The hyperbolic formal affine Demazure algebra

In the present paper we extend the construction of the formal (affine) Demazure algebra due to Hoffnung, Malag\'on-L\'opez, Savage and Zainoulline in two directions. First, we introduce and study the notion of an extendable weight lattice in the Kac-Moody setting and show that all the definitions and properties of the formal (affine) Demazure operators and algebras hold for such lattices. Second, we show that for the hyperbolic formal group law the formal Demazure algebra is isomorphic (after extending the coefficients) to the Hecke algebra.Comment: Final version. Accepted for publication in Algebras and Representation Theory. ALGE-D-15-0016

Holocene reconstruction of spruce budworm-fire interactions in the mixed boreal forest of Québec (Canada) / Chronologie Holocène de l’interaction entre la tordeuse des bourgeons de l’épinette et les feux dans la forêt mixte du Québec (Canada)

Within the context of a changing climate, multi-millennial reconstructions are fundamental to our understanding of the range of variability in key ecosystem processes such as insect outbreaks and wildfires. Reconstructions spanning the Holocene allow us to observe how natural disturbances have behaved, and interacted in different climate phases and may provide a sustainable forest management framework going forward. However, for our understanding at vast temporal scales to be robust and accurate, we require the use of adequate proxies that have been validated and calibrated. I use the eastern Canadian mixed boreal forest as a model system to validate, and calibrate the use of a novel paleo-proxy, lepidopteran scales, to detect spruce budworm outbreaks in recent history, and then reconstruct spruce budworm, and wildfire events over the course of the Holocene. I demonstrated that lepidopteran scale accumulations in lake surface sediment are able to detect local spruce budworm outbreaks as these achieved high agreement with aerial surveys conducted in the late 20th century (1967-1986; 2010-present). Using the same surface sediment cores, I then assessed whether annually interpolated lepidopteran scale accumulations and tree-ring records both detected local spruce budworm impacts, and if the recorded impacts were synchronous. I demonstrated that each proxy individually identified local spruce budworm impacts at a periodicity of approximately 16 to 32 years coinciding with known outbreak return intervals, and that, when compared to each other, both proxies detected similar outbreak periodicities. Further, I demonstrated that the proxy record signals were relatively synchronous, and that the relationship between the two records suggests that large lepidopteran scale accumulations translate to a greater percentage of affected trees in a stand, and to greater recorded growth suppression i.e., narrower ring-widths. The validation and calibration of this novel proxy therefore provided a more robust and accurate foundation to interpret lepidopteran scale accumulations at multimillennial time scales. Finally, I reconstructed spruce budworm and wildfire events in the mixed boreal forest at lake Buire throughout the Holocene. The frequency of spruce budworm and wildfire events exhibited a negative correlation for the majority of the Holocene suggesting a linked interaction at the millennial and local/extra-local scales where one disturbance inhibits the presence of the other. Further, disturbance event frequencies oscillated during the Holocene following the postglacial establishment ofbalsam fir, and the switch in the dominant disturbance tended to coincide with rapid significant climate change events. The present study advanced our understanding of the long-term range of variability of the main disturbances of the mixed boreal and their interactions. The results of this thesis contribute to the body of knowledge of forest ecology, and disturbance interactions and provide insight into potential frameworks that could be utilized in sustainable forest management. Dans le contexte des changements climatiques, les reconstructions plurimillénaires sont fondamentales à notre compréhension de la variabilité des processus écosystémiques tels que les épidémies d'insectes et les feux de forêt. Les reconstitutions couvrant l'Holocène nous permettent d'observer comment ces perturbations naturelles se sont comportées et ont interagi au cours de différentes phases climatiques et ont le potentiel de fournir un cadre pour la gestion durable des forêts. Cependant, pour que notre compréhension à de vastes échelles temporelles soit robuste et précise, nous devons utiliser des proxys adéquats qui ont été validés et calibrés. J'utilise la forêt boréale mixte de l'est du Canada comme système modèle pour valider et calibrer l'utilisation d'un nouveau paléo-proxy, les écailles de papillon, afin de détecter les épidémies de tordeuse des bourgeons de l'épinette dans l’histoire récente et ensuite de reconstruire les événements liés à la tordeuse et aux feux de forêt au cours de l'Holocène. J'ai démontré que les accumulations d'écailles de papillon dans les sédiments de surface des lacs sont capables de détecter les épidémies locales de la tordeuse, car elles concordent bien avec les relevés aériens effectués à la fin du XXe siècle (1967-1986; 2010-présent). En utilisant les mêmes carottes de sédiments de surface, j'ai ensuite évalué si les accumulations d'écailles de papillon interpolées annuellement et les cernes de croissance détectaient aussi bien les impacts locaux de la tordeuse des bourgeons de l'épinette, et si ces impacts enregistrés étaient synchrones. J'ai démontré que chaque proxy identifiait individuellement les impacts locaux de la tordeuse, coïncidant avec les intervalles des épidémies connues, et que, comparées l'une à l'autre, les deux approximations détectaient des périodicités d'épidémies similaires. De plus, j'ai démontré que les signaux enregistrés par les proxys étaient relativement synchrones. La relation entre les deux proxys suggère que les grandes accumulations d'écailles se traduisent par un plus grand pourcentage d'arbres affectés dans un peuplement, et par des cernes plus étroits. La validation et l'étalonnage de ce nouvel indicateur ont donc fourni une base plus solide et précise pour interpréter les accumulations d’écailles à des échelles de temps plurimillénaires. Enfin, j'ai reconstitué les événements liés à la tordeuse des bourgeons de l'épinette et aux feux de forêt dans la forêt boréale mixte au lac Buire tout au long de l'Holocène. J’ai observé une corrélation négative entre la fréquence des épidémies de la tordeuse et des feux de forêt pendant la majeure partie de l'Holocène, ce qui suggère une interaction liée aux échelles millénaire et locale/extra-locale, où une perturbation inhibe la présence de l'autre. Aussi, la fréquence des perturbations a oscillé au cours de l'Holocène suite à l'établissement postglaciaire du sapin baumier, et que la perturbation dominante semblait être déterminé par des évènements de changements climatique rapides et significatifs. Cette étude a permis de mieux comprendre la variabilité à long terme des principales perturbations de la forêt boréale mixte et leurs interactions. Les résultats de cette thèse contribuent à l’ensemble des connaissances sur l’écologie forestière et les interactions entre les perturbations et donnent un aperçu de cadres potentiels qui pourraient être utilisés dans la gestion durable des forêts

Assessing Wind Impact on Semi-Autonomous Drone Landings for In-Contact Power Line Inspection

In recent years, the use of inspection drones has become increasingly popular for high-voltage electric cable inspections due to their efficiency, cost-effectiveness, and ability to access hard-to-reach areas. However, safely landing drones on power lines, especially under windy conditions, remains a significant challenge. This study introduces a semi-autonomous control scheme for landing on an electrical line with the NADILE drone (an experimental drone based on original LineDrone key features for inspection of power lines) and assesses the operating envelope under various wind conditions. A Monte Carlo method is employed to analyze the success probability of landing given initial drone states. The performance of the system is evaluated for two landing strategies, variously controllers parameters and four level of wind intensities. The results show that a two-stage landing strategies offers higher probabilities of landing success and give insight regarding the best controller parameters and the maximum wind level for which the system is robust. Lastly, an experimental demonstration of the system landing autonomously on a power line is presented

Current crowding issues on nanoscale planar organic transistors for spintronic applications

The predominance of interface resistance makes current crowding ubiquitous in short channel organic electronics devices but its impact on spin transport has never been considered. We investigate electrochemically doped nanoscale PBTTT short channel devices and observe the smallest reported values of crowding lengths, found for sub-100 nm electrodes separation. These observed values are nevertheless exceeding the spin diffusion lengths reported in the literature. We discuss here how current crowding can be taken into account in the framework of the Fert–Jaffrès model of spin current propagation in heterostructures, and predict that the anticipated resulting values of magnetoresistance can be significantly reduced. Current crowding therefore impacts spin transport applications and interpretation of the results on spin valve devices

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Special management in the human dominated landscape : bird species of the Georgia Basin

The expansion of urban and rural areas is likely to effect bird species within these areas because some do well in these habitat types while others do not. I used size, nesting substrate, diet, migratory pattern, and sociability to investigate if these life history traits determine the presence or absence of species in habitats dominated by humans and what native species will not as a consequence require special management. Based on the 5 traits size, diet, nesting substrate, migratory pattern and sociability, 47 species of birds found in the Georgia Basin were organized into guilds to determine whether or not the individual traits were associated with the presence or absence of the species within a human dominated habitat. Organizing the species into guilds was also used to determine if the 47 species could be used to represent the response of all native species. The association of each individual species to human dominated habitats was also determined. Size and nesting substrate were found to be significant while the three other traits were not. However, the trends obtained from all traits indicate that medium sized, omnivorous, migratory, social species that nest above 2 metres in height and on man-made structures are more likely to be found in human dominated habitats.Forestry, Faculty ofUnreviewedUndergraduat

The effects of single-objective management on disturbances in central interior dry forests of British Columbia

Mule deer are an important game species, and have become the focus of applying a particular silvicultural treatment that enhances habitat while allowing timber harvesting. Mule deer winter range management (MDWRM) involves the proportional removal of trees based on their diameter and abundance resulting in a multilayered, Douglas-fir dominated forest with a clumpy tree distribution. I assessed changes in forest stand attributes brought about by MDWRM through time and how these attributes related to stand susceptibility to the western spruce budworm, Douglas-fir beetle, and wildfire using a randomized complete block single factor mixed-effects model with subsampling. In the short-term, MDWRM significantly changed (p<0.05) forest stand attributes by decreasing sub-canopy tree density and basal area, canopy cover, leaf area index, and increasing large surface fuel load. In the long-term, most attributes recovered to untreated levels. Relative to untreated stands, treated stands maintained a multilayered structure and an abundance of Douglas-fir trees thus their susceptibility to the western spruce budworm did not change through time. In the short-term, a reduction in mature host-tree density lowered susceptibility to the Douglas-fir beetle. With subsequent forest recovery, long-term susceptibility did not differ relative to untreated stands. In the treated stands the likelihood of crown fire was greater shortly after than longer after treatment. This was likely due to more large surface fuels immediately following treatment. In addition, I extrapolated the effects of MDWRM across eligible stands of interior British Columbia in a hypothetical simulation to evaluate the current and forecasted landscape-level fire risk. The forecasted forest under widespread application of MDWRM resulted in a homogenized landscape dominated by low fire risk. Further, widespread application of MDWRM may result in a fire resilient landscape, but with consequences for other ecological processes. The present study contributes to our understanding of the relationship between single-objective management and subsequent stand susceptibility to biotic and abiotic disturbances. I concluded that understanding this relationship should play an important role in responsible resource management.Forestry, Faculty ofGraduat

Problématiques et enjeux du tourisme de chasse : Vers une meilleure connaissance du marché

La chasse est une activité importante tant au niveau économique que pour la conservation de la faune. À partir d’une revue extensive de la littérature, cet article documente cinq problématiques majeures entourant le tourisme de chasse : les conflits entre usagers, l’image négative de la chasse, la méconnaissance du marché, les difficultés de promotion de la chasse et le manque de relève. Afin d’assurer la présence d’un bassin suffisant de chasseurs touristiques, l’article propose de concentrer les efforts dans l’amélioration de la connaissance du marché, ce qui aura un effet direct ou indirect sur les autres problématiques. Les auteurs concluent avec des suggestions d’axes de recherches appliquées afin de remédier aux cinq problématiques majeures. L’article vise à aider les gestionnaires privés, publics, associatifs et les citoyens dans leurs efforts pour assurer la pérennité du tourisme de chasse dans un esprit de développement durable