On the Use of Angled, Dynamic Laser Beams to Improve Stereolithography Surface Finish

Improved surface finish of Stereolithography (SLA) parts is an important goal for furthering the resolution of the technology. In order to improve the surface finish, a dynamic laser beam with changing angle, beam size, beam shape, and irradiance distribution is proposed. In this paper, an analytical irradiance model of an angled, dynamic laser beam in the SLA process is presented. This model is used to simulate cured shapes of SLA builds. Simulated build shapes are compared to established SLA analytical models and conclusions are drawn on the accuracy of the developed model.Mechanical Engineerin

Use of Parameter Estimation for Stereolithography Surface Finish Improvement

In order to improve Stereolithography (SLA) surface finish, a systematic approach based on estimation of process parameters is needed. In this paper, the exposure on a desired SLA build surface is formulated as a function of process parameters. The deviation of exposure on this surface from the critical exposure, which is the threshold that determines curing in the SLA process, is formulated using least squares minimization. By applying inverse design techniques, SLA process parameters that satisfy this least squares minimization are determined. Application of parameter estimation formulation to important SLA geometries is presented and the results, including surface finish improvement, are discussed.Mechanical Engineerin

A conceptual design study for the secondary mirror drive of the shuttle infrared telescope facility (SIRTF)

Various conceptual designs for the secondary mirror actuator system to be used in the Shuttle Infrared Telescope Facility (SIRTF) were evaluated. In addition, a set of design concepts was developed to assist in the solution of problems crucial for optimum performance of the secondary mirror actuator system. A specific conceptual approach was presented along with a plan for developing that approach and identifying issues of critical importance in the developmental effort

Women and Work in Hamilton, Ontario: A Case Study and a Research Challenge

This article tests two hypotheses about the labour force participation of women in Hamilton in 1911: first, that single women took paid jobs to compensate for lack of jobs or low earnings among male kin; second, that the need for labour in their households discouraged single women from entering the labour force. These hypotheses are tested by using the entire population of Hamilton, as recorded in the 1911 census. Neither hypothesis receives strong confirmation. The tentative conclusion is that non-material motives were likely to be highly significant in the movement of women into paid labour in this period. This article uses only a small fraction of the sources available on the subject of women and work in Canada, and new empirical riches offer unprecedented opportunities for historians interested in women and work.Le présent article met à l’épreuve deux hypothèses concernant la participation des femmes sur le marché du travail à Hamilton en 1911 : premièrement, que les femmes célibataires occupaient des emplois rémunérés pour faire contrepoids au chômage ou à la sous-rémunération des hommes; deuxièmement, que les travaux ménagers dont il fallait s’occuper décourageaient les femmes célibataires d’intégrer le marché du travail. Aucune de ces hypothèses, vérifiées à l’aune du recensement complet de la population de Hamilton en 1911, ne s’avère entièrement. La conclusion provisoire fait valoir que des motifs non matériels ont sans doute eu un rôle très important dans l’intégration des femmes à la population active à cette époque. Cette recherche fait appel à une fraction à peine des sources disponibles sur la question des femmes et de la main-d’œuvre au Canada. Ce genre de nouvelles données empiriques ouvre des débouchés sans précédent pour les historiens s’intéressant à la question des femmes et du marché du travail

Modified Delphi Investigation of Lesson Planning Concepts for Physical Education Teacher Education

Improving the methods of instructing future educators, through program evaluation and improvement, should be a goal of all teacher education programs. In physical education, the National Association for Sport & Physical Education created standards for initial preparation of physical education teachers. The six standards for preparation include Planning and Implementation, which include tenants pertaining to unit and lesson planning. Despite the significant importance of planning in the growth of preservice teachers as they complete a Physical Education Teacher Education (PETE) program, there is currently no consensus on what concepts to be included in lesson planning for physical education teacher education. The purpose of the study was to determine the essential lesson planning concepts for PETE. Following a nationwide pilot study of PETE programs in the United States to gather lesson planning concepts, a modified Delphi investigation using PETE experts was conducted to gain consensus on the pertinent lesson planning concepts for preservice teachers. Results of the study indicated 31 lesson planning concepts that experts found essential for preservice teachers to use when planning for teaching vignettes, peer teaching experiences and student teaching. Implications for use in PETE programs are also discussed

Surgical Approaches in Shoulder Arthroplasty

Shoulder arthroplasty is a complex procedure that is becoming increasingly more utilized throughout the world. Due to the numerous static and dynamic stabilizers of the glenohumeral joint, along with the relative proximity to vital neurovascular structures, great care must be taken to access the joint in a safe and effective manner. To date, there are two well-described approaches utilized in shoulder arthroplasty: the deltopectoral approach and the anterosuperior approach. Both of these approaches are effective in accessing the glenohumeral joint; however, due to their anatomic location, they both have distinct advantages and disadvantages. The aim of this book chapter is to describe the methodology for approaching the glenohumeral joint through each of these approaches, as well as to discuss the advantages and disadvantages of utilizing each. In addition, we aim to discuss the various methodologies for closing these wounds and, briefly, to discuss the other approaches described in the orthopedic literature

Effects of elevated atmospheric carbon dioxide concentrations on water and acid requirements of soybeans grown in a recirculating hydroponic system

Establishing mass budgets of various crop needs, i.e. water and nutrients, in different environments is essential for the Controlled Ecological Life Support System (CELSS). The effects of CO2 (500 and 1000 umol mol (exp -1)) on water and acid use (for pH control) by soybeans in a recirculating hydroponic system were examined. Plants of cvs. McCall and Pixie were grown for 90 days using the nutrient film technique (NFT) and a nitrate based nutrient solution. System acid use for both CO2 levels peaked near 4 weeks during a phase of rapid vegetative growth, but acid use decreased more rapidly under 500 compared to 1000 umol mol (exp GR) CO2. Total system water use by 500 and 1000 umol mol (exp -1) plants was similar, leaving off at 5 weeks and declining as plants senesced (ca. 9 weeks). However, single leaf transpiration rates were consistently lower at 1000 umol mol (exp -1). The data suggest that high CO2 concentrations increase system acid (and nutrient) use because of increased vegetative growth, which in turn negates the benefit of reduced water use (lower transpiration rates) per unit leaf area

Non-Newtonian gravity or gravity anomalies?

Geophysical measurements of G differ from laboratory values, indicating that gravity may be non-Newtonian. A spherical harmonic formulation is presented for the variation of (Newtonian) gravity inside the Earth. Using the GEM-10B Earth Gravitational Field Model, it is shown that long-wavelength gravity anomalies, if not corrected, may masquerade as non-Newtonian gravity by providing significant influences on experimental observation of delta g/delta r and G. An apparent contradiction in other studies is also resolved: i.e., local densities appear in equations when average densities of layers seem to be called for