The study was designed to investigate disease resistance of lucerne (M. sativa subsp. sativa) genetic material (cultivars and breeding material) under field conditions, to evaluate Sclerotinia stem and crown rot and aluminium resistance under laboratory conditions, and to develop Sclerotinia stem and crown rot and aluminium resistant populations. / Ištirti liucernos (M. sativa subsp. sativa ir M. sativa subsp. varia) genetinės medžiagos - įvairių veislių ir Lietuvos agrarinių ir miškų mokslų centro (LAMMC) Žemdirbystės instituto selekcinės medžiagos atsparumą ligoms lauko sąlygomis, įvertinti atsparumą vėžiui ir aliuminiui laboratorinėmis sąlygomis bei suformuoti atsparias aliuminiui ir vėžiui populiacijas.

In July 1980 the National Government selected a proposal by the Fletcher-Alusuisse-Gove consortium for the establishment of an aluminium smelter which would take up the last and greatest part of a 5000 Gigawatt-hour electricity concession. This decison provides a convenient end-point for a long and complicated period of energy planning where a major concern has been the utilisation of surplus energy resources. The history of this decision will be traced in this study beginning with the discovery of the surplus energy resources in 1978. A considerable part of this decision-making has been conducted inside the government bureaucrary and in secret. This study focuses exclusively on this bureaucratic decisionmaking providing a detailed discussion of the energy planning issues and also endeavouring to treat the decision as the outcome of organisational processes. It is an important theoretical concern that only through an understanding of behavioural processes can the importance of managing the decision process be fully appreciated. Some of the circumstances in which this study was undertaken must be mentioned in order to explain the approach that has been adopted. The structure of this study has been largely determined by the requirements of a second report which is a detailed chronology of events commissioned by the Treasury. It has been through producing this Treasury report that access has been permitted to departmental files providing by far the greatest amount of research material. Access to government officials has also been assisted. However, because of the requirements of the Treasury report and the sensitivity of the issues covered, it has not been possible to interview key participants in the decision outside the government bureaucracy. It should also be noted that the controversy which has marked the public debate on the aluminium smelter and associated issues has also been evident in the bureaucratic decisionmaking where sharp interdepartmental differences appeared. This context has meant that when the interviewing was carried out in late 1980 and early 1981, many officials still felt unable to give a completely frank and detailed account of events. Despite these circumstances, many officials have been of considerable assistance to me and have been very generous with their valuable time. In particular I wish to acknowledge the assistance given to me by Mr Rob Laking and Mr Howard Fancy. I am also grateful for the kind and patient supervision offered to me by Professor Keith Jackson and for the generous services of Mr Richard Kennaway and Dr. Keith Ovenden.

Dans les cuves d'électrolyse d'aluminium, le milieu de réaction très corrosif attaque les parois de la cuve, ce qui diminue leur durée de vie et augmente les coûts de production. Le talus, qui se forme sous l'effet des pertes de chaleur qui maintiennent un équilibre thermique dans la cuve, sert de protection naturelle à la cuve. Son épaisseur doit être contrôlée pour maximiser cet effet. Advenant la résorption non voulue de ce talus, les dégâts générés peuvent s'évaluer à plusieurs centaines de milliers de dollars par cuve. Aussi, l'objectif est de développer une mesure ultrasonore de l'épaisseur du talus, car elle serait non intrusive et non destructive. La précision attendue est de l'ordre du centimètre pour des mesures d'épaisseurs comprenant 2 matériaux, allant de 5 à 20 cm. Cette précision est le facteur clé permettant aux industriels de contrôler l'épaisseur du talus de manière efficace (maximiser la protection des parois tout en maximisant l'efficacité énergétique du procédé), par l'ajout d'un flux thermique. Cependant, l'efficacité d'une mesure ultrasonore dans cet environnement hostile reste à démontrer. Les travaux préliminaires ont permis de sélectionner un transducteur ultrasonore à contact ayant la capacité à résister aux conditions de mesure (hautes températures, matériaux non caractérisés...). Différentes mesures à froid (traité par analyse temps-fréquence) ont permis d'évaluer la vitesse de propagation des ondes dans le matériau de la cuve en graphite et de la cryolite, démontrant la possibilité d'extraire l'information pertinente d'épaisseur du talus in fine. Fort de cette phase de caractérisation des matériaux sur la réponse acoustique des matériaux, les travaux à venir ont été réalisés sur un modèle réduit de la cuve. Le montage expérimental, un four évoluant à 1050 °C, instrumenté d'une multitude de capteurs thermique, permettra une comparaison de la mesure intrusive LVDT à celle du transducteur, dans des conditions proches de la mesure industrielle.

This investigation confirmed that plant reaction to Al was directed through the disruption of intercellular co-ordination existing between the cell populations comprising the root meristem. The first detectable response to A1 in the root involved disruption of Golgi apparatus function in the cap periphery. Ultrastructural changes in the cap periphery coincided with the presence of A1 in these cells. Conspicuous physiological changes involving cell enlargement, cell metabolism and root elongation were identified in cells initially remote from the site(s) of A1 uptake. Communication between A1-damaged peripheral root cap cells and the cell populations of the cap and proximal meristems, quiescent centre and region of cell growth was therefore indicated. A decrease in amyloplast numbers in response to increasing AI concentration coincided with diminished Golgi apparatus activity in the peripheral cap. These changes preceded detectable reductions in mitotic activity, indicated by decreases in cap volume and root length, and it was consequently suggested that control of intercellular activities in the root meristem may be directed through polysaccharide metabolism. Low concentrations of A1 (≤ 1,25 mg dm ¯³) produced a positive growth response in the primary root. This coincided with an increase in mean cap volume and these events were interpreted as an A1-induced release of the proximal meristem from growth inhibition originating in the cap. Experiments which followed the effect of decapping on the morphology of quiescent centre cells in the presence and absence of A1 supported the existence of a Golgi apparatus-derived morphogen involved in the control of Golgi apparatus secretory activity and plastid differentiation. In contrast to the controls (0 ABA). treatment of decapped roots with 2 X 10[-4] and 5 X 10[-5] M abscisic acid inhibited the development of Golgi apparatus secretory activity and plastid differentiation. It is postulated therefore, that an early response to AI may involve inhibition of the basipetal movement of an endogenous growth inhibitor originating in the cap, which may be ABA. The presence of A1 in the nutrient solution caused an efflux of H[+] from the root. Some of the more adverse plant responses to AI were initiated at A1 concentrations where the molar ratio of charge between Ca[2+] and A1[3+] favoured A1. An hypothesis for an electrophysiological plant response to A1 involving membrane hyperpolarisation by Al ions is developed. Chemical analysis of plant fractions did not connect A1-induced nutrient disorders with the primary expression of A1 toxicity. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1986.

The current, commercially available, press and sinter Al-Mg-Si-Cu alloys are based on wrought or cast alloy compositions and have not been tailored for the press and sinter process. The limited development of the Al-Mg-Si-Cu alloys for the press and sinter process can be partly attributed to a poor understanding of the effects of processing conditions on the sintering behaviour. The primary objective of this work was to investigate and understand the effects of processing conditions on the sintering behaviour of Al-Mg-Si-Cu-(Sn) alloys. Dilatometry was used in conjunction with other experimental techniques to elucidate and understand the expansion and shrinkage events that occur during the liquid-phase sintering of Al-Mg-Si-Cu-(Sn) powder metallurgy alloys. Samples were uni-axially pressed from elemental metal powder blends, de-waxed, and then sintered in a horizontal push-rod dilatometer to record the dimensional changes in the pressing direction. The processing conditions examined included the alloy composition, temperature, green density and atmosphere. A liquid forms during heating due to reactions between the alloying elements and the aluminium. This liquid is initially non-wetting on the oxide layer of the aluminium particles, resulting in separation of the particles, which is manifested by expansion of the sample. The oxide is reduced as sintering progresses, alleviating the non-wetting conditions. When more liquid forms, further expansion occurs, despite the improved wetting conditions. It is proposed that atmospheric oxygen and/or nitrogen can react with the liquid, forming a solid phase (‘shell’) at the liquid-vapour interfaces. These shells prevent the liquid from wetting the particles, resulting in further expansion and preventing shrinkage. Unbalanced diffusivities (the Kirkendall effect) between the aluminium and silicon contribute to the expansion. A mechanism is proposed to account for the transition to shrinkage, whereby the shells at the liquid-vapour interface rupture when there is a rapid increase in the volume of contained liquid. The liquid then flows out and over the shells, onto the aluminium substrate, causing shrinkage. Magnesium and nitrogen delay the transition to shrinkage by facilitating nitride shell formation at the solid-liquid interface. Silicon and tin cause an earlier transition to shrinkage by increasing the liquid volume. In addition, tin promotes shrinkage by segregating to the liquid-vapour interfaces, limiting the thickness of the shells at the liquid-vapour interfaces. The two dominant liquid-phase shrinkage mechanisms during the sintering of Al-Mg-Si-Cu-(Sn) alloys are rearrangement and pore-filling. Contact-flattening is not a dominant shrinkage mechanism, but may occur concurrently with the other mechanisms. If contact flattening occurs, a decrease in the pressure of isolated pores increases the total shrinkage rate. Nitrogen increases the shrinkage rate during rearrangement by restricting grain-growth. Magnesium increases the shrinkage rate during rearrangement by reducing the solid-liquid interface energy. Magnesium and nitrogen are essential for the formation of nitride within isolated pores, which decreases the pore pressure and increases the contribution of contact-flattening on the total shrinkage rate. Silicon reduces the beneficial influence of magnesium during rearrangement by diluting the magnesium content in the liquid. Silicon increases the pore-filling rate due to an increase in the liquid volume. Magnesium increases the pore-filling rate by facilitating aluminium nitride formation within isolated pores and by increasing the pore-filling. Tin additions can decrease the pore-filling rate due to its segregation to the liquid-vapour interface, limiting the consumption of nitrogen within isolated pores.

This thesis focuses on closed-cell aluminium foams (ALPORAS and ALULIGHT) and on sandwich panels comprising these foams laminated with 2/2 twill carbon fibre (MTM56/0300) skins. The thesis experimentally and analytically investigates the response of foam-only panels (ALPORAS) to indentation with various indenter sizes and shapes; and also studies the behaviour of sandwich panels to contact damage caused quasi-statically or by impact. Quasi??static uniaxial compression testing is used to determine the mechanical properties of the foams (ALPORAS and ALULIGHT). It is revealed that the plastic collapse strength (σ* pl) obtained from the stress??strain curves is lower than the values predicted by the Gibson-Ashby theoretical model. This phenomenon is explained by the fact that the aluminium foams tested are imperfect, non-homogeneous and non-isotropic, and show a distinct cell elongation. Whereas, the Gibson-Ashby theoretical model was based on the finite element method applied to the response of a unit tetrakaidecahedral closed cell having flat faces. The experimental work shows that the deformation of the foam-only panels to indentation is caused by progressive crushing of the cell bands and by shearing and tearing of the cell walls. This thesis presents new analytical models for the response of the foam-only panels and estimates the applied deformation load in all types of indentation. By fitting the experimental load-displacement curves, the shear strength (τ* pl) and the tear energy (γ) are deduced. Compared to the literature, more consistent results are obtained for the shear strength (τ * pl) and the tear energy (γ) from all types of indentation. It is also suggested to determine (τ * pl) and (γ) through indentations with long punches (FEP and LCP), instead of hemi-spherical or cylindrical indenters, because indentation on enclosed areas shows some indenter size dependence. It is concluded that thinner panels are not suitable for the determination of the tear energy (γ) since the densification of the foam is achieved before the tear resistance is fully engaged. Another objective of this thesis is to study the response of sandwich panels comprising a closed??cell aluminium foam core and laminated with carbon fibre skin to quasi-static and impact local damage. Special attention is paid to the residual (remnant) strength in bending of the already indented sandwich panels (quasi-statically or by impact) up to the failure point. The remnant strength in bending is determined by carrying out four point bending strength tests. The local damage is located on either the compressive or on the tensile side of the sandwich panels. Thus, the capacity of the panels to resist transverse loads after they have been locally damaged at contact is investigated. The contact damage on the sandwich panels is experimentally simulated using spherical indenters. The quasi-static indentation is carried out at a low constant velocity (0.5mm/min) ?? the induced contact damage is found to be independent on the sample thickness but dependent on the indenter diameter. On the contrary, the impact test indicates velocity-dependence of the failure mode of the sandwich panel (i.e. skin breakage or punch through) which is found from the load-displacement curves. The results reveal that there is a correlation between the area of the contact damage and the remnant strength, and that the use of metal foam cores leads to high contact damage resilience of composite structures.

This thesis focuses on closed-cell aluminium foams (ALPORAS and ALULIGHT) and on sandwich panels comprising these foams laminated with 2/2 twill carbon fibre (MTM56/0300) skins. The thesis experimentally and analytically investigates the response of foam-only panels (ALPORAS) to indentation with various indenter sizes and shapes; and also studies the behaviour of sandwich panels to contact damage caused quasi-statically or by impact. Quasi??static uniaxial compression testing is used to determine the mechanical properties of the foams (ALPORAS and ALULIGHT). It is revealed that the plastic collapse strength (σ* pl) obtained from the stress??strain curves is lower than the values predicted by the Gibson-Ashby theoretical model. This phenomenon is explained by the fact that the aluminium foams tested are imperfect, non-homogeneous and non-isotropic, and show a distinct cell elongation. Whereas, the Gibson-Ashby theoretical model was based on the finite element method applied to the response of a unit tetrakaidecahedral closed cell having flat faces. The experimental work shows that the deformation of the foam-only panels to indentation is caused by progressive crushing of the cell bands and by shearing and tearing of the cell walls. This thesis presents new analytical models for the response of the foam-only panels and estimates the applied deformation load in all types of indentation. By fitting the experimental load-displacement curves, the shear strength (τ* pl) and the tear energy (γ) are deduced. Compared to the literature, more consistent results are obtained for the shear strength (τ * pl) and the tear energy (γ) from all types of indentation. It is also suggested to determine (τ * pl) and (γ) through indentations with long punches (FEP and LCP), instead of hemi-spherical or cylindrical indenters, because indentation on enclosed areas shows some indenter size dependence. It is concluded that thinner panels are not suitable for the determination of the tear energy (γ) since the densification of the foam is achieved before the tear resistance is fully engaged. Another objective of this thesis is to study the response of sandwich panels comprising a closed??cell aluminium foam core and laminated with carbon fibre skin to quasi-static and impact local damage. Special attention is paid to the residual (remnant) strength in bending of the already indented sandwich panels (quasi-statically or by impact) up to the failure point. The remnant strength in bending is determined by carrying out four point bending strength tests. The local damage is located on either the compressive or on the tensile side of the sandwich panels. Thus, the capacity of the panels to resist transverse loads after they have been locally damaged at contact is investigated. The contact damage on the sandwich panels is experimentally simulated using spherical indenters. The quasi-static indentation is carried out at a low constant velocity (0.5mm/min) ?? the induced contact damage is found to be independent on the sample thickness but dependent on the indenter diameter. On the contrary, the impact test indicates velocity-dependence of the failure mode of the sandwich panel (i.e. skin breakage or punch through) which is found from the load-displacement curves. The results reveal that there is a correlation between the area of the contact damage and the remnant strength, and that the use of metal foam cores leads to high contact damage resilience of composite structures.

Thesis (doctoral)--Universität-Gesamthochschule-Duisburg, 1989. / Includes bibliographical references (p. 256-272).

Zugl.: Dortmund, Universiẗat, Diss., 2007.

Proefschrift Universiteit van Amsterdam. / Met lit. opg. - Met samenvatting in het Nederlands.