Blockchain, the technology behind cryptocurrency, enables decentralized and distrustful parties to maintain a unique and consistent transaction history through consensus, without involving a central authority. The decentralization, transparency, and consensus-driven security promised by blockchain are unprecedented and can potentially enable a wide range of new applications that prevail in the decentralized zero-trust model. While blockchain represents a secure-by-design approach to building zero-trust applications, there still exist outstanding security bottlenecks that hinder the technology's wider adoption, represented by the following two challenges: (1) blockchain as a distributed networked system is multi-layered in nature which has complex security implications that are not yet fully understood or addressed; (2) when we use blockchain to construct new applications, especially those previously implemented in the centralized manner, there often lack effective paradigms to customize and augment blockchain's security offerings to realize domain-specific security goals. In this work, we provide answers to the above two challenges in two coordinated efforts. In the first effort, we target the fundamental security issues caused by blockchain's multi-layered nature and the consumption of external data. Existing analyses on blockchain consensus security overlooked an important cross-layer factor---the heterogeneity of the P2P network's connectivity. We first provide a comprehensive review on notable blockchain consensus protocols and their security properties. Then we focus one class of consensus protocol---the popular Nakamoto consensus---for which we propose a new analytical model from the networking perspective that quantifies the impact of heterogeneous network connectivity on key consensus security metrics, providing insights on the actual "51% attack" threshold (safety) and mining revenue distribution (fairness). The external data truthfulness challenge is another fundamental challenge concerning the decentralized applications running on top of blockchain. The validity of external data is key to the system's operational security but is out of the jurisdiction of blockchain consensus. We propose DecenTruth, a system that combines a data mining technique called truth discovery and Byzantine fault-tolerant consensus to enable decentralized nodes to collectively extract truthful information from data submitted by untrusted external sources. In the second effort, we harness the security offerings of blockchain's smart contract functionality along with external security tools to enable two domain-specific applications---data usage control and decentralized spectrum access system. First, we use blockchain to tackle a long-standing privacy challenge of data misuse. Individual data owners often lose control on how their data can be used once sharing the data with another party, epitomized by the Facebook-Cambridge Analytica data scandal. We propose PrivacyGuard, a security platform that combines blockchain smart contract and hardware trusted execution environment (TEE) to enable individual data owner's fine-grained control over the usage (e.g., which operation, who can use on what condition/price) of their private data. A core technical innovation of PrivacyGuard is the TEE-based execution and result commitment protocol, which extends blockchain's zero-trust security to the off-chain physical domain. Second, we employ blockchain to address the potential security and performance issues facing dynamic spectrum sharing in the 5G or next-G wireless networks. The current spectrum access system (SAS) designated by the FCC follows a centralized server-client service model which is vulnerable to single-point failures of SAS service providers and also lacks an efficient, automated inter-SAS synchronization mechanism. In response, we propose a blockchain-based decentralized SAS architecture dubbed BD-SAS to provide SAS service efficiently to spectrum users and enable automated inter-SAS synchronization, without assuming trust on individual SAS service providers. We hope this work can provide new insights into blockchain's fundamental security and applicability to new security domains. / Doctor of Philosophy / Blockchain, the technology behind cryptocurrency, enables decentralized and distrustful parties to maintain a unique and consistent transaction history through consensus, without involving a central authority. The decentralization, transparency, and consensus-driven security promised by blockchain are unprecedented and can potentially enable zero-trust applications in a wide range of domains. While blockchain's secure-by-design vision is truly inspiring, there still remain outstanding security challenges that hinder the technology's wider adoption. They originate from the blockchain system's complex multi-layer nature and the lack of effective paradigms to customize blockchain for domain-specific applications. In this work, we provide answers to the above two challenges in two coordinated efforts. In the first effort, we target the fundamental security issues caused by blockchain's multi-layered nature and the consumption of external data. We first provide a comprehensive review on existing notable consensus protocols and their security issues. Then we propose a new analytical model from a novel networking perspective that quantifies the impact of heterogeneous network connectivity on key consensus security metrics. Then we address the external data truthfulness challenge concerning the decentralized applications running on top of blockchain which consume the real-world data, by proposing DecenTruth, a system that combines data mining and consensus to allow decentralized blockchain nodes to collectively extract truthful information from untrusted external sources. In the second effort, we harness the security offerings of blockchain's smart contract functionality along with external security tools to enable two domain-specific applications. First, eyeing on our society's data misuse challenge where data owners often lose control on how their data can be used once sharing the data with another party, we propose PrivacyGuard, a security platform that combines blockchain smart contract and hardware security tools to give individual data owner's fine-grained control over the usage over their private data. Second, targeting the lack of a fault-tolerant spectrum access system in the domain of wireless networking, we propose a blockchain-based decentralized spectrum access system dubbed BD-SAS to provide spectrum management service efficiently to users without assuming trust on individual SAS service providers. We hope this work can provide new insights into blockchain's fundamental security and applicability to new security domains.

Consensus conferences evolved as a response to the public's increasing dissatisfaction with technocratic decision-making processes that are judged to have repeatedly failed to serve its interests. The staging of the first Australian consensus conference at Old Parliament House in Canberra in March 1999 therefore presented an ideal opportunity to analyse the evolution of this new kind of policy input from its conception through to its implementation and subsequent evaluation. This thesis set out to provide an analysis of that trajectory using elements of the theoretical approach known as actor-network theory (ANT). Previous analyses of consensus conferences have generally provided only limited evaluations of single aspects of the entire process of setting up, implementing and evaluating such a conference. Furthermore, many of the early evaluations were conducted by reviewers or units which were themselves internal to the consensus conference under scrutiny. My own analysis has tried to offer broader, although inevitably less detailed, coverage, using a perspective from contemporary social theory that offers particular advantages in analysing the creation of short-term networks designed for specific purposes. By describing and analysing the role of this relatively new policy-making instrument, I have explored the different sub-networks that operate within the consensus conference process by focussing on the ways in which the conference was organised and how the relationships between the organisers and the participants helped to shape the outcomes. Thus the entire consensus conference sequence from idea to outcome can be thought of as a construction of a network to achieve at least one immediate goal. That goal was a single potential policy input, a consensus position embodied in the report of the lay panel. To realise that goal, the network needed to be recruited and stabilised and its members made to converge on that collective statement. But how is it that a range of disparate actors, including lay and expert, are mobilised to achieve that particular goal and what are the stabilisation devices which enable, or fail to enable this goal to be reached? In the context of the first Australian consensus conference, three key alignment devices emerged: texts, money and people. Yet it is clear from the evidence that some of these network stabilisation devices functioned poorly or not at all. This thesis has drawn attention to the areas in which they were weak and what importance that weakness had for the kind of policy outcome the consensus conference achieved. The role and extent of these powerful stabilisation devices in networks was therefore a vital issue for analysis. If one of the criteria to evaluate the success of a consensus conference is that it provides the stimulus to hold another, then the Australian conference must be deemed so far a failure. No further Australian consensus conference is planned. However, Australia stands to forfeit a number of advantages if no further consensus conferences or similar occasions are organised. Policy formation in contemporary democracies has had to accommodate an increasing array of new participants in order to track more effectively the diversity of potentially significant opinions on complex policy issues. This process requires new and transparent ways to educate and inform the public on policy issues and to ensure that policy makers are better informed about the needs and concerns of their community. As the evidence presented in thesis for the Australian example and its predecessors overseas suggests, consensus conferences have the potential to play a role in the contemporary policy-making context. But the realisation of that potential will vary according to their institutional contexts and the capacity of the actors to create the temporarily most stable and productive network out of the heterogeneous human and material resources to hand.

This thesis proposes a distributed observer design for a class of nonlinear systems that arise in the application of model reduction techniques. Distributed observer design techniques have been proposed in the literature to address estimation problems over sensor networks. In large complex sensor networks, an efficient technique that minimizes the extent of the required communication is highly desirable. This is especially true when sensors have problems caused by physical limitations that result in incorrect information at the local level affecting the estimation of states globally. To address this problem, scalable algorithms for a suitable distributed observer have been developed. Most algorithms are focussed on large linear dynamical systems and they are not directly generalizable to nonlinear systems. In this thesis, scalable algorithms for distributed observers are proposed for a class of large scale observable nonlinear system. Distributed systems models multi-agent systems in which each agents attempts to accomplish local tasks. In order to achieve global objectives, there should be agreement regarding some commonly known variables that depend on the state of all agents. These variables are called consensus states. Once identified, such consensus states can be exploited in the development of distributed consensus algorithms. Consensus algorithms are used to develop information exchange protocols between agents such that global objectives are met through local action. In this thesis, a higher order observer is applied in the distributed sensor network system to design a distributed observer for a class nonlinear systems. Fusion of measurement and covariance information is applied to the higher order filter as the first method. The consensus filter is embedded in the local nonlinear observer for fusion of data. The second method is based on the communication of state estimates between neighbouring sensors rather than fusion of data measurement and covariance. The second method is found to reduce disagreement of the states estimation between each sensor. The performance of these new algorithms is demonstrated by simulation, and the second method is effectively applied over the first method. / Thesis (Master, Chemical Engineering) -- Queen's University, 2012-12-12 11:22:49.113

In this paper, a view of non-compliance in practical healthcare is provided that identifies certain non-compliant behaviours as rational. This view of rational non-compliance is used to update a current form of doctor patient relationships with the aim of reducing non-compliance. In addition to reforming one standard doctor patient relationship model, the normative implications of understanding non-compliance as a rational form of human behaviour are described.

Sensor network plays a significant role in determining the performance of network inference tasks. A wireless sensor network with a large number of sensor nodes can be used as an effective tool for gathering data in various situations. One of the major issues in WSN is developing an efficient protocol which has a significant impact on the convergence of the network. Parameter estimation is one of the most important applications of sensor network. In order to model such large and complex networks for estimation, efficient strategies and algorithms which take less time to converge are being developed. To deal with this challenge, an approach of having multilayer network structure to estimate parameter and reach convergence in less time is estimated by comparing it with known gossip distributed algorithm. Approached Multicast multilayer algorithm on a network structure of Gaussian mixture model with two components to estimate parameters were compared and simulated with gossip algorithm. Both the algorithms were compared based on the number of iterations the algorithms took to reach convergence by using Expectation Maximization Algorithm.Finally a series of theoretical and practical results that explicitly showed that Multicast works better than gossip in large and complex networks for estimation in consensus building strategies.

Wimbledon is one of the most popular annual sports tournament. In the Gentlemen's Single 2009 the top seeded and defending champion Rafael Nadal withdrew from the tournament due to injury days prior to the tournament. Here, we try to analyze the effects of Nadal's withdrawal especially on the ability/strength of the main competitor Roger Federer by using bookmakers expectancies to estimate the unknown abilities of the players and compare them for two different odds sets. The comparison shows that the bookmakers did not incorporate Nadal's withdrawal adequately, assigning too high expected winning probabilities to Federer and Murray. / Series: Research Report Series / Department of Statistics and Mathematics

abstract: I investigate two models interacting agent systems: the first is motivated by the flocking and swarming behaviors in biological systems, while the second models opinion formation in social networks. In each setting, I define natural notions of convergence (to a ``flock" and to a ``consensus'', respectively), and study the convergence properties of each in the limit as $t \rightarrow \infty$. Specifically, I provide sufficient conditions for the convergence of both of the models, and conduct numerical experiments to study the resulting solutions. / Dissertation/Thesis / Masters Thesis Mathematics 2018

Within the field of multi-robot control, there is a large focus in research involving consensus. In this thesis two parts will be studied. The first development of this thesis is a consensus-based robot arm platform. To implement, two robotic arms are developed and studied. The most effective robot arm is then utilized to create a robot arm network testbed. Consensus is used to coordinate several robot arms and decentralize system computation. The research explores a platform to facilitate consensus on a group of robotic arms. The second development is in Cartesian coordinate collective motion. This collective motion control combines consensus through coupling of Cartesian coordinates. The controller is presented with simulation and experimental validation. Integration of both parts of the thesis is then discussed in application. An example is provided to demonstrate usefulness. In conclusion, this thesis provides more control to a system of ground robots using collective motion and consensus-based robot arms.

Cryptocurrencies like Bitcoin have proven to be a phenomenal success. The underlying techniques hold huge promise to change the future of financial transactions, and eventually the way people and companies compute, collaborate, and interact. At the same time, the current Bitcoin-like proof-of-work based blockchain systems are facing many challenges. In more detail, a huge amount of energy/electricity is needed for maintaining the Bitcoin blockchain. In addition, their security holds if the majority of the computing power is under the control of honest players. However, this assumption has been seriously challenged recently and Bitcoin-like systems will fail when this assumption is broken. This research proposes novel blockchain designs to address the challenges. We first propose a novel blockchain protocol, called 2-hop blockchain, by combining proof-of-work and proof-of-stake mechanisms. That said, even if the adversary controls more than 50% computing power, the honest players still have the chance to defend the blockchain via honest stake. Then we revise and implement the design to obtain a practical cryptocurrency system called Twinscoin. In more detail, we introduce a new strategy for difficulty adjustment in the hybrid blockchain and provide an analysis of it. We also show how to construct a light client for proof-of-stake cryptocurrencies and evaluate the proposal practically. We implement our new design. Our implementation uses a recent modular development framework for blockchains, called Scorex. It allows us to change only certain parts of an application leaving other codebase intact.

The strong normative expectation that dictates we should help our elderly parents is a largely unrecognised evolutionary puzzle. Why do we invest so heavily in our parents when they are long past their reproductive years? Adult children looking after their own offspring often face a double burden of care, and choosing to help aging parents is often in conflict with the primary evolutionary task of parenthood - your own genetic posterity by ensuring your children become parents themselves. Despite the large altruism literature, no one has yet addressed this particular issue. This thesis investigates this theoretical paradox and adds to the sparse empirical work on kin and nonkin-directed altruism. As a test of the two most popular Inclusive Fitness evolutionary explanations of altruistic behaviours; Kin Selection (Hamilton, 1964) and Reciprocal Altruism (Trivers, 1971), this study takes a side-wise look at helping attitudes and behaviours across multiple types of relationships. A Choice Model experiment assessed 453 people from all Australian states stratified by age (145 16-24 year olds; 162 25-54 year olds, and 146 over 55 year olds). Participants responded to sixteen hypothetical situations where they could choose to help only one person from two persons requiring their help. The scenarios contained ten variables (relationship type; sex, type of help; history of reciprocation etc.) that were systematically varied. Data was analysed using Hierarchical Bayesian estimation methods, and after factoring out our general tendency toward a species wide cooperation, found broad support for Inclusive Fitness principles. Generally, there was a clear pattern of helping behaviour that saw friends as of at least equal importance to more distant relatives (cousins etc). Elderly parents are helped for no better reason than they are needy and this is an unequivocal demonstration of our species’ primary social imperative - cooperation - a clear inference that adult children are looking for the rewards that cooperation brings. This research also provides interesting insights into the nature of extended family dynamics as a sequelae of our rapid social evolution. / Doctor of Philosophy (PhD)