Deterministic models for the transmission dynamics of HIV/AIDS and trichomonas vaginalis (TV) in a human population are formulated and analysed. The models which assumed standard incidence formulations are shown to have globally asymptotically stable (GAS) disease-free equilibria whenever their associated reproduction number is less than unity. Furthermore, both models possess a unique endemic equilibrium that is GAS whenever the associated reproduction number is greater than unity. An extended model for the co-infection of TV and HIV in a human population is also designed and rigorously analysed. The model is shown to exhibit the phenomenon of backward bifurcation, where a stable disease-free equilibrium (DFE) co-exists with a stable endemic equilibrium whenever the associated reproduction number is less than unity. This phenomenon can be removed by assuming that the co-infection of individuals with HIV and TV is negligible. Furthermore, in the absence of co-infection, the DFE of the model is shown to be GAS whenever the associated reproduction number is less than unity. This study identifies a sufficient condition for the emergence of backward bifurcation in the model, namely TV-HIV co-infection. The endemic equilibrium point is shown to be GAS (for a special case) when the associated reproduction number is greater than unity. Numerical simulations of the model, using initial and demographic data, show that increased incidence of TV in a population increases HIV incidence in the population. It is further shown that control strategies, such as treatment, condom-use and counselling of individuals with TV symptoms, can lead to the effective control or elimination of HIV in the population if their effectiveness level is high enough. / Dissertation (MSc)--University of Pretoria, 2017. / DST-NRF SARChI Chair in Mathematical Models and Methods in Biosciences and Bioengineering (M3B2) / Mathematics and Applied Mathematics / MSc / Unrestricted

In this thesis we study a novel approach to on-line learning of artificial neural networks, called backward modelling, and apply it to active learning in the sensorimotor loop. At first the mathematic foundations of this approach are elaborated. We observe effects like spontaneous symmetry breaking, response increasing, and generalisation improvement at a theoretical level. We then justify the theory with experimental results on some synthetic problems, in order to understand the phenomena clearly. Finally we consider a simple robot with an adaptive world model. In the case the controller of the robot is just covering a sub-space of the actuator space we realise degenerated world representations in the world model with passive learning and standard learning algorithms. We show that backward modelling and active learning point out degeneracies in the world model and correct them with direct exploration. A special kind of active learning evolves from the use of backward modelling which directly queries patterns on the fly. Additionally, different strategies are investigated in order to control the interplay of controller based and active learning based behaviour.

Diese Diplomarbeit untersucht die Optimierung eines Mean-Variance Portfolios auf einem vollständigen Markt unter der Bedingung, dass die Insolvenz des Investors ausgeschlossen ist. Hierbei wird die duale Methode (auch Martingalmethode genannt)

In this thesis, I describe the main ideas and summarize the results of four refereed papers I contributed to (three times as the second author and once as the first author). The first step of each of these papers was the identification of genetically related asteroid and their membership confirmation. Since members of asteroid pairs and clusters have a very similar heliocentric orbits, we employed and further developed methods based on backward orbital integrations. The chronologically first paper Pravec et al. (2018) deals with asteroid clusters and their similarity to asteroid pairs. The second paper Pravec et al. (2019) is a complex study of 93 asteroid pairs with many interesting results, such as the existence of binary asteroids among asteroid pairs. The third paper Moskovitz et al. (2019) deals with an identification of asteroid pairs in the near-Earth population and a detail study of two probable asteroid pairs. The fourth paper, Fatka et al. (2020), studies the phenomenon of cascade disruption in asteroid clusters, which results in multiple generations (with different ages) of escaped secondaries in some asteroid clusters.

Uses rule based AI (forward and backward chaining) to model legal decision making by judges. / AI to model legal decision making (c) Eric Engle

The purpose of this thesis is to explore how to enable forward traceability of textile and fashion products at product level, using BC based traceability solutions. The study finds that within TC industry, forward traceability using available technologies (RFIDs, NFCs, QR codes ) is technically possible, however there could be impending regulatory, legal, technical implications of using these technologies. These implications may result in a slew of added compliance requirements, risk assessments and resources allocations from brands and retailers. As a result, this study uncovered that using QR codes with BC technology offers a suitable forward traceability solution which has the potential to set off most of the implications explored during this study. Moreover, to attain forward traceability at product levels, a complete mechanism involving readiness from customers, suppliers and all other stake holders is required. All these stake holders need to be connected to the central BC network, where data is protected and made tamper proof. Lastly, forward tracing at product levels is a futuristic concept, as TC industry is still majorly focused on the backward traceability, however this study finds that forward traceability at product levels may pave its way as a beneficial component of overall sustainability.

Numerous practical applications exist where dispersed solid particles are transported within a turbulent accelerating or decelerating gaseous flow. The large density variation between phases creates the potential for significant differences in velocity known as velocity slip. Flow over a backward facing step provides a well characterized, turbulent, decelerating flow useful for measuring the relative velocities of the solid and gaseous phases in order to determine velocity slip and particle drag. Numerous investigations have been conducted to determine the gas phase velocity in a backward facing step for both laminar and turbulent flows and therefore the gas phase flow is well know and documented. Furthermore, some studies have also been conducted to determine the velocity of various sizes of spherical particles in a backward facing step and compared with their corresponding gas phase velocities. Few if any velocity measurements have been made for non-spherical particles in a backward facing step. In this work, a Phase Doppler Particle Analyzer (PDA) was used to measure gas and particle phase velocities in a backward facing step. The step produced a 2:1 increase in cross sectional area with a Reynolds number of 22,000 (based on step height) upstream of the step. Spherical particles of 1 – 10 μm with an average diameter of 4μm were used to measure the gas phase velocity. At least three sizes in the range of (38 – 212 μm) for four different particles shapes were studied. The shapes included: spheres, flakes, gravel, and cylinders. Since the PDPA is not able to measure the size of the non-spherical particles, the particles were first separated into size bins and a technique was developed using the PMT (photo multiplier tubes) gain to isolate the particle size of interest for each size measured. The same technique was also used to measure terminal velocities of the particles in quiescent air. The measured gas phase velocity and spherical solid phase particles were in good agreement with previous measurements in the literature. The results showed relative velocities between the particles and gas phase to be in the range of 0 – 3 m/s which is in transition between stokes flow and fully developed turbulent flow. Drag coefficients were an order magnitude higher for non-spherical particles in turbulent flows in comparison to stokes flow which agreed reasonably well with quiescent terminal velocity drag. This information is valuable for modeling turbulent two-phase flows since most assumptions of the drag are currently based on correlations from empirical data with particles moving through a still fluid.

National and international research on governmental privatization efforts reflects myriad successes and failures. However, little is known about the effectiveness of family safety privatization efforts in the state of Florida. In Brevard County, Florida, family safety privatization efforts have been underway for several years now, and while evaluations are taking place, they do not reflect one key piece of information—the perceptions of family safety workers. A snowball sample was obtained from former and current child safety workers and open- and closed-ended questions were administered with a total of 15 former and current family safety workers who work or worked for several different public and private family safety agencies within Brevard County, Florida. Information was obtained regarding perceptions of privatization to adequately and more efficiently do the work of public entities. The results show two primary areas of interest. The model of care which has been instituted post-privatization (CARES) has been perceived as more effective than the former state model; the strongest problematic themes that developed concerned power, control, and the perception of unfairness. These themes are explored using a backwards mapping approach and recommendations for continued growth and cohesion are explored.

Micro particle image velocimetry (microPIV) is a non-intrusive tool for visualizing flow in micron-scale conduits. Using this investigative instrument, two experimental studies were performed to understand flow behaviors in microfluidic channels - a sudden expansion step flow and laminar velocity profile variation in diffusion driven mixing. First, flow in a backward facing step feature (1:5 expansion ratio) in a microchannel was taken as the subject of microPIV flow visualization. The onset and development of a recirculation flow was studied as a function of flow rate. This flow pattern was further used to investigate two major parameters affecting microPIV measurements; the depth-of-focus and recording time-intervals between images in a microPIV image pair. The onset of recirculation was initiated at flow rates that correspond to Reynolds numbers, Re > 95, which is well beyond the typical working range of microfluidic devices (Re=0.01-10). The recirculation flow has a 3D structure due to the dimensions of the microchannel and the effect of no slip condition on the walls. Ensemble cross-correlation was found not to be sensitive to variations of depth-of-focus and the output flow fields were similar as long as the overall optical focus remained within the upper and lower bounds of the microchannel. However, variations of time intervals between images in a microPIV pair, resulted in quantitatively and qualitatively different flow patterns for a given constant flow rate and depth-of-focus. In the second experiment, the effect of the laminar velocity profile and its variation on mixing phenomena at the reduced scale is studied. It is shown that the diffusive mass flux between two miscible streams, flowing in a laminar regime in a microchannel, is enhanced if the velocity at their diffusion interface is increased. Based on this idea, an in-plane passive micromixing concept is proposed and implemented in a working device (sigma micromixer). This mixer shows considerable mixing performance by periodically varying the flow velocity profile, such that the maximum of the profile coincides with the transversely progressing diffusion fronts repeatedly throughout the mixing channel. microPIV has been used to visualize the behavior of laminar flow inside the micromixer device and to confirm the periodic variation of the velocity profile through the mixing channel.

Helicopter operations in the vicinity of small naval surface vessels often require excessive pilot workload. Because of the unsteady flow field and large mean velocity gradients, the envelope for flight operations is limited. This experimental investigation uses a 1:144 scale model of the U.S. Navy destroyer DDG-81 to explore the problem. Both active and passive flow control techniques were used to improve the flow field in the helicopter's final decent onto the flight deck. Wind tunnel data was collected at a set of grid points over the ship's flight deck using a single component hotwire. Results show that the use of porous surfaces decreases the unsteadiness of the flow field. Further improvements are found by injecting air through these porous surfaces, causing a reduction in unsteadiness in the landing region of 6.6% at 0 degrees wind-over-deck (WOD) and 8.3% at 20 degrees WOD. Other passive configurations tested include fences placed around the hangar deck edges which move the unsteady shear layer away from the flight deck. Although these devices cause an increase in unsteadiness downstream of the edge of the fence when compared to the baseline, the reticulated foam fence caused an overall decrease in unsteadiness in the landing region of 12.1% at 20 degrees WOD. / Master of Science