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Thermoacoustic devices represent a significant future opportunity in the fields of energy generation and refrigeration. A key component of this type of device is the regenerator, where the conversion between acoustic energy and thermal energy takes place. This conversion occurs due to an externally imposed temperature gradient on the wall of the regenerator channels. Hence, this study concerns the physics of sound waves in the proximity of such walls. It establishes a new analytical framework which clarifies the disturbance energy conservation in thermoacoustic devices. In this framework, a thermoacoustic production term is proposed to quantify the generation or consumption of disturbance energy originating from the temperature gradient. An extended disturbance energy flux term is identified to account for wave growth or decay through the regenerator. The disturbance energy balance relation states that the disturbance energy flux equals the thermoacoustic production less the viscous and thermal dissipation resulting from gradients of fluctuating velocity and temperature. The analytical framework is implemented into an axisymmetric cylindrical domain; the two-dimensional nature of this work helps to uncover that the wave always decays in the region close to the wall. A dimensional analysis is conducted to identify the controlling parameters, namely the Womersley, Helmholtz and Prandtl numbers. A parametric study of the Womersley and Helmholtz numbers is conducted to showcase the new analytical methodology; the results make it possible to optimize the geometry, wave properties and working conditions of a thermoacoustic device according to the preference of its efficiency, loss and output. This study then validates the analysis in an actual thermoacoustic engine environment. A straight waveguide with a loudspeaker at one end and wave absorbing material at the other simulates a travelling-wave condition of various frequencies. A novel regenerator consisting of 671 thin stainless-steel tubes were inserted into two copper heat exchangers to form an integral block. The design enables reproduction of the geometry and a known, constant, precisely controlled wall temperature gradient as in the model. The selection of material also encourages radial heat conduction while minimising the axial one. The experimental results show excellent agreement with the numeral model and validates the analytical framework proposed. The maximum measured wave growth was 1.76 when the temperature difference between hot and cold end of the regenerator was 303K.

Efferocytosis, the clearance of apoptotic cells including apoptotic neutrophils by macrophage phagocytosis, is a key cellular mechanism for resolution of inflammation and tissue repair. Cyclin-dependent kinases (CDKs) 7 and 9 phosphorylate RNA polymerase II that is vital for neutrophil transcriptional capacity. CDK inhibitors such as R-roscovitine, and the more selective inhibitor AT7519, induce neutrophil apoptosis and promote resolution of several mouse models of inflammation including acute lung inflammation. The hypothesis investigated here was that AT7519 would promote neutrophil apoptosis (i) in the infarcted heart, leading to macrophage polarisation, angiogenesis, reduced infarct expansion and retention of cardiac function and (ii) in the peritoneum, enhancing resolution of sterile peritonitis. AT7519 (1μM) induced apoptosis of mouse unstimulated-bone marrow derived neutrophils and thioglycollate-stimulated neutrophils in vitro in a time- and caspase-dependent manner, but did not alter activation assessed by calcium flux in response to the synthetic formyl peptide (fMLF) or platelet-activating factor (PAF). Only high concentrations of AT7519 (10 μM) induced monocyte/macrophage apoptosis and this was likely due to saturated phagocytosis of apoptotic neutrophils induced by high concentration of AT7519. Myocardial infarction (MI) was induced by coronary artery ligation in adult male mice and infarct volume was assessed 7 or 21 days later by in vitro optical projection tomography (OPT). The novel use of OPT for this purpose was validated by demonstrating correlation with infarct volume obtained by late-gadolinium enhanced magnetic resonance imaging in vivo and with infarct area assessed by histological staining (Masson’s Trichrome) in tissue sections. AT7519 (30 mg/kg i.p.) increased the number of apoptotic neutrophils (cleaved caspase-3 and Ly6G +ve) in the heart when administered after MI, but this was not associated with any subsequent alteration in macrophage polarisation, vessel density, infarct expansion or structural and functional remodelling of the left ventricle. In contrast, induction of neutrophil apoptosis by AT7519 (30mg/kg i.p.) successfully promoted macrophage polarisation and the resolution of inflammation associated with peritonitis elicited by either 10% thioglycollate or by 1mg zymosan. AT7519 treatment also reduced the number of CD19+ B cells, Foxp3+CD4+ T cells and eosinophils in peritoneal lavage, and prolonged the phase of monocyte recruitment in zymosan-induced peritonitis. In conclusion, AT7519 successfully induced mouse neutrophil apoptosis in vitro, as well as in vivo in experimental MI and peritonitis. Subsequent promotion of inflammation resolution in peritonitis was not matched by improved outcome following MI. Unexpected effects of CDK inhibition on monocytes, T cells and eosinophils that are necessary for myocardial infarct repair may have compromised any beneficial effects resulting from promotion of in situ neutrophil apoptosis. CDK inhibition may therefore have therapeutic potential for the treatment of peritonitis, but not for prevention of infarct expansion and detrimental ventricular remodelling after MI.

Tropilaelaps mercedesae (small mite) is one of two major honey bee ectoparasitic mite species responsible for the colony losses of Apis mellifera in Asia. Although T. mercedesae mites are still restricted in Asia (except Japan), they may diffuse all over the world due to the ever-increasing global trade of live honey bees (ex. Varroa destructor). Understanding the ecological characteristics of T. mercedesae at molecular level could potentially result in improving the management and control programs. However, molecular and genomic characterization of T. mercedesae remains poorly studied, and even no genes have been deposited in Genbank to date. Therefore, I conducted T. mercedesae genome and transcriptome sequencing. By comparing T. mercedesae genome with other arthropods, I have gained new insights into evolution of Parasitiformes and the evolutionary changes associated with specific habitats and life history of honey bee ectoparasitic mite that could potentially improve the control programs of T. mercedesae. Finally, characterization of T. mercedesae transient receptor potential channel, subfamily A, member 1 (TmTRPA1) would also help us to develop a novel control method for T. mercedesae.

An efficient and flexible modelling and simulation toolset for solving spatially-resolved models of photovoltaic (PV) devices is developed, and its application towards a quantitative description of localised electrical behaviour is given. A method for the extraction of local electrical device parameters is developed as a complementary approach to the conventional characterisation techniques based on lumped models to meet the emerging demands of quantitative spatially-resolved characterisation in the PV community. It allows better understanding of the effects of inhomogeneities on performance of PV devices. The simulation tool is named PV-Oriented Nodal Analysis (PVONA). This is achieved by integrating a specifically designed sparse data structure and a graphics processing unit (GPU)-based parallel conjugate gradient algorithm into a PV-oriented numerical solver. It allows more efficient high-resolution spatially-resolved modelling and simulations of PV devices than conventional approaches based on SPICE (Simulation Program with Integrated Circuit Emphasis) tools in terms of computation time and memory usage. In tests, mega-sub-cell level test cases failed in the latest LTSpice version (v4.22) and a PSpice version (v16.6) on desktop PCs with mainstream hardware due to a memory shortage. PVONA efficiently managed to solve the models. Moreover, it required up to only 5% of the time comparing the two SPICE counterparts. This allows the investigation of inhomogeneities and fault mechanisms in PV devices with high resolution on common computing platforms. The PVONA-based spatially-resolved modelling and simulation is used in various purposes. As an example, it is utilised to evaluate the impacts of nonuniform illumination profiles in a concentrator PV unit. A joint optical and electrical modelling framework is presented. Simulation results suggest that uncertainties introduced during the manufacturing and assembly of the optical components can significantly affect the performance of the system in terms of local voltage and current distribution and global current-voltage characteristics. Significant series resistance and shunt resistance effects are found to be caused by non-uniformity irradiance profiles and design parameters of PV cells. The potential of utilising PVONA as a quality assessment tool for system design is discussed. To achieve quantitative characterisation, the PVONA toolset is then used for developing a 2-D iterative method for the extraction of local electrical parameters of spatially-resolved models of thin-film devices. The method employs PVONA to implement 2-D fitting to reproduce the lateral variations in electroluminescence (EL) images, and to match the dark current-voltage characteristic simultaneously to compensate the calibration factor in EL characterisations. It managed to separate the lateral resistance from the overall series resistance effects. The method is verified by simulations. Experimental results show that pixellation of EL images can be achieved. Effects of local shunts are accurately reproduced by a fitting algorithm. The outcomes of this thesis provide valuable tools that can be used as a complementary means of performance evaluation of PV devices. After proper optimisation, these tools can be used to assist various analysis tasks during the whole lifecycle of PV products.

The thesis presents the development and validation of novel computational technology for modelling and analysis of damage and failure in quasi-brittle materials. The technology is demonstrated mostly on concrete, which is the most widely used quasi-brittle material exhibiting non-linear behaviour. Original algorithms and procedures for generating two-dimensional (2D) and three-dimensional (3D) heterogeneous material samples are developed, in which the mesoscale features of concrete, such as shape, size, volume fraction and spatial distribution of inclusions and pores/voids are randomised. Firstly, zero-thickness cohesive interface elements with softening traction-separation relations are pre-inserted within solid element meshes to simulate complex crack initiation and propagation. Monte Carlo simulations (MCS) of 2D and 3D uniaxial tension tests are carried out to investigate the effects of key mesoscale features on the fracture patterns and load-carrying capacities. Size effect in 2D concrete is then investigated by finite element analyses of meso-structural models of specimens with increasing sizes. Secondly, a 3D meso-structural damage-plasticity model for damage and failure analysis of concrete is developed and applied in tension and compression. A new scheme for identifying interfacial transition zones (ITZs) in concrete is presented, whereby ITZs are modelled by very thin layers of solid finite elements with damage-plasticity constitutive relations. Finally, a new coupled method named non-matching scaled boundary finite element-finite element coupled method is proposed to simulate crack propagation problems based on the linear elastic fracture mechanics. It combines the advantage of the scaled boundary finite element method in modelling crack propagation and also preserves the flexibility of the finite element method in re-meshing. The efficiency and effectiveness of the developed computational technology is demonstrated by simulations of crack initiation and propagation problems.

Due to quiet operation, no moving parts, long lifespan and compact structure, the thermoelectric application has become a potential green technology which has been used in different areas in the efforts of contributing to achieve simplified and compact system structures and environmental friendliness. Its applications cover a wide range from the earliest application on kerosene lamp to aerospace applications, transportation tools, industrial utilities, medical services, electronic devices and temperature detecting & measuring facilities. Its disadvantage lies in the low conversion efficiency which only converts small amount (for Bi2Te3, up to 5%) of harvested energy to electrical power. It makes the use of the TEG system far from being economically feasible due to long cost recovery period. Consequently, its use is limited to specialised area where it is unnecessary to consider the cost of the thermal energy input and system cost recovery. This research aims to explore a way of widening the application range of thermoelectric generation based on introducing a potential direction of improving energy utilisation efficiency to a higher level by adopting thermoelectric cogeneration concept in residential house. It focuses on investigating the practicality of using thermoelectric applications in domestic sectors where the large amount of heat is exhausted to environment without being used and developing thermoelectric cogeneration system to generate electricity and produce pre-heated water for domestic use by recovering the waste heat from the domestic boiler and utilising the on-site solar energy. With the conversion efficiency given by the current commercially available thermoelectric modules, the optimised heat exchanging regimes and systems for thermoelectric applications have been comprehensively studied from the aspects of system design, integration, experimental study, numerical simulation and modification. The importance and necessity of effective heat exchanging methods have been emphasised by the experimental and numerical proofs for the development of a domestic thermoelectric cogeneration system with higher thermal efficiency. The impacts of this domestic energy solution have been evaluated from the aspects of the improvement for outdoor environment and indoor energy profile, as well as economic benefit. For the flue gas heat exchanger, the model with sudden expansion and gradual constriction has been identified gives in terms of overall performance. The model with sudden expansion, gradual constriction and staggered pipe layout and the one with sudden expansion, gradual constriction and inline pipe layout show better overall performance than other models. Among these two models, the one with staggered pipe layout shows better performance than the one with inline pipe layout in the velocity range of 3.6m/s-5m/s, whilst the one with inline pipe layout shows better performance between 0-3.6m/s. For the cold side heat exchanger, the one with four ø5mm branch channel angled at 90 against the main channel delivers the best overall performance out of 9 cooling plates built according to three variables. Experimental studies show the one-stage TCS produces more power than the two-stage TCS does when the heat input is supplied at 47W and 60W. As the heat input increases, the power output of two-stage TCS gets closer to that of one-stage TCS. In the system construction and assembly, uneven assembly can lead to a 20% drop in conversion efficiency. The pressure load at 18lpsi gives the highest power output out of five load values, which are 136psi, 159psi, 181psi, 204psi and 227psi, respectively. In comparison with individual assembly, module thickness difference in whole assembly degrades the system conversion efficiency. The cost recovery period of deploying this system in a residential house installed with a 24kW boiler and a 1 m2 solar collector has been evaluated. Based on the conversion efficiency and thermal efficiency that is 4% and 67% at 130C temperature difference. the house can produce 98W electricity and 1640W useable heat when the boiler is running and the contribution from the solar energy is included. It takes less than 4.2 years to recover the system cost.

Evolution shapes biological systems to better match their desired functions. Hence, we can assume that sensory systems are adapted to optimize information processing. Nevertheless surprisingly little is known about how sensory systems are optimised, or organised, in relation to the information sampling and processing they perform. In particular, our understanding is limited on certain fundamental issues: (1) what are the roles of individual ionchannels in coding information in specialised neural networks, (2) how does information transfer through synapses, and (3) how are different types of information (motion/colour) routed and processed for higher order visual functions. Dipteran compound eyes provide highly useful model systems for examining the basic mechanisms involved in visual information processing; in particular, for assessing how graded potentials code visual information. For this thesis, I have performed extracellular and intracellular recordings from photoreceptors and their primary interneurones, large monopolar cells (LMC), in Calliphora and Drosophila, to investigate the three essential questions mentioned above. This thesis provides systematic characterisations of: (1) Drosophila dSK channels, small conductance calcium-activated potassium channels; (2) Adapting dynamics of postsynaptic quantal bumps in the first visual synapse in Calliphora; (3) in vivo spectral sensitivities of Drosophila R1-R6 photoreceptors and LMCs in wild-type and in selected mutant and transgenic flies. Together with collaborations inside/outside our laboratory, my study: (1) identified the functional roles and gain control of dSK channels in the first synaptic circuits in the fly eye and also clarified how intrinsic activities of neural network compensates for missing or faulty ion channels; (2) characterised how postsynaptic unitary voltage events (or bumps) adapted dynamically to maximize the rate of information transfer at the fly first visual synapse; 3) provided the first in vivo spectral sensitivity functions of Drosophila R1-R6 photoreceptors and LMCs, and demonstrated that functional inputs, from photoreceptors that have different spectral sensitivities, improve motion discrimination and robustness of perception.

Construction is complex and comprises a multitude of knowledge-driven activities and business interests from participating organisations with the people involved being subject to different organisational and disciplinary practices. People are fundamental to success because human capabilities in learning, innovating and changing creative directions are vital to long term development of organisations. In the last two decades, researchers have found that human resource (HR) management has positive effects on the organisational performance. However, the processes through which HR management lead to organisational performance are contested. This research proposes a framework to investigate the effects of employees' behaviours and organisational learning on organisational performance and the impacts of HR practices on those effects in the context of Chinese construction enterprises. The research design adopts a multi-method approach, integrating positivism and interpretivism, to understand the complex relationship between HR practices, organisational learning, individual behaviour, and organisational performance. By consulting two experienced academic researchers and industry experts, the pilot study improves the understanding and implementation of the measurement instruments employed. Both quantitative and qualitative approaches are adopted in data collection and analysis: 326 valid respondents through questionnaire survey are received, and structural equation modelling is adopted to test individual behaviour and organisational learning as mediating variables of the relationship between HR practices and organisational performance respectively. Middle-level managers in Chinese construction firms are interviewed, and a cognitive map is produced to reveal the possible mediating variables and the cause-effect relationships between organisational learning and individual behaviour. The cause-effect route identified from the cognitive map is tested by structural equation modelling method, i.e., individual in-role behaviour as a mediating variable between organisational learning and performance. In conclusion, from the theoretical perspective, the results reveal the following. (1) Individual in-role behaviour has highly significantly positive effect on organisational performance. Organisational learning has very highly significantly positive effect on organisational performance. Both individual in-role behaviour and organisational learning have mediating effects on the relationship between HR practices and organisational performance. (2) HR practices positively affect individual in-role behaviour indirectly through organisational learning. Individual in-role behaviour mediates the relationship between organisational learning and organisational performance. (3) HR practices also affect organisational performance via the path-way of social capital, individual perceived organisational support, organisational citizenship behaviour (OCB), and co-worker productivity. For the practical implications, Chinese construction companies should implement the following to improve organisational performance. (1) Recognize the importance of employees' in-role behaviour, and design HR practices to motivate employees to apply their knowledge, skills and abilities in job-related performance, and to retain qualified and experienced staff. (2) View organisational learning as an important component of competitive advantage in the process of organisational development, and motivate and enhance organisational learning by the employment of HR practices and the creation of social capital. (3) Recognize the importance of OCBI (i.e. organisational citizenship behaviour directed toward the benefit of other individuals), and try to elicit employees' OCBI by improving employees' perceived organisational support.

Web services have been widely adopted as a new distributed system technology by industries in the areas of, enterprise application integration, business process management, and virtual organisation. However, lack of semantics in current Web services standards has been a major barrier in the further improvement of service discovery and composition. For the last decade, Semantic Web Services have become an important research topic to enrich the semantics of Web services. The key objective of Semantic Web Services is to achieve automatic/semi-automatic Web service discovery, invocation, and composition. There are several existing semantic Web service description frameworks, such as, OWL-S, WSDL-S, and WSMF. However, existing frameworks have several issues, such as insufficient service usage context information, precisely specified requirements needed to locate services, lacking information about inter-service relationships, and insufficient/incomplete information handling, make the process of service discovery and composition not as efficient as it should be. To address these problems, a context-based semantic service description framework is proposed in this thesis. This framework focuses on not only capabilities of Web services, but also the usage context information of Web services, which we consider as an important factor in efficient service discovery and composition. Based on this framework, an enhanced service discovery mechanism is proposed. It gives service users more flexibility to search for services in more natural ways rather than only by technical specifications of required services. The service discovery mechanism also demonstrates how the features provided by the framework can facilitate the service discovery and composition processes. Together with the framework, a transformation method is provided to transform exiting service descriptions into the new framework based descriptions. The framework is evaluated through a scenario based analysis in comparison with OWL-S and a prototype based performance evaluation in terms of query response time, the precision and recall ratio, and system scalability.

The quasi-one-dimensional cuprate PrBa2Cu408 and purple bronze Li0.9Mo6O17 have been studied by electrical and thermal transport, to test an empirical law, the Wiedemann Franz law in the possible one-dimensional limit. In strictly one-dimensional interacting systems, the Fermi liquid picture breaks down and a new generic quantum many-body state, the so-called Tomonaga-Luttinger liquid emerges, where the low energy excitations are uncoupled collective modes of spin and charge.

In science and engineering fields, linear system theories have been well established both in the time and frequency domain and have wide applications in practice. The study of nonlinear systems has received increasing attention since the early twentieth century, because there are limitations of the use of linear systems in representing real systems especially in explaining important nonlinear phenomena such as harmonics and chaos.

The insertion sequence ISY100 is a member of the IS630/Tc1/mariner superfamily of transposable elements. An in vivo transposition assay was set up in this study, confirming the TA target preference of ISY100 and showing that 30 bp from each end of ISY100 is sufficient for efficient transposition. Purified His-tagged transposase bound the transposon ends, protecting approximately 26 bp from cleavage by DNase I at each end. Two helix-turn-helix DNA binding motifs linked by an ‘AT-hook’-like sequence were predicted in the N-terminal domain of ISY100 transposase. Supercoiled plasmid containing ISY100 ends, and synthetic linear transposon ends were tested for cleavage by transposase in vitro. Cleavage products were observed and the cleavage sites were mapped. Linear DNA fragments containing single ISY100 ends were cleaved mainly one nucleotide inside the transposon end to produce a 3’ OH and one nucleotide outside the transposon end to produce a 5’ phosphate. Changes in the flanking TA dinucleotides at either one end or both ends of ISY100, reducing the efficiency of transposition in vivo. These changes also reduced the efficiency of cleavage in vitro. Changes at only one end inhibited cleavage at both ends implying communication between the two transposon ends. Synthetic pre-cut transposon ends were tested in an in vitro integration assay, and transposase catalysed the insertion of transposon 3’-OH ends into a target plasmid. Transposase mediated efficient integration of a mini-ISY100, pre-excised by transposase or restriction enzyme, into TA targets in vitro, confirming that excised transposon fragments are intermediates in the reaction. Target sequences of ISY100 from published data and this study were analyzed, yielding the consensus target sequence ADWTAWHT, in which the central TA is the duplicated target dinucleotide. When the Zif268 DNA-binding domain of Tn3 resolvase, transposition occurred into TA dinucleotides to one side of a Zif268 binding site with elevated frequency. This could be developed into a genetic tool for target-specific integration.

In conventional digital control an analogue signal is converted into multi-bit digital format with an analogue-to-digital (A/D) converter. A control law is implemented into some digital hardware architecture, resulting in a digital control signal after processing. This digital signal is reverted to analogue format by a digital-to-analogue (D/A) converter or converted to a series of high-frequency pulses by a pulse-width-modulation (PWM) logic, hence being able to drive a physical system. The A/D and D/A converters can be any precision according to the system requirement, e.g. 12-bit in many cases. This thesis, however, proposes one-bit processing for real-time control, which is a new concept in digital control.

The main work of this thesis starts with Chapter 2. Chapter 2 concerns the second homotopy module of a finitely presented group of type F3. We define the second higher order Dehn functions by considering the comparison between the "volume" and the "surface area" of nullhomotopies of spherical maps into CW complexes. We show that the second order Dehn function of groups of type F3 is an invariant of quasi-isometry type. In Chapter 3, we translate the concept of the second order Dehn function of finite group presentations to FDT monoid presentations by introducing a well-placed retraction relation between any two two-complexes and showing some invariance results. We show that the second order Dehn function of an FDT monoid at a fixed element is an invariant of isomorphism type. In Chapters 4, we give upper bounds for asynchronously combable groups with departure function. In Chapter 5, we first give the general upper bounds for direct products. Then we concentrate on the calculations for the optimal bounds of second order Dehn functions of direct products of the form G0 x F where the second order Dehn function of G0 is bounded by a linear function and F is a free group of finite rank. Some interesting examples are given. In Chapters 6, we carry out calculations for the upper bounds of second order Dehn functions of H N N-extensions, amalgamated free products, and split extensions, and finally in Chapter 7, some nice upper bounds as well as lower bounds for the second order Dehn functions of groups of the form Z2 x &phis;F are established where F is a free group of finite rank.

There is growing use of business intelligence (BI) for better management decisions in industry. However, empirical studies on BI are still scarce in academic research. This research investigates BI from an organizational agility perspective. Organizational agility is the ability to sense and respond to market opportunities and threats with speed, and BI can help in the sensing role of organizational agility. Drawing on the systems theory, dynamic capabilities framework, and literature on competitive advantage, organizational agility, business intelligence, and IT infrastructure flexibility, we hypothesize that BI use and IT infrastructure flexibility are major sources of organizational agility. We developed a research model to examine the effects of BI and IT infrastructure flexibility on organizational agility. This model also examines how organizational agility mediates the effects of BI and IT infrastructure flexibility on an organization's competitive advantage. Survey data were collected and used to assess the model. The results support the hypothesis that BI and IT infrastructure flexibility are significant sources of organizational agility, and organizational agility partially mediates the effects of BI and IT infrastructure flexibility on an organization's competitive advantage. This research is a pioneer work that empirically investigates the significance of BI in the business context. It also demonstrates from the organizational agility perspective that information technology and systems have strategic values for organizations, as they are significant sources of organizational agilities and competitive advantages. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]

Digital platforms are growing rapidly, leading to increased competition. While conventional wisdom posits that in competitive arenas some platforms will flourish and others might decline, the nuanced dynamics of digital platform competition can sometimes yield mutual benefits. This dissertation examines these dynamics and the resultant spillovers across diverse digital platforms.The first chapter studies the spillovers between entrant and incumbent platforms. We study the impacts of cost-effective token incentives in the competition between two decentralized exchange platforms. The entrant platform, Sushiswap, launched token incentives to lure liquidity providers away from the incumbent, Uniswap, who then retaliated with its own token incentives. Our analysis shows that the incumbent's own token incentives attract more liquidity to the platform. Yet, surprisingly, the token incentives from its competitor also bring more liquidity and trade volume to the incumbent. We further examine the potential mechanisms by analyzing the role of network effects and information diffusion.The second chapter analyzes the spillovers between a dominant digital market and its competitors. We investigate the potential impact of consumer experiences on Amazon.com in fostering a broader market comfort in the online retail landscape. Specifically, we focus on the adoption of Amazon Prime, a paid membership that lowers transaction costs on Amazon. Using a bank transaction panel, our findings indicate that after adopting Prime, adopters increase their spending on non-Amazon retailers. However, this increase occurs only among novice users of the digital market. Adopters demonstrate additional evidence of increased market comfort: stronger increases in apparel merchants than in electronics, and increased rates of online returns and variety of stores purchased from. The third chapter evaluates spillovers induced by different market structures. The cryptocurrency exchange landscape has experienced heightened market fragmentation due to the emergence of numerous trading platforms. Beyond the surge of traditional centralized exchanges (CEXs) like Binance, the accelerated growth of decentralized exchanges (DEXs), exemplified by Uniswap, further intensifies this trend. We focus on the effects of new market entrants, both CEXs and DEXs, on the aggressiveness of token pair orders and price impact. Our findings reveal distinct influences exerted by CEXs and DEXs. While both augment trade volume (in USD) and elevate order submission aggressiveness, the underlying mechanisms diverge. CEXs see an uptick in the number of trades without a corresponding rise in trade size. DEXs, conversely, often report larger individual trades without a surge in their frequency, possibly attributed to substantial blockchain transaction fees and the inherent price predictability due to automated pricing on DEXs. Notably, CEX fragmentation broadens the overall spread, whereas DEXs don't exhibit a significant sway.

A fundamental goal of mobile network service providers is to guarantee the networking services' reliability, which includes two major goals: reliable network access and security of the communication channels. As today's mobile network is getting larger and more complex, traditional protocols and systems for satisfying the above goals, which are mainly based on rules and experiences, are no longer scalable or effective. On the other hand, together with the growth of the mobile network scale is the growth of the mobile service data. The rich context and knowledge behind the large-scale network service data can provide us with new opportunities to understand the network states and support the design of reliable network systems. Therefore, this thesis research mainly focuses on exploring and designing data-driven approaches to enhance mobile network service reachability and security. Specifically, this paper focuses on two challenging problems faced by the mobile service providers regarding network service reliability.The first problem is how to automatically and efficiently recognize the root cause of a network accessibility problem experienced by the end-device users in cellular network services. Specifically, we design and implement an automatic troubleshooting system named NeTExp. NeTExp learns to identify the root causes of a user-side service problem through deep neural networks (DNNs) that are capable of extracting the complex spatial-temporal features of the massive cellular network log data. It also uses advanced weakly-supervised learning methods for training the models and thus overcomes the data limitation challenges in practice. The system is trained and validated using an extensive period of network and customer care data from a major US cellular service provider.The second problem is how to enable low-cost and fast peer-to-peer authentication among a large mobile network ecosystem, such that secure mobile channels can easily be guaranteed for any pair of devices in the network. The critical challenge is that many mobile devices, especially IoT devices, do not have the capability to maintain the certificate revocation status for a vast device universe during the authentication process. To solve this problem, we design a fast on-device authentication prototype called TinyCR. TinyCR utilizes super-efficient data structures to maintain the certificate revocation status on each device locally. It also enables fast synchronization in response to any changes in the certificate universe. Through evaluation, we show TinyCR outperforms other state-of-the-art certificate revocation checking protocols regarding memory cost, checking efficiency, and synchronization cost. Those new features of TinyCR can well enhance the peer-to-peer channel security in a large mobile network.

For machines working alongside with humans, it is necessary to understand humans' mental states, including desires, beliefs and intentions for better interactions. In addition, humans also need to understand machines' capabilities and limitations to trust and rely on machines approriately. Achieving such bidrectional mental state alignment is crucial to the success of human-machine collaboration. This dissertation addresses this core challenge from both directions, spanning the domains of embodied artificial intelligence, autonomous driving and human-robot interaction. In the first direction of machines understanding humans, I propose a virtual environment for embodied agents and human users to work on daily activities via simulation. To enable embodied agents to better understand and execute human commands, I propose a benchmark allowing them to actively ask questions to resolve language ambiguities. For autonomous driving systems to have an accurate mental model of drivers, I propose a novel protocol to evaluate the effects of human-machine interfaces on drivers' situational awareness in different traffic conditions. In the second direction, I study how robots can generate communicative actions to be better understood by humans. I propose i) an action parsing algorithm based on an And-Or graph representation to generate explanations of task plans, ii) a task and motion planning framework to calibrate robot reachable workspace by expressive motions. My works culminate in building a computational framework for bidirectional value alignment, which is evaluated in the human-machine collaborative scout exploration game.

Immigrants are an indispensable component of communities in the United States. Regarding the roles government of all levels play in immigration laws or/and services, the federal government plays a significant role in national immigration policies and state legislatures also retain their powers in passing their own laws or policies on immigration. Local governments also pass local laws, provide services and conduct inclusive programs for their immigrant populations. Over the past two decades, more scholars have begun to study local governments’ policies and decisions, with some scholarship focusing on local governments’ services for immigrants. Some studies regard the effect of immigrants on local employment and on local governments’ services for immigrants. However, what factors determine local governments’ staffing and facility engagement with their immigrant populations is an intriguing and unanswered question. To date, no scholarship has addressed the question: Why do localities differ in their facility and working staff engagement with their immigrants? This project aims to address that gap using both quantitative and qualitative approaches. Utilizing 2018 Local Government & Immigrant Communities Survey (ICMA 2019), American Community Surveys (ACS) 2013-2017 (U.S. Census Bureau 2020) and data from three other sources, this project conducts a quantitative analysis of more than 1000 local governments across the United States to test, among several given theories, which factors influence local governments’ decisions concerning facility and staff engagement with their immigrants. This research also uses interviews and four case studies to explore how these factors influence local governments’ engagement with their immigrants. The findings show that in addition to the local needs factor and the political factor, some other unexpected factors such as immigrant organizations, the higher governments’ influence, and the network with other local governments all influence this engagement. The insights gleaned from this project will allow local governments to include the new factors and perspectives into their policymaking process regarding their immigrant populations.

Zinc-air batteries (ZABs) are regarded as one of the most promising candidates for the next-generation green and sustainable energy storage solutions, due to their eco-friendliness, safety and low-cost. Despite of the high energy density, the overall battery performance is restricted and governed by kinetically-sluggish oxygen electrocatalysis, thus requiring adequate catalysts to ensure sufficient reaction rate. The thesis starts with the design of ultra-low loaded platinum (Pt) catalysts, aiming to substantially reduce the Pt content. Therefore, atomic distributed Pt (~0.026 wt.%) material with nitrogen (N)-coordination and co-doped phosphorus (P) electronic modulation in porous carbon substrate was fabricated, which consequently showed an excellent and stable activity towards oxygen reduction reaction (ORR) and good performance of primary ZABs with a highly selective 4-electron pathway. The results of X-ray absorption spectroscopy (XAS), electron microscopy, electron energy loss spectroscopy and computational simulations attributed the activity to the synergy between the Pt-Nx motif and nearby P species. Subsequently, to totally replace the precious metals, manganese (Mn) was introduced into N and P co-doped mesoporous carbon, forming MnNxPy complex. The composite afforded a high ORR activity in alkaline media, overwhelming the commercial Pt benchmark. To further improve ORR performance, atomic iron (Fe) with N and P co-coordination embedded carbon hollow spheres was also synthesized, presenting excellent bifunctional oxygen electrocatalytic activity for ZABs. XAS revealed the tuned electronic structure of Mn and Fe by the heteroatom-coordination, leading to the high activities. Following these findings, iron-nickel (Fe-Ni) dual-metal pairs with N-coordination in porous carbon were designed and prepared to enhance the insufficient oxygen evolution (OER) performance of the above catalysts. The Fe-Ni dimers thus synergistically and effectively conducted respective ORR and OER on Fe and Ni sites as unveiled by XAS and computational simulations, breaking the limitation of Scaling Relations and offering exceptional rechargeable ZAB performance. Finally, the last section outlined future perspectives of the carbon-based single atomic catalysts. It is encouraged to conduct research on addressing the conflicts between high power density and large energy density. Also, scalable production of carbon based single atomic catalysts for ORR/OER would be of great values for the wider application of ZABs. Last but not least, the in-depth understanding on the oxygen electrocatalysis mechanism is highly plausible.