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Thesis (MTech (Technology : Mechanical Engineering))--Cape Peninsula University of Technology, 2006 / Recent years have witnessed a tremendous growth and significant advances in "smart" composites and "smart" composite structures. These smart composites integrate active elements such as sensors and actuators into a host structure to create improved or new functionalities through a clever choice of the active elements and/or a proper design of the structure. Such composites are able to sense a change in the environment and make a useful response by using an external feedback control system. Depending on their applications. smart composites usually make use of either the joint properties of the structure or the properties of the individual elements within the composites. The accumulation in the understanding of materials science and the rapid developments in computational capabilities have provided an even wider framework for the implementation of multi-functionality in composites and make "smart" composites "intelligent". This thesis is a contribution towards the global endeavour to innovate using smart structures to enhance our everyday lives. One of the phenomena of shape memory alloys. the shape memory effect was put to use in the development of an active surface. Here the pre-stressed shape memory alloy (in its de-twinned martensitic state) is surrounded or embedded in a non-SMA matrix material. This active surface can be used in a variety of applications that requires active shape control to change the shape of a flexible structure member such as a submarine stem, aerospace control surfaces and aircraft wings. An experimental protocol was developed to treat or stabilize shape memory alloys that are used as actuators within composite structures. Shape memory alloys exhibit complex behaviour during their quasi-plastic material response. The complex behaviour includes variability in yield values and the transformation region/range.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2005 / The working characteristics of a shape memory alloy element providing either sensor or actuator capability is specified by the beginning and/or completion temperatures of the actuation (Le. austenitic start and finish temperatures and martensitic start and finish temperatures), the working actuator stroke (i.e. load induced twinned=:>de-twinned martensitic phase transformation also known as quasi-plastic deformation), and the working actuator force (provided by the temperature induced de-twinned martensite

Image processing systems have typically exhibited a high degree of application specificity. This makes it unlikely that any of the processing tasks for one application can be applied to another. Research has also found that such systems had not made use of knowledge about human perception although, it can be argued, such knowledge is independent of the application. This thesis takes the view that the structures which people perceive in pictures are of considerable importance to supporting picture-based human computer interaction. However, the design of systems which process pictures based on knowledge of human perception presents two major challenges. The first relates to determining the appropriate psychological knowledge that the computational modelling effort will be based upon. The second relates to the testing and evaluation of systems that aim to generate perceptually-valid structures, which poses significant problems because such systems are concerned with perceptual structures rather than semantic interpretations. An approach to developing picture processing systems is proposed that overcomes these problems. The approach represents a development strategy that exploits psychological theory in constructing image processing algorithms. The aim of these algorithms is to generate structures that match those perceived by humans. The approach enables new algorithms to be developed as additional psychological knowledge becomes available. Given appropriate training, users of such systems are able to see in images the structures that are generated by the system. The thesis presents the results of a study of perceptual and computational approaches to the processing of pictures. Motivations for and the development of a computational model based on perceptual grouping are described. A thorough evaluation of the computational model is performed which highlights both its value and limitations. Specific applications of the computational model in areas such as shape emergence in design, and pictorial databases, are then considered.

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Tropical cyclone (TC) size is integral in determining the spatial extent of TC impacts and is influenced by environmental wind shear and the overall moisture environment. Since initial TC size is related to future TC size, research focused on understanding the influences of TC size away from land can lead to a more complete understanding of the extent of coastal impacts associated with landfalling TCs. This study considers TCs located in an area of low to moderate wind shear located at least 100 km from major land masses. An empirical orthogonal function (EOF) analysis is used to distinguish different environments based on the large-scale spatial pattern of total column water vapor (TCWV) surrounding the TC. Using these EOF patterns, four separate categories (groups) are created. Principal component (PC) scores indicate the time steps most contributing to the EOF pattern for each group and ultimately determine the time steps included in each group. TC sizes among the groups are compared using size metrics based on the wind field and shape metrics based on the precipitation field. These metrics are considered at the central timestep identified in the EOF analysis as well as a 48-hour window centered on the central timestep. There are no significant differences in the wind field size, but TCs with moisture to the southeast are the largest in terms of overall precipitation area. This suggests that moisture affects the size of the precipitation field but not the wind field. However, more research is needed to confirm this relationship. Storms with moisture to the southeast are also more intense and younger than TCs in other groups and show signs of inner core organization and subsequent intensification while TCs in the other groups do not. TCs in an extremely dry environment or with dry air to the southeast of the TC center are generally smaller, less closed, less solid, and older than TCs with moisture to the southeast and TCs with dry air to the northwest of the TC center. An additional analysis comparing the same size and shape metrics between TCs experiencing easterly and westerly shear is also completed. The wind shear results suggest that, while easterly shear is more commonly associated with younger and intensifying TCs regardless of moisture group, an environment with westerly shear is more favorable for intensification of TCs with moisture to the southeast due to the alignment of moisture and upward motion. Future work will investigate the physical processes contributing to these precipitation shape and size differences between groups and wind shear directions. / Master of Science / The size of tropical cyclones (TCs) is heavily influenced by moisture and wind shear. Wind shear is defined as the changing of wind direction with vertical height in the atmosphere. Research focused on investigating how moisture and wind patterns affect the size and structure of TCs can lead to a better understanding of the physical extent of impacts associated with landfalling TCs and advise more effective emergency preparedness plans. This research considers TC time steps located over the ocean and in a calm wind environment. From here, time steps are divided into four groups representing common moisture patterns in the Atlantic basin. TC size is evaluated using size and shape metrics designed to capture the spatial extent and layout of wind and rain associated with the storm. This research also compares the evolution of these size and shape metrics to better understand how the environment around the TC changes over time. Results show that the extent of wind associated with the storm is similar across all groups but TCs with moisture to the southeast are the largest in terms of overall rain area. This suggests that moisture affects the extent of precipitation but not the extent of wind or that wind data are inaccurate. Additionally, TCs with moisture to the southeast are younger and stronger than storms in the other groups. TCs in extremely dry environments and TCs with dry air to the southeast are generally smaller, weaker, and older than TCs in the other groups. In looking at the evolution of these size and shape metrics, TCs with moisture to the southeast group become stronger with time while TCs in the other groups do not. An additional analysis comparing TCs experiencing different wind patterns is completed. Results of this show that, while easterly wind shear, characterized by surface winds out of the west and upper level winds out of the east, is more commonly associated with strengthening TCs when moisture is not considered, TCs with moisture to the southeast in an environment with westerly wind shear are more likely to strengthen over time due to the alignment of moisture with favorable environmental conditions within the storm by the overall wind pattern. Westerly shear is characterized by winds at the surface out of the east and upper level winds out of the west. Future work should focus on the environmental processes contributing to the size and shape differences observed between moisture groups and wind patterns.

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A shape memory polymer (SMP) is stimuli-responsive with the fantastic capacity to “memorize” a temporary shape under certain conditions and to recover to its permanent shape upon exposure to certain external stimulus (e.g. heat, light, electromagnetic field). In the past few decades, various SMPs have been investigated and applied in the area of aerospace, biomedicine, and textiles, etc. Recently, a special type of SMP called a ‘two-way reversible shape memory polymer’ or ‘reversible shape memory polymer’ (RSMP) capable of transitioning between two temporary shapes without the need for reprogramming after each change has attracted the attention of many researchers. In this class of polymer, the semicrystalline RSMP was studied considerably due to the various chain structures produced by relatively simple synthesis routes. The crystallization-induced elongation (CIE) and melting-induced contraction (MIC) of the oriented crystal domains has been theorized as the main mechanism of semicrystalline RSMP. However, most RSMPs are predominantly thermosets, which implies significant drawbacks regarding reprocessing and recycling. This thesis focuses on the development of RSMP based on polyolefin materials, especially novel high-performance polyolefin elastomers, due to the advantages of high crystallizability, varying chain structures, tunable and broad melting transitions, and low cost. The thesis starts off by demonstrating the reversible shape memory effect (RSME) of the thermoplastic ethylene/1-octene diblock copolymer, which contains the ethylene-rich hard segments and the 1-octene-rich soft segments. The delicately designed chain structure exhibited a broad melting transition and strong physical crosslinks, which contributed to the resulting RSME and the CIE/MIC effect at load-free conditions. Furthermore, the commercially available polyolefin elastomer blends demonstrated the RSME. The utilization of commercial products and simple processing method to achieve a thermoplastic RSMP offers easy production in large scale and low costs. The second part of the thesis developed a polyolefin-based RSMP with reconfigurable network by introducing a transesterification catalyst into a crosslinked poly(ethylene-co-vinyl acetate). The network reconfiguration achieved a dynamic covalent polymer network by breaking the ester bonds and reconnecting. The third part of the thesis explored a new RSMP foam material developed by utilizing polyolefins. The polyolefin elastomers of differing compositions were blended and foamed to fabricate the porous structure. The RSME in a load-free condition was then demonstrated successfully. This thesis represents significant progress in the development of polyolefin-based RSMPs, outlining new structural design, processability improvements, and potential applications. / Thesis / Doctor of Philosophy (PhD) / Shape memory polymer (SMP) is stimuli-responsive capable of “memorizing” a temporary shape and yet recovering to its permanent shape upon a certain external trigger. SMPs are widely studied and applied in the areas of aerospace, biomedicine, textile, etc. On the other hand, a reversible shape memory polymer (RSMP) is a new type of SMP that can shift back and forth between two different temporary shapes without the need of reprogramming between transitions, and has been applied in soft actuators, microrobotics, and artificial muscles. In this thesis, unique polyolefin-based RSMP were developed with good reprocessability and shown in new application scenarios. Firstly, a thermoplastic semicrystalline polymer was demonstrated to exhibit the reversible shape memory effect (RSME) by using a lab-designed ethylene/1-octene diblock copolymer and commercial polyolefin elastomer blends. Subsequently, the reprocessability of a crosslinked poly(ethylene-co-vinyl acetate) (PEVA) RSMP was improved by introducing a dynamic covalent polymer network. Finally, transitional changes between shapes was amplified by developing a RSMP foam by utilizing polyolefin elastomer blends. This thesis represents significant progress in the study of polyolefin-based RSMPs.

The present dissertation investigates perceptual grouping and shape completion in motion in younger and older observers. The first set of experimental results, Chapter 2, provides a set of exploratory experiments which characterize the nature of a motion grouping task, uncovering accurate direction discrimination when the stimulus contains a cue for global grouping, but compelling illusory motion when the stimulus does not contain that cue. Chapter 3 builds on the findings of Chapter 2 by measuring biases in motion integration that lead to the illusory motion. Chapter 3 extends this paradigm into older adult observers, and explores various stimulus variants and tasks to add to the characterization of this effect. In Chapter 4 the concepts of grouping and motion perception are examined in the context of shape completion by measuring the accuracy of aspect ratio, size, and area discrimination in younger and older adults. Chapter 4 concludes that older adults are worse at discriminating characteristics of shapes, but are similarly affected by incomplete or occluded stimuli as younger adults. On the whole, the dissertation demonstrates several novel findings in the perceptual organization literature, and investigates many of these phenomena into older adults populations. Throughout the dissertation, a central theme concerns the concept of behavioural measurement of perceptual processes, and consequently many of the phenomena are studied using several types of measurements and tasks to ensure a complete picture of the perceptual experience. The current dissertation presents a novel and important addition to the current literature in perceptual grouping and shape completion. / Dissertation / Bachelor of Arts (BA) / The visual experience of a human observer is the result of perceptual processing of the brain. The current dissertation focuses on a subset of these processes that concern the grouping of segmented parts into a single shape, while those segmented parts are in motion. This type of visual experience occurs regularly, in situations where part of a visual scene is occluded such as when viewing a moving object through a window occluded by window blinds. In general, we measure an observer's ability to identify the sources of motion, and the ability to infer the shape of the grouped object. In each experiment, the physical stimulus is varied while observers complete tasks using this stimulus. The dissertation characterizes perceptual organization processes using a number of different tasks, stimuli and paradigms in both younger and older adults. Each experimental result characterizes the perceptual abilities of younger and older observers, contributing to the literature of visual perceptual organization in aging.