Yes / Most clinically available prosthetic feet have a rigid attachment or incorporate an “ankle” device allowing elastic articulation during stance, with the foot returning to a “neutral” position at toe-off. We investigated whether using a foot with a hydraulically controlled articulating ankle that allows the foot to be relatively dorsiflexed at toe-off and throughout swing would increase minimum toe clearance (MTC). Twenty-one people with unilateral transtibial amputation completed overground walking trials using their habitual prosthetic foot with rigid or elastic articulating attachment and a foot with a hydraulic ankle attachment (hyA-F). MTC and other kinematic variables were assessed across multiple trials. When using the hyA-F, mean MTC increased on both limbs (p= 0.03). On the prosthetic limb this was partly due to the device being in its fully dorsiflexed position at toe-off, which reduced the “toes down” foot angle throughout swing (p = 0.01). Walking speed also increased when using the hyA-F (p = 0.001) and was associated with greater swing-limb hip flexion on the prosthetic side (p = 0.04), which may have contributed to the increase in mean MTC. Variability in MTC increased on the prosthetic side when using the hyA-F (p = 0.03), but this did not increase risk of tripping.

This thesis presents a series of direct numerical simulations (DNS) performed in order to understand the discrepancy in the literature regarding turbulent asymptotic suction boundary layers (TASBLs) at low Reynolds numbers. The hypothesis to be tested is that the main reason for higher turbulence intensities observed in experiments compared to DNS is that the latter exhibits intermittent patches of laminar flow, developing both temporally and spatially. This hypothesis is confirmed here by comparing simulations with and without tripping, where the former removed patches of laminar flow thereby establishing a fully developed turbulent state with higher turbulence intensities compared to its naturally developing counterpart. The DNS were performed at different suctions rates corresponding to Reynolds numbers above the critical value of 270. The statistics taken from the simulations at different streamwise positions also support the developing character of the flow with increasing intermittency further downstream. Thus, it can be concluded that the actual flow state at these marginal Reynolds numbers is indeed an intermittent one, with lower fluctuation values as the experimental data would indicate.

PURPOSE. To determine the effects of blurring vision on whole-body center-of-mass (CM) dynamics and foot-clearance parameters in elderly individuals performing a single step up to a new level. METHODS. Twelve healthy subjects (mean age, 72.3 ±4.17 years) performed a single step up to a new level (heights of 73 and 146 mm). Trials were undertaken with vision optimally corrected and with vision diffusively blurred by light-scattering lenses (cataract simulation). CM and foot-clearance parameter data were assessed by analyzing data collected by a five-camera, three-dimensional (3-D) motion analysis system. RESULTS. When vision was blurred, subjects took 11% longer to execute the stepping task (P < 0.05), mediolateral displacement of the point of application of the ground reaction force vector (i.e., weighted average of all pressures over the area in contact with the ground; the so called center of pressure, CP) decreased from 37.6% of stance width to 28.3% (P < 0.01), maximum distance between the mediolateral position of the CM and CP decreased by 9.8 mm (P < 0.01), and toe clearance (distance between tip of shoe and edge of step) increased in both the horizontal (28%) and vertical (19%) direction (P < 0.05). CONCLUSIONS. These findings suggest that when vision was blurred, subjects used a twofold safety-driven adaptation: First, to increase dynamic stability they ensured that the horizontal position of their CM was kept close to the center of the base of support and second, they increased horizontal and vertical toe clearance while swinging their lead limb forward to reduce the risk of tripping.

A new power system controlled separation scheme is proposed to prevent the propagation of cascading failures across a transmission network should it undergoes a major disturbance, thereby reducing the possibility of a large-scale blackout. This scheme is developed based on a set of conjectures, which state the following: (i) the locations of out-of-step operations are independent of the severity and the location of the initial faults; (ii) these out-of-step operations occur sequentially over a sufficiently long duration so that relay blocking and transfer tripping can take place to minimize the load-generation imbalance in the formed islands. To verify these conjectures, extensive dynamic stability simulations are executed on a 30-bus and a 517-bus system, which exhibit characteristics suitable for this study. Furthermore, we verify that these out-of-step operations do depend on the prevailing system topology and the operating conditions. / Master of Science

No / Department of Health

The increasing volume of renewable and intermittent generation that is being connected to power systems means that system operators need more advanced dynamic control tools to manage the increase in congestion and the resulting pressure on system constraints. The introduction of synchronised measurement technology provides the wide area real-time measurements that are essential to develop and implement adaptive online solutions for current network issues. The objective of the research presented in this thesis is to design intelligent system integrity protection schemes (SIPS) that protect transmission lines and power transformers from thermal overloading. An intelligent protection scheme should be able to identify the fault severity, predict the post disturbance trend of system states, continue monitoring specific vulnerable system variables and propose an accurate solution that is tailored to the actual system conditions and the specific contingencies that have occurred. The intent of this research is to contribute to the development of adaptive protective schemes that are enabled by modern synchronized measurement technologies for future power systems. The research presented in this thesis focuses on the creation of novel Operational Tripping Schemes (OTSs) that explicitly satisfy both the functionality and economical requirements by integrating an improved assessment of thermal behaviour of the monitored assets. Novel OTSs are proposed for both transmission lines and transformers and they can be considered to be intelligent, adaptive and efficient SIPS for the thermal protection of system assets. A novel functional block is proposed that be included within the OTS and that uses optimization theory to determine the lowest cost solution to overheating in the time available. Furthermore, case studies have been conducted to verify the performance of each novel OTS using simulations of a full GB system model.

Made available in DSpace on 2014-12-17T14:08:31Z (GMT). No. of bitstreams: 1 GustavoHVPP.pdf: 1012393 bytes, checksum: d85648d797f788ab43d046f3e32bca54 (MD5) Previous issue date: 2008-11-03 / The new oil reservoirs discoveries in onshore and ultra deep water offshore fields and complex trajectories require the optimization of procedures to reduce the stops operation during the well drilling, especially because the platforms and equipment high cost, and risks which are inherent to the operation. Among the most important aspects stands out the drilling fluids project and their behavior against different situations that may occur during the process. By means of sedimentation experiments, a correlation has been validated to determe the sedimentation particles velocity in variable viscosity fluids over time, applying the correction due to effective viscosity that is a shear rate and time function. The viscosity evolution over time was obtained by carrying out rheologic tests using a fixed shear rate, small enough to not interfere in the fluid gelling process. With the sedimentation particles velocity and the fluid viscosity over time equations an iterative procedure was proposed to determine the particles displacement over time. These equations were implemented in a case study to simulate the cuttings sedimentation generated in the oil well drilling during stops operation, especially in the connections and tripping, allowing the drilling fluid project in order to maintain the cuttings in suspension, avoiding risks, such as stuck pipe and in more drastic conditions, the loss of the well / As novas descobertas de reservat?rios de petr?leo em campos onshore e offshore em l?minas d ?guas ultra-profundas e de trajet?rias complexas demandam a otimiza??o dos processos de perfura??o para reduzir as opera??es de paradas durante a perfura??o de um po?o, especialmente devido ao elevado custo das plataformas, equipamentos e dos riscos que s?o inerentes ? opera??o. Dentre os aspectos mais importantes destaca-se o projeto de fluidos de perfura??o e o estudo de seu comportamento frente a diferentes situa??es que podem ocorrer durante o processo. Atrav?s de experimentos de sedimenta??o, foi validada uma correla??o para determina??o da velocidade de sedimenta??o de part?culas em fluidos de viscosidade vari?vel com o tempo, aplicando-se as devidas corre??es para viscosidade efetiva que ? fun??o da taxa de deforma??o e do tempo. A evolu??o da viscosidade com o tempo foi obtida atrav?s de ensaios reol?gicos utilizando uma taxa de deforma??o fixa, pequena o suficiente para n?o interferir no processo de gelifica??o do fluido. Com as equa??es de velocidade de sedimenta??o de part?culas e da viscosidade do fluido com o tempo foi proposto um procedimento iterativo capaz de determinar o deslocamento das part?culas com o tempo. Essas equa??es constitutivas foram aplicadas no estudo de caso para simula??o da sedimenta??o dos cascalhos gerados na perfura??o de um po?o de petr?leo durante paradas operacionais, especialmente as conex?es e manobras, possibilitando o projeto do fluido de perfura??o de maneira a manter os cascalhos em suspens?o, evitando riscos, como por exemplo, a pris?o da coluna de perfura??o e em condi??es mais dr?sticas, a perda do po?o

The capital maintenance rules stem from the English company law and were primarily aimed at protecting the rights of a company’s creditors. Before the introduction of the Companies Amendment Act 37 of 1998, a company was prohibited from purchasing its own shares. After this legislation was passed, a company was able to do so, provided that it satisfied the solvency and liquidity test and also complied with the new statutory provisions set out by sections 85 to 89 of the Companies Act 61 of 1973. Section 48 of the Companies Act 71 of 2008 now regulates the acquisition by a company of its own shares, as well as the acquisition of shares in its holding company by a subsidiary company. The above actions also fall under the ambit of a “distribution” as defined in the Act and therefore need to satisfy the requirements of section 46 of the Act as well. Unlike its predecessor, the provisions in the new Act are very broad and devoid of guidelines. The emphasis is placed on companies satisfying the principles of solvency and liquidity. Non-adherence to these provisions gives rise to the personal liability of the company’s directors. The provisions of section 48 do not apply where a dissenting shareholder exercises his appraisal rights in terms of section 164 of the new Act, or where a company redeems redeemable securities. These exceptions do, however, still amount to “distributions” and will accordingly need to satisfy the requirements contained in section 46 of the Act. Redeemable securities were initially not exempted from the provisions of section 48. This would potentially have given rise to a situation where a company could approach a court in terms of section 48(6) to reverse a redemption of its securities. It would have had dire consequences for financing by way of redeemable securities. In terms of the Companies Amendment Act 3 of 2011 redeemable securities are now specifically exempted from the provisions of section 48. In terms of the new Act a subsidiary company is allowed to purchase shares in its holding company to a maximum of 10% in the aggregate of the issued shares of any share class, provided that no voting rights attached to such shares may be exercised. The new Act fails to properly address some of the issues regarding the “round-tripping” of dividends and the declaration of a dividend in specie that were already identified as far back as 2001. Where the consideration for a repurchase constitutes a “dividend” as defined in the Income Tax Act 58 of 1962, the company will be liable to pay secondary tax on companies in respect thereof. If a distribution does not constitute a dividend, capital gains tax is payable with regard to it. Share repurchases are allowed in terms of Canadian corporate law after the legislative reform which occurred in that country during the 1970’s. The Canadian Business Corporations Act contains provisions that bear a striking resemblance to the provisions of the new Act adopted in South Africa. Whilst the basis and rationale behind the new corporate legislation cannot be faulted, a host of issues and concerns still remain. The unfortunate consequence is that the new Act lacks transparency and is fraught with clumsy errors. Copyright / Dissertation (LLM)--University of Pretoria, 2012. / Mercantile Law / unrestricted

The thesis discusses a series of related techniques that prepare and transform raw linguistic data for advanced processing in order to unveil hidden grammatical patterns. A threedimensional array is identified as a suitable data structure to build a data cube to capture multidimensional linguistic data in a computer's temporary storage facility. It also enables online analytical processing, like slicing, to be executed on this data cube in order to reveal various subsets and presentations of the data. XML is investigated as a suitable mark-up language to permanently store such an exploitable databank of Biblical Hebrew linguistic data. This concept is illustrated by tagging a phonetic transcription of Genesis 1:1-2:3 on various linguistic levels and manipulating this databank. Transferring the data set between an XML file and a threedimensional array creates a stable environment allowing editing and advanced processing of the data in order to confirm existing knowledge or to mine for new, yet undiscovered, linguistic features. Two experiments are executed to demonstrate possible text-mining procedures. Finally, visualisation is discussed as a technique that enhances interaction between the human researcher and the computerised technologies supporting the process of knowledge creation. Although the data set is very small there are exciting indications that the compilation and analysis of aggregate linguistic data may assist linguists to perform rigorous research, for example regarding the definitions of semantic functions and the mapping of these functions onto the syntactic module. / Thesis (PhD (Information Technology))--University of Pretoria, 2008. / Information Science / unrestricted

This thesis considers Confessional poetry and Black Arts poetry against the backdrop of the political and social culture of the 1950s that influenced the styles of these two major poetic movements. I examine Sylvia Plath's and Nikki Giovanni's distinct poetic personas and the language they employ in relation to each other as representatives of confessional and Black Arts poetry, two poetic styles often thought to be inherently opposed to each other, one personal and one political. I identify connections between these seemingly different poets and movements through close readings of key poems by Plath and Giovanni that situates them within second-wave feminism and the civil rights movements of the 1960s. I argue that both poets devise an alternate persona language that is especially exaggerated to create defiant personas of resistance as a direct response to the constricting political conditions in the United States at mid-century.