No description available.

This thesis gives an outline of the ionosphere and studies that were conducted to investigate / Thesis (M.Sc.) - University of KwaZulu-Natal, 2009.

No description available.

No description available.

No description available.

Research in incorporating natural fibers in composites has been in progress for a few decades where the various mechanical, electrical and acoustic properties of such composites were explored. Natural fiber composites (NFCs) have few benefits over the traditional glass or carbon fiber composites such as light weight, low manufacturing cost and requiring less energy for production. NFC is also bio-degradable and recyclable. The primary objectives of this research are to explore the static and dynamic properties of the hemp and linear low density polyethylene (LLDPE) and determine impact absorbing capability using the above mentioned properties. LLDPE is surface-treated with maleic anhydride grafted polyethylene (MA-g-PE) and sodium hydroxide (NaOH). A melt-mixing process is employed where LLDPE is compounded with the hemp fibers in 10%, 20% and 30% vol. fraction. Tensile and flexural properties are measured. The material is characterized by propagating Lamb waves generated using a dropped dead weight. Time-frequency information is extracted from a thin disc-like specimen using the Gabor Wavelet Transform (GWT) so as to characterize the material. Detection of defect is also established using the generated waves and GWT. Using Gabor wavelet coefficients, the dispersion and attenuation of the specimen are determined in different material directions. Comparison of attenuation of the waveforms is observed at different locations providing the knowledge of materials homogeneity, the materials behavior due to an impact and its impact absorbing character.

The wavefront construction (WFC) method is an effective tool to compute seismic ray fields and has wide applications. This paper applies the WFC method to a heterogeneous earth model represented as a 3-D grid instead of a sequence of smooth layers, as the layered model is insufficient for the regions with complex geological structures. In order to utilize gridded models, highly heterogeneous models must be smoothed for reliable numerical results. A new velocity gradient smoothing method is proposed that is able to control quantitatively the smoothness of the velocity model while preserving the main structural characteristics of the original model. A modified inverse distance weighting method is applied to obtain velocities or densities at an arbitrary point in the model for successive wavefront propagation. A very complex 3-D grid model based on the standard Marmousi reference model is tested to compare the new approach to alternative smoothing schemes, and the first arrival travel times from the WFC method are compared with results from an eikonal solver. These results are obtained more quickly, but the algorithm is restricted to computing only first arrivals. However, comparison helps to establish the accuracy of the WFC solutions and assess the influence of the smoothing schemes. The modeling comparisons verify the effectiveness of the proposed smoothing methods and the enhanced performance of the WFC algorithm with the 3-D grid model.

Thesis (M App Sc) -- University of South Australia, 1992

Typewritten copy / Includes bibliography. / 74 leaves : diag. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, 1957?

Thesis (Ph.D.)--University of Adelaide, 1957? / Typewritten copy. Includes bibliography.