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No description available.

The primary aim of the magnetic recording industry is to increase storage capacities and transfer rates whilst maintaining or reducing costs. In multiple-track tape systems, as recorded track dimensions decrease, higher precision tape transport mechanisms and dedicated coding circuitry are required. This leads to increased manufacturing costs and a loss of flexibility. This thesis reports on the performance of a low precision low-cost multiple-track tape transport system. Software based techniques to study system performance, and to compensate for the mechanical deficiencies of this system were developed using occam and the transputer. The inherent parallelism of the multiple-track format was exploited by integrating a transputer into the recording channel to perform the signal processing tasks. An innovative model of the recording channel, written exclusively in occam, was developed. The effect of parameters, such as data rate, track dimensions and head misregistration on system performance was determined from the detailed error profile produced. This model may be run on a network of transputers, allowing its speed of execution to be scaled to suit the investigation. These features, combined with its modular flexibility makes it a powerful tool that may be applied to other multiple-track systems, such as digital HDTV. A greater understanding of the effects of mechanical deficiencies on the performance of multiple-track systems was gained from this study. This led to the development of a software based compensation scheme to reduce the effects of Lateral Head Displacement and allow low-cost tape transport mechanisms to be used with narrow, closely spaced tracks, facilitating higher packing densities. The experimental and simulated investigation of system performance, the development of the model and compensation scheme using parallel processing techniques has led to the publication of a paper and two further publications are expected.

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No description available.

Self-compacting concrete (SCC) can flow into place and compact under its own weight into a uniform void free mass even in areas of congested reinforcement. The research reported in this thesis examined the production of SCC with readily available UK materials, with the overall aims of evaluating test methods and establishing a suitable mix design procedure. There have been significant recent developments and applications of SCC in several countries, notably Japan. A literature survey gave an understanding of the advantages and properties of SCC, test methods and the range of constituent materials and their relative proportions for its successful production. A range of SCC mixes can be produced with the common features of a lower aggregate content than conventional concrete and the use of superplasticizers. Most mixes also contained one or more of pulverized fuel ash, ground granulated blast furnace slag and an inert powder filler. A four stage experimental programme was carried out: *tests on pastes to assess the effect of the types and proportions of the powders and superplasticizers on the rheology. *tests on mortars to determine suitable dosage of superplasticizers for high fluidity, low segregation and low loss of workability with time after mixing. Flow spread and funnel tests were used. *tests on fresh concrete to enable suitable types and quantities of coarse aggregate to be combined with these mortars to produce SCC. Fluidity and viscosity were measured using slump flow and V-funnel tests, and passing ability using L- and U-type tests. Two-point workability tests were also carried out, and a novel way of assessing segregation resistance was developed. *tests on hardened concrete to determine compressive strength, bond to reinforcement and drying shrinkage. A mix design procedure, based on a method suggested by Japanese workers, has been developed. This includes optimisation of the mix with a linear optimisation tool from a commercial spreadsheet package.

In most mine clearing or earth moving equipment such as bulldozers, the working tool is a blade. The blade geometry and operating conditions, such as cutting speed, cutting angle, and cutting depth, have a great effect on overall machine productivity. Most of the published experimental studies confirm these effects. However experimental studies are expensive and their results are highly dependant on the accuracy of measurement devices and the reliability of experimental procedures employed. Numerical techniques have recently shown more promise especially with the current increase in computational power and development of more sophisticated material models. However in order to simulate the soil-tool interface process accurately, careful selection of the appropriate material model for the soil and the interface is required. This should, ideally, be based on a reasonable number of material parameters that have direct physical meaning. In this study a review of the available constitu tive models for soil (particularly sand) and soil-tool interface was carried out. This review study concluded by selecting the so called hypoplastic model as the most appropriate to simulate the sandy soil behavior over a wide range of stresses. Some modifications were carried out on this selected hypoplastic model to optimize it for simulation of the soil-tool interaction process, which is characterized by monotonic loading and high deformation. The modified model was verified numerically and then implemented into the finite element method via an ABAQUS user defined subroutine UMAT. Then the implemented model was verified through analysis of some benchmark problems and results were compared with results from different classical failure criteria. The finite element analysis revealed the high performance of the hypoplastic model in simulating sand behaviour. Finally an analysis of various factors affecting soil-tool interaction was carried out in both two-dimensions and three-dimensions. Results revealed the significant effect of both geometry and operating conditions on blade cutting forces and confirmed the ability of the finite element method to analyze the soil-tool interaction process.

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This thesis considers the tensile deformation characteristics of polypropylene fibre reinforced hardened cement paste having heterogeneous fibre geometries and a range of volume concentrations. Polypropylene fibres were prepared under various manufacturing conditions using a laboratory extruder, to ascertain the effect of these conditions on fibre characteristics. The relevant properties of cement paste likely to influence the polypropylene fibres and the eventual composite were investigated. An investigation of continuous aligned fibre composites in tension, containing various volume concentrations of fibres, showed that multiple cracking occurred despite the elastic modulus of the fibre being considerably lower than that of the hardened cement paste. Factors which enabled fibre/matrix contact to be maintained during the multiple cracking process, despite the unfavourable Poisson's ratio of polypropylene, were considered. Discontinuous aligned fibre composites were tested in tension, to ascertain the effect of volume concentration and length of fibres on the shear stress transfer between fibre and matrix and on multiple cracking. Composites containing parallel fibres, with fibre directions at varying angles to the direction of applied tensile stress, allowed an assessment to be made of the role of inclination. Crack distributions, pull-out behaviour of fibres and the ultimate stress of composites were investigated. Finally, random fibre reinforced composites were evaluated to provide a comparison with the Continuous, Discontinuous and Inclined fibre reinforced systems. In addition to determining the mechanical deformation of the various composites, the acoustic emission associated with internal deformation mechanisms was studied. This was undertaken with equipment capable of monitoring a range of acoustic pulse parameters.

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