Déformation contrôlée d'une membrane par actionnement piézoélectrique : application au refroidissement de composants électriques à forte dissipation

La maîtrise de la température des composants à forte dissipation, notamment dans les systèmes électroniques nomades, constitue un verrou à leurs développements. Que ce soit pour l'électronique de puissance ou les calculateurs, les densités de puissance requièrent l'utilisation de systèmes de refroidissement de plus en plus performants, en particulier dans le cas des microprocesseurs qui associent miniaturisation et augmentation des fréquences d'horloge. Les conséquences sont multiples, limitation des performances, augmentation de la consommation et du taux de défaillance. C'est dans ce contexte que le projet CANOPEE, réunissant un consortium de partenaire industriel et académique, propose de développer et démontrer les avantages d'une solution technologique active récemment brevetée et appelée OnduloTrans. Elle consiste en un dispositif échangeur-pompe, permettant à la fois d'obtenir un excellent transfert thermique et d'assurer le pompage du fluide caloporteur. OnduloTrans est une solution active de refroidissement basée sur la déformation dynamique d'une paroi d'un canal. Le dispositif est fixé directement à l'aplomb du composant à refroidir. Le canal est déformé suivant une onde progressive pour créer un pompage péristaltique. L'intensification des transferts est obtenue lorsque les variations dynamiques des dimensions du canal viennent perturber la couche limite à l'interface conduction/convection. Le travail de la thèse consiste à concevoir et développer une solution d'actionnement intégrée permettant de mouvoir la paroi souple. Il s'accompagnera d'essais concrets témoignant des performances thermiques de cette solution. L'actionnement mis en oeuvre doit respecter les contraintes hydrauliques et thermiques de l'application embarquée visée, tout particulièrement le faible encombrement et une consommation électrique minimale. La difficulté réside dans les critères antagonistes que sont la production d'une onde progressive de grande amplitude dans un milieu aux dimensions centimétriques. Le manuscrit s'articule en trois parties. Dans un premier temps les solutions d'actionnement envisageables seront explorées. Pour ce faire, la solution OnduloTrans est d'abord décrite. Un état de l'art des solutions de conversion électromécanique, puis des micropompes péristaltiques est entrepris. Les phénomènes hydrauliques propres au micropompage péristaltique sont abordés pour cerner la problématique du développement de l'actionnement. Ensuite les deux chapitres suivants détaillent l'étude de deux solutions piézoélectriques distinctes. Une première solution piézoélectrique à onde discrète est développée dans le second chapitre. Elle consiste en une répartition d'actionneurs flextensionnels le long de la paroi souple. Une méthodologie de prédimensionnement basée sur des modèles mécaniques simples est présentée. L'onde progressive créée étant très particulière, une méthode analytique de calcul du débit, validée par simulations numériques, permet d'étudier l'influence de la commande des actionneurs. Un prototype est finalement réalisé avec l'aide des partenaires. De nombreux essais sont ensuite réalisés afin de valider les différentes hypothèses et déterminer les premières performances hydrauliques et thermiques du dispositif. Le troisième chapitre aborde une solution à onde progressive continue et actionnement intégré à la membrane. Le but est ici de prouver le concept de pompage péristaltique par flexion contrôlée d'une plaque intégrant une couche piézoélectrique. Un modèle de dimensionnement 1D constitué de tronçons piézoélectriques répartis à la surface est tout d'abord présenté. La répartition des segments piézoélectriques fait ensuite l'objet d'une étude paramétrique afin de définir judicieusement leur disposition, ceci en vue de maximiser le débit théorique. Cette étude paramétrique est finalement couplée à une optimisation des commandes électriques, évaluée par les résultats d'un prototype

The twitaholic next door.: scalable friend recommender system using a concept-sensitive hash function

International audienceIn this paper we present a Friend Recommender System for micro-blogging. Traditional batch processing of mas- sive amounts of data makes it di cult to provide a near- real time friend recommender system or even a system that can properly scale to millions of users. In order to over- come these issues, we have designed a solution that repre- sents user-generated micro posts as a set of pseudo-cliques. These graphs are assigned a hash value using an original Concept-Sensitive Hash function, a new sub-kind of Locally- Sensitive Hash functions. Finally, since the user pro les are represented as a binary footprint, the pairwise comparison of footprints using the Hamming distance provides scalability to the recommender system. The paper goes with an online application relying on a large Twitter dataset, so that the reader can freely experiment the system

Spatial evolution of friction of a textured wafer surface

Abstract Mechanical failure of integrated circuits and micro-electro-mechanical systems (MEMS) demands new understanding of friction in small devices. In present research, we demonstrated an in situ approach to measure sliding friction of a patterned surface composing multi-materials and structures. The effects of materials and surface morphology on friction and electrical contact resistance were investigated. The material transfer at the interface of dissimilar materials was found to play dominating roles in friction. The current work provides important insights from the fundamentals of friction that benefit the design of new micro-devices.</jats:p

Health science communication strategies used by researchers with the public in the digital and social media ecosystem : a systematic scoping review protocol

Introduction The optimisation of health science communication (HSC) between researchers and the public is crucial. In the last decade, the rise of the digital and social media ecosystem allowed for the disintermediation of HSC. Disintermediation refers to the public’s direct access to information from researchers about health science-related topics through the digital and social media ecosystem, a process that would otherwise require a human mediator, such as a journalist. Therefore, the primary aim of this scoping review is to describe the nature and the extent of the literature regarding HSC strategies involving disintermediation used by researchers with the public in the digital and social media ecosystem. The secondary aim is to describe the HSC strategies used by researchers, and the communication channels associated with these strategies. Methods and analysis We will conduct a scoping review based on the Joanna Briggs Institute’s methodology and perform a systematic search of six bibliographical databases (CINAHL, EMBASE, IBSS, PubMed, Sociological Abstracts and Web of Science), four trial registries and relevant sources of grey literature. Relevant journals and reference lists of included records will be hand-searched. Data will be managed using the EndNote software and the Rayyan web application. Two review team members will perform independently the screening process as well as the full-text assessment of included records. Descriptive data will be synthesised in a tabular format. Data regarding the nature and the extent of the literature, the HSC strategies and the associated communication channels will be presented narratively. Ethics and dissemination This review does not require institutional review board approval as we will use only collected and published data. Results will allow the mapping of the literature about HSC between researchers and the public in the digital and social media ecosystem, and will be published in a peer-reviewed journal

Bench-stable frustrated Lewis pair chemistry : fluoroborate salts as precatalysts for the C-H borylation of heteroarenes

While the organotrifluoroborate group is commonly used as a leaving group in cross-coupling reactions, we now show that their high stability can be used to protect the Lewis acidic moieties of frustrated Lewis pair catalysts. Indeed, the air and moisture-stable trifluoro- and difluoroborate derivatives of bulky (tetramethylpiperidino)benzene are shown to be conveniently converted to their dihydroborane analogue which is known to activate small molecules. An efficient synthesis route to these stable and convenient precatalysts, their deprotection chemistry and their benchtop use for the dehydrogenative borylation of heteroarenes is presented

Spontaneous reduction of a hydroborane to generate a B-B single bond using a Lewis pair

The ansa‐aminohydroborane 1‐NMe2‐2‐(BH2)C6H4 crystallizes in an unprecedented type of dimer containing a B−H bond activated by one FLP moiety. Upon mild heating and without the use of any catalyst, this molecule liberates one equivalent of hydrogen to generate a diborane molecule. The synthesis and structural characterization of these new compounds, as well as the kinetic monitoring of the reaction and the DFT investigation of its mechanism, are reported

Metal-free borylation of heteroarenes using ambiphilic aminoboranes : on the importance of sterics in frustrated lewis pair C-H bond activation

Two novel frustrated Lewis pair (FLP) aminoboranes, (1-Pip-2-BH2-C6H4)2 (2; Pip = piperidyl) and (1-NEt2-2-BH2-C6H4)2 (3; NEt2 = diethylamino), were synthesized and their structural features were elucidated both in solution and in the solid state. The reactivity of these species for the borylation of heteroarenes was investigated and compared to previously reported (1-TMP-2-BH2- C6H4)2 (1; TMP = tetramethylpiperidyl) and (1-NMe2-2-BH2-C6H4)2 (4; NMe2 = dimethylamino). It was shown that 2 and 3 are more active catalysts for the borylation of heteroarenes than the bulkier analogue 1. Kinetic studies and DFT calculations were performed with 1 and 2 to ascertain the influence of the amino group of this FLP-catalyzed transformation. The C-H activation step was found to be more facile with smaller amines at the expense of a more difficult dissociation of the dimeric species. The bench-stable fluoroborate salts of all catalysts (1F-4F) have been synthesized and tested for the borylation reaction. The new precatalysts 2F and 3F are showing higher reaction rates and yields for multi-gram scale syntheses

Communicating science in the digital and social media ecosystem : scoping review and typology of strategies used by health scientists

Background: The public's understanding of science can be influential in a wide range of areas related to public health, including policy making and self-care. Through the digital and social media ecosystem, health scientists play a growing role in public science communication (SC). Objective: This review aimed to (1) synthesize the literature on SC initiated by health scientists targeting the public in the digital and social media ecosystem and (2) describe the SC strategies and communication channels used. Methods: This scoping review was based on the Joanna Briggs Institute Methodological Framework. A systematic search was performed in 6 databases (January 2000 to April 2018). Title and abstract screening, full-text review, data charting, and critical appraisal were performed independently by two review authors. Data regarding included studies and communication channels were synthesized descriptively. A typology of SC strategies was developed using a qualitative and inductive method of data synthesis. Results: Among 960 unique publications identified, 18 met inclusion criteria. A third of publications scored good quality (6/18, 33%), half scored moderate quality (9/18, 50%), and less than a fifth scored low quality (3/18, 16%). Overall, 75 SC strategies used by health scientists were identified. These were grouped into 9 types: content, credibility, engagement, intention, linguistics, planification, presentation, social exchange, and statistics. A total of 5 types of communication channels were identified: social networking platforms (eg, Twitter), content-sharing platforms (eg, YouTube), digital research communities (eg, ResearchGate), personal blogs and websites (eg, WordPress), and social news aggregation and discussion platforms (eg, Reddit). Conclusions: Evidence suggests that multiple types of SC strategies and communication channels are used by health scientists concurrently. Few empirical studies have been conducted on SC by health scientists in the digital and social media ecosystem. Future studies should examine the appropriateness and effectiveness of SC strategies for improving public health-related outcomes and identify the barriers, facilitators, and ethical considerations inherent to the involvement of health scientists in the digital and social media ecosystem

Time-of-Flight X-ray Measurements for Computed Tomography

Time-of-flight (ToF) measurements is a possible alternative to anti-scatter grids in computed tomography (CT). Simulations have shown a possible 75% reduction in the detrimental scattering contribution with a 100 ps FWHM timing resolution. A test bench comprising a pulsed X-ray source and a time-correlated detector has been designed to demonstrate the feasibility of time-of-flight measurements of X-rays using readout electronics inherited from a ToF-positron emission tomography project. A 86 ps FWHM coincidence time resolution have been achieved with 511 keV annihilation gamma-rays and a 155 ps FWHM timing jitter with a 120 kVp pulsed X-rays source.Comment: 5 pages, 10 figures including 3 tables, submitted to IEEE Transactions on Radiation and Plasma Medical Sciences on 2023/10/0