The aims of the present study were to evaluate: i.) mixtures of spring barley (Hordeum vulgare L.) by combining cultivars differing in plant height or time of maturity, and ii) mixtures of cultivars of cocksfoot (Dactylis glomerata L.) and timothy (Phleum pratense L.) based on differences in maturity group. Experiments were conducted on mixtures of cultivars of spring barley and on mixtures of cocksfoot and timothy. The grain yields of all the mixtures tested in 1985 were similar. Of 4 mixtures tested, Midas/Triumph and Kym/Klaxon outyielded (though not significantly) their respective highest yielding pure stand component. Within mixtures, the taller or the earlier maturing component was more aggressive than the other component. All four mixtures produced relative yield totals (RYT) greater than 1.0. The highest RYT's came from mixing cultivars of different maturities. In the second experiment, in 1986, Triumph outproduced both Doublet and Klaxon, having more ears and grains per M2. The mixtures did not vary in grain yield from the mean of their pure stand components. In mixtures, the taller component was generally more dominant. In contrast to the previous year, all three mixtures tested in 1986 had yields approximately double those of the previous year, and RYT's less than 1.00. In the third experiment, application of fertiliser had a significant effect on the grain yield of pure stands and mixtures. At low fertilty, Triumph outproduced Doublet in both number of grains per area and grain yield, though at moderate fertility the opposite was true. In mixture, Triumph outcompeted Doublet at both low and moderate fertility levels. It produced more ears and grains per m2 and thus higher grain yields. The relative yields of Triumph were higher than those of Doublet. Similar results were found in glasshouse experiments. An experiment was set up in 1985, and ran over for 3 years, to investigate the performance of mixtures of early and late cultivars of cocksfoot and timothy. In the establishment year, there was no difference between total dry matter yield of full density pure stands of cocksfoot and timothy, though cocksfoot produced more tillers but less total harvestable leaf area than timothy. In the second year, full density pure stands of timothy produced higher total dry matter, mean number of tillers and total harvestable leaf area than full density pure stands of cocksfoot. In the third year (the only year when fertiliser was applied), full density pure stands of cocksfoot produced higher total dry matter, mean number of tillers and total harvestable leaf area than full density pure stands of timothy. Arguably, the best overall yield came from early cocksfoot/late timothy because it had one very high yielding year and in no year was RYT less than 1.0. The results from all the experiments suggest that mixtures can in some circumstances outyield the midmonoculture yields of their components. This occurs when (i) the components are of contrasting types ( e.g. in morphology and growth pattern) and (ii) when pure stand yields are inherently low. This reinforces the opinion that mixtures may be of greatest benefit in low input agricultural systems.

Fatigue cracking is one of the primary modes of distress in asphalt pavements that has an important economic impact. Fatigue resistance characterization of an asphalt mixture is a complex issue due to: (i) composite nature of the material, (ii) gradation of aggregate particles, (iii) variation of asphalt film thickness, (iv) air voids distributions, (v) asphalt binder nonlinear viscoelastic behavior, (vi) effects of binder oxidative aging as a function of time, and (vii) micro crack healing during rest periods. Different methods to assess fatigue cracking in asphalt materials are available in the literature. However, there is no methodology to characterize fatigue cracking behavior of asphalt materials that is independent of the mode of loading (controlled-strain or controlled-stress). The objective of this research is to develop a new methodology to characterize fatigue cracking of the fine aggregate matrix (FAM) portion of asphalt mixtures using dynamic mechanical analyses (DMA). This is accomplished through different, but related, approaches. The first approach relies on identifying the various mechanisms of energy dissipation during fatigue cracking that are manifested in: (i) nonlinear viscoelastic deformation, (ii) fracture, and (iii) permanent deformation. Energy indices were derived to quantify each of these energy dissipation mechanisms and to quantify fatigue cracking irrespective of the mode of loading. The first outcome of the approach is a fatigue damage parameter (crack growth index) that provides comparable results for a given material even when tested under different modes of loading and different load (strain or stress) amplitudes. The developed fatigue characterization method has a lower coefficient of variation when compared to conventional parameters (number of load cycles to failure or cumulative dissipated energy). The crack growth index parameter was also qualitatively and quantitatively compared to three dissipated energy methods available in the literature. The second outcome of this research is a constitutive model that can describe both asphalt mixtures’ nonlinear viscoelastic response and fatigue damage in one formulation. Nonlinear viscoelastic as well as damage parameters were obtained for both modes of loading. This second approach has the advantage that the constitutive model can be implemented in a numerical framework to describe the response of asphalt mixtures under various boundary conditions.

Flammability is an important factor of safe practices for handling and storage of liquid mixtures and for the evaluation of the precise level of risk. Flash point is a major property used to determine the fire and explosion hazards of a liquid, and it is defined as the minimum temperature at which the vapor present over the liquid at equilibrium forms a flammable mixture when mixed with air. Experimental tests for the complete composition range of a mixture are time consuming, whereas a mixture flash point can be estimated using a computational method and available information. The information needed for mixture flash point predictions are flashpoints, vapor pressures, and activity coefficients as functions of temperature for each mixture component. Generally, sufficient experimental data are unavailable and other ways of determining the basic information are needed. A procedure to evaluate the flash point of binary mixtures is proposed, which provides techniques that can be used to estimate a parameter that is needed for binary mixture flash point evaluations. Minimum flash point behavior (MFPB) is exhibited when the flash point of the mixture is below the flash points of the individual components of the mixture. The identification of this behavior is critical, because a hazardous situation results from taking the lowest component flash point value as the mixture flash point. Flash point predictions were performed for 14 binary mixtures using various Gex models for the activity coefficients. Quantum chemical calculations and UNIFAC, a theoretical model that does not require experimental binary interaction parameters, are employed in the mixture flash point predictions, which are validated with experimental data. MFPB is successfully predicted using the UNIFAC model when there are insufficient vapor liquid data. The identification of inherent safety principles that can be applied to the flammability of binary liquid mixtures is also studied. The effect on the flash point values of three binary mixtures in which octane is the solute is investigated to apply the inherent safety concept.

Polycyclic aromatic hydrocarbons (PAHs) are environmentally significant because of their ubiquity and the toxicity of some. Their recalcitrance and persistence makes them problematic environmental contaminants. Microbial degradation is considered to be the primary mechanism of PAH removal from the environment. Biodegradation kinetics of individual PAHs by pure and mixed cultures have been reported by several researchers. However, contaminated sites commonly have complex mixtures of PAHs whose individual biodegradability may be altered in mixtures. Biodegradation kinetics for fluorene, naphthalene, 1,5-dimethylnaphthalene and 1- methylfluorene were evaluated in sole substrate systems, binary and ternary systems using Sphingomonas paucimobilis EPA505. The Monod model was fitted to the data from the sole substrate experiments to yield biokinetic parameters, (qmax and Ks). The first order rate constants (qmax/Ks) for fluorene, naphthalene and 1,5- dimethylnaphthalene were comparable, although statistically different. However, affinity constants for the three compounds were not comparable. Binary and ternary experiments indicated that the presence of another PAH retards the biodegradation of the co-occurring PAH. Antagonistic interactions between substrates were evident in the form of competitive inhibition, demonstrated mathematically by the Monod multisubstrate model. This model appropriately predicted the biodegradation kinetics in mixtures using the sole substrate parameters, validating the hypothesis of common enzyme systems. Competitive inhibition became pronounced under conditions of: Ks1 << Ks, S1 >> Ks1 and S1 >> S. Experiments with equitable concentrations of substrates demonstrated the effect of concentration on competitive inhibition. Ternary experiments with naphthalene, 1,5-dimethylnapthalene and 1-methylfluorene revealed preferential degradation, where depletion of naphthalene and 1,5-dimethylnapthalene proceeded only after the complete removal of 1-methylfluorene. The substrate interactions observed in binary and ternary mixtures require a multisubstrate model to account for simultaneous degradation of substrates. However, developing models that account for sequential degradation may be useful in scenarios where PAHs may not be competitive substrates. These mixture results prove that substrate interactions must be considered in designing effective bioremediation strategies and that sole substrate performance is limited in predicting biodegradation kinetics of complex mixtures.

Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xiv, 119 p.: ill. (some col.). Includes abstract and vita. Advisor: Theodore T. Allen, Dept. of Industrial and Systems Engineering. Includes bibliographical references (p. 111-119).

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Cardiovascular diseases are the major cause of death worldwide. It is a group of diseases, which affect the heart, the vasculature and the brain. Lifestyle and metabolic risk factors are major contributors to cardiovascular ill-health. In addition to these risk factors, a growing number of scientific studies show that some environmental pollutants, e.g. lead and mercury, can adversely affect cardiovascular health. Despite the increasing amount of knowledge from human and animal studies, cardiovascular effects of lead, mercury species or their mixtures are not well understood. It is also unknown if safe exposure thresholds for these metals exist or the underlying mechanisms of action for the elicitation of cardiovascular toxicity. The first set of studies had the objectives to elucidate the range of effects of single exposure to lead, inorganic mercury or methylmercury on the cardiovascular system. Therefore, male Wistar rats were exposed to a broad range of doses of lead, inorganic mercury or methylmercury for four weeks through the drinking water. Cardiovascular health of the rats was assessed by measuring the blood pressure and the cardiac electrical activity after four weeks of exposure, while the heart function and blood flow in the carotid artery was measured at baseline and at the end of the exposure duration. The study showed that all three metals differ in their effects on the cardiovascular system. Lead showed bi-phasic dose-response curves for several cardiovascular end-points. No cardiovascular effects were observed for inorganic mercury, while methylmercury showed linear dose-response curves. Based on these results, safe levels of exposure for lead and methylmercury were derived. The second study applied the same experimental design as the previous study in order to investigate the cardiovascular effects of combined exposures to lead, inorganic mercury and methylmercury. The mixture ratios were based on reference and exposure values published in the scientific literature. The adverse cardiovascular effects, which were observed for single exposures were reversed for the mixtures indicating antagonism. In contrast to single exposures, mixtures negatively affected the electrical activity of the heart (synergism), which could lead to arrhythmias and heart failure. The third set of studies focused on the exploration of oxidative stress, kidney function and damage, and global DNA methylation as potential mechanisms of action for the development of elevated blood pressure. Results for lead showed an increase in oxidative stress but not mercury. While only lead was associated with kidney damage, only inorganic mercury was related to altered global DNA methylation. Methylmercury appears to elevate blood pressure through a not investigated mechanism. Therefore, oxidative stress and kidney damage seem to be associated with elevated blood pressure but not global DNA methylation. Overall, the research presented in this thesis shows that lead, inorganic mercury and methylmercury and their mixtures have the ability to adversely affect the cardiovascular system. However, each metal affected the cardiovascular system differently and surprisingly, mixtures showed antagonism or synergism depending on the examined end-point, which was reflected in the results of the mechanistic study. As health problems of the cardiovascular system, e.g. hypertension, occur mainly in the adult population and in particular the elderly, cardiovascular effects should be considered as an important end-point for this age group in addition to neurodevelopmental effects in children.

Thesis (M.Sc.) -- University of Adelaide, Department of Physical and Inorganic Chemistry, 1977.