Thesis (PhD (Physics))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Radioactivity is well known and well understood, but its usefulness in industrial applications to optimise processes or increase economic viability is not yet fully utilised by many industries. This study focuses on the measurement of natural radioactivity and its application in heavy mineral separation and vineyard soil classification. The gamma radiometry set-up consisted of a high purity germanium detector, a Marinelli beaker as sample container and associated electronics. It was calibrated for laboratorybased measurements by minimising the background radiation with the use of lead castle and energy and resolution calibrations. Furthermore, detection parameters were optimised; these included the counting time, the selection of gamma rays used for analysis of a sample, the peak area calculation for the detector dead time and the detector efficiency. Given that the samples had different densities and volumes, the detector efficiency had to be corrected for volume and density effects. After implementation of the corrections and optimisations the detection system was tested and found able to accurately measure radioactivity concentrations. The systematic measurement errors for 238U were 5.1 % in the case of the heavy mineral sands and 34.3 % for the vineyard soils, 4.5 % for the 232Th concentrations and 4.7 % for 40K concentrations. Statistical errors were kept below 2 %. The application of radiometry has not been done before at any South African heavy mineral separation plant. For this reason radiometry is suggested as an easier, faster and cheaper alternative to X-ray fluorescence (XRF) for effective implementation of grade control for zircon to improve the cost benefit of the heavy mineral separation process. Zircon is an example of a heavy mineral that is worldwide in demand with a consumption of more than a million tonnes per year. It is used in a wide range of industrial applications and products that include tiles, sanitary ware and plasma displays. South Africa is the second largest producer of zircon in the world and also has the second largest reserve of available zircon, making this mineral a viable source of income for several years to come. Radioactivity, in the form of uranium and thorium, and other impurities such as iron oxide and titanium oxide are found in the crystal lattice of zircon. For it to be a sellable product, the sum of the uranium and thorium concentrations must be less than 500 parts per million for prime or first grade zircon and less than 1000 parts per million for second grade zircon. At present the concentrations of uranium and thorium in zircon concentrates are measured on a whole rock basis by XRF during and at the end of the processing cycle before the final products are ready to be shipped. This is not an ideal situation as the grab samples are taken periodically and are not necessarily representative of the stream or final assignment and has resulted in significant losses by the producer. The solution is to accurately measure the uranium and thorium concentrations fast or immediately, preferably the measurements must be made online and in real time so that processing decisions can be implemented quickly to optimise the final product. Heavy mineral sand samples were obtained from the various separation processes in a Mineral Separation Plant and their 238U and 232Th concentrations determined. The results indicated that the samples’ uranium to thorium ratios together with their total concentrations can be used to differentiate between the samples (i.e. separation processes). The measurement results were compared with those obtained with XRF. The correlations with radiometry were excellent for the uranium (r2 = 0.992), thorium (r2 = 0.998) and total concentrations (r2 = 0.998). Radiometric measurements were also conducted by decreasing the counting time from 3600 s to 1 s to investigate its effect on the accuracy of the results. Correlations between the different times and 3600 s ranged from excellent to good. The obtained results are then used to recommend that radiometry is used in a Mineral Separation Plant to verify that the zircon and zirkwa meet the specifications, to optimise the entrance feed and the other separation processes and to monitor the tailings streams. Finally the practical aspects of the implementation of radiometry are discussed. As a second application was radiometry applied in an agricultural pilot study to demonstrate the applicability of radiometry as a possible useful tool in soil classification. The creation of a vineyard is a long term and expensive investment and its yield and quality will be influenced by many factors such as the type of soil, viticultural preparations and climate. Information on the different soil types in a vineyard is therefore indispensable for the optimisation of land use with respect to vine cultivar, wine quality and production. Soil samples were obtained from Kanonkop, Simonsig and Spier vineyards and their 238U, 232Th and 40K concentrations determined, assuming that fertilisers would have no effect on the results. The difference in 40K concentrations were related to the clay fraction of the soil and demonstrated that the Kanonkop and Simonsig soils are fine-grained and clay-rich compared to the sandy coarse-grained soils of Spier. The uranium and thorium concentrations were indicators of whether the mineralogy of the soil is the same as the underlying bedrock as well as soil maturity. The measurement results were compared with those obtained with XRF. The correlation with radiometry were poor for the uranium concentrations (r2 = 0.314), as many of the samples concentrations were below the XRF detection limit. The correlations were excellent for both thorium (r2 = 0.985) and potassium (r2 = 0.999). As a positive result from the findings of the study was an in-situ measurement performed by Newman et al. for the radiometric mapping of a Simonsig vineyard for soil classification. / AFRIKAANSE OPSOMMING: Radioaktiwiteit is wel bekend en word goed verstaan, tog is die gebruik daarvan in industriele toepassings om prosesses te optimiseer of winsgrense te verhoog nog nie deur baie industrië ten volle benut nie. Hierdie studie fokus op die meting van natuurlike radioaktiwiteit en die toepassing daarvan in swaar mineraal skeiding en wingerd grond klassifikasie. Die gamma radiometrie opstelling het bestaan uit ‘n hoë suiwerheid germanium detektor, 'n Marinelli beker as monster houer en verwante elektronika. Dit was gekalibreer vir laboratorium gebaseerde metings deur die vermindering van die agtergrondstraling met die gebruik van lood kasteel en energie en resolusie kalibrasies. Verder was deteksie parameters geoptimaliseer, dit sluit in die teltyd, die keuse van gammastrale wat gebruik word vir die ontleding van 'n monster, die piek area berekening, die korreksie vir die detektor se dooie tyd en die detektor doeltreffendheid. Gegee dat die monsters van mekaar verskil het in terme van dighteid en volume was dit nodig om die detektor doeltreffendheid te korrigeer vir volume en digtheid effekte. Na die implementering van die korreksies en optimalisasie was die detektor stelsel getoets en was gevind dat radioaktiwiteit konsentrasies akkuraat gelewer kan lewer. Die sistematiese meet foute vir 238U was 5.1 % vir die mineraal sand en 34.3 % vir wingerd grond, 4.5 % vir 232Th konsentrasies en 4.7 % vir 40K konsentrasies. Statistiese foute was onder 2 % gehou. Die toepassing van radiometrie was nog nie voorheen by enige Suid-Afrikaanse swaar mineraal skeidings aanleg gedoen nie. Vir die rede is radiometrie voorgestel as ‘n makliker, vinniger en goedkoper alternatief teenoor XSF vir effektiewe implementering van graad beheer vir zirkon om die koste voordeel van die swaar mineral skeiding proses te verbeter. Zirkon is ‘n voorbeeld van ‘n swaar mineraal wat wêreldwyd in aanvraag is met ‘n verbruik van meer as ‘n miljoen ton per jaar. Dit word in ‘n wye reeks van industriele toepassings en produkte gebruik onder andere teëls, sanitêre ware en plasma skerms. Suid Afrika is die tweede grootste vervaardiger van zirkon in die wêreld en het ook die tweede grootste reserwe van besikbare zirkon. Dit veroorsaak dat die mineraal ‘n lewensvatbare brom van inkomste is vir nog etlike jare. Radioaktiwiteit, in die vorm van uraan en thorium, word tesame met ander onsuiwerhede soos ysteroksied en titaanoksied in zirkon se kristal rooster gevind. Om ‘n verkoopbare produk te wees moet die som van die uraan en thorium konsentrasies minder wees as 500 dele per miljoen vir prima en eerste graad zirkon en minder wees as 1000 dele per miljoen vir tweede graadse zirkon. Huidiglik word die uraan en thorium konsentrasies in die zirkon konsentraat gemeet op ‘n heel gesteente basis met X-straal fluoroskopie (XSF) gedurende en op die einde van die prosesering siklus net voor die finale produk reg is om versend te word. Dit is nie die ideale situasie nie, want die monsters word periodies geneem en is nie noodwendig verteenwoordigend van die stroom of die finale produk nie en het al tot beduidende verliese deur die vervaardiger gelei. Die oplossing is om die uraan en thorium konsentrasies vinnig of onmiddelik te meet, verkieslik moet die metings inlyn en intyds gedoen word om verwerkings besluite vinnig geimplementeer kan word om die finale produk te optimaliseer. Swaar mineraal sand monsters was verkry van die verskeie skeidingsprosesse in ‘n Mineraal Skeidings Aanleg en hul 238U en 232Th konsentrasies bepaal. Die resultate het aangetoon dat die monsters se uraan en thorium verhoudings saam met hul totale konsentrasies gebruik kan word om te onderskei tussen die monsters (oftewel die skeiding prosesse). Die meting resultate was vergelyk met dié verkry met XSF. Die korrelasies met radiometrie was uitstekend vir die uraan (r2 = 0.992), thorium (r2 = 0.998) en totale konsentrasies (r2 = 0.998). Radiometriese metings was ook uigevoer deur die teltyd te verminder van 3600 s tot 1 s om die uitwerking daarvan op die akkuraatheid van die resultate te ondersoek. Korrelasies tussen die verskillende tye en 3600 s het gewissel van uitstekend tot goed. Die bevindinge was dan gebruik om aan te beveel dat radiometrie in a Mineraal Skeidings Aanleg gebruik kan word om te verifeer dat daar aan die zirkon en zirkwa spesifikasies voldoen word, om die begin voer en ander skeidings prosesse te optimaliseer en ook die uitskot strome te monitor. Laastens is die praktiese aspekte van die implementering van radiometrie bespreek. Vir die tweede toepassing was radiometrie toepgepas in ‘n loods studie in die landbou om die toepaslikheid van radiometrie as ‘n moontlike nuttige instrument in grond klassifikasie te demonstreer. Die skepping van ‘n wingerd is ‘n lang termyn en duur belegging waarvan die opbrengs en kwaliteit beinvloed sal word deur vele faktore, onder andere die tipe grond, wynbou voorbereidings en die klimaat. Inligiting oor die verskillende grond tipes in ‘n wingerd is daarom onmisbaar vir die optimalisering van land gebruik in betrekking tot die wingerdstok kultivar, wyn kwaliteit en produksie. Radiometrie is toegepas om te demonstreer die toepaslikheid daaran as ‘n moontlike nuttige instrument in grond klassifikasie. Grondmonsters was verkry vanaf Kanonkop, Simonsig en Spier wingerde en hul 238U, 232Th en 40K konsentrasies bepaal met die aanname dat kunsmis nie ‘n uitwerking op die resultate sou hê nie. Die verskil in 40K konsentrasies was verwant aan die kleifraksie van die grond en het getoon dat die Kanonkop en Simonsig gronde is fyn korrelrig en kleiryk is in vergelyking met die sanderige growwe korrel grond van Spier. Die uraan en thorium konsentrasies het gedui op die samestelling van die grond en ook aangedui watter grond dieselfde is as die onderliggende rots. Die meting resultate was vergelyk met dié verkry met XSF. Die korrelasie met die radiometrie was sleg vir die uraan konsentrasies (r2 = 0.314) aangesien baie van die monster konsentrasies laer was as die XSF deteksie limiet. Die korrelasies was uitstekend vir beide thorium (r2 = 0.985) en kalium (r2 = 0.999). As ‘n positiewe resultaat van die studie se bevindinge was ‘n in-situ meting gedoen deur Newman et al. om ‘n Simonsig wingerd radiomeries te karteer vir grond klassifasie.

The convergence of multiservice heterogeneous networks and ever increasing Internet applications, like peer to peer networking and the increased number of users and services, demand a more efficient bandwidth allocation in optical networks. In this context, new architectures and protocols are needed in conjuction with cost effective quantitative methodologies in order to provide an insight into the performance aspects of the next and future generation Internets. This thesis reports an investigation, based on efficient simulation methodologies, in order to assess existing high performance algorithms and to propose new ones. The analysis of the traffic characteristics of an OC-192 link (9953.28 Mbps) is initially conducted, a requirement due to the discovery of self-similar long-range dependent properties in network traffic, and the suitability of the GE distribution for modelling interarrival times of bursty traffic in short time scales is presented. Consequently, using a heuristic approach, the self-similar properties of the GE/G/∞ are being presented, providing a method to generate self-similar traffic that takes into consideration burstiness in small time scales. A description of the state of the art in optical networking providing a deeper insight into the current technologies, protocols and architectures in the field, which creates the motivation for more research into the promising switching technique of 'Optical Burst Switching' (OBS). An investigation into the performance impact of various burst assembly strategies on an OBS edge node's mean buffer length is conducted. Realistic traffic characteristics are considered based on the analysis of the OC-192 backbone traffic traces. In addition the effect of burstiness in the small time scales on mean assembly time and burst size distribution is investigated. A new Dynamic OBS Offset Allocation Protocol is devised and favourable comparisons are carried out between the proposed OBS protocol and the Just Enough Time (JET) protocol, in terms of mean queue length, blocking and throughput. Finally the research focuses on simulation methodologies employed throughout the thesis using the Graphics Processing Unit (GPU) on a commercial NVidia GeForce 8800 GTX, which was initially designed for gaming computers. Parallel generators of Optical Bursts are implemented and simulated in 'Compute Unified Device Architecture' (CUDA) and compared with simulations run on general-purpose CPU proving the GPU to be a cost-effective platform which can significantly speed-up calculations in order to make simulations of more complex and demanding networks easier to develop.

The aim of this work is to study the in-vitro aerodynamic performance of a new inhaled theophylline formulation prepared by supercritical fluids technique. For the analysis of the output from the in-vitro tests (and further in-vivo tests) a new, fast, sensitive high performance liquid chromatographic (HPLC) method was developed and validated for the determination of theophylline and other related derivatives in aqueous and urine samples using new packing materials (monolithic columns). These columns achieve efficient separation under lower backpressure and shorter time comparing to other traditionally or newly introduced C18 columns. Solution enhanced dispersion by supercritical fluid (SEDS) process has been applied for the production of anhydrous theophylline as pure crystals in the range 2-5 μm to be used as new inhaled dry powder formulation for asthma. Fifteen theophylline samples have been prepared under different experimental conditions. The drug produced by this method has been subject to a number of solid-phase analytical procedures designed to establish the crystal structure [X-ray powder diffraction (XRPD)], the structure and conformation [(FTIR), Fourier-transform Raman spectroscopy (FT-Raman)], and the morphology and particle size [scanning electron microscope (SEM)]. While, thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC) have been used to monitor any phase transition or polymorphic changes after processing. All these analytical techniques gave a satisfactory indication of the solid-state chemistry of the processed particles and assess the development of new inhalation product. The performance of inhaled SEDS theophylline with or without a carrier was evaluated using the developed HPLC method. Three samples having different particle sizes were selected out of the prepared powders by SEDS technique to be tested. The dose sampling unit and the Anderson Cascade Impactor were used to determine the in-vitro emitted dose and the deposition profiles of SEDS samples, respectively. The effect of different inhalation flows was studied using two different flows 28.3, and 60 L min-1 with 4 L inhalation volume. Different DPI devices were investigated in this study; Easyhaler® and Spinhaler®. The particle size has an important effect on the aerodynamic behaviour and deposition profile of inhaled drug, the smaller the particles the greater the total lung deposition. The presence of a carrier improves the respirable fraction for all the tested formulations.

Potentially harmful elements (PHEs) have been researched in a wide variety of disciplines, including pedology, chemistry, pollution science and medicine. Within the scientific community, emphasis has usually been placed on the toxic elements, such as cadmium, chromium, lead and arsenic, but rarely has there been consideration of interactions between PHEs, the sediment matrix and processes occurring in the sediments. Dredging of canals is needed for navigability purposes and consequently testing of dredged sediments (to assess whether sediments are hazardous) and landfilling can be costly for British Waterways facing constantly changing regulations and reduction in government grants. PHE mobility and availability in canal sediments can be affected by oxygen availability, pH and Redox. Remediation is thus becoming a priority for British Waterways to limit their operational costs. Zeolites, a type of remediation tool, have been widely studied in the past 30 years due to their attractive properties, such as molecular-sieving, high cation exchange capacities and their affinity for PHEs. The pilot study to investigate the efficiency of the clinoptilolite showed that there was a concentration difference between PHEs adsorbed by the clinoptilolite and the PHE concentration lost from the sediments from three sites in the West Midlands. Thorough characterisation of the sediments was needed to understand the speciation of the PHEs and the secondary processes occurring in the sediments. The different components of the sediments were analysed using various analytical methods, such as X-Ray Fluorescence spectroscopy (XRF), particle size and X-ray Diffraction (XRD) for the solid-inorganic phase, Ion Chromatography (IC) and Inductively Coupled Plasma-Optical Emissions Spectroscopy (ICP-OES) for the liquid phase (pore water), Gas Chromatography-Mass Spectrometry (GC-MS) and organic loss on ignition for the organic phase, pH and Redox for the electrochemistry of the sediments and Scanning Electron Microscope with Energy Dispersive X-Ray analysis (SEM-EDX) for microscopy and imaging. The British Geological Survey (BGS) sequential extraction method was used to investigate the different phases in the sediments. pH remained near neutral for all three sites and Redox remained anoxic. Organic contents for all three sites were around 30% and contained most of the polycyclic aromatic hydrocarbons considered hazardous. Pore water showed only high concentrations of sulphates but low concentrations of PHEs, suggesting PHEs were not mobile. Sequential extraction confirmed the other results showing that PHEs were mainly associated with stable phases, such as iron and manganese oxides or sulphides. The results have been taken into consideration to design a new remediation strategy to maximise efficiency of the zeolite.

<p>Fans are often used in equipment such as home appliances andelectronic equipment where the margin of profit is small butcustomers demands on a low noise level are high. Therefore,methods for predicting the noise emitted by an applicationincluding one or several fans are desirable in order toimprove, accelerate and reduce the cost of low-noise design.The Noise Shaping Technology (NST) has been developed withinthe EC-project NABUCCO in order to fulfil the aboverequirements on a prediction method. According to NST, thenoise source (not necessary a fan) is described by one orseveral noise descriptors, CSSs, and the correspondingtransmission paths through the structure described by one orseveral transfer functions, ACFs. In this thesis, theapplicability of NST is evaluated on a cabinet for electronicequipment where small axial cooling fans constitute the primarysources of the airborne sound.</p><p>As an axial fan is a complex source of sound,simplifications are necessary when modelling its acousticproperties. Therefore, the sound radiation of an axial fan infree space was examined by expanding the generated soundpressure field into spherical harmonics. The conclusion on asource model for the cabinet example, where the fans are moreor less In-duct mounted, is a modified single axial dipole. Themodel is expected to be valid in the entire frequency range ofinterest except in the mid-frequency range where the modaldensity is low. In order to improve the source model in thisfrequency range, a future model based on a rotating dipole isproposed.</p><p>The sound power of a small axial fan is measured in an ISO10302 test-rig. In order to take account of flow conditions,acoustically transparent ducts have been developed. These shallbe attached to the test-rig when measuring the sound power ofthe fan. A simple but practical method of how to correct thesound power for the baffling effect of the test-rig has alsobeen developed. Finally, the sound power can be converted intodipole force, which is the airborne CSS corresponding to thesingle axial dipole model.</p><p>The corresponding airborne transfer function (ACF), i.e.,from dipole force at the source point to sound pressure at thereceiver point, is measured reciprocally by taking use ofLyamshevs reciprocity relation.</p><p>From multiplication of the CSS and the ACF, the soundpressure can be predicted. The prediction shows quite goodagreement with the measured values.</p><p><b>Keywords:</b>axial fan, airborne sound, sourcecharacterisation, transmission path analysis, In-duct,spherical harmonics, rotating dipole, installation effects, ISO10302, flow conditions, baffling effect, acousticallytransparent ducts, Lyamshevs reciprocity relation, reciprocity,CSS, ACF, GSM, NST.</p>

<p>In this study the practical work with the EU Water Framework starts on the island of Gotland. 33 lakes and 32 streams have been characterized and classified regarding to their ecological status. The aim with the characterisation is to create a uniform discription of all waterbodies and a comparable estimation for the future. The aim with the classification is both to study the waterbodies ecological status and to gain knowledge of where the resources should be concentrated so that the ecological status in all waterbodies will be good in 2015.</p><p>The characterisation has been done according to the EU Water Framework Directive, and the factors that have been applied are the mean depth and area of the lake. The length and size on the catchment area are the factors that have been used on streams. The classification is issued from biological, chemical and hydromorphological elements. The biological elements in both lakes and streams are fish and benthic macroinvertebrates. The chemical elements in lakes consist of total phosphorus, total nitrogen, quotient total nitrogen/total phosphorus, chemical oxygen demand, alkalinity and pH-value. The chemical elements in streams consist of area-specific losses of total phosphorus and total nitrogen, chemical oxygen demand, alkalinity and pH-value. The hydromorphological elements are lakes that are regulated, streams that have been straightened out and streams that have something stopping sawing fish.</p><p>The result of the characterisation shows five different sea types: large and deep seas, meanlarge and deep seas, meanlarge and shallow seas, small and deep seas as well as small and shallow seas. The result from the classification shows that 26 lakes have high or good ecological status. However, this still means that the seven lakes Asträsk, Bogeviken, Bondansträsk, Fridträsk, Inre Stockviken, Mjölhatteträsk and Paviken have moderate ecological status. 15 streams have good or high ecological status, while nine have moderate status. These nine streams are Burgsvikenån, Gothemsån, Ireån, Halorån, Lummelundaån, Närkån, Snoderån, Vägumeån as well as Västergarnsån. The ecological status could not be decided in eight streams, due to the low number of facts. All lakes and streams with moderate ecological status, except Bondansträsk, have recieved this estimation as a result of the high substance of nutrients. While fish in Bondansträsk is not good, the lake recieved the estimation moderate status.</p> / <p>I detta examensarbete inleds det praktiska arbetet med ramdirektivet för vatten på Gotland. I enlighet med vattendirektivet har 33 gotländska sjöar och 32 gotländska vattendrag karakteriserats och klassificerats utifrån ekologisk status. Syftet med karakteriseringen är att skapa en enhetlig beskrivning av samtliga vattenförekomster, vilket ger ett jämförbart underlag inför fortsatta bedömningar av sjöar och vattendrag på Gotland. Syftet med klassificeringen är att dels ta reda på den ekologiska statusen för gotländska ytvatten, dels att få kunskap om var resurserna bör läggas för att en god ekologisk status skall uppnås till år 2015.</p><p>Karakteriseringen utfördes enligt vattendirektivets system B, och de faktorer som användes är maxdjup och sjöarea för sjöar samt längd och avrinningsområdets area för vattendrag.</p><p>Detta resulterade i fem sjötyper: stora och djupa sjöar, stora och grunda sjöar, mellanstora och grunda sjöar, små och djupa sjöar samt små och grunda sjöar. Vattendragen indelades i fyra typer: långa vattendrag med stort avrinningsområde, långa vattendrag med mellanstort avrinningsområde, korta vattendrag med mellanstort avrinningsområde samt korta vattendrag med litet avrinningsområde.</p><p>Klassningen utgick, i enlighet med vattendirektivet, från biologiska, kemiska och hydromorfologiska faktorer. Den biologiska klassningen i både sjöar och vattendrag gjordes med utgångspunkt från fisk och bottenfauna. Den kemiska bedömningen i sjöar gjordes utifrån totalfosfor, totalkväve, fosfor/kväve-kvot, kemisk syreförbrukning, alkalinitet och pH-värde. För vattendrag har arealspecifik förlust av fosfor och kväve, kemisk syreförbrukning, alkalinitet och pH-värde använts. Den hydromorfologiska bedömningen gjordes med hänsyn tagen till rätning av vattendrag, vandringshinder i vattendrag samt reglering av sjöar.</p><p>Resultatet av klassificeringen visar att hela 26 av de 33 undersökta gotländska sjöarna har hög eller god ekologisk status, och sju sjöar, Asträsk, Bogeviken, Bondansträsk, Fridträsk, Inre Stockviken, Mjölhatteträsk och Paviken, har måttlig ekologisk status. 15 av de 32 undersökta vattendragen har hög eller god ekologisk status, medan nio vattendrag, Burgsvikenån, Gothemsån, Ireån, Halorån, Lummelundaån, Närkån, Snoderån, Vägumeån samt Västergarnsån, har måttlig ekologisk status. Vidare har ekologisk status inte kunnat bestämmas för åtta vattendrag, då inte tillräckligt med data funnits för att kunna genomföra en rättvis bedömning. Samtliga sjöar och vattendrag som har måttlig ekologisk status, förutom Bondansträsk, har erhållit denna bedömning på grund av alltför höga halter respektive transporter av näringsämnena kväve och fosfor. Bondansträsk har fått detta omdöme eftersom tillstånd och avvikelse från jämförvärde för fisk inte är helt bra.</p>

<p>A whisker is a common name of single crystalline inorganic fibre of small dimensions, typically 0.5-1 μm in diameter and 20-50 μm in length. Whiskers are mainly used as reinforcement of ceramics. This work describes the synthesis and characterisation of new whisker types. Ti0.33Ta0.33Nb0.33CxN1-x, TiB2, B4C, and LaxCe1-xB6 have been prepared by carbothermal vapour–liquid–solid (CTR-VLS) growth mechanisms in the temperature range 900-1800°C, in argon or nitrogen. Generally, carbon and different suitable oxides were used as whisker precursors. The oxides reacted via a carbothermal reduction process. A halogenide salt was added to form gaseous metal halogenides or oxohalogenides and small amount of a transition metal was added to catalyse the whisker growth. In this mechanism, the whisker constituents are dissolved into the catalyst, in liquid phase, which becomes supersaturated. Then a whisker could nucleate and grow out under continuous feed of constituents. </p><p>The syntheses of TiC, TiB2, and B4C were followed at ordinary synthesis conditions by means of mass spectrometry (MS), thermogravimetry (TG), differential thermal analysis (DTA) and quenching. The main reaction starting temperatures and reaction time for the different mixtures was revealed, and it was found that the temperature inside the crucible during the reactions was up to 100°C below the furnace set-point, due to endothermic nature of the reactions. Quench experiments showed that whiskers were formed already when reaching the temperature plateau, but the yield increased fast with the holding time and reached a maximum after about 20-30 minutes. Growth models for whisker formation have been proposed.</p><p>Alumina based composites reinforced by (2-5 vol.%) TiCnano and TiNnano and 25 vol.% of carbide, and boride phases (whiskers and particulates of TiC, TiN, TaC, NbC, (Ti,Ta)C, (Ti,Ta,Nb)C, SiC, TiB2 and B4C) have been prepared by a developed aqueous colloidal processing route followed by hot pressing for 90 min at 1700°C, 28 MPa or SPS sintering for 5 minutes at 1200-1600°C and 75 MPa. Vickers indentation measurements showed that the lowest possible sintering temperature is to prefer from mechanical properties point of view. In the TiNnano composites the fracture mode was typically intergranular, while it was transgranular in the SiCnano composites. The whisker and particulate composites have been compared in terms of e.g. microstructure and mechanical properties. Generally, additions of whiskers yielded higher fracture toughness compared to particulates. Composites of commercially available SiC whiskers showed best mechanical properties with a low spread but all the other whisker phases, especially TiB2, exhibited a great potential as reinforcement materials. </p>

Postmodernism is a complex concept to grasp, and although artists frequently create postmodernist work, a cognitive approach to it is difficult. This study is therefore unique in its aim to support creative writers in the formation (creation and representation) of postmodernist characters. Thus, this study contributes to the theory of creative writing, within the current zeitgeist and associated writing styles. A zeitgeist is the collective universal subconscious of the world within a specific epoch and is recognisable in the identity of the people that live during that zeitgeist, as well as in the art of the time. Postmodernism, as the contemporary zeitgeist, implies a postmodernist identity (or identities), which can creatively be represented in the artwork (literary text - prose). Through an integrated threefold study of Postmodernism (and postmodernist identity), "character" as covered in literary theory and the "creation and representation" of character as covered in the theory of creative writing, a paradigm is postulated to support the creative writer in the creation and representation of postmodernist characters. The paradigm manages postmodernist characters within three overlapping categories that approach characters as (1) icons that represent postmodernist people, as (2) literary motives that illustrate postmodernist themes and, as (3) containers of postmodernist discourses. Such a paradigm is not to be considered a model or recipe, but is instead to be viewed as an angle of approaching postmodernist characters and as a launch pad from where the creative writer must further rely on his or her own creativity, talent and dexterity. The paradigm therefore keeps in mind both the limitlessness of Postmodernism and the dynamism of the creative process. / Thesis (M.A. (Afrikaans and Dutch))--North-West University, Potchefstroom Campus, 2006

This thesis presents a new type of solar simulator and new measurement methods that allow for fast power rating of photovoltaic devices and for fast performance measurements for energy rating and energy yield predictions indoors under controlled, and more realistically simulated outdoor conditions. A novel indoor measurement system for photovoltaic device characterisation based on light emitting diodes (LEDs) as the light sources is described. The solar simulator is capable of reproducing spectral changes seen in natural sunlight, with its intricacies of variable air mass and weather conditions, to a better match than previously possible. Furthermore, it allows measurements under varying light intensity and device temperature. The prototype LED-based solar simulator developed is characterised and its measurement quality is analysed. The system achieves a class BAA solar simulator classification with a class B spectral match, class A light intensity uniformity and a class A temporal stability. It is the first system of its kind that meets the standards of a solar simulator in spectral match to the standard sunlight spectrum and in terms of minimum light intensity. An uncertainty analysis shows that calibration uncertainty for crystalline silicon solar cells is 5% in maximum power with a 95.45% level of confidence. Recommendations for further versions of the solar simulator are given and show potential of reducing this uncertainty down to 2.9% across all measurement spectra (1.8% with a primary calibrated reference cell). A new method for automated power-rating of single- and multi-junction devices is developed. The method uses a unique spectral response measurement and fitting method. It eliminates the need of external measurement equipment for determining spectral response. A simulated characterisation of an amorphous silicon single- and double-junction solar cell show accuracy of better than 0.5% in maximum power. First measurements on the LED-based solar simulator show a measurement error of 4.5% in maximum power, which is due to a lack of measurement feedback of spectral output and measurement irradiance. The first three-dimensional performance matrix for use in photovoltaic energy rating is reported, utilising the LED-based solar simulator. Device characteristics are measured indoors under varying irradiance, temperature and spectrum. A measurement method is detailed and utilised on a crystalline and amorphous silicon solar cell. It allows for the first time a direct investigation of spectral effects on photovoltaic devices under controlled conditions. Results show that amorphous silicon devices are very sensitive to changes in spectrum. Thus, spectral effects should not be neglected in energy yield predictions for such devices.

Nearly 60 m tonnes of waste is produced annually in Europe from “plastic packaging” engendering significant challenges for legislative controls and minimisation of environmental impact. There is an increasing demand for biodegradable packaging, which can be disposed of with minimum environmental impact, but the growing market is still in its infancy predominantly due to a lack of materials having environmental, practical and economic suitability. This research project dealt with some processing challenges of environmentally friendly packaging materials from renewable resources, as a long term solution to mitigate some issues associated with oil based plastic packaging. In this work, novel Polylactic acid (PLA) and starch based composites were developed with the requisite technical properties to fill the gap in the food packaging and cosmetic packaging industry. It was found that starch can be incorporated in a PLA matrix at the 10% level without difficulty in processing in the presence of 2% methyldiphenyl diisocyante. The blend shows properties similar to pure PLA. It was also found that the elongation at break and impact properties of PLA can be increased remarkably by the addition of a biostrength impact modifier. Furthermore, mixing of PLA and starch in the blend is efficient when the PLA particle size is reduced. It was also found that flexible and tougher PLA/starch blend pellets, that can be injection moulded, can be produced by an extrusion process with a range of additives. Each additive has a maximum level that exhibits optimum properties. The blends also established that 15% starch can be incorporated into the PLA matrix to reduce the cost without any processing difficulties. Encouragingly, the presence of an impact modifier in the PLA/starch blends has shown more desirable properties. Furthermore, the mechanical properties of the pellets exposed to increased residence time in the injection moulding barrel and of the test specimens stored for 9 months at 21ºC were also satisfactory for the new blend. The overall results exhibited some attractive properties in the tri blend system, which can be easily adopted by the plastics industry for development of an injection moulded product within the scope of applications such as dry food packaging or cosmetic packaging. A further finding of this project is that biodegradation under a home composting environment can be improved by incorporating starch and certain other modifiers into PLA.