Two aspects of the theory of barotropic modons are examined in this thesis. First, sufficient neutral stability conditions are derived in the form of an integral constraint for westward and eastward-travelling modons. It is shown that eastward-travelling and westward-travelling modons are neutrally stable to perturbations in which the energy is contained mainly in spectral components with wavenumber magnitudes (|ƞ|) satisfying |ƞ|<κ and |ƞ|>κ, respectively, where κ is the modon wavenumber. These results imply that when κ/|ƞ|>1 the slope of the neutral stability curve proposed by McWilliams et al.(l98l) for eastward-travelling modons must begin to increase as κ/|ƞ| increases. The neutral stability condition is computed with mesoscale wavenumber eddy energy spectra representative of the atmosphere and ocean. Eastward-travelling atmospheric modons are neutrally stable to the observed seasonally- and annually-averaged atmospheric eddies. The neutral stability of westward-travelling atmospheric modons and oceanic modons cannot be inferred on the basis of the observed wavenumber eddy energy spectra for the atmosphere and ocean. Second, a leading order perturbation theory is developed to describe the propagation of barotropic modons in a slowly varying medium. Two problems are posed and solved. A perturbation solution is obtained describing the propagation of an eastward-travelling modon modulated by a weak bottom Ekman boundary layer. The results predict that the modon radius and translation speed decay exponentially and that the modon wavenumber increases exponentially, resulting in an exponential amplitude decay in the streamfunction and vorticity. These results agree with the numerical solution of McWilliams et al.(l98l). A leading order perturbation theory is also developed describing modon propagation over slowly varying topography. Nonlinear hyperbolic equations are derived to describe the evolution of the slowly varying modon radius, translation speed and wavenumber for arbitrary finite-amplitude topography. To leading order, the modon is unaffected by meridional gradients in topography. Analytical perturbation solutions for the modon radius, translation speed and wavenumber are obtained for small-amplitude topography. The perturbations take the form of westward and eastward-travelling transients and a stationary component proportional to the topography. The general solution is applied to ridge-like and escarpment-like topographic configurations. / Science, Faculty of / Mathematics, Department of / Graduate

The dynamic behaviour of an active-passive motion compensation system for handling towed marine vehicles is examined, and a mathematical model developed. In the analysis, the passive system considered is pneumatic, while the active system is electro-hydraulic. The towed body is assumed to be a point mass subjected to hydrodynamic drag, and attached to the motion compensator by means of a linear spring representing the cable. It is not intended, in this project, to model the towed body in greater detail. The equations of the passive, active, and towed body systems are derived, and linearized to permit a relatively simple frequency-domain solution. A time simulation based on the nonlinear equations, including Coulomb friction in the compensator, is developed for use on an IBM Systeis/370 computer. A laboratory model is used to conduct experiments at three frequencies, and the results indicate good agreement between the linear, simulation, and real models. Extension of the equations to cover multi-frequency inputs, two-dircensiona1 towing cables, and slow-acting servovalves is also discussed to facilitate application to marine systems. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

There are two major purposes of this study. First, it will attempt to ascertain whether self-concept, as measured by a self-concept scale, will fluctuate significantly due to a recent ego inflating or deflating experience, and if so, how lasting and in what areas are the effects. Secondly, it will note whether or not the low self-concept individual is more susceptible to changes in self-concept due to these environmental changes than the high self-concept individual.

Garnet structured cubic LLZO crystal (Li56La24Zr16O96) is one of the most promising solid electrolytes for next-generation solid-state lithium-ion batteries. Ab initio molecular dynamics simulations have been employed to study the impacts of lithium vacancy defect and doping concentration on the lithium ionic conductivity and stability of LLZO. The number of lithium atoms in a unit cell of LLZO has been reduced from 56 to 53, where 56 lithium atoms represent the structure of stoichiometric LLZO, i.e., Li7La3Zr2O12. Similarly, the effect of Al and Ga doping on the conductivity and stability of LLZO material was also investigated. Our computational results confirm that both the defects help in enhancing the conductivity of LLZO and the concentration of defect introduced controls the trade-off between the conductivity and stability. Overall, this study provides a valuable insight into the enhancement of conductivity of cubic LLZO garnet material along with structural stability.

BACKGROUND: Recently osseodensification has been introduced as a novel approach to management of the recipient site. The concept had been described in 2013 by Huwais which has revolutionized the way we approach an osteotomy site as we may obtain densification of the bone rather than its complete removal. AIM: We hypothesize that proper manipulation of the recipient site will induce cellular activities to accelerate new bone formation. We compared bone formation in a critical defect created by the osseodensification method or regular osteotomy under ex-vivo static calvarial culture. MATERIALS AND METHODS: Under sterile conditions, calvaria from 7-9-day-old neonatal CD-1 mice (n = 15) were dissected and trimmed. Densah™ burs were used to create 2.0 mm diameter defects. Clockwise rotation of the bur produced "Conventional Osteotomy," whereas counter-clockwise rotation created "Osseodensification." Five randomly selected calvaria halves for control and test groups were used to evaluate morphological changes, at 7, 14, and 28 days utilizing the Image J software. Statistical analyses were performed using SPSS software. RESULTS: Defect closure was significantly greater in the osseodensification group compared to the conventional group at post-operative day7 (p = 0.028), day 14 (p = 0.046) and day 28 (p=0.015). The original defects in both groups were not significantly different. CONCLUSION: Results showed that osseodensification lead to faster wound healing. Clinical studies have shown that osseodensification leads to better bone density around implants. These outcomes suggest that the compressed edge of a bone defect can accelerate the healing cascade by increasing cellular activity.

PURPOSE: The aim of this study was to evaluate the stability of different orthognathic surgical procedures. METHODS: CBCT scans of 61 patients who had orthognathic surgery were reviewed. These included pre-operative (T0), postoperative (T1), and at least one year postoperative (T2) (12-47 months) scans. All subjects had undergone maxillomandibular advancement surgery, with 23 subjects having clockwise rotation, and 38 having counterclockwise rotation of the mandibular occlusal plane. Mimics Innovation Suite™ Research Edition software (version 21) (Leuven, Belgium) was used for analysis. Thirty-seven parameters were chosen that represented the maxillary and mandibular segments. Measurements between points and/or planes were used to detect the sagittal, vertical, and transverse movements in each time interval. Linear mixed models analysis was used to detect significant differences between time points. Linear regression analysis was used to evaluate the correlations between the amount of surgical movement and the postoperative changes. RESULTS: Overall, 17 measurements showed significant differences between T1 and T2 (postoperative). 11 measurements presented statistically significant time point differences according to either direction of rotation. Only one measurement showed statistically significant difference between T1-T2 (Left ramus plane- Mid sagittal plane) in clockwise group while 8 other measurements were found significantly different between T1-T2 in the counterclockwise group. CONCLUSION: Except for mandibular advancement measured at right and left mental foramen to right and left lingulae, and interlingula distance, bimaxillary advancement surgeries with clockwise or counterclockwise rotation of the mandibular occlusal plane were stable at least for one year. The main difference between clockwise and counter clockwise surgeries was found in the vertical changes of the posterior maxilla and the distance between the right and left mental foramen to the coronal plane.

A research report submitted to the Faculty of Health Sciences, University of the Witwatersrand Gauteng, May 2018 / Background The trunk is the centre of the kinetic chain, connecting upper and lower limbs and transferring energy during movement. Proximal stability serves as a base for quality movements distally. Trunk muscle stability and strength-endurance are associated with sporting performance. Asymmetrical sport-specific adaptation in the morphometry of the trunk muscles has been investigated and described in cricket pace bowlers, but not linked to or described in terms of the association with bowling performance. Aim The aim of this study is to investigate the association between bowling performance and trunk muscle stability, strength-endurance and thickness in adolescent pace bowlers. Method In this observational cross-sectional study, bowling performance, namely ball release speed and accuracy, was measured by means of a radar gun and accuracy target in the outdoor nets of the respective schools, where the 46 pace bowlers, aged 13-18 years old, were invited from. Trunk muscle stability was measured as the level passed on the Sahrmann Stability Scale and strength-endurance as the failing time in seconds according to the Bourbon Trunk Muscle Strength Test. Ultrasound imaging measured the thickness of external oblique, internal oblique, transversus abdominis and lumbar multifidus in millimetre. Spearman’s correlations were used to determine associations between individual variables and a multiple linear regression analysis calculated predictors of bowling performance, including independent variables such as age, height and weight. Statistical significance was set at p<0.05. Results No association was found between trunk muscle stability and ball release speed (r=0.278; p=0.061) or accuracy (r=0.026; p=0.866). Stability, however, accounted for a 60.7% variance in ball release speed (p=0.004), increasing ball release speed by 3.570 units per unit increase in stability. Strength-endurance of the trunk muscle chains did not correlate to ball release speed (r=-0.039-0.214; p=0.154-0.796) or accuracy (r=-0.062-0.131; p=0.385-0.801). A moderate and fair relationship was found between ball release speed and transversus abdominis (r=0.543; p=0.0001) at rest and contracted (r=0.440; p=0.002), respectively. Non-dominant transversus abdominis showed a fair relationship with height at rest (r=0.458, p=0.001) and a moderate correlation with weight (r=0.625, p<0.001). On the dominant side, transversus abdominis at rest, showed a moderate relationship to ball release speed (r=0.564; p<0.001), height (r=0.539; p<0.001) and weight (r=0.611; p<0.001). Thickness of bilateral transversus abdominis at rest had an R-square value of .67 and ball release speed increased with 5.133 units for each unit increase in the thickness of the non-dominant transversus abdominis and 4.677 for that on the dominant side. Accuracy did not correlate with any independent variable, but weight (R-square value .207) was found to increase accuracy by .766 units for each unit increase. Bowling performance was found to be predicted by age (R-square value 0.084). Conclusion A direct association between bowling performance and trunk muscle stability and strength-endurance was not found. Trunk muscle stability – as a suppressor variable – was found to be a predictor of ball release speed. Trunk muscle thickness accounted for the variance in ball release speed and weight for that of accuracy. These findings implicate that adolescent pace bowlers may be able to improve ball release speed by increasing trunk muscle stability and bilateral transversus abdominis thickness. However, future research is needed to confirm this statement. / LG2018

Pyrolysis oil is produced from biomass when a feedstock is rapidly heated in a non-oxidizing environment during a short residence time. While pyrolysis oil is inexpensive, major issues prevent the facile use of this oil product ‘as produced’. Principally, since the rapid condensation results in a product not in thermodynamic equilibrium, the oil components continue to react until equilibrium is reached. Understanding how and why these reactions—including polymerization—occur in pyrolysis oil is important in designing treatments to stabilize or transform pyrolysis oil before further upgrading. Physical and chemical changes in pyrolysis oils are investigated as a function of temperature and time to simulate the aging process during storage. The effects of alcohol addition on pyrolysis oil stability during high temperature treatment are investigated. The pretreatment of pyrolysis oil with low-cost alcohols is promising prior to hydrotreating or catalytic cracking.

While there have been several rich studies that have provided insight into the teachings of Xenophon that emerge from a careful reading of the Cyropaedia, the problem of reconciling the apparent good rule of Cyrus with the ruin of his empire persists. I argue that this problem can be reconciled by focusing on the problem that Xenophon initially informs us he is interested in, political stability.

Power transmission systems frequently experience new power flow pattern due to several factors that increase uncertainties in the system. For instance, load shape uncertainty, uncertainty due to penetration of renewable sources, changing standards, and energy de-regulation threaten the reliability and security of power transmission systems. This demands for more rigorous analysis and planning of power transmission systems. Stability issues in power transmission system are more pronounced with the penetration of utility-scale Photo-Voltaic (PV) sources. Synchronous generators provide inertia that helps in damping oscillations that arise due to fluctuations in the power system. Therefore, as PV generators replace the conventional synchronous generators, power transmission systems become vulnerable to these abnormalities. In this thesis, we study the effect of reduced inertia due to the penetration of utility-scale PV on the transient stability of power transmissions systems. In addition, the effect of increased PV penetration level in the system during normal operating condition is also analyzed. The later study illustrates that the PV penetration level and the placement of PV sources play crucial roles in determining the stability of power transmission systems. Given increasing uncertainties in power transmission systems, there is a need to seek an alternative to deterministic planning approach because it inherently lacks capability to cover all the uncertainties. One practical alternative is the probabilistic planning approach. In probabilistic planning approach, an analysis is made with a wide variety of scenarios by considering the probability of occurrence of each scenario and the probability of contingencies. Then, the severity of the contingencies risk associated with each planning practice is calculated. However, due to the lack of techniques and tools to select wide varieties of scenarios along with their probability of occurrence, the probabilistic transmission planning approach has not been implemented in real-world power transmission systems. This thesis presents a technique that can select wide varieties of scenarios along with their probability of occurrence to facilitate probabilistic planning in Electricity Reliability Council of Texas (ERCOT) systems. / Master of Science / Reliability of power transmission systems are threatened due to the increasing uncertainties arising from penetration of renewable energy sources, load growth, energy de-regulation and changing standards. Stability issues become more prevalent than in past due to increasing load growth as the demand for reactive power increases. Several researchers have been studying the impact of increased load growth and increased penetration of renewables on the dynamic stability of the distribution system. However, far less emphasis has been given to the power transmission system. This thesis presents the transient stability analysis of power transmission systems during overloading conditions. Our study also facilitates identification of weak areas of the transmission system during overloading condition. In addition, the impact of replacing conventional synchronous generator by Photovoltaics (PV) on voltage stability of the system is also analyzed. With increasing uncertainties in transmission systems, it is necessary to carefully analyze a wide variety of scenarios while planning the system. The current approach to transmission planning i.e., the deterministic approach does not sufficiently cover all the uncertainties. This has imposed the need for the probabilistic transmission planning approach where the overall system is planned based on the analysis of wide varieties of scenarios. In addition, by considering the probability of occurrence of a scenario, the probability of contingencies and severity of contingencies risk associated with each planning practice is calculated. However, there is no well-established approach that is capable of selecting wide varieties of scenarios based on their probability of occurrence. Due to this limitation, probabilistic approach is not widely implemented in real-world power transmission systems. To address this issue, this thesis presents a new technique, based on K-means clustering, to select scenarios based on their probability of occurrence.