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Robots are sophisticated machines which are specially designed to have the capabilities to handle operations, on behalf of human, in many different scenarios. In the past decades, the design of robot systems has been evolving and there are increasing numbers of possible applications of robot. Some systems can even be able to overcome the individual limitations and handle complex problems by combining the strengths of multiple robots. To reduce the risk of human life, robots are now being put into missions under extremely dangerous or hazardous environment where human intervention is not tolerable , such as search-and-rescue missions inside damaged buildings after natural disasters and cleaning up of radioactive materials in nuclear accidence. Even though robots are dispensable, if they are damaged, disabled or trapped, the mission would not be accomplished. Therefore, the longevity of a robot system is always a challenge for robotic operations in such difficult environments. To tackle this challenge, many studies focus on improving the design of individual robot, minimizing the chance of robot failure; or the way that how functioning robots may share the job of the failed robots. The way that how other robots can help failed robots recover, however, has yet to be widely discussed. This thesis studies the feasibility of having multi-robot system with different automatic cooperative recovery abilities on top of its primary functions. A novel cooperative recovery framework is proposed for generic control among system primary functions and recovery behaviours. A number of experiments have been done to study the influence of cooperative recovery on a multi-robot system and how it can affect the system in terms of system performance, sustainability and overhead. An Immunity-based cooperative recovery model has also been created to overcome the drawback introduced by cooperative recovery, finding a balance between the two system objective among system productivity and longevity. Two modified versions of cooperative recovery model are also included in this study to further maximize the system potential. / published_or_final_version / Industrial and Manufacturing Systems Engineering / Doctoral / Doctor of Philosophy

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Enzymes are proteins necessary to maintain essential biochemical processes taking place in all living organisms. Many of them have found applications in industrial sectors such as biotechnology, production of pharmaceuticals and other fine chemicals. The search for new and efficient biocatalysts requires specialised methodology designed for biochemical characterisation and selection of those with potential applications.

M.Sc. (Geology) / The purpose of this investigation is to produce a' general survey of palygorskite deposits in South Africa with reference to their probable extent, mineralogical composition and the most important chemical and physical properties of the clay. Furthermore it is an attempt to provide a suitable beneficiation process so as to make beneficiated local palygorskite comparable with or superior to imported palygorskite. It is also an attempt to determine whether South African beneficiated palygorskite could replace imported material in e$tablished industrial applications. To these ends pa1ygorskites from seven geographical areas in South Africa were investigated. The characterization of the pa1ygorskites involved the following tests: Identification and semi-quantitative analysis of mineral phases in each sample by means of X-ray diffraction. Chemical analyses, differential thermal analyses, oil absorption measurements, surface area determinations, pH measurements, bulk density measurements and viscosity determinations. Electron microscopy of two end products of the beneficiation pro~ess was also carried out to determine the physical difference between magnetic and non-magnetic palygorskite.

Magister Scientiae - MSc / The nitrilases are an important class of industrial enzymes that are found in all phyla. These enzymes are expressed widely in prokaryotes and eukaryotes. Nitrilases convert nitriles to corresponding acids and ammonia. They are used in industry as biocatalysts because of their specificity and enantioselectivity. These enzymes belong to the nitrilase superfamily in which members share a common αββα structural fold and a unique cys, glu,lys catalytic triad with divergent N- and C-terminals.There are four atomic structures of distant homologues in the superfamily, namely 1ems, 1erz, 1f89 and 1j31. All structures have two-fold symmetry which conserves the αββα-αββα fold across the dimer interface known as the A surface. The construction of a 3D model based on the solved structures revealed the enzyme has two significant insertions in its sequence relative to the solved structures, which possibly correspond to the C surface. In addition there are intermolecular interactions in a region of a conserved helix, called the D surface. These surfaces contribute additional interactions responsible for spiral formation and are absent in the atomic resolution homologues.The recombinant enzyme from R.rhodochrous J1 was expressed in E. coli BL21 cells and eluted by gel filtration chromatography as an active 480 kDa oligomer and an inactive 80 kDa dimer in the absence of benzonitrile. This contradicts previous observations, which reported the native enzyme exists as an inactive dimer and elutes as a decamer in the presence benzonitrile. Reducing SDS-PAGE showed a subunit atomic mass of ~40 kDa. EM and image analysis revealed single particles of various shapes and sizes, including c-shaped particles, which could not form spirals due to steric hindrances in its C terminal.Chromatographic re-elution of an active fraction of 1-month old J1 nitrilase enabled us to identify an active form with a mass greater than 1.5 MDa. Reducing SDS-PAGE, N-terminal sequencing and mass spectroscopy showed the molecular weight was ~36.5 kDa as result of specific proteolysis in its C terminal. EM revealed the enzyme forms regular long fibres. Micrographs (109) were recorded on film using a JEOL 1200EXII operating at 120 kV at 50K magnification. Two independent 3D reconstructions were generated using the IHRSR algorithm executed in SPIDER. These converged to the same structure and the resolution using the FSC 0.5 criterion was 1.7 nm. The helix structure has a diameter of 13nm with ~5 dimers per turn in a pitch of 77.23 Å. Homology modeling and subsequent fitting into the EM map has revealed the helix is built primarily from dimers, which interact via the C and D surfaces. The residues, which potentially interact across the D surface, have been identified and these confer stability to the helix. The conservation of the insertions and the possibility of salt bridge formation on the D surface suggest that spiral formation is common among microbial nitrilases. Furthermore, the presence of the C terminal domain in J1 nitrilase creates a steric hindrance that prevents spiral formation. When this is lost – either by specific proteolysis or autolysis - an active helix is formed. / South Africa

Submitted in fulfilment of the academic requirements for the degree of Master of Science in School of Molecular and Cell biology University of the Witwatersrand Johannesburg, South Africa / Esterases are hydrolytic enzymes that have many industrial applications. They are used in food, pharmaceutical, pulp and paper, cosmetics, biofuels and many other industries. This gives research of these enzymes major importance. Esterase genes received from CSIR Biosciences were cloned in E. coli DH5α cells. The plasmids carrying these genes were pET20b(+) for genes named Est1, Est2, Est3, Est4, Est5, Est6, Est7, Est8, Est9, Est10, Est12, Est13, Est14 and pET28a(+) for Est11. These plasmids were extracted from the cloning host and transformed into the expression host which was E. coli BL21. The cells were then induced for expression and the presence of the protein bands representing the products of expression were confirmed by running the crude enzyme extract on SDS-Page. The enzyme extracts were tested for activity using pNp-acetate. All 14 esterases were active and they were characterised in terms of pH optima, temperature optima and kinetics. The enzymes showed a pH range of 6.0 to 9.0 and temperature range of 30°C to 50°C. The enzymes were investigated for substrate specificity and they showed a greater preference for short acyl chain substrates over long acyl chain substrates. Further testing was done for activity of the enzymes using α-naphthylbutyrate and naphthol AS-D chloroacetate alongside lipases. A total of 87 enzymes were tested using these colorimetric assays and 36 of the enzymes were found to be active including all 14 esterases. These 36 enzymes were tested for use in enzymatic resolution of three different chemical compounds available as racemic mixtures. No success was observed for two of the compounds but one of them showed some enantioselectivity. This research will be furthered on at large scale to allow continued synthesis of potential HIV-1 protease inhibitors.

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Microbial nitrile hydratases are important industrial enzymes that catalyse the conversion of nitriles to the corresponding amides. A thermostable, cobalt-type Bacillus sp. RAPc8 microbial nitrile hydratase was cloned and expressed in E.coli. In this study the primary aim was to determine the molecular structure of Bacillus sp. RAPc8 microbial nitrile hydratase.