Ho Chiu Man. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 100-103). / Text in English; abstracts in English and Chinese. / Ho Chiu Man. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Historical Background --- p.1 / Chapter 1.2 --- Motivations of the Project --- p.3 / Chapter 1.3 --- Outline of Thesis --- p.4 / Chapter 2 --- Review on a One-dimensional Vibrating Cavity --- p.5 / Chapter 2.1 --- The R Function --- p.5 / Chapter 2.2 --- Photon Generation --- p.7 / Chapter 2.3 --- Instantaneous Mode Expansion --- p.10 / Chapter 2.4 --- Vacuum Energy Density --- p.15 / Chapter 3 --- Graphical Method --- p.17 / Chapter 3.1 --- Construction of R-function --- p.17 / Chapter 3.2 --- Fixed-point Analysis --- p.19 / Chapter 3.3 --- A Special Class of Mirror Trajectories --- p.23 / Chapter 3.4 --- Further Analysis --- p.27 / Chapter 4 --- Wave Evolution in a One-dimensional Vibrating Cavity --- p.32 / Chapter 4.1 --- Instantaneous Mode Expansion Method --- p.32 / Chapter 4.2 --- Transformation Method --- p.34 / Chapter 4.3 --- R-Method --- p.34 / Chapter 4.4 --- Consistency between Different Methods --- p.35 / Chapter 5 --- Floquet's Theory --- p.40 / Chapter 5.1 --- System of Linear Differential Equations with Time-dependent Coefficients --- p.40 / Chapter 5.2 --- Fundamental Set of Solutions and Matrizant --- p.41 / Chapter 5.3 --- System of Linear Differential Equations with Periodic Coefficients --- p.42 / Chapter 5.4 --- Possible Properties of the Solution --- p.43 / Chapter 5.5 --- Eigenvalues for the One-dimensional Vibrating Cavity --- p.44 / Chapter 6 --- Photon Creation in an Oscillating Spherical Cavity --- p.46 / Chapter 6.1 --- Mode Decomposition --- p.46 / Chapter 6.2 --- Bogoliubov Transformation --- p.48 / Chapter 6.3 --- Photon Creation --- p.51 / Chapter 6.4 --- Mean Electric Field Operator --- p.53 / Chapter 6.5 --- Illustrations and Observations --- p.54 / Chapter 7 --- Multiple Scale Analysis --- p.61 / Chapter 7.1 --- Photon Creation by First-order Multiple Scale Analysis --- p.61 / Chapter 7.2 --- Parametric Resonance --- p.64 / Chapter 7.3 --- Nonstationary Medium --- p.71 / Chapter 7.4 --- Photon Statistics --- p.74 / Chapter 7.5 --- Finite Temperature Correction --- p.75 / Chapter 8 --- Squeezing Effect of the Classical Waves --- p.76 / Chapter 8.1 --- Squeezing Effect in the One-dimensional Vibrating Cavity --- p.76 / Chapter 8.2 --- Squeezing Effect in the Oscillating Spherical Cavity --- p.81 / Chapter 9 --- Supersymmetric Approach to Photon Generation --- p.88 / Chapter 9.1 --- Field Quantization --- p.88 / Chapter 9.2 --- Adiabatic Approximation --- p.90 / Chapter 9.3 --- Scattering Interpretation --- p.91 / Chapter 9.4 --- Supersymmetric Approach --- p.93 / Chapter 9.5 --- Examples --- p.94 / Chapter 10 --- Conclusion --- p.98 / Bibliography --- p.100

Cho, Chi Lam. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 63-65). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese.

La photoionisation à pression atmosphérique (APPI) permet d’analyser des biomolécules hydrophobes donc difficilement observables avec les sources d’ions connues comme l’électro-nébulisation (ESI) ou la désorption-ionisation laser assistée par matrice (MALDI). Elle permet d’étudier les interactions d’un faisceau de photons irradiant dans l’ultraviolet grâce à un nébullisat, à pression atmosphérique, contenant un mélange de molécules. Elle génère de nombreuses fragmentations et permet d’obtenir d’emblée sans expérience MS/MS supplémentaire des fragments non observables avec les autres techniques de fragmentation en source. Le but de ce travail a été d’étendre le champ d’application de l’APPI à des biomolécules plus ou moins polaires et d’approfondir l’élucidation des voies de fragmentations par la compréhension des mécanismes réactionnels mis en jeu. Les expériences faites à l’aide de la lampe au krypton ont permis d’obtenir des spectres riches de fragments divers voire même exotiques et caractéristiques d’une longueur d’onde fixée à 10,0 eV et minoritairement à 10,6 eV. L’utilisation du rayonnement synchrotron a donné l’avantage d’ajouter une dimension supplémentaire à ces spectres APPI-MS qui est la variation de longueur d’onde (4-20 eV ou 300-60 nm). Ce nouveau paramètre apporte des informations complémentaires grâce à l’étude de l’évolution des réactions mises en jeu selon les longueurs d’ondes choisies. L’étude des mécanismes APPI a donc mené à la mise en évidence de réactions mettant en jeu des électrons ou menant à des ions fragments radicalaires provenant de réactions jamais observées auparavant avec les sources d’ions connues. L’utilisation combinée de la source APPI et du rayonnement synchrotron est un outil très efficace pour la caractérisation de nouvelles molécules grâce à cette grande variation de longueur d’ondes possible apportant même des informations supplémentaires à celles obtenues avec la lampe au krypton à même longueur d’onde. / Atmospheric Pressure Photionisation (APPI) allows for the analysis of hydrophobic biomolecules which are unobservable with the common ionization techniques as electrospray ionization (ESI) or the matrix assisted laser desorption ionization (MALDI). This allows for the study of the interactions between a photon beam irradiating in the VUV thanks to a nebulisate and a mixture of molecules at atmospheric pressure. It generates numerous fragment ions, many of which are unobservable with the other in-source fragmentation techniques, and immediately provides structural information with no supplementary MS/MS experiment. The goal of this work was to spread the application of APPI to more or even less polar biomolecules and to elucidate their fragmentation pathways through a deepened understanding of reaction mechanisms involved. The experiments utilized a krypton lamp which provided rich mass spectra of various and even exotic fragment ions and characteristics of a wavelength fixed mainly at 10.0 eV and in a smaller proportion at 10.6 eV. The use of synchrotron radiation gave the advantage of adding a supplementary dimension to these APPI-MS spectra which is the wavelength variation (4-20 eV or 300-60 nm). This new parameter brings complementary information coming from the reactions never seen before with the known ion sources. The combined use of APPI source and synchrotron radiation is a very effective tool for the characterization of new molecules thanks to the large possibility of wavelength variation providing supplementary information to that obtained with the krypton lamp at the same wavelength.

No description available.

This thesis is concerned with the use of the open source computational fluid dynamics (CFD) software package, OpenFOAM® for predicting and analysing the behaviour of a near-shore oscillating wave surge converter (OWSC), when subject to various types of ocean wave conditions in a numerical wave tank (NWT). OpenFOAM® which utilises a Finite Volume Method (FVM) is used to solve the incompressible, Reynolds Averaged Navier-Stokes (RANS) equations for a two-phase fluid, based on a Volume of Fluid (VOF) phase-fraction approach to capture the interface between the air and water phases. Preliminary studies on classic wave-structure interaction benchmark cases, involving a fixed and a vertically oscillating semi-immersed horizontal cylinder are carried out. The gradual transition of the linear to non-linear behaviour of the horizontal and vertical forces induced on a fixed cylinder when subject to various regular waves, and the amplitude ratios of the surface waves elevations generated by the prescribed oscillatory motion of the cylinder, are shown to provide good overall agreement within the limitations of the relevant theory and the experimental data in the literature. The OWSC is modelled with the inclusion of a Power Take-Off (PTO) system, using a linear damping restraint, and simulated in two-dimensional (2D) and three-dimensional (3D) setups. The 2D and 3D numerical results, such as the surface wave elevations, flap angular velocity, PTO torque and flap angular displacement, compare well with one another and with the experimental data for operational regular head-on and oblique wave conditions. Small discrepancies between numerical results and experimental data are likely to be caused by non-linear behaviour of the PTO system. Pressure distributions on the flap surfaces and forces induced on the flap and hinge of the OWSC for various wave conditions are also presented. The effects between 2D and 3D wave-structure interactions become more significant when subject to large waves that break during impact. Comparison between the full scale and 1:24 scale numerical results of the OWSC shows no significant evidence of viscous and scaling effects. The validated 2D OWSC model is also subject to embedded focused waves, to predict the worse possible scenario of wave loading in extreme wave conditions. The delay of the focus event breaking is shown to affect the slamming behaviour for the larger focus event wave heights. Incorporation of a focused wave at different phase positions within a background of regular waves reveals that the focus event wave height has little effect on the peak tangential force on the flap during the slamming event, when a PTO cut-off mechanism is implemented to prevent excessive torque surges. In contrast, the peak radial force on the flap and the maximum resultant force on the hinge appear to respond more sensitively to the focus event wave height. It has been demonstrated that OpenFOAM® is able to provide a comprehensive understanding of the complex hydrodynamic analysis and prediction of highly non-linear wave-structure interactions for an OWSC, which give useful guidance and confidence to WEC developers on the design considerations relevant to the OWSC systems.

The study of arterial wave propagation is essential to understand the physiopathology of the cardiovascular system, as waves carry clinically relevant information. Impedance analysis was used for such type of studies, where results were presented in the frequency domain, but it was difficult to relate specific events to time points within the cardiac cycle. Therefore, a mathematical tool called wave intensity analysis was developed, initially using measurements of pressure and velocity (PU approach). However, the need to acquire such measurements in a non-invasive, direct and simultaneous fashion led to the development of the DU approach, a type of wave intensity analysis carried out using vessel diameter and flow velocity waveforms, thus giving up the pressure measurement. It is the only available technique, at present, able to extract wave intensity information without relying on distally recorded pressure measurements and on non-simultaneous recordings. Due to its non-invasive nature for collecting the required measurements, this technique has a potential use in clinical and research settings to investigate physiological changes under rapid perturbations, such as the ones introduced by exercise. In this thesis, the DU approach is performed by only using an ultrasound device and to extract information about cardio-arterial interaction in the human common carotid artery. In the first experimental chapter of this thesis, a reproducibility study of common carotid DU-derived wave intensity parameters was conducted on a healthy young cohort, both at rest and during exercise (semi-recumbent cycling). Carotid diameter and blood flow velocity features, as well as wave intensity parameters such as forward compression, backward compression and forward expansion wave peaks and energies, were overall fairly reproducible. In particular, diameter variables exhibited higher reproducibility and lower dispersion than corresponding velocity variables, whereas wave intensity energy variables exhibited higher reproducibility and lower dispersion than corresponding peaks. Local wave speed, calculated via lnDU-loop, a technique based only on local measurements of diameter and velocity and often associated with the DU approach, was also reproducible. It is possible to conclude that the DU-derived wave intensity analysis is reliable both at rest and during exercise. In a subsequent study, DU-derived wave intensity analysis was performed on a young trained cohort to investigate the contribution of cardiac and peripheral vascular alterations to common carotid wave intensity parameters, under rapid physiological perturbations, such as semi-recumbent cycling at incremental workrates, and subsequent recovery. Judging by the increase in local wave speed, the common carotid artery stiffened substantially as workrate increased whilst peak and energy of the forward and backward compression waves also increased, due to enhanced ventricular contractility, which was associated with larger reflections from the cerebral microcirculation and other vascular beds in the head. However, the reflection indices remained unchanged during exercise, highlighting that the increased magnitude of reflections is mainly due to the enhanced contractility, rather than changes in vascular resistance, at least at the carotid artery in young healthy individuals. The forward expansion wave increased during exercise, as the left ventricle actively decelerated blood flow in late systole, potentially improving filling time during diastole. In the early recovery, the magnitude of all waves returned to baseline value. Finally, the X wave, attributed to the reflection of the backward compression wave, had a tendency to increase during exercise and to return to baseline value in early recovery. A further development of wave intensity analysis came with the reservoir-wave approach, able to separate, from the pressure and velocity waveforms, the component solely due to the reservoir volume, for the correct evaluation of backward- and forward-travelling waves. A number of issues, however, still remains, involving specifically the lack of consensus over the fitting technique and over the value of the asymptotic pressure value (P ∞),used for the determination of the reservoir waveform. Therefore, to give a contribution to the debate involving the more correct model for the pressure and velocity reservoir-wave approach, a study aimed to investigate various common carotid hemodynamic and wave intensity parameters, using different fitting techniques and values of P ∞ currently available in literature, was performed and described in the last chapter of this thesis. The study demonstrated that different fitting method and values of P ∞ could bring significant variations in values and trends of hemodynamic and wave intensity parameters. However, despite the changes in the shape of the reservoir pressure waveform, its peak and integral with respect to time tended to remain constant. This is an important feature, because both reservoir peak pressure and its integral have been used in clinical settings for the calculation of diagnostic indicators. The reservoir and excess velocity peaks, instead, changed more significantly. This outcome, together with the concomitant substantial change in excess pressure peak and integral, may greatly affect wave intensity parameters. Wave intensity parameters were, in fact, significantly more sensitive to fitting techniques and values of P ∞ than pressure parameters. Finally, the wave speed did not substantially change, leading to the conclusion that the calculation of local vessel distensibility and/or compliance, when calculated from the excess components of the waveforms, seemed insensitive to fitting techniques and values of P ∞.

No description available.

Research Doctorate - Doctor of Philosophy (PhD) / The impact of a small particle with a wear surface can lead to very high strain-rates in the material being encountered. Often predictive erosion models are based on material property parameters taken from quasistatic test conditions. However, the material properties of the impacted wear surface can change dramatically with strain and strain-rate, leaving some doubt as to the validity of an erosion model based on quasistatic parameter values. In this study, a new stress-wave monitoring process is developed for the study of material characteristics and erosion phenomena, at strain-rates approaching 10e6s-1. For this study a newly designed piezo-electric transducer was used to monitor the stress-waves produced by small erosive particle impact events. A computational study was also conducted to aid in the transducer design and location distance from the impact source by considering the effects caused by spatial averaging. Spatial averaging affects the recorded stress-wave signal and is caused by the curvature of the stress-wave as the wave passes through the flat piezo-electric sensing element. This study was conducted using a computational and experimental approach. The joint study allowed significant knowledge to be gained for the study of elasto-plastic impact and stress-wave motion. Finite element analysis (FEA) was used to model the experimental system in detail. The stress-waves produced by the experimental process were directly compared to the FEA model. Once the FEA model was validated, detailed information from the impact event at the surface could be obtained from the model, which would otherwise be difficult if not impossible to obtain experimentally. The issues of wave dispersion have been an underlying problem in the correct interpretation of stress-wave phenomena for many years. The impact of the wear surface causes stress-waves with many frequency components, each component propagating through the wear material at distinct wave velocities. Wave dispersion causes the initial stress-wave pulse to be dispersed into many waveforms. In this study the longitudinal stress-wave was the main waveform studied. FEA simulations were conducted for a purely elastic impact and an impact causing significant plastic deformation of the surface. A comparison between these waveforms showed that in the case of impacts causing plastic deformation, the initial part of the stress-wave, measured from the time of arrival to the first peak, corresponded to the elastic stress component of the impact event at the surface. The characterisation of the waveform in regards to elastic and plastic stress components at the surface was significant for validating model parameters of the Johnson-Cook material model. The stress-wave monitoring process was applied in the first instance to erosive particle impacts to AISI 1020 steel at impact velocities up to 104m/s. A specially designed erosion apparatus, fitted with a modified double disc system was used to impact the 10mm thick steel plate. The piezo-electric transducer was firmly clamped to the rear surface, directly behind the point of impact to obtain the stress-wave signals produced by impacts of 0.4mm zirconia spheres. The study showed that the contact interface of the wear material and the piezo-electric transducer could cause a phase change and amplitude reduction of the stress-wave transmitted to the transducer at wave frequencies above 0.9MHz. The results showed that the most likely cause for the phase shift to occur was the restriction of tensile stresses across the contact interface. For wave frequencies below 0.9MHz, no phase shift or amplitude reduction was apparent in the experimental stress-wave recordings. The combined experimental / FEA study was shown to be able to validate the strain-rate parameter of the Johnson-Cook model. The parameters, which could not be validated by the stress-wave monitoring process, were the parameters relating to plastic deformation of the surface, which were the strain-hardening terms of the Johnson-Cook model. These terms were later validated by studying the extent of plastic deformation at the surface, which occurred in the form of impact craters. By comparing the predicted impact crater depths from the FEA model with the experimental results, the strain-hardening parameters of the Johnson-Cook model could be validated. The robustness of the stress-wave monitoring process was proven for the impact study of ultra high molecular weight polyethylene (UHMWPE) and vinyl ester resin (VER). Unlike AISI 1020 steel, little is know about the high strain-rate response of these polymers. Initial estimates of material property parameters were made by applying computational curve fitting techniques to the stress-strain curves of similar polymers, which were from published results obtained from split Hopkinson’s pressure bar method. The impact and stress-wave study showed UHMWPE and VER to be highly sensitive to strain-rate effects. The main effect was a substantial increase in hardness with increasing strain-rate and it was considered that the hydrostatic stress component contributed to the strain hardening of the polymers. The stress-wave monitoring and FEA computational techniques developed in this study were implemented in the development of an improved erosion model. The model form is similar to that of the well-known Ratner-Lancaster model. The Ratner-Lancaster model assumes wear rate to be proportional to the inverse of deformation energy, where deformation energy is approximated as the product of the ultimate stress and ultimate strain. The improved Ratner-Lancaster model uses the Johnson-Cook model to obtain the von-Mises stress as a function of strain. The area integral of the stress-strain curve is used to derive the deformation energy capacity of the material in the deformed zone close to the surface. The model accounts for strain, strain-rate and thermal effects and is therefore more soundly based on material deformation characteristics valid for erosion events than the Ratner-Lancaster model assumptions. The model developed in this work was applied to the erosion study of 1020 steel, UHMWPE and VER, with good correlation being obtained between experimental erosion rates and model predictions.

Copies of author's previously published articles, inserted. Bibliography: p. 165-179. Reports on the development of a scalable high power laser for gravitational wave interferometry.

Bibliography: p. 165-179. Electronic publication; Full text available in PDF format; abstract in HTML format. Reports on the development of a scalable high power laser for gravitational wave interferometry. Electronic reproduction.[Australia] :Australian Digital Theses Program,2001.