The dominance of Android and iOS have created a duopoly in the smartphone market. In this context, both Android and iOS need to select high quality apps from its massive number of app developers to recommend to app consumers. Generally speaking, when the market is small, the platform like Android and iOS can allocate resources to manual test the app quality for selection; but as the market size increased, the required resource for selection is also increased and would challenge the platform’s capability, thus the platform faces the selection difficulty. Unlike iOS, Android adopts an open strategy to compete against iOS for innovative developers. This strategy has led to inadvertent consequences including: "fragmentation" issues, weakened governance power, entry of non-competent developers and, notably, vetting of the quality of apps and developers. An app market is a two-sided platform based market. Research in platforms (Gawer and Cusumano, 2013) have primarily focused on what the technology platform owners should do. They assume that developers will equally respond to their platform strategy, for example, leaving the market when the platform owner sets higher barriers or enters when the platforms are more friendly. A few recent platform literatures (Boudreau, 2012; Eisenmann et al., 2011) start to look at developers’ unequal behaviour, such as developers with different competence would have different switching behaviours between different markets. However, in a duopoly setting, developers have limited alternatives but continue to work with both markets. The duopoly setting is interesting as the communication of app quality is critical for competition, and this thesis aims to examine the competent developers’ strategic behaviours from the lens of signal theory. I argue that competent developers will engage in costly actions to compete against non- competent counterparts in such a duopoly context. For example, competent developers will spend time to make their apps to be unique and innovative in the Android app market, or enhance the technology used in their apps to protect app consumers’ privacy, and other more behaviours discussed in the thesis. It is inspired to understand these unique behaviour by competent developers as strategic signals to communicate their innovative behaviour in the app economy. Information asymmetry (Stiglitz, 2002) is believed to cause the difficulty for platform selection based on the developer’s innovativeness in such a crowded space. Based on the signalling theory (Spence, 1973), the thesis develops a signalling selection model to understand the motivation and implication of these strategic signals. iOS is not open and is, therefore, difficult to collect research data. To study strategic signals, I collected a panel data set composed of 93% of all apps and their developers in the Google Play Store which is the official Android app market. The thesis firstly filtered out all developers who are featured as "Top Developer" by Google in the Google Play Store. They are treated as innovative developers. The thesis then filtered out all non-featured developers who are relevant to these innovative developers and treated them as non-innovative developers. The thesis qualitatively and quantitatively analyses innovative developers’ strategic behaviour in the Google Play Store. It is found that these strategic signals are unlikely to be generated by non-innovative developers because they have a higher cost. The cost could be due to, for example, the R&D on technology advancement, the challenge of creative business model design, etc. It provides the platform owner with an opportunity to observe these signals only uniquely by innovative developers, and feedback with featuring awards. These awards would bring huge customer access and generate large long-term benefits on business performance. The benefits motivate the innovative developers to continue on these strategic signals generation, which increases the availability of innovative apps. The signals can also be observed by other developers and motivate non-featured developers to learn from featured innovative developers to increase their featuring opportunity, which is studied as the peer effect in the thesis. This peer effect in learning enables the opportunity for the platform owner to develop and maintain the app market into an ecosystem. Rather than managing all developers, as emphasised by existing platform strategies, this thesis argues the platform owner can focus on selecting a small number of innovative developers to influence the large developers community with the signalling selection model. The contribution of this thesis is to shift the focus of platform strategy from platform centric to developer centric. I argue that innovative developers would behave differently from others. Their strategic behaviour serves as a signal for the platform owner to vet the quality of innovativeness. The thesis studied a duopoly context of app economy where switching is limited to two dominant platforms. It develops a signalling selection model to solve the selection difficulty of innovativeness in such a unique context. According to my knowledge, it is the first time the signalling theory has been applied to the app economy. The selection of innovativeness is friendly to newly entranced developers which is less focused by existing platform centric strategies. The research on app economy is still rare but the importance of the app economy is significantly increased in daily life. The large-scale data set, methodology and results from this research should be valuable for future research in the app economy.

Yersinia pseudotuberculosis is a mammalian enteropathogen and is the direct ancestor of Y. pestis, the causative agent of the plague. For its pathogenicity, Y. pseudotuberculosis harbours a 70 kb virulence plasmid which encodes the components of the type three secretion system (T3SS) and effector proteins. These effectors serve to evade the host immune system and induce apoptosis of mammalian cells. Consistent with many Gram-negative bacteria, Yersinia facilitate cell: cell signalling through the production and sensing of N-acylhomoserine lactones (AHLs), which functions to mediate the expression of downstream target genes. This cell-cell communication is known as quorum sensing (QS) and is facilitated by two LuxI/R-type systems in Y. pseudotuberculosis: YtbI/R and YpsI/R, and several AHL molecules. Behaviours under QS control include motility, biofilm formation, clumping and the regulation of the T3SS. Recently, QS was reported to repress the T3SS whilst the T3SS attenuated biofilm formation on Caenorhabditis elegans. Colonising both the soil/water environment and the mammalian gut, Y. pseudotuberculosis exhibits a biphasic lifestyle whereby it exerts strict temperature-dependent control over the expression of pYV-encoded genes. The switch between these two lifestyles is govered by a pair of virulence regulators: LcrF is a transcriptional activator that targets pYV-encoded genes and is key for the assembly of the T3SS. Conversely, YmoA is a histone-like protein that represses transcription of lcrF through chromatin compaction. Considering the repression of the T3SS by QS, this study set out to investigate whether this regulation is mediated by a relationship between QS and LcrF/YmoA. By using chromosomal promoter:lux fusions, QS was identified to be an activator of YmoA at both 22oC and 37oC whilst a regulatory relationship between QS and LcrF was also identified. To investigate these links further, AHL profiling of the lcrF and ymoA mutants identified YmoA as a repressor of AHL biosynthesis whilst a very subtle repression was observed in ΔlcrF, suggesting that LcrF may influence AHL synthesis indirectly. Assessing the impact of LcrF and YmoA on the QS-mediated phenotypes of Yop secretion, biofilm formation and motility extended these observations. LcrF had no effect on any of the phenotypes examined supporting the hypothesis of either an indirect mode of regulation, or no regulation at all. In contrast, YmoA influenced both motility and biofilm formation. A decreased motility of ΔymoA was observed on both semi-solid agar and in liquid whereby both the speed and the percentage of motile cells was altered. This suggests an activating role of YmoA on motility. Interestingly, QS is known to repress motility therefore it is likely that YmoA-regulation of motility occurs irrespective of QS. Comparable to that of the QS synthase mutant (ΔypsI/ytbI), biofilm was attenuated in ΔymoA yet restored when cells were cured of the virulence plasmid supporting the hypothesis that the type three-secretion injectisome disrupts biofilm formation. This attenuation of biofilm formation in ΔymoA, in conjunction with the activation of ymoA by QS, led to the hypothesis that the repression of the T3SS by QS works through YmoA. Considering these results, evidence for an interaction between QS and virulence regulators LcrF and YmoA has been confirmed. We propose a model whereby YmoA is the missing link in the QS-mediated repression of the T3SS. Activation of YmoA by QS leads to increased repression of lcrF and subsequently, of the T3SS resulting in the de-repression of this system in the absence of QS.

I propose that dominant discourses on veiling objectify Muslim women and do not engage with Muslim women dialogically as subjects capable of agency and selfdefinition. In this thesis I explore this problem critically within two different contexts, namely in selected Muslim minority contexts of Europe and America, and in the particular Muslim majority context of Iran. I illustrate that these highly politicized discourses often instrumentalise representations of Muslim women for their respective ideological agendas. I then present an alternative mode of engagement with the issue of veiling by examining the varying, marginalized voices, subjectivities and agency of Muslim women in their understandings of this phenomenon. It is imperative to question stereotypes and universalistic assumptions concerning Muslim women's bodies, modesty, dressing and agency in order to advocate a new gender consciousness which sees women as subjects. The various discourses of the veil reflect that Muslim women's choices and opinions are divided. As such, it is important to listen to Muslim women's voices to be able to create a discourse that is based on dialogue, authentic representations, mutual understanding and respect.

This dissertation is a formal study of musical bow revivals in South Africa, based on an assessment of the instruments' historical and current usage, and functions. This study is also the inevitable result of my responses to certain musical experiences during the past three years, and which generated in me a personal commitment to the practice of African cultural music, which I 'discovered' through studies with Dizu Plaatjies and other African music specialists, who also speak through this study. My growing interest drew me to musical bows, which have become my principal instruments for musical compositions, and also personal expression. The primary focus of the dissertation is current bow practice in the Eastern and Western Cape, and certain areas in KwaZulu Natal, and personal interaction with people who became my main informants and teachers.

This report details procedures for transferring data between the HP-75 and HP-9845 microcomputers, and between the HP-75 and HP-86 microcomputers. Specific guidance is given on the mechanics of interfacing the computers. Software is provided for each computer that will enable the user to transfer data between computers.

In this thesis we formalise and study computational aspects of group decision making for rational, self-interested agents. Specifically, we are interested in systems where agents reach consensus according to endogenous thresholds. Natural groups have been shown to make collective decisions according to threshold-mediated behaviours. An individual will commit to some collective endeavour only if the number of others having already committed exceeds their threshold. Consensus is reached only where all individuals express commitment. We present a family of models that describe fundamental aspects of cooperative behaviour in multi-agent systems. These include: coalition formation, participation in joint actions and the achievement of individuals’ goals over time. We associate novel solution concepts with our models and present results concerning the computational complexity of several natural decision problems arising from these. We demonstrate potential applications of our work by modelling a group decision problem common to many cohesive groups: establishing the location of the group. Using model checking tools we compute the effects of agents’ thresholds upon outcomes. We consider our results within an appropriate research context.

Hyper-heuristics are a class of high-level search methodologies which operate over a search space of heuristics rather than a search space of solutions. Hyper-heuristic research has set out to develop methods which are more general than traditional search and optimisation techniques. In recent years, focus has shifted considerably towards cross-domain heuristic search. The intention is to develop methods which are able to deliver an acceptable level of performance over a variety of different problem domains, given a set of low-level heuristics to work with. This thesis presents a body of work investigating the use of selection hyper-heuristics in a number of different problem domains. Specifically the use of crossover operators, prevalent in many evolutionary algorithms, is explored within the context of single-point search hyper-heuristics. A number of traditional selection hyper-heuristics are applied to instances of a well-known NP-hard combinatorial optimisation problem, the multidimensional knapsack problem. This domain is chosen as a benchmark for the variety of existing problem instances and solution methods available. The results suggest that selection hyper-heuristics are a viable method to solve some instances of this problem domain. Following this, a framework is defined to describe the conceptual level at which crossover low-level heuristics are managed in single-point selection hyper-heuristics. HyFlex is an existing software framework which supports the design of heuristic search methods over multiple problem domains, i.e. cross-domain optimisation. A traditional heuristic selection mechanism is modified in order to improve results in the context of cross-domain optimisation. Finally the effect of crossover use in cross-domain optimisation is explored.

This thesis focus on the analysis of digitized microscopic image, especially on IHC stained colour images. The corresponding contributions focused on the automatic detection of stain colour and glands, the segmentation and quantification of cell nuclei, the analysis of liver cirrhosis and the development of a semi-automatic toolbox. Colour is the most important feature in the analysis of immunostained images. We developed a statistical colour detection model for stain colour detection based on the histograms of collected colour pixels. This is acting on the approach "what you see is what you get" which outperforms the other methods on the detection of several kinds of stain colour. Verifying the presence of nuclei and quantifying positive nuclei is the foundation of cancer grading. We developed a novel seeded nuclei segmentation method which greatly improves the segmentation accuracy and reduces both over-segmentation and under-segmentation. This method has been demonstrated to be robust and accurate in both segmentation and quantification against manual labelling and counting in the evaluation process. The analysis of gland architecture, which reflects the cancer stage, has evolved into an important aspect of cancer detection. A novel morphology-based approach has been developed to segment gland structures in H-DAB stained images. This method locates the gland by focusing on its morphology and intensity characteristics, which covers variations in stain colours in different IHC images. The evaluation results have demonstrated the improvements of accuracy and efficiency. For the successive development of three methods, we put them in a semi-automatic toolbox for the aid of IHC image analysis. It can detect different kinds of stain colour and the basic components in an IHC image. The user created models and parameters can be saved and transferred to different users for the reproduction of detection results in different laboratories. To demonstrate the flexibility of our developed stained colour detection technique, the tool has been extended to the analysis of liver cirrhosis. It is a novel method based on our statistical colour detection model which greatly improves the analysis accuracy and reduces the time cost.

X-ray micro computed tomography (µCT) is increasingly applied in plant biology as an imaging system that is valuable for the study of root development in soil, since it allows the three-dimensional and non-destructive visualisation of plant root systems. Variations in the X-ray attenuation values of root material and the overlap in measured intensity values between roots and soil caused by water and organic matter represent major challenges to the extraction of root system architecture. We propose a novel technique to recover root system information from X-ray CT data, using a strategy based on a visual tracking framework embedding a modiffed level set method that is evolved using the Jensen-Shannon divergence. The model-guided search arising from the visual tracking approach makes the method less sensitive to the natural ambiguity of X-ray attenuation values in the image data and thus allows a better extraction of the root system. The method is extended by mechanisms that account for plagiatropic response in roots as well as collision between root objects originating from different plants that are grown and interact within the same soil environment. Experimental results on monocot and dicot plants, grown in different soil textural types, show the ability of successfully extracting root system information. Various global root system traits are measured from the extracted data and compared to results obtained with alternative methods.

Location-based experiences depend on the availability and reliability of wireless infrastructures such as GPS, Wi-Fi, or mobile phone networks; but these technologies are not universally available everywhere and anytime. Studies of deployed experiences have shown that the characteristics of wireless infrastructures, especially their limited coverage and accuracy, have a major impact on the performance of an experience. It is in the designers’ interest to be aware of technological restrictions to their work. Current state of the art authoring tools for location-based experiences implement one common overarching model: the idea of taking a map of the physical area in which the experience is to take place and then somehow placing virtual trigger zones on top of it. This model leaves no space for technological shortcomings and assumes a perfect registration between the real and the virtual. In order to increase the designers’ awareness of the technology, this thesis suggests revealing the wireless infrastructures at authoring time through appropriate tools and workflows. This is thought to aid the designers in better understanding the characteristics of the underlying technology and thereby enable them to deal with potential problems before their work is deployed to the public. This approach was studied in practice by working with two groups of professional artists who built two commercially commissioned location-based experiences, and evaluated using qualitative research methods. The first experience is a pervasive game for mobile phones called ‘Love City’ that relies on cellular positioning. The second experience is a pervasive game for cyclists called ‘Rider Spoke’ that relies on Wi-Fi positioning. The evaluation of these two experiences revealed the importance of an integrated suite of tools that spans indoors and outdoors, and which supports the designers in better understanding the location mechanism that they decided to work with. It was found that designers can successfully create their experiences to deal with patchy, coarse grained, and varying wireless networks as long as they are made aware of the characteristics.