M.Sc., Faculty of Science, University of the Witwatersrand, 2011

Against the background of principal-agent and transaction-cost theoretical considerations, this study addresses the question whether relational competencies relate to trust within cooperative relationships, taking into account also situational and personal factors. In its conclusion, the study presents an experimentally confirmed model (n = 282) that shows the strong causal relationship between relational competencies and trust allowing boundary-spanning agents to exert influence on the development and maintenance of complex cooperative relationships characterized by long-term objectives.

A área de recuperação de informação baseada em conteúdo visual vem ganhando importância graças ao volume de material visual existente (imagens e vídeo digitais), compartilhado e distribuído principalmente via Internet, e à capacidade de processamento alcançada pelos computadores pessoais na última década. Novas formas de consumo, manipulação e exploração de vídeo digital podem ser criadas através da organização e indexação apropriada desse material. A delimitação de tomadas fornece uma base para a abstração e estruturação de vídeo, agregando quadros contíguos em seqüências de mesmo contexto, isto é, trechos com unidade em termos de tempo e espaço. Nesta dissertação são apresentados os conceitos básicos de delimitação de tomadas e métodos tradicionais utilizados nesse tipo de segmentação, bem como vários resultados experimentais obtidos a partir de seqüências reais de TV. É analisada a distribuição das diferenças entre quadros sucessivos, calculada através de seus histogramas, na tentativa de caracterizar as transições entre tomadas e obter melhores parâmetros para a segmentação. Obtêm-se experimentalmente mais evidências que comprovam a superioridade da medida de intersecção de histogramas sobre outras medidas. A principal contribuição do trabalho consiste no desenvolvimento de um algoritmo baseado no método twin-comparison, que apresenta melhor desempenho que o método original na detecção dos limites de tomadas por utilizar análise local da variação visual entre os quadros do vídeo. / Visual content based information retrieval is an area of increasing importance due to the large volume of available material (digital images and videos), shared and distributed mainly by the internet, and the processing power achieved by personal computer in the last ten years. New ways to consume digital video and to manipulate and explore its visual information can be made by appropriately organizing and indexing this material. The shot boundary detection is a fundamental tool to video abstraction and structuring, combining near frames into sequences with similar context, segments with space and time unity. This work presents the basic concepts about shot boundary detection, traditional methods used and several experimental results obtained from a real TV data set. The distribution of differences of neighboring frames, calculated from histogram comparison, is used to define the transitions between frames and to obtain better parameters for segmentation. Our experimental results show the superiority of the histogram intersection method over other measures. Our main contribution is the development of a new algorithm based on the twin-comparison method, extended with local analysis of visual content variation between video frames. This algorithm was tested over hours of TV data, and performs better than the original method.

by Leung Tin Chi. / Bibliography: leaf 32 / Thesis (M.Phil.)--Chinese University of Hong Kong, 1982

Lam, Hiu Fung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 58-60). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese.

本論文將詳述對湍流熱對流系統改變邊界條件的三組實驗。 / 第一組實驗中，在寬高比等於1 的圓柱形對流槽中，通過平滑板和由金字塔狀規則排列的粗糙表面的板的組合，我們對五個對流槽進行測量。对實驗測量得到Nu 和Ra 的关系式，进行两个指数函数关系式的叠加--分别是由GL 模型提出的主体主导的（1/2）指数和边界层主导的(1/4)指数关系式。两个关系式的系数之比表明，粗糙板可以提高主体的贡献，而且将系统从边界层主导转变到主体主导。而對各個板上的測量顯示，改變平板的條件，比如恒定熱量或者恒定溫度條件，以及同一個對流槽中另外一塊板是否粗糙板，該平板的傳熱沒有發生變化。而對於粗糙版，讓它處於恒定熱量或者恒定溫度條件，得到不同的結果；同一個槽中另外一塊板是平板或者粗糙板，該粗糙板的傳熱也會受影響。 / 第二組實驗中，在平滑板组成的对流槽，和两块粗糙板组成的对流槽中，我们添加高分子聚合物，进一步研究添加的效果。对于平滑板的对流槽，研究观察到热传递效率Nusselt 数在添加聚合物之后降低。而且，添加的聚合物越多，Nu 降低越多，在聚合物浓度大约120ppm 的时候，Nu 降低了接近12%，而且保持不变。而对于粗糙板组成的对流槽，当聚合物浓度大于120ppm 的时候，Nu 提高了大约4%。 / 第三組實驗，在两块平滑板组成的圆柱形对流槽中，我们也对底板边界层内的速度场进行了实验测量。结果表明，在倾斜角度小于1°的时候，速度边界层的厚度δ[subscript v]与雷诺数的指数关系，与理论给的平流边界层的结果接近。当倾斜角度比较大的时候，边界层厚度与雷诺数的指数随着角度减小。 在不同瑞利数下，同一个倾斜角度时，测量得到的水平速度剖面通过标准化后，得到的形状是一致不变的。而对于不同的角度，标准化的形状之间，是有区别的。 / In this thesis three sets of experiments of turbulent Rayleigh-Bénard convection with modified boundary conditions are presented. / The first set of measurements were made in cylindrical cells with aspect ratio one and with various combinations of smooth and rough plates in the form of regularly-arrayed pyramids. The experimental results suggest that the Nu - Ra relationship can be represented by the combination of two power laws, corresponding to the bulk dominant regime (exponent=1/2) and boundary layer dominant one (exponent=1/4) of the Grossmann-Lohse model. The behaviors of the coefficients of the two power laws suggest that the roughness of the plate can enhance the contribution of bulk and push the system to change from the boundary dominant state to bulk dominant state. A further examination of the individual plates reveal that the heat transport properties of smooth plates are insensitive to the surface and boundary conditions of the other plate of the same cell, whether smooth or rough, or whether under constant flux or constant temperature. The heat transport properties of the rough plates, on the other hand, appear to depend on surface and boundary conditions of the other plate of the same cell. / In the second set of experiments we study the effect of polymer additives in two Rayleigh-Bńard convection cells, one with smooth top and bottom plates and the other with rough top and bottom plates. For the cell with smooth plates, a reduction of the measured Nusselt number (Nu) was observed. Furthermore, the amount of Nu reduction increases with increasing polymer concentration (c), reaching ~12% for c = 120 ppm and an apparent level-off thereafter. For the cell with rough plates, however, an enhancement (~4%) of Nu was observed when the polymer concentration is greater than 120 ppm. / The third set of experiments investigates the properties of the velocity boundary layer in turbulent Rayleigh-Bénard convection in a cylindrical cell when it is tilted with respect to gravity. It is found that at small tilt angles (θ ≤ 1°), the measured viscous boundary layer thickness δ[subscript v] scales with the Reynolds number Re with an exponent close to that for a Prandtl-Blasius laminar boundary layer. For larger tilt angles, the scaling exponent of δ[subscript v] with Re decreases with θ. The normalized mean horizontal velocity profiles measured at the same tilt angle but with different Ra are found to have an invariant shape. But for different tilt angles, the shape of the normalized profiles is different. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Wei, Ping = 改變邊界條件下的熱湍流對流系統 : 傳熱性質及邊界層的實驗研究 / 韋萍. / "November 2012." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 148-158). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese. / Wei, Ping = Gai bian bian jie tiao jian xia de re tuan liu dui liu xi tong : chuan re xing zhi ji bian jie ceng de shi yan yan jiu / Wei Ping. / Table of Contents --- p.vii / List of Figures --- p.xxii / List of Tables --- p.xxiv / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background of Turbulence --- p.1 / Chapter 1.2 --- Rayleigh-Bénard convection system --- p.4 / Chapter 1.2.1 --- Physical picture --- p.4 / Chapter 1.2.2 --- Structure of Rayleigh-Bénard convection --- p.8 / Chapter 1.2.3 --- Previous investigation about Rayleigh-Bérnard Convection --- p.11 / Chapter 1.3 --- Motivation of the thesis --- p.15 / Chapter 1.4 --- Organization of this thesis --- p.17 / Chapter 2 --- Experimental apparatus and method --- p.18 / Chapter 2.1 --- Experimental apparatus --- p.18 / Chapter 2.1.1 --- The convection cell with smooth conducting plate --- p.18 / Chapter 2.1.2 --- The rough conducting plate --- p.20 / Chapter 2.2 --- Experimental techniques --- p.21 / Chapter 2.2.1 --- Temperature measurements --- p.21 / Chapter 2.2.2 --- Particle Image Velocimetry (PIV) --- p.23 / Chapter 2.3 --- Correction of heat flux measurment --- p.25 / Chapter 3 --- Convective Heat Transfer in Bulk- and Boundary-Dominated Regimes in Turbulent Thermal Convection --- p.28 / Chapter 3.1 --- Introduction --- p.29 / Chapter 3.2 --- Apparatus and experimental method --- p.31 / Chapter 3.3 --- Results and discussion --- p.34 / Chapter 3.3.1 --- Homogenity of temperature measurement over plate --- p.34 / Chapter 3.3.2 --- The heat transport measurement Nu --- p.40 / Chapter 3.3.3 --- Different heat transport behaviors over smooth and rough plates --- p.41 / Chapter 3.3.4 --- Fluctuations of local temperature --- p.47 / Chapter 3.3.5 --- Velocity and Reynolds number measurement --- p.48 / Chapter 3.3.6 --- Comparison with theoretical model and understanding . --- p.50 / Chapter 3.4 --- Summary --- p.52 / Chapter 4 --- Enhanced and Reduced Heat Transport in Turbulent Thermal Convection with Polymer Additives --- p.54 / Chapter 4.1 --- Introduction --- p.55 / Chapter 4.2 --- Experimental setup and methods --- p.58 / Chapter 4.2.1 --- The convection cell and experimental parameters --- p.58 / Chapter 4.2.2 --- Characterization of Polymer --- p.59 / Chapter 4.2.3 --- Measurement of the polymer solution viscosity --- p.62 / Chapter 4.3 --- Results --- p.65 / Chapter 4.3.1 --- The Nusselt number measurement --- p.65 / Chapter 4.3.2 --- Fluctuations of Nu and the local temperature --- p.72 / Chapter 4.3.3 --- Velocity and Reynolds number behavior --- p.83 / Chapter 4.4 --- Discussions --- p.90 / Chapter 4.5 --- Summary --- p.94 / Chapter 5 --- Viscous boundary layer properties in turbulent thermal convection in a cylindrical cell: the effect of cell tilting --- p.97 / Chapter 5.1 --- Introduction --- p.98 / Chapter 5.1.1 --- Boundary layer measurements in turbulent thermal convection --- p.98 / Chapter 5.1.2 --- Organization of the chapter --- p.102 / Chapter 5.2 --- Experimental apparatus --- p.103 / Chapter 5.2.1 --- Convection cell --- p.103 / Chapter 5.2.2 --- PIV measurement --- p.104 / Chapter 5.3 --- Results and discussion --- p.104 / Chapter 5.3.1 --- Temperature profile and fluid properties --- p.106 / Chapter 5.3.2 --- Velocity profiles and the Reynolds number scaling --- p.106 / Chapter 5.3.3 --- The viscous boundary layer and its scaling with Ra and Re --- p.114 / Chapter 5.3.4 --- Fluctuations and statistical properties of the velocity field in the boundary layer --- p.121 / Chapter 5.3.5 --- Properties of shear stresses and near-wall quantities --- p.125 / Chapter 5.3.6 --- Dynamical scaling and the shape of velocity profiles in the boundary layer --- p.130 / Chapter 5.4 --- Summary --- p.138 / Chapter 6 --- Conclusion --- p.141 / Chapter 6.1 --- Conclusion of our work --- p.141 / Chapter 6.1.1 --- Comparison of the thermal convection with modified plates --- p.142 / Chapter 6.1.2 --- The effect of polymer additives in smooth and rough cells --- p.143 / Chapter 6.1.3 --- Velocity field with tilting angles --- p.144 / Chapter 6.2 --- Perspectives for further investigation --- p.146 / Bibliography --- p.148

During take-off, the aerodynamic performance of a transonic engine intake is dominated by the flow-field over the nacelle lower lip, around which the flow might accelerate to supersonic speeds. A shock wave might appear and impinge on the incoming boundary layer. Flow separation may result from this interaction, leading to severe flow distortion. In order to maximise fuel efficiency by reducing aerodynamic drag, slimmer nacelle designs are currently being pursued by manufacturers. Understanding the impact of design choices on the development of shock-wave boundary layer interactions (SBLI) is crucial, as these phenomena have a severe effect on the stability of the flow inside the nacelle. The available literature is rather scarce and unable to assess the nature and severity of SBLIs, which remain to be addressed in the context of nacelles at incidence. To address this shortcoming, a novel experimental rig has been designed exclusively to assess the detrimental effects resulting from shock-induced separation for a number of intake lip shapes and inflow conditions. For the reference intake shape, the flow field around the lower lip during on-design take-off conditions was found to be relatively benign, with minimal shock-induced separation. As incidence is increased by 2◦, from the reference incidence of 23◦, this separation gets noticeably larger and unsteadiness develops. The downstream boundary layer is more distorted and reflects the losses across the interaction. This is exacerbated at even higher incidence. Increasing the mass flow rate over the lip up to 15% of the initial value had only minor effects on performance. The parametric investigation revealed a significant effect of lip shape on the position and severity of the SBLI. In particular, a slimmer nacelle performed poorly, favouring shock development very close to the lip nose and promoting large scale separation as the incidence increases. From correlation studies based on the parametric investigation, it appears that the extent of shock-induced separation is the main factor affecting the aerodynamic performance. Somewhat surprisingly, this was found to be independent of shock strength but potentially related to the severity of the diffusion downstream of the shock. Alongside delaying flow reattachment, this diffusion is also likely to have a direct detrimental effect on the boundary layer development close to the engine fan.

by Xin-liang Qiu. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (p. 98-103). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese. / by Xin-liang Qiu.

長期以來，人們知道壁面受限湍流中的聚合物添加劑將顯著降低摩擦阻力，但是對聚合物在熱對流熱傳輸的影響還沒有太多研究。作為第一步，一項最近的工作[1]研究了在穩態邊界層流中熱量傳輸是怎樣被聚合物添加劑所影響的。在這項工作中[1]，聚合物是用Oldroyd-B模型來描述，這個模型允許聚合物無限伸展而沒有限制。 / 在這篇論文中，我們用一個更加真實的聚合物模型來研究聚合物在穩態邊界層流中對熱量傳輸的影響。我們採用FENE-P（有限擴展非線性彈性Peterlin）模型，在這個模型中，聚合物僅可以被伸展到一個最大的長度。聚合物的有限伸展性由參數L來衡量，它是聚合物最大長度與平衡長度的比例。基於該模型，我們發現，相對於與聚合物溶劑在底板處粘度相同的牛頓流體，熱量傳輸可以被提高或者被降低，這取決於聚合物不同的L值。而在不同的L值下，流場中底板的阻力始終加強。在早期的工作中，可以用一個隨位置改變的有效粘度來理解聚合物的效果。我們探討了聚合物的有效粘度和流速場是怎樣被聚合物改變的，以理解這個問題。我們也對熱量傳輸與不同參數的依賴關係進行了研究，這些參數包括威森博格數，普朗特數和聚合物對零剪切下溶劑粘度作出的貢獻的比例。 / It has long been known that friction drag will be reduced signicantly due to polymer additives in turbulent wall-bounded flows, but the effect of polymers on heat transport in thermal convection has not been studied much. As a rst step, a recent work [1] has studied how heat transport in a steady-state boundary layer flow might be influenced by the addition of polymers. In this work [1], polymers are modeled by the Oldroyd-B model, in which they can be extended innitely without a limit. / In this thesis, we study the effect of polymers on the heat transport in steady-state boundary layer flow using a more realistic model of polymers. We apply the FENE-P (nite extensible nonlinear elastic-Peterlin) model, in which the polymers can only be extended up to a maximum length. The nite extensibility of the polymers is measured by the parameter L, which is the ratio of the maximum length to the equilibrium one. Based on the model, we nd that compared to a Newtonian flow with the same viscosity as that of the polymer solution at the plate, heat transport can be enhanced or reduced depending on L. The fraction drag is always enhanced by the polymers for all different L. In the earlier work, the effect of the polymers has been understood to produce an effective viscosity that is position-dependent. We have explored the effective viscosity of the polymers and how the velocity eld is modied by the polymers to understand our results. We have also studied how the results depend on the different parameters, including Weissenberg number, Prandtl number and the ratio of polymer contribution to the total zero-shear viscosity. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Wang, Yiqu = 有限伸展的聚合物對邊界層流中熱量傳輸的改變 / 王異曲. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 68-69). / Abstracts also in Chinese. / Wang, Yiqu = You xian shen zhan de ju he wu dui bian jie ceng liu zhong re liang chuan shu de gai bian / Wang Yiqu. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Prandtl-Blasius boundary layer flow --- p.7 / Chapter 3 --- Earlier work with Oldroyd-B polymers --- p.13 / Chapter 4 --- Theoretical formulation of the problem with polymers of finite extensibility --- p.20 / Chapter 4.1 --- Equations of motion --- p.20 / Chapter 4.2 --- Quantities of interest --- p.30 / Chapter 5 --- Checking validity of fixed angle approximation --- p.34 / Chapter 6 --- Results and Discussion --- p.42 / Chapter 6.1 --- Calculations --- p.42 / Chapter 6.2 --- The effect on heat transport --- p.45 / Chapter 6.3 --- The effect on drag --- p.48 / Chapter 6.4 --- The velocity field due to polymers --- p.49 / Chapter 6.5 --- Effective viscosity --- p.55 / Chapter 6.6 --- Dependence on Weissenberg number --- p.58 / Chapter 6.7 --- Dependence on Prandtl number --- p.61 / Chapter 6.8 --- Dependence on the ratio of polymer contribution to the total zero-shear viscosity --- p.64 / Chapter 7 --- Conclusion --- p.66

The main focus of this work was to investigate the nature of unsteady boundary-layer development over finite domains, with the behaviour of the boundary layer on a rotating sphere in an unbounded, rotating fluid used as a prototype. The sphere and its surrounding fluid are assumed to be initially rotating as a solid body, and the evolution of a boundary layer on the sphere is analysed in cases where the sphere has been smoothly slowed, or brought to a state of rotation in an opposite sense to its initial conditions. It may be seen that a characteristic property of this flow is that the boundary layer is bi-directional; over most of the streamwise domain for the flow, whether the flow is positive or negative in the streamwise coordinate direction depends on the transverse location being considered. This fact leads to challenges in the numerical evaluation of the flow field due to the parabolic nature of the boundary-layer equations. A further consideration is the implication that these regions of reversed flow cause the flow field to contain minima and maxima in the streamwise velocity component. This has been shown in a little-known study by Cowley et al. (1985) to cause the boundary layer to become susceptible to asymptotically short-scale perturbations with large frequencies. The unsteady boundary layer on a rotating sphere under these conditions is consequently shown to be extremely challenging to compute numerically. It is also found that using local approximations at the ends of the finite domain, which in the case of the sphere are the pole and equator, to investigate the two-dimensional boundary layer can cause difficulties, as in some cases there exist steady, spatial perturbations to a boundary-layer state which introduce short spatial scales. The instabilities and other features analysed in this work are framed largely in the context of the rotating sphere, but the causes of the phenomena are found to be sufficiently generic that they may be observed in other physical contexts. To demonstrate this, the shallow katabatic flow down a cooled slope is briefly investigated, and the above mathematical features are again uncovered.