Porous silica beads produced by nanofluid emulsion freezing

It is shown that porous spherical particles can be obtained via the freezing of silica nanoparticle aqueous suspensions emulsified in a continuous oil phase. After two freeze-thaw cycles, nanoparticles turn aggregated into flocculated objects with microstructure that depends upon emulsion volume fraction and droplet size. For low volume fractions, regular microspheres are produced while for large ones, irregular beads with several tens of micrometer radius are formed. Electronic microscopy, mercury porosimetry and nitrogen adsorption are used to get insights into these porous particles typical radius, pore size distribution, surface area and pore network structure. All exhibit mesopores that result from inter-nanoparticle spacing after flocculation. An unexpected macroporous domain appears which is not observed when drying non-emulsified suspensions. This macroporosity is interpreted as the signature of dendrite formation during the undercooled period, right before freezing occurs. Beside this additional macroporosity, the protocols presented in this article constitute also promising emulsion-based routes for porous material synthesis with original geometry, chemical composition and porosity.Comment: 20 pages, 8 figure

Exploiting textual source information for epidemiosurveillance

In recent years as a complement to the traditional surveillance reporting systems there is a great interest in developing methodologies for early detection of potential health threats from unstructured text present on the Internet. In this context, we examined the relevance of the combination of expert knowledge and automatic term extraction in the creation of appropriate Internet search queries for the acquisition of disease outbreak news. We propose a measure that is the number of relevant disease outbreak news detected in function of the terms automatically extracted from a set of example Google and PubMED corpora. Due to the recent emergence we have used the African swine fever as a disease example. (Résumé d'auteur

Multi-Objective Design Optimization of the Leg Mechanism for a Piping Inspection Robot

This paper addresses the dimensional synthesis of an adaptive mechanism of contact points ie a leg mechanism of a piping inspection robot operating in an irradiated area as a nuclear power plant. This studied mechanism is the leading part of the robot sub-system responsible of the locomotion. Firstly, three architectures are chosen from the literature and their properties are described. Then, a method using a multi-objective optimization is proposed to determine the best architecture and the optimal geometric parameters of a leg taking into account environmental and design constraints. In this context, the objective functions are the minimization of the mechanism size and the maximization of the transmission force factor. Representations of the Pareto front versus the objective functions and the design parameters are given. Finally, the CAD model of several solutions located on the Pareto front are presented and discussed.Comment: Proceedings of the ASME 2014 International Design Engineering Technical Conferences \& Computers and Information in Engineering Conference, Buffalo : United States (2014

Une analyse des écrits sur les impacts du jeu sur l’apprentissage

Cet article présente une synthèse des publications récentes (1998-2005) qui traitent des impacts du jeu, en tant que formule pédagogique, sur l’apprentissage. Constatant une grande variété d’approches, une certaine disparité dans la manière de présenter et d’interpréter les résultats, et souhaitant vérifier si les jeux éducatifs ont un impact réel sur l’apprentissage, les auteurs ont procédé à une recension des écrits sur le sujet à partir d’une grille d’analyse validée. Ces impacts sont détaillés après un résumé des attributs essentiels du jeu, attributs sur lesquels cette recherche a été fondée pour être menée à bien. L’analyse des écrits montre que le jeu a des impacts positifs sur l’apprentissage.This article presents a synthesis of recent (1998-2005) publications on the impact of play, as a pedagogical technique, on learning. While confirming that there are a great number of approaches, a certain disparity in the way of presenting and interpreting results, and hoping to verify if educational games have a real impact on learning, the authors used a validated analysis grid to produce a review of the literature in this area. The authors present a summary of the essential attributes of games, these attributes being used to frame this research, as well as details regarding the impacts noted. The analysis shows that play has positive impacts on learning.Este artículo presenta una síntesis de las publicaciones recientes (1998-2005) que tratan de los impactos del juego, como formula pedagógica, sobre el aprendizaje. Al observar una gran variedad de enfoques, una cierta disparidad en la manera de presentar y de interpretar los resultados, y con el deseo de comprobar si los juegos educativos tienen un real impacto sobre el aprendizaje, los autores procedieron a una recensión de los escritos sobre el tema a partir de una matriz de análisis validada. Estos impactos se detallan a continuación de un resumen de los atributos esenciales del juego, atributos que fundamentaron esta investigación para poder llevarla a cabo. El análisis de los escritos muestra que el juego tiene impactos positivos sobre el aprendizaje

Microstructure Formation in Freezing Nanosuspension Droplets

The structural evolution of suspensions upon freezing is studied with optical microscopy in a suspended droplet configuration. Droplets have millimeter size and consist in an aqueous mixture of silica particles while the surroundings phase is hexane. Freeze-thaw cycles are applied to this system and a two-step freezing mechanism evidenced. A fast adiabatic growth of dendrites that invade the full droplets is first observed, and occurs within a few milliseconds. Then a slow process lasts for several seconds and corresponds to the release of solidification latent heat into the hexane phase. The striking feature of this work is to evidence that after the first freeze-thaw cycle flocculated microstructures are generated. When a second cycle is performed, microstructures further flocculate and generate, for dense silica suspensions, stable porous spheres of the size of the droplets. A phenomenological description based on repulsion or engulfment of particles by solidifying ice fronts is proposed

The Arctic Twittersphere and the Russian Invasion of Ukraine

Social media use has grown in popularity in recent years, becoming a primary source of information for many. Several scholarly inquiries have analyzed how the Arctic region has been portrayed in traditional media. However, no study has comprehensively detailed how the region has been presented on social media. The objective of this article is to sketch the contours of the Arctic discussion on Twitter and to inquire whether significant geopolitical events impact the nature of the online discussion. Using tweets on Arctic issues published between January 2020 and August 2022, we assessed the timing, prevalence, and nature of messages about the circumpolar North. Overall, the Arctic conversation on Twitter is first and foremost an Arctic climate conversation, focusing on climate change, Arctic sea ice, and permafrost thawing. Climate issues are the most salient ones and are treated independently from other topics by online users. We assessed whether the Russian invasion of Ukraine changed this dominance. We found that the Arctic Twittersphere remained still predominantly focused on climate issues, although the invasion increased Arctic military security discussions dissociated from other diplomatic or natural-resources considerations.Ces dernières années, l’utilisation des médias sociaux a gagné en popularité, devenant une source primaire d’information pour bien des gens. Plusieurs enquêtes de recherche universitaire ont analysé la manière dont la région de l’Arctique a été représentée dans les médias traditionnels. Cependant, aucune étude n’a entrepris de démontrer en détail comment la région est présentée dans les médias sociaux. L’objectif de cet article consiste à esquisser les contours de la discussion au sujet de l’Arctique sur Twitter et à se demander si les événements géopolitiques importants ont des incidences sur la nature des discussions en ligne. À l’aide de gazouillis sur les enjeux de l’Arctique publiés de janvier 2020 à août 2022, nous avons évalué les dates, la fréquence et la nature des messages portant sur le nord circumpolaire. Dans l’ensemble, la conversation au sujet de l’Arctique sur Twitter porte principalement sur le climat de l’Arctique, plus précisément le changement climatique, la glace de mer de l’Arctique et la fonte du pergélisol. Les enjeux climatiques sont les enjeux les plus importants et ils sont traités indépendamment des autres sujets par les utilisateurs en ligne. Nous avons évalué si l’invasion de l’Ukraine par la Russie a changé cette prédominance. Nous avons constaté que la Twittersphère de l’Arctique a principalement continué de se concentrer sur les enjeux climatiques, bien que l’invasion ait eu pour effet d’intensifier la discussion sur la sécurité militaire de l’Arctique, dissociée des autres considérations diplomatiques ou des considérations propres aux ressources naturelles