (0D objects) are promising materials for various optical applications because of their intense light emission. However, they remain particularly sensitive to their chemical, dielectric and mechanical environment, which leads to instabilities in their structure and organisation, as well as strong disruption of their radiative channels. Among the many directions of research to stabilise organic dyes, one innovative strategy (2016-2020) is to encapsulate these emitting molecules in boron nitride nanotubes (BNNTs). The latter acts as a dielectric sheath that guarantees chemical protection, 1D alignment and a dielectric environment due to their crystallinity and large optical gap (>5.5eV). The main objective of this thesis was to measure and understand the impact of 1D confinement of one or more types of molecules encapsulated in BNNTs on the optical properties of Mol@BNNT systems. We therefore studied the fluorescence properties of Mol@BNNTs in the spectral, time and polarisation domains as a function of their composition. Mol@BNNTs were studied using three complementary types of sample: individual Mol@BNNTs on substrates, transparent polymer films containing Mol@BNNTs or a dispersion of Mol@BNNTs in organic or aqueous solvents. The first, bibliographical, chapter describes boron nitride nanotubes (BNNTs) and their specific features compared with other low-dimensional 1D and 2D materials. The second part deals with light-matter interaction in low-dimensional materials. Finally, the state of the art concerning the encapsulation of molecules in nanotubes, and more specifically in BNNTs, is presented. The second chapter describes the optical characterisation techniques used and the sample preparation protocols. Chapter 3 addresses the question of the impact of the organisation of α-sexithiophene molecules confined in BNNTs on their optical properties, in particular through the study of the polarisation of their fluorescence. Chapter 4 presents the different strategies explored during the thesis to modulate, post-encapsulation, the fluorescence signal of 6T@BNNTs along the axis of a BNNT. The first part is devoted to the origins of a post-encapsulation diffusion mechanism induced by the mechanical deformation of 6T@BNNTs. The second part examines the possibility of locally quenching fluorescence along a Mol@BNNT or a carpet of Mol@BNNTs by a photo-induced mechanism. Chapter 5 looks at the characterisation of the time-resolved fluorescence of these nanohybrids. These results initially led to the observation of a surprising decrease in the fluorescence lifetime of 6T molecules in BNNTs. This led us to study the dipolar interaction of single molecules as a function of their distance within BNNTs and to highlight a strong superradiance signature in these systems.
ED Sciences et environnements
Top-down control of birds on insect herbivory in trees: effects of climate and urbanisation at multiple scales
by Laura SCHILLE (BIOGECO - BIOdiversité, Gènes & Communautés)
The defense will take place at 14h30 - Airial - salle des chênaies INRAE – Institut National de la Recherche Agronomique UMR 1202 – Biodiversité, Gènes et Ecosystèmes Site de Recherches Forêt Bois de Pierroton – Domaine de l'Hermitage 69, route d'Arcachon 33612 CESTAS Cedex France
in front of the jury composed of
- Bastien CASTAGNEYROL - Directrice de recherche - Université de Bordeaux - Directeur de these
- Luc BARBARO - Chargé de recherche - INRAE, UMR DYNAFOR - CoDirecteur de these
- Emmanuelle PORCHER - Professeure des universités - Muséum National d'Histoire Naturelle, Paris - Rapporteur
- Nathalie MACHON - Professeure des universités - Muséum national d'Histoire naturelle, Paris - Rapporteur
- Kevin DARRAS - Chargé de recherche - INRAE, UR EFNO - Examinateur
Insectivorous birds actively contribute to the regulation of herbivorous insect populations, thus playing a key role in terrestrial ecosystem dynamics. The theory suggests that bird community diversity covaries with the number of functions they perform, as communities that are more diverse explore broader functional spaces and utilize available resources more effectively. However, global changes might alter this relationship. The question then becomes whether these changes affect the structure of bird communities and their associated functions in the same way, or if these variables respond differently. Additionally, biogeographical patterns may be locally altered by biotic and abiotic factors. Thus, this combination of factors operating at different scales can modify the tri-trophic cascade, acting independently, antagonistically, or synergistically on bird communities, herbivore communities, and the characteristics of the trees they feed on. The main objective of this thesis was to explore the effects of increasing temperatures and urbanization, in interaction with local factors such as the quantity and diversity of forest habitats, on the relationship between diversity and predation function of insectivorous birds. To this end, we worked at multiple nested scales, from the tree and its immediate surroundings to the continental scale. We employed innovative methods based on acoustic ecology, citizen science, and automated recognition algorithms to characterize bird communities in a standardized and large-scale manner, and we developed experimental approaches to assess the reproducibility of these methods. Our results indicate that increasing temperatures and urbanization have significant impacts—positive and negative, respectively—on the taxonomic and functional diversity of insectivorous bird communities. However, we observed a decoupling between community structure and associated ecosystem functions in response to these changes. This suggests a need to reconsider the general applicability of the theory linking community diversity to the number of functions they perform. Furthermore, the quantity and diversity of forest habitats are local factors that modulate the effects of climate and urban factors, which structure bird communities and the tri-trophic cascades they initiate on a larger scale. Finally, our work has contributed to advancing methods for studying biodiversity dynamics and its functions.
ED Sociétés, Politique, Santé Publique
Scaling up complex public health interventions - conceptual and methodological aspects
by Nolwenn STEVENS (Bordeaux Population Health Research Center)
The defense will take place at 9h30 - à venir Site Universitaire de la Victoire Université de Bordeaux 3 ter place de la Victoire 33000 Bordeaux
in front of the jury composed of
- François ALLA - Professeur des universités - praticien hospitalier - Université de Bordeaux - Directeur de these
- Cyrille DELPIERRE - Directeur de recherche - Inserm, Université de Toulouse - Rapporteur
- Isabelle AUJOULAT - Professeur des universités - Université Catholique de Louvain - Rapporteur
- Henri BERGERON - Directeur de recherche - CNRS Science Po - CoDirecteur de these
- Linda CAMBON - Titulaire chaire prévention - Université de Bordeaux - Examinateur
- Aurore MARGAT - Maîtresse de conférences - Université Sorbonne Paris-Nord - Examinateur
Politicians, researchers and stakeholders all share a desire to mobilise evidence to build public health policy. This strategy is motivated by a desire for equity, a duty to ensure safety and effectiveness, and a need to make rational use of resources. Scaling up interventions would be the way to achieve this strategy. However, this is not easy. It is necessary to mark out and secure this path so that scaling up is no longer a risky gamble. This is the ambition we have pursued in this thesis. Our research was guided by four main questions: What do we mean by 'scaling up'? How do we scale up? How can it be made safe? What challenges does population health intervention research face in terms of scaling up? All these questions are limited to the case of complex population-based interventions. To meet our objectives, we conducted two successive studies. We carried out a review of the international literature on conceptual frameworks and models, guides and tools developed for scaling up public health interventions. We then conducted semi-structured interviews with a variety of stakeholders who had experience of scaling up a public health intervention in the French context, with the aim of gathering their experiences and perceptions of the process. Our research has enabled us to shed light on the very concept of scaling up, and to propose a definition. In addition, we propose to consider it as a composite concept, incorporating those of implementation, dissemination and sustainability. It has also made it possible to describe the range of strategies that can be adopted to deploy it, whether these concern: i) the territorial expansion of the intervention, ii) the sustainability of the intervention, and finally iii) its relevance to reality. In addition, this process is supported by organisational approaches that enable the dynamic to be set in motion and a set of eight essential activities. Finally, a set of conditions will have to be collected, and certain obstacles will have to be avoided. The literature has identified 30 levers and 28 obstacles to scaling up. Among these, the testimonies of experimenters have highlighted 6 catalyst factors and 6 inhibitors, enabling us to develop and detail the most fundamental conditions influencing the process. Finally, our research proposes to demystify evidence-based intervention but to encourage the adoption of evidence-based approaches. It also suggests considering evidence that is useful, plural, relative and grounded. Questions relating to the generalisability of results, intrinsically linked to the ambition of scaling up, require further exploration. Recognition of the identity of the intervention, linked to what underpins its effectiveness, is an imperative that needs to be consolidated methodologically. As announced by the expression "science of solutions", we suggest that we take our academic vision beyond interventions and transform the knowledge gained from intervention research into substrates that enable the emergence of solutions adapted to the issues and situations at stake. Finally, embarking on a policy of scaling up interventions would also require: greater transparency in the process of selecting interventions, a redirection of funding from leadership to support services and activities, and the introduction of monitoring systems. The identification or creation of expert resource structures to support the various stakeholders in this complex process could be a great help.