Pure magnesium (Mg) and its alloys with calcium (Ca) and both Ca and zinc (Zn) have potential as bioresorbable bone implant materials provided the corrosion rate can be controlled. Thus, corrosion behaviour was investigated for pure Mg, Mg-2Ca, and Mg-2Ca-1Zn cast alloys subjected to either no heat treatment or to solutionizing and aging heat treatment. In addition, corrosion behaviour was investigated for surface modifications involving the deposition of silver (Ag) nanoparticles. These materials and constructs were all nominally biocompatible in that they would not elicit a strong and immediate adverse tissue reaction when implanted in bone. Static immersion tests in Hanks’ balanced salt solution were performed to evaluate the corrosion behaviour. The Mg-2Ca alloy exhibited the highest corrosion rate when compared with pure Mg and Mg-2Ca-1Zn for any length of immersion time. For short immersion times (48 hours), solutionizing followed by natural aging reduced the corrosion rate of Mg-2Ca alloy, but this heat treatment did not seem to have an effect on the corrosion rate of Mg-2Ca-1Zn alloy. As well, for short immersion times (48 hours), solutionizing and artificial aging also did not seem to have a large effect on corrosion rates for either Mg-2Ca or Mg-2Ca-1Zn, when compared to solutionizing and natural aging. Corrosion behaviour of surface-modified samples was sensitive to certain features of the Ag depositions. It was found that when the deposited Ag tracks were thick and wide, the corrosion rate of Ag-deposited samples increased significantly when compared to samples without any Ag deposition. However, when the Ag tracks were thinner and somewhat narrower, the corrosion rate did not appear to be much higher than that of samples without Ag deposition. Therefore, controlled Ag deposition may not be too detrimental to the corrosion behaviour of Mg and Mg alloys. The corrosion product morphology appeared to be similar for both the samples deposited with Ag and samples without any Ag. Needle-like formations were observed in small areas on the corroded surfaces. X-ray diffraction revealed Mg(OH)₂ as the main corrosion product. Because energy dispersive X-ray analysis consistently revealed multiple elements in the corrosion products (such as Mg, O, Ca, P, small amounts of C, and sometimes Cl), it was concluded that other compounds (possibly hydroxyapatite, magnesium chloride, and/or magnesium- and calcium-containing phosphates) may have formed in addition to the Mg(OH)₂.

Die Qualität von Lehre an Hochschulen ist durch die hohe Wirkungskraft von Prüfungen eng mit der Qualität von Prüfungen verbunden. Schriftliche Prüfungen können sehr verschieden ausgestaltet sein und Lehrende können sie über ganz unterschiedliche Wege erstellen. Eine Applikation, die zum Erreichen von pädagogisch-didaktischen sowie formalen Qualitätszielen bei schriftlichen Prüfungen beitragen will, muss diese unterschiedlichen Formen und Vorgehensweisen berücksichtigen. In diesem Beitrag wird anhand von ausgewählten Benutzersichten und Arbeitsschritten aufgezeigt, wie dies durch eine in der Entwicklung befindliche Applikation für das Erstellen von schriftlichen Prüfungen erreicht werden soll.

Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1989. / Includes bibliographical references (leaves 201-215) / Microfiche. / xxi, 215 leaves, bound ill. 29 cm

This thesis presents the design, construction and experiments done on a microcontroller board called 'SMARTY BOARD' targeted at small mobile robot applications. The primary motivation for this work was the lack of commercially available and cheap controller boards that would have all their components including interfaces on a single board. Having a single board simplifies the construction of programmable robots that can be used as platforms for teaching and learning robotics. Reducing the cost of the board as much as possible was one of the main design objectives. The target user groups for this device are the secondary and tertiary students, and hobbyists. Previous studies have shown that equipment cost is one of the major obstacles for teaching robotics in Australia. The other design objectives were robustness, reliability and functionality of the board. Most of the early technological learners such as high school students lack experience and expert knowledge for interfacing a controller board with other components. To prevent the learners from making errors, connectors on our board have been made foolproof (the user cannot damage the components of the board by plugging cables in the wrong sockets). Commercially available designs lack these essential features. After reviewing the commercially available micro-controller boards with respect to their suitability as teaching tools, we concluded that none of the existing microcontroller boards met our requirements. We then designed a new controller board based on previous boards. The main advantage of this new controller board is that it is a single board whereas the other controller boards are multi-board. Moreover, it is more foolproof. The new controller board was demonstrated at high-school seminars. In these demonstrations the new controller board was used for controlling two robots that we built. These robots are available as kits. The response from the high school teachers was very positive. The board has been selected as the platform for a robotic competition.

Thesis (PhD)--University of South Australia, 2001

Thesis (M Eng) -- University of South Australia, 1992

Accurate placement of pesticide droplets on to crop and weed surfaces is a key step in controlling pests and weeds in agricultural production systems. Droplets impact on plant surfaces, depositing pesticides that give protective coverage on crops and destructive coverage for insect or fungi pests and weeds. Coverage is complex and is determined by a multitude of interactions between factors such as size and density of spray droplets, relative humidity and turbulence of the air through which the droplets travel, and the physical characteristics of the target plant leaves, branches and stems that go to make up the architecture of their canopy. There are, however, concerns over the effect of pesticides on the environment and public health. This thesis combines three dimensional (3-D) computer modelling techniques, physical measurements of droplet movement and impact on a canopy in a wind tunnel and risk management techniques to maximise the effectiveness of pesticides and enable risks to public health and the environment from agricultural spraying activities to be minimised. L-studio, a Windows based software environment for creating simulation models of plant architecture was used in this study. A particle trajectory model, based on the combined ballistic and random-walk approach proposed by Mokeba et al. (1997) and Cox et al. (2000) was used to model spray droplet movement. Algorithms were included in the spray model to account for evaporation of droplets, entrained air and movement of air around the spray, collection efficiency, and droplet splash. Existing functional-structural plant models of cotton (Gossypium hirsutum L.) and sow thistle (Sonchus oleraceus L.) and a static empirical model of immature grass weeds have been combined with the spray model. An environmental program has been used to take the location of the leaves in 3-D space from the plant model and determine if spray droplets will impact on them. Wind tunnel measurements were made to determine initial droplet properties (droplet size, velocity, trajectory, density and fluid properties) and droplet impact characteristics (retention and splash). The results from these measurements were then used to define parameters within the spray model. Additional experiments to measure spray drift and spray deposition on various plant surfaces within the wind tunnel were used to evaluate the combined spray and plant architecture model. The combined spray and plant architectural model developed and evaluated in this thesis has provided a new method to study the influence of plant architecture on spray distribution. This work has shown that 3-D plant architecture can influence the amount of spray depositing on leaf surfaces. Deposition on plant surfaces was also found to increase with decreased wind speed and reduced release height. Droplet size did not have a significant influence on spray deposition onto broadleaf plants such as cotton or sow thistle. There was however, a tendency for fine sprays to give a higher deposit on small, narrow grass leaves. Spray drift was found to increase with decreasing droplet size, increasing the range of droplet sizes generated by a nozzle, decreasing sheet velocity (initial velocity of droplets), increasing wind speed, increasing (difference between dry and wet bulb temperature), decreasing liquid density and increasing release height. The combined spray and architectural model has also enabled the study of how effects such as droplet splash and retention can influence the distribution of the spray. In this study it was found that there was little difference in modelled spray drift, amount of spray on the ground or amount of spray on the cotton plant between situations where most droplets splash on impact and where no droplet splash on impact. Although the total amount of spray retained on the plant surface was similar for both situations, it was found that there were more droplets on the plant under the splash scenario leading to better coverage of the spray over the plant. These results indicate that the majority of the smaller splash droplets were re-distributed onto other parts of the plant rather than becoming lost as spray drift or ground deposit. Decision trees have been used in this thesis to characterise the benefits and risks from pesticide applications. Results from model simulations and/or physical measurements are used to estimate the relative proportion of the spray depositing on plant surfaces, depositing on the ground and drifting away from the treatment area. These deposition results give a measure of pesticide exposure that can be incorporated into the risk management framework to investigate the influence of various application scenarios. The applicability of this approach is shown by the example of endosulfan sprayed on cotton to control Helicoverpa spp. The decision tree model can be used to quickly compare different scenarios, such as deciding which application method should be used. It can be used to effectively aid spray decisions to maximise the effectiveness of pesticides and minimise risks to public health and the environment from agricultural spraying activities.

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