Improved soil water conservation has become an important subject in semi-arid areas due to low and erratic rainfall which is often combined with higher temperatures to provide unsuitable conditions for successful crop productivity. Dryland agriculture remains vulnerable to yield losses in these areas. This calls for implementation of conservation agricultural practices that would improve dryland maize productivity. An on-station field trial was started in 2007 at Zeekoegat experimental farm (24 kilometers north of Pretoria), to establish the effect of different conservation agriculture practices on soil and plant properties. The experimental lay-out was a split-plot randomized complete block design, replicated three times, with each replicate split into two tillage systems (whole plots) and then each whole plot (reduced tillage (RT) and conventional tillage (CT)) was subdivided into 12 treatments (two fertilizer levels x 6 cropping patterns). The present study explored the impacts of different tillage practices, cropping patterns and fertilization levels on soil water content, soil temperature and dryland maize productivity during the 2010/11 and 2011/12 growing seasons. To improve the quality of soil water content (SWC) data, the effect of correction for concretions on soil bulk density and the relationship between volumetric soil water content (SWC) vs neutron water meter (NWM) count ratios was also investigated. Corrections for concretions on soil bulk density did not improve NWM calibrations in this study. In all seasons, significantly higher mean SWC was found under RT treatment than in CT at all depths except at 0-300 mm. For example, during the 2010/11 growing season, SWC under RT was 1.32 % and 1.10 % higher than CT for the 300 – 1350 mm and 0 – 1350 mm soil profiles, respectively. The mean weekly SWC was consistently higher for RT throughout both the growing seasons. Significantly higher SWC was also found under monoculture at all soil depths (except at 0-300 mm during 2011/12) compared to treatments under intercropping. For example, during 2010/11, at 0-300mm, SWC under maize monoculture was 1.72 % higher than under intercropping. The maximum and minimum soil temperatures were significantly higher at 100 and 400 mm soil depths under CT than under RT during 2010/11. During 2011/12, significantly higher minimum soil temperatures at 100 mm depth and lower temperature differences (maximum – minimum soil temperatures) at 400 mm depth were observed under intercropping. Despite the higher SWC and reduced soil temperature under RT, the maize seeds emergence rate was lower and plant stand was reduced. This is attributed to other factors associated with RT systems such as increased soil penetration resistance which often leads to poor root development. The lower soil temperatures under RT were generally within the range that would not be expected to inhibit growth and uptake of nutrients. Slower growth under RT resulted in lower biomass and grain yield. Plants that received high fertilizer rates grew more vigorously than plants under lower fertilizer levels when water was not a limiting factor, but produced lower grain yield due to water shortage in March, especially in 2011/12. The harvest index was therefore lower for treatments that received high fertilizer levels. Maize biomass under monoculture x low fertilizer level was significantly lower compared to other fertilizer x cropping pattern treatments. Maize plant growth under intercropping was improved throughout the seasons, which led to significantly higher grain yield than under maize monoculture. It is therefore recommended that farmers in dryland areas take the advantage of intercropping maize with legumes to obtain higher maize productivity. Further research should focus on investigating the possibility of roots restrictions occurring under RT conditions and under various environmental and soil conditions. / Dissertation (MScAgric)--University of Pretoria, 2014. / lk2014 / Plant Production and Soil Science / MScAgric / Unrestricted

Il y a des nombreuses méthodes capables de produire des modèles numériques très précis des systèmes électromagnétiques. Si la précision demandée est très importante ou la nature du phénomène modélisé est très complexe, il faudra résoudre un nombre élevé d’équations. Si le modèle est utilisé dans des applications où de nombreux paramètres doit être prises en compte, comme c’est le cas de la conception optimale, la résolution de ces équations est souvent très couteuse.Pour éviter ce calcul, des algorithmes de réduction de modèle ont été développés. Il s’agit de procédures permettant de trouver des modèles réduits qui représentent la relation entrée/sortie du modèle fin de manière très précise mais en utilisant un nombre réduit d’équations.Dans cette thèse, les techniques de réduction de modèles sont analysées et améliorées. Une attention particulière est faite à la technique de correspondance des moments. Les problèmes de placement des points d’expansion, de stabilité et de précision sont plus particulièrement étudiés. Cela a permit la simulation et conception optimale de modèles électromagnétiques complexes qu’un jeu de bus bar et un problème de diffusion d’ondes.De plus, nous avons développé une méthode d'échantillonnage adaptatif. Des algorithmes classiques d’optimisation ont été couplés aux modèles réduits permettant l’accélération des calculs. Les méthodes proposées ont été testés dans des problèmes électromagnétiques obtenus par la méthode « Partial Equivalent Circuit Element (PEEC) ». / There are many available methods capable of producing High-Fidelity Models (HFM) of electromagnetic systems. If the required precision is very high or the nature of the phenomenon that is being modeled is complex, a very large number of equations may have to be solved. If the model is used for applications where many different geometries or parameters must be considered, as is the case in design optimization, solving these equations many times can be very time consuming.To avoid the burden of this computation, Model Order Reduction (MOR) algorithms have been developed. They consist in procedures of finding Reduced Order Models (ROMs) that accurately describe the input/output behavior of the High-Fidelity Model but using only a very small number of equations.In this work, MORs techniques are analyzed and improved. Special attention is paid to Moment Matching. Problems like placement of expansion points, stability and numerical robustness are investigated. This has allowed the simulation and optimization of complex electromagnetic device. As examples of application we have presented a laminates bus bar and a wave scattering problem.In addition to that, a smart adaptive way of sampling the design space to allow fast optimization has been developed. The sampled points are used to perform interpolation and approximate the objective function in a very fast manner. Classic optimization techniques have also been coupled with the Reduced Order Models, accelerating the computations. The proposed approaches have been tested mainly in electromagnetic problems obtained by the Partial Equivalent Circuit Element (PEEC) method.

Water splitting through photoelectrochemical reaction is widely regarded as a major method to generate H2 , a promising source of renewable energy to deal with the energy crisis faced up to human being. Efficient exploitation of visible light in practice of water splitting with pure TiO2 material, one of the most popular semiconductor material used for photoelectrochemical water splitting, is still challenging. One dimensional TiO2 nanotubes is highly desired with its less recombination with the short distance for charge carrier diffusion and light-scattering properties. This work is based on TiO2 NTPC electrode by the optimized two-step anodization method from our group. A highly crystalized p-type Cu2O layer was deposited by optimized pulse potentiostatic electrochemical deposition onto TiO2 nanotubes to enhance the visible light absorption of a pure p-type TiO2 substrate and to build a p-n junction at the interface to improve the PEC performance. However, because of the real photocurrent of Cu2O is far away from its theoretical limit and also poor stability in the aqueous environment, a design of rGO medium layer was added between TiO2 nanotube and Cu2O layer to enhance the photogenerated electrons and holes separation, extend charge carrier diffusion length (in comparison with those of conventional pure TiO2 or Cu2O materials) which could significantly increase photocurrent to 0.65 mA/cm2 under visible light illumination (>420 nm) and also largely improve the stability of Cu2O layer, finally lead to an enhancement of water splitting performance.

Detonation is a supersonic mode of combustion that is modeled by a system of conservation laws of compressible fluid mechanics coupled with the equations describing thermodynamic and chemical properties of the fluid. Mathematically, these governing equations admit steady-state travelling-wave solutions consisting of a leading shock wave followed by a reaction zone. However, such solutions are often unstable to perturbations and rarely observed in laboratory experiments. The goal of this work is to study the stability of travelling-wave solutions of detonation models by the following novel approach. We linearize the governing equations about a base travelling-wave solution and solve the resultant linearized problem using high-order numerical methods. The results of these computations are postprocessed using dynamic mode decomposition to extract growth rates and frequencies of the perturbations and predict stability of travelling-wave solutions to infinitesimal perturbations. We apply this approach to two models based on the reactive Euler equations for perfect gases. For the first model with a one-step reaction mechanism, we find agreement of our results with the results of normal-mode analysis. For the second model with a two-step mechanism, we find that both types of admissible travelling-wave solutions exhibit the same stability spectra. Then we investigate the Fickett’s detonation analogue coupled with a particular reaction-rate expression. In addition to the linear stability analysis of this model, we demonstrate that it exhibits rich nonlinear dynamics with multiple bifurcations and chaotic behavior.

Gasoline compression ignition (GCI) engines show promise in meeting stringent new environmental regulations, as they are characterized by high efficiency and low emissions. Simulations using chemical kinetic models provide an important platform for investigating the behaviors of the fuels inside these engines. However, because real fuels are complex, simulations require surrogate mixtures of small numbers of species that can replicate the properties of real fuels. Accordingly, the development of high fidelity, well-validated kinetic models for surrogates is critical in order to accurately replicate the combustion chemistry of different fuels under engine-related conditions. This work focuses on the development of combustion kinetic models to better understand gasoline fuel combustion in GCI engines. An updated iso-octane detailed kinetic model was developed based on new thermodynamic group values and recently evaluated rate coefficients from literature. The model was validated against a wide range of experimental data and conditions. The iso-octane model was further used in 0D simulations for a homogeneous charge compression ignition (HCCI) engine. The results showed that the low-temperature heat release in engines increases with engine boosting when the addition of alky radicals to molecular oxygen is more favored. Ethanol addition was also found to act as a radical sink which inhibits the radical pool formation and results in lower reactivity. Although detailed models provide clarification of the combustion chemistry, their high computational cost impedes their utilization in 3-D engine simulations. Hence, a reduced model for toluene primary reference fuels was developed and validated against ignition delay time and flame speed experiments from literature. The model was then used in numerically investigating the effects of the fuel’s physical properties using hollow-cone and multi-hole injectors in a partially premixed compression ignition (PPCI) engine. It was concluded that the effects of physical properties are evident in multi-hole injection cases, which is attributable to the differences in mixture stratification. Finally, reduced models for multi-components surrogates for three full-blend fuels (light naphtha-Haltermann straight-run naphtha and GCI fuels) were developed. The models were validated against ignition delay time experiments from the literature and tested in 3D engine simulations.

<div>Vacuum is needed in many applications and, there are many types of pumps that can provide the vacuum level needed. One widely used pump is the liquid-ring vacuum pump, which does not involve any solid-solid contacts at interfaces where moving and stationary parts meet. Though liquid-ring vacuum pumps are efficient and robust, manufacturers have aggressive goals on improving efficiency, performance, and range of operations.</div><div> </div><div> In this research, time-accurate computational fluid dynamic (CFD) analyses were performed to study the flow mechanisms in a liquid-ring vacuum pump to understand how it works and how the design can be improved. Based on the understanding gained, a physics based reduced order model was developed for preliminary design of the liquid ring vacuum pumps.</div><div> </div><div> In the CFD analyses, the liquid (water) was modeled as incompressible, the gas (air) as an ideal gas, and turbulence by the shear-stress transport model. The gas-liquid interface was resolved by using the volume-of-fluid method, and rotation of the impeller was enabled by using a sliding mesh. Parameters examined include the suction pressure (75, 300, and 600 Torr) and the impeller's rotational speed (1150, 1450 and 1750 rpm) with the temperature of the gas at the inlet of the suction chamber kept at 300 K and the pressure at the outlet of the exhaust chamber kept at one atmosphere. The CFD solutions generated were verified via a grid sensitivity study and validated by comparing with experimental data. When compared with experiments, results obtained for the flow rate of the gas ingested by the pump had relative errors less than 6\% and results obtained for the power consumed by the pump had relative errors less than 13\%.</div><div> </div><div> Results obtained show the shape of the liquid ring to play a dominant role in creating the expansion ratio or the vacuum needed to draw air into the pump through the suction port and the compression ratio needed to expel the air through the discharge ports. Results were generated to show how centrifugal force from rotation and how acceleration/deceleration from the difference in pressure at the pump's inlet and outlet along with the eccentricity of the impeller relative to the pump's housing affect the shape of the liquid ring. Results were also generated to show how the rotational speed of the impeller and the pressure at the suction port affect the nature of the gas and liquid flow in the pump and the pump’s effectiveness in creating a vacuum. </div><div> </div><div> With the knowledge gained from the CFD study, a physics-based reduced-order model was developed to predict air ingested and power consumed by the pump as well as the liquid ring shape and pressure of the gas and liquid in the pump as a function of design and operating parameters. This model was developed by recognising and demonstrating that the amount of air ingested and power consumed by the pump is strongly dependent on the shape and location of the liquid ring surface. The flow rates of the gas ingested by the pump and the power consumed by the pump predicted by the model were compared with experimental data and relative errors were less than 12\% and 17\% respectively.</div>

The purpose of this study was to develop a robust fluid-structure-interaction (FSI) technology that can accurately model non-linear flutter responses for sub- and transonic fluid flow. The Euler equation set governs the fluid domain, which was spatially discretised by a vertex-centred edge-based finite volume method. A dual-timestepping method was employed for the purpose of temporal discretisation. Three upwind schemes were compared in terms of accuracy, efficiency and robustness, viz. Roe, HLLC (Harten-Lax-Van Leer with contact) and AUSM+-up Advection Up-stream Splitting Method). For this purpose, a second order unstructured MUSCL (Monotonic Upstream-centred Scheme for Conservation Laws) scheme, with van Albada limiter, was employed. The non-linear solid domain was resolved by a quadratic modal reduced order model (ROM), which was compared to a semi-analytical and linear modal ROM. The ROM equations were solved by a fourth order Runge-Kutta method. The fluid and solid were strongly coupled in a partitioned fashion with the information being passed at solver sub-iteration level. The developed FSI technology was verified and validated by applying it to test cases found in literature. It was demonstrated that accurate results may be obtained, with the HLLC upwind scheme offering the best balance between accuracy and robustness. Further, the quadratic ROM offered significantly improved accuracy when compared to the linear method. / Dissertation (MEng)--University of Pretoria, 2011. / Mechanical and Aeronautical Engineering / unrestricted

Kontanter har använts i flera århundranden och är ett sedvanligt betalningsmedel mellan privatpersoner och på inköpsstället. I takt med teknikens framfart har alltfler betalningsmedel utvecklats och anpassats till marknaden. Idag sker cirka 70 procent av alla köp i butik med kort. Detta gör att kontanternas användning plötsligt ifrågasätts och därmed väljer majoriteten av Sveriges storbanker att succesivt avveckla den manuella kontanthanteringen. Tanken är att försöka lära konsumenter och företag att använda alternativa lösningar som utgör substitut till kontanter. Dock beror efterfrågan på kontanter utav en demografisk utveckling. Kontantanvändningen är högre bland äldre och de har också format sina vanor under längre tid. För andra grupper såsom landsbygdsföretag, funktionshindrade, papperslösa och turister är kontanter essentiella, vilket gör att de hamnat i kläm vid avvecklandet. Andra har personliga preferenser till kontanters nytta såsom integritet, förtroende, tid, vana eller andra värderingar. Problemet blir således en demokratisk fråga där alla skall ha rätt till grundläggande betaltjänster. Studiens syfte är därför att förstå denna process och vilka effekter som uppstår när de flesta storbanker väljer att avveckla den manuella kontanthanteringen. Syftet har delats in i tre huvudproblem:      Vems ansvar är det när en av de grundläggande betaltjänsterna försvinner i samhället?      Vilka blir konsekvenserna med en minskad kontanthantering?      Vilka alternativa lösningar finns det för problemen? Sammanfattningsvis kom studien fram till att bankernas avveckling av kontanthantering har skett snabbare än nya lösningar har introducerats i samhället. Effekterna av denna avveckling har medfört problem för flera grupper. Resultaten visar även att bankerna kunde ha effektiviserat och avgiftsbelagt kontanter innan avvecklingen skedde. / Cash has been used for centuries and is a customary mean of payment between individuals and on the place of purchase. As technology progresses, a growing number of different payment services has developed and been adapted to the market. Today, approximately 70 percentages of all purchases in the stores is made by card. This has suddenly challenged the use of cash and therefore the majority of Sweden’s major banks have chosen to gradually phase out the manual cash management. The idea is to try to get consumers and businesses to use alternative solutions, which are substitutes for cash. However, the demand for cash depends on demographical conditions. The use of cash is more frequent among eldest and they have also shaped their habits over a longer time. For other groups, such as small firms on the countryside, disabled, undocumented migrants and tourists, cash is essential, so they are left in a jam. Others have personal preferences related to the use of cash such as integrity, trust, time, habits, or other values. Everyone is entitled to basic payment services, thus becomes the problem a question of democracy. The purpose of the study is to understand this process and to be aware of the effects that arise when most of the major banks will interrupt their manual cash management. The purpose has been divided into three main parts:  Whose responsibility is it when one of the basic payment services disappears in the society?  What are the consequences when there is a reduction of cash?  What are the alternative solutions? Overall, the study concluded that the banks' reduction of cash has been faster than the introductions of new solutions have been introduced into society. The effect of this decision has caused problems for several groups. The results of the study show that the banks could have improved the efficiency and they could also have introduced a fee on cash before the settlement was made.

Fluid-structure interactions appear in many industrial applications in the field of energy technology. As the components are more and more pushed to higher performance, taking fluid-structure interaction phenomena into account has a great impact on the design as well as in the cost and safety. Internal flows related to propulsion systems in aerodynamics area are of our interest; and particularly aeroelasticity and flutter phenomena. A new 2D flexible generic model, so called bump, based on previous studies at the division of Heat and Power Technology about fluid-structure interactions is here presented. The overall goal is to enhance comprehension of flutter phenomenon. The current study exposes a preliminary experimental campaign regarding mechanical behaviour on two different test objects: an existing one made of polyurethane and a new one of aluminium. The setup is built in such a way that it allows the bumps to oscillate until 500Hz. The objective is to reach this frequency range by remaining in the first bending mode shape which is indeed considered as fundamental for flutter study. In this manner being as close as possible to the bending flutter configuration in high-subsonic and transonic flows will provide a deeper understanding of the shock wave boundary layer interaction and the force phase angle related to it. The results have pointed out that the bumps can reach a frequency of 250Hz by remaining in the first bending mode shape. The one in polyurethane can even reach frequency up to 350Hz; however, amplitude is higher than the theoretical one fixed to 0.5mm. Then unsteady pressure measurements for one operating point have been performed based on using recessed-mounted pressure transducers with Kulite fast response sensors. Variation amplitudes and phases of the unsteady pressure are thus correlated with the vibrations of the model. The operating point has been defined with respect to previous studies on the same static geometric model in order to use steady state base line; the steady flows appear consistent with each other. The results have pointed out that the shock wave induces strong amplification of the steady static pressure; however, this rise decreases when the reduced frequency increases. Finally some elements regarding propagating waves are suggested in the analysis for deeper investigations on such complex phenomena.

Objetivo: Comparar el riesgo de caries dental utilizando dos herramientas de evaluación en niños de 7 a 11 años que asisten a la Institución Educativa Policía Nacional del Perú Juan Ingunza Valdivia en el año 2019 en el distrito del Callao-Perú. Materiales y Métodos: El grupo de estudio estuvo conformado por 265 niños entre 7 a 11 años de edad, las herramientas utilizadas para comparar el riesgo de caries dental fueron: Cariograma Reducido el cual evalúo experiencia de caries, consumo y frecuencia de la dieta, flúor, presencia de enfermedad, higiene oral y dictamen clínico. Por otro lado, la herramienta Riesgo Biológico de Caries evaluó la experiencia de caries, higiene oral y diario dietético. El exámen clínico se realizó en un solo tiempo para ambas herramientas, evaluando la higiene oral según Greene y Vermillion y la experiencia de caries con el índice CPOD y ceod. Resultados: Se determinaron los datos sociodemográficos, identificándose mayor población en el género femenino con 58.11%, la edad de 9 años predominó con 33.96% y en cuanto al nivel socioeconómico la clase D predominó con 67.55%. Por otro lado, cuando se determinó el riesgo de caries dental utilizando la herramienta Cariograma Reducido según los datos sociodemográficos, se identificó que existen diferencias significativas entre la edad y nivel socioeconómico, mientras que no existe diferencia en relación al género. (p= 0.372). Al determinar el riesgo de caries con la herramienta Riesgo Biológico de Caries con los datos sociodemográficos, se encontró que existen diferencias significativas entre la edad y nivel socioeconómico con el uso de esta herramienta, pero no existe diferencia en relación al género. (p= 0.777). El análisis estadístico univariado se realizó mediante la estadística descriptiva (frecuencia relativa y absoluta) y el análisis bivariado mediante la prueba Chi- cuadrado de Pearson para comparar el riesgo de caries con ambas herramientas. Conclusión: Existen diferencias estadísticamente significativas entre las herramientas Cariograma Reducido y Riesgo Biológico de Caries en los diagnósticos de riesgo de caries en sus niveles moderado y alto. (p < 0.001). / Objective: Compare the risk of dental caries using two assessment tools in children from 7 to 11 years old who attend the Juan Ingunza Valdivia National Police Educational Institution in 2019 in the Callao district -Perú. Materials and Methods: The study group consisted of 265 children between 7 to 11 years of age, the tools used to compare the risk of dental caries were: Reduced Cariogram which evaluated the experience of caries, consumption and frequency of diet, fluoride, presence of disease, oral hygiene and clinical opinion. On the other hand, the Biological Caries Risk tool evaluated the experience of caries, oral hygiene and dietary diary. The clinical examination was performed in a single time for both tools, evaluating oral hygiene according to Greene and Vermillion and the experience of caries with the CPOD and ceod index. Results: Sociodemographic data were determined, identifying a greater female population with 58.11%, the age of 9 years prevailed with 33.96% and as for the socioeconomic level, class D predominated with 67.55%. On the other hand, when the risk of dental caries was determined using the Reduced Cariogram tool based on sociodemographic data, it was identified that there are significant differences between age and socioeconomic level, while there is no difference in relation to gender. (p = 0.372). When determining the risk of caries with the Biological Caries Risk tool with sociodemographic data, it was found that there are significant differences between age and socioeconomic level with the use of this tool, but there is no difference in relation to gender. (p = 0.777). The univariate statistical analysis was made using descriptive statistics (relative and absolute frequency) and bivariate analysis using Pearson's Chi-square test to compare caries risk with both tools. Conclusion: There are statistically significant differences between the Reduced Cariogram and Caries Biological Risk tools in caries risk diagnoses at their moderate and high levels. (p <0.001). / Tesis