Includes bibliographical references (p. 124-131).

Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 524-542).

Thesis (M. Phil.)--University of Hong Kong, 1988.

Within a decade, multicore processors emerged and revolutionised the world of computing. Nowadays, even a low-end computer comes with a multi-core processor and is capable running multiple threads simultaneously. It becomes impossible to make the best computation power out from a computer with a single-threaded program. Meanwhile, writing multi-threaded software is daunting to a lot of programmers as the threads share data and involve complicated synchronisation techniques such as locks and conditions. Software transactional memory is a promising alternative model that programmers simply need to understand transactional consistency and segment code into transactions. Programming becomes exciting again, without races, deadlocks and other issues that are common in lock-based paradigms. To pursue high throughput, performance-oriented computers have several multicore processors per each. A processor’s cache is not directly accessible by the cores in other processors, leading to non-uniform latency when the threads share data. These computers no longer behave like the classical symmetric multiprocessor computers. Although old programs continue to work, they do not necessary benefit from the added cores and caches. Most software transactional memory implementations fall into this category. They rely on a centralised and shared meta-variable (like logical clock) in order to provide the single-lock atomicity. On a computer with two or more multicore processors, the single and shared meta-variable gets regularly updated by different processors. This leads to a tremendous amount of cache contentions. Much time is spent on inter-processor cache invalidations rather than useful computations. Nevertheless, as computers with four processors or more are exponentially complex and expensive, people would desire solving sophisticated problems with several smaller computers whenever possible. Supporting software transactional consistency across multiple computers is a rarely explored research area. Although we have similar mature research topics such as distributed shared memory and distributed relational database, they have remarkably different characteristics so that most of the implementation techniques and tricks are not applicable to the new system. There are several existing distributed software transactional memory systems, but we feel there is much room for improvement. One crucial area is the conflict detection mechanism. Some of these systems make use of broadcast messages to commit transactions, which are certainly not scalable for large-scale clusters. Others use directories to direct messages to the relevant nodes only, but they also keep visible reader lists for invalidation per node. Updating a shared reader lists involves cache invalidations on processors. Reading shared data on such systems are more expensive compared to the conventional low-cost invisible reader validation systems. In this research, we aim to have a distributed software transactional memory system, with distributed clock validation for conflict detection purpose. As preparation, we first investigate some issues such as concurrency control and conflict detection in single-node systems. Finally, we combine the techniques with a tailor-made cache coherence protocol that is differentiated from typical distributed shared memory. / published_or_final_version / Computer Science / Doctoral / Doctor of Philosophy

No description available.

This thesis is concerned with the formation and nature of intravesicular solids in chemical and biological systems. The precipitation of Ag₂O within unilamellar vesicle microvolumes is described in detail. Formation of small (<10nm) single-domain cubic Ag₂O crystallites occurs on membrane diffusion of hydroxide ions. Nucleation initiates at a single site on the inner membrane surface followed by slow crystal growth. No precipitation is observed below an extravesicular pH (pH_OUT) of <u>ca</u>. 11.0. Permeable intravesicular nitrate ions permit hydroxide influx only when a critical membrane potential gradient is surpassed. Above a pH_OUT of 11.0 rate of precipitation is dependent on the rate of crystal growth. Kinetics are firstorder with respect to intravesicular Ag(I) concentration and approximately first-order with respect to hydroxide concentration below a pH_OUT of 12.0. Solubility equilibria for intra-and extravesicular Ag₂O formation are the same. Further <u>in situ</u> intravesicular precipitation reactions are described for FeO(OH) (crystalline), FeO(OH) (amorphous), Ag₂SiO₃ (crystalline), CoSiO₃ (amorphous), Co(OH)₂ (amorphous), Ag₂S (crystalline), CoS (amorphous), and Agl (crystalline). Precipitation of single oxidation state compounds is the same in vesicle space as for normal aqueous solution. For a mixed valency state solid, Fe₃0₄, intravesicular precipitation results in an amorphous material compared with a crystalline material prepared in aqueous solution. Inclusion of pre-formed Fe₃0₄, into vesicles is of potential use as a magnetic drug carrier system and n.m.r. relaxation probe. Intravesicular silica deposition in <u>Stephenaoeca diplocostata</u> Ellis is investigated. Siliceous costal strips are found to be extremely amorphous in structure, have surfaces active to Co(II) and Fe(III) ions, and demineralise from their centre of axis. T-joins of costal strips in intact loricae are found to be joined by a connective material containing amorphous silica centred around a filamentous material of unknown composition. Sectioned material indicates that silicification possibly initiates on an organic preformer laid down within an elongated intracellular vesicle. Potential EM stains, K₅SiPhGeW₁₁0₃₉, Gd(fod)₃, and t-BuNH₃[(nC₂₂H₄₅PO₃)₂Mo₅O₁₅] interact with vesicle bilayers resulting in observable images in the EM. Binding of K₅SiPhGeW₁₁0₃₉ can be followed by ¹H n.m.r. spectroscopy . Gd(fod)₃ loaded vesicles are potential n.m.r. probes for protein - membrane binding studies.

The objective of modeling, verification, and synthesis of hierarchical hybrid mission control for underwater vehicle is to (i) propose a hierarchical architecture for mission control for an autonomous system, (ii) develop extended hybrid state machine models for the mission control, (iii) use these models to verify for logical correctness, (iv) check the feasibility of a simulation software to model the mission executed by an autonomous underwater vehicle (AUV) (v) perform synthesis of high-level mission coordinators for coordinating lower-level mission controllers in accordance with the given mission, and (vi) suggest further design changes for improvement. The dissertation describes a hierarchical architecture in which mission level controllers based on hybrid systems theory have been, and are being developed using a hybrid systems design tool that allows graphical design, iterative redesign, and code generation for rapid deployment onto the target platform. The goal is to support current and future autonomous underwater vehicle (AUV) programs to meet evolving requirements and capabilities. While the tool facilitates rapid redesign and deployment, it is crucial to include safety and performance verification into each step of the (re)design process. To this end, the modeling of the hierarchical hybrid mission controller is formalized to facilitate the use of available tools and newly developed methods for formal verification of safety and performance specifications. A hierarchical hybrid architecture for mission control of autonomous systems with application to AUVs is proposed and a theoretical framework for the models that make up the architecture is outlined. An underwater vehicle like any other autonomous system is a hybrid system, as the dynamics of the vehicle as well as its vehicle level control is continuous whereas the mission level control is discrete, making the overall system a hybrid system i.e., one possessing both continuous and discrete states. The hybrid state machine models of the mission controller modules is derived from their implementation done using TEJA, a software for representing hybrid systems with support for auto code generation. The verification of their logical correctness properties has been done using UPPAAL, a software tool for verification of timed automata a special kind of hybrid system. A Teja to Uppaal converter, called dem2xml, has been created at Applied Reserarch Lab that converts a hybrid (timed) autonomous system description in Teja to an Uppaal system description. Verification work involved developing abstract models for the lower level vehicle controllers with which the mission controller modules interact and follow a hierarchical approach: Assuming the correctness of level-zero or vehicle controllers, we establish the correctness of level-one mission controller modules, and then the correctness of level-two modules, etc. The goal of verification is to show that any valid meaning for a mission formalized in our research verifies the safe and correct execution of actions. Simulation of the sequence of actions executed for each of the operations give a better view of the combined working of the mission coordinators and the low level controllers. So we next looked into the feasibility of simulating the operations executed during a mission. A Perl program has been developed to convert the UPPAAL files in .xml format to OpenGL graphic files. The graphic files simulate the steps involved in the execution of a sequence of operations executed by an AUV. The highest level coordinators send mission orders to be executed by the lower level controllers. So a more generalized design of the highest level controllers would help to incorporate the execution of a variety of missions for a vast field of applications. Initially, we consider manually synthesized mission coordinator modules. Later we design automated synthesis of coordinators. This method synthesizes mission coordinators which coordinate the lower level controllers for the execution of the missions ordered and can be used for any autonomous system.

The increasing complexity of net-centric warfare requires assets to cooperate to achieve mission success. Such cooperation requires the integration of many heterogeneous systems into an interoperable system-of-systems (SoS). Interoperability can be considered a metric of an architecture, and must be understood as early as the conceptual design phase. This thesis approaches interoperability by first creating a general definition of interoperability, identifying factors that affect it, surveying existing models of interoperability, and identifying fields that can be leveraged to perform a measurement, including reliability theory and graph theory. The main contribution of this thesis is the development of the Architectural Resource Transfer and Exchange Measurement of Interoperability for Systems of Systems, or ARTEMIS methodology. ARTEMIS first outlines a quantitative measurement of system pair interoperability using reliability in series and in parallel. This step incorporates operational requirements and the capabilities of the system pair. Next, a matrix of interoperability values for each resource exchange in an operational process is constructed. These matrices can be used to calculate the interoperability of a single resource exchange, IResource, and layered to generate a weighted adjacency matrix of the entire SoS. This matrix can be plugged in to a separate model to link interoperability with the mission performance of the system of systems. One output of the M&S is a single value ISoS that can be used to rank architecture alternatives based on their interoperability. This allows decision makers to narrow down a large design space quickly using interoperability as one of several criteria, such as cost, complexity, or risk. A canonical problem was used to test the methodology. A discrete event simulation was constructed to model a small unmanned aircraft system performing a search and rescue mission. Experiments were performed to understand how changing the systems' interoperability affected the overall interoperability; how the resource transfer matrices were layered; and if the outputs could be calculated without time- and computationally-intensive stochastic modeling. It was found that although a series model of reliability could predict a range of IResource, M&S is required to provide exact values useful for ranking. Overall interoperability ISoS can be predicted using a weighted average of IResource, but the weights must be determined by M&S. Because a single interoperability value based on performance is not unique to an architecture configuration, network analysis was conducted to assess further properties of a system of systems that may affect cost or vulnerability of the network. The eigenvalue-based Coefficient of Networked Effects (CNE) was assessed and found to be an appropriate measure of network complexity. Using the outputs of the discrete event simulation, it was found that networks with higher interoperability tended to have more networked effects. However, there was not enough correlation between the two metrics to use them interchangeably. ARTEMIS recommends that both metrics be used to assess a networked SoS. This methodology is of extreme value to decision-makers by enabling trade studies at the SoS level that were not possible previously. It can provide decision-makers with information about an architecture and allow them to compare existing and potential systems of systems during the early phases of acquisition. This method is unique because it does not rely on qualitative assessments of technology maturity or adherence to standards. By enabling a rigorous, objective mathematical measurement of interoperability, decision-makers will better be able to select architecture alternatives that meet interoperability goals and fulfill future capability requirements.

Errors are inherent to all spatial datasets and give rise to a level of uncertainty in the final product of a geographic information system (GIS). There is growing recognition that the uncertainty associated with spatial information should be represented to users in a comprehensive and unambiguous way. However, the effects on decision-making of such representations have not been thoroughly investigated. Studies from the psychological literature indicate decision-making biases when information is uncertain. This study explores the effects of representing spatial uncertainty, through an examination of how decision-making may be affected by the introduction of thematic uncertainty and an investigation of the effects of different representations of positional uncertainty on decision-making. / Two case studies are presented. The first of these considers the effects on decision-making of including thematic uncertainty information within the context of an airport siting decision task. An extremely significant tendency to select a zone for which the thematic classification is known to be of high certainty was observed. The reluctance to select a zone for which the thematic classification is of low certainty was strong enough to sometimes lead to decision-making that can only be described as irrational. / The second case study investigates how decision-making may be affected by different representations of positional uncertainty within the context of maritime navigation. The same uncertainty information was presented to participants using four different display methods. Significant differences in their decisions were observed. Strong preferences for certain display methods were also exhibited, with some representations being ranked significantly higher than others. / The findings from these preliminary studies demonstrate that the inclusion of uncertainty information does influence decision-making but does not necessarily lead to better decisions. A bias against information of low certainty was observed, sometimes leading to the making of irrational decisions. In addition, the form of uncertainty representation itself may affect decision-making. Further research into the effects on decision-making of representing spatial uncertainty is needed before it can be assumed that the inclusion of such information will lead to more informed decisions being made.

Thesis (MScIng)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.