Dispersal syndromes in challenging environments: A cross‐species experiment

Dispersal is a central biological process tightly integrated into life-histories, morphology, physiology and behaviour. Such associations, or syndromes, are anticipated to impact the eco-evolutionary dynamics of spatially structured populations, and cascade into ecosystem processes. As for dispersal on its own, these syndromes are likely neither fixed nor random, but conditional on the experienced environment. We experimentally studied how dispersal propensity varies with individuals' phenotype and local environmental harshness using 15 species ranging from protists to vertebrates. We reveal a general phenotypic dispersal syndrome across studied species, with dispersers being larger, more active and having a marked locomotion-oriented morphology and a strengthening of the link between dispersal and some phenotypic traits with environmental harshness. Our proof-of-concept metacommunity model further reveals cascading effects of context-dependent syndromes on the local and regional organisation of functional diversity. Our study opens new avenues to advance our understanding of the functioning of spatially structured populations, communities and ecosystems. Keywords: context-dependent dispersal; dispersal strategy; distributed experiment; predation risk; resource limitatio

Role of Kv1 Potassium Channels in Regulating Dopamine Release and Presynaptic D2 Receptor Function

Dopamine (DA) release in the CNS is critical for motor control and motivated behaviors. Dysfunction of its regulation is thought to be implicated in drug abuse and in diseases such as schizophrenia and Parkinson's. Although various potassium channels located in the somatodendritic compartment of DA neurons such as G-protein-gated inward rectifying potassium channels (GIRK) have been shown to regulate cell firing and DA release, little is presently known about the role of potassium channels localized in the axon terminals of these neurons. Here we used fast-scan cyclic voltammetry to study electrically-evoked DA release in rat dorsal striatal brain slices. We find that although G-protein-gated inward rectifying (GIRK) and ATP-gated (KATP) potassium channels play only a minor role, voltage-gated potassium channels of the Kv1 family play a major role in regulating DA release. The use of Kv subtype-selective blockers confirmed a role for Kv1.2, 1.3 and 1.6, but not Kv1.1, 3.1, 3.2, 3.4 and 4.2. Interestingly, Kv1 blockers also reduced the ability of quinpirole, a D2 receptor agonist, to inhibit evoked DA overflow, thus suggesting that Kv1 channels also regulate presynaptic D2 receptor function. Our work identifies Kv1 potassium channels as key regulators of DA release in the striatum

Modeling of Transitional Flows on Roughened Surfaces for Icing Applications

RÉSUMÉ: RÉSUMÉ Le givrage est de la plus haute importance dans le domaine de l'aéronautique, d'une part puisqu'il demeure dans son ensemble assez incompris, et de l'autre puisqu'il existe des requis complexes de certification aéronautique liés au givrage des pièces composant les aéronefs. Suite à plusieurs accidents, ces normes requièrent maintenant de prédire les géométries de glaces qui peuvent s'amonceler sur des appareils soumis à des conditions de givrage critiques. Sous ces conditions, différents types de glace peuvent s'accumuler sur les surfaces de l'avion, comme du verglas ou des cristaux de glace qui, selon le cas, se traduisent par des géométries complexes qui affectent drastiquement les performances de vol. Pour modéliser et prédire ces formes de glace, des tests expérimentaux sont effectués, mais des outils et modèles numériques de plus en plus complexes sont aussi utilisés. Par contre, en se rapprochant de la température de fusion de l'eau, un film d'eau peut se créer et divers mécanismes liés au givrage entrent alors en jeu. Ces mécanismes plus complexes sont difficiles à modéliser et on remarque une perte de précision des outils prédictifs pour la glace de type verglas. Des modèles plus physiques doivent alors être ajoutés aux codes de givrage actuels afin d'améliorer les prédictions et de répondre aux plus récentes normes de certification. L'objectif de ce projet de recherche est d'améliorer les prédictions des formes de glace de type verglas, apparaissant à plus hautes températures, sur des aéronefs soumis à diverses conditions de vol. Afin de répondre à cet objectif, une modélisation plus proche de la physique des phénomènes entourant le givrage a été ajoutée dans le logiciel maison CHAMPS, correspondant aux standards actuels des codes de givrage de seconde génération. Les formes de glace sont obtenues en employant en séquence divers modules: un module pour l'aérodynamique, un module pour l'accumulation de goutelettes, un module pour les échanges thermodynamiques de surface et un module pour l'évolution de la structure de glace. L'aérodynamique est identifiée comme étant le module pouvant être amélioré et deux composantes principales ont été implémentées : la prédiction de la transition laminaire turbulente de la couche limite et la modélisation de la rugosité locale de glace. Ces deux phénomènes influent directement le transfert de chaleur convectif permettant le givrage. Les formes de glace obtenues sur des cas analysés dans le tunnel de recherche de givrage NASA Lewis ont été étudiées en considérant les modèles de façon conjointe. Le givrage étant un phénomène disparate et peu reproductible, certains ont examiné l'effet d’un modèle stochastique sur les formes de glace obtenues, en plus des modèles suggérés dans ce travail. Premièrement, l'écoulement aérodynamique est simulé par un solveur des équations moyennées de Reynolds en volumes finis. Les modèles de turbulence utilisés par CHAMPS sont vérifiés et validés, car ils servent de base au développement des nouvelles méthodes précédemment énumérées. Des équations de transport supplémentaires, permettant de prédire la transition laminaire turbulente, sont ensuite ajoutées aux modèles de turbulence actuels. Cela permet d'obtenir une représentation plus physique de la couche limite à la paroi du profil. Cette dernière influence directement le transfert de chaleur convectif qui affecte le gel de la glace. Les équations de transition sont vérifiées en comparant à des valeurs du coefficient local de friction obtenues par tests de soufflerie sur des profils standards. Deuxièmement, différents modèles de rugosité sont introduits i) pour représenter l'état de surface de la glace s'accumulant sur les géométries et ii) pour augmenter le transfert de chaleur convectif sur la surface initiale. Une rugosité uniforme basée sur la hauteur équivalente en grains de sable est d'abord proposée, correspondant à la méthode usuellement utilisée en recherche et en industrie. Elle est ensuite couplée aux équations de transition en employant une équation de transport de rugosité qui déplace le point de transition en amont de l'écoulement selon la hauteur de rugosité. Le transfert de chaleur associé à une hauteur de rugosité est vérifié en comparant à des résultats numériques de codes bien établis. L'effet des modèles sur les formes de glaces obtenues est étudié sur des cas expérimentaux. ABSTRACT: ABSTRACT Icing is of the utmost importance in the aeronautical field since it remains rather misunderstood and there are complex certification requirements related to the icing of aircraft components. Following several accidents, these standards now require the prediction of ice geometries that can accumulate on aircraft subjected to critical icing conditions. Under these conditions, different types of ice can agglomerate on the aircraft surfaces, such as ice crystals or glaze ice. Depending on the case, this can lead to complex geometries that drastically impact flight performance. To model and predict these ice forms, experimental tests are performed, but complex numerical tools and models are also used. On the other hand, when approaching the melting temperature of the water, a film can be created and various mechanisms related to icing come into play. These more complex mechanisms are difficult to model and a loss of accuracy of the predictive tools is noticed. More physical models must then be added to the current icing codes to improve the predictions and meet the latest certification standards. The objective of this research project is to improve the prediction of glaze ice shapes, appearing at higher temperatures, on aircraft subjected to various flight conditions. To meet this objective, more physical modeling of the phenomena surrounding icing has been added to the in-house software CHAMPS, corresponding to the current standards of second-generation icing codes. The ice shapes are obtained by using various modules in sequence: a module for aerodynamics, a module for droplet accumulation, a module for surface thermodynamic exchanges and a module for ice structure evolution. Aerodynamics is identified as the module that can be improved and two main components have been implemented: the prediction of the laminar-turbulent boundary layer transition and the modeling of the local ice roughness. These two phenomena directly impact the convective heat transfer allowing icing. The ice shapes obtained on cases analyzed in the NASA Lewis Icing Research Tunnel have been studied by considering the coupled effect of the models. As icing is a chaotic and poorly reproducible phenomenon, some have examined the effect of a stochastic model on the resulting ice shapes, in addition to the models suggested in this work. First, the aerodynamic flow is simulated by a finite volume Reynolds-averaged Navier–Stokes solver. The turbulence models used by CHAMPS are verified and validated, as they serve as a basis for the development of the new methods listed above. Additional transport equations to predict the turbulent laminar transition are then added to the current turbulence models. This allows the obtention of a more physical representation of the boundary layer at the wall of the airfoil. This has a direct influence on the convective heat transfer that impacts the freezing of the ice. The transition equations are verified through comparisons with values of the local friction coefficient obtained by wind tunnel tests on standard wing shapes. Secondly, different roughness models are introduced i) to represent the surface of the ice accumulating on the geometries and ii) to increase the convective heat transfer on the clean surface. A uniform roughness based on the equivalent sand grain height is first proposed, as it is usually used in research and industry. It is then coupled to the transition equations by a roughness transport equation that moves the transition point upstream according to the roughness height. The heat transfer associated with a roughness height is verified through comparison to well-established numerical code results. The impact of the models on the obtained ice shapes is studied with experimental cases. The results show that a region of laminarity can be captured by the models, modifying the ice shapes. On the other hand, imposing a unique roughness value could trigger the transition too close to the stagnation point. Thirdly, models are implemented to determine locally the amplitude of the surface roughness on the ice geometry. These models are calibrated using experimental results of ice shapes and roughness, employing local variables computed by the different modules of the solver. The effects of these models on a series of two-dimensional icing cases are studied, as well as the coupling with the recently implemented transitional model

A procedure to optimize the geometric and dynamic designs of assistive upper limb exoskeletons

The need for upper limb assistive and wearable exoskeletons is growing in various fields, e.g. either to support patients with neuromuscular disabilities or to reduce the effort strains on workers. These exoskeletons should reduce the efforts required by the user during functional tasks (dynamic consideration) and should fit the user’s size (geometric consideration). This is a tedious task, due to the 3D human-exoskeleton interactions, and to the complex and interdependent selection of the power transmission characteristics, i.e. motors or passive elements. There are still few guidelines and few clear procedures to support geometric and dynamic syntheses of these exoskeletons. The objective of this study is to develop a procedure for geometric and dynamic syntheses of assistive upper limb exoskeletons, to serve as a tool to optimize their design. Firstly, a geometric optimization of the exoskeleton dimensions enabled to satisfy the kinematic loop closures between the exoskeleton and the user for a maximum of positions while carrying out specific functional tasks and avoiding collisions with the body segments. Secondly, through an optimal control problem, the dynamic characteristics of the exoskeleton were obtained by minimizing the user’s joint torques for the functional tasks. Closing the kinematic loops of the exoskeletons with optimized dimensions was achieved for all positions of the user while carrying out the functional tasks, which was 10.8% more than with a visual identification of the dimensions. The resulting dynamic parameters could reduce the user’s joint torque to less than 10.6% of the human-only simulations for nearly all joints and tasks. These results showed that the geometric and dynamic synthesis procedures were successful. This is important, as it can enable the development of dedicated exoskeletons, such as lighter and smaller exoskeletons. The future perspectives will be to build an optimization framework, where the geometric and dynamic parameters could be optimized together, and to minimize the user’s muscle forces instead of joint torques for specific design purposes