Des études récentes ont montré qu’une mesure électrique permettait de caractériser les interfaces multi-contacts. Ces recherches initiées dans les milieux granulaires sont transposées dans un cadre technologique dédié au monitoring et au diagnostic des défauts dans les roulements. Cette méthode innovante exploite la richesse et la sensibilité d’une mesure électrique localisée et corrélée à l’état de chargement d’un roulement. Pour démontrer le potentiel de cette méthode, des mesures électriques expérimentales sont effectuées sur un banc de roulements et l’analyse des signaux révèle des similitudes avec les traditionnelles méthodes de surveillance. D’un point de vue numérique, le roulement est modélisé avec la méthode des éléments discrets (MED), d’ordinaire dédiée à l’étude des milieux granulaires, à partir de laquelle le comportement mécanique du roulement en dynamique est reproduit. Une formulation électromécanique est ensuite introduite pour en déduire une grandeur électrique numérique d’un roulement en fonctionnement, à comparer avec l'expérimentation. Des signatures électriques typiques en réponse à des sollicitations complexes (défauts, jeux, balourds, etc) sont étudiées et l’étude du comportement mécanique des bagues ouvre des perspectives intéressantes pour comprendre et modéliser leur endommagement. Alors que de nombreuses études ont été menées sur le suivi vibratoire des roulements, le recours à une méthode électrique localisée, sans capteur, est inexploité et prometteur / Recent studies have shown that an electric measurement made it possible to characterize the multi-contacts interfaces. The research initiated in granular media are transposed in a technological environment dedicated to monitoring and diagnosis of defects in bearings. This innovative method exploits the richness and sensitivity of a localized electrical measurement and correlated to the bearing load status. To demonstrate the potential of this method, experimentals electrical measurements are performed on a bench and signal analysis reveals similarities with traditional monitoring methods. From a numerical point of view, the bearing is modeled with the discrete element method (DEM), usually dedicated to the study of granular media, from which the mechanical behavior of the bearing dynamic is well reproduced. Electromechanical formulation is then introduced to derive a numerical electrical quantity of a bearing in operation, compared with the experiment. Typical electrical signatures in response to complex stresses (defects, clearance, imbalance, etc.) are studied. Studies of the mechanical behavior of rings opens interesting perspectives to understand and model their damage. While many studies have been conducted on the vibration monitoring of bearings, the use of a localized electrical method without sensor is still untapped and has promising results

La plupart des études de fretting analyse la réponse des matériaux en contact à partir de critères issus directement des paramètres caractéristiques des cycles de fretting (ouverture du cycle, énergie dissipée, raideur de contact...). La première partie de cette étude s’intéresse à l’influence du dispositif, premier élément du triplet tribologique, sur la réponse en glissement total d’un contact sphère/plan. Le rôle du mode de commande (déplacement imposé ou force actionneur imposée), de la rigidité statique et dynamique du dispositif (analyse vibratoire) et de la nature des matériaux (ductile, fragile ou peu adhérent) sur la forme des cycles est analysée de manière à distinguer les contributions respectives du dispositif et des matériaux. La seconde partie de cette étude est consacrée à une analyse de l’influence des paramètres opératoires (charge normale, déplacement, fréquence, intensité électrique) de couples CuSn6-CuSn6 pour application à la connectique embarquée bas niveau, où le fretting représente l’une des principales causes des défaillances des contacts électriques par perte de conductivité électrique. Une analyse de la variance a permis de hiérarchiser et d’identifier les couplages existants entre les paramètres opératoires et les réponses tribologiques et électriques. Un examen approfondi des signaux d’émission acoustique (amplitude EA, émissivité, énergie absolue, fréquence du centroïde…) et de la résistance électrique du contact a permis une compréhension temporelle des mécanismes locaux de dégradation des contacts synthétisée par une approche troisième corps. / Most fretting studies analyze material’s responses using criteria directly issued from characteristic parameters of the fretting loops (loop aperture, dissipated energy, contact stiffness...). The first part of this study concerns the influence of the device, first element of the tribological triplet, on the gross slip response of a ball-on-flat contact. The role of the static and dynamic device stiffness (vibratory analysis), of the control system mode (imposed displacement or imposed actuator force) and of the material type (ductile, brittle or non-adherent) on the loop shape is analyzed in order to distinguish the respective contributions of devices and materials. The second part of this study concern the analysis of the influence of operating parameters (normal force, displacement, frequency, current intensity) for CuSn6-CuSn6 pairs for low current onboard connectors applications. An analysis of variance allowed to prioritize and identify existing linkages between the operating parameters and the tribology and electrical responses. An examination of acoustic emission signals (amplitude AE, emissivity, absolute energy, centroid frequency…) and the electrical resistance of contact allowed a temporal understanding of local mechanisms of degradation synthesized by an approach third body.

Homophobic attitudes, irrational fears and negative attitudes against gay men and lesbians exist on the college campus (Lance, 2002; Rankin, 2003). Educators wishing to change these attitudes need to know what types of intervention would be effective. This investigation empirically assessed the degree of homophobia in a group of college students, and changes in the degree of homophobia following two levels of educational intervention that were rooted in educational theories and social contact theory. A 25-item scale developed by Hudson and Ricketts to measure the degree of negative attitudes toward gay men and lesbians was used in English classes at a southeastern university. This study examined the relationship between different demographic groups and the degree of change obtained as a result of the interventions. Findings did not suggest that either interaction with gay men and lesbians in the form of a speaker panel or viewing a “coming out” episode of the Ellen show reduced homophobia to a significant extent. Results did demonstrate the Caribbeans and right wing authoritarians tend to be more homophobic. Post hoc analysis investigated factors that may have contaminated the interventions. Speaker Identification was a significant predictor of change in degree of homophobia.

For years, electron beam induced deposition has been used to fabricate electrical contacts for micro and nanostructures. The role of the contact resistance is key to achieve high performance and efficiency in electrical devices. The present thesis reports on the electrical, structural and chemical characterization of electron beam deposited platinum electrodes that are exposed to different steps of thermal annealing and how they are used in four-probe devices of ultrathin graphite (uG) flakes (<100nm thickness). The device integration of liquid phase exfoliated uG is demonstrated, and its performance compared to devices made with analogous mechanically exfoliated uG. For both devices, similar contact resistances of ~2kΩ were obtained. The electrical measurements confirm a 99.5% reduction in contact resistance after vacuum thermal annealing at 300 °C. Parallel to this, Raman characterization confirms the formation of a nanocrystalline carbon structure over the electrode. While this could suggest an enhancement of the electrical transport in the device, an additional thermal annealing step in air at 300 °C, promoted the oxidation and removal of the carbon shell and confirmed that the contact resistance remained the same. Overall this shows that the carbon shell along the electrode has no significant role in the contact resistance. Finally, the challenges based on topographical analysis of the deposited electrodes are discussed. Reduction of the electrode’s height down to one-third of the initial value, increased surface roughness, formation of voids along the electrodes and the onset of platinum nanoparticles near the area of deposition, represent a challenge for future work.

No description available.

Much evidence has revealed that heterosexuals’ attitudes towards sexual minorities can be predicted by their amount of contact with sexual minority individuals. As contact with sexual minorities increases, attitudes toward these groups tend to become more positive. However, there has been little investigation into the possible mechanisms that explain this relationship. The aim of this study was to examine knowledge as a mediating factor in the relationship between contact and attitudes. The present study suggests that the strong correlation between contact and attitudes is, at least in part,in part due to increased knowledge. Data was gathered from a survey of 1580 participants who responded to the Study of Attitudes towards Sexual Minorities Survey. Mediation was tested using the bootstrap (Preacher & Hayes, 2008) method. Results showed that when accounting for knowledge, the relationship between contact and attitudes was significantly reduced for three groups (gay men, lesbians, bisexuals). These findings suggest that knowledge does indeed partially mediate the relationship between contact and attitudes. This information could be helpful for future interventions aimed at promoting positive attitudes towards sexual minorities.

No description available.

No description available.

Nucleic acids have been identified as procoagulant species in plasma and in vivo animal studies. It is believed that the nucleic acids act as physiological activators of the contact system. However, in order to obtain a better understanding of the role of nucleic acids in the activation of the contact system it is important to analyze and evaluate the individual proteins of the contact system that are stimulated by nucleic acids and identify accompanying proteins required to mediate the nucleic acid-stimulated activation. Previous works suggested that nucleic acids stimulate the activation of factor XII (FXII) in the presence of prekallikrein (PK) and high molecular weight kininogen (HK). In this study we will confirm if both PK and HK are required for nucleic acid-stimulated activation of FXII. We will also study the role of nucleic acids in the activation of PK in the presence or absence of activated FXII (FXIIa) and HK. Previous works also identified that zinc (Zn2+) accelerates surface-mediated activation of FXII by PK and HK, and PK by FXIIa and HK. We will be evaluating zinc’s ability to enhance nucleic acid-stimulated activation of both FXII and PK. We have found that nucleic acids stimulate activation of FXII in the presence of PK and this furthered upon addition of HK. Nucleic acids also stimulate the activation of PK in the presence of FXIIa and this is furthered upon addition of HK. Nucleic acids have stimulated activation of FXII and PK in a dose dependent manner in the presence of the aforementioned accompanying proteins. We have showed that Zn2+ enhances activation of the contact system. Zn2+ enhances nucleic acid-stimulated, PK/HK-mediated activation of FXII. It also enhances nucleic acid-stimulated, FXIIa/HK-mediated activation of PK. These findings enrich our understanding of the role of nucleic acids and zinc in the contact system. / Thesis / Master of Science (MSc)

Thesis (M.S.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / 2999-01-01