Reinforcement of natural rubber

In this article, we report on recent investigations on filled natural rubber. These investigations include a mechanical characterization as well as a molecular analysis based on measurements of chain orientation. It is demonstrated that at intermediate strains, the increase in the moduli can be explained by the inclusion of rigid particles in the soft matrix and from molecular interactions between the rubber and the filler. These interactions can be evaluated by equilibrium swelling and by orientational measurements. With regard to the unfilled formulation, carbon black– and silanized‐filled natural rubber exhibit increases in the cross‐linking density ascribed to filler‐polymer links, whereas a large decrease in the orientational level, evidenced by birefringence and by infrared dichroism, is observed when silica is added without any coupling agent. Finally, two specific effects—the Payne and Mullins effects, both related to energy dissipation phenomena—are discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2301–2316, 2002     

Glass transition and molecular dynamics in poly(dimethylsiloxane)/silica nanocomposites

The molecular dynamics of a series of poly(dimethylsiloxane) networks filled with silica nanoparticles synthesized in situ was investigated using thermally stimulated depolarization currents, broadband dielectric relaxation spectroscopy and differential scanning calorimetry. The techniques used cover together a broad frequency range (10⁻³-10⁹ Hz), thus allowing to gain a more complete understanding of the effects of the nanoparticles on the chain dynamics. In addition to the α relaxation associated with the glass transition of the polymer matrix, we observe in dielectric measurements a slower α relaxation which is assigned to polymer chains close to the polymer/filler interface whose mobility is restricted due to interactions with the filler surface. The thickness of the interfacial layer is estimated to be about 2.1-2.4 nm. Differential scanning calorimetry shows a change in the shape of the glass transition step, as well as a decrease in both the degree of crystallinity and the crystallization rate by the addition of silica.     

Human Factors Effects and Analysis in Maintenance: A Power Plant Case Study

This paper proposes a methodical approach for identifying and reducing human error in maintenance activities, the human factors effect and analysis. Human factors effect and analysis presents a roadmap for selecting significant human factors affecting maintenance management as well as the most effective solutions using cost–benefit analysis. Safety and operational consequences of each human factor are compared to preventive and recovery risk controls to select the preferred risk control method. Because human factor programs are not implemented in many maintenance departments, quantitative data are rare. Thus, expert judgment may help to compare potential solutions. In order to show the applicability of the proposed approach a power plant in Kenya is selected as a case study. Procedure usage, fatigue, knowledge and experience, and time pressure are identified as the most important human factors. Training, task planning /shift management, knowledge management, scheduling as well as incident report programs are the most cost‐effective solutions for performing human factors program. The proposed approach would improve system reliability by recognizing human related failures. Furthermore, unexpected incident and accident may be reduced having knowledge about potential risk factors. Copyright © 2016 John Wiley & Sons, Ltd.     

Démarches méthodologiques pour approcher les points de vue d'enseignants et enseignantes sur des QSV en lien avec le vivant

Les avancées dans le domaine des biotechnologies ainsi que des questions relatives à la santé publique soulèvent des enjeux sociaux, éthiques et culturels se répercutant dans la recherche et l'enseignement des sciences. L'intégration scolaire de contenus liés à ces enjeux fait appel à des approches d'enseignement dont la visée intègre l'objectif de formation de citoyennes et citoyens réfléchis et critiques. La nécessité d'adopter des méthodes de recherche favorisant l’émergence de la pluralité des points de vue d'enseignantes et enseignants de sciences se pose alors devant la diversité de ces enjeux. Le recours à des méthodes issues de l'interactionnisme symbolique (récits de vie, groupes de discussion) peut répondre à cette nécessité. C'est ce que montre cet article qui illustre le caractère heuristique de ces démarches ainsi que la multidimensionnalité, la pluralité et l'hétérogénéité des points de vue pouvant être recueillis.     

Effect of strain on the properties of a styrene–butadiene rubber filled with multiwall carbon nanotubes

Multiwall carbon nanotubes were dispersed in a styrene–butadiene copolymer. The effect of nanotube concentration on the tensile characteristics of the composites was examined. Electrical properties carried out under uniaxial extension show an increase in resistivity upon gradual stretching. A second stretch performed after total release of the stress was shown to lead to a flat response in resistivity. Atomic force microscopy was used to examine orientational effects and changes in filler structure occurring upon application of an uniaxial deformation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Pairwise Rigid Registration Based on Riemannian Geometry and Lie Structures of Orientation Tensors

Journal of Mathematical Imaging and Vision - Pairwise rigid registration can be developed by comparing local geometry encoded by intrinsic second-order orientation tensors which allows to model the...     

Influences d’un stage muséal sur le sentiment d’autoefficacité en sciences de futurs enseignants

Résumé

Cette étude qualitative, ancrée dans l’approche sociale-cognitive de la théorie de l’autoefficacité de Bandura, s’intéresse à quatre stagiaires dont le stage d’enseignement s’est déroulé au Musée canadien de la nature. Les données du questionnaire STEBI, combinées aux entrevues semi-dirigées ont permis d’analyser l’évolution du sentiment d’autoefficacité en sciences chez les stagiaires. Les résultats révèlent un accroissement du score STEBI, alors que l’apprentissage vicariant et la possibilité de répétition favorisent une meilleure connaissance de soi et une pratique réflexive chez les stagiaires du palier élémentaire. Les résultats témoignent du potentiel d’un tel stage pour rehausser le sentiment d’autoefficacité en sciences.