A Study of Different Modeling Choices For Simulating Platelets Within the Immersed Boundary Method

The Immersed Boundary (IB) method is a widely-used numerical methodology for the simulation of fluid-structure interaction problems. The IB method utilizes an Eulerian discretization for the fluid equations of motion while maintaining a Lagrangian representation of structural objects. Operators are defined for transmitting information (forces and velocities) between these two representations. Most IB simulations represent their structures with piecewise-linear approximations and utilize Hookean spring models to approximate structural forces. Our specific motivation is the modeling of platelets in hemodynamic flows. In this paper, we study two alternative representations - radial basis functions (RBFs) and Fourier-based (trigonometric polynomials and spherical harmonics) representations - for the modeling of platelets in two and three dimensions within the IB framework, and compare our results with the traditional piecewise-linear approximation methodology. For different representative shapes, we examine the geometric modeling errors (position and normal vectors), force computation errors, and computational cost and provide an engineering trade-off strategy for when and why one might select to employ these different representations.Comment: 33 pages, 17 figures, Accepted (in press) by APNU

Influences on young people's physical activity in Scotland : a socio-ecological approach

Aim: I describe the original contribution my work has made to understanding individual, social and environmental influences on physical activity among young people in Scotland. The work I present is based on six publications from five studies. Design/Methodology/Approach: Two studies used quantitative methods and include a 5-year longitudinal study and a cross-sectional pupil and school-level study. Data were collected through self-administered questionnaires. Three studies used qualitative methods including focus group discussions, photography and descriptive writing. All studies involved adolescents (10-15 years) attending schools in Scotland. Key Findings: My longitudinal evidence showed significant gender and developmental effects through early-mid adolescence, particularly at the primary-secondary school transition. While boys reported higher levels of physical activity than girls at all ages, baseline physical activity was a significant predictor of later activity levels for both genders. The importance of social influences was evident across my research. Survey data showed boys to report higher peer support, parental support and independent play than girls. Among both genders, peer, paternal and maternal support decreased with age, whereas independent play increased. Time spent with friends was particularly important and was further highlighted in qualitative findings. Being with friends was a benefit of active travel to school, walking, and general physical activity. Other factors influencing physical activity included proximity and access to local facilities, and the school environment. Most notable was the importance of cost and value for money. In general, pupils were satisfied with school facilities, but felt time for physical education (PE) could be increased. Among adolescent girls, survey data showed the best predictor of physical activity to be hours allocated to PE in fourth year of secondary school. Provision of PE and extra-curricular clubs are likely to be of greater importance to girls’ participation than schools facilities. Longitudinal data showed girls reporting lower levels of perceived competence, self-esteem and physical self-worth than boys at each age. Furthermore, girls’ physical perceptions decreased markedly over time, whereas among boys, only perceived competence decreased, while global esteem increased. Influences on physical activity participation were shown to be context specific, e.g. pupils reported not having bicycle storage as a barrier to cycling to school. Walking was a popular activity among girls, although areas in which walking took place, and reasons for walking could differ between geographical locations. Conclusions: In line with the socio-ecological model, my findings demonstrate the complex interaction of individual, social and environmental factors on physical activity participation among young people. They highlight the need for all sectors to work together in developing the most suitable interventions, considering the activity, its context and the population being targeted

Formation and structural characterization of Ni nanoparticles embedded in SiO₂

Face-centered cubic Ni nanoparticles were formed in SiO₂ by ion implantation and thermal annealing. Small-angle x-ray scattering in conjunction with transmission electron microscopy was used to determine the nanoparticle size as a function of annealing temperature, whereas the local atomic structure was measured with x-ray absorption spectroscopy. The influence of finite-size effects on the nanoparticle structural properties was readily apparent and included a decrease in coordination number and bond length and an increase in structural disorder for decreasing nanoparticle size. Such results are consistent with the non-negligible surface-to-volume ratio characteristic of nanoparticles. In addition, temperature-dependent x-ray absorption spectroscopy measurements showed the mean vibrational frequency (as obtained from the Einstein temperature) decreased with decreasing nanoparticle size. This reduction was attributed to the greater influence of the loosely bound, under-coordinated surface atoms prevailing over the effects of capillary pressure, the former enhancing the low frequency modes of the vibrational density of statesThis work was financially supported by the Australian Synchrotron and the Australian Research Council with access to equipment provided by the Australian Nanofabrication Facility

Gastro-oesophageal reflux disease - Impact of guidelines on GP management

Copyright © 2008 Royal Australian College of General Practitioners Copyright to Australian Family Physician. Reproduced with permission. Permission to reproduce must be sought from the publisher, The Royal Australian College of General Practitioners.Background: This program examined the impact of clinical guidelines and a 3 year self audit process on general practitioners’ diagnosis and management of gastro-oesophageal reflux disease. Methods: Nine hundred and sixty-six Australian GPs participated in a retrospective five step clinical audit reporting on data for 28 622 patients. Results: General practitioners demonstrated significant improvements in their diagnosis and management of gastro-oesophageal reflux disease across the audit period, including: - a significant 3% decrease in use of endoscopy - improved GP assessment and identification of risk factors and exacerbants - significant increases in GP recommendations for patient weight loss and dietary change (7 and 10% respectively) - a significant 4% reduction in patient use of medications that may exacerbate reflux symptoms. Discussion: The findings provide a snapshot of current diagnostic and management practices in Australian general practice, and highlight the benefits of clinical audit as a tool for eliciting evidence based, guideline driven practice change.Catherine N Kirby, Leon Piterman, Mark R Nelson and John Den

Development of liquid oxygen cooled 110MM ROLLER and tandem ball bearings at up to .5 x 106 DN values for the oxidizer turbopump of the M-1 engine Technology report

Bearing package design suitability for M-1 liquid oxygen turbopum