Modelling and performance evaluation of the IEEE 802.11 DCF for real-time control

Popular wireless networks, such as IEEE 802.11/15/16, are not designed for real-time applications. Thus, supporting real-time quality of service (QoS) in wireless real-time control is challenging. This paper adopts the widely used IEEE 802.11, with the focus on its distributed coordination function (DCF), for soft-real-time control systems. The concept of the critical real-time traffic condition is introduced to characterize the marginal satisfaction of real-time requirements. Then, mathematical models are developed to describe the dynamics of DCF based real-time control networks with periodic traffic, a unique feature of control systems. Performance indices such as throughput and packet delay are evaluated using the developed models, particularly under the critical real-time traffic condition. Finally, the proposed modelling is applied to traffic rate control for cross-layer networked control system design.

Sensor fault-tolerant observer applied in satellite attitude control

The observing failure and feedback instability might happen when the partial sensors of a satellite attitude control system (SACS) go wrong. A fault diagnosis and isolation (FDI) method based on a fault observer is introduced to detect and isolate the fault sensor at first. Based on the FDI result, the object system state-space equation is transformed and divided into a corresponsive triangular canonical form to decouple the normal subsystem from the fault subsystem. And then the KX fault-tolerant observers of the system in different modes are designed and embedded into online monitoring. The outputs of all KX fault-tolerant observers are selected by the control switch process. That can make sense that the SACS is part-observed and in stable when the partial sensors break down. Simulation results demonstrate the effectiveness and superiority of the proposed method.

Decision support for the safe design and operation of unmanned aircraft systems

Unmanned Aircraft Systems (UAS) describe a diverse range of aircraft that are operated without a human pilot on-board. Unmanned aircraft range from small rotorcraft, which can fit in the palm of your hand, through to fixed wing aircraft comparable in size to that of a commercial passenger jet. The absence of a pilot on-board allows these aircraft to be developed with unique performance capabilities facilitating a wide range of applications in surveillance, environmental management, agriculture, defence, and search and rescue. However, regulations relating to the safe design and operation of UAS first need to be developed before the many potential benefits from these applications can be realised. According to the International Civil Aviation Organization (ICAO), a Risk Management Process (RMP) should support all civil aviation policy and rulemaking activities (ICAO 2009). The RMP is described in International standard, ISO 31000:2009 (ISO, 2009a). This standard is intentionally generic and high-level, providing limited guidance on how it can be effectively applied to complex socio-technical decision problems such as the development of regulations for UAS. Through the application of principles and tools drawn from systems philosophy and systems engineering, this thesis explores how the RMP can be effectively applied to support the development of safety regulations for UAS. A sound systems-theoretic foundation for the RMP is presented in this thesis. Using the case-study scenario of a UAS operation over an inhabited area and through the novel application of principles drawn from general systems modelling philosophy, a consolidated framework of the definitions of the concepts of: safe, risk and hazard is made. The framework is novel in that it facilitates the representation of broader subjective factors in an assessment of the safety of a system; describes the issues associated with the specification of a system-boundary; makes explicit the hierarchical nature of the relationship between the concepts and the subsequent constraints that exist between them; and can be evaluated using a range of analytic or deliberative modelling techniques. Following the general sequence of the RMP, the thesis explores the issues associated with the quantified specification of safety criteria for UAS. A novel risk analysis tool is presented. In contrast to existing risk tools, the analysis tool presented in this thesis quantifiably characterises both the societal and individual risk of UAS operations as a function of the flight path of the aircraft. A novel structuring of the risk evaluation and risk treatment decision processes is then proposed. The structuring is achieved through the application of the Decision Support Problem Technique; a modelling approach that has been previously used to effectively model complex engineering design processes and to support decision-making in relation to airspace design. The final contribution made by this thesis is in the development of an airworthiness regulatory framework for civil UAS. A novel "airworthiness certification matrix" is proposed as a basis for the definition of UAS "Part 21" regulations. The outcome airworthiness certification matrix provides a flexible, systematic and justifiable method for promulgating airworthiness regulations for UAS. In addition, an approach for deriving "Part 1309" regulations for UAS is presented. In contrast to existing approaches, the approach presented in this thesis facilitates a traceable and objective tailoring of system-level reliability requirements across the diverse range of UAS operations. The significance of the research contained in this thesis is clearly demonstrated by its practical real world outcomes. Industry regulatory development groups and the Civil Aviation Safety Authority have endorsed the proposed airworthiness certification matrix. The risk models have also been used to support research undertaken by the Australian Department of Defence. Ultimately, it is hoped that the outcomes from this research will play a significant part in the shaping of regulations for civil UAS, here in Australia and around the world.

Frank-starling control of a left ventricular assist device

A physiological control system was developed for a rotary left ventricular assist device (LVAD) in which the target pump flow rate (LVADQ) was set as a function of left atrial pressure (LAP), mimicking the Frank-Starling mechanism. The control strategy was implemented using linear PID control and was evaluated in a pulsatile mock circulation loop using a prototyped centrifugal pump by varying pulmonary vascular resistance to alter venous return. The control strategy automatically varied pump speed (2460 to 1740 to 2700 RPM) in response to a decrease and subsequent increase in venous return. In contrast, a fixed-speed pump caused a simulated ventricular suction event during low venous return and higher ventricular volumes during high venous return. The preload sensitivity was increased from 0.011 L/min/mmHg in fixed speed mode to 0.47L/min/mmHg, a value similar to that of the native healthy heart. The sensitivity varied automatically to maintain the LAP and LVADQ within a predefined zone. This control strategy requires the implantation of a pressure sensor in the left atrium and a flow sensor around the outflow cannula of the LVAD. However, appropriate pressure sensor technology is not yet commercially available and so an alternative measure of preload such as pulsatility of pump signals should be investigated.

Why do policy decision-makers opt for command and control environmental regulation? An economic analysis with special reference to Sri Lanka

This chapter examines why policy decision-makers opt for command and control environmental regulation despite the availability of a plethora of market-based instruments which are more efficient and cost-effective. Interestingly, Sri Lanka has adopted a wholly command and control system, during both the pre and post liberalisation economic policies. This chapter first examines the merits and demerits of command and control and market-based approaches and then looks at Sri Lanka’s extensive environmental regulatory framework. The chapter then examines the likely reasons as to why the country has gone down the path of inflexible regulatory measures and has become entrenched in them. The various hypotheses are discussed and empirical evidence is provided. The chapter also discusses the consequences of an environmentally slack economy and policy implications stemming from adopting a wholly regulatory approach. The chapter concludes with a discussion of the main results.

Content analysis of international research in geographical and environmental education : eighteen years of academic publishing

This paper examines the history of the IRGEE Journal in terms of its sustainable future. The development of geographical and environmental education is evaluated, as reflected from the articles published in the Journal “International Research in Geographical and Environmental Education” (IRGEE). A content analysis of all papers and forum sections which have appeared in the journal since Volume 1 Number 1 was published in 1992 has been conducted, examining the content of as many as 526 articles. The method was a content analysis, and revealed themes which have experienced an increasing or declining interest over the 18 years of publication of IRGEE (1992-2009), while other themes have remained current during this period. The main findings of this analysis are: a) the total number of articles has increased more than threefold, b) articles related to geographical education (sensu stricto) outweighed those related to environmental education, c) the themes “syllabi, textbooks, curricula” and “values, attitudes” attract the attention of researchers with increasing strength and d) emerging subjects, such as GIS and sustainability have appeared dynamically in the last years.

Locally weighted learning model predictivek control for elastic joint robots

This paper proposes an efficient and online learning control system that uses the successful Model Predictive Control (MPC) method in a model based locally weighted learning framework. The new approach named Locally Weighted Learning Model Predictive Control (LWL-MPC) has been proposed as a solution to learn to control complex and nonlinear Elastic Joint Robots (EJR). Elastic Joint Robots are generally difficult to learn to control due to their elastic properties preventing standard model learning techniques from being used, such as learning computed torque control. This paper demonstrates the capability of LWL-MPC to perform online and incremental learning while controlling the joint positions of a real three Degree of Freedom (DoF) EJR. An experiment on a real EJR is presented and LWL-MPC is shown to successfully learn to control the system to follow two different figure of eight trajectories.

Approaches to access control under uncertainty

The ultimate goal of an access control system is to allocate each user the precise level of access they need to complete their job - no more and no less. This proves to be challenging in an organisational setting. On one hand employees need enough access to the organisation’s resources in order to perform their jobs and on the other hand more access will bring about an increasing risk of misuse - either intentionally, where an employee uses the access for personal benefit, or unintentionally, through carelessness or being socially engineered to give access to an adversary. This thesis investigates issues of existing approaches to access control in allocating optimal level of access to users and proposes solutions in the form of new access control models. These issues are most evident when uncertainty surrounding users’ access needs, incentive to misuse and accountability are considered, hence the title of the thesis. We first analyse access control in environments where the administrator is unable to identify the users who may need access to resources. To resolve this uncertainty an administrative model with delegation support is proposed. Further, a detailed technical enforcement mechanism is introduced to ensure delegated resources cannot be misused. Then we explicitly consider that users are self-interested and capable of misusing resources if they choose to. We propose a novel game theoretic access control model to reason about and influence the factors that may affect users’ incentive to misuse. Next we study access control in environments where neither users’ access needs can be predicted nor they can be held accountable for misuse. It is shown that by allocating budget to users, a virtual currency through which they can pay for the resources they deem necessary, the need for a precise pre-allocation of permissions can be relaxed. The budget also imposes an upper-bound on users’ ability to misuse. A generalised budget allocation function is proposed and it is shown that given the context information the optimal level of budget for users can always be numerically determined. Finally, Role Based Access Control (RBAC) model is analysed under the explicit assumption of administrators’ uncertainty about self-interested users’ access needs and their incentives to misuse. A novel Budget-oriented Role Based Access Control (B-RBAC) model is proposed. The new model introduces the notion of users’ behaviour into RBAC and provides means to influence users’ incentives. It is shown how RBAC policy can be used to individualise the cost of access to resources and also to determine users’ budget. The implementation overheads of B-RBAC is examined and several low-cost sub-models are proposed.

A reliable real-time transport protocol for networked control systems over wireless networks

Deploying wireless networks in networked control systems (NCSs) has become more and more popular during the last few years. As a typical type of real-time control systems, an NCS is sensitive to long and nondeterministic time delay and packet losses. However, the nature of the wireless channel has the potential to degrade the performance of NCS networks in many aspects, particularly in time delay and packet losses. Transport layer protocols could play an important role in providing both reliable and fast transmission service to fulfill NCS’s real-time transmission requirements. Unfortunately, none of the existing transport protocols, including the Transport Control Protocol (TCP) and the User Datagram Protocol (UDP), was designed for real-time control applications. Moreover, periodic data and sporadic data are two types of real-time data traffic with different priorities in an NCS. Due to the lack of support for prioritized transmission service, the real-time performance for periodic and sporadic data in an NCS network is often degraded significantly, particularly under congested network conditions. To address these problems, a new transport layer protocol called Reliable Real-Time Transport Protocol (RRTTP) is proposed in this thesis. As a UDP-based protocol, RRTTP inherits UDP’s simplicity and fast transmission features. To improve the reliability, a retransmission and an acknowledgement mechanism are designed in RRTTP to compensate for packet losses. They are able to avoid unnecessary retransmission of the out-of-date packets in NCSs, and collisions are unlikely to happen, and small transmission delay can be achieved. Moreover, a prioritized transmission mechanism is also designed in RRTTP to improve the real-time performance of NCS networks under congested traffic conditions. Furthermore, the proposed RRTTP is implemented in the Network Simulator 2 for comprehensive simulations. The simulation results demonstrate that RRTTP outperforms TCP and UDP in terms of real-time transmissions in an NCS over wireless networks.

Wide area control through aggregation of power systems

This thesis was a step forward in improving the stability of power systems by applying new control and modelling techniques. The developed methods use the data obtained from voltage angle measurement devices which are synchronized with GPS signals to stabilize the system and avoid system-wide blackouts in the event of severe faults. New approaches were developed in this research for identifying and estimating reduced dynamic system models using phasor measurement units. The main goal of this research is achieved by integrating the developed methods to obtain a feasible wide-area control system for stabilizing the power systems.

Aircraft collision avoidance using spherical visual predictive control and single point features

This paper presents practical vision-based collision avoidance for objects approximating a single point feature. Using a spherical camera model, a visual predictive control scheme guides the aircraft around the object along a conical spiral trajectory. Visibility, state and control constraints are considered explicitly in the controller design by combining image and vehicle dynamics in the process model, and solving the nonlinear optimization problem over the resulting state space. Importantly, range is not required. Instead, the principles of conical spiral motion are used to design an objective function that simultaneously guides the aircraft along the avoidance trajectory, whilst providing an indication of the appropriate point to stop the spiral behaviour. Our approach is aimed at providing a potential solution to the See and Avoid problem for unmanned aircraft and is demonstrated through a series.

Development and implementation of the Australian universities radiation therapy student clinical assessment form

Purpose: Prior to 2009, one of the problems faced by radiation therapists who supervised and assessed students on placement in Australian clinical centres, was that each of the six Australian universities where Radiation Therapy (RT) programmes were conducted used different clinical assessment and reporting criteria. This paper describes the development of a unified national clinical assessment and reporting form that was implemented nationally by all six universities in 2009. Methods: A four phase methodology was used to develop the new assessment form and user guide. Phase 1 included university consensus around domains of student practice and assessment, and alignment with national competency standards; Phase 2 was a national consensus workshop attended by radiation therapists involved in student supervision and assessment; Phase 3 was an action research re-iterative Delphi technique involving two rounds of a mail-out to gain further expert consensus; and stage 4 was national piloting of the developed assessment form. Results: The new assessment form includes five main domains of practice and 19 sub-domain criteria which students are assessed against during placement. Feedback from the pilot centre participants was positive, with the new form being assessed to be comprehensive and complemented by the accompanying user guide. Conclusion: The new assessment form has improved both the formative and summative assessment of students on placement, as well as enhancing the quality of feedback to students and the universities. The new national form has high acceptance from the Australian universities and has been subject to wide review by the profession.

Open and networked initiatives and the digital transformation of academic publishing in China

Many aspects of China's academic publishing system differ from the systems found in liberal market based economies of the United States, Western Europe and Australia. A high level of government intervention in both the publishing industry and academia and the challenges associated with attempting to make a transition from a centrally controlled towards a more market based publishing industry are two notable differences; however, as in other countries, academic communities and publishers are being transformed by digital technologies. This research explores the complex yet dynamic digital transformation of academic publishing in China, with a specific focus of the open and networked initiatives inspired by Web 2.0 and social media. The thesis draws on two case studies: Science Paper Online, a government-operated online preprint platform and open access mandate; and New Science, a social reference management website operated by a group of young PhD students. Its analysis of the innovations, business models, operating strategies, influences, and difficulties faced by these two initiatives highlights important characteristics and trends in digital publishing experiments in China. The central argument of this thesis is that the open and collaborative possibilities of Web 2.0 inspired initiatives are emerging outside the established journal and monograph publishing system in China, introducing innovative and somewhat disruptive approaches to the certification, communication and commercial exploitation of knowledge. Moreover, emerging publishing models are enabling and encouraging a new system of practising and communicating science in China, putting into practice some elements of the Open Science ethos. There is evidence of both disruptive change to old publishing structures and the adaptive modification of emergent replacements in the Chinese practice. As such, the transformation from traditional to digital and interactive modes of publishing, involves both competition and convergence between new and old publishers, as well as dynamics of co-evolution involving new technologies, business models, social norms, and government reform agendas. One key concern driving this work is whether there are new opportunities and new models for academic publishing in the Web 2.0 age and social media environment, which might allow the basic functions of communication and certification to be achieved more effectively. This thesis enriches existing knowledge of open and networked transformations of scholarly publishing by adding a Chinese story. Although the development of open and networked publishing platforms in China remains in its infancy, the lessons provided by this research are relevant to practitioners and stakeholders interested in understanding the transformative dynamics of networked technologies for publishing and advocating open access in practice, not only in China, but also internationally.

Control, shift, insert : living and enacting policy in teachers' day/night work

This thesis investigates the experiences of teachers who trialled an electronic curriculum and assessment tool in the wider context of text-mediated ruling relations organising their work. Problematised as policy and text, this tool is interrogated as a 'solution' to problems perceived in teachers' work in an era of increased accountability. It provides evidence that teachers' work is shaped by forces operating outside their control and mediated by the policy discourses and subjectivities available to them.

Passive control of a biventricular assist device with compliant inflow cannulae

Rotary ventricular assist device (VAD) support of the cardiovascular system is susceptible to suction events due to the limited preload sensitivity of these devices. This may be of particular concern with rotary biventricular support (BiVAD) where the native, flow-balancing Starling response is diminished in both ventricles. The reliability of sensor and sensor-less based control systems which aim to control VAD flow based on preload have limitations and thus an alternative solution is desired. This study introduces a compliant inflow cannula (CIC) which could improve the preload sensitivity of a rotary VAD by passively altering VAD flow depending on preload. To evaluate the design, both the CIC and a standard rigid inflow cannula were inserted into a mock circulation loop to enable biventricular heart failure support using configurations of atrial and ventricular inflow, and arterial outflow cannulation. A range of left (LVAD) and right VAD (RVAD) rotational speeds were tested as well as step changes in systemic/pulmonary vascular resistance to alter relative preloads, with resulting flow rates recorded. Simulated suction events were observed, particularly at higher VAD speeds, during support with the rigid inflow cannula, while the CIC prevented suction events under all circumstances. The compliant section passively restricted its internal diameter as preload was reduced, which increased the VAD circuit resistance and thus reduced VAD flow. Therefore, a compliant inflow cannula could potentially be used as a passive control system to prevent suction events in rotary left, right and biventricular support.