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This thesis is concerned with the development of a new ab initio Monte Carlo method for the evaluation of exact, basis set correlation energies. A simple set of rules acting on signed walkers allow for the simulation of the underlying imaginary-time Schrödinger equation in a finite space of Slater determinants. These rules return probabilistic events which are stochastically realised in each step of the algorithm. The antisymmetric space in which the dynamic operates precludes the emergence of Bosonic solutions, and the Fermion sign problem is countered without approximation by inclusion of annihilation events between walkers of different sign. The method is applied to many molecular systems described by common Gaussian basis sets. Single point calculations, binding curves, basis set expansions and detailed studies of ionisation potentials are included. In these investigations, the method is compared to several alternative quantum chemical methods as well as exact full configuration interaction results to asses its qualities. The method is found to significantly reduce the memory and CPU requirements compared to exact diagonalisation methods, and includes an effective parallelisation scheme which scales almost linearly up to thousands of processors. This extends the scope of exact multireference calculations and allows for larger systems than previously possible to be treated.

This work concerns the roles of neuron glia interactions in the control of neuronal survival during Central Nervous System (CNS) development in Drosophila. The question of whether glia are required to maintain neuronal survival in insects was addressed. Firstly, the GAL4 system was used to achieve in vivo targeted genetic ablation of glia. Secondly, plasmid rescue and P-element excision were exploited to locate and mutate genes which might participate in neuron glia interactions. Targeted glial ablation did not affect pioneer neuron survival. However, increased apoptosis was observed among the FasII and 22C10 expressing subsets of the follower neurons. Targeted ablation only of the interface glia was sufficient to induce follower neuron apoptosis. This difference in the survival requirements of pioneer and follower neurons may be instructive in patterning of the CNS. Neuronal apoptosis was rescued by ablating glia in an apoptosis deficient genetic background, and by expressing the p35 apoptosis inhibitor under the neural elav promoter. Hence the loss of neighbouring glia induces nonautonomous neuronal apoptosis. The Mz1131 enhancer-trap line, expressed in the interface glia, was used to examine the effects of mutating a putative glial gene upon CNS development. Lethal Mz1131 mutants displayed increased apoptosis of lateral glia and FasII expressing neurons, but not of 22C10 expressing neurons. The fasciculation and defasciculation of the longitudinal axon tracts as also affected. Both lethality and the characteristic GAL4 expression pattern of Mz1131 were lost upon P-element excision. Nonradioactive southern blotting revealed that line Mz1131 contains multiple P-insertions. Identification of sequences neighbouring P-insertions, and complementation tests revealed a mutation at the sin3A locus.

The high temperature pyrolysis of butane, in the region 545°C -600°C, has been studied with special emphasis on the effect of reactor wall conditions. The use of a steel reaction vessel, both unpacked, and packed with steel balls, has added the hydrogen atom recombination reaction to the widely accepted, totally homogeneous reaction mechanism. Using this well substantiated, purely homogeneous system as our base the induced heterogeneous component has been, to a great degree, clearly defined. The effects on reaction rate, reaction orders, and Arrhenius parameters have been quantified. Throughout the study the variability of the ratio f C / (C +C )was strongly in evidence; moreover, the Arrhenius equations ~e uc;d 3 from this ratio show remarkable agreement with those derived from homogeneous data, implying that the fundamental chain propagation steps are the same in the homogeneous and heterogeneous environments. Chain lengths under the condition of this work were calculated to be vastly reduced, from those in the purely homogeneous system but not substantially so to totally suppress the homogeneous reaction. A much higher surface to volume ratio than was achieved in this work would seemingly be required to significantly reduce reaction rate further. A computed description of the system has been attempted with encouraging, if not total, success. If we are prepared to accept something approaching unit wall efficiency for the recombination of hydrogen atoms at the reactor surface then the observed reduction in reaction rate can be totally accounted for by the inclusion of this reaction in the homogeneous mechanism. It was noted, however, that under certain conditions of the study the decrease in reaction rate could not be fully explained in this way even if the wall efficiency was assumed to be unity. These results, obtained in the packed vessel at 833 K and at various pressures, have led to the postulation of an additional wall reaction. The observed variability of the ratio fC2/i(C1+C3) points to this reaction being a preferential, possibly selective, reaction of 2-Butyl on the vessel wall.