http://hdl.handle.net/2374.OX/4070 2013-05-24T05:36:45Z http://hdl.handle.net/2374.OX/104381 Baculovirus Expression and Purification of Wild Type and Mutant Full-Length Human LRRK2 Wang, Wen LRRK2 is a complex 285 kD protein in which the most prevailing mutations G2019S and R1441C are linked to autosomal dominant Parkinson disease (PD). This study has established an expression and purification system to produce active recombinant proteins of the LRRK2, to examine whether the mutations alter the LRRK2 activity and what mechanism underlies the alteration. Both bacterial and baculovirus expression systems were attempted to express and purify the proteins. The active full-length LRRK2 proteins (wild type, G2019S and R1441C) were obtained via the baculovirus system. The bacterial expression system was used for expression and purification of the LRRK2 kinase domain (LRRK2-KD) (wild type and G2019S) but it displayed no activity. The purified recombinant proteins obtained via the baculovirus expression system were analyzed in kinase assays. Our preliminary estimates of Km and Vmax may provide insight regarding the mechanism of LRRK2 activation by PD-linked mutations. 2009-04-09T22:40:40Z http://hdl.handle.net/2374.OX/104379 A Computational Study of the Ignition of Premixed Methane and Oxygen via a Hot Stream Deans, Matthew Charles With methane being a fuel to be utilized in the future of space exploration, alternative ignition systems need to be developed. This study computationally focuses on the ignition of methane and oxygen mixtures in a counterflow configuration by a heated stream. Most combustion systems have non-uniform and/or non-homogenous flow, species, and temperature fields. This configuration allows for the study of both chemical kinetics as well as convective-diffusive transport effects. The effects of strain rate, pressure, and equivalence ratio on ignition are examined. A catalytic simulation code is used to generate ranges of combustion product composition and temperature when using a catalytic reactor for the hot stream. The vitiation of these into the hot stream is conducted to determine their influence on ignition. Tests with the individual components in a range up to the maximum possible achievable level will be carried out to determine the separate effects. A combined case simulating the potential of an actual catalytic igniter is also run to confirm the feasibility of such a technology and the combined effects of the different species. 2009-04-09T22:40:28Z http://hdl.handle.net/2374.OX/104377 The Role of Developmental Bias in a Simulated Evo-devo System Psujek, Sean Thomas The success of the Modern Synthesis has resulted in forces of evolutionary change other than natural selection being marginalized. However, recent work has attempted to show the importance of non-selective influences in shaping organic form. One such force is developmental bias, the differential produced of phenotypes. I use a simulation model of neural development to explore questions of general interest about developmental systems. From an analysis of the bias in the production of phenotypic variants in the developmental model, I find the pattern of developmental bias varies strongly with the genotype even among phenotypically-neutral genotypes. In addition to this genotype-dependent developmental bias (local bias), an intrinsic bias exists in the developmental system (global bias). I also show that developmental bias varies among related genotypes that produce the same phenotype. Finally, I illustrate how a pattern of bias emerges from the manner in which mutations affect the regulatory structure of the wild-type genotype. These results suggest that developmental bias could have a strong influence on the direction of evolutionary modification. In subsequent analyses exploring the interaction of developmental bias and selection during adaptive evolution, I find developmental bias guides phenotypic transitions with the result that multiple phenotypic pathways are taken towards the target phenotype across simulations. I also find higher-fitness phenotypes often become accessible with the accumulation of selectively-neutral mutations. The change in accessibility is due to alterations of the regulatory structure of the genotypes through the neutral mutations. This lability of developmental bias recommends a comparative approach to the experimental investigation of bias in natural systems. The alteration of phenotypic accessibility following the accumulation of neutral mutations can be conceptualized as a population moving along a network of isofitness genotypes linked by mutations (neutral networks). The phenotypes produced by non-fitness-neutral neighbors of the neutral genotypes are likely to vary as the population moves to different regions of the network. These networks are created by the mutational operator and the degeneracies of the dual mappings of genotype to phenotype and phenotype to fitness. Topological properties of the neutral networks could lead to insights into the impact on evolvability of developmental systems. 2009-04-09T22:40:15Z http://hdl.handle.net/2374.OX/104375 The low cycle fatigue behavior of aluminum alloy based particulate composites Liu, Changqi MB85 (Al-3.5%Cu-2.4%Mg Alloy reinforced with SiC particulates) and 2014 (Al-4.2%Cu-1.5%Mg alloy reinforced with Al2O3 particulate) composites were heat-teated to underaged and overaged conditions followed by low cycle fatigue testing with total strain control. The results include three aspects: (i) Bauschinger effect and internal residual stress, (ii) Cyclic work hardening behavior, and (iii) Fatigue life and low cycle fatigue damage processes. X-ray diffraction techniques were used to measure the residual internal stress to compare with the Bauschinger measurements. SEM and TEM were used to characterize the microstructures before, during, and after the test. In light of a literature review on the above aspects, the possible mechanisms occuring during cyclic deformation and fatigue are discussed. The main results are as follows: (1) Bauschinger parameters (σb and β^1) increase with increasing plastic prestrain (εp). (2) Reinforcements and heat treatment conditions have strong effects on the BEPs: BEPOA > BEPUA in the same material; BEPCP > BEPCT in the same heat treatment; BEP20%SiC > BEP15%SiC in the same heat treatment. (3) Internal stress may be measured both by Bauschinger Effect and by x-ray diffraction. Both results are comparable. (4) Cyclic deformation behavior is strongly affected by the reinforcements and heat treatment conditions. For a given composite material and a fixed heat treatment condition, the cyclic deformation behaviors is determined by the initial plastic strain. (5) The Manson-Coffin expression can be used to predict the fatigue life of the composites. 2009-04-09T22:39:59Z