Analysis and design of Piezoelectric sonar transducers.

PhDIn this study techniques are developed for the analysis and design of piezoelectric sonar transducers based on equivalent circuit representations. For the purposes of analysis, equivalent circuits capable of accurately representing every element of a transducer in the full operating frequency range, are developed. The most convenient fashion in which these equivalents could be derived is also discussed. For the purposes of design the accurate equivalents are approximated by L-C-R circuits. The limits of both representations are discussed in detail. The technique of analysis developed is capable of determining the frequency characteristics as well as the transient response to any electrical or acoustic input which can be specified analytically or numerically in the time domain. The design technique is based on the formulation of a ladder-type generalized circuit incorporating the essential components of any transducer. The generalised circuit is then used to extract particular bandpass filter designs which possess wide passbands and which are mechanically realizable. By this procedure it is found possible to design transducers exhibiting bandwidths of around 100%. The performance of a 'test' transducer constructed to verify both analysis and design theories is also discussed

On Gaugino Condensation in String Theory

openWe derive the precise form of the low-energy four-dimensional EFT for type IIB string theory compactified on the complex cone over Kähler-Einstein del Pezzo surfaces, including N spacetime-filling D3-branes and assuming Minkowski externally. We explicitly derive the theory for the K\"ahler modulus in the simplest case of a complex cone over the complex projective plane, with a stack of four D7-branes and one O7-plane wrapped around the base of the cone. An effective scalar potential appears in the theory, due to gaugino condensation taking place at low energies over the D7-branes stack, exhibiting a runaway direction and an unstable de Sitter vacuum. We find an explicit cosmological-like solution for the K\"ahler modulus, showing that the warped volume of the internal complex projective plane inflates with time in a runaway fashion. We conclude that type IIB string theory compactified on the complex cone over the complex projective plane, with four D7-branes and one O7-plane wrapped around the complex projective plane, is unstable. We explicitly derive the ten-dimensional equations of motion for maximally symmetric time-dependent metric perturbations by means of an ad hoc procedure, and we exhibit both stationary and time-dependent solutions, whose boundary conditions are imposed in part by the gaugino condensate stress-energy tensor. We partially fix the free parameters of the time-dependent solution using the results from the four-dimensional low-energy EFT. This thesis contains also an introduction to string compactifications, to the KKLT scenario and to the literature about ten-dimensional effects of gaugino condensation.We derive the precise form of the low-energy four-dimensional EFT for type IIB string theory compactified on the complex cone over Kähler-Einstein del Pezzo surfaces, including N spacetime-filling D3-branes and assuming Minkowski externally. We explicitly derive the theory for the K\"ahler modulus in the simplest case of a complex cone over the complex projective plane, with a stack of four D7-branes and one O7-plane wrapped around the base of the cone. An effective scalar potential appears in the theory, due to gaugino condensation taking place at low energies over the D7-branes stack, exhibiting a runaway direction and an unstable de Sitter vacuum. We find an explicit cosmological-like solution for the K\"ahler modulus, showing that the warped volume of the internal complex projective plane inflates with time in a runaway fashion. We conclude that type IIB string theory compactified on the complex cone over the complex projective plane, with four D7-branes and one O7-plane wrapped around the complex projective plane, is unstable. We explicitly derive the ten-dimensional equations of motion for maximally symmetric time-dependent metric perturbations by means of an ad hoc procedure, and we exhibit both stationary and time-dependent solutions, whose boundary conditions are imposed in part by the gaugino condensate stress-energy tensor. We partially fix the free parameters of the time-dependent solution using the results from the four-dimensional low-energy EFT. This thesis contains also an introduction to string compactifications, to the KKLT scenario and to the literature about ten-dimensional effects of gaugino condensation

A survey of late Anglo-Saxon and Viking-Age strap-ends from Britain

This thesis presents a national survey of the Late Anglo-Saxon and Viking-age strap-end, one of the commonest manifestations of ornamental metalwork from the period. This survey is based on approximately 1,400 strap-ends, enabling, for the first time, a detailed investigation of various themes concerning their manufacture, circulation, and use. The introduction (1) describes the organisation and contents of the thesis in light of past work on the subject. A background chapter (2) sets out a methodological framework for the study and then introduces some relevant theoretical considerations. A classification of Late Saxon and Viking-age strap-ends (3) presents the defining characteristics of morphology and decoration relating to a sub-division of the corpus into typological groups. Chapter (4) discusses the variety of contexts in which Late Saxon strap-ends are discovered - highlighting the limitations and implications of each for subsequent interpretation. Evidence of their manufacture and associated technology is evaluated in Chapter (5). Extended analysis and interpretation then proceeds in the following three chapters. The chronology and distribution of Late Saxon strap-ends are discussed in (6) and (7) respectively. Chapter (8) is primarily contextual, exploring the possible function/s of these artefacts, and the production systems involved in their manufacture. Chapter (9) offers general conclusions and suggestions for refining the present study and strategies for future research. Appendices include a comprehensive checklist of individual strap-ends recorded in the survey (1), a preliminary checklist of examples recorded outside the survey area (2), and contextual information relating to strap-ends discovered in stratified, archaeological contexts (3). These are intended to provide the principle source of reference for the classificatory and thematic discussions which form the main text