Mesoscopic Analysis of Structure and Strength of Dislocation Junctions in FCC Metals

We develop a finite element based dislocation dynamics model to simulate the structure and strength of dislocation junctions in FCC crystals. The model is based on anisotropic elasticity theory supplemented by the explicit inclusion of the separation of perfect dislocations into partial dislocations bounding a stacking fault. We demonstrate that the model reproduces in precise detail the structure of the Lomer-Cottrell lock already obtained from atomistic simulations. In light of this success, we also examine the strength of junctions culminating in a stress-strength diagram which is the locus of points in stress space corresponding to dissolution of the junction.Comment: 9 Pages + 4 Figure

An Exploration of Comfort and Discomfort Amongst Children and Young People with Intellectual Disabilities Who Depend on Postural Management Equipment

© 2016 John Wiley & Sons Ltd Background: The natural response to the intrusive bodily sensation is positional change. This study explored how children and young people (CYP) with intellectual disabilities had their comfort needs met when using adaptive positioning equipment. Methods: Thirteen qualitative case studies were undertaken. A parent, a teacher/key worker and a therapist for each CYP were interviewed, and daily routines were observed, with selective video recording. Single case and cross case analyses were undertaken. Results: Attentive caregivers read the behavioural expressions of the CYP and responded reassuringly, safeguarding them from discomforting experiences. Threats to comfort include the restrictive nature of some equipment accessories, positioning errors and procedural stretching. Conclusions: The same item of equipment can be both comfortable and uncomfortable. Given the social and interactional world in which the CYP live and learn, it is others who must accept responsibility for ensuring their optimal level of comfort

Ionospheric scintillation effects on GPS measurements and algorithms to improve positioning solution accuracy

2017 Summer.Includes bibliographical references.The ionosphere is an important cause of disturbances on GNSS signals, especially in high latitudes and equatorial areas. Previous studies indicate that while ionospheric scintillation may cause abrupt, random fluctuations in carrier phase measurements, its impact on pseudorange is less serious. Since modern GNSS receivers, especially those for high precision applications, use carrier phase-smoothed pseudoranges to improve accuracy of position solutions, there exists the need to have a better understanding of the scintillation effects on carrier phase measurements and developing means to mitigate scintillation induced errors in navigation solutions. In this thesis, scintillation impacts are demonstrated on carrier phase and pseudorange measurements using real scintillation data collected at high latitudes and equatorial areas, and the effect on positioning is investigated and mitigated. To obtain a more insightful and quantitative understanding of the impact, the data was used to generate position solutions using standard navigation processing algorithms. The results clearly indicate that sudden carrier phase discontinuities during strong scintillation lead to the degradation of carrier-smoothed pseudorange accuracy and consequently, results in large position errors. During strong scintillation with no carrier phase discontinuities, comparatively smaller position errors are found due to phase fluctuations that cause small changes in the range measurements. Based on this analysis, we give examples of several approaches to mitigate these problems, and use these approaches to present adaptive positioning techniques to mitigate scintillation induced position errors. One algorithm simply replaces the carrier-smoothed pseudorange with the unsmoothed pseudorange for satellites that are affected by outages on the carrier phase measurements, or if strong scintillation is detected. Another adaptive algorithm uses the GDOP to determine if a scintillating satellite can be completely removed from the navigation processing to improve positioning accuracy. Results show that the algorithms that substitute the unsmoothed pseudorange increase errors by 24.5% as compared to a conventional technique that repairs cycle slips, which indicates that it is still best to use the carrier-smoothed pseudoranges as long as there are no discontinuities. Results from the adaptive technique based on the analysis of the GDOP show a reduction of maximum errors on average by 13% on all of the data sets when comparing to a conventional algorithm. It was also found that a new carrier-smoothing technique can reduce maximum errors by 7.9% on average. Alternative approaches for future improvements are also discussed