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This thesis is a contribution to the existing body of research on logarithmic arithmetic and signal processing. The implementation of log2 arithmetic circuits using modem digital hardware has been an area of active research for over 40 years. In this time over 400 academic papers in journals and conferences have been published and more than 40 patent applications submitted. At the time of writing there are at least 6 different research groups around the world actively working on new algorithms for conversion to and from the logarithmic domain and using logarithmic arithmetic and logarithmic signal processing in a wide range of academic, industrial, consumer and scientific applications. This thesis is separated into two sections. The first section deals with algorithms for logarithmic and anti-logarithmic conversion. It includes an overview and comparison of existing conversion algorithms before presenting two new conversion architectures which are more computationally efficient and suitable for implementation in both ASIC and VLSI technologies. The second section presents material published by the author on two specific applications of logarithmic signal processing where a Hybrid-Logarithmic Number System (Hybrid-LNS or Hybrid-Log) approach has been used. The first is the analysis, design· and implementation of a Discrete Cosine Transform (and its inverse) architecture which has been optimised for use in image compression applications such as JPEG and MPEG. The second describes the TOTEM neural network processor before discussing its implementation in both full-custom IC and FPGA technologies. The concentration. on Hybrid-LNS solutions indicates that this thesis does not discuss in any significant detail the problem of performing addition and subtraction in the logarithnlic domain. There has been extensive research into this problem in recent years and it · is beyond the scope of this thesis. This work is intended to add to the continued debate about the advantages/disadvantages of Hybrid-LNS architectures over "pure" logarithmic or LNS processors.

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Real-world problems commonly require the simultaneous consideration of multiple, often conflicting, objectives. Solving a multiobjective optimisation problem (MOP) is concerned with finding an ideal set of tradeoff solutions which are close to and uniformly distributed across the optimal tradeoff surface. Convergence and diversity are thus essential requirements .of multiobjective optimisers, which are sometimes also required to focus on pertinent areas of the search space. Evolutionary computation (EC) techniques are stochastic, population-based, global search techniques well suited for solving MOPs. However, EC techniques can often involve a large number of objective function calculations which can make the convergence towards optimal tradeoff surfaces computationally expensive. Additionally, in the evolutionary multiobjective optimization community, the bi-objective case is the most heavily studied. Conclusions drawn from such low-dimensional frameworks used to be generalized for all problems' dimensions. Research, however, has shown that high-dimensional problems (> 3 objectives) can possess different characteristics. One of the most important challenges faced in such optimisation scenarios is the conflict between convergence and diversity of solutions. In this study, new approaches are proposed for enhancing the convergence and diversification capacities of so~e of the best multiobjective evolutionary optimisers (MOEAs). The inclusion of quality metrlcs as indicators is implemented as an approach for solving the conflict between solutions' convergence and diversity in high-dimensional optimisation problems. Moreover, a convergence acceleration technique for MOEAs which exploits the objective space, where the goal and objectives lies,is devised and assessed. In the final part of the study, some established progressive preference articulation techniques are examined, and their utility for tackling MOPs is discussed from the viewpoint of the decision maker. Progressive preference articulation techniques are effective methods for supporting the decision maker in guiding the search into pertinent regions of interest and coping with the curse of dimensionality.

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This thesis develops two Calculi for Higher Order Communicating Systems. Both calculi consider sending and receiving processes to be as fundamental as nondeterminism and parallel composition. The first calculus called CHOCS is an extension of Milner's CCS in the sense that all the constructions of CCS are included or may be derived from more fundamental constructs. Most of the mathematical framework of CCS carries over almost unchanged. The operational semantics of CHOCS is given as a labelled transition system and it is a direct extension of the semantics of CCS with value passing. A set of algebraic laws satisfied by the calculus is presented. These are similar to the CCS laws only introducing obvious extra laws for sending and receiving processes. The power of process passing is underlined by a result showing that the recursion operator is unnecessary in the sense that recursion can be simulated by means of process passing and communication. The CHOCS language is also studied by means of a denotational semantics. A major result is the full abstractness of this semantics with respect to the operational semantics. The denotational semantics is used to provide an easy proof of the simulation of recursion. Introducing processes as first class objects yields a powerful metalanguage. It is shown that it is possible to simulate various reduction strategies of the untyped λ-Calculus in CHOCS. As pointed out by Milner, CCS has its limitations when one wants to describe unboundedly expanding systems, e.g. an unbounded number of procedure invocations in an imperative concurrent programming language P with recursive procedures. CHOCS may neatly describe both call-by-value and call-by-reference parameter mechanisms for P. We also consider call-by-name and lazy parameter mechanisms for P. The second calculus is called Plain CHOCS. Essential to the new calculus is the treatment of restriction as a static binding operator on port names. This calculus is given an operational semantics using labelled transition systems which combines ideas from the applicative transition systems described by Abramsky and the transition systems used for CHOCS. This calculus enjoys algebraic properties which are similar to those of CHOCS only needing obvious extra laws for the static nature of the restriction operator. Processes as first class objects enable description of networks with changing interconnection structure and there is a close connection between the Plain CHOCS calculus and the π-Calculus described by Milner, Parrow and Walker: the two calculi can simulate one another. Recently object oriented programming has grown into a major discipline in computational practice as well as in computer science. From a theoretical point of view object oriented programming presents a challenge to any metalanguage since most object oriented languages have no formal semantics. We show how Plain CHOCS may be used to give a semantics to a prototype object oriented language called 0.

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The communicating sequential processes (CSP) formalism, introduced by Hoare, is an event-based approach to distributed computing. The action-system formalism, introduced by Back & Kurki-Suonio, is a state-based approach to distributed computing. Using weakest-precondition formulae, Morgan has defined a correspondence between action systems and the failures-divergences model for CSP. Simulation is a proof technique for showing refinement of action systems. Using the correspondence of Morgan, Woodcock & Morgan have shown that simulation is sound and complete in the CSP failures-divergences model. In this thesis, Morgan's correspondence is extended to the CSP infinite- traces model in order to deal more properly with unbounded nondeterminism. It is shown that simulation is sound in the infinite-traces model, though completeness is lost in certain cases. The new correspondence is then extended to include a notion of internal action. This allows the definition of a hiding operator for action systems that is shown to correspond to the CSP hiding operator. Rules for simulation steps involving internal actions are developed. A parallel operator for action systems is defined, in which interaction is based on synchronisation over shared actions. This operator is shown to correspond to the CSP parallel operator. The correspondence between action systems and CSP is extended again so that actions may have input and output parameters. This allows parallel action- systems to pass values on synchronisation. The original motivation for the work described in this thesis was the use of the action system formalism in the development of telecommunications systems, where interaction is often based on synchronised value-passing. The techniques developed here are applied to a series of case studies involving telecommunications-type systems. The techniques are used to refine and decompose abstract specifications of these systems into parallel sub-systems that interact via synchronised value-passing.

We increasingly spend a vast amount of time on the Web and much of that time is spent reading. One of the main differences between reading non-Web based text and reading on the Web is the presence of hyperlinks within the text, linking various related Web content and webpages together. Some researchers and commentators have claimed that hyperlinks hinder reading because they are a distraction that may have a negative effect on the reader’s ability to process the text. However, very few controlled experiments have been conducted to verify these claims. In the experiments documented here we utilise eye tracking as a new methodology for examining how we read hyperlinked text. During reading we move our eyes in order to bring new information into our fovea where the highest visual acuity is present. There is a well-documented tight link between when and where we look and what we process. By measuring eye movements, we can gain insights into the ongoing cognitive processing that is occurring during a task. Eye movements have been used extensively to help us to understand the cognitive processing that occurs during reading, but there has been very little research into how our reading differs when we read information on the Web. Therefore, in this thesis we examine the influences of hyperlinks on reading on the Web.