No description available.

No description available.

Concern regarding grinding media wear is as old as the invention of the tumbling mill itself. Over the years many techniques have been tried in an attempt to minimize costs associated with grinding. These have included experimentation with different metals, non-metals and different shapes. Through all this, steel grinding balls have proved the most effective media for comminution in tumbling mills. / As old as the tumbling mill is, no accurate technique for estimating the wear of the ball charge has been developed. The mining industry still utilizes the Bond Abrasion test that was developed in the early 1960s. This test which is based solely on the ore properties is inadequate giving a standard deviation in excess of 100%. This can results in high degree of error which for greenfield applications can indicate profitability for non-profitable operations and vice versa. / Peter Radziszewski proposed a decoupled total grinding media wear model that could be used to predict grinding media instead of using the Bond abrasion test. This new model had a standard deviation of 56%, which was a great improvement over the bond abrasion wear estimates. This new model also allowed for the first time, the three wear modes, abrasion, corrosion and impact, responsible for grinding media wear to be quantified. This was an important development as the ability to identify the dominant wear mode in any given operation gives operators a chance to target reduction of wear. The current mining trend is towards exploitation of lower grade ores as the higher grades become depleted. These low-grade ores require finer grinding for the liberation of the value minerals. This in turn means higher ball consumption and higher beneficiation costs. The reduction of ball wear to minimise the overall cost of ore processing operation is going to be a primary concern for all concentrators. / The objective of the research that forms the basis of this thesis was to improve the accuracy of the decoupled grinding media wear model. This was achieved by refining the tests and methodologies used to determine the wear components that make up the decoupled grinding media wear model, performing fundamental testwork to determine a more accurate structure of the decoupled model, and validating this new model. / The new model termed the "modified decoupled grinding media wear model", gives better accuracy in predicting grinding media wear than both the Bond abrasion test and the original decoupled model.

We investigate nonperturbative effects due to instantons in N = 2 supersymmetric SU(N) Yang-Mills models, with the aim of testing the exact results predicted for these models. In two separate semiclassical calculations we obtain the one-instanton contribution to the Higgs condensate u(_3) = (TrA(^3)) and to the prepotential F. Comparing our results with the exact predictions, we find complete agreement except when the number of flavours of fundamental matter hypermultiplets, N(_f), takes certain values. The source of the u(_3) discrepancy is an ambiguity in the parameterization of the hyperelliptic curves from which the exact predictions are derived when N(_f) ≥ N. This ambiguity can easily be fixed using the results of instanton calculations. The discrepancy associated with T appears in the finite N(_f) = 2N models. For these models we are unable to modify the curves to agree with the instanton calculations when N > 3. Our one-instanton calculation of the prepotential is facilitated by a multi-instanton calculus which we construct, starting from the general solution of Atiyah, Drinfeld, Hitchin and Manin. Our calculus comprises: (i) the super-multi-instanton background, (ii) the su persymmetric multi-instanton action and (iii) the supersymmetric semiclassical collective coordinate measure. Our calculus has application to supersymmetric Yang-Mills theory with gauge group U(N) or SU(_N). We employ our instanton calculus to derive results at arbitrary k-instanton levels. In N =2 supersymmetric SU(N) Yang-Mills theory, we derive a closed form expression for the A;-instanton contribution to the prepotential. This amounts to a solution, in quadratures, of the low-energy physics of the theory, obtained from first principles. In supersymmetric SU(2) Yang-Mills theory, we use our calculus to investigate multi-instanton contributions to higher-derivative terms in the Wilsonian effective action. Using a scaling argument, based on general properties of the SU(2) k-instanton action and measure, we show that in the finite, massless N = 2 and N = 4 models, all k-instanton contributions to the next-to- leading higher-derivative terms vanish. This confirms a nonperturbative nonrenormalization theorem due to Dine and Seiberg.

Thesis (MSc Microbiology)--University of Pretoria, 2007. / Includes bibliographical references. Available on the Internet via the World Wide Web.

Thesis (doctoral)--Vereinigte Friedrichs-Universität Halle-Wittenberg. / Vita. Includes bibliographical references (p. [3]-5).

Thesis (MPhil) -- AUT University, 2008. / Includes bibliographical references. Also held in print (x, 89 leaves : ill. ; 30 cm.) in the Archive at the City Campus (T 621.194 ZHA)

Universität Jena, 1742, Thesis. / At head of title: Q.B.V.D. - Goldsmiths'-Kress no. 07887.1. - OCLC, 25012218. - Reproduction of original from Kress Library of Business and Economics, Harvard University.

Berlin, Humboldt-Univ., Diss., 2003. / Computerdatei im Fernzugriff.

Berlin, Humboldt-Univ., Diss., 2003. / Computerdatei im Fernzugriff.