The subject of this thesis is the investigation of two dimensional helium mixtures adsorbed on Grafoil. Heat capacity and Nuclear Magnetic Resonance (NMR) measurements were used in the temperature range of 1 mK to 90 mK. This work represents the first systematic study of monolayer fluid helium mixtures adsorbed in Grafoil at low mK temperatures, extends previous experimental observations on solid helium mixtures and explores the ground state of 3He on top of three layers of 4He. The experimental setup consists of a dilution refrigerator with a nuclear de magnetisation stage with the possibility to achieve ultra low temperatures of 0.3 mK. An NMR setup was constructed to perform continuous wave NMR measurements and was satisfactorily used to obtain data for this thesis. A series of automated, computer controlled data acquisition programmes was also developed to measure and analyse the signals. The study involved the investigation of three different types of mixtures on the second and third layer of Grafoil. The study of fluid mixtures lead for the first time, to evidence of finite solubility of 2D 3He in fluid 4He. It was also possible to explore, within the data collected, the phenomenon of phase separation within a monolayer mixture. Furthermore, the possibility of 3He condensation and stratification effects in this system were also argued as an alternative scenario. A study of solid helium mixtures supported previous observations of delocalised 3He tunnelling excitations and a model was constructed to interpret the data. Additional data in this mixture at various 3He concentrations provided evidence of finite solubility of 3He in 2D solid 4He. Finally, additional measurements were undertaken on 3He on top of three layers of 4He. A number of new and interesting features were observed. The new data suggest the possibility of a phase transition below 10 mK

This thesis focuses on the appropriateness of the inviscid potential flow model for determining the manoeuvring characteristics of a body moving through fluid. This model is widespread in many key applications for ships, submarines, aircraft, rockets, missiles, as well as for the swimming of marine animals and the flying of birds. Despite the widespread use, there are important anomalies in the theory, in particular relating to the lift induced by shed vorticity. These anomalies have been identified in the recent publication by Chadwick which states that the lift has been calculated incorrectly, and apparent agreement in wing theory is fortuitous due to "two wrongs" in the theory giving the right answer. In this thesis, the inviscid flow is further investigated, and the work of Chadwick is extended and developed further. In the first two chapters, careful description of the basic fluid concepts and then derivation of the fluid equations is given. In chapter four, the lift and drag on a wing are considered. The lift evaluation comes out to be half that expected and this is in agreement and essentially repeats the analysis in Chadwick's recent paper [1]. However, the analysis is extended to evaluate the drag, and surprisingly the drag is determined to be infinite. In chapter five, further investigation into the lift on a thin wing is undertaken, and it is seen that there is uncalculated jump in the lift at the trailing edge. This is calculated from the pressure integral across the trailing edge. Finally, in chapter six, inviscid flow slender body theory is investigated. A complete near field expansion is given for a singularity distribution of sources over an infinite line by using the Fourier transform method. In this thesis, this result is extended for the finite line by using the integral splitting technique. By taking the ends to infinity, the result for the infinite line is recovered and the two methods shown to be equivalent for this specific case. The method presented here relies upon allowing a singular wake to exist behind the body. This introduces non-uniqueness in the matching and the implications of this are discussed. Appropriate references to other researchers are given in individual introductions for each chapter.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.