Lo, Yun Chuen. / Thesis (M.Sc.)--Chinese University of Hong Kong, 1992. / Includes bibliographical references (leaves 69-70). / Summary --- p.1 / Introduction --- p.2 / Methods --- p.6-15 / Subjects / Sample treatment / Protocol / "Equipment, reagents and assays" / Results --- p.15-58 / Technical aspects / Assay characteristics / Stability / Biological variation / Discussion --- p.58-68 / Acknowledgements --- p.68 / References --- p.69

Résumé: Le comportement des turbomachines (pompes, compresseurs) fonctionnant à des conditions hors conception, et particulièrement aux débits partiels, est sujet à des phénomènes d'instabilité qui pourraient affecter leur performance et peuvent être dramatiques pour les machines ou leur environnement. Cette étude se concentre sur la décrochage tournant dans un diffuseur lisse radial. L'objectif est proposer un modèle théorique pour prédire rapidement les caractéristiques de décrochage tournant. Une étude expérimentale est effectuée en premier pour obtenir les caractéristiques de décrochage tournant dans un transparent diffuseur lisse d’une roué radiale. L'effet de décrochage tournant sur la performance du diffuseur est discuté basé sur les mesures de pression statique. Le résultat montre que décrochage tournant amélioré la récupération de la diffuseur pression, et les raisons sont proposes. Basé sur la configuration expérimentale, une analyse de stabilité linéaire qui est construit par l'équation de continuité, l'équation de la quantité de mouvement et les équations de vorticité, est propose. Les caractéristiques expérimentales de décrochage tournant: le nombre et la vitesse de propagation des cellules de décrochage tournant, sont calculés théoriquement. Le taux de croissance dans le modèle linéaire, est proposé pour déterminer la critique condition de décrochage tournant, et le dominant mode de décrochage tournant lorsque différents modes existent par intermittence. La théorique vitesse et pression fluctuations sont tracées pour décrire le débit du diffuseur à l'état de décrochage. Les capacités et les limites de la linéaire stabilité analyse sont conclues par la comparaison entre les résultats théoriques et expérimentaux. Ensuit, une non linéaire stabilité analyse est étendue pour considérer les non linéaires combinaisons qui sont négligées dans le modèle linéaire. L'objectif est donner des corrections (par termes non linéaires) aux résultats linéaires, les conclusions et les discussions sont faites à la fin. / Abstract:The behavior of work-absorbing turbomachines (pumps, compressors) operating at off design conditions, and especially at partial flow rates, is subject to instability phenomena that could affect their performance and can be dramatic for the machines or their environment. This study is focused on the rotating stall in the vaneless diffuser, the objective is to propose a theoretical model to fast predict the characteristics of such an instability. An experimental study is performed first to obtain those characteristics of rotating stall in a transparent vaneless diffuser of a radial impeller. The effect of rotating stall on the diffuser performance is discussed based on the static pressure measurements. The result shows rotating stall improved the diffuser pressure recovery, and the reasons are proposed. Based on the experimental setup, a linear stability analysis which is constructed by the continuity equation, momentum equation and vorticity equations, is proposed. The experimental characteristics of rotating stall: number and propagation velocity of stall cells, are theoretical calculated. The growth rate in the linear model, is proposed to determine the critical stall condition, and the dominant stall mode when different stall modes exist intermittently. The theoretical velocity and pressure fluctuations are also plotted to show the diffuser flow at stall condition. The abilities and limits of the linear stability analysis are concluded through the comparisons between theoretical and experimental results. Based on the linear model, a nonlinear stability analysis is extended to consider the nonlinear combinations which are neglected in the linear model, the aim is to give corrections (from nonlinear terms) to the linear results of rotating stall, the conclusions and discussions are made at the end.

Chen Zhiyong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 54-57). / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgement --- p.ii / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Nonlinear Control --- p.1 / Chapter 1.2 --- Global Stabilization --- p.2 / Chapter 1.3 --- Output Regulation --- p.3 / Chapter 1.4 --- Contributions of the Thesis --- p.4 / Chapter 2 --- Global Robust Stabilization of Cascaded Polynomial Systems --- p.5 / Chapter 2.1 --- Introduction --- p.5 / Chapter 2.2 --- Preliminaries --- p.6 / Chapter 2.3 --- Basic Results --- p.8 / Chapter 2.4 --- The Algorithm --- p.11 / Chapter 2.5 --- An Example --- p.14 / Chapter 2.6 --- Concluding Remarks --- p.16 / Chapter 3 --- Output Regulation of Singular Nonlinear Systems by Normal Output Feedback --- p.18 / Chapter 3.1 --- Introduction --- p.18 / Chapter 3.2 --- Preliminaries --- p.20 / Chapter 3.3 --- Main Result --- p.24 / Chapter 3.4 --- An Example --- p.34 / Chapter 3.5 --- Concluding Remarks --- p.35 / Chapter 4 --- Robust Output Regulation of Singular Nonlinear Systems --- p.37 / Chapter 4.1 --- Introduction --- p.37 / Chapter 4.2 --- Problem Description and Standard Assumptions --- p.38 / Chapter 4.3 --- A Preliminary Result --- p.40 / Chapter 4.4 --- Solvability of the Problem --- p.48 / Chapter 4.5 --- Concluding Remarks --- p.51 / Chapter 5 --- Conclusions --- p.52 / Bibliography --- p.54 / Biography --- p.58

In 14th August 2003, the Northeast USA suffered its worst power outage event in history. The power disturbance spreading through the system caused mal-trips of the distance relay remote back-up protections, which indeed contributed to the power outage cascading a wide area. The power outage in the Northeast USA was constrained by the presence of HVDC interconnections between the HVAC networks in Ontario and New York. The system collapse did not progress beyond the HVDC interconnection interface with Quebec. The HVDC link can regulate the voltage and current therefore impacts on the performance of the protection and system stability. The distance relay mal-operations were one of the main cause of the Northeast USA blackout as well as the other recent major large area blackouts which were pointed out by the previous papers. This thesis is focus on investigate how HVDC interconnections contribute to maintaining the power system stability. The research work investigated the performance of a distance relay to faults and disturbance on networks containing HVDC interconnection. The research work was carried out by modelling and testing a classic signal processing distance relay in a simple AC network which was based on Kunder’s two areas system using MATLAB/SIMULINK at first. Then the modeled distance relay’s performance was investigated by combining the distance relay and a simple HVDC link based on the Kunder’s two areas system. The research work firstly combined the signal processing distance relay and the HVDC link together to investigate the distance relay’s performance when the protected feeder containing DC link. The distance relay’s performance was investigated when the protected feeders containing HVDC link under fault conditions and power swing conditions. For comparison, a similar power system without HVDC link was also simulated.

Many environments are inaccessible or hazardous for humans. Remaining debris after earthquake and fire, ship hulls, bridge installations, and oil rigs are some examples. For these environments, major effort is being placed into replacing humans with robots for manipulation purposes such as search and rescue, inspection, repair, and maintenance. Mobility, manipulability, and stability are the basic needs for a robot to traverse, maneuver, and manipulate in such irregular and highly obstructed terrain. Hexapod walking robots are as a salient solution because of their extra degrees of mobility, compared to mobile wheeled robots. However, it is essential for any multi-legged walking robot to maintain its stability over the terrain or under external stimuli. For manipulation purposes, the robot must also have a sufficient workspace to satisfy the required manipulability. Therefore, analysis of both workspace and stability becomes very important. An accurate and concise inverse kinematic solution for multi-legged robots is developed and validated. The closed-form solution of lateral and spatial reachable workspace of axially symmetric hexapod walking robots are derived and validated through simulation which aid in the design and optimization of the robot parameters and workspace. To control the stability of the robot, a novel stability margin based on the normal contact forces of the robot is developed and then modified to account for the geometrical and physical attributes of the robot. The margin and its modified version are validated by comparison with a widely known stability criterion through simulated and physical experiments. A control scheme is developed to integrate the workspace and stability of multi-legged walking robots resulting in a bio-inspired reactive control strategy which is validated experimentally.

"The maintenance and inspection of societal structures and equipment such as skyscrapers, bridges, and ship hulls are important to maintaining a safe lifestyle. Improper maintanance and delayed inspection can lead to catastrophic failure. In lieu of placing humans in potential harm, mobile robotic machining systems can be used to enable remote repair and maintenance within constrictive, hazardous, and inaccessible environments. Due to their intrinsic high mobility and 6-DOF control, hexapod walking robots are a salient solution to mobile machining. However, the static structure of traditional hexapod robots can be rather limiting when attempting to traverse over irregular terrain or manipulating objects. This research realizes a new scalable hexapod robot and analyzes the lateral stable workspace of the robot under different external loading conditions. The scalable design allows the robot to extend its legs which enhances the workspace and improves stability while manuevering through constrictive and irregular terrain. The design incorporates two additional prismatic joints into the legs of the traditional hexapod robot design providing a compact, rigid, and efficient design. The electronic printed circuit boards were designed and assembled in-house. A distributed control architecture was implemented to off-load low-level leg control to dedicated leg controllers. An analysis on the lateral stable workspace of the scalable hexapod robot under different external loading conditions is presented. A dynamic stable workspace criterion is derived. The stable workspace criterion provides a metric for comparing stable workspaces between hexapod robots with different configurations. Multiple simulations and physical experiments were conducted to demonstrate the advantages of a scalability in hexapod designs."

This thesis details potential design improvements by exploiting a new general grid model utilizing multiple wind and solar energy plants. A single renewable energy plant which relies on wind speed or solar insolation is unreliable because of the stochastic nature of weather patterns. To allow such a plant to match the requirements of a variable load some form of energy storage must be incorporated. To ensure a low loss of load expectation (LOLE) the size of this energy storage must be large to cope with the strong fluctuations in energy production. It is theorized that by using multiple renewable energy plants in separate areas of a region, the different weather conditions might approach a probabilistically independent relationship. The probability of energy generated from combined plants will then approach a Gaussian distribution by the central limit theorem. While maintaining the same LOLE as a single renewable plant this geographic separation model theoretically stabilizes the energy production and reduces the system variables: energy storage size, energy storage efficiency, and cumulative plant capacity. New generic weather models that incorporate levels of independence are created for wind speeds and solar insolations at different locations to support the geographic separation model. As the number of geographically separated plants increases and the weather approaches independence the system variables are reduced.

Epilepsy -- the condition of recurrent, unprovoked seizures -- manifests in brain voltage activity with characteristic spatio-temporal patterns. One of the patterns typically observed during a seizure is a traveling wave. To characterize these waves, we analyze high-density local field potential (LFP) data recorded in vivo from human cortex during a seizure from three patients. We show that traveling wave patterns emerge in the LFP with consistent quantitative features. Using a mean-field approach we model the neuronal population activity observed in the LFP and obtain explicit traveling wave solutions for this model. We then employ the LFP data to constrain the model and obtain parameter configurations that support traveling wave solutions with features consistent with the observed LFP waves. In particular, our model formulation is able to capture the "reverberation" of the activity following the traveling wave that was found in the clinical data. We obtain biologically reasonable parameter estimates for two important features: the timescales of the model and the extent of the connectivity. In this way, we link the observed LFP waves during seizure to proposed biological mechanisms. We also study the linear stability of the traveling wave solutions by constructing an Evans function. We find for some parameters the existence of two waves: one wave is slow and narrow whereas the other wave is fast and wide. Moreover, the fast and wide wave has speed and width consistent with the observed LFP waves. We numerically analyze the Evans function to determine stability (instability) of the fast (slow) wave.

From the alignment of magnets to the melting of ice, the transition between different phases of matter underpins our exploitation of materials. Both a quantum and a classical phase can undergo an instability into another state. In this thesis, we study the stability of matter in both contexts: topological states and crystalline solids. We start with the stability of fractional quantum Hall states on a lattice, known as fractional Chern insulators. We investigate, using exact diagonalization, fractional Chern insulators in higher Chern bands of the Harper-Hofstadter model, and examine the robustness of their many-body energy gap in the effective continuum limit. We report evidence of stable states in this regime; comment on two cases associated with a bosonic integer quantum Hall effect; and find a modulation of the correlation function in higher Chern bands. We next examine the stability of molecules using variational and diffusion Monte Carlo. By incorporating the matrix of force constants directly into the algorithms, we find that we are able to improve the efficiency and accuracy of atomic relaxation and eigenfrequency calculation. We test the performance on a diverse selection of case studies, with varying symmetries and mass distributions, and show that the proposed formalism outperforms existing restricted Hartree-Fock and density functional theory methods. Finally, we analyze the stability of three-dimensional crystals. We note that for repulsive Coulomb crystals of point nuclei, cubic systems have a zero matrix of force constants at second order. We investigate this by constructing an analytical model in the tight-binding approximation, and present a phase diagram of the most stable crystal structures, as we tune core and valence orbital radii. We reconcile our results with calculations in the nearly free electron regime, as well as current research in condensed matter and plasma physics.

Magister Scientiae Dentium - MSc(Dent) / Three dental laboratories in the Cape Town Metropole that were known to fabricate “flexible” or NMCDs for dental practices were identified and were invited to participate in the study. Their participation consisted of emailing photographs of completed metal-frame, acrylic and flexible RPDs and their casts prior to sending them to the practices for delivery to patients. Specimens were collected until a total of 20 metal-frame, 20 acrylic resin and 20 flexible RPDs were received. A design was drawn for each submitted RPD. For each RPD, an “ideal” design was drawn, using the image of the cast. This was done by two observers, who are experienced members of staff in the Department of Restorative Dentistry (Prosthetics), independently. The designs from both observers were later compared for similarity. Where differences existed in the designs, these were resolved by means of discussion until agreement was reached. Each ideal design served as the control for each clinical design.The number of rests, their configuration, the type of support, number of clasps, the presence of indirect retention, cross-arch stabilization, the number of teeth whose periodontal tissues were covered by design components for each design among the different denture type groups, and corresponding control designs were identified and reported. The ratios of teeth replaced/teeth covered per denture type groups and per classification, and corresponding control designs were compared.