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Facteurs environnementaux et individuels de la migration saisonnière chez le bouquetin des Alpes
No full textMigration is a critical movement tactic allowing animals to cope with seasonal and predictable variations of their environment. Hence, migration plays a key role in individual performance, demography and distribution of migratory species, and ecosystem functioning. Understanding the causes and consequences of these movements and how they can vary according to individual differences is therefore crucial as migratory behaviours have largely regressed at a global scale due to ongoing environmental changes. Throughout this thesis, I investigated the environmental and individual drivers of partial migration in a mountain and emblematic ungulate, the Alpine ibex Capra ibex. Using GPS data from 17 ibex populations monitored across the Alps, I studied the effects of spatial and temporal variations in environmental conditions, very marked in alpine environments, as well as the importance of pronounced life-history trait differences between sexes and individual ibex to explain individuals’ choice to migrate, their timing of migration, and migration corridors used within populations. In a first time, a comparative analysis of habitat selection during migration revealed common drivers among ibex populations that we used to build a model able to predict migration routes. Minimising energy expenditure while looking for safety and forage is the main driver of migration corridors. This trade-off in habitat selection highlights that migration can be a costly and risky movement and, as such, an individual’s choice to migrate should result from a costs/benefits balance that depends both on environmental conditions and individual characteristics. Thus, in a second time, we showed that the choice to migrate in male ibex varies between years, their propensity to migrate increasing when vegetation dynamics lead to a better access to high-quality vegetation for migrant individuals. Although it is also true for female ibex at the population scale, their migratory behaviour turned out to depend on another major event within their annual cycle: reproduction. In spring, females migrate more when their parturition date is late compared to vegetation phenology, allowing them to increase their access to high quality resources during the period following parturition. Consequently, contrary to males that migrate when the peak of green-up is reached on their winter range, migration timing in females is related to the peak of green-up but also constrained by parturition timing, particularly when females migrate after parturition. In autumn, migration departure varies according to weather conditions, males and females leaving their summer ranges after onset of snow cover, ending the access to vegetation. By leading to a better understanding of migratory behaviours in the species and its plasticity, and highlighting the importance of these movements, this work also contributed to set the foundations of the first European scientific collaboration around ibex and allowed the species to be included in the first world atlas of ungulate migrations. The results of this thesis highlight that ongoing environmental changes, in particular rapid climate warming in the Alps, will lead to changes in migratory behaviours of ibex, which raises questions on the potential consequences at broader scales, on population demography, individual flows between populations, and on the functioning of alpine ecosystems.La migration est une tactique de déplacement essentielle permettant aux animaux de répondre aux variations saisonnières et prévisibles de leur environnement. Elle joue donc un rôle clé dans la performance des individus, la démographie et la distribution des espèces migratrices, et le fonctionnement des écosystèmes. Comprendre les causes et conséquences de ces déplacements et comment celles-ci varient en fonction des différences propres à chaque individu est donc un enjeu crucial dans un contexte où les comportements migratoires sont fortement impactés par les changements globaux. Au cours de cette thèse, je me suis intéressé aux facteurs environnementaux et individuels déterminant la migration partielle chez un ongulé de montagne emblématique et à enjeux de conservation, le bouquetin des Alpes Capra ibex. Grâce aux suivis GPS de 17 populations de bouquetins sur l’ensemble de l’arc alpin, j’ai pu étudier l’effet des variations spatiales et temporelles des conditions environnementales, très marquées en milieu alpin, mais aussi le rôle des différences de traits d’histoire de vie prononcées entre sexes et entre individus, pour expliquer le choix des individus de migrer, la phénologie de la migration et les couloirs de migration empruntés au sein des populations. Dans un premier temps, l’analyse de la sélection de l’habitat durant la migration a permis de mettre en évidence des caractéristiques communes à l’échelle des populations et d’établir un modèle pour prédire les couloirs de migration. Le compromis entre dépense énergétique, recherche de nourriture et sécurité est apparu comme le facteur majeur qui détermine les couloirs de migration. Ce compromis dans la sélection de l’habitat souligne que la migration reste un déplacement potentiellement coûteux et risqué. De fait, le choix de migrer pour un individu devrait dépendre d’un rapport coûts/bénéfices qui peut varier en fonction des conditions environnementales mais aussi de caractéristiques individuelles. Dans un deuxième temps, nous avons ainsi mis en évidence que le choix de migrer chez les bouquetins mâles variait entre années, leur propension à migrer augmentant lorsque la dynamique de pousse de la végétation permet un meilleur accès à la végétation de qualité pour les individus migrateurs. Bien que cela soit aussi vrai à l’échelle de la population pour les femelles, leur comportement de migration s’est révélé plus contraint car dépendant d’un autre événement majeur au sein du cycle annuel : la reproduction. Au printemps, les femelles migrent lorsque la date de la mise-bas est plus tardive par rapport à la phénologie de la végétation, ce qui leur permet d’augmenter leur accès aux ressources de qualité durant la période qui suit la mise-bas. Par conséquent, contrairement aux mâles dont le départ en migration est synchronisé avec le pic de croissance de la végétation, le départ en migration des femelles est à la fois lié à ce pic de disponibilité des ressources mais aussi dépendant de la date de mise-bas, d’autant plus si les celles-ci migrent après la naissance du cabri. À l’automne, le départ en migration dépend de l’installation du manteau neigeux qui privent mâles et femelles de l’accès à la végétation. En apportant une meilleure compréhension des comportements de migration chez cette espèce et de leur plasticité, et en soulignant l’importance de ces déplacements, ce travail aura aussi permis de faire émerger une collaboration scientifique européenne autour du bouquetin des Alpes et d’intégrer l’espèce au premier atlas mondial des migrations d’ongulés. Les résultats de cette thèse laissent présager que les changements globaux en cours, notamment le réchauffement climatique accentué en milieu alpin, modifieront les comportements des bouquetins, et questionnent donc les potentielles conséquences, à plus larges échelles, sur la démographie et les flux entre populations, et le fonctionnement des écosystèmes alpins
Image‐based robotics enhance precision and efficiency in lateral UKA: A comparative study of 135 UKAs
No full textInternational audiencePurpose : Robotic‐assisted lateral unicompartmental knee arthroplasty (UKA) remains technically demanding due to the complex biomechanics of the lateral compartment. Image‐based (IBRA) and imageless (ILRA) robotic systems have both demonstrated superior accuracy compared to conventional mechanical instrumentation, but have not yet been directly compared in lateral UKA. This study aimed to evaluate their respective accuracy and surgical efficiency. Methods This retrospective study included 135 patients who underwent lateral UKA using either IBRA or ILRA systems. Post‐operative radiographic outcomes included hip–knee–ankle (HKA) alignment, posterior tibial slope (PTS) and joint line (JL) restoration. Surgical time was assessed as a secondary outcome. Target zones were HKA 180°–185°, PTS 2°–8° and JL ± 2 mm. Results IBRA showed higher rates of HKA inliers (94.9% vs. 78.9%, p = 0.011) and JL restoration (76.2% vs. 31.6%, p < 0.001) compared to ILRA. PTS accuracy was similar between groups ( p = 0.30). Operative time was significantly shorter with IBRA (61.6 ± 13.5 vs. 81.9 ± 26.1 min, p < 0.001). Conclusion IBRA outperformed ILRA in terms of alignment accuracy and surgical duration. These findings support the added value of IBRA systems in lateral UKA. Level of Evidence Level IV, retrospective case series study
Reduced fidelities for free fermions out of equilibrium: From dynamical quantum phase transitions to Mpemba effect
No full textInternational audienceWe investigate the out-of-equilibrium dynamics after a quantum quench of the reduced fidelities between the states of a subregion at different times. Precisely, we consider the fidelity between the time-dependent state of and its initial value, as well as with the state at infinite time. We denote these fidelities as the reduced Loschmidt echo (RLE) and the final-state fidelity (FSF), respectively. If region is the full systems, the RLE coincide with the standard Loschmidt echo. We focus on quenches from Gaussian states in several instances of the XY spin chain. In the hydrodynamic limit of long times and large sizes of , with their ratio fixed, the reduced fidelities admit a quasiparticle picture interpretation. Interestingly, for some quenches in the hydrodynamic regime the RLE features a complicated structure with an infinite sequence of nested lightcones, corresponding to quasiparticles with arbitrary large group velocities. This leads to a ''staircase'' of cusp-like singularities in the time-derivative of the fidelity. At the sub-hydrodynamic regime for some quenches the RLE exhibits cusp-like singularities, similar to the so-called dynamical quantum phase transitions (DQPT). We conjecture a criterion for the occurrence of the DQPT and for the ''critical'' times at which the singularities occur. Finally, we discuss the hydrodynamic limit of the FSF. In particular, we show that it provides a valuable tool to detect the so-called quantum Mpemba effect
RED LIGHTS ON GREEN HYDROGEN: THE CASE OF HYPHEN GREEN HYDROGEN DEVELOPMENT IN THE TSAU ||KHAEB NATIONAL PARK
No full textInternational audienceTo reach the net-zero emissions goal by 2050, many nations have identified hydrogen as a key solution. In its green form, produced from renewable energy sources, hydrogen could contribute significantly to decarbonizing society. However, significant challenges remain: less than 1% of hydrogen produced globally is currently green. Estimations from the International Energy Agency suggest global demand could increase from 97 million tons to 400 million tons by 2050. Therefore, meeting decarbonization targets will require large-scale projects of green hydrogen development. This large-scale production of green hydrogen requires vast areas exposed to strong and steady wind and/or high solar radiations to produce hydrogen from renewables. Despite being among the highest consumers of hydrogen, European, Korean, or Japanese territories do not have enough territorial resources. As a result, numerous territories in Africa and Latin America are being identified as strategic locations to support the projected global surge in demand for green hydrogen, particularly for applications in road and maritime transport as well as industrial processes. This presentation examines a case in Namibia, where 20,000 km² of a southwestern national park have been allocated for the development of a global green hydrogen hub. Drawing on reports and semi-structured interviews from a fieldwork in 2025, this study explores the creation of such ex-nihilo energy territories, focusing on stakeholders’ interplays and power dynamics. Through the controversies it generates, the project reveals the environmental impact of the massive infrastructure required to meet global green hydrogen demand. The local analysis will be complemented by a reflection on the integration of this project into national networks, as well as on the dynamics that may be considered neocolonial in nature. In this context, the narratives of energy transition will be critically analyzed through the lens of a just transition
Les émotions positives et le sens de la vie
No full textThis dissertation aims to explore the role of positive emotions in the feeling of meaning in life. Although the idea that giving meaning to one's own life may contribute to well-being is intuitive, the literature often distinguishes between psychological well-being and life's meaning. On the one hand, well-being is often defined in terms of satisfaction and positive mood. On the other hand, meaning in life is generally linked to objective elements, such as making a positive contribution to the world. For example, a dissatisfied cardiothoracic surgeon is still considered to have a meaningful life, while a person who is constantly in a good mood but pursuing no significant goal would be seen as having a life devoid of meaning.However, despite the straightforward division between psychological and objective elements of the good life, mixed theories on the meaning of life have sparked researchers' interest in defending the view that for life to be meaningful, significant activities must be accompanied by a positive feeling. Meaning in life is no longer constituted solely by objective elements; it also requires the subjective element of experiencing positive affects. This, however, presents a challenge: if pursuing an important goal generates pleasure, this could reduce the goal to a mere means of obtaining hedonic gratification, making the life of a surgeon who derives satisfaction from her work seem similar to that of a person whose sole aim is to have fun.My project draws on the psychology of emotions to show that the positive emotions related to playful activities differ from those associated with meaningful activities. More specifically, I focus on the distinction between self-centred positive emotions and self-transcendent positive emotions. While this distinction has been extensively theorized in positive psychology, it remains underexplored empirically.The first part of my experimental research aims to test this distinction and demonstrate that self-transcendent emotions differ from self-centred emotions in their ability to generate a feeling of meaning in life. This part of my dissertation focuses on creating a taxonomy of positive emotions based on subjective experience. Indeed, my results show that self-transcendent positive emotions can be distinguished into two different families of emotions, Social and Epistemic. I then examine how different families of positive emotions vary according to contexts — sensory pleasure vs. pursuit of important goals — and explore their connection with the sense of meaning in life. My findings suggest that only one of the two families of self-transcendent emotions, the Social family, is linked to the sense that life is meaningful. Finally, I explore how belonging to a social group can trigger this feeling, identifying the specific emotions tied to this experience.Cette thèse explore le rôle des émotions positives dans le sentiment que la vie a un sens. Bien que l'idée que donner un sens à sa propre vie contribue au bien-être soit intuitive, la littérature distingue souvent le bien-être psychologique du sens de la vie. De plus, le bien-être est défini en termes de satisfaction et d'humeur positive tandis que le sens de la vie est généralement défini par des éléments objectifs, comme apporter une contribution positive au monde. Par exemple, un chirurgien cardiothoracique insatisfait est souvent perçu comme ayant une vie pleine de sens, tandis qu'une personne constamment de bonne humeur mais dépourvue d'objectifs significatifs est généralement considérée comme ayant une vie sans véritable sens.Cependant, malgré cette distinction entre les éléments psychologiques et objectifs qui composent « la vie bonne », les théories mixtes sur le sens de la vie défendent l'idée que, pour qu'une vie ait un sens, les activités significatives doivent s'accompagner d'expériences affectives positives. Le sens de la vie ne repose plus uniquement sur des critères objectifs : il incorpore également un aspect subjectif, à savoir le vécu émotionnel positif. Cela soulève néanmoins un défi : si la poursuite d’un objectif important génère du plaisir, cet objectif pourrait être réduit à un simple moyen d’obtenir une gratification hédonique. Par exemple, la vie d’un chirurgien qui tire de la satisfaction de son travail pourrait alors paraître similaire à celle d’une personne dont le seul but est de s’amuser.Mon projet s’appuie sur la psychologie des émotions pour montrer que les émotions positives associées aux activités ludiques diffèrent de celles qui accompagnent des activités significatives. Plus précisément, je m’intéresse à la distinction entre les émotions positives centrées sur soi et les émotions positives transcendantes. Bien que cette distinction ait été largement théorisée en psychologie positive, elle reste encore sous-explorée d’un point de vue empirique.La première partie de ma recherche expérimentale vise à tester cette distinction et à démontrer que les émotions transcendantes se distinguent des émotions centrées sur soi par leur capacité à générer un sentiment de sens à la vie. Cette partie de ma thèse se concentre sur l’élaboration d’une taxonomie des émotions positives fondée sur l’expérience subjective. Mes résultats révèlent que les émotions positives transcendantes peuvent être subdivisées en deux familles distinctes : les émotions sociales et les émotions épistémiques.J’examine ensuite comment ces différentes familles d’émotions positives varient en fonction des contextes — plaisir sensoriel ou poursuite d’objectifs importants — et j’étudie leur lien avec le sentiment de sens de la vie. Mes résultats suggèrent que seule la famille des émotions transcendantes sociales est liée au sentiment que la vie a un sens. Enfin, j’étudie comment l’appartenance à un groupe social peut activer ce sentiment, en identifiant les émotions spécifiques associées à cette expérience
Stabilization of Fe-N4 sites by platinum during oxygen reduction reaction in acid medium
No full textInternational audienceThe deployment of proton-exchange-membrane fuel cells is hindered by the large amount of Pt required for anode and cathode electrocatalysis. While Fe–N–C materials have shown promising initial oxygen reduction reaction (ORR) activity, they lack durability. Key degradation mechanisms include direct demetallation of Fe-N 4 sites and indirect deactivation caused by reactive oxygen species. Enhanced durability of Fe–N–C materials can be achieved by interfacing them with a low amount of Pt nanoparticles (NPs) or even Pt single atoms. 1-2 The original idea was to lean on the known activity of bulk Pt and Pt NPs towards H 2 O 2 electroreduction. However, different Pt and Fe active sites can emerge in the current process for preparing Pt/Fe-N-C hybrid materials due to a relatively high-temperature step needed to reduce the Pt salt, leading to the transformation of some Fe-N 4 sites into Pt@FeO x core-shell structures, etc. The presentation will show that it is possible to add controlled amounts of Pt NPs (0.25-2.0 wt. %) via a soft polyol method, resulting in unmodified Fe coordination, well-defined Pt structures and stable Pt/Fe–N–C hybrids. The approach is first validated for various mainstream Fe–N–Cs, including ZIF-8-derived Fe-N-C, aerogel derived Fe-N-C and silica-templated Fe-N-C. With operando techniques, we demonstrate that the Pt addition nearly suppresses H 2 O 2 production during ORR and strongly reduces the Fe leaching rate during ORR, while post mortem Mössbauer spectroscopy reveals that the highly active but unstable Fe(III)N 4 site is partially stabilized. The similar H 2 O 2 electroreduction activity of Pt/Fe–N–C and Fe–N–C and other analyses point toward a long-distance electronic effect of Pt NPs in stabilizing FeN 4 sites. This key stability property of Fe-N 4 sites during ORR brought by a low amount of Pt is experimentally elusive to understand. Possible synergistic effects between Pt and Fe-N 4 sites were further studied with density functional theory and a proposed mechanism will be presented that could explain the experimental observations. Fig. 1 . Characterization of catalysts in PEMFC or in gas diffusion electrode (GDE) setup. a) Chronoamperometry at U = 0.5 V, b) Online ICP-MS results conducted in a GDE setup in O 2 -saturated 0.1 M HClO 4 electrolyte, the Fe dissolution rates of Fe–N–C Aero and Pt/Fe–N–C Aero were normalized to catalyst loading during an accelerated stress test (AST) consisting of 200 square cycles of 3.2 s at -49.7 mA·cm -2 and 2.1 s at -0.1 mA·cm -2 . The aerogel-derived Fe-N-C catalyst (Fe-N-C Aero ) has an Fe content of 1.25 wt. %, and 1 wt. % Pt NPs was deposited onto it to form the Pt/Fe-N-C Aero hybrid. References: Mechler, A. K.; Sahraie, N. R.; Armel, V.; Zitolo, A.; Sougrati, M. T.; Schwämmlein, J. N.; Jones, D. J. ; Jaouen, F.; Electrochem. Soc. 2018 , 165, F1084. Bae, G.; Kim, M. M.; Han, M. H.; Cho, J.; Sougrati, M-T.; Kim, J.; Lee, K-S.; Joo, S. H.; Goddard, W. A.; Oh, H-S.; Kim, H.; Jaouen, F.; Choi, C. H.; Nature Catal. 2023 , 6, 1140-1150. Figure
On Closure Properties of Read-Once Oblivious Algebraic Branching Programs
No full textWe investigate the closure properties of read-once oblivious Algebraic Branching Programs (roABPs) under various natural algebraic operations and prove the following. - Non-closure under factoring: There is a sequence of explicit polynomials that have -sized roABPs such that some irreducible factor of does not have roABPs of superpolynomial size in any order. - Non-closure under powering: There is a sequence of polynomials with -sized roABPs such that any super-constant power of does not have roABPs of polynomial size in anyorder (and requires exponential size in any order). - Non-closure under symmetric compositions: There are symmetric polynomials that have roABPs of polynomial size such that do not have roABPs of subexponential size. (Here, denote the elementary symmetric polynomials in variables.) These results should be viewed in light of known results on models such as algebraic circuits, (general) algebraic branching programs, formulas and constant-depth circuits, all of which are known to be closed under theseoperations. To prove non-closure under factoring, we construct hard polynomials based on expander graphs using gadgets that lift their hardness from sparse polynomials to roABPs. For symmetric compositions, we show that the circulant polynomial requires roABPs of exponential size in every variable order
Multiphysics model for design optimization of a monolithic photoelectrochemical cell device
No full textInternational audienc
Measurement of branching fractions and asymmetries in decays
No full textInternational audienceA study of and baryon decays to the final states and is performed using collision data collected by the LHCb experiment, corresponding to an integrated luminosity of . The decays and are observed for the first time, with significances reaching eight standard deviations. The branching fractions and integrated asymmetries are measured for the , , and decays. For the decay , the asymmetries are measured in different regions of the Dalitz plot. No evidence of violation is observed