Dichloro-diphenyl-trichlorethane (DDT) is a chemical used in malaria control through indoor residual spraying (IRS) and has saved numerous lives in the past six decades. DDT use is restricted/banned under the Stockholm Convention on Persistent Organic Pollutants. Passive air sampling using polyurethane foam was conducted in South Africa to evaluate the presence and trends of DDT and its metabolites. Three sampling sites were used, namely, Barberspan Nature Reserve (rural agricultural), Vanderbijlpark (urban industrial) and Molopo Nature Reserve (isolated nature reserve). Sampling was conducted for a period of one year in 2008. Back trajectories from the three sampling sites were generated using HYSPILT to determine the sources of DDT metabolites to the sampling areas. Forward trajectories were also generated to determine the movement, distribution, and fate of DDT from the areas under Indoor residual spray of DDT for malaria control in South Africa and Swaziland. Chemical analysis was conducted by the RECETOX (Mazaryk University) in the Czech Republic. DDT metabolites (o,p’-DDE, p’p’-DDE, o.p’-DDD, p,p’-DDD, o,p’-DDT p,p’-DDT) were analysed using a GC-ECD (HP 5890). Vanderbijlpark had the highest concentrations of DDT metabolites throughout the year. Barberspan had the second highest concentration and Molopo the least. Seasonal changes in concentration were much the same at the three sites. %p,p’-DDT of ΣDDT is consistent with IRS spraying months in South Africa and Swaziland. A combinations of backward and forward trajectories, together with the temporal pattern of change of the %p,p’-DDT of ΣDDT support the deduction that DDT sampled from the three study sites (to some degree) came from IRS areas in South Africa and Swaziland. The presence of DDT in Molopo Nature Reserve and Barberspan is evidence of long-range transportation over dry semi-desert areas. Back-trajectories indicate the possible source of DDT were the IRS areas in the provinces of Limpopo, Mpumalanga, and KwaZulu-Natal. Some air masses to the sampling sites came from the sprayed areas. The forward trajectories also revealed that the DDT sprayed during IRS could undergo LRT. The DDT metabolites were able to travel to neighbouring countries such as Mozambique, Namibia, Zimbabwe and Botswana. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2013

Dichloro-diphenyl-trichlorethane (DDT) is a chemical used in malaria control through indoor residual spraying (IRS) and has saved numerous lives in the past six decades. DDT use is restricted/banned under the Stockholm Convention on Persistent Organic Pollutants. Passive air sampling using polyurethane foam was conducted in South Africa to evaluate the presence and trends of DDT and its metabolites. Three sampling sites were used, namely, Barberspan Nature Reserve (rural agricultural), Vanderbijlpark (urban industrial) and Molopo Nature Reserve (isolated nature reserve). Sampling was conducted for a period of one year in 2008. Back trajectories from the three sampling sites were generated using HYSPILT to determine the sources of DDT metabolites to the sampling areas. Forward trajectories were also generated to determine the movement, distribution, and fate of DDT from the areas under Indoor residual spray of DDT for malaria control in South Africa and Swaziland. Chemical analysis was conducted by the RECETOX (Mazaryk University) in the Czech Republic. DDT metabolites (o,p’-DDE, p’p’-DDE, o.p’-DDD, p,p’-DDD, o,p’-DDT p,p’-DDT) were analysed using a GC-ECD (HP 5890). Vanderbijlpark had the highest concentrations of DDT metabolites throughout the year. Barberspan had the second highest concentration and Molopo the least. Seasonal changes in concentration were much the same at the three sites. %p,p’-DDT of ΣDDT is consistent with IRS spraying months in South Africa and Swaziland. A combinations of backward and forward trajectories, together with the temporal pattern of change of the %p,p’-DDT of ΣDDT support the deduction that DDT sampled from the three study sites (to some degree) came from IRS areas in South Africa and Swaziland. The presence of DDT in Molopo Nature Reserve and Barberspan is evidence of long-range transportation over dry semi-desert areas. Back-trajectories indicate the possible source of DDT were the IRS areas in the provinces of Limpopo, Mpumalanga, and KwaZulu-Natal. Some air masses to the sampling sites came from the sprayed areas. The forward trajectories also revealed that the DDT sprayed during IRS could undergo LRT. The DDT metabolites were able to travel to neighbouring countries such as Mozambique, Namibia, Zimbabwe and Botswana. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2013

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Dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg for the Degree of Master of Science / Various techniques and procedures suited to monthly forecasting are investigated and tested. These include using the products generated by atmospheric general circulation models during a 17-year hindcast experiment, and downscaling the forecast circulation to regional rainfall in South Africa using circulation indices and canonical correlation analysis. The downscaling methods are evaluated using the cross-validation technique. Various model forecast bias-correction methods and skill-enhancing ensemble techniques are employed to improve the 30-day prognosis of the model. Forecasts from the general circulation model and each technique are evaluated. Those demonstrating reasonable skill over the southern Africa region, and which are feasible when considering available resources, are adopted into a strategy which can be used operationally to produce monthly outlooks. Various practical issues regarding the operational aspects of long-term forecasting are also discussed. / Andrew Chakane 2019

The development of some ability for forecasting low rainfalls would be helpful in Tuvalu as rainwater is the only source of fresh water in the country. The subsurface water is brackish and saline so the entire country depends totally on rainwater for daily domestic supplies, agricultural and farming activities. More importantly, these atolls are often influenced by droughts which consequently make inadequate drinking water an issue. A simple graph-based forecasting scheme is developed and presented in this thesis for forecasting below average mean rainfall in Funafuti over the next n-month period. The approach uses precursor ocean surface temperature data to make predictions of below average rainfall for n = 1, 2 12. The simplicity of the approach makes it a suitable method for the country and thus for the Tuvalu Meteorological Service to use as an operational forecasting tool in the climate forecasting desk. The graphical method was derived from standardised monthly rainfalls from the Funafuti manual raingauge for the period January 1945 to July 2007. The method uses lag-1 and-lag 2 NINO4 sea surface temperatures to define whether prediction conditions hold. The persistence of predictability tends to be maintained when the observed NINO4 ocean surface temperatures fall below 26.0oC. Although the developed method has a high success probability of up to 80 percent, this can only be achieved when conditions are within the predictable field. A considerable number of below average rainfall periods are not within the predictable field and therefore cannot be forecast by this method. However, the graphical approach has particular value in warning when an existing drought is likely to continue.

No description available.

No description available.

An electrochemical detection method based on long range surface plasmon waveguides is proposed and demonstrated in this integrated article thesis. This dissertation uses CYTOP gold (Au) waveguides supporting long range surface plasmon polaritons (LRSPPs) in conjunction with grating couplers as well as Au waveguides embedded on a one-dimensional photonic crystal (1DPC) supporting Bloch LRSPPs integrated grating couplers. Grating couplers for Au stripe waveguides embedded in Cytop are demonstrated and analyzed. Grating couplers are used in a broadside coupling scheme where a laser beam incident on a stripe of Au on Cytop. The use of gratings for excitation of LRSPPs simplifies optical alignment and does not require high-quality input and output edge facets. Over a broad operating wavelength range, optical experiments are performed to demonstrate coupling loss and determine the efficiency of grating coupling using both a cleaved bow-tie PM fiber and a lensed PM fiber. The coupling loss and grating coupling efficiency of both types of fibers are also calculated numerically. Fluoropolymers with refractive indices close to water, such as CYTOP, are widely used to make waveguide biosensors today. Due to its low glass transition temperature, CYTOP presents limitations to fabrication processes. A truncated 1D photonic crystal may replace a low-index polymer cladding such as CYTOP to support Bloch LRSPPs within the bandgap of the 1DPC over limited wavenumbers and wavelength range. As a result of the high sensitivity of Au stripe Bloch LRSPP waveguide biosensors and their compatibility with high levels of integration, microelectrode systems that can be integrated with such optical biosensors are examined. A chip bearing a Au LRSPP waveguide that can also function as a working electrode (WE), a Pt counter electrode (CE), and Pt/Cu electrical contact pads, is used to demonstrate the electrochemical performance of LRSPPs waveguides. The cyclic voltammetry measurements were performed at different scan rates and concentrations of potassium ferricyanide as the redox species on Au LRSPPs waveguides. By fitting our experimental data to the Randles-Sevcik equation, we find the diffusion coefficient of potassium ferricyanide. The results from CV measurements obtained from chips are compared with commercial macroscopic electrodes. The CV measurements are also compared with theoretical results computed using the Butler-Volmer equation to determine the rate constant of the redox species at zero potential. A waveguide containing a stripe of Au that propagates infrared surface plasmon polaritons (SPPs), acting simultaneously as an electrode in a three-electrode electrochemical cell is also examined. Under SPP excitation, cyclic voltammetry was measured as a function of incident optical power and wavelength (1350 nm). In oxidation and reduction reactions, energetic electrons are separated from energetic holes. Under SPP excitation, redox current densities increase by 10×. With the SPP power, the oxidation, reduction, and equilibrium potentials drop by as much as 2× and separate in correlation with the photon energy. According to electrochemical impedance spectroscopy, charge transfer resistance dropped by almost 2× under SPP excitation. During SPP excitation, the temperature of the working electrode is monitored in situ and independent control experiments are performed to isolate thermal effects. Measurements of chronoamperometry with SPPs modulated at 600 Hz yield a rapid current response modulated at the same frequency, ruling out thermally enhanced mass transport. The observation is attributed to the opening of optically controlled non-equilibrium redox channels associated with the energetic carrier transfer to the redox species. During CV and chronoamperometry measurements, convolutional voltammetry is performed by monitoring the SPP output power versus the applied voltage. Using both experimental and theoretical methods, we demonstrate that the SPP output power is proportional to the electrochemical current convolution. A SPP voltammogram confirms that signal changes are mainly caused by differences in refractive index between reduced and oxidized forms of redox species. In addition, we demonstrate that energetic carriers resulted from SPP absorption significantly improved electrochemical sensitivity. As a complementary electrochemical technique, convolutional voltammetry is useful since the signal is related directly to the concentration of electroactive species on the working electrode (WE) and independent of the scan rate. As a probe of electrochemistry taking place in waveguides, surface plasmon polaritons (SPPs) propagating along one are sensitive. In such a waveguide, the optical output power is proportional to the time convolution of the electrochemical current density, eliminating the need to calculate the latter a posteriori via numerical integration. It is demonstrated that a waveguide WE provide an optical response that can be experimentally validated by chronoamperometry and cyclic voltammetry measurements under SPP excitation for a few potassium ferricyanide (redox species) concentrations in potassium nitrate (electrolyte) and various scan rates. Cyclic voltammetry measurements taken under increasing SPP power produce a regime where SPPs no longer act solely as the probe, but also act as a pump, producing energetic electrons and holes via their absorption in the WE. The energetic carriers enhance (10×) redox current densities as well as the convolution signal measured directly as the optical output power over time.

Thesis (M.S.)--University of Wisconsin--Madison, 1984. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 67).

Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 75-76).