Copper (Cu) has high thermal conductivity and is thus ideal for high heat flux, thermal heat sink applications in fusion power applications. Divertor designs for future fusion power plants will expose Cu alloys to extreme thermal (>10 MW m^-2) and neutron fluxes (200 dpa) that destabilise the microstructure of Cu. To improve stability, strength and creep resistance, alloying additions are used commercially, but these compromise thermal conductivity. Dispersed oxide particles may offer the opportunity for improved mechanical stability and creep resistance even at very low volume fractions (<1%) while avoiding large reductions in thermal conductivity. However there are few studies on the processing-performance of oxide dispersion strengthened Cu alloys. In this thesis, novel oxide dispersion strengthened Cu alloys were prepared by room temperature mechanical alloying of Y₂O₃ and the mechanism of dispersion investigated. A small fraction of Y₂O₃, up to 1%, was shown to disperse effectively during mechanical alloying at room temperature in Cu. Both severe fragmentation and some local disassociation of the Y and O occurred, allowing for re-precipitation of fine nanoparticles <10 nm during consolidation and exposure to elevated temperatures. A model alloy of Cu-2 wt.% Y₂O₃ alloy had a mean oxide particle diameter of 7.1 ± 6.0 nm and a mean particle number density of 8.24 x 10²² m^-3 following consolidation. Ternary Ti additions were investigated for nanoparticle refinement and best design alloy with a composition of Cu-0.25Y₂O₃-0.25Ti was produced that had a mean nanoparticle diameter of 3.2 ± 1.5 nm and a mean particle number density of 2.36 x 10²³ m^-3 , which after thermal ageing for 545 h at 350 °C, was largely unchanged at 3.8 ± 1.7 nm, and 1.74 x 10²³ m^-3 respectively. Comparing favourably with commercial Al₂O₃ dispersion strengthened Cu, the alloy had a narrower particle size distribution and a higher particle number density. The fine dispersed oxide nanoparticles gave good grain boundary pinning, retaining an ultrafine mean grain size of 220 nm after thermal ageing. Thermal conductivity of the Ti-containing alloy was 332 ± 16W m_-1 K_-1 , and the addition of Ti increased the thermal conductivity with increasing temperature. The creep resistance was evaluated by small punch testing and in-house produced alloys outperformed commercial alloys at 350 °C. The work in this thesis indicates that mechanically alloyed Cu-Y₂O₃ or Cu-Y₂O₃-Ti alloys, with further development and evaluation, have potential as thermal heat-sink materials for fusion divertor application.

L’étude de l’interaction entre une impulsion électromagnétique et un matériau dispersif est un vieux sujet qui remonte au moins au tournant du vingtième siècle avec Sommerfeld et Brillouin. Depuis lors, de nombreux scientifiques ont apporté leur contribution mais il reste un certain nombre de questions, y compris dans des domaines supposés complètement défrichés. Le but de cette thèse est d’aborder, de la manière la plus systématique qui soit, les problèmes les plus emblématiques du domaine de ce qu’il est convenu d’appeler “l’électrodynamique classique dans la matière”. Dans un premier temps, nous avons cherché à répondre à la question simple et fondamentale suivante: un certain nombre de points expérimentaux étant donnés trouver une procédure qui permette d'obtenir un modèle analytique pour la permittivité. Maintenant équipé d’un modèle phénoménologique pour la permittivité, on s’attache à déterminer les caractéristiques essentielles liées à la propagation d’une impulsion électromagnétique dans un milieu arbitrairement dispersif. Après quoi, nous changeons de dimension en nous attaquant aux problèmes tridimensionnels. Nous commençons par l’étude du champ électromagnétique diffusé par une particle chargée ponctuelle oscillant à une fréquence fixe donnée, et placée à côté d’un objet. La dernière partie est une partie plus pratique où l'on aborde des problèmes qui touchent à la technologie. Chercher les résonances de structures ouvertes n’est pas une mince affaire et met en scène des résonances dans le plan complexe. Ici on détermine à la main les QNM (Quasi-Normal Modes) d’une cavité Fabry-Pérot. / The study of the interaction between electromagnetic pulses with dispersive and possible passive materials has a long tradition that can be traced, at least, to the works of Sommerfeld and Brillouin. As time has passed many scientist have contribute to a better understanding of this kind of phenomena. However some well established concepts need to be revisited and some questions remain open. The aim of this thesis is then, to tackle in a very systematic way, some of the most representative problems in this area that has been called “classical electrodynamics in matter”: I) We have developed a mathematical procedure that allows to find analytical models that in the frequency domain fulfils two fundamental physical properties: reality in time domain and causality. II) Our second task is to determine the velocity of an electromagnetic pulse that propagates in a highly dispersive medium. III) The problem of describing the electromagnetic field generated by an oscillating charge and itsinteraction with some dispersive 3D-object is also studied. The first part deals with the pure description of an EM field generated by arbitrary charge density $\rho$ and corresponding current density $j$. Second part is related to the interaction of this polyharmonic EM field and a dispersive object (a sphere). IV) Finding the resonant frequencies and consequently the resonant modes is a well known problem in physics, when the fields are not strictly confined and can leak to the whole universe we can say that we are dealing with Quasi Normal Modes (QNMs). In this thesis we give a brief and straightforward way of deriving the QNMs of a Fabry-Perot cavity.

No description available.

[pt] Neste trabalho, o problema de valor de contorno associado à estrutura de uma linha microstrip blindada é formulado em termos de uma representação rigorosa de modos híbridos, superposição de modos TE e TM. As equações resultantes são então transformadas, através da aplicação do método de Galerkin no domínio espectral, para obtenção da equação característica para as propriedades de dispersão de linhas microstrip blindadas. As principais vantagens deste método são sua simplicidade e convergência rápida. Foi elaborado um programa de computador para cálculo dos parâmetros, e foram realizadas comparações com resultados experimentais e com expressões empíricas apresentadas por outros autores. A influência da variação da altura da blindagem superior é também considerada. / [en] The boundary value problem associated with the shielded microstrip-line structure is formulated in terms of a rigorous hybrid-mode representation, superposition of the TE and TM fields. The resulting equations are subsequently transformed, via the application of Galerkin’s method in the spectral domain, to yield a characteristic equation for the dispersion properties of shielded microstrip lines. Among the advantages of the method are its simplicity and rapid convergence. A computer program for the parameters is presented, and numerical results are compared with some experimental results and with theoretical and empirical results presented by other authors. The behavior with the variation of the height of the top cover is also considered.

M.Ing. / Lightwave systems used in the core transport network of telecommunication systems operate in the second transmission window. The 1550 nm wavelength region exhibits the lowest attenuation coefficient, thus expanding the repeater distance in the network. However, the influence of the large dispersion coefficient associated with the second transmission window limits the operating speed of the network to 2.5 Gbit/s or less. In order for the network to operate at higher bit-rate, a dispersion management scheme is needed. In this research, the performance of negative dispersion fibre used as a dispersion compensating module is investigated. The negative dispersion fibre used in this study was the AVANEX PureForm DCM. The dispersion coefficient of the DCM measured at 1525 nm, 1545 nm and 1565 nm were given as -918 , -987 and -1047 respectively. The optimal operating condition of the DCM was obtained by considering various dispersion management configurations i.e. post-compensation, pre-compensation and symmetric compensation. The DCM was tested on a single span, single channel system operating at a speed of 10 Gbit/s with the transmitting wavelength of 1551.2 nm, over 60 km of convention single mode fibre. Furthermore, the performance of the system at 55 km and 65 km were also used to examine the results for the over- and under compensation links respectively. The results obtained for 100% dispersion cancellation for the pre-, post- and symmetric configuration showed an increase in the extinction ratio of 2.09 dB, 2.72 dB and 2.37 dB respectively. Similarly, the Q-factor was estimated to equal 13.67, 11.296 and 13.167 respectively. The results indicate similar performance for all the configurations considered, analysis of the eye-diagrams reveals that the post-compensation configuration would ultimately yield the best results. This is due to the fact that eye diagram recovered from this setup has minimal deformation. The experiments for an extremely over-compensated link, i.e. 40 km, showed an increase from 9.49, obtained with no compensation, to 10.63. However, for the extremely under-compensated link i.e. 80 km, the extinction ratio only manages to improve from 4.88 dB to 8.63 dB.

No description available.

Ce travail de thèse concerne la formulation et la mise en œuvre d'un ensimage thermoplastique, respectueux de l'environnement et utilisable à une échelle industrielle. La première étape du projet a été d'adapter les moyens et les ingrédients de formulation aux contraintes industrielles. La formule d'ensimage est basée sur une dispersion aqueuse de particules de polymère thermoplastique (PEI) obtenue par la technique d'émulsion/évaporation. Le choix de la technique de dispersion et du solvant volatil ont été les premières modifications apportées à la formulation d'ensimage qui existait à l'échelle laboratoire. Une optimisation de la dispersion aqueuse a été nécessaire pour répondre aux contraintes industrielles de stabilité, de température et de mise en œuvre. La seconde étape a été l'optimisation de la dispersion aqueuse d'ensimage par une modélisation prédictive puis sa validation expérimentale. L'étude prédictive (QSPR) a permis de se focaliser sur deux paramètres essentiels influençant la stabilité de la dispersion : la vitesse d'émulsification et la concentration en tensioactif. La validation expérimentale nous a permis de confirmer l'importance de ces paramètres et ainsi mieux maîtriser l'élaboration des dispersions. Afin de répondre aux exigences industrielles, notamment en termes de comportement rhéologique, une nouvelle formule d'ensimage a été élaborée. Cette dernière met à profit le comportement viscoélastique de tubules formés par l'association CTAC/acide salicylique, pour préparer des dispersions aqueuses stables. Il s'agit là du premier exemple d'utilisation de tubules pour disperser dans l'eau des particules de polymère par la technique d'émulsion/évaporation. La stabilité de la dispersion a été mesurée à 22h et les propriétés de la dispersion permettent une redispersion aisée de la formulation même après déstabilisation. Enfin cette dispersion d'ensimage a fait l'objet de tests laboratoires et pilotes pour réaliser, respectivement, un film sur plaques de graphite et un ensimage sur fibres de carbone HexTow(r) IM7 sur la chaîne d'ensimage de notre partenaire industriel. Les résultats ont montré un ensimage abondant et qui montrait de bonnes propriétés d'adhésion dans le matériau composite final. Cette dispersion d'ensimage a été brevetée par Airbus Defence & Space. / This PhD project is related to the development of an eco-friendly thermoplastic sizing formulation and its implementation as sizing, usable at an industrial scale. The first step of the project was to adjust the preparation and the ingredients of this formulation to the industrial requirements. The sizing formulation is based on an aqueous dispersion of thermoplastic polymer particles (PEI) obtained by an emulsion/solvent evaporation process. The choice of the dispersion method and the volatile solvent were the first modifications achieved on the sizing formulation which was available at a laboratory scale. An optimization of the aqueous dispersion was necessary to meet the industrial requirements of stability, temperature and implementation. The second step was the optimization of the aqueous sizing dispersion by a predictive model, and then its experimental validation. The predictive study (QSPR) permitted to focus on two essential parameters affecting the stability of the dispersion: the stirring speed and the surfactant concentration. The experimental validation permitted to confirm the importance of these parameters and consequently a better understanding of the dispersion process. In order to satisfy the industrial requirements, especially in terms of rheological behavior, a new sizing formulation was elaborated. This latter takes advantage of the visco-elastic behavior of the tubules formed by the association CTAC / salicylic acid, to formulate stable aqueous dispersions. This is the first example of use of tubules to disperse polymer particles in water by emulsion/solvent evaporation process. The stability of dispersion was measured to 22 hours and the proprieties of this dispersion permit an easy redispersion of formulation even after destabilization. Finally, this sizing dispersion was tested in laboratory and industry to make, respectively, film on carbon slab and sizing on carbon fibers HexTow(r) IM7 using industrial sizing means. The results showed an abundant sizing and good adhesion properties in the final composite material. This sizing dispersion was patented by Airbus Defence & Space.

Electrophoretic displays (EDPs) are an attractive low power technology for small to large area displays. Such display technology has seen a surge of research interest with the launch of successful e-readers in the market place, owing to their lower power consumption and paper-like quality. This work aims to look at the influence of shape on the electrophoretic mobility of particles for such devices. Crosslinked poly(methyl methacrylate) (PMMA) precursor particles with a narrow size distribution were produced by non aqueous dispersion polymerisation utilising a pump-feed method. To produce shape anisotropic particles an adapted version of the dynamic swelling method for polar media was chosen. Suitable monomers were screened by the use of Hansen solubility theory to find monomers which interact with PMMA but not the solvent. It was found that 2- hydroxyethyl methacrylate (HEMA) and N-hydroxyethyl acrylamide (HEAm) were two such suitable monomers, methyl methacrylate (MMA) was also used as a control series.It was found that cluster-like particle morphologies could be produced by the MMA system by the inclusion of small quantities of crosslinking monomer. This was due to precipitation of higher molecular weight polymer segments to the seed particle surface. The cluster-like morphology could be enhanced by use of a polar crosslinking monomer and by sequential reactions. For the polar system, it was found that the reactions with pure monomer were unclean, due to the solubility mismatch of the monomer and the solvent system. This was overcome by a copolymerisation with MMA. The system showed different particle morphologies could be produced by varying the polar monomer content. In one case a sample of pure dumbbell-like particles could be produced. These dumbbell-like particles are thought to be chemical as well as shape anisotropic owing to monomer composition. EPD evaluation for the particles was undertaken and showed that all particles can become highly charged in low dielectric constant media, but that the shape anisotropic particles are prone to adsorption to the cell walls and electrodes.The work outlined in this thesis shows the first reporting of shape anisotropic polymeric particles produced in low dielectric constant solvents system.

This study focused on the dispersal and dispersion of southern elephant seals, Mirounga leonina, at Marion Island in relation to their natal site, and to their site of first reproduction. Movements from the natal site to terrestrial haulouts used for reproduction, and between successive reproductive sites, were defined as dispersal, while movements from the natal site to sites used for purposes other than reproduction, were defined as dispersion. Some 33000 records collected over 12 years, of haul outs at 54 different sites of 5700 tagged seals, formed the database analysed. Both male and female seals were found to use sites closer to their natal site than expected, for reproductive, moult and winter haulouts. However, breeding seals used sites closer to their site of first reproduction than their natal site, on subsequent reproductive haulouts. No difference was found between the mean distances dispersed to moult sites and to winter haulout sites, but distances of dispersal were significantly less than distances of dispersion. Female seals dispersed further than males to reproductive sites, but no difference between the sexes was apparent for moult and winter dispersion. While the number of male seals hauling out to reproduce was too small to assess the effects of various factors on the dispersal of males, a number of factors influenced the dispersion of male seals, and dispersion and dispersal of female seals. These included age, isolation of natal site, anthropogenic disturbance, natal harem size and natal harem pre-weaning mortality. A number of hypotheses are proposed to explain the reasons behind the results found, and the direction of future research concerning the movements of southern elephant seals and their choice of terrestrial environment is suggested. / Dissertation (MSc (Zoology))--University of Pretoria, 2006. / ab2013 / Zoology and Entomology / unrestricted

Horizontal and vertical variations of copper, cobalt, iron, manganese, molybdenum, nickel, zinc, organic carbon and pH were studied in a small bog close to a known copper-mineral occurrence in the foothills of the Cascade Mountains, British Columbia This bog consists of up to 3 m thickness of moderately decomposed, water saturated, fetid organic material underlain by glacial till that almost completely covers the contact between copper-mineralized Nicola Group volcanic rocks and porphyry dykes. Soils with more than 16% organic carbon and 0.1% Hl-reducible sulphur are enriched in copper, cobalt, nickel, zinc and molybdenum. Sympathetic relationships between nickel and zinc and between cobalt and copper are demonstrated by correlation analysis of metal data. Metals generally increase down organic soil profiles, but fall sharply in the till except at the western end of the bog where small areas of concealed till have up to 0.57<> copper and 100 ppm molybdenum. Iron and manganese are generally higher in the till than in organic soil although these metals are locally very abundant in near surface fibrous organic material. Reducing, subsurface bog waters generally have higher dissolved iron, manganese and organic carbon, but lower copper contents than do surface waters. However, several subsurface water samples from the area underlain by copper-rich till contain up to 1 ppm copper. Copper is also very abundant in springs water flowing from a probable fault zone west of the bog; in seepages draining humic gleysolic soils surrounding the west side of the bog and in acid, semi-stagnant surface water. Small, irregularly shaped grains of pyrite, chalcopyrite, covellite, native copper and framboidal pyrite are scattered throughout the organic soils. Copper sulphide and native copper grains are restricted to two areas at the eastern and western ends of the bog occurring between 1 and 3 m depth. Framboidal pyrite, however, has a wider spatial distribution in organic soils than the copper and copper-iron sulphide mineral grains. Copper and iron are principally derived through oxidation of sulphides,disseminated in the underlying volcanic rocks, by circulating ground water which then discharges into the bog along concealed fault zones. Ground water,- percolating through reduced till beneath organic soils and through humic gleysolic soils,dissolves cobalt, nickel, zinc, manganese, iron and molybdenum which then migrate through the bog as simple ions, complex ions or soluble metal-fulvate complexes. A major proportion of the dissolved copper, cobalt, nickel and zinc is probably immobilized by adsorption and complexing to solid humic and fulvic acid fractions in the soil. Authigenic copper and iron sulphides also form through reaction of metals with sulphide ions produced from biogenic sulphate reduction. Stability relationships between copper and iron minerals indicate that the grain textures reflect changes in Eh, pH, sulphide ion activity, metal ion activity and possibly dissolved organic carbon abundance. Hydrous oxides of iron and possibly manganese form close to the bog surface where metal-rich solutions discharge into the oxidizing environment. Molybdenum is also concentrated in the acid fibrous organic layer due to immobility of the acid molybdenate ion. Abundant copper may be adsorbed from the metal-rich surface water by plants and is then bound to proteins forming the cell-wall membrane. This form of copper is relatively stable and the metal will only be released from the association during advanced organic diagensis. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate