VictorJuiz/thesis huggingface dataset:
Studies of solute distribution at solid-liquid interfaces

An attempt has been made in this thesis to put on a sound basis, the relation between interface morphology and distribution of solute in alloys solidifying in a cellular or dendritic manner.
Specimens have been grown under precisely known and regulated conditions and quenching by rapid withdrawal into water has ensured that the solute distribution existing in the liquid has been retained in the solid. Electron microprobe analysis coupled with optical microscopy studies have then been used to give information concerning the effect of growth variables on the nature of the interface.
The results of this work fall into two distinct parts. First, data are presented which relate to the tips of the cells or dendrites solidified under conditions involving convective flow or transport by diffusion only, and with both heavy and light solutes. Second, extensive annealing of the initial structure behind the tips has been investigated to establish the mechanism involved in post-solidification ripening.
It has been found that over the range of experimental conditions used, the amount of lateral segregation produced by cells and dendrites increases with increasing growth velocity and concentration and with a decrease in the value of the imposed temperature gradient. The results suggest that the solute segregation adjusts until the average gradient of liquidus temperature normal to the interface is equal to the imposed temperature gradient. At the same time as lateral segregation increases, there is a gradual change in morphology from simple cells to cells with branches and finally to crystallographic dendrites which have well-developed side arms. Increasing growth rate was found to cause a decrease in the size of branched cells and dendrites, However, the size of simple cells appears to be independent of growth velocity and alloy concentration but is linked to the magnitude of the concentration gradient at the tips.
In specimens in which there is convection in the melt, a boundary layer exists, inside which there is no stirring. Outside this layer the liquid is fully mixed. The thickness of the layer was found to depend on alloy concentration, and temperature gradient, both variables which affect the magnitude of the density inversion.
Annealing of the cellular structure behind the growth front was found to occur by removal of solute-rich liquid from the cell walls to the cell corners. When the interface plane is (100) or (111) this takes place randomly, but if it is (110), then cell walls disappear preferentially in one direction. The reason for this has been discussed and the conclusion reached that the mechanism causing changes in cell structure is the reduction in surface area of the solute-rich liquid films.
Annealing in the branched cell and dendrite specimens takes place by the disappearance of branches or secondary arms behind the interface, the rate of disappearance depending on concentration and being essentially different for the two morphologies involved. The results presented give the spacing of arms as a function of time allowed for annealing.
Interaction of laser beam with solids

The present investigation is an extension of earlier work in this laboratory on the interaction of laser beams with metallic surfaces. It was conducted with a view to understanding the different processes involved in a laser surface interaction. Initial experiments (Chapter Five) were performed with low laser intensity, so that the Richardson effect was not prominent. The results were interpreted in terms of a double-photon photoeffect. The idea of such a double-photon photoeffect was also supported by the nonlinear optical absorption and double-photon photo- conductivity in a CdS crystal (Chapter Eight).
The effect of linear absorption (single-photon absorption) process was investigated for metal surfaces and the results were interpreted in terms of a temperature rise of the target surface. When high intensity laser pulses were incident onto metal surfaces, the generation of a cloud of ionized particles was observed. The cloud was found to move away from the target in a plasma state. The various properties of this plasma and the mechanism of the generation of current signals by the directed motion of the different species of the charges in an applied electric field has been investigated in Chapter Six. In the same chapter, experiments on the reverse photoelectric effect (photo- electric emission from the surrounding metal parts by the high energy photons generated from the metal plasma) showed a positive contribution to the shape of the current signals by such electrons.
Finally, the controversial chenomena of 'rear-side electron emission' was further investigated in Chapter Seven. It was concluded that the observed current recorded at a collector placed at the rear side of the target when the front surface was irradiated with a focussed Q-switched laser beam could be explained in terms of a capacitance effect. The electrostatic coupling between a collector and any neighbouring metal part, because of the stray capacitance between them, will be of considerable importance when a rapid voltage change of the collector is concerned.
The results of all the experiments were summed up and a general conclusion of the work was presented in Chapter Nine.
The interaction of intermediate energy nucleons with nuclei

Measurements have been made of the differential cross-sections for (p,n) reactions at 98.5 MeV on the 1p-shell nuclei 7Li, 9Be, B, 12C and 160 over an angular range of 0°-45° (lab) . Angular distributions for transitions to excited states of the residual nuclei as well as their ground states were obtained. The energy resolution was ~1.2 MeV (f.w.h.m.) and the angular resolution 3.2° (f.w.h.m.). The angular distributions are subject to an error which varies systematically with angle and could be up to &pm; 10% at 12.5°, though it is thought likely to be less than this. The absolute normalization error is &pm; 14%.
The experiments were done using the neutron time of flight facility on the Harwell 2.79 m synchrocyclotron,, Thin targets were bombarded with the internal proton beam of the synchrocyclotron and the neutron time of flight spectra determined using a 100 m flight path.
The experimental systems were considerably modified prior to. the experiment and an investigation was carried out to determine the optimum energy resolution obtainable. It proved impossible to achieve the hoped for 0.5 MeV (f.w.h.m.).
An improved value was obtained for the degree of excitation of the 0.431 level in 7Be in the 7Li(p,n) reaction and this is compared with an impulse approximation prediction (Mahalanabis, 1964). The two values agree within experimental error, but the prediction is somewhat higher than the experimental value.
All the angular distributions established were discussed in terms of the structures of the states involved. The results are compared with previous (p,n) work at 100 MeV (Saltmarsh, 1965), 30 MeV and 50 MeV (Clough, 1969; Clough, 1970). Comparison is also made with results from 12C(p,p') experiments (Hasselgren, 1965; Jacmart, 1964).
Shape fits to the angular distributions were made using a DWBA computer code (Friedman, 1966), The DWBA formulation is discussed, and the methods by which the code could be used to further analyse the results in order to determine the effective nucleon-nucleon interaction is explained.
It is thought that future developments in the study of (p,n) reactions at this energy are likely to be towards achieving considerably improved energy resolution, and a precise absolute normalization of the cross-sections.
The respiratory functions of blood

Current views on the nature of the haemoglobin-oxygen equilibria have been reviewed and the need for improved experimental techniques stated. A multiple-addition mixing technique for investigation of the equilibria, together with the neccessary ancillary techniques, has been developed and an exhaustive mathematical analysis of the results, using a specially written computer programme, described. A detailed validation of the techniques has been carried out and their particular advantages and disadvantages compared with other techniques.
The multiple-addition mixing technique has been used to investigate the effects of pH on the parameters of some of the more important models for the haemoglobin- oxygen equilibria and the results compared with those predicted from theoretical considerations.
None of the models considered emerged as a complete description of the data obtained and guidelines for the development of new models have been given.
Hypersonic boundary layers

The design, instrumentation, and calibration of the Oxford University Hypersonic Gun Tunnel is described. The calibration included the determination of the working section Mach Number, total temperature, total pressure, and unit Reynolds Number. The performance was compared with theoretical estimates.
Measurements of boundary layer transition on the outside surface of a hollow cylinder model using shadowgraph and surface pitot techniques are described. Transition experiments on the model in various European wind tunnels are compared and a correlation based on nozzle wall boundary layer aerodynamic noise radiation is discussed.
Heat transfer measurements on the surface of a 10° total angle sharp cone and a flat plate were made and compared with theoretical predictions. Transition location based on changes in the heat transfer rate was determined for the two models and compared with the hollow cylinder results. Effects of model wall curvature were shown to be present and were correlated by the ratio of boundary layer thickness to wall radius of curvature.
A fine hot wire constant temperature anemometer probe was developed and used to measure fluctuation levels through the transitional boundary layer of a flat plate. Strong fluctuation intensities were found within the boundary layer upstream of the region where transition begins based on mean surface heat transfer measurements. These fluctuations appeared to be due to large turbulent eddies generated near the model leading edge and were initially located in the boundary layer at a y/δ location consistent with compressible stability theory.
Studies in fretting fatigue with special reference to the effect of stress distributions on the fatigue strength of assembled components

When an assembly (such as a shrink-fitted shaft/hub configuration) is subjected to oscillating loads, two components of the assembly may experience oscillating slip relative to each other, giving rise to fretting on the interface between the two components. If, subsequently, a fatigue failure originates in that fretting region, the nominal failure stress is often considerably lower than the fatigue strength of the appropriate material.
The object of the research reported in this thesis was to investigate a hypothesis which explains the (relatively) low magnitude of fretting fatigue strengths as a consequence of macroscopic stress concentrations in the fretted region. Such stress concentrations are a function of the overall geometry of the assembly and it was suggested that, as a result, stress distributions in assemblies should be similar to stress distributions in geometrically similar one-piece (solid) components. In an assembly, high stress concentrations near an interface are partially relieved by slip (which gives rise to fretting) and it was thought that an assembly should be stronger, therefore, than the equivalent solid. Even so, it was expected that a detailed analysis of the stress distribution in an assembly would predict stress concentrations of sufficiently high magnitude to explain failure under the low nominal stresses found in practice, thus demonstrating that fretting, itself, does not greatly affect fatigue strengths.
Fatigue tests were carried out using solid and assembled specimens of various shapes and a method was developed, using finite element techniques, to analyse the stresses in the assemblies, taking full account of slipping. The theoretical stress analysis showed that, for certain geometries and systems of loading, the stress distributions in an assembly may differ considerably from those in a geometrically similar solid. Furthermore, when the fatigue results were examined in the light of the stress analysis, it was apparent that fretting can reduce the fatigue strength of a material by more than 60%.
To explain this result, a new hypothesis is proposed. It is suggested that under conditions of oscillating slip, the discontinuous contact between two surfaces of an assembly results in large stress concentrations in the regions of actual contact. It is shown that such stress concentrations can be of sufficient magnitude and affect a sufficiently large volume of material to cause failure at a nominal stress considerably lower than the fatigue strength of the material concerned. Such a hypothesis is supported by the results of this investigation and also by the results of several other workers.
Vortex formation in a two-dimensional periodic wake

Flow visualization techniques have been used for quantitative determination of the distribution of vorticity in a two-dimensional incompressible periodic wake formed behind a bluff body at a Reynolds number of 1.5 x 104.
Following the suggestion of Gerrard (1966) the vorticity distribution in the wake was considered as an ordered subdivision of the shed circulation into no more than three identifiable and measurable parts. This permitted a single algebraic summation of the circulation quantities involved.
To trace the history of the transport of circulation in the formation region of the wake, a technique was developed which used small countable particles ejected from the point of separation into one of the shear layers. The number rate of ejection of particles was known and controlled accurately so that the particle density could be related to the vorticity in the shear layer. Having established that the particles remain implicitly with the rotational fluid, it is shown that the quantity of circulation transferred to any location is pro- portional to the number of particles carried into the same region.
By application of flow visualization techniques developed for this specific purpose, the number of particles carried to any region of interest in the wake could be determined. By means of these measurements, all the terms in the proposed circulation distribution equation was evaluated independently and the equation shown to be satisfied.
Not only do these results verify the Gerrard flow model; but also they provide the first known quantitative information concerning the actual distribution and history of the circulation within the formation region. In the case of the final vortex strength comparison is possible with the work of other investigators and here good agreement was found.
As the particles are a vital tool in the investigation considerable efforts were devoted towards establishing the validity of their use as a flow marker in accelerating and shearing flows. This phase included also the solution of the mechanical problems of handling and measurement associated with the controlled ejection of particles into the shear layer. This work is described separately in Part II of the thesis.
The third part of the thesis is devoted to a general wake inquiry in which the particle technique is employed to explore certain subsidiary aspects of the wake flow not covered in Part I.. These topics included the determination of the size of the dead fluid region, measurements of the injection mode of circulation into the dead fluid region and also effects of the ambient turbulence upon the formation of region and residual vortex strength in the fully formed vortices.
Computational problems in linear algebra

In this thesis we consider the problems that arise in computational linear algebra when the matrix involved is vary large and sparse. This necessarily results in the emphasis throughout being mostly on iterative methods, but we begin with a chapter in which the usual direct methods for the solution of linear equations are summarized with the very large problem in mind. Methods for band-matrices and block tridiagonal matrices are considered and compared. Kron's method of tearing is described briefly.
The basic and well-established techniques of iterative solution of linear equations are described. Sufficient conditions for convergence are stated and the convergence is established under these conditions. A section is devoted to the problem of deciding when the iterations may be terminated. The method of Kaczmarz is given more emphasis than is usual in the literature, a symetric version is introduced and rigorous proofs of convergence are given.
Matrices with "property A" are defined and the usual associated results are given. The methods of Carré and Kularud for finding the optimum relaxation parameter in SOR are described and compared with a new technique. We also consider methods for finding the best relaxation parameter in symmetric SOR .
Block iterative methods are described briefly, including Varga'a result on the comparison of different splittings.
Gradient and semi-iterative methods are considered in detail, including the cases of non-symmetric and symmetric non-definite matrices, and are compared for numerical stability.
For the eigenvalue problem we again summarize some well-known methods with an emphasis on the very large matrix. We give an example of the accurate results that can be expected from Lanezos' method of minimised iterations without re-orthogonalisation and show how such results can be guaranteed. Inverse iteration, the Rayleigh quotient iteration and Rutishauser's L-R algorithm are considered. We also devote a chapter to iterative methods that yield continually improving approximations to an eigenvector and corresponding eigenvalue. These are very economical in storage but have received little attention in the literature.
We introduce the concept of "numerical rank", since rank really has no meaning for a matrix given by rounded numbers. We give means of finding bounds for this numerical rank.
The extension of the methods to complex matrices is considered briefly and we conclude with a description of some problems that may give rise to large sparse matrices. We consider in particular the so-called "L-membrane" problem and use a conformal transformation. In this way we also illustrate the problem of the solution of an elliptic equation over an area with a curved boundary. We consider the iteration of Federenko, which has its most obvious application in the field of elliptic equations. The thesis is concluded with two further examples, from linear analysis of variance and front surveying, each of which is likely to involve large sparse matrices.
Problems in functional analysis

This thesis is concerned with two, rather different, areas of analysis. A major part is devoted to problems in distributive lattice theory. Motivated by the Priestley representation theorem for a distributive lattice L we obtain information about the lattices of ideals, filters and congruence relations of L. Using purely lattice-theoretic means we give extension theorems for homomorphisms in the class of pseudocomplemented distributive lattices. These are analogous to the classical Hahn-Banach theorem. Finally, Lρ-spaces are constructed from matrix measures and their properties investigated.
Chapter 1 marshals material used in subsequent chapters. In §1.2 the Priestley representation theorem is stated which allows a distributive lattice with zero and identity to be identified with the clopen decreasing subsets of a certain ordered topological space; the relevant theory of ordered spaces is summarized. The class of distributive lattices with pseudocomplementation is defined in §1.3 together with the equational subclasses. The Priestley duality for a pseudocomplemented lattice L is given as well as for the centre and dense set of L.
The contribution of HLA class I-mediated CD8+ T cell responses to HIV-1 immune control and evolution

CD8+ T cells are a critical component of the adaptive immune response to HIV infection. The CD8+ response is orchestrated by presentation of HIV peptides in association with HLA Class I molecules on the surface of infected cells. Disease outcome varies according to HLA phenotype, with some alleles being characteristically associated with sustained viraemic control, and others with more rapid progression to AIDS. In order to evade the CD8+ T cell response, HIV selects escape mutations that reduce or abrogate HLA Class I presentation or disrupt recognition by T cell receptors. These mutations often occur in predictable combinations, termed HLA 'footprints', in response to selection pressure imposed by specific alleles.
In the setting of a recent failed T cell vaccine trial, these studies aim to improve characterisation of favourable CD8+ T cell responses and to investigate the impact of HLA footprints on future viral evolution.
The analyses highlight the potential benefit of selection of mutations that impose a viral fitness cost. By partially crippling the virus, these polymorphisms can contribute to viraemic control. The evolutionary effects of an HLA footprint are shown to be significant both in mediating convergent evolution, and in driving patterns of viral evolution across global populations. Studies of HLA-B*35 in HIV demonstrate that Class I alleles can have differential impacts according to the subtype of infecting virus. In this instance, there is evidence of disease control mediated by CD8+ T cell responses to HIV Gag. Finally, this work explores in vitro viral suppression assays as a tool for quantifying the CD8+ T cell response in individual subjects, presenting optimisation of techniques for assessing bulk and individual HLA-Class I restricted responses to HIV.
Overall, these data contribute to the development of an HIV vaccine by enhancing our understanding of a successful CD8+ T cell response, suggesting the need to consider immunogens that match the strain of infecting virus, and investigating in vitro methods for assessing vaccine outcomes.