Understanding III-nitride semiconductors on the nanoscale

The III-nitride semiconductor materials system is used in thin-film-based optoelectronic devices. GaN and InGaN in particular have been used to produce efficient blue and green light emitting diodes. However, III-nitride thin films typically contain very high densities of dislocations, a line defect known to negatively affect device performance and lifetimes, but despite this the performance of III-nitride-based devices is much less affected by dislocations than devices based on other semiconducting systems. These dislocations have been the subject of extensive study but experimental and theoretical reports still present conflicting data. In particular, dislocations do not exist in isolation in III-nitride thin films, but can interact with point defects, dopants and alloying elements, and may induce local compositional segregation in III-nitride alloy epilayers. This thesis presents a study of the structure and properties of dislocations in GaN and InGaN and of their interactions with point defects, dopants and alloying elements. Specifically, a new theoretical analysis of a common extended dislocation core in GaN is presented and the conclusions are verified by experimental data. Random alloy microstructures are predicted and analysed for InGaN quantum wells of different thicknesses, followed by a theoretical and experimental study of the variation in InGaN alloy composition around dislocation cores. Finally, the mechanisms by which dislocation cores can act as preferential diffusion pathways for native point defects are studied, providing insight into possible mechanisms by which compositional segregation or dislocation movement could occur. The methods presented here have a broad relevance beyond the III-nitride materials system and highlight the importance of assessing the interactions of dislocations with other defects, to achieve a better understanding of dislocation properties and their influence on device performance.Open Acces

Turning Up the Heat on Energy Monitoring in the Home

The use of domestic electrical energy monitoring systems is becoming more common however gas usage has received comparatively little attention. This paper presents a new technique for monitoring gas-powered heating and hot water usage in the home integrated into a prototype energy monitoring platform. Compared to usual meter-based approaches this technique provides finer-grained usage data and uses simple temperature sensors. The main motivation for this work is to provide more meaningful energy information to users for inclusion in novel mobile and embedded applications. This is part of ongoing work which aims to reduce energy use among teenagers in the UK and make lasting attitude changes. The development and findings from a prototype deployed in a typical UK house over 7 days are presented. The findings highlight the utility of the technique and simplicity of the sensing approach. The novel requirements that inspired the development of this technique are also presented

Perspectives On Change: The Coeducational Transition of Saint Anselm College 1969-1979

This study examines Saint Anselm College’s transition to a fully coeducational Benedictine Catholic liberal arts college between 1969 and 1979, employing a twofold data sample comprised of archival documents and oral history interviews with early female alumnae, who experienced campus life firsthand during the 1960s and 1970s. The researcher conducted analysis of historical documents available at Saint Anselm College, including: presidential files, minutes of the monastic and Advisory Board of Trustees meetings, college yearbooks, Registrar and Dean’s Office data, college catalogues, Advancement Office data, New Hampshire College and University Council (NHCUC) data, New England Association of Schools and Colleges (NEASC) accreditation data, and correspondence between administrators at Saint Anselm College and the Roman Catholic Diocese of Manchester and other Catholic colleges and universities in the Greater Manchester, New Hampshire area. These varied archival data samples, coupled with rich firsthand oral history interviews provided critical evidence concerning the factors that contributed to Saint Anselm College’s full transition to coeducation and the significant impacts involving campus culture and environment, resulting from the College’s decision to transition to a fully coeducational institution

Constructing the Cool Wall: A Tool to Explore Teen Meanings of Cool

This paper describes the development and exploration of a tool designed to assist in investigating ‘cool’ as it applies to the design of interactive products for teenagers. The method involved the derivation of theoretical understandings of cool from literature that resulted in identification of seven core categories for cool, which were mapped to a hierarchy. The hierarchy includes having of cool things, the doing of cool activities and the being of cool. This paper focuses on a tool, the Cool Wall, developed to explore one specific facet of the hierarchy; exploring shared understanding of having cool things. The paper describes the development and construction of the tool, using a heavily participatory approach, and the results and analysis of a study carried out over 2 days in a school in the UK. The results of the study both provide clear insights into cool things and enable a refined understanding of cool in this context. Two additional studies are then used to identify potential shortcomings in the Cool Wall methodology. In the first study participants were able to populate a paper cool wall with anything they chose, this revealed two potential new categories of images and that the current set of images covered the majority of key themes. In the second study teenagers interpretations of the meaning of the images included in the Cool Wall were explored, this showed that the majority of meanings were as expected and a small number of unexpected interpretations provided some valuable insights

Too Cool at School - Understanding Cool Teenagers

Cool can be thought about on three levels; the having of cool things, the doing of cool stuff and the being of cool. Whilst there is some understanding of cool products, the concept, of being cool is much more elusive to designers and developers of systems. This study examines this space by using a set of pre-prepared teenage personas as probes with a set of teenagers with the aim of better understanding what is, and isn’t cool about teenage behaviours. The study confirmed that teenagers are able to rank personas in order of cool and that the process of using personas can provide valuable insights around the phenomenon of cool. The findings confirm that cool is indeed about having cool things but in terms of behaviours cool can be a little bit, but not too, naughty

Constructing the Cool Wall: A tool to explore teen meanings of cool

This paper describes the development and exploration of a tool designed to assist in investigating ‘cool’ as it applies to the design of interactive products for teenagers. The method involved the derivation of theoretical understandings of cool from literature that resulted in identification of seven core categories for cool, which were mapped to a hierarchy. The hierarchy includes having of cool things, the doing of cool activities and the being of cool. This paper focuses on a tool, the Cool Wall, developed to explore one specific facet of the hierarchy; exploring shared understanding of having cool things. The paper describes the development and construction of the tool, using a heavily participatory approach, and the results and analysis of three studies. The first study was carried out over 2 days in a school in the UK. The results of the study both provide clear insights into cool things and enable a refined understanding of cool in this context. Two additional studies are then used to identify potential shortcomings in the Cool Wall methodology. In the second study participants were able to populate a paper cool wall with anything they chose, this revealed two potential new categories of images and that the current set of images covered the majority of key themes. In the third study teenagers interpretations of the meaning of the images included in the Cool Wall were explored, this showed that the majority of meanings were as expected and a small number of unexpected interpretations provided some valuable insights

Improving Validity and Reliability in Children’s Self Reports of Technology Use

Researchers working in child computer interaction are constantly seeking new methods and new techniques that will enable them to carry out more valid and more reliable research. Much of this research typically considers the design and development of new products and of new interactive techniques and researchers seek to understand how easy such innovations are for children, how much fun they are to use and how attractive they may be for use. The impact of prior technology use on the children’s responses in those contexts is the core concern of this thesis. The thesis provides a set of tools (survey instruments and guidelines) that can be used by the CCI research community to ascertain the prior experience of children with any technology and with any task. These tools are generated using theory, experience and literature and are validated through user studies. The PETT survey tool comprises three questionnaires, CTEQ, CTUQ and CTHQ and an associated user guide that clearly articulates how to use PETT and demonstrates the flexibility of PETT to be used in many contexts. The guidelines (RWC, SWC and SRT) can be applied on three levels, for general use in research with children, in the design of surveys and in the specifics of designing self-report tools for prior technology experience

Helium distributions in ocean island basalt olivines revealed by X-ray computed tomography and single-grain crushing experiments

X-ray computed tomography of individual olivine crystals in basalts from Ofu and Olosega islands, American Samoa, reveals that a small fraction of the olivines contain the vast majority of the fluid inclusions. Single-grain crushing experiments demonstrate that He and CO_2 reside primarily in these inclusions. Low CO_2 pressures in most grains, corresponding to depths of less than 1 km, provide evidence of ubiquitous decrepitation and associated pressure reduction in the fluid inclusions. Even so, the olivines with the highest inclusion volumes yielded sufficient He to obtain precise He concentrations and isotopic compositions. Within analytical uncertainty, ^3He/^4He ratios are homogeneous among the olivines from each basalt, but among basalts, the ratios range from 21 to 35 Ra. The total range in C/^3He ratio within the analyzed olivines is from 3.6 × 10^7 to 1.5 × 10^(10), and varies by nearly an order of magnitude within the olivines from each basalt. We postulate that this wide range of C/^3He ratios is caused by grain-scale decoupling of C and ^3He due to extensive He diffusion out of fluid inclusions through the olivine lattice during magma ascent and cooling. If so, primary Ofu-Olosega magmas probably had C/^3He ratios less than 4 × 10^8, which is lower than previous estimates for hotspot magmas