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This thesis carries out a series of empirical investigations into the nature and evolutionary process of asset bubbles in global stock markets. It also provides insight into the issue of market predictability with the consideration of price bubbles in the US, and how those results might inspire policymakers to prevent future bubbles. We start by reviewing the rational bubble theories which are used for modelling bubble process and discuss the rationale of the relevant testing methods for discovering bubbles. Overall, three main testing procedures are selected in Chapter 3 with the purpose of concluding whether bubbles exist in the global stock markets. Eventually, we confirm the presence of bubbles globally, and provide clear dates for each bubble's origination and collapse. The bubble dates obtained provide a timeline for stock market exuberance, and their overlapping periods suggest that bubbles can migrate between countries. However, there has been very little research on this latter issue. Therefore, in Chapter 4 we undertake a large-scale empirical analysis to investigate the bubble transmission mechanism. Our vector autoregressive (VAR) and volatility results confirm that for some countries a contagion effect exists, leading to bubble migration between countries. Finally, in Chapter 5, we are particularly interested in whether empirical results on the predictability of stock market data by the dividend-price ratio is affected by the presence of a bubble, and by borrowing Campbell-Shiller's model but adding selected monetary variables, we further assess the forecasting performance of common monetary policy indictors in predicting the movement of price-dividend ratios in both bubble and non-bubble periods.

Liquid mixtures are ubiquitous in industry and in nature, and demonstrate remarkably more complex behaviour than pure fluids, which is still to be revealed. Particularly, commercial coolants are mixtures and the complexity in their flow behaviour is due to the interplay between phenomena driven by thermal and concentration gradients. This thesis considers predominantly binary mixtures wherein one component is more volatile than the other. The thesis focuses on multiphase dynamics presented in liquid mixtures. Given the volatility difference, there is always phase-change under temperature gradients. A bubble generated in that mixture has dynamics which will be subjected to the surrounding flow, temperature and concentration fields. The bubble will eventually grow until it occupies the entirety of the tube leaving behind a thin evaporating layer of the mixture. Thus the thesis work focusses on i) investigations of the bubble dynamics (during its slow growth phase) and ii) the instabilities in the evaporating layer (once the bubble occupies the whole cross section of the tube). The first part of this thesis investigates the counter/co-current thermocapillary propulsion of bubbles in the so-called self-rewetting liquids by means of direct numerical simulations (DNS) and validated by experiments. In self-rewetting liquids, surface tension presents a peculiar non-monotonic dependence on temperature. A DNS model based on the volume-of-fluid method is developed to study the dynamics of bubbles inside of a horizontal channel with constant flow rate and constant temperature gradient in the flow direction. A parametric study is performed to investigate the influence of the viscous drag and thermocapillary forces on the bubble motion. Four distinct regimes of bubble migration are determined: counter-current propulsion, damped oscillations, sustained oscillations and co-current migration. A map is provided in the parameter space of Reynolds and capillary numbers showing these regimes. Each regime is discussed in detail and the mechanism that leads to sustained oscillations at low capillary numbers is discussed. The results are compared against the theoretical prediction for the bubble equilibrium position and frequency of the oscillations reported in the literature. Next, experiments are performed to investigate the thermocapillary migration of bubbles in self-rewetting liquids inside of a horizontal circular channel with constant flow rate and constant temperature gradient in the flow direction. The motion of the bubbles is recorded with a CCD camera from the top while the temperature at the channel wall is recorded with an IR-camera from the side. The influence of the flow rate and the temperature gradient on the bubble motion is investigated. It has been observed that the flow rate has a decreasing linear relationship with the bubble velocity while the temperature gradient has an increasing linear relationship with the bubble velocity during the countercurrent motion. The experiments validate the numerical findings and these are presented in the flow-regime map. The third part of this thesis is devoted to the study of the stability of the evaporation of a horizontal thin liquid layer which consists of a binary mixture of volatile liquids heated from below by means of linear stability analysis and transient numerical simulations. The effect of vapour recoil, thermo- and solute-capillarity and the van der Waals interactions are considered. The long-wave approximation is used to derive the evolution equations for the free interface and the concentration of the components. A linear stability analysis is performed to derive the growth rate of the instabilities for the case of quasi-equilibrium evaporation and non-equilibrium evaporation. The developed linear theory describes two modes of instabilities: i) a monotonic instability mode where the perturbations simply grow until the liquid layer is ruptured if the thermo-capillary and the solute-capillary force enhance each other and ii) an oscillatory instability mode where perturbations oscillate if the thermo-capillary and the soluto-capillary forces compete with each other. A parametric study is performed to investigate how these modes depend on the ratio between the thermal and solutal Marangoni numbers and on the volatility ratio of the components. The mechanisms of the instabilities are discussed in detail. The linear theory is validated against transient simulations and show a good agreement in the comparison of the growth rates. Lastly, the evolution of the interface for the two instability modes is analysed by means of transient simulations.

A novel one-way coupled Euler-Lagrangian approach, including bubble-bubble collisions, coalescence and variable bubble radius, was developed in the context of simulating large numbers of cavitating bubbles in complex geometries using direct numerical simulation (DNS) and large-eddy simulation (LES). This dissertation i) describes the development of the Euler-Lagrangian approach, ii) outlines the novel bubble coalescence model derived for this approach and iii) describes simulations performed of bubble migration in a turbulent boundary layer, bubble coalescence in a turbulent pipe ow and cavitation inception in turbulent flow over a cavity. The coalescence model uses a hard-sphere collision model is used and determines coalescence stochastically. The probability of coalescence is computed from a ratio of coalescence timescales, which are dynamically determined from the simulation. Coalescence in a bubbly, turbulent pipe ow (Re#28; = 1920) in microgravity was simulated with conditions similar to experiments by Colin et al. [1] and excellent agreement of bubble size distribution was obtained. With increasing downstream distance, the number density of bubbles decreases due to coalescence and the average probability of coalescence decreases due to an increase in overall bubble size. The Euler-Lagrangian approach was used to simulate bubble migration in a turbulent boundary layer (420 < Re#18; < 1800). Simulation parameters were chosen to match Sanders et al. [2], although the Reynolds number of the simulation is lower than the experiment. The simulations show that bubbles disperse away from the wall as observed experimentally. Mean bubble diffusion and profiles of bubble concentration are found to be similar to the passive scalar results, except very near the wall. The carrier-fluid acceleration was found to be the reason for moving the bubbles away from the wall. The one-way coupled Euler-Lagrangian approach was applied to simulate the experiment of cavitating turbulent ow over a cavity by Liu and Katz [3]. The classical Rayleigh-Plesset equation is integrated using adaptive time-stepping to accurately and efficiently solve for the change of the bubble radius over time. The one-way coupled Euler-Lagrangian model predicts cavitation inception at the trailing edge of the cavity and also in the vortices shed from the leading edge, in qualitative agreement with experiment.

Samples of pure nickel have been implanted with 500keV helium ions, at a dose of 10[17]ions/cm[2], followed by annealing in vacuo at 750°C (&ap;0.6T[m]) for various time periods to allow bubble nucleation and growth to occur. A transverse sectioning technique has been developed to allow TEM studies of the complete depth distribution of cavities, hence allowing the mechanisms for bubble growth at 750°C in nickel to be identified. It was found that after 2 hours annealing, a fine layer of cavities developed, corresponding well with the gas deposition profile calculated using the E-DEP-1 code. Subsequent annealing resulted in cavity growth on the periphery of the layer by vacancy collection, the principal vacancy sources being the irradiated surface and grain boundaries in the bulk of the material. Cavity growth in the peak implanted region was found to be suppressed due to the lack of vacancies and with bubble migration being hindered as a result of high bubble pressures, hence migration and coalescence did not occur until cavities approached their equilibrium pressure. The same bubble growth mechanisms were found to prevail after implantation of 5x10[16]ions/cm[2] and also after 250keV He implantation. The growth of helium bubbles has been compared to neon bubbles after implantation with 500keV Ne ions at two doses: 7.8x10[16]ions/cm[2] to obtain the same peak gas concentration and 2.9x10[15]ions/cm[2] to achieve the same peak displacement damage, followed by annealing. The cavity density was found to be established by the gas concentration, the displacement damage apparently having little or no effect, even after an approximately 27-fold increase. The growth mechanisms observed after Ne implantation appeared to be the same as those for He, although the bubbles after low dose Ne implantation achieved equilibrium conditions more rapidly, due to the lack of implanted gas. He and Ne have been compared after high energy implantation at 500°C, in the Variable Energy Cyclotron at Harwell to a peak gas concentration of 250ppm. For 4MeV He, an inhomogeneous cavity distribution was observed, compared to a relatively uniform cavity layer after 17MeV Ne implantation. However, the observed cavity sizes and number densities were found to be similar. Finally, nickel has been irradiated at 500°C with a mixed beam of 51MeVNi[6+]/17MeVNe[2+] ions, to 250ppm Ne together with 30dpa displacement damage, and compared to an irradiation with 51MeVNi[6+] ions without inert gas, as well as with 17MeVNe[2+] ions. The void number density profile resulting from the single heavy ion irradiation was similar to the computed damage profile, although the peak was &ap;10% deeper than that predicted. A depression in the swelling profile was observed in this peak region resulting from a reduction in cavity size, a bimodal distribution being observed. The effect of simultaneous gas deposition was to increase the cavity nucleation and reduce cavity size. This phenomenon was found to be dominant in the region corresponding to the implanted gas layer, however the gas appeared to influence cavities produced at greater depths, with an overall reduction in swelling.