An interfacial study of III-V materials

Z-contrast imaging, using a high-angle annular dark field detector, can be used to characterise III-V heterostructures. GaAs/AlAs heterostructures were grown using MBE and prepared for TEM using a cross-sectional method. SuperSTEM 1 was used to investigate both the GaAs-on-AlAs and the AlAs-on-GaAs interfaces as a function of specimen thickness. The analysis of the images showed that the apparent interface widths varied with thickness in an unexpected manner. The measured GaAs-on-AlAs interface widths remained constant with thickness while the AlAs-on-GaAs interface widths increased. Furthermore, the apparent width of the GaAs layer increased with increasing thickness. The actual interfacial width can be a result of either surface stepping during MBE growth or inter-diffusion of the Type-3 atoms. To assist the interpretation of these results, a series of interfacial models were created and explored using a modified version of the frozen phonon multislice simulation. The models consisted of terraced, vicinal and diffused interfaces. The model results indicate that a diffuse interface can be used to describe the characteristics observed in the experimental images. However, probe scattering from the interfacial region can be counter intuitive. A systematic study of these effects is presented outlining complications that can occur when interpreting interfacial structures using HAADF imaging

How Much Do They Make? New Evidence on the Early Career Earnings of Canadian Trade Certificate

This paper provides new evidence on the early career earnings of Canadians who obtain a trade certificate. The analysis uses comprehensive national level administrative data on individuals who received a trade certificate between 2008 and 2016 linked to their tax information at Statistics Canada in order to link earnings to their individual characteristics and details related to their certification. In this paper we track their yearly employment earnings from their first full year following certification onward, to a maximum of 9 years. Overall, journeypersons in nationally accredited Red Seal trades earn more than those in non-Red Seal trades, those in Mechanical and Electrical trades earn the most, and journeywomen earn only 47% of what journeymen do overall, largely driven by their being concentrated in a relatively narrow set of low-paying trades

Conflict & Communication: Consequences Of Female Nest Confinement In Yellow-Billed Hornbills

This thesis was originally submitted in 2012 via the Graduate Union. Unfortunately it never made it to the UL so has been resubmitted in 2018.The most striking feature of hornbills (Bucerotiformes) is their unusual nesting behaviour. Before laying, a female hornbill enters the nest in a tree cavity. Uniquely among birds, she then seals the nest entrance using her faeces and locally available materials, leaving a narrow gap only 1 cm wide. Through this tiny slit, the female is totally dependent on her mate for between 40 days in the smallest hornbills and up to 130 days in the largest. Once walled in the nest, the female will lay her eggs and shed all of her wing and tail feathers. The male then becomes completely responsible for provisioning his mate and a few weeks later, the chicks. When her feathers have regrown, the female breaks out of the nest, often before the chicks are fully grown. The chicks then reseal the entrance until they too are ready to fledge. This thesis describes attempts to better understand the nesting behaviour of hornbills. The first chapter introduces hornbill ecology and behaviour and highlights their potential as model systems for studying conflict and communication. Chapter 2 describes the methods used to set up a study population of Southern Yellow-Billed Hornbill (Tockus leucomelas) consisting of 47 occupied nest boxes, over 35km2 in the Southern Kalahari Desert, South Africa. Chapter 3 summarises behaviour over three breeding seasons from October 2008 to April 2011. Female feather moult followed a precise staggered pattern, unlike other populations. Widespread filial cannibalism by females of both eggs and chicks was observed for the first time. The possible proximate causes of cannibalism are explored. Egg cannibalism allowed females to recoup some of their energetic investment, while cannibalism of chicks served as an efficient mechanism of brood reduction for nests with low paternal feeding rate. Chapter 4 investigates how females communicate need for nesting materials to males. Females altered the rate and structure of their begging calls when experimentally deprived of nest lining and males in turn delivered more nest materials. Chapter 5 examines the factors that determine how long females remain in the nest. Females with larger broods stayed in the nest longer, irrespective of their own or their chicks’ condition or male feeding rates. This raises questions about the role of mothers in the nest. Chapter 6 addresses this issue, demonstrating that females controlled sibling competition in the nest. Experimental temporary removal of mothers led to increased intrabrood aggression and more uneven food distribution in the brood, with larger chicks taking a greater share. The final chapter draws these findings together and the potential for future research is discussed.NER

Experimental evaluation of interfaces using atomic-resolution high angle annular dark field (HAADF) imaging

Aberration-corrected highangleannulardarkfield (HAADF) imaging in scanning transmission electron microscopy (STEM) can now be performed at atomic-resolution. This is an important tool for the characterisation of the latest semiconductor devices that require individual layers to be grown to an accuracy of a few atomic layers. However, the actual quantification of interfacial sharpness at the atomic-scale can be a complicated matter. For instance, it is not clear how the use of the total, atomic column or background HAADF signals can affect the measured sharpness or individual layer widths. Moreover, a reliable and consistent method of measurement is necessary. To highlight these issues, two types of AlAs/GaAs interfaces were studied in-depth by atomic-resolutionHAADFimaging. A method of analysis was developed in order to map the various HAADF signals across an image and to reliably determine interfacial sharpness. The results demonstrated that the level of perceived interfacial sharpness can vary significantly with specimen thickness and the choice of HAADF signal. Individual layer widths were also shown to have some dependence on the choice of HAADF signal. Hence, it is crucial to have an awareness of which part of the HAADF signal is chosen for analysis along with possible specimen thickness effects for future HAADF studies performed at the scale of a few atomic layers

Iminosugar inhibitors of carbohydrate-active enzymes that underpin cereal grain germination and endosperm metabolism

Starch is a major energy store in plants. It provides most of the calories in the human diet and, as a bulk commodity, it is used across broad industry sectors. Starch synthesis and degradation are not fully understood, owing to challenging biochemistry at the liquid/solid interface and relatively limited knowledge about the nature and control of starch degradation in plants. Increased societal and commercial demand for enhanced yield and quality in starch crops requires a better understanding of starch metabolism as a whole. Here we review recent advances in understanding the roles of carbohydrate-active enzymes in starch degradation in cereal grains through complementary chemical and molecular genetics. These approaches have allowed us to start dissecting aspects of starch degradation and the interplay with cell-wall polysaccharide hydrolysis during germination. With a view to improving and diversifying the properties and uses of cereal grains, it is possible that starch degradation may be amenable to manipulation through genetic or chemical intervention at the level of cell wall metabolism, rather than simply in the starch degradation pathway per se