The N/Z, or ratio of neutron to proton, degree of freedom may be used to study intermediate energy nuclear collisions to give information about the origin of emitted collision fragments. Establishing under what conditions the onset of N/Z equilibrium occurs will give a better understanding of the physics of the equation of state through the use of simulation codes. If the nuclear equation of state can be elucidated in terms of the N/Z dependent component and how the N/Z dependent component varies with density, then the equilibrium ratio of protons to neutrons inside high density neutron stars can be inferred, allowing for prediction of cooling rates and supernovae mechanisms. In the current study, isotopic and isobaric ratios at thetalab=40o with cuts of 10% and 20% most central events, respectively, are studied for their N/Z equilibration signals. Light charged particles, or LCPs, are found to be emitted from systems which have not yet fully N/Z combined; the fragments with A=3 are emitted from the least equilibrated systems. Intermediate mass fragments, or IMFs, are seen to be emitted by N/Z equilibrated sources, within statistical error bars. The N/Z tracer method is used with ratios of isotopes and isobars to see how the amount of nuclear stopping or N/Z mixing changes as a function of the centrality of the event. The N/Z observable is used to reinvestigate earlier findings of the isotope and isobar ratio observables and shows the progression (or lack of it, in some cases) of the N/Z equilibration. This observable has proven to be a clear and sensitive tool to use when considering the differences in N/Z mixing of the systems at two energies.

none

Inaug.-Diss.--Freie Universität, Berlin. / Vita. Bibliography: p. 5-25.

Thesis--Copenhagen. / Summary in German. Includes bibliographical references.

Thesis (M. Sc.)--University of Hong Kong, 1959. / Type-written copy. Includes bibliographical references (leaves 124-126).

Abstract The aim of this study was to evaluate plant growth, grain yield and symbiotic N contribution by 32 cowpea genotypes, at Taung in South Africa. The data from a 2-year field study conducted in 2005 and 2006 showed that genotypes Fahari, Pan 311 and Glenda exhibited the highest dry matter yield and N contribution as they produced 2.9-, 2.7- and 3.5-fold more dry matter than cv. ITH98-46 and yielded 2.7-, 2.2- and 3.2-fold more N than cultivar ITH98-46 from IITA. Except for Benpila, all the 32 cowpea genotypes derived between 52.0 and 80.9% of their N nutrition from symbiotic fixation in 2005, with IT82D-889, Botswana White, IT93K-2045-29 and Ngonji exhibiting the highest %Ndfa values. The genotype Fahari showed the highest amount N-fixed (182 kg N-fixed/ha), followed by Pan 311, Glenda, TVu11424 and Mamlaka which contributed 160, 146, 130 and 125 kg N/ha, respectively. Genotypes Pan 311, Fahari and Glenda were among those that produced highest grain yield in 2005 and except for CH14 and IT86S-2246 (which produced 131 kg N/ha each), Fahari, Glenda and Pan 311, were again the highest in symbiotic N contribution (112, 106 and 105 kg N/ha, respectively). Grain yield was similarly high in Glenda, Pan 311 and Fahari (3.3, 3.1 and 2.9 t/ha, respectively) in 2006. In general, these data show that genotypes that fixed more N also produced more biomass and grain yield and are therefore, the best candidates for inclusion in cropping systems as biofertilizers.

Abstract In this study, 30 cowpea genotypes were assessed for symbiotic N2 fixation in 2005, and 15 of them were reevaluated in 2006 using the 15N natural abundance technique. Shoot dry matter yield of cowpea genotypes increased significantly in cvs. Vuli-1, Glenda, IT93K-2045- 29, IT90K-59, Omondaw, Apagbaala, and IT84S-2246 in 2005 producing about 3.0 to 3.6-fold more biomass relative to cv. Vallenga. In 2006, seven out of the 15 cowpea genotypes tested (namely, IT97K-499-39, TVu11424, Botswana White, IT84S-2246, Sanzie, Brown Eye, and Glenda) also produced more dry matter than cv. CH14. Shoot δ15N values ranged from −0.58‰ to 1.49‰ in 2005, and −1.51‰ to 1.40‰ in 2006, and these resulted in %Ndfa values of 63.5–86.7% and 56.2–96.3%, respectively. The amount of N-fixed was 49–178 kg N ha−1 in 2005 and 62–198 kg N ha−1 in 2006. Furthermore, there was a direct relationship between the level of symbiotic N nutrition and plant growth, and between grain yield and amount of N-fixed in 2005 and 2006. As a result, genotypes that fixed the most N also produced the largest biomass and the greatest amount of grain yield. The observed relationship between N2 fixation and biomass confirmed our view that cowpea (and other grain legumes) can be concurrently selected for higher N2 fixation, superior plant growth, and greater grain yield. The high levels of N-fixed by many of the cowpea genotypes in this study suggest that they can contribute large amounts of N to cropping systems in African agriculture.

No description available.

N-Acetylneuraminic acid synthase (NANAS) is an enzyme responsible for the biosynthesis of N-acetylneuraminic acid (NANA). NANA is the most common form of a group of nine carbon sugar molecules called the sialic acids. NANA production is common in mammalian cells for vital physiological processes. A few species of microorganisms, including pathogenic bacteria such as Neisseria meningitidis and Campylobacter jejuni, are known to synthesise NANA by their bacterial NANAS. These pathogenic bacteria synthesise NANA for molecular mimicry, allowing them to evade the host immune system. This thesis examines the NANAS enzymes from N. meningitidis and C. jejuni. Inhibitory studies with these enzymes were explored by performing enzyme kinetics with substrate analogues and a product analogue which structurally mimic the natural substrates or product of NANAS. Inhibition constants were determined for a variety of analogues to give insight in to how the enzyme accommodates its substrates within the active site of NANAS. This study may be a useful step in the development of alternative antibiotics for bacterial meningitis and other diseases in the future. NANAS catalyses a condensation reaction between phosphoenolpyruvate (PEP) and N-acetyl mannosamine (ManNAc). Both PEP and ManNAc analogues were explored as inhibitors of the enzymes. Results from this study show that increasing steric bulk of the substituents at C3 of PEP unexpectedly delivers more potent inhibition of the enzyme. This finding suggests that a slightly modified binding position of the PEP analogue within the PEP binding site of the enzyme may be responsible for the inhibition. A reduced acyclic analogue of ManNAc was found to be an effective inhibitor of the enzymes. This finding indicates how important the acyclic form of ManNAc is in the reaction mechanism catalysed by this enzyme.

No description available.