Computer-Aided Cut-off Grade Optimisation for Open Pit Mines

A mine planning team is tasked among other duties with designing a feasible mine plan which in turn maps out the daily running of the mining project. A mine plan revolves around a cut-off grade which is thoughtfully and uniquely selected while considering various aspects such as grade tonnage distribution, economic and operational parameters specific to a mine. Selection of a cut-off grade can be a daunting task often involving iterative and lengthy mathematical formulas which take huge amounts of time to execute, often leaving room for error. In the occurrence of such errors, a mining project can be faced with sequential outcomes that could even lead to premature closure. The cut-off grade is therefore a strategic variable that determines the economic viability of a mine, and hence return on investment. It is critical that the cut-off grade is optimal so as to maximise the net present value. Lane’s approach is a model that utilises several steps to yield one cut-off grade value. This algorithm is flexible and can be adjusted to include other factors specific to a mine. Regrettably, many mining companies continue to operate using inaccurate cut-off grades wrongly calculated or assumed. This has continuously led to frustrations due to losses and prematurely abandoned mines. This study focused on the development and implementation of an easy to use computer application based on Lane’s approach that runs on Windows platform, and hence targeting a larger user base for choosing an optimum cut-off grade for open pit mines. Keywords: Cut-Off Optimisation, Cut-Off Optimiser, Optimum Cut-Off Grades, Whittl

Hypertension and obesity among HIV patients in a care programme in Nairobi

Objective: To determine the prevalence of hypertension and obesity among HIV patients enrolled in the Sex Worker Outreach Programme (SWOP), Nairobi, Kenya.Design: A retrospective a study.Setting: SWOP managed by the University of Manitoba, Nairobi team.Subjects: We selected clinic visit records from HIV patients seen between 2011 and 2014, which had valid blood pressure and age entries.Interventions: We analysed data to determine prevalence and correlates of hypertension and obesity in the study population. Associations were tested using chi-square for categorical variables and t-test for continuous variables.Main outcome measures: Hypertension and obesity.Results: Three thousand one hundred ninety seven subjects were included in the study. All were HIV-positive and most (97.8%) were on ART. The mean age was 39.7 years (standard deviation = 8.8) and 72.4% of the subjects were female. The prevalence of hypertension was 7.7% (246/3197) and 31% of the study cases (798/2590) were either overweight or obese. Males were more likely to have hypertension (p < 0.001) while females were more predisposed to obesity (p < 0.001).Conclusion: Hypertension and obesity are important co-morbidities among HIV patients. Preventive and management strategies should be adopted as part of the comprehensive packages on offer at all existing HIV care and ART centres targeting those enrolled for services as well as their relatives and the community at large

SPATIAL ANALYSIS OF SOIL FERTILITY MANAGEMENT USING INTEGRATED HOUSEHOLD AND GIS DATA FROM SMALLHOLDER KENYAN FARMS

Although soil fertility is recognized as a primary constraint to agricultural production in developing countries, use of fertilizer in Sub-Saharan Africa is declining. Smallholder farmers still rely heavily on livestock manure for soil fertility management. To explore the determinants of soil fertility management practices, including both the use of cattle manure and inorganic fertilizer, data are used from a sample of 3,330 geo-referenced farm households across Central and Western Kenya. A bivariate probit model is applied to jointly examine the use of the two technologies. Particular attention is given to measures of location related to market access and agroclimate, which in the adoption literature have typically been addressed using crude proxies. To avoid such proxies, GIS-derived variables are integrated into the household decision model. Their use also allows the spatial prediction of uptake based on parameter estimates. The results show clearly the derived-demand nature of soil fertility services, based on markets for farm outputs. They also illustrate that supply of manure for soil fertility amendments is conditioned by demand for livestock products, especially milk. The integration of GIS-derived variables is shown to better estimate the effects of location than the usual measures employed, and offers scope to wider use in technology adoption research.spatial analysis, soil fertility, market access, technology adoption., Farm Management, Land Economics/Use, Q12, Q16,

Modelling malaria transmission dynamics in irrigated areas of Tana River County, Kenya

Development of irrigation schemes is usually associated with escalation of the malaria problem. Mathematical models can be used to explain the effects of irrigation on malaria transmission dynamics. This study aimed at developing and validating a one-host one-vector deterministic model made up of a mosquito population sub-module and disease transmission sub-module. Model parameters were obtained from the literature. Data covering the year 2013 were collected and these included the amount of irrigation water per unit area of irrigated land, rainfall, temperature and prevalence of malaria from the local hospitals. The Fuzzy distribution function was used to relate rainfall and irrigation patterns with oviposition and mortality rates of acquatic stages of mosquitoes. The model was fitted to malaria prevalence data obtained from the local hospitals by varying the parameters of the Fuzzy distribution function. Parameter values that gave the least variance between predicted and observed prevalence were used. The model was implemented in MS Excel using difference equations.The model fitted the data well and predicts an upsurge in the number of malaria cases 2-3 months after the rains or active irrigation. The model could be used to predict the prevalence of malaria in this area enabling decision makers to implement appropriate control measures in good time. Data from non-irrigated areas and covering a longer period of time should be collected for more rigorous model validation and simulation of the effectiveness of various the interventions

Hypertension and obesity among HIV patients in a care programme in Nairobi

Objective: To determine the prevalence of hypertension and obesity among HIV patients enrolled in the Sex Worker Outreach Programme (SWOP), Nairobi, Kenya.Design: A retrospective astudy.Setting: SWOP managed by the University of Manitoba, Nairobi team.Subjects: We selected clinic visit records from HIV patients seen between 2011 and 2014, which had valid blood pressure and age entries.Interventions: We analysed data to determine prevalence and correlates of hypertension and obesity in the study population. Associations were tested using chi-square for categorical variables and t-test for continuous variables.Main outcome measures: Hypertension and obesity.Results: Three thousand one hundred ninty seven subjects were included in the study. All were HIV-positive and most (97.8%) were on ART. The mean age was 39.7 years (standard deviation = 8.8) and 72.4% of the subjects were female. The prevalence of hypertension was 7.7% (246/3197) and 31% of the study cases (798/2590) were either overweight or obese. Males were more likely to have hypertension (p < 0.001) while females were more predisposed to obesity (p < 0.001).Conclusion: Hypertension and obesity are important co-morbidities among HIV patients. Preventive and management strategies should be adopted as part of the comprehensive packages on offer at all existing HIV care and ART centres targeting those enrolled for services as well as their relatives and the community at large

Epidemiology of malaria in irrigated parts of Tana River County, Kenya

Irrigation schemes introduced in areas of high malaria endemicity often amplify malaria burden especially if no mitigation or adaptation measures are implemented (Renshaw et al., 1998). Thias study was conducted in Bura and Hola irrigation schemes in Tana River County to (i) understand the knowledge, attitude and practices of the community in relation to malaria control and transmission, (ii) determine malaria prevalence and the associated risk factors of infection and (iii) develop and validate a transmission model for analyzing the effects of irrigation on malaria burden. A cross sectional survey was conducted in 48 households where 160 people were screened for malaria parasites using Rapid Diagnostic Test. A deterministic model was developed and validated using field data. The community demonstrated good knowledge on causes, symptoms, transmission and control of malaria. The main malaria control measure was use of bed nets where one net was shared by two people. Only 12% of the households practice environmental management to control malaria. Treatment of malaria was mainly based on Artemether-lumefantrine (AL) which is freely available in the government health facilities. The prevalence of malaria was 5% with the clinical records showing a declining trend of malaria cases. Households located ≤5kms to the nearest facility had lower risk of malaria infection (OR=0.104, p-value=0.013) than those located >5kms. Household size was also associated with malaria infection (OR=1.685, p-value=0.022). The model predicted the observed prevalence data. The high usage of bed nets and AL could have led to the observed decrease in malaria prevalence despite the intensification of irrigated agriculture. The model developed could be used to predict the prevalence of malaria in this area enabling decision makers to implement appropriate control measures in good time

Development of smallholder dairying in Eastern Africa with particular reference to Kenya

Large increases in demand for milk and dairy products projected for the next 25 years represent exciting market opportunities for smallholders in eastern Africa. With the exception of Kenya, traditional cattle production systems based on indigenous breeds dominate milk production in the region, yet they contribute relatively little to marketed production, mainly because of poor access to major urban markets. Kenya, which has over 85% of the dairy cattle population, dominates dairy production and marketing in the region. Its per capita milk availability is four to seven times higher than the other countries in the region. The widespread adoption of dairy cattle in Kenya was stimulated by several interacting factors: the conducive policy and institutional environments provided by successive Governments; the presence of significant dairy populations (owned by settler farmers); a sub-tropical geography suitable for dairy cattle; and, smallholder communities who kept cattle and who had milk as an important part of their diet. Today most of Kenya’s 3 million dairy cattle are kept by smallholders in crop-livestock systems in areas of high and medium cropping potential. Generally 1-2 dairy cows (mostly Holstein Friesian or Ayrshire) comprise 50% of the herd, the other half consisting of female calves and heifers. In the high potential areas feeding is mainly cut-and-carry with planted Napier grass (Pennisetum purpureum) and crop residues, especially from maize and bananas, supplemented by forage gathered from common properties around the farm. On average total daily milk output is 10 kg per farm, of which a quarter is for home consumption and the rest sold. In the late 1980s, sales were mainly through local dairy co-operative societies, with some to neighbours. However, following market liberalisation in 1992, marketing channels have diversified. It is estimated that approximately 80% of marketed milk is not processed or packaged, but instead is bought by the consumer in raw form. The factors driving the continued importance of the informal market are traditional preferences for fresh raw milk, which is boiled before consumption, and unwillingness to pay the costs of processing and packaging. Raw milk markets offer both higher prices to producers and lower prices to consumers. In Kenya, therefore, as elsewhere in the tropics, market-oriented smallholder dairy farms are concentrated close to urban consumption centres because the effects of the market over-ride many production factors. Less proximate production occurs only in those regions where there is an efficient market infrastructure. As infrastructure develops, markets become more efficient and urban consumers develop stronger preferences for pasteurised milk, the advantages of proximity will be reduced and production may well move away from intensive peri-urban systems and shift to more extensive systems (as the New Zealand dairy industry illustrates on a global scale). Until these infra-structural improvements occur, and because of the ready availability of cheap human capital (labour) and the relative expense of financial capital, smallholder dairy production and informal raw milk marketing are likely to predominate for the foreseeable future. Consequently it is anticipated that the industrialised model of dairy production, processing and marketing will remain a minor contributor in Kenya and elsewhere in the region