Sensorer kan användas för att uppmäta små partiklar som flyger omrking i luften och därmed skapa en bild av luftkvaliteten. Dessa sensorer sitter monterade på en så kallad sensornod. Sensornoder kan kopplas ihop för att skapa större sensornätverk. Problemet som tacklas i denna rapport är implementationen av stöd för en ny typ av sensor, Cubic PM2105, i en existerande sensornodsplatform. Utökat stöd för fler sensorer i ett sensornätverk breddar valmöjligheterna och möjliggör potentiellt att den bättre sensor kan användas. Vidare utvärderas även Cubic PM2105 i förhållande till en existerande sensor, Plantower PMS5003, i sensornodsplatformen. Detta görs genom korrelationsanalys baserat på mätdata de båda sensorerna samlat in vid samma tidpunkt och geografiska position. Resultatet visar på dålig korrelation mellan de två sensorerna. Dock kan detta resultat ifrågasattas då korrelationsanalysen baserades på relativt lite mätdata, samtidigt som endast en uppsättning sensorer användes. En teori för det dåliga resultatet är att fläkten på Cubic sensorn är svagare, och inte lyckas ta in tillräckligt med partiklar. Om detta beror på det specifika exemplaret eller andra orsaker är okänt. Med drivrutiner för Cubic PM2105 implementerat är det dock nu möjligt att utföra längre tester med fler uppsättningar sensorer för att på ett bättre sätt utvärdera korrelationen mellan sensorerna. / Sensors can be used to measure small particles in the air and hence create a picture of the air quality. These sensors are mounted on a so called sensor node. Sensor nodes can be connected to create a bigger sensor network. The problem being tackled in this report is the implementation of support for a new type of sensor, Cubic PM2105, in an existing sensor node platform. Extended support for more sensors in a sensor network widens the possibilities and enables the potential to use the better sensor. Further, Cubic PM2150 is evaluated in relation to a sensor already supported by the platform, Plantower PMS5003. This is done through correlation analysis based on the data collected from the both sensors simultaneously at the same location. The result shows poor correlation between the two sensors. However, this result can be questioned as the correlation analysis based on relatively little measurement data, while only one set of sensors was used. One theory for the poor result is that the fan in the Cubic sensor is weaker, and fails to take in a sufficient amount of particles. If this is a result of the specific pair of sensors used or due to other reasons is unknown. However, with drivers for Cubic PM2105 implemented, it is now possible to perform longer tests with more sets of sensors to better evaluate the correlation between the sensors.

The complex and coupled physical processes taking place in the atmosphere, ocean and land surface are described in Global Circulation Models (GCMs). These models have become the main tools to simulate climate variability and project future climate change. GCMs have the potential to give physically reliable estimates of climate change at global, continental or regional scales, but their projections are currently of too course horizontal resolution to capture the smaller scale features of climate and climate change. This situation stems from the fact that GCM simulations, which are effectively three-dimensional simulations of the coupled atmosphere-ocean-land system, are computationally extremely expensive. Therefore, downscaling techniques are utilised to do perform simulations over preselected areas that are of sufficiently detailed to represent the climate features at the meso-scale. Dynamic regional climate models (RCMs), based on the same laws of physics as GCMs but applied at high resolution over areas of interest, have become the main tools to project regional climate change. The research presented here utilises the Conformal-Cubic Atmospheric Model (CCAM), a variable-resolution global atmospheric model that can be applied in stretched-grid mode to function as a regional climate model. As is the case with RCMs, CCAM has the potential to improve climate simulations along rough topography and coastal areas when applied at high spatial resolution, whilst side-stepping the lateral boundary condition problems experienced by typical limited-area RCMs. CCAM has been developed by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia. The objective in the study is to test capability of a regional climate model, CCAM, to realistically simulate cumulus convection at different spatial scales over regions with steep topography, such as the eastern escarpment of South Africa. Since both GCMs and RCMs are known to have large biases and shortcomings in simulating rainfall over the steep eastern escarpment of southern Africa and in particular Lesotho, the paper “Model simulations of rainfall over southern Africa and its eastern escarpment” (Chapter 3) has a focus on verifying model performance over this region. In the paper the CCAM simulations include six 200 km resolution Atmospheric Model Intercomparison Project (AMIP) simulations that are forced with sea surface temperatures and one 50 km resolution National Centre for Environmental Prediction (NCEP) reanalysis simulation that is forced with sea surface temperatures and synoptic scale atmospheric forcings. These simulations are verified against rain gauge data sets and satellite rainfall estimates. The results reveal that at these resolutions the model is capable of simulating the key synoptic-scale features of southern African rainfall patterns. However, rainfall totals are often drastically overestimated. A key aspect of model performance is the representation of the diurnal cycle in convection. For the case of South Africa, the realistic representation of the complex patterns of rainfall over regions of steep topography is also of particular importance. At a larger spatial scale, the model also needs to be capable of representing the west-east rainfall gradient found over South Africa. The ability of CCAM to simulate the diurnal cycle in rainfall as well as the complex spatial patterns of rainfall over eastern South Africa is analysed in “High Resolution Rainfall Modelling over the Eastern Escarpment of South Africa” (Chapter 4). The simulations described in the paper have been performed at 8km resolutions in the horizontal and span a thirty-year long period. These are the highest resolution climate simulations obtained to date for the southern African region, and were obtained through the downscaling reanalysis data of the European Centre for Medium-range Weather Forecasting (ECMWF). The simulations provide a test of the robustness of the CCAM convective rainfall parameterisations when applied at high spatial resolution, in particular in representing the complex rainfall patterns of the eastern escarpment of South Africa. / M (Geography and Environmental Management), North-West University, Potchefstroom Campus, 2015

The complex and coupled physical processes taking place in the atmosphere, ocean and land surface are described in Global Circulation Models (GCMs). These models have become the main tools to simulate climate variability and project future climate change. GCMs have the potential to give physically reliable estimates of climate change at global, continental or regional scales, but their projections are currently of too course horizontal resolution to capture the smaller scale features of climate and climate change. This situation stems from the fact that GCM simulations, which are effectively three-dimensional simulations of the coupled atmosphere-ocean-land system, are computationally extremely expensive. Therefore, downscaling techniques are utilised to do perform simulations over preselected areas that are of sufficiently detailed to represent the climate features at the meso-scale. Dynamic regional climate models (RCMs), based on the same laws of physics as GCMs but applied at high resolution over areas of interest, have become the main tools to project regional climate change. The research presented here utilises the Conformal-Cubic Atmospheric Model (CCAM), a variable-resolution global atmospheric model that can be applied in stretched-grid mode to function as a regional climate model. As is the case with RCMs, CCAM has the potential to improve climate simulations along rough topography and coastal areas when applied at high spatial resolution, whilst side-stepping the lateral boundary condition problems experienced by typical limited-area RCMs. CCAM has been developed by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia. The objective in the study is to test capability of a regional climate model, CCAM, to realistically simulate cumulus convection at different spatial scales over regions with steep topography, such as the eastern escarpment of South Africa. Since both GCMs and RCMs are known to have large biases and shortcomings in simulating rainfall over the steep eastern escarpment of southern Africa and in particular Lesotho, the paper “Model simulations of rainfall over southern Africa and its eastern escarpment” (Chapter 3) has a focus on verifying model performance over this region. In the paper the CCAM simulations include six 200 km resolution Atmospheric Model Intercomparison Project (AMIP) simulations that are forced with sea surface temperatures and one 50 km resolution National Centre for Environmental Prediction (NCEP) reanalysis simulation that is forced with sea surface temperatures and synoptic scale atmospheric forcings. These simulations are verified against rain gauge data sets and satellite rainfall estimates. The results reveal that at these resolutions the model is capable of simulating the key synoptic-scale features of southern African rainfall patterns. However, rainfall totals are often drastically overestimated. A key aspect of model performance is the representation of the diurnal cycle in convection. For the case of South Africa, the realistic representation of the complex patterns of rainfall over regions of steep topography is also of particular importance. At a larger spatial scale, the model also needs to be capable of representing the west-east rainfall gradient found over South Africa. The ability of CCAM to simulate the diurnal cycle in rainfall as well as the complex spatial patterns of rainfall over eastern South Africa is analysed in “High Resolution Rainfall Modelling over the Eastern Escarpment of South Africa” (Chapter 4). The simulations described in the paper have been performed at 8km resolutions in the horizontal and span a thirty-year long period. These are the highest resolution climate simulations obtained to date for the southern African region, and were obtained through the downscaling reanalysis data of the European Centre for Medium-range Weather Forecasting (ECMWF). The simulations provide a test of the robustness of the CCAM convective rainfall parameterisations when applied at high spatial resolution, in particular in representing the complex rainfall patterns of the eastern escarpment of South Africa. / M (Geography and Environmental Management), North-West University, Potchefstroom Campus, 2015

Negative Poisson’s ratio, or auxetic, materials present the possibility of designing structures and components with tailored or enhanced mechanical properties. This thesis explores the phenomenon of auxetic behaviour in cubic crystals using classical and quantum modelling techniques and assesses the validity of these techniques when predicting auxetic behaviour in cubic elemental metals. These techniques are then used to explore the mechanism of this behaviour. The findings of the atomistic modelling are then used as a template to create networks of bending beams with tailored Poisson’s ratio behaviour.

Electrochemical Impedance Spectroscopy (EIS) was used to develop a novel methodology for studying ionic interaction with lipids arranged in a lipid cubic phase (LCP). Studying different types of ions, both cations and anions, validated the method. A free-standing LCP membrane was formed between two cell compartments and impedance experiments were carried out in a 2-electrode setup to estimate dielectric properties of the membrane, exposed to the following electrolyte solutions at different concentrations: KCl, CsBr, CaCl2, MgCl2, CsCl, NaCl, NaOAc and NaTryptophan. Two different LCP were used in this setup, i.e: Monoloein/water and the ternary system of monoolein/dioleoylphosphatidylcholine/water (MO/DOPC/H2O). SAXRD measurements were performed to determine the space group of the cubic phase and confirm the stability of the LCP during measurements. Membrane resistances and capacitances were found from equivalent circuit fitting to the impedance data. The membrane resistance was shown to be related to ionic interaction with the lipid head group in the water channels of the LCP. Membrane capacitance were correlating to condensing and swelling effect of LCP due to the exposure of ions. The results correlated well with the SAXRD results and earlier published data. The results also indicate that these membranes become less permeable to ions as they increase in size as well as in charge or polarity.  Cyclic voltammetry was used to study the applications of a LCP for modification of the bioanode in a biofuel cell. The monoolein cubic phase was used to host Glucose oxidase (GOx) and a freely diffusing ferrocene carboxylate was used as mediator. The supported cubic phase had an intrinsic resistance in the same order of magnitude as the freestanding MO-LCP membrane as measured with EIS. / Elektrokemisk impedans spektroskopi har använts för att utveckla en ny metod för att studera joners växelverkan med lipider som bildat en kubisk fas. Olika typer av joner, både positiva och negativa, användes för att validera metoden. Ett fristående membran uppbyggt av en kubisk fas separerade två avdelningar i en elektrokemisk cell. Cellen fylldes med elektrolyt-lösningar och impedansmätningar kunde utföras mellan två platina elektroder placerade i vardera avdelning. Membranet exponerades för följande elektrolytlösningar av olika koncentration: KCl, CsBr, CaCl2, MgCl2, CsCl, NaCl, NaOAc and NaTryptofan. Två olika kubiska faser användes i denna uppställning, dvs: Monoloein/vatten och det ternära systemet monoolein/dioleoylfosfatidylkolin/vatten(MO/DOPC/H2O). Med hjälp av SAXRD kunde den kubiska fasens kristallstruktur bestämmas och dess stabilitet under mätningarna bekräftas. De dielektriska egenskaperna hos membranet bestämdes genom att anpassa impedansspektrat till en ekvivalent krets bestående av resistanser, kapacitanser och konstant-faselement. Membranresistansen visade sig vara relaterad till jonernas växelverkan med lipidhuvudgruppen i vattenkanalerna i kubiska fasen. Ju starkare växelverkan desto högre var resistansen. Membrankapacitansen kunde korreleras med kondenserande och uppsvällande effekter på kubiska fasen förorsakade av exponeringen till joner. Resultaten bekräftades av SAXRD mätningar och även tidigare publicerade data. Resultaten indikerar också tydligt att permeabiliteten hos membranet minskar med ökad jonstorlek, jonladdningoch polaritet hos jonen. Cyklisk voltammetri användes för att studera en tillämpning av kubiska fasen i en tänkt applikation som bioanod i en biobränslecell. Elektroden modifierades med en kubisk fas innehållande GOx och tillsammans med en fritt diffunderande ferrocen karboxylat som mediator, där oxidation av glukos studeras. Det visade sig att den kubiska fasen hade en resistans av samma storleksordning som det fristående membranet uppmätt med impedansspektroskopi.

The “infrastructure” of quadratic fields is a body of theory developed by Dan Shanks, Richard Mollin and others, in which they relate “reduced ideals” in the rings and sub-rings of integers in quadratic fields with periodicity in continued fraction expansions of quadratic numbers. In this thesis, we develop cubic analogs for several infrastructure theorems. We work in the field K=Q(), where 3=m for some square-free integer m, not congruent to ±1, modulo 9. First, we generalize the definition of a reduced ideal so that it applies to K, or to any number field. Then we show that K has only finitely many reduced ideals, and provide an algorithm for listing them. Next, we define a sequence based on the number alpha that is periodic and corresponds to the finite set of reduced principal ideals in K. Using this rudimentary infrastructure, we are able to establish results about fundamental units and reduced ideals for some classes of pure cubic fields. We also introduce an application to Diophantine approximation, in which we present a 2-dimensional analog of the Lagrange value of a badly approximable number, and calculate some examples.

Crystallographic texture in polycrystalline HCP and cubic materials, often developed during thermomechanical deformations, has profound effects on properties at the macroscopic or component level. Given the respective natures of current detection techniques, a non-destructive, three-dimensional bulk texture detection method for these materials has not yet been developed. This thesis aims to achieve this goal through systematic studies on the relationship between ultrasonic wave velocity and texture. The feasibility of such development is firstly reviewed via the combination of computational and experimental studies on exemplary HCP materials. Numerical results obtained via a representative volume element (RVE) methodology reveal that the wave speed varies progressively and significantly with changing texture, and experimental ultrasound studies combined with EBSD characterisation demonstrate distinguished velocity profiles for samples with different textures. Thus the possibility of the development is demonstrated from these combined results. A novel convolution theorem is then presented, which couples the single crystal wave speed (the kernel function) with polycrystal orientation distribution function to give the resultant polycrystal wave speed function. Firstly developed on HCP and then successfully extended to general anisotropic materials, the theorem expresses the three functions as harmonic expansions thus enabling the calculation of any one of them when the other two are known. Hence, the forward problem of determination of polycrystal wave speed is solved for all crystal systems with verifications on varying textures showing near-perfect representation of the sensitivity of wave speed to texture as well as quantitative predictions of polycrystal wave speed. More importantly, the theorem also presents a solution to the long-standing inverse problem for HCP and cubic materials, with proof of principle established where groups of HCP and cubic textures are recovered solely from polycrystal wave velocities through the theorem and the results show good agreements with the original textures. Therefore the theorem opens up the possibility of developing a powerful technique for bulk texture measurement and wave propagation studies in HCP, cubic materials and beyond.

Esta tese está dirigida ao estudo das propriedades elétricas e ópticas das camadas cúbicas de InN, GaN (intrínseco), GaN:Si (tipo-p), GaN:Si (tipo-n) e AlGaN. Por meio da técnica de efeito Hall e utilizando a configuração de Van der Pauw foram obtidas as curvas de resistividade, concentração e mobilidade em função da temperatura das camadas e através destas curvas é determinada a energia de ativação dos aceitadores e doadores. Também através das mesmas curvas são estudados os principais mecanismos que predominam no espalhamento dos portadores. Em alguns casos um comportamento anômalo foi observado (curvas de concentração e mobilidade do InN e GaN:Si (tipo-p)) e os resultados foram corrigidos utilizando-se o modelo de duas camadas e/ou modelo de duas bandas. Para o material c-InN medimos sua resistividade, concentração e mobilidade na região de baixas temperaturas para investigar um possível caráter supercondutor da amostra. Abordaremos também nesta tese o estudo teórico e experimental sobre a transição metal-semicondutor nos nitretos. Para o estudo das propriedades ópticas das camadas foi utilizada a técnica de caracterização de Raman. Por meio desta técnica e utilizando a configuração de retro espalhamento foram caracterizadas as camadas cúbicas de GaN (intrínseco), GaN:Si (tipo-p), GaN:Si (tipo-n) e AlGaN. Dos espectros, foram obtidas as posições dos picos pertencentes aos fônons transversal-ópticos (TO) e longitudinal-ópticos (LO). Verificou-se o caráter cúbico das camadas e estudou-se a origem da banda que aparece entre as posições dos modos TO e LO do material. / The thesis is devoted to the study of electrical and optical properties of cubic InN, GaN (undoped), GaN:Si (type-p), GaN:Si (type-n) and AlGaN epitaxial films. For the study of the electrical properties were measured the resistivity, concentration and mobility curves as a function of the temperature by means of Hall effect and Van der Pauw configuration technique. From these curves were obtained the activation energy of donor and acceptors levels and were studied the main dominant mechanisms for the electron scattering. In some cases an anomalous behavior of the curves was observed and was corrected using the two layer model. For the study of the superconductivity character of the cubic InN sample was measured its resistivity, concentration and mobility in the low temperature region. The thesis is also devoted to the theoretical and experimental studies of the metal-non-metal transitions in the nitrites.The optical studies of the GaN (undoped), GaN:Si (type-p), GaN:Si (type-n) and AlGaN films were done by means of Raman characterization according to a backscattering configuration. From the spectra were obtained the position of the TO and LO phonon peaks, was verified the cubic character of the films and was studied the behavior of the band found between the TO and LO phonon peaks.

Superfícies funcionais dependem do controle das características das superfícies de um material para obter-se um desempenho funcional desejado. Essas superfícies têm importância em diversas áreas na engenharia, como: eletrônica, ótica, energia e tribologia. No campo da tribologia, uma aplicação é em virabrequins. A funcionalização da superfície adiciona micro cavidades que diminuem o atrito e aumentam as forças de sustentação do virabrequim. Para isso, essas cavidades possuem uma geometria específica, uma microrampa. Devido a essa forma especial, a fabricação dessas microrampas é complexa, já tendo sido alcançada empregando a metodologia de texturização com rebolos padronizados. Essa metodologia consiste na inscrição de padrões geométricos no rebolo durante a dressagem, posteriormente transferidos para a peça. Como a indústria moderna utiliza rebolos de CBN de ligante vitrificado para a retificação de virabrequins, a metodologia de texturização supracitada deve ser aplicável a esse ferramental. Esse trabalho descreve o desenvolvimento de uma unidade de dressagem capaz de inscrever padrões geométricos em rebolos de CBN vitrificados, sendo seu projeto baseado em análise modal. O trabalho apresenta as restrições de projeto, conceitos de solução, simulações dinâmicas e modelagem do processo de texturização. Para maximizar a resposta dinâmica, a unidade foi projetada para operar próxima de sua frequência natural. A unidade projetada é capaz de inscrever padrões geométricos no rebolo utilizando um disco dressador rotativo, e as texturas das peças produzidas com esse rebolo padronizado apresentam boa precisão geométrica para a aplicação em virabrequins. / Engineered surfaces rely on the control of the surface characteristics of a material to achieve a desired functional performance. These functional surfaces are important in several areas of engineering, such as: electronics, optics, energy and tribology. On tribology field, an application is in crankshafts. The surface functionalization is achieved by adding micro-cavities that reduce friction and increase crankshaft lift forces. These cavities have a specific geometry, called microramp. Due to this special geometry, manufacturing microramps is a complex process, having been achieved using the methodology of texturizing via grinding. This methodology consists in the inscription of geometric patterns in the grinding wheel during the dressing operation, later transferred to the piece. As the modern industry uses vitrified CBN grinding wheels for crankshaft grinding, the texturing methodology should be applicable to this tool. This work describes the development of a dressing unit capable of inscribing geometric patterns in vitrified CBN grinding wheels, having its design based on modal analysis. The work presents the design constraints, solution concepts, dynamic simulations and modeling of the texturing process. To maximize dynamic response, the unit is designed to operate near its natural frequency. The designed unit can inscribe geometric patterns on the grinding wheel using a rotating dressing disc, and the textures of the parts produced have good geometric precision for crankshaft applications.

Superfícies funcionais dependem do controle das características das superfícies de um material para obter-se um desempenho funcional desejado. Essas superfícies têm importância em diversas áreas na engenharia, como: eletrônica, ótica, energia e tribologia. No campo da tribologia, uma aplicação é em virabrequins. A funcionalização da superfície adiciona micro cavidades que diminuem o atrito e aumentam as forças de sustentação do virabrequim. Para isso, essas cavidades possuem uma geometria específica, uma microrampa. Devido a essa forma especial, a fabricação dessas microrampas é complexa, já tendo sido alcançada empregando a metodologia de texturização com rebolos padronizados. Essa metodologia consiste na inscrição de padrões geométricos no rebolo durante a dressagem, posteriormente transferidos para a peça. Como a indústria moderna utiliza rebolos de CBN de ligante vitrificado para a retificação de virabrequins, a metodologia de texturização supracitada deve ser aplicável a esse ferramental. Esse trabalho descreve o desenvolvimento de uma unidade de dressagem capaz de inscrever padrões geométricos em rebolos de CBN vitrificados, sendo seu projeto baseado em análise modal. O trabalho apresenta as restrições de projeto, conceitos de solução, simulações dinâmicas e modelagem do processo de texturização. Para maximizar a resposta dinâmica, a unidade foi projetada para operar próxima de sua frequência natural. A unidade projetada é capaz de inscrever padrões geométricos no rebolo utilizando um disco dressador rotativo, e as texturas das peças produzidas com esse rebolo padronizado apresentam boa precisão geométrica para a aplicação em virabrequins. / Engineered surfaces rely on the control of the surface characteristics of a material to achieve a desired functional performance. These functional surfaces are important in several areas of engineering, such as: electronics, optics, energy and tribology. On tribology field, an application is in crankshafts. The surface functionalization is achieved by adding micro-cavities that reduce friction and increase crankshaft lift forces. These cavities have a specific geometry, called microramp. Due to this special geometry, manufacturing microramps is a complex process, having been achieved using the methodology of texturizing via grinding. This methodology consists in the inscription of geometric patterns in the grinding wheel during the dressing operation, later transferred to the piece. As the modern industry uses vitrified CBN grinding wheels for crankshaft grinding, the texturing methodology should be applicable to this tool. This work describes the development of a dressing unit capable of inscribing geometric patterns in vitrified CBN grinding wheels, having its design based on modal analysis. The work presents the design constraints, solution concepts, dynamic simulations and modeling of the texturing process. To maximize dynamic response, the unit is designed to operate near its natural frequency. The designed unit can inscribe geometric patterns on the grinding wheel using a rotating dressing disc, and the textures of the parts produced have good geometric precision for crankshaft applications.