These studies were conducted to determine the response of cowpea cultivars differing in seed coat colour to storage and reduced water availability during germination, and to relate these to the chemical composition of their seed coats. Seeds of five cowpea cultivars were stored under simulated tropical conditions (30°C/75.5% r.h.) for 6 months, subjected to accelerated ageing (40°C/100% r.h.) for 6 days or controlled deterioration (40°C/20% m.c.) for 4 days. Unpigmented seeds showed more rapid deterioration which was revealed by low germinations, high leachate conductivity and poor vital staining with 2, 3, 5 Triphenyl Tetrazolium Chloride (TTC). These differences were attributed to differences in moisture contents that occurred in storage as well as genotypic differences. Increased susceptibility to imbibition damage occurred during storage particularly in unpigmented seeds. The seed vigour parameters at the end of the stimulated tropical storage correlated well with accelerated ageing, suggesting the possible use of rapid ageing to predict the storage potential of cowpea seeds. Percentage radicle emergence was high in the pigmented cultivars germinated at -0.0015, -0.1 and -0.15 MPa and lower in unpigmented cultivars as matric potential was reduced. Imposition of reduced water availability (-0.15 Mpa) after 12, 24 and 48 hours germination at -0.0015 MPa led to slower rates of radicle emergence in all seeds transferred at 12 and 24 hours. In the unpigmented cultivars, these early transfers led to reduced radicle emergence after 7 days and low final normal germination after transfer to -0.0015 MPa for a further 7 days. This deleterious effect was revealed by poor vital staining of the embryonic axes. Protein synthesis of root tips after 24 hours -0.0015 MPa, 96 hours -0.15 MPa followed by a recovery period of 48 hours -0.0015 MPa was twice as much in the pigmented cultivar which explained its greater ability to recover from stress. Screening of a further ten cultivars for tolerance of reduced water availability revealed three groupings, (1) unpigmented cultivars that showed low final normal germination and rapid rates of water uptake in water, (2) smooth-coated pigmented cultivars that showed high final germination and slow rates of water uptake and (3) wrinkled -coated pigmented cultivars which showed intermediate germination and high rates of water uptake.

Theoretical expressions essentially based on the Flory-Stockmayer statistics of gelation were experimentally examined for their applicability beyond the gel point. By studying the crosslinking process of a polyester network formed from 1,3,5-benzenetriacetic acid and 1,10-decamethylene glycol beyond the gel point, the validity of the expressions was quantitatively confirmed, and their limitations were delineated. / On stepwise degradation of a similar network, increasingly large soluble fractions were obtained at each step, and their weight-average molecular weights increased as the degelation point was approached. The molecular weights and distributions of these fractions were in close quantitative agreement with theory, i.e., they represented a near-mirror image of the molecular weights of sol fractions obtained on crosslinking beyond the gel point. Similar results were obtained by degrading a network prepared by the random crosslinking of monodisperse primary chains of polystyrene. / Experimental support was thus obtained for treating random network degradation by reversing the statistics of the Flory-Stockmayer theory of gelation.

No description available.

No description available.

Concrete is probably the most widely used construction material in the world. In the Arabian Gulf region, deterioration of concrete due to the aggressive environment is recognized to be the main factor affecting their structural integrity. The durability of concrete structures can be preserved by various protection methods; however, using cement replacement materials is one of the most effective and economic methods of maintaining their stability as well as extending their service life. The aim of this project is to study four interrelated aspects, namely, (1) the effect of hot environment on the properties of fresh concrete incorporating mineral admixtures, (2), the influence of exposure environment on the engineering properties of hardened concrete, under various curing conditions, without and with mineral admixture, (3), the differences in porosity and pore structure of the same set of mixes, and, (4) the effect of outdoor exposure on the durability-related properties of concrete. To achieve the above aims, the experimental programme involved the study of five different mixes of combinations of silica fume/slag and silica fume. The effects of real exposure to the Arabian Gulf environment of these mixes subjected to four curing regimes, namely, continuous water curing, no water curing after demolding, and air drying after 3 and 7 days of initial water curing were investigated. The properties investigated include (1) consistency and setting times of cement pastes, workability and workability loss with time, (2) engineering properties such as compressive strength, dynamic modulus of elasticity, pulse velocity, shrinkage, expansion and thermal expansion, (3) microstructural properties such as porosity and pore size distribution, (4) durability-related properties such as permeability, water absorption and carbonation depth. The results show that exposure to hot environment results in rapid setting times, faster loss of slump, higher porosity, coarser pore structure and more permeable concretes. It was found that part cement replacement by silica fume and slag improves the quality of concrete mixtures, refined the pore structure and produced concretes with very low porosity and continuous pore diameter in both indoor and outdoor environment. The properties of concrete containing mineral admixture appear to be more sensitive to poor curing than the plain concrete, with the sensitivity increasing with increasing amount of slag in the mixture.

No description available.

No description available.

The demands placed on back-up rolls in hot strip mills have been investigated by a combination of literature and industrial studies. The tribological operating conditions have been established and the maximum local loads and pressure distributions at the work roll/back-up roll interface have been obtained by processing mill and roll schedule data using a computer program (commercial software developed by V AI Industries (UK) Ltd) and applying the theories of contact mechanics. After a study of the responses of the rolls to these demands and possible failure mechanisms, research has centred on surface initiated damage whereby cracks can propagate into the roll substrate potentially reaching the internal residual stress fields and leading to catastrophic failure. A proposed qualitative contact and fracture mechanics model, for the rolling contact fatigue and spalling failure, has been quantified theoretically using published methods for determining the stress intensity factors at the tips of pressurised and water lubricated, inclined rolling contact fatigue cracks. The predictions of the quantitative model in terms of crack directions and lengths have been validated by microscopic observation of the morphologies cracks produced in test discs used in the "SUROS" Rolling-Sliding Testing Machine and also in a sample of material spalled from a back-up roll. The quantitative failure model includes criteria for crack branching either upwards leading to micro spalling or downwards (potentially catastrophic) and the link between these two cases has been related quantitatively to the value of the mode I threshold for the roll material. After linking mechanics to microstructure and quantifying the interactions between wear and rolling contact fatigue in this case, practical quantitative recommendations have been made for the design of bainitic back-up roll materials, back-up roll redressing procedures and the surface roughness of both the work rolls and back-up rolls presented to the mill.

This is the first study to explore the ability of an enzyme to recognize and repair spontaneous age-dependent damage to its own sequence. Protein (D-aspartyl/L-isoaspartyl) carboxyl methyltransferase (PCM) is known to repair damage that arises from a spontaneous isomerization of aspartyl and asparaginyl residues in other proteins during aging. As PCM contains several conserved aspartyl and asparaginyl residues, this dissertation tested whether PCM can serve as a methyl acceptor in its own methylation reaction. In investigating the ability of PCM to automethylate, it was discovered that PCM is damaged. The mechanism of this automethylation reaction was determined to be an intermolecular, high affinity, slow turnover reaction and was limited to a subpopulation of damaged PCM molecules, termed ��PCM. / Graduation date: 1996

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