Abstract Matrix solid-phase dispersion and gas chromatography-mass spectrometry were used for the rapid screening of 36 pesticides in agricultural products. Homogenized sample (0.5 g), C8-modified silica (0.5 g) and Na2SO4 (1 g) were mixed and transferred to a cartridge containing activated silica (0.5 g). Best recoveries (>60%) were found using dichloromethane-ethyl acetate (4:1) for elution. Analytical characteristics at spiking levels (10–100 lg/kg) were calculated for each pesticide. Matrix effects were studied by comparing the slopes of the matrix-matched calibration curves. Fruit and vegetable samples from South Africa complied with EU and South African current regulation, except for cypermethrin in green beans.

published_or_final_version / Civil and Structural Engineering / Master / Master of Philosophy

It is well known that the perturbed GUE matrix model has a combinatorial interpretation involving graphs embedded in Riemann surfaces. Generating functions for these graphs in the case of an even potential have been studied by many authors. The case of a cubic potential has also been studied. Using string equations, we construct "valence independent" formulas for map generating functions. These formulas hold for arbitrary polynomial potentials. We derive "edge Toda equations," which we use together with our valence independent formulas to generalize formulas of Ercolani, McLaughlin and Pierce to the case of an arbitrary odd or even valence. We derive a valence independent formula for the equilibrium measure for eigenvalues of the matrix model. Using this formula for the equilibrium measure we show that our valence independent formulas for generating functions can also be derived from the Riemann-Hilbert problem for orthogonal polynomials, and from the loop equations.

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Matrix acidizing is a well stimulation procedure where acid is injected down the wellbore or coil tubing and into the reservoir near the wellbore region. Wellbore damage is a common issue in the oil field. The primary goal of matrix acidizing in carbonate reservoirs is to bypass wellbore damage by creating highly conductive channels that go several feet into the formation, known as wormholes. The goal of laboratory experiments is to find an optimum injection rate to create dominant wormholes and provide this information to the field. To conduct various experiments, core flooding setups are created. The setup consists of a core holder, accumulator, overburden pump, injection pump, accumulator, pressure sensors, and a back pressure regulator. Results from matrix acidizing core flooding in laboratory conditions provide an understand for wormhole growth, acid diversion, injection rates, and adds a variety of liquid chemicals for testing at reservoir pressures and temperatures. The first objective was to design, assemble, and test a matrix acidizing parallel core flooding apparatus. The apparatus was rated for 5,000 psi and 250 ºF. Combinations of the various mechanical components were chosen appropriately to meet the requirements. Electrical wiring and data acquisition hardware was assembled. LabVIEW software code was written for controlling temperature and recording data. The second objective was to create a documented method for conducting experiments.

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