Letters to the Editor

Dubois Patrick. KERGOMARD (Mme Pauline). In: , . Le dictionnaire de pédagogie et d'instruction primaire de Ferdinand Buisson : répertoire biographique des auteurs. Paris : Institut national de recherche pédagogique, 2002. pp. 90-91. (Bibliothèque de l'Histoire de l'Education, 17

IMPACT: The Journal of the Center for Interdisciplinary Teaching and Learning. Volume 1, Issue 1, Summer 2012

Impact: The Journal of the Center for Interdisciplinary Teaching & Learning is a peer-reviewed, biannual online journal that publishes scholarly and creative non-fiction essays about the theory, practice and assessment of interdisciplinary education. Impact is produced by the Center for Interdisciplinary Teaching & Learning at the College of General Studies, Boston University (www.bu.edu/cgs/citl)

Quantum revival for elastic waves in thin plate

Quantum revival is described as the time-periodic reconstruction of a wave packet initially localized in space and time. This effect is expected in finite-size systems which exhibits commensurable discrete spectrum such as the infinite quantum well. Here, we report on the experimental observation of full and fractional quantum revival for classical waves in a two dimensional cavity. We consider flexural waves propagating in thin plates, as their quadratic dispersion at low frequencies mimics the dispersion relation of quantum systems governed by Schr\"{o}dinger equation. Time-dependent excitation and measurement are performed at ultrasonic frequencies and reveal a periodic reconstruction of the initial elastic wave packet.Comment: submitted to the special issue of EPJ ST in honor of scientific legacy of Roger Maynar

Réduction des contraintes secondaires en tension dans les pales en céramique de rotors de turbine en configuration renversée

Depuis quelque temps, un groupe de chercheurs du Groupe d'innovation Createk de l'Université de Sherbrooke travaille sur une nouvelle configuration de rotor de turbine qui utilise un carénage rotatif structurel pour tenir des pales en céramique sous compression, sous l’action du champ centrifuge. Cette configuration de rotor, baptisée Inside-Out Ceramic Turbine (ICT) vise à augmenter la température d'entrée de la turbine (TIT) pour les petites turbines, pour lesquelles le refroidissement et les techniques de fabrication complexes sont d'un coût prohibitif. Plusieurs prototypes et itérations du rotor ICT ont été testés au cours des dernières années, augmentant le temps de fonctionnement et la température d’opération atteignables. Au fur et à mesure que la confiance de l'équipe dans le rotor ICT s'améliore, les problèmes auxquels il est confronté deviennent importants à identifier et à résoudre. Cette thèse vise à étudier et à améliorer la fiabilité des pales en céramique dans des conditions normales de fonctionnement. Ceci est essentiel à l'adoption de la technologie ICT dans un grand nombre de moteurs. La thèse est découpée en trois parties : (1) isoler la cause la plus probable de défaillance des pales grâce à l'observation des résultats expérimentaux et numériques passés, (2) quantifier l'influence relative des principaux paramètres de conception sur la fiabilité des pales à l’aide d’un modèle numérique, et (3) tester des solutions potentielles qui ciblent les variables de conception les plus critiques, pour obtenir une meilleure fiabilité des pales ICT. Les pales étant en céramique technique monolithique, actuellement en nitrure de silicium, elles supportent mal les contraintes en tension. Le niveau de contrainte le plus élevé dans les pales s’avère être à l'interface avec les composants métalliques de support, car les pales sont maintenues en place par friction sous une force normale importante, et des contraintes élevées en tension se manifestent à l'interface. Cela demande de réduire d'abord le nombre d'interfaces au minimum, c'est-à-dire uniquement au niveau du bout de pale en appui contre le carénage structurel tournant. Deuxièmement, à cette interface subsistante, les efforts pour réduire le coefficient de frottement, ainsi que pour réduire la différence de dilatation thermique et de déformation tangentielle entre la pale et le carénage, sont essentiels pour obtenir de faibles contraintes en tension à l'extrémité de la pale. La validation expérimentale des revêtements a été menée avec succès : le revêtement de barrière thermique (TBC) appliqué entre l'extrémité de la pale et le carénage pourrait augmenter la température de l'extrémité de la pale et diminuer la température du carénage, conduisant ainsi à une meilleure correspondance de la dilatation thermique ; le nitrure de bore hexagonal (hBN) est un lubrifiant solide à haute température qui réduit considérablement le coefficient de frottement, même sous une charge extrême, et pourrait conduire à au moins doubler la tolérance à la différence de déformation. Ainsi, un double revêtement de TBC et de hBN devrait réduire la charge en bout de pale. Les niveaux de contrainte réels dépendent de la géométrie de la pale et de la conception globale de la turbine, mais un outil numérique simple a été développé qui permet au concepteur de déterminer quel niveau de réduction de frottement et d'ajustement de dilatation thermique est nécessaire pour obtenir une fiabilité adéquate dans la pale.Abstract : For some time now, a group of researchers in the Createk Innovation Group at Université de Sherbrooke have been working on a novel turbine rotor configuration which uses a structural, rotating shroud to compress ceramic blades under centrifugal load. This rotor configuration, dubbed Inside-Out Ceramic Turbine (ICT) aims at increasing turbine inlet temperature (TIT) for small turbines, for which intricate cooling and complex manufacturing techniques are prohibitively costly. Several prototypes and iterations of the ICT rotor have run over the last years, achieving consistently better run times and firing temperatures. As the team’s confidence in the ICT rotor improves, the issues facing it become important to identify and address. This thesis aims at investigating and improving reliability of the ceramic blades under normal operating conditions. This is central to the adoption of ICT technology in mainstream engines. The thesis is cut into three parts: (1) isolating the most probable cause of failure in the blades through observation of past experimental and numerical results, (2) quantifying the relative influence of the main design parameters on blade reliability through a numerical model, and (3) testing potential solutions which target the most critical design variables, to achieve a better reliability in the ICT blades. As the blades are made of monolithic technical ceramic, currently silicon nitride, they do not tolerate tensile stress fields well. The highest stress level in the blades was found to be at the interface with supporting metallic components, as the blades are maintained in place through friction under large normal force, and a strain mismatch is present at the interface. This leads to first reduce the number of interfaces to a minimum, i.e., only at the blade tip pressing up against the rotating structural shroud. Second, at this remaining interface, efforts to reduce coefficient of friction especially, as well as reduce thermal expansion mismatch and hoop strain between the blade tip and the shroud, are key to achieving low tensile stresses at the blade tip. Experimental validation of coatings was successfully conducted: thermal barrier coating (TBC) applied between the blade tip and the shroud, could increase blade tip temperature and decrease shroud temperature, thus leading to a closer match in thermal expansion; hexagonal boron nitride (hBN) is a high temperature solid lubricant which significantly reduces coefficient of friction, even under extreme load, and could lead to at least double the amount of strain mismatch tolerance. Thus, a double coating of TBC and hBN is expected to reduce the load at the blade tip. Actual stress levels depend on blade geometry and overall turbine design, but a simple numerical tool was developed which could allow the designer to determine what level of friction reduction and thermal expansion fit is required to achieve an adequate reliability in the blade

Open abstracts: a new peer review feature that helps scholars develop connections and encourages transdisciplinarity

The peer review process has been subjected to a steady stream of criticism in recent years. This has driven certain innovations, from revealing the content of the process post-publication, to crowdsourcing initiatives. Patrick Riechert and Frédéric Dubois introduce a new peer review feature that is currently being piloted on the journal, Internet Policy Review. Authors are invited to submit abstracts for a proposed paper, and will quickly receive two short peer reviews from scholars established in the journal’s community, with the possibility of additional feedback from the crowd. It is hoped this new feature will encourage transdisciplinarity and generational exchange, allow emerging researchers to find their way, and help scholars find one another and develop connections

Genetic risk variants in intestinal inflammatory disorders

PhDThis thesis includes work on the genetics of intestinal inflammatory disorders, concentrating on coeliac disease and Crohn’s disease. It explores how common genetic variants influence risk of complex phenotypes including immunological intolerance to gluten (coeliac disease) and intolerance to therapeutic agents (azathioprine and mercaptopurine) used in the treatment of intestinal inflammatory diseases. Finally it presents work aiming to move from genetic associations with complex phenotypes to understanding of how these variants modulate immunological processes. Results of a large genome wide association study that identified more than 13 new genetic risk regions influencing susceptibility to coeliac disease are presented. Results of a genome wide association study of azathioprine and 6-mercaptopurine-induced pancreatitis in inflammatory bowel disease-affected individuals are presented. Finally, a cell cytokine release assay for the prostaglandin EP4 receptor was developed, with a view to investigating how SNPs associated with Crohn’s disease in the 5p13.1 region influence EP4 receptor signalling and contribute to disease pathogenesis. This work highlights some of the challenges in moving from SNP-disease associations identified in GWASs to understanding how genetic variants change biological processes

A DTN routing scheme for quasi-deterministic networks with application to LEO satellites topology

We propose a novel DTN routing algorithm, called DQN, specifically designed for quasi-deterministic networks with an application to satellite constellations. We demonstrate that our proposal efficiently forwards the information over a satellite network derived from the Orbcomm topology while keeping a low replication overhead. We compare our algorithm against other well-known DTN routing schemes and show that we obtain the lowest replication ratio without the knowledge of the topology and with a delivery ratio of the same order of magnitude than a reference theoretical optimal routing

The Theia Soteria: Alternative Design for Safer Initial Entry During Laparoscopic Procedures

Laparoscopic procedures account for 15 million surgeries worldwide [1], with the initial entry into the peritoneal cavity accounting for 33-50% of all major laparoscopic complications [7]. This initial entry is the most dangerous as surgeons must enter the cavity using a sharp object with no visibility and space between the outer surface of the cavity and internal tissues. During the initial entry into the peritoneal cavity, the patients undergoing laparoscopic procedures are at a high risk for damage to internal organs and vasculature, necessitating the development of a device to protect these internal tissues and increase patient safety