Temporally selective attention allows for the preferential processing of stimuli presented at particular times, and is reasoned to be important for processing rapidly presented information such as speech. Recent event-related potential (ERP) evidence demonstrates that listeners direct temporally selective attention to times that contain word onsets in speech. This may be an effective listening strategy since these moments provide critical information to the listener, but the mechanism that underlies this process remains unexplored. In three experiments, putative attention cues including word recognition and predictability were manipulated in both artificial and natural speech and ERP responses at various times were compared to determine how listeners selectively process word onsets in speech. The results demonstrate that listeners allocate attention to word-initial segments because they are less predictable than other times in the speech stream. Attending to unpredictable moments may improve spoken language comprehension by allowing listeners to glean the most relevant information from an otherwise overwhelming speech signal.

<p>  </p> <p>Predators and parasites are critical, interconnected members of the community and have the potential to influence host populations. Predators, in particular, can have direct and indirect impacts on disease dynamics. By removing hosts and their parasites, predators alter both host and parasite populations and ultimately shape disease transmission. Our ability to accurately predict disease dynamics requires understanding the ecological effects of predation on prey and host densities and its role in the coevolution of host resistance and parasite virulence. While the impact of predators on disease dynamics has received considerable attention, research has focused on selective predation on infected prey. There is, however, substantial evidence that some predators avoid infected prey, preferentially attacking uninfected individuals. Such different strategies of prey selectivity by predators modulate host-parasite interactions, changing the fitness payoffs both for hosts and their parasites. I use empirical results and theoretical predictions as a framework to discuss the mechanisms by which predation for infected versus uninfected individuals can affect disease dynamics. First, by integrating hypotheses from behavioral ecology and disease ecology, I outlined novel perspectives that complement the prevailing view of selective predation of infected individuals (Chapter 1). Then, exploring short-term ecological outcomes and long-term host-parasite coevolution, I investigated patterns of <em>Daphnia dentifera</em> host population densities and host susceptibility over several generations under different types of predation pressure, including selective predation on infected and uninfected individuals (Chapter 2). Finally, building on the results of this research, I developed a high school project-based lesson plan that facilitates the instruction of the nature of science, implementing on-going ecological research in activities to improve student learning based on a constructivist approach to learning (Chapter 3). Together this research highlights the differential ecological and evolutionary outcomes of host-parasite interactions under varying community contexts.</p>

Selective encryption (SE) methods for images often encrypt the sign bits, i.e., the most significant bits (MSBs) of the codewords corresponding to key syntax elements (in compressed images) or to pixel intensities (for uncompressed images). Our work is motivated by the key observation that the binary code (BC) used for these representations has an impact on the quality of the reconstruction at the eavesdropper (Eve), which can be regarded as a measure of the degree of security of the encryption (the lower the quality, the higher the level of security). Therefore, we address the design of BCs that enhance the security of MSB-based SE by increasing the degradation at Eve’s side when she uses a simple replacement attack (replacing all MSBs either by 0s or by 1s). We first consider the scenario of fixed-length BCs, i.e., where all the codewords have the same length. We formulate the design problem as an optimization problem with the objective of maximizing the distortion at Eve’s without any constraint or with a constraint on the entropy of the MSBs in order to shorten the size of the MSB stream to reduce the computational overhead of encryption. We show that the problem can be cast as a binary integer linear program equivalent to a weighted non-bipartite graph matching problem, for which polynomial-time solution algorithms exist. We empirically assess the performance of the optimized BCs on a Mixed Gaussian source, as well as on Gaussian and Laplacian sources, the latter two being commonly used to model the distribution of transform coefficients and prediction residuals. Our experiments lead to the conclusion that MSB-based SE schemes could benefit from the proposed BC designs. For the case of uncompressed images, we also propose a family of structured BCs for the pixel intensity values. These BCs are constructed such that intensity values that are close have reconstructions that are far apart. As a result, the reconstruction with the replacement attack significantly destroys the smooth areas and blurs the edges, therefore increasing the degree of security. Next, we focus on the construction of variable-length BCs for the non-zero quantized AC coefficients in JPEG compressed images. For this, we first formulate the BC design problem as the problem of maximizing the distortion at Eve’s side with a constraint on the entropy. This problem can also be cast as a weighted non-bipartite graph matching problem and, therefore, can be solved efficiently. Furthermore, by gaining insights from the optimization results, a simpler and faster method for BC design is devised, which consists of only swapping a few codewords in the original code used in JPEG. We assess the practical performance of the proposed BCs for the SE method of JPEG images that encrypts only the MSBs of the non-zero quantized AC coefficients, along with the full encryption of the DC coefficients. Our experimental results show that high visual security can be achieved with only a small sacrifice in compression efficiency. In addition, the proposed BCs can be tuned to achieve various levels of degradation at Eve’s side, a property that is convenient for certain applications. / Thesis / Doctor of Philosophy (PhD)

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Renewable and clean energy is urgently needed to cope with the climate crisis. Photovoltaics (PV) has been the fastest growing technology in the clean energy market due to its low cost, and the abundance of solar energy. The capacity of silicon-based PV is rapidly expanding with evolving technologies. Passivating the solar cell’s electrical contacts is a widely accepted strategy for the PV industry to improve device power conversion efficiency (PCE). Polycrystalline silicon (Poly-Si) passivating contacts are one of the promising concepts in the emerging class of passivating contacts. In this dissertation, the passivation mechanism of Poly-Si passivating contacts is investigated. Moreover, the influence of dopant diffusion on the passivation quality is revealed. To address the side-effects of dopant diffusion, a thin buffer layer is inserted between the Poly-Si(p) layer and the $SiO_x$ layer. With such a buffer layer, the passivation of the Poly-Si passivating contact is improved, which in turn, enhances the device PCE. In addition to passivating contacts, this dissertation also explores carrier-selective contact of crystalline silicon (c-Si) and low work function metal – Li. Li is a very reactive metal which makes the fabrication process a challenge. To overcome such a challenge, the c-Si/ Li contact is fabricated by thermally decomposing stable $Li_3N$ powder instead of metal evaporation. The c-Si/Li contact shows an excellent electron-selective transport performance with a 0.39 eV energy barrier. Full-area Si/Li rear contact devices are fabricated, and >19% PCE and >80% fill factor are achieved. To accelerate the device optimization, a physical model embedded machine-learning approach is applied to transparent conductive oxide (TCO) materials optimization. In this work, empirical correlations between sputtering parameters and the deposited TCOs’ electrical properties are established. Then a Bayesian Parameter Estimation (BPE) algorithm is applied to learn the empirical model. With this BPE network, the TCOs’ electrical properties are successfully predicted with limited material characterizations. Thanks to the combination of BPE and a physical model network, the material optimization process is significantly accelerated. In summary, this dissertation explores different aspects to develop novel passivating and carrier-selective contacts for c-Si solar cells, and introduces an approach to accelerate the development processes.

Ultrafast lasers are valuable research and manufacturing tools. The ultrashort pulse duration is comparable to electron-lattice relaxation times, yielding unique interactions with matter, particularly nonlinear absorption, melting, and ablation. The field of ultrafast laser manufacturing is rapidly evolving with advances in related laser technologies. The applications of ultrashort pulse lasers in additive manufacturing aim to fill gaps left by conventional techniques especially on the nano- and micro-scale. Concurrently, uptake of ultrafast fiber lasers for micromachining has increased, and may replace the Ti:Sapphire laser as the ultrafast laser of choice. Both additive and subtractive manufacturing are accomplished with ultrafast lasers which presents the possibility of hybrid, all-in-one devices using a single laser source. As one such combination of laser techniques, ultrashort pulse surface modification of additively manufactured metals is an area of limited investigation. This thesis aims to address the ever-changing landscape of ultrafast laser manufacturing by 1) reviewing ultrafast laser additive manufacturing techniques and recent advancements 2) comparing the design, operation, and micromachining potential of a commercial ultrafast Ti:Sapphire and ultrafast fiber laser, and 3) investigating femtosecond ablation of as-printed additively manufactured Ti-6Al-4V at a range of parameters to test the feasibility of surface feature control. Ultrafast laser additive manufacturing is still in its infancy with mostly niche applications. The ultrafast fiber laser architecture is found to deliver a platform that is easier to operate and maintain and has superior micromachining throughput relative to Ti:Sapphire lasers. In our experimental work, five main surface morphologies are obtained by femtosecond ablation of a rough Ti-6Al-4V surface: laser-induced periodic surface structures (LIPSS), undulating grooves, micro-ripples, grooves, and micro-cavities. Transitions between ablation regimes and evolutions of the surface under increasing pulse energy and number of pulses are observed. These patterns allow for control over the surface geometry without the need for post-printing polishing. / Thesis / Master of Applied Science (MASc) / Ultrafast pulsed lasers of <10 picoseconds pulse duration are commonly used to modify, melt, or ablate materials. As an important research and manufacturing tool, ultrafast lasers and techniques have seen great change in the past two decades. Additive manufacturing has emerged as an area in which ultrafast lasers are becoming increasingly prevalent. To make sense of this continuously evolving landscape, this thesis 1) reviews ultrafast laser additive manufacturing techniques, applications, and advances towards industrial use and commercialisation, 2) compares the setup, operability, and characteristics for two ultrafast laser designs, and 3) investigates the surfaces produced by ultrafast laser irradiation of an additively manufactured titanium alloy part. The surface morphologies that are produced are categorised into five main patterns: laser-induced periodic surface structures, undulating grooves, micro-ripples, grooves, and micro-cavities. Each is a distinct pattern that may allow for tuning of the surface properties with respect to the wettability and biocompatibility.

This dissertation explores how children with and without developmental coordination disorder (DCD) ‘look’ and ‘see’: how they integrate vision and attention to guide arm and hand movements during a visuomotor task. Chapter 1 provides the thesis context, reviewing the vision and attention literature, outlining the role of these processes in motor performance, and reviewing what is known about vision and attention in children with DCD. Chapter 1 includes a discussion on eye tracking to measure visual attention, and outlines the thesis purpose and objectives.Chapter 2 focuses on children with DCD, detailing their presentation and clinical management. This chapter serves to increase the reader’s understanding of the difficulties children with DCD experience, and to demonstrate the need for intervention to prevent the profound consequences that can impact their quality of life. Chapter 3 presents a study that explores how children with and without DCD employ vision and attention to accomplish a visuomotor task in a natural setting, using a novel eye tracking design. Highlighted here are important differences during visuomotor task performance: compared to their peers, children with DCD did not use predictive gaze to attend to relevant task objects, but rather used vision to guide their arm/hand throughout the task. Chapter 4 outlines lessons learned from using an eye tracker with children with DCD, describing the children for whom eye tracking was not reliable, and discussing equipment and participant factors that impact eye tracker use. Recommendations for future research using eye tracking with the DCD population are provided. Finally, Chapter 5 discusses the clinical and research implications of the studies conducted here. Insights gained regarding visual attention differences between children with and without DCD are discussed in the context of interventions to improve health outcomes in children with DCD and the design of future eye tracking studies. / Dissertation / Doctor of Philosophy (PhD)

The application of uniformly distributed RC networks as feedback elements in the design of active circuits has been investigated. Distributed RC structures were fabricated using Mylar Film, Teledeltos resistance paper and metallic foil, and used to experimentally verify the predicted responses of particular active and passive configurations. By exploiting the frequency selective feedback provided by a distributed notch filter it was possible to construct an active band-pass filter operating at 1 MHz which achieved a Q of 50 without the use of inductance. For the design it was important that the notch parameter was deliberately chosen to be less than optimum (i.e., a< 17.78) so that the feedback circuit did not apply positive feedback in the region of the notch frequency. Application of positive feedback (a> 17.78) and sufficient amplifier gain would convert the active filter into a feedback oscillator. As predicted, the band-pass filter response was strongly influenced by the amplifier gain and phase characteristic, while amplifier impedance exerted only minor effects. / Thesis / Master of Engineering (ME)

京都大学 / 新制・課程博士 / 博士(情報学) / 甲第24932号 / 情博第843号 / 新制||情||141(附属図書館) / 京都大学大学院情報学研究科知能情報学専攻 / (主査)教授 神谷 之康, 教授 西田 眞也, 准教授 吉井 和佳 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DFAM

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