<p> Traditionally, seasonal forcing has been considered to be the major cause of the influenza seasonality. However, Andreasen [2003] showed that repetitive introductions of new strains can lead to cyclic dynamics. The cyclic dynamic produced by his model is not seasonal, because the length of seasons cannot be defined in his model. In this report, we develop a model that combines a stochastic mutation process with a two-strain competition process governing the spread of the mutant strain. This model can produce stable seasonal dynamics. If we introduce a small seasonal forcing to the transmission rate, the length of a season can be regulated to one year if the unforced system oscillates with a period close to one year. If the system has a period that is far from one year, then the forced system may behave chaotically.</p> / Thesis / Master of Science (MSc)

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Yes / This paper presents a simulation study into the characteristics of a vehicle experiencing steering drift under straight line braking. Simulation modelling has been performed using a multi-body dynamics analysis based on a model of an actual vehicle. Front and rear suspension parameters have been modelled as rigid links joined with flexible bushes so as to assess their effect on a vehicle while braking. Suspension geometry and alignment settings, which define characteristic responses such as lateral acceleration, yaw velocity, toe, and caster angles of a vehicle in a transient manoeuvre, are primary to a vehicle¿s directional stability. Any symmetric inconsistencies in these settings will potentially affect a vehicle¿s performance. The findings from this research have increased the understanding of the causes of steering drift during braking conditions.

Flazasulfuron is one of the newest sulfonylurea (SU) herbicides to be registered for use in the fine turf industry. Flazasulfuron is safe for use on bermudagrass (Cynodon dactylon), and zoysiagrass (Zoysia japonica) yet controls several grass, broadleaf, and sedge weeds. In fine turf, flazasulfuron controls cool-season grasses such as tall fescue (Festuca arundinacea) and perennial ryegrass (Lolium perenne) without harming warm-season grasses. Although SU herbicides like flazasulfuron bring several potential benefits to turfgrass markets, there are also several concerns related to using these herbicides in turfgrass areas. For many plant species, SU herbicides can cause phytotoxicity or death at less than 1 g ai/ha-1indicating small quantities of active ingredient are required to cause problems if herbicide moves in the environment. Herbicide moves to nontarget plants either after it has been applied via lateral relocation or during application via spray drift. Trials were conducted to evaluate flazasulfuron and trifloxysulfuron sodium tracking, runoff and drift in turfgrass environments. Field trials were conducted at six locations across the US to evaluate effects of irrigation, herbicide treatment, nontreated buffer distance, and time of tracking on creeping bentgrass (Agrostis stolonifera) putting green response to dislodged herbicide residues. Although average turf injury did not exceed 2%, significant differences were noted when treated plots were irrigated prior to tracking. In addition, putting green injury was negatively correlated and normalized difference vegetative index was positively correlated with increasing buffer distance. Data indicate the importance of post treatment irrigation to reduce lateral relocation of SU herbicides like flazasulfuron and trifloxysulfuron sodium in turfgrass. In other studies, herbicides were applied to turfgrass on 7 to 11 % slopes and perennial ryegrass injury was assessed at various distances down slope following an irrigation or rainfall event. Herbicide movement in runoff water was indicated by perennial ryegrass discoloration as much as 18 m below treated plots when excessive herbicide rates were applied to saturated soils. Based on perennial ryegrass injury, flazasulfuron at the rates tested was equivalent or more mobile than trifloxysulfuron sodium and equivalent or less mobile than pronamide when subjected to irrigation or rainfall soon after application to saturated soils. To assess spray drift, a bioassay based on corn height reduction was conducted and corn plants were exposed to potential spray drift in field conditions using conventional turfgrass spray equipment. A sprayer was operated when wind speeds were between 6.4 and 9.6 km h-1 and sentry plants were placed various distances between 0 and 30 m down wind. Wind speeds and direction were confirmed with anemometers and neutrally-buoyant balloons. Herbicide drift was not detected beyond 4.6 m downwind of either herbicide application. Data suggest a 5- to 8-m nontreated buffer area should sufficiently protect neighboring cool-season turfgrasses and other plants against flazasulfuron drift, runoff, and tracking as long as product is not applied to saturated soils and irrigated prior to traffic. / Master of Science in Life Sciences

Le gisement d'or Amaruq (Nunavut, CA) est situé dans la ceinture de roches vertes néoarchéennes du Groupe de Woodburn Lake. La glaciation Wisconsinienne a entraîné l'érosion du socle, le transport et la formation de dépôts de till masquant le substrat rocheux et les minéralisations associées. Le projet de recherche a pour but de caractériser la signature géochimique et minéralogique du gisement Amaruq dans le till jusqu'à 8,6 km en aval de la minéralisation. Des échantillons de la minéralisation ont été prélevés afin de déterminer la composition chimique des minéraux indicateurs tels que l'or, la scheelite et la tourmaline. Dans le gisement, la tourmaline et la scheelite sont en association paragénétique avec l'or. Le till a été échantillonné le long de 2 transects orientés NNO, parallèles à la direction principale de l'écoulement glaciaire et orthogonaux à la direction du gisement. Les analyses en composantes principales (ACP) de la géochimie du till décrivent la covariance des éléments enrichis dans les roches mafiques à ultramafiques (Fe, Mg, Mn, Ni, Co, Cr) et la minéralisation aurifère (Au, As, Cu, Zn) avec une composante principale 1 (CP1) négative à l'opposé de la variance en éléments enrichis dans les roches felsiques (Si, Al, Na, K, Ba, Be, Hf, Zr, Rb, Sr, U, Th et les éléments des terres rares) avec une CP1 positive. Les échantillons en amont glaciaire ont des scores CP1 uniquement positifs par rapport à des scores CP1 plus hétérogènes en aval. L'analyse discriminante des moindres carrés partiels (PLS-DA) montre que 86 % de l'or et 100 % de la scheelite de la minéralisation d'Amaruq se classifient dans le champ de composition chimique typique des gisements d'or orogénique. Dans le till, 63 % de l'or et 74 % de la scheelite se classifient dans le champ des gisements d'or orogénique. La PLS-DA de l'or du till ne permet pas de distinguer sa provenance entre l'amont et l'aval du gisement. En amont glaciaire, 9 % des grains de scheelite ont une signature chimique similaire à celle du gisement contre 81 % de la scheelite en aval glaciaire. Ces résultats indiquent que la scheelite en amont du gisement est dérivée d'autres sources que la minéralisation d'or orogénique tandis que la scheelite en aval glaciaire provient en majeure partie de la minéralisation affleurante. La faible abondance de tourmaline dans le gisement et le faible nombre de grains de tourmaline identifiés dans les échantillons de till montrent que la tourmaline n'est pas un minéral indicateur pertinent pour cette étude. La caractérisation géochimique et minéralogique du till définit l'origine de la minéralisation érodée et permet son utilisation en prospection glacio-sédimentaire en aval du gisement d'or orogénique Amaruq. / The Amaruq gold deposit (Nunavut, CA) is located in the Neoarchean greenstone belt of the Woodburn Lake Group. The Wisconsinan glaciation caused bedrock erosion, transport and deposition of till masking the bedrock and associated mineralization. The aim of the research project is to characterize the geochemical and mineralogical signature of the Amaruq deposit in till up to 8.6 km down-ice of the mineralization. Core samples from the mineralization were collected to determine the chemical composition of indicator minerals such as gold, scheelite and tourmaline. In the deposit, tourmaline and scheelite are in paragenetic association with gold. Till was sampled along 2 NNW-oriented transects, parallel to the main direction of ice flow and orthogonal to the strike of the deposit. Principal component analysis (PCA) of till geochemistry describes the covariance of enriched elements in mafic to ultramafic rocks (Fe, Mg, Mn, Ni, Co, Cr) and gold mineralization (Au, As, Cu, Zn) with a negative principal component 1 (PC1) as opposed to the variance in enriched elements in felsic rocks (Si, Al, Na, K, Ba, Be, Hf, Zr, Rb, Sr, U, Th and rare earth elements) with a positive PC1. Up-ice samples have positive PC1 scores compared to more heterogeneous PC1 scores for down-ice samples. Partial least squares discriminant analysis (PLS-DA) shows that 86 % of the gold and 100 % of the scheelite from the Amaruq deposit plot in the orogenic gold deposits field whereas in till, 63 % of the gold and 74 % of the scheelite plot in the field for orogenic gold deposits. The PLS-DA of gold in till does not distinguish its provenance between up-ice and down-ice. Up-ice of the mineralization, 9 % of scheelite grains have a chemical signature similar to that of the deposit in contrast to 81 % of down-ice scheelite. The results indicate that scheelite up-ice of the deposit has other sources than orogenic gold mineralization whereas down-ice scheelite was eroded mainly from Amaruq outcropping mineralization. The low abundance of tourmaline in the deposit and the low number of tourmaline grains identified in the till samples shows that tourmaline is not a useful indicator mineral for this study. The geochemical and mineralogical characteristics of till define the origin of the eroded mineralization and can be used for glacio-sedimentary prospecting down-ice from the Amaruq orogenic gold deposit.

Safeners protect crops by enhancing their ability to metabolize various compounds, including herbicides. They primarily work by increasing the crop's tolerance to herbicide damage, activating herbicide-metabolizing proteins, and aiding in their detoxification. This study aimed to investigate the chemical effects of safeners in tomato cultivation and focus on injury reduction and tissue protection. The experiment followed a randomized factorial design (5x4) with four replications repeated twice. We evaluated the effects of herbicides (dicamba, 2,4-D, metribuzin, and sulfentrazone at 1/100) and safeners (benoxacor, fenclorim, melatonin, 2,4,6-T, and an untreated control). Safeners were applied to the seeds before sowing, and herbicides were used as a foliar spray 25 days after sowing (DAS). Visual injury was evaluated 7, 14, and 21 days after application (DAA). Biomass measurements were taken 21 DAA. Results showed that preconditioning tomato seeds with 2,4,6-T, melatonin, and fenclorim 7 DAA significantly decreased injury by 25, 25, and 23%, respectively. Moreover, applying melatonin, benoxacor, and 2,4,6-T 21 DAA led to significantly greater dry biomass, which increased by 1.5, 1.42, and 1.44 times, respectively, compared to the control. This research provides valuable insights into the chemical effects of benoxacor, fenclorim, 2,4,6-T, and melatonin safeners in tomato cultivation. The findings demonstrate the potential for preconditional tomato plants with 2,4,6-T, melatonin, and fenclorim to reduce injury while applying melatonin, benoxacor, and 2,4,6-T can increase dry biomass. Understanding plant defense mechanisms and the protective effects of safeners against herbicide damage contributes to developing effective weed management strategies.

Integrating nanometer-sized pores into low-k ILD films is one of the approaches to lower the RC signal delay and thus help sustain the continued scaling of microelectronic devices. While increasing porosity of porous dielectrics lowers the dielectric constant (k), it also creates many reliability and implementation issues. One of the problems is the little understood metal ion diffusion and drift in porous media. Here, we present a rigorous simulation method of Cu diffusion based on Master equation with elementary jump probabilities within the contiguous dielectric film, along the pore boundary, from the dielectric matrix to the pore boundary, and from the pore boundary to the matrix material. In view of the diffusional jump distance being as large as 2 nm, the nano-pores being on a similar length scale, and the film thickness being only a few tens of nanometers, the conventional diffusion equation in differential equation form is grossly inadequate and elementary jump frequencies are required for a proper description of the Cu diffusion in porous dielectric. The present atomistic approach allows a consistent implementation of Cu ion drift in electric field by lowering and raising of the diffusion barriers along the field direction. This will help understand the behavior of Cu interconnects under thermal or electric stress at an atomistic level. Another approach to lower the increasing RC delays is to bring memory and logic closer by integrating memory in the BEOL. Resistive RAM is one such memory is not transistor based and thus, does not require a silicon substrate. Thus, it offers the possibility of integration directly into the back-end reducing memory to logic distance from 1000s of µm to a 10s of nm. This 3D integration also allows for increased density as well. However, one barrier in the implementation of RRAM in the back end is the use of expensive as well as non-BEOL native material in conventional Cu/TaOx/Pt resistive devices. In this thesis, we present our research about functionality of RRAM with porous low-k dielectrics (which are a candidate for CMOS ILD), and through the similar elementary jump simulations, discuss the impact of porosity in dielectrics on the functionality of RRAM. Lastly, we present a cheaper replacement for Pt as the counter electrode in RRAM and show that it functions as good as Pt. This work addresses following three areas: 1. Modeling of diffusion in porous dielectrics through elementary jump based simulation. The model is based on random walk theory of elementary particle jumps. Initially, qualitative simulations are conducted without actual parameters. It is shown that Cu diffusion in porous dielectrics decreases quasi-linearly with porosity. Furthermore, it is shown that morphology of the pores may have a greater effect on diffusivity compared to porosity. The simulations are then calibrated with parameters, and the result is shown to yield a similar diffusivity times as actual process time. 2. Modeling of Cu ions drift in porous dielectrics under electric stress. First, the model is explained, and then qualitative simulation results are presented for porous dielectrics with varied porosities and morphologies. 3. Research to find a suitable replacement for Pt as the counter electrode in RRAM devices. The research methodology is discussed and a much cheaper Rh is selected as the potential replacement for Pt. Successful functionality of Rh based resistive devices is presented. / Master of Science / As electronic devices are being scaled for integrating more functions and higher computation, the internal delays are increasing, which may become a bottleneck in performance. To resolve this issue of internal delay, new materials are being proposed to replace the conventional materials to make the chip. One promising material like that are the porous dielectrics, to replace the conventional dielectrics used to manufacture electronic chips. The introduction of ‘air pores’ inside the dielectric used in chips may improve the delay, but it leads to several thermal and electrical reliability concerns. In this thesis, we argue that using differential equations to simulate effects on the nano-scale to explore such reliability issues is insufficient, and a simulation method based on individual atom/ion movement should be used to describe it. Here we provide a simulation model to explain the diffusivity of copper under thermal stress, as well as movement of Cu ions during electric stress in porous dielectrics, using our particle movement based simulation model, and prove that it delivers correct results. Secondly, the delay is especially significant for processor to memory communication. Thus, integrating memory close to processor is another method to reduce the delay. Resistive RAM (RRAM) is one such novel RAM technology that can be integrated close to processor. However due to usage of non-native as well as expensive materials, RRAM has not been commercially integrated close to processor. In this thesis, we also present a functioning RRAM using cheaper materials, as well as materials that are native to present electronics.

O desempenho das Máquinas de Medir a Três Coordenadas (MM3Cs) fica limitado por diversos fatores, que atuam de maneira conjunta gerando os denominados erros volumétricos. Para a temperatura de 20ºC os erros geométricos podem ser considerados constantes, uma vez que variam muito lentamente com o tempo. Porém, se a temperatura é alterada estes erros mudam em grandeza e comportamento, gerando os denominados erros térmicos. Alguns trabalhos têm sido desenvolvidos com o objetivo de estudar e modelar os erros térmicos, porém os resultados alcançados são, ainda, incipientes. Este trabalho apresenta o equacionamento das componentes do erro volumétrico das MM3Cs considerando as influências térmicas. A medelagem foi aplicada a uma MM3C do tipo \"Ponte Móvel\" e combina transformações homogêneas, técnicas de regressão e mínimos quadrados. As grandezas dos erros geométricos e das variações termicamente induzidas destes erros foram coletadas utilizando-se do interferômetro laser, do esquadro mecânico, do nível eletrônico, etc. Os valores das temperaturas foram monitorados através de termopares do tipo T (Cobre-Constantan). Verificou-se que a Máquina não experimenta deformações, além, das provocadas pela livre dilatação dos seus componentes. A partir do modelo proposto foram sintetizadas as componentes do erro volumétrico, os resultados foram discutidos e comparados com aqueles obtidos através da medição de um anel padrão, constatando-se a excelente capacidade do modelo na previsão do erro volumétrico da máquina. No caso, erros da ordem de grandeza de 10 &#956m foram reduzidos em pelo menos 75%, enquanto que para erros maiores que 10 &#956m a eficiência do modelo foi de 90%. / Performance of coordinate measuring machines (CMMs) is limited by numerous factors that operate simultaneously and generate volumetric errors. The most significant portion of the volumetric error is produced by geometric errors. At the temperature of 20ºC, geometric errors can be considered at steady states, once their variation in time is considerably slow. However, if temperature is modified, these errors change in magnitude and behaviour, generating the thermal induced errors. Some work has been developed aiming to study and model the thermal errors, but the achieved results are still incipient. This work presents the derivation of the components of the volumetric error considering its thermal influences. The method was employed and applied to moving bridge CMM and combines homogeneous transformation, regression techniques and least squares methods. The magnitudes of the geometric errors and its thermally induced variations were collected by means of a laser interferometer system, mechanical square, electronic level, etc. Temperature data were monitored by means of T-type thermocouples (copper-constantan). It was verified that the CMM was not susceptible to deformations other than the ones due to the dilatation of its components. From the proposed model, the components of volumetric error were synthesized; the results were discussed and compared to the ones obtained from the measurement of a ring plug, observing the outstanding ability of the model to predict the volumetric error of the machine. Errors of 10 &#956m in magnitude were reduced in at least 75%, whilst errors greater than 10 &#956m, presented a reduction efficiency of 90%. It was verified that the CMM was not susceptible to deformations other than the ones due to the dilatation of its components.

The thesis will focus on documenting, analysing and interpreting the motifs for the ceramics of Rorke’s Drift Art and Craft Centre Ecumenical (Evangelical) Lutheran Church (RDACC ELC, often called ELC Art and Craft Centre, hereinafter referred to as ‘Rorke’s Drift’) which were donated to the University of KwaZulu-Natal by Mark Bernstein. It is hoped that local indigenous narratives and visual designs in relation to Basotho and Zulu cultural identity will be outlined in the form of a catalogue. All vessel forms in the Bernstein Collection (as it will be referred to in this thesis) will focus on the figurative works and iconographic signifiers that represent local cultures. Ceramic works by the following ceramists will form the main argument of my thesis: Gordon Mbatha, Dinah Molefe, Ivy Molefe, Ephraim Ziqubu, Lindumusa Mabaso and Joel Sibisi of the Pottery Workshop. / Thesis (M.A.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.