A method of excitation of CO2 lasers using multiple electric discharges, with individual stabilisation resistors on both sides of the discharge, to obtain stable, and uniformly distributed volume of excited gas is demostrated. A number of different electrode configurations relevant to axial and transverse excitation have been investigated in both parallel (current flow in adjacent discharges in the same direction), and anti-parallel (current flow in adjacent electrodes in the opposite direction). The results have been applied to a high flow rate axial flow laser system. Measurements of power output indicate that an increase of 18% was obtained using multiple discharge compared with a single discharge of the same total current. The results were also applied to a transverse flow system and cw operation was obtained.

A capacitor-run motor is often necessary where silent running, low starting current, high efficiency and power factor and overload capacity are required. When a capacitor motor is used in control or similar applications a knowledge of the variation in performance over a range of supply frequency is often important, and this has been investigated by previous workers using analyses of varying validity. For example, in early studies it was common to base performance calculations on the revolving field theory, when a general lack of agreement was found between calculated and test values. This occurred particularly in the starting wlnding under running conditions, and was attributed usually to saturation and to space harmonics of mmf. The crossfield theory provides a useful alternative to the revolving-field theory for analyses of single-phase motors, and when applied to the capacitor motor it is found that a much more accurate prediction of the machine performance is obtained. This thesis investigates the behaviour of a small singlephase capacitor-run induction motor with relation to variable frequency supplies and different capacitor values. The performance of the capacitor motor is calculated, using an equivalent circuit developed from basic cross-field theory considerations. However, before calculating the performance of the motor, the experimental determination of the parameters involved is necessary. From the equivalent circuit for no-load and locked rotor conditions, a set of voltage/current equations was obtained. Use of these equations requires a very complicated set of mathematical procedures to determine the required parameters, and no solution could be found. This difficulty was overcome by the extensive use of a digital computer, enabling the parameters to be obtained by the Newton-Raphson method of numerical iteration. Using these parameters, the predicted performance of the machine was compared with that obtained from an extensive experimental investigation. The agreement which was found to exist confirms both the validity of the theoretical analysis and the accuracy of the measurement from which the parameters were derived.

Following a brief introduction to 6utline the relevance and scope of the thesis (Chapter 1), the initial half of this work (Chapters 2-7) concerns original and compiled information regarding theoretical aspects and literature review. The second half of the thesis (Chapters 8-12) involves novel studies at both laboratory (Chapters 8 and 10) and pilot, plant (Chapters 9 and 11) scale. The academic and technical literature is critically reviewed with regard to the rotating cylinder as a reactor geometry. Particular attention 'is paid to the electrodeposition of metals, in powder form, in a rotating cylinder electrode reactor (R.C.E.R). In an overall attempt to present and characterise the R.C.E.R, hydrodynamics (Chapter 2) and mass transport (Chapter 3) are extensively reviewed and discussed. In order to place the R.C.E.R. in relation to other reactor geometries, mass transport to various electrode types (Chapter 4) is reviewed; and novel/important electrochamical reactors are featured (Chapter 5). One of the major parts of the thesis (Chapter 6) presents fundamental design equations and an extensive review of laboratory and commercial cell/reactor 'design. Applications of the R.C.E.R. are also discussed in Chapter 6, with particular regard to e1ectrodeposition. The concluding section on literature and theoretical aspects (Chapter 7) briefly covers the production, use and properties of metal powders, especially those produced by electrode position. [... continues].

Currently available microcomputer development systems/tools become rather inefficient when employed to debug real-time malfunctions; that is, intermittent or even unrepeatable hardware/software malfunctions encountered in time-critical applications. A new debugging technique, namely the Action-replay Debugging Technique, is proposed which can efficiently deal with a large class of these malfunctions. The aim of the Action-replay Debugging Technique is to provide an environment which is suitable for real-time debugging. In particular, an identical processor to the target, or a simulator of it, is forced to re-execute, or Action-replay, repeatedly and at any desirable speed the exact program path which the target processor traversed during the original interaction wi th its real-time environment. During successive "Action-replays" the user can investigate the system's behaviour (including timing characteristics) without real-time constraints which normally exist in time-critical applications.

With the more widespread use of multi- processors and distributed computing systems, programmers need a simple, reliable interface to them. This thesis describes language constructs, and mechanisms for their support, that can be used in the implementation of fault-tolerant concurrent processes. The basic language structure is the Atomic Action, supported by a modified recovery cache mechanism. This combines the collection of recovery data with the locking of resources and allows recovery blocks to be integrated with Atomic Actions. Synchronisation between actions is discussed, as well as a means of detecting and breaking deadlocks, based on the use of a "blocking graph". Reliable communication and cooperation between actions is considered, and several constructs are investigated. The limitations of Shared Atomic Actions are identified, and, further, the use of a form of reliable "secretary" is shown to lead to unnecessary recovery activity. These problems are resolved by structures based on a classification of resources by the way they are used in programs. Also contained in the thesis are descriptions of trial implementations of some of the mechanisms described, and a discussion of existing concurrent programming techniques.

This thesis explores the problem of making accurate assessments of the performance of high level language interpreter programs which are embedded in some more complex system. The overall system performance will be determined by all the software and hardware components present; but in order either to analyse and improve particular components, or to select between alternative versions of components, the concept of the performance of individual components is important. A model is developed for the abstract behaviour of software components playing the role of an interpreter by considering their interaction with the program code which is being interpreted and with the underlying virtual machine which is, in turn, interpreting them. This model enables a flexible definition of performance by relating the interactions in which an interpreter takes part. A methodology is recommended for assessing experimentally the performances defined within such a framework. The performances of an interesting selection of pseudo-machine and high level interpreter implementations of Lispkit and Prolog are then assessed and conclusions drawn.

The thesis comprises (1) 8 critical interpretation of Swets's contribution to information retrieval, (2) development (i.e. "extension") of the formalism, as so interpreted, and (3) a description of an experiment that identifies hypotheses consistent with the extended formalism. The early sections of the thesis place the original contribution by Swets in the contexts of both signal-detection theory and information retrieval theory. It is then argued that as the original theoretical contribution is ambiguous in key respects, an interpretation of it is necessary. The interpretation given constitutes an initial development of Swets's work but other developments, not simply a consequence of the interpretation of the original description by Swets, are also put forward. The major one of these is the explicit incorporation in the formalism of logical search expressions. Elementary logical conjuncts of search terms are seen as (1) being weakly ordered by "document ordering expressions", and (2) having probability-pairs attached to disjunctions of them defined by the ordering. A major part of the thesis is the identification of novel hypotheses, expressed within the extension of the original formalism, which relate to triples of: (1) instances of information need in medicine, represented by prespecified partitionings of a medical-literature data base (MEDLARS), (2) an analytical document ordering expression, and (3) an algorithmically-derived set of terms characterising the information need. An enhancement is suggested to data base management programs that at present employ only user-specified logical search expressions by way of search input, this enhancement stemming directly from the extension of the original formalism. The broad conclusion of the thesis is that when the original contribution of Swets is suitably interpreted and extended, a robust, hospitable conceptual framework for describing information retrieval at the macroscopic level is provided.

The work falls into two separate parts, involving respectively kinematic and dynamic aspects of planar linkage mechanisms. The first and major part reported in Part I concerns the development of a procedure for optimal allocation of tolerances and clearances in plane linkage mechanisms. The theory developed takes into account the sensitivity of the mechanism output to small deviations in the parameter dimensions and the cost-tolerance relationships for the parameters. A procedure is then derived from the theory and incorporated into a computer program to allocate tollerances to linear dimensions and angles, and clearances to the joints in the mechanism. To demonstrate the applicability of the method to a wide range of planar linkage mechanisms, a number of examples are given which include 4-, 6-, 8- and 10-bar linkages. Part II describes the investigation of possible methods for maintaining contact in the joints of a plane four-bar mechanism by means of mass redistribution, the aim being to reduce or eliminate vibration due to impact in joints with clearance. An optimization routine is used with constraints upon the magnitude of the joint forces and the rate at which those forces change direction based on a 'no-clearance' analysis. The method was applied to several examples with little success due to inherent limitations of the analysis method used.

The project investigates the theory and design of varactor diode frequency multiplier circuits. Special consideration is given to multipliers which use series-tuned transmission-line cavities for filtering and impedance matching and an assessment is made of the merits of these cavities. Practical multiplier circuits are constructed in microstripline and are tested with the objective of verifying the analytical predictions. The theory of the series-tuned cavity is given and its performance is predicted by computer plots of the insertion loss when it is used between a 50-Ω source and a 50-Ω, load. These predicted results are verified on experimental series-tuned cavities in which the transmission lines are of two types, namely, coaxial lines and microstriplines, and the predictions are used in due course in the design of the multiplier circuits. A new method of analysis for frequency multiplier circuits is introduced in which the device equation is written in terms of a Chebyshev expansion. The coefficients of the terms in the device equation are then given by the results of a spectrum test on the device and this has the considerable advantage that the device law will include the effects of parasitics caused by the test circuit which will be similar to those which occur when the device is used in a multiplier circuit. The method can be used to analyse both shunt mode and series mode multipliers and is used here on three particular circuits: the shunt-diode doubler, the shunt-diode triplet and the shunt-diode triplet with idler. Expressions are obtained for the power delivered to the load resistance and the input and output capacitances of the diode. The main achievement of the analysis is that it produces a method for finding the conditions for matching a non-linear reactive diode to a source and a load so that the harmonic power delivered to the load at the required output frequency can be maximised. Measurements on practical shunt-diode doublers using microstrip technology are reported and they indicate that the predictions given by the analysis of doubler circuit operation are of the correct order. The foundations for the design of microstrip series-tuned cavity multipliers have been laid and further investigations, especially with regard to multipliers with idlers, would be of value.

No description available.