Characterization of Thin Walled Ti-6Al-4V Components Reduced via Electron Beam Melting

Direct-metal energy beam SFF processes typically produce layers by scanning the contours and then filling in the area within the contour. Process parameters used to solidify contours are often different from those for fill areas. It is to be expected, therefore, that the contour and fill area regions will have different microstructures. This can have important ramifications for thin walled components such as biomedical implants whose slices have very little fill area. This paper characterizes the metallurgical differences in contour and fill areas in titanium components produced via Electron Beam Melting. The implications of these properties for thin walled components are described.Mechanical Engineerin

L’évaluation des SAMI (système d’apprentissage multimédia interactif) : de la théorie à la pratique

Cet article traite de la mise au point d'une stratégie de collecte de données visant à regrouper et à analyser les facteurs sous-jacents au développement d'une interactivité significative dans des situations d'apprentissage médiatisé. Les auteurs ont conçu un modèle adapté d'analyse axée principalement sur une approche qualitative; ils ont utilisé à cette fin des méthodes intégrant la technique de l'entrevue, l'observation directe et l'analyse de protocoles. Celles-ci ont permis de cerner les facteurs perceptifs, transactionnels, cognitifs, pédagogiques et évaluatifs qui peuvent diriger la prise de décision des concepteurs de systèmes d'apprentissage multimédia interactifs. Des mises à l'essai de ce modèle à l'aide de concepteurs issus des milieux de formation scolaire ont indiqué la pertinence et le raffinement des analyses possibles.This article describes the development of a data collection strategy whose aim is to classify and analyse the factors underlying interaction in mediated learning situations. The authors present a model for analysis that is centred principally on a qualitative approach which integrates an interview technique, direct observation, and protocol analysis. These methods were used to describe perceptual, transactional, cognitive, pedagogical, and evaluative factors that could influence decisions made by those who develop interactive multimedia learning systems. Results of trials using this model by developers who work in training and in school contexts show the possible value and the detail that these analyses offer.Este articulo discute la preparacion de una estrategia de recoleccion de datos que busca reagrupar y analizar los factores subyacentes al desarrollo de una interactividad significativa en situaciones de aprendizaje mediatizado. Los autores han creado un modelo adaptado de anâlisis basado principalmente en un enfoque cualitativo, utilizando para es to métodos que integran la técnica de entrevistas, la observation directa y el anâlisis de protocolos. Estos métodos han permitido distinguir los factores perceptuales, transaccionales, cognos-citivos, pedagogicos y evaluativos que pudieran dirigir la toma de decisiones de los disenadores de sistemas de aprendizaje interactivo multimedios. Ensayos de este modelo con disenadores en ambitos de formation y escolar han indicado la pertinencia y el refinamiento del anâlisis posible.Dieser Artikel befasst sich mit der Aufstellung einer Datenerfassungs-strategie, die bezweckt, die Vorrausetzungen fur die Entwicklung einer signifikanten Interaktion in mediatisierten Lernsituationen zusammenzustellen und zu analysieren. Die Verfasser haben ein hauptsâchlich auf qualitatives Vbrgehen hin konzipiertes Untersuchungsmodell entworfen, wobei sie Methoden benùtzten, die das Interview, die direkte Beobachtung und die Protokollanalyse integrieren. Mit diesen Metiioden konnten die Perzeptions-, Transaktions-und Kognitionsfaktoren, sowie die pâdagogischen und die Beurteilungsfaktoren erfasst werden, die fur die Autoren neuer interaktiver Multimedia-Lernsysteme wichtig sind. Das Modell wurde mit Hilfe von von der Bildung oder Schule her kommenden Autoren erprobt; die Relevanz der Untersuchungen wurde dabei bestâtigt

Characterization of High Alloy Steel Produced Via Electron Beam Melting

Electron Beam Melting (EBM) is a direct-to-metal freeform fabrication technique in which a 4 kW electron beam is used to melt metal powder in a layer-wise fashion. As this process is relatively new, there have not yet been any independently published studies of the high alloy steel microstructural properties. This paper describes the EBM process and presents results of microstructural analyses on H13 tool steel processed via EBM.Mechanical Engineerin

Analyse de la multimédiatisation des messages et évaluation de leur efficacité dans un système d'apprentissage multimédia interactif (SAMI)

Par ce travail de recherche, nous visions avant tout à définir et à valider un ensemble de règles de design qui permettraient de mieux exploiter les différents médias dans les SAMI. Pour mettre ces principes de design à l’épreuve, nous avons conçu un SAMI et une instrumentation originale qui tire partie de tout le potentiel des NTIC. Ce qui ressort le plus de la mise à l'essai du simulateur et de la validation de nos principes est la préférence de nos étudiants pour les messages écrits au détriment des messages audiolinguistiques apprécié les séquences vidéo surtout quand elles servaient à “raconter” des histoires et les mettaient ainsi en situation réaliste de résolution de problème. Finalement, les messages audiolinguistiques ont été spécialement efficaces pour donner des directives aux étudiants. Nous en concluons que si ses capacités propres sont bien exploitées, chaque type de message et chaque média permet de répondre à des situations spécifiques au bénéfice de certains étudiants et d’atteindre certains objectifs pédagogiques précis.Québec Université Laval, Bibliothèque 201

Experiments In Layered Electro-Photographic Printing 267

Electro-photographic printing processes employed by products such as laser printers and photocopiers are commonly used to deposit and fuse thin layers of thermoplastic powder onto paper. This report describes preliminary experiments aimed at adapting the electro-photographic printing process for use as a layered manufacturing technique. 3-D electro-photographic printing holds considerable potential as an inexpensive freeform fabrication technique that is suitable for office environments. The possibilities for selective coloring are also discussed.Mechanical Engineerin

Fine-sorting One-dimensional Particle-In-Cell Algorithm with Monte-Carlo Collisions on a Graphics Processing Unit

Particle-in-cell (PIC) simulations with Monte-Carlo collisions are used in plasma science to explore a variety of kinetic effects. One major problem is the long run-time of such simulations. Even on modern computer systems, PIC codes take a considerable amount of time for convergence. Most of the computations can be massively parallelized, since particles behave independently of each other within one time step. Current graphics processing units (GPUs) offer an attractive means for execution of the parallelized code. In this contribution we show a one-dimensional PIC code running on Nvidia GPUs using the CUDA environment. A distinctive feature of the code is that size of the cells that the code uses to sort the particles with respect to their coordinates is comparable to size of the grid cells used for discretization of the electric field. Hence, we call the corresponding algorithm "fine-sorting". Implementation details and optimization of the code are discussed and the speed-up compared to classical CPU approaches is computed

Decision-making on intra-household allocation of bed nets in Uganda: do households prioritize the most vulnerable members?

Abstract Background Access to insecticide-treated bed nets has increased substantially in recent years, but ownership and use remain well below 100% in many malaria endemic areas. Understanding decision-making around net allocation in households with too few nets is essential to ensuring protection of the most vulnerable. This study explores household net allocation preferences and practices across four districts in Uganda. Methods Data collection consisted of eight focus group discussions, twelve in-depth interviews, and a structured questionnaire to inventory 107 sleeping spaces in 28 households. Results In focus group discussions and in-depth interviews, participants almost unanimously stated that pregnant women, infants, and young children should be prioritized when allocating nets. However, sleeping space surveys reveal that heads of household sometimes receive priority over children less than five years of age when households have too few nets to cover all members. Conclusions When asked directly, most net owners highlight the importance of allocating nets to the most biologically vulnerable household members. This is consistent with malaria behaviour change and health education messages. In actual allocation, however, factors other than biological vulnerability may influence who does and does not receive a net.http://deepblue.lib.umich.edu/bitstream/2027.42/109479/1/12936_2014_Article_3219.pd

A rat model of early stage osteonecrosis induced by glucocorticoids

<p>Abstract</p> <p>Background</p> <p>Glucocorticoid (GC)-induced osteonecrosis (ON) is an important complication of medical therapy. The exact pathomechanisms of ON has not been clearly elucidated. There is a need for a reproducible animal model that better approximates the clinical scenario.</p> <p>Methods</p> <p>To determine the genetic susceptibility of rats to develop GC-induced femoral head ON, we evaluated 5 different inbred strains of rats (Spontaneous Hypertensive Rat, Wistar Kyoto, Wistar Furth, SASCO Fisher and Lewis). Prednisone pellets (dosage of 1.82-2.56 mg/kg/day) were implanted subcutaneously for 90. After 90 days, the femurs were resected and examined histologically and radiographically. Pathological and histological examination was performed. Hematoxylin and eosin (H & E) staining was used to delineate the femoral head osteonecrosis lesions as well as abnormalities of articular cartilage and growth plate.</p> <p>Results</p> <p>The greatest differences in H & E staining were seen in the Wistar Kyoto and Wistar Furth groups. In these groups 4 out of 5 and 3 out of 5, respectively, steroid-induced rats revealed growth plate disruption with acellular areas. The TUNEL apoptosis staining assay for apoptosis revealed that 4 out of 5 of Wistar Kyoto rats, 5 out of 5 of Wistar Furth, 2 out of 4 of surviving Lewis and 2 out of 2 of the surviving spontaneous hypertensive rats had apoptotic osteocytes in trabeculae, whereas none of the Fisher rats showed apoptotic osteocytes.</p> <p>Conclusions</p> <p>We postulate that Wistar Kyoto, Wistar Furth and spontaneous hypertensive rats may be strains of rats more susceptible to develop ON of the femoral head while Fisher rats were the most resistant.</p

Freeform Fabrication of Titanium Aluminide via Electron Beam Melting Using Prealloyed and Blended Powders

Titanium aluminide (TiAl) is an intermetallic compound possessing excellent high-temperature performance while having significantly lower density than nickel-based superalloys. This paper presents preliminary results of experiments aimed at processing TiAl via the electron beam melting (EBM) process. Two processing routes are explored. The first uses prealloyed powder, whereas the second explores controlled reaction synthesis. Issues such as processing parameters, vaporization of alloying elements, microstructure, and properties are discussed