ii ABSTRACT Percolation phenomena involving the electrical conductivity, dielectric constant, Hall coefficient, magnetoconductivity, relative magnetoresistivity, 1/ f noise and thermoelectric power are investigated in graphite (G) and hexagonal boron-nitride (BN) powder mixtures. Two kinds of systems are used in the experiments: highly compressed discs and parallelepipeds, cut from these discs, as well as 50%G-50%BN and 55%G-45%BN powder mixtures undergoing compression. The measured DC conductivities follow the power-laws 0"( <p, 0) ex: (<p-<Pc)t (<p > <Pc) and O"(<p, 0) ex: (<Pc-<Pti (<p < <Pc), and the low frequency (lOOHz & 1000Hz) dielectric constant varies as c( <p, W ~ 0) ex: (<Pc - <P )-S( <P < <Pc), where <Pc is the percolation threshold, t and s are the conductivity exponents, and s is the dielectric exponent. Near the percolation threshold and at high frequencies, the AC conductivity varies with frequency as 0"( <p, w) ex: WX and the AC dielectric constant varies as c( <p, w) ex: w-Y, where the exponents x and y satisfy the scaling relation x + y = 1. The crossover frequency We scales with DC conductivity as Wc ex: O"q( <p, 0) (<p > <Pc), while on the insulating side, Wc ~ 1, resulting in q ~O for the three G-BN systems. The loss tangent tan t5( <p, w) (<p < <Pc) is found to have a global minimum, in contrary to the results of computer simulations. The Hall constant could not be measured using existing instrumentation. The measured magnetoconductivity and relative magnetoresistivity follow the power-laws - 6. 0" ex: (<p - <Pc)3.08 and 6.R/ R ex: (<p - <Pc)O.28 respectively. These two exponents, iii 3.08 and 0.28, are not in agreement with theory. The 1/ f noise was measured for the conducting discs and parallelepipeds. The normalized 1/ f noise power varies as Sv I V2 ex RW with the exponents w = 1.47 and 1.72 for the disc and parallelepiped samples respectively. Furthermore, the normalized noise power near the percolation threshold is, for the first time, observed to vary inversely with the square-root of sample volume. Based on the Milgrom-Shtrikman-Bergman-Levy (MSBL) formula, thermoelectric power of a binary composite is shown to be a linear function of the WiedemanFranz ratio. A scaling scheme for the Wiedeman-Franz ratio for percolation systems is proposed, which yields power-law behavior for the thermoelectric power. The proposed power-laws for the thermoelectric power can be written as (Sm - Md ex (<p - <Pc)h 1 for <P > <Pc and as (Sm - /~1d ex (<Pc - <p)-h2 for <p < <Pc, where Sm is the thermoelectric power for the composites, Afl is a constant for a given percolation system, and hI and h2 are the two critical exponents. The experimental thermoelectric power data for the G-BN conducting parallelepipeds was fitted to the above powerlaw for <p > <Pc. A least squares fit yielded the exponent hI = -1.13 and parameter MI =9.511l V I I< respectively.

Three adsorption theories--Langmuir, B.E.T., and Freundlich--were applied to boron interaction with Aiken clay loam and Vernal sandy loam soils to determine which bests describes the system. Column studies were conducted to obtain constants related to mass fluid flow and fluid dispersion within the column. An inert ion was used to obtain the pore volume and to calculate the fluid dispersion coefficient. These data were used to solve the material balance equation by the explicit numerical method developed by Lai for a digital computer. The output from the computer was a predicted profile boron distribution within the soil column. The soil columns were undergoing saturated flow and 10 ppm boron solution was introduced at the top and allowed to flow for a specified period of time, at which time the column was segmented and analyzed for boron to obtain the experimental profile boron distribution within the soil column. The experimental and predicted profiles were compared.

Os aços com adição de boro temperados e revenidos têm sido utilizados em diversas aplicações que exigem um compromisso entre boas propriedades mecânicas e baixo custo, como por exemplo, indústria automotiva, de petróleo e na fabricação de plataformas marítimas e tubulações. Estudos termodinâmicos indicam que uma pequena adição de boro altera significativamente o diagrama de fases, aumentando a estabilidade dos carbonetos pela substituição de C por B na estrutura cristalina. A avaliação da cinética de precipitação foi realizada indiretamente pela medição da variação de resistividade elétrica de amostras tratadas em temperaturas de 790, 810 e 830°C. Foi possível traçar a curva de precipitação (JMAK) para cada temperatura e propor um diagrama TTP que indicou que as temperaturas testadas estão situadas na parte superior da curva \"C\". A confirmação do fenômeno de precipitação foi obtida por microscopia eletrônica de varredura (MEV-FEG), indicando que a técnica indireta foi eficaz para predição do fenômeno. A cinética de coalescimento foi avaliada em amostras tratadas em 880°C de forma direta, por microscopia óptica e microscopia eletrônica de varredura, e de forma indireta, por avaliação da energia absorvida em ensaio de impacto Charpy. A determinação da distribuição de tamanho de borocarbonetos em cada condição testada forneceu indícios de que o mecanismo de controle do crescimento é reação na interface. Foi possível, satisfatoriamente, correlacionar o tamanho médio de borocarboneto com a resistência ao impacto Charpy, indicando que a susceptibilidade à fragilização pelo coalescimento de borocarbonetos independe da região da barra laminada. / Boron added steels in quenched and tempered condition have been used in many applications with mechanical properties and low-cost requirements, i.e., automotive, petrochemical and O&G industries. Thermodynamic simulations have shown that boron addition promotes significant change in phase diagram due to carbide stability increase by replacement of carbon by boron. Precipitation kinetic was evaluated by electrical resistivity in samples heat-treated at 790°C, 810°C, and 830°C. It was possible to estimate the precipitation curve (JMAK) for each temperature and to propose a TTP diagram which indicates that tested temperatures were in the upper region of the C-shape curve. Precipitation phenomenon was confirmed by FEG-SEM analysis, indicating that electrical resistivity measurement was effective to evaluate precipitation at these conditions. Coarsening kinetic was evaluated in samples heat-treated at 880°C by Microscopy and by absorbed energy in Charpy impact test. The borocarbide size and distribution determination provided evidence of interface reaction-controlled mechanism. A correlation between absorbed energy in impact test and average borocarbide size was proposed, indicating that embrittlement susceptibility by borocarbide coarsening has no dependence of rolled bar region.

No description available.

Bibliography: leaves 178-195.

Strawberries are an extremely perishable fruit mainly due to their soft texture and sensitivity to fungal infection. The fungal pathogen Botrytis cinerea is responsible for grey mould on strawberries and is the main causal agent of postharvest decay and subsequent economic loss. As an alternative to fungicides, manipulation of plant nutrition, such as calcium and boron, has been suggested as a means of disease management. This project investigated the effects of calcium and boron application on fruit quality and grey mould development in strawberry. The effect of calcium on fruit quality, grey mould development and leaf blight in strawberry cultivars ‘Aromas’ and ‘Selva’ was investigated through preharvest and postharvest applications. To determine the effect of preharvest application, calcium sulphate in 0.25X strength Hoagland’s solution was applied at 0, 100, 300 and 500 ppm Ca through fertigation. Fully-ripened fruit were harvested and evaluated for postharvest quality at harvest and then after storage at 10⁰C, 90±5% RH for 2 to 10 days. Although fruit firmness of both cultivars declined slightly during storage, this was not affected by preharvest calcium application. Similarly, preharvest calcium treatment had no effect on the external appearance, pH, soluble solids content (SSC) or titratable acidity (TA). No grey mould development was observed on fruit at harvest when flowers were inoculated with a conidia suspension of B. cinerea (10⁴ conidia per mL). However, fruit harvested from plants that received calcium at any concentration had less incidence of grey mould during storage at 10⁰C, 90±5% RH for 14 days than fruit harvested from plants that received no calcium for both cultivars. For ‘Aromas’, 79% and 51% of fruit, and for ‘Selva’, 69% and 43% of fruit, showed rot when treated with 0 and 500 ppm Ca, respectively. The shelf life of ‘Aromas’ and ‘Selva’ increased by about 8% when plants received 500 ppm Ca in comparison with plants that received 0 ppm Ca. After 7 days of incubation at 22 to 24⁰C, there was no difference between blight lesions on wound-inoculated detached leaves from different calcium treatments for either cultivar. However, the lesions on ‘Selva’ were smaller than on ‘Aromas’. The calcium levels in leaves from plants that received calcium at any concentration were adequate for strawberry growing and significantly higher (P < 0.05) than in leaves from plants that received 0 ppm Ca. However, calcium treatment did not ensure transfer of calcium to fruit tissues. Calcium lactate and calcium chloride were used as postharvest calcium treatments at 1500, 3000 and 4500 ppm Ca. Fruit of ‘Selva’ were dipped in calcium solution for 5 min and wound-inoculated with B. cinerea (10⁶ conidia per mL). Calcium lactate and calcium chloride at 3000 and 4500 ppm Ca, respectively, were most effective in delaying Botrytis rot development on ‘Selva’ after 7 days of storage at 10⁰C, 90±5% RH. Storage for least 24 h after calcium dips prior to inoculation was required to delay the development of fruit rot. Fruit harvested early in the season seemed to be less susceptible to grey mould than those harvested later. However, calcium treatment tended to be more effective when applied to late-season fruit. Preharvest boron treatment, applied as for calcium but at 0, 0.25, 0.5 and 1.0 ppm B, had no effect on fruit firmness of either cultivar. However, firmness of ‘Aromas’ fruit was slightly greater than ‘Selva’ fruit for all treatments. The amount of boron applied had no effect on the external appearance, pH, SSC or TA for either cultivar after storage of fruit for up to 10 days. Application of boron had no effect on fruit grey mould development in either cultivar. Furthermore, boron had minimal effect on the incidence of blight on woundinoculated detached leaves of ‘Aromas’ 7 days after inoculation. However, blight lesion diameters on ‘Selva’ leaves in the 1.0 ppm B treatment (8.0 mm) were significantly smaller (P < 0.001) than in the 0 ppm B treatment (13.0 mm). Phytotoxicity was observed in boron treatments even at the level considered optimum for strawberry growing. Severity increased with increasing boron concentration but no consistent effect on flower death or flower abortion was observed. In conclusion, strawberry is sensitive to boron toxicity. Calcium may enhance fruit firmness and, consequently, delay grey mould development if calcium penetrates the fruit. Postharvest calcium treatment tended to be more effective in delaying development of grey mould when applied to late-season fruit. Calcium lactate is a potential alternative to calcium chloride for reducing decay caused by B. cinerea in strawberry without providing undesirable bitterness. This finding may provide a basis for application in industry. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1331382 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine 2008

Bibliography: leaves 200-223. / xii, 225, [15] leaves, [19] leaves of plates : ill. (some col.), maps (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1995?

1 v. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, Waite Agricultural Research Institute, 1993

Bibliography: leaves 178-195. / xiv, 195 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemistry, 2001

"January 2004" / Bibliography: leaves 163-184. / v, 184 leaves : ill. (some col.), photos ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, School of Chemistry and Physics, Discipline of Chemistry, 2004