The galvanic isolation of fibre optic transmission offers a distinct advantage in the design of a telemetry system to meet intrinsic safety requirements. So far the usage of fibre optics in instrumentation systems has been largely confined to the implementation of point to point links due to the difficulties encountered in tapping into an optical fibre. Recent developments in the use of intelligence within instrumentation systems, however, have generally tended to concentrate on the concept of multiplexed signal paths. The aim of the work here has been to realise an intrinsically safe fibre optic multi-drop bus utilising an unbroken fibre as the transmission path. The technique employed involves the modulation of light within the fibre using an acoustic wave to vary the characteristics of a multi- mode fibre resulting in a differential phase modulation of the propagating modes. Since the system is unidirectional the use of two-way protocols is precluded and instead the method adopted uses the technique of allowing collisions of data to occur on the basis that they can be detected and the corrupted data can be subsequently ignored.

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Considerable progress has been made in understanding implant wear and developing numerical models to predict certain aspects of wear for new orthopaedic devices. However, any model of wear could be improved through a more accurate representation of the biomaterial micromechanics, including time-varying dynamic and inelastic behaviour such as viscous and plastic deformation as well as any history-dependent evolution of its microstructural properties. Under in-vivo conditions, the contact surface of the UHMWPE tibial insert evolves as a result of applied loads and complex multidirectional motions of the femoral component against it. Overt time, severe inelastic deformations and damage mechanisms occur and ultimately lead to wear. This process is accompanied by the release of UHMWPE debris in the surrounding tissues with the direct consequences of triggering an in ammatory response that leads to osteolysis and subsequently periprosthetic implant loosening. In that case a revision surgery is required. Motivated by these facts, the current research effort has been motivated by the need to gain a mechanistic insight into the micromechanical mechanisms associated with wear of UHMWPE in knee arthroplasty. To this end, two main lines of focus have been followed in this work. One line of focus concerns the inelastic mechanisms of deformation such as creep and plasticity since they are critical in altering the contact properties of the articulating surface of UHMWPE components, leading to damage and formation of wear debris. Therefore, the relative contributions of elastic, creep, and plastic deformations on the contact area, and so contact pressure has been investigated through different numerical techniques. Additionally, contact pressure is a critical input parameter of computational wear algorithms, and it is therefore essential to establish the nature of and quantify the interplay between contact pressure, contact area, creep and plastic deformations. What are the consequences of neglecting creep deformations on wear predictions? A first approach to investigate these aspects consisted in conducting a series of physicallybased finite element analyses replicating the mechanical characteristics and operating conditions of an AMTI Knee Simulator. Experimental creep testing on a unicondylar knee replacement system in a physiologically representative context was simulated. In both studies, linear elastic, plastic and time-varying visco-dynamic properties of computational models were benchmarked using literature data to predict contact deformations, pressures and areas. Results indicate that creep deformations have a significant effect on both experimental and simulated contact pressures at the surface of the UHMWPE tibial insert. The use of a purely elastoplastic constitutive model for UHMWPE lead to compressive deformations of the insert which were in general smaller than those predicted by a creep-capturing viscoelastic model. At high compressive loads, inelastic deformation mechanisms dominate the mechanical response of UHMWPE components by altering the surface geometry (i.e. contact area), and therefore the contact pressure. The second line of focus concerns the study of the role of transient and permanent polymer chain realignment during multidirectional sliding, and its potential correlation to wear. The main working hypothesis is that the evolution of the UHMWPE microstructure during multidirectional pin-on-disk (POD) tests can provide information on possible correlations between wear, sliding track characteristics and the mechanics of UHMWPE. Therefore, finite element-based POD tests were used to investigate the effects of motion paths in simulated multidirectional sliding motions on metrics related to the mechanical response of UHMWPE, with particular attention to evolution of molecular chain realignment. For this purpose, the concept of anticoaxiality as a measure of molecular chain realignment (or anisotropy) has been introduced. The concept of anticoaxiality as a measure of molecular chain realignment (or anisotropy) was introduced to quantify the deviation from mechanical isotropy of UHMWPE microstructure. Results from these metrics support the hypothesis that multidirectional sliding as well as long sliding distances produced microstructural changes in UHMWPE, resulting in an enhanced likelihood of material damage, and so wear.

The apparent mass of the seated human body and the transmissibility to the upper-body (i.e., the spine and the pelvis) during vertical vibration excitation have been reported to have resonance frequencies around 5 Hz. With fore-and-aft excitation the apparent mass shows a first peak around 1 Hz and second mode around 2 to 3 Hz. Little is known about how the motion of the upper-body during excitation in one direction is affected by the addition of vibration in an orthogonal direction (i.e., the cross-axis coupling). The principal objective of the research reported in this thesis was to identify how the resonances in the apparent mass and transmissibility, and their association, depends on the magnitude of the inline vibration excitation and the addition of an orthogonal vibration excitation. The research was also designed to investigate the characteristics necessary in mathematical models that represent the cross-axis coupling and nonlinearity evident in the biodynamic responses of the human body. The movement of the body (over the first, fifth and twelfth thoracic vertebrae, the third lumbar vertebra, and the pelvis) in the fore-and-aft and vertical directions (and in pitch at the pelvis) was measured in 12 seated male subjects during random vertical vibration excitation (over the range 0.25 to 20 Hz) at three vibration magnitudes (0.25, 0.5 and 1.0 ms-2 r.m.s.) and during fore-and-aft vibration excitation over the same frequency range and at the same three vibration magnitudes. At the highest magnitude of vertical excitation the effect of adding fore-aft excitation (at 0.25, 0.5, and 1.0 ms-2 r.m.s.) was investigated. Similarly, at the highest magnitude of fore-and-aft excitation the effect of adding vertical vibration (at 0.25, 0.5, and 1.0 ms-2 r.m.s.) was investigated. The forces in the fore-and-aft and vertical directions on the seat surface were also measured so as to calculate apparent masses. The subjects adopted a normal upright posture, an erect posture, and a slouched posture. Resonance frequencies in the apparent mass and transmissibility during vertical excitation decreased with increasing magnitude of vertical excitation and with the addition of fore-and-aft excitation. The modulus of the first peak in the apparent mass and transmissibility during fore-and-aft excitation decreased with increasing magnitude of fore-and-aft excitation and with the addition of vertical excitation. Complex vibration modes in the upper-body appear to be responsible for the resonances in both the vertical and the fore-and-aft apparent masses. Compared to the normal upright posture, the erect posture tended to increase the resonance frequency in the apparent mass and transmissibility associated with vertical excitation but decrease the resonance frequency in the apparent mass and transmissibility associated with fore-and-aft excitation. The association between resonances in the transmissibility to the upper body and the resonance in the apparent mass varied with vertical excitation but not with fore-aft excitation. A seven degree-of-freedom multi-body model indicated that the resonance frequency in the vertical apparent mass on the seat and the vertical transmissibility to the upper-body with either vertical or dual-axis excitation is sensitive to the vertical stiffness of tissues beneath the pelvis and closely related to the vertical motion of the upper body. It has also been shown that the first mode of the fore-and-aft apparent mass and the fore-and-aft transmissibility can be attributed to the fore-and-aft movement of the upper-body due to the pelvis pitch, while the second mode can be attributed to the fore-and-aft movement of the upper-body caused by shear deformation of the pelvis tissue. It is suggested that a mathematical model developed with single-axis excitation can represent the biodynamic response with dual-axis excitation by changing these sensitive parameters (e.g., the stiffness of the tissue beneath the pelvis). A finite element human body model with flexible bodies representing the tissue beneath the pelvis and thighs and rigid bodies representing other body segments provided sensible prediction of the first resonance frequencies and the associated modulus in the vertical inline and fore-and-aft cross-axis apparent mass on the seat and the transmissibility to the lumbar spine, as well as the pressure distribution on the seat surface. With the flexible bodies assigned the material properties of nonlinear low density foam, the model was allowed to reflect the softening effect (i.e., a reduce in the resonance frequency of the vertical apparent mass) when the when the magnitude of the vertical excitation was increased.

The effect of technology on music has been indisputably profound. As a cultural descendant of the traditions first established by notation and printing, recorded music technology has transformed our understanding and use of music in all sorts of ways. Whether or not different technologies have had a positive or negative effect, however, is a subject of much debate. Traditional histories of recorded music technology demonstrate a tendency either to treat each new platform as truly revolutionary, or to elide the differences between them to such an extent that significant socio-­cultural and socio-­economic transformations become occluded. Revisiting this history with an open mind—and a degree of cultural and temporal distance—permits a perspective of progression, from which the ramifications of recorded music technologies become more accurately discernible. This thesis highlights six characteristics of recorded music, all of which have been affected at various times and in various ways by the evolution of recording technology. Without exception, every new platform for recorded music has improved upon at least one of these six characteristics, although not necessarily without detriment to one of the others. It is in the scope of these improvements that digital music files, as a platform, are fundamentally different to any of their predecessors. Far from simply continuing or exaggerating the trend that forms the customary narrative of the traditional histories of recorded music, digital music files have completely reengineered our relationship with and understanding of the production, distribution, and consumption of music in a very profound way. The thesis explores these changes, and offers some frank yet ultimately encouraging insights as to what the social future of music may hold.

The influence of building occupancy and user behaviour on energy usage has been identified as a source of uncertainty in current understanding of operational buildings, and yet it is rarely directly monitored. Gathering data on the occupancy of buildings in use is essential to improve understanding of how energy is used relative to the actual energy requirements of building users. This thesis covers the application of occupancy measurement and processing techniques in order to address the gap in knowledge around the contextual understanding of how occupants’ changing use of a building affects this building’s optimum energy demand in real time. Through targeted studies of running buildings, it was found that typical current occupancy measurement techniques do not provide sufficient context to make energy management decisions. Useable occupancy information must be interpreted from raw data sources to provide benefit: in particular, many slower response systems need information for pre-emptive control to be effective and deliver comfort conditions efficiently, an issue that is highlighted in existing research. Systems utilising novel technologies were developed and tested, targeted at the detection and localisation of occupants’ personal mobile devices, making opportunistic use of the existing hardware carried by most building occupants. It was found that while these systems had the potential for accurate localisation of occupants, this was dependent on personal hardware and physical factors affecting signal strength. Data from these sources was also used alongside environmental data measurements in novel algorithms to combine sensor data into a localised estimation of occupancy rates and to estimate near-future changes in occupancy rate, calculating the level of confidence in this prediction. The developed sensor combination model showed that a selected combination of sensors could provide more information than any single data source, but that the physical characteristics and use patterns of the monitored space can affect how sensors respond, meaning a generic model to interpret data from multiple spaces was not feasible. The predictive model showed that a trained model could provide a better prediction of near-future occupancy than the typically assumed fixed schedule, up to an average of approximately two hours. The systems developed in this work were designed to facilitate the proactive control of buildings services, with particular value for slower-response systems such as heating and ventilation. With the application of appropriate control logic, the systems developed can be used to allow for greater energy savings during low or non-occupied periods, while also being more robust to changing occupant patterns and behaviours.

Numerical modeling of free convection in porous enclosures is investigated in order to determine the best approaches to solve the problem in two and three dimensions considering their accuracy and computing time. Two case studies are considered: sloping homogeneous porous enclosures and layered porous enclosures due to their relevance in the context of geothermal energy. The governing equations are based on Darcy's law and the Boussinesq approximation. The mathematical problem of free convection in 2D homogeneous porous enclosures is solved following the well known stream function approach and also in terms of primitive variables. The numerical schemes are based on the Finite Volume numerical method and implemented in Fortran 90. Steady-state solutions are obtained solving the transient problem for long simulation times. The case study of a sloping porous enclosure is used for comparison of the results of the two models and for validation against results reported in the literature. The two modeling approaches generate consistent results in terms of the Nusselt number, the stream function approach however, turns out a faster computational algorithm. A parametric study is conducted to evaluate the Nusselt number in a 2D porous enclosure as a function of the slope angle, Rayleigh number and aspect ratio. The convective modes can be divided into two classes: multicellular convection for small slope angles and single cell convection for large angles. The transition angle between these convective modes is dependent on both the Rayleigh number and the aspect ratio. High Rayleigh numbers allow multicellular convection to remain in a larger interval of angles. This study is extended to the three-dimensional case in order to establish the range of validity of the 2D assumptions. As in the 2D modeling, two different approaches to solve the problem are compared: primitive variables and vector potential. Similarly, both approaches lead to equivalent results in terms of the Nusselt number and convective modes, the vector potential model however, proved to be less mesh-dependent and also a faster algorithm. A parametric study of the problem considering Rayleigh number, slope angle and aspect ratio showed that convective modes with irregular 3D geometries can develop in a wide variety of situations, including horizontal porous enclosure at relatively low Rayleigh numbers. The convective modes obtained in the 2D analysis (multicellular and single cell) are also present in the 3D case. Nonetheless the 3D results show that the transition between these convective modes follows a complex 3D convective mode characterized by the interaction of transverse and longitudinal coils. As a consequence of this, the transition angles between multicellular and single cell convection as well as the location of maxima Nusselt numbers do not match between the 2D and 3D models. Finally in this research, three-dimensional numerical simulations are carried out for the study of free convection in a layered porous enclosure heated from below and cooled from the top. The system is defined as a cubic porous enclosure comprising three layers, of which the external ones share constant physical properties and the internal layer is allowed to vary in both permeability and thermal conductivity. A parametric study to evaluate the sensitivity of the Nusselt number to a decrease in the permeability of the internal layer shows that strong permeability contrasts are required to observe an appreciable drop in the Nusselt number. If additionally the thickness of the internal layer is increased, a further decrease in the Nusselt number is observed as long as the convective modes remain the same, if the convective modes change the Nusselt number may increase. Decreasing the thermal conductivity of the middle layer causes first a slight increment in the Nusselt number and then a drop. On the other hand, the Nusselt number decreases in an approximately linear trend when the thermal conductivity of the layer is increased.

No description available.

No description available.

High-speed serial links in modern communication systems often require the Bit-Error-Rate (BER) to be at the level of 10 −12 or lower. From the industry perspective, major drawbacks in high volume production test for the serial links with low BER are the excessive test time for comparing each captured bit for error detection and costly instrumentation. In this thesis, we focus on developing a novel BER estimation methodology and its implementation. We propose a novel BER estimation methodology and an effective self-test system, which not only eliminates the usage of expensive measuring instruments, but also significantly reduces the test time. In the proposed BER estimation, we show that the total jitter (TJ) spectral information of a test SerDes is successfully estimated from the known TJ distribution of a golden SerDes. We propose a novel BER estimation formula that incorporates not only the TJ spectral information of the serial data, but also the TJ spectral information of the recovered clock. Our proposed estimation formula enables efficient BER estimation without excessive test time, and its accuracy does not depend on the jitter present in the serial data stream of the SerDes. The experimental results demonstrate that the test time for the proposed BER estimation is in the order of seconds, which translates to the test time savings of more than hundred times compared to the traditional BER measurement for the same accuracy. To implement the proposed BER estimation methodology, we have developed a novel time-to-digital converter (TDC). This design effectively measures the delay between two signals and converts it into the digital format. Performance of the TDC has been evaluated and presented using ModelSim and SPICE simulation. / Electrical and Computer Engineering