Browsing by Subject "Mathematical modeling"

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    Exploring the seasonality of reported treated malaria cases in Mpumalanga, South Africa
    (Public Library of Science, 2013) Silal, Sheetal Prakash; Barnes, Karen I; Kok, Gerdalize; Mabuza, Aaron; Little, Francesca
    South Africa, having met the World Health Organisation's pre-elimination criteria, has set a goal to achieve malaria elimination by 2018. Mpumalanga, one of three provinces where malaria transmission still occurs, has a malaria season subject to unstable transmission that is prone to sporadic outbreaks. As South Africa prepares to intensify efforts towards malaria elimination, there is a need to understand patterns in malaria transmission so that efforts may be targeted appropriately. This paper describes the seasonality of transmission by exploring the relationship between malaria cases and three potential drivers: rainfall, geography (physical location) and the source of infection (local/imported). Seasonal decomposition of the time series by Locally estimated scatterplot smoothing is applied to the case data for the geographical and source of infection sub-groups. The relationship between cases and rainfall is assessed using a cross-correlation analysis. The malaria season was found to have a short period of no/low level of reported cases and a triple peak in reported cases between September and May; the three peaks occurring in October, January and May. The seasonal pattern of locally-sourced infection mimics the triple-peak characteristic of the total series while imported infections contribute mostly to the second and third peak of the season (Christmas and Easter respectively). Geographically, Bushbuckridge municipality, which exhibits a different pattern of cases, contributed mostly to the first and second peaks in cases while Maputo province (Mozambique) experienced a similar pattern in transmission to the imported cases. Though rainfall lagged at 4 weeks was significantly correlated with malaria cases, this effect was dampened due to the growing proportion of imported cases since 2006. These findings may be useful as they enhance the understanding of the current incidence pattern and may inform mathematical models that enable one to predict the impact changes in these drivers will have on malaria transmission.
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    A kinetic study on anaerobic reduction of sulphate, Part I: Effect of sulphate concentration
    (Elsevier, 2002) Moosa, S; Nemati, M; Harrison, S T L
    The kinetics of anaerobic reduction of sulphate was studied in continuous bioreactors. The effects of initial sulphate concentration and its volumetric loading on the kinetics of reaction and activity of sulphate-reducing bacteria were investigated. The increase in initial concentration of sulphate in the range 1.0–Full-size image (<1 K) enhanced the reaction rate from 0.007–Full-size image (<1 K). For a given initial sulphate concentration increasing the volumetric loading rate of sulphate led to a linear increase in volumetric reduction rate. The initial concentration of sulphate did not have a significant effect on maximum specific growth rate (μm), decay coefficient (kd) on bacterial yields (Yx/sulphate and Yx/acetate), with the values of these coefficients being Full-size image (<1 K) bacteria/g sulphate and Full-size image (<1 K) bacteria/g acetate, respectively. The saturation constant (Ks) was an increasing linear function of initial sulphate concentration, with the lowest and highest values being 0.027 and Full-size image (<1 K), respectively. Using the experimental data a kinetic model, incorporating terms for the effects of initial and residual concentrations of sulphate and biomass, was developed.