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M. Tech. (Department of Information Communication Technology, Faculty of Applied and Computer Sciences), Vaal University of Technology. / Too many options on the internet are the reason for the information overload problem to obtain relevant information. A recommender system is a technique that filters information from large sets of data and recommends the most relevant ones based on people‟s preferences. Collaborative and content-based techniques are the core techniques used to implement a recommender system. A combined use of both collaborative and content-based techniques called hybrid techniques provide relatively good recommendations by avoiding common problems arising from each technique. In this research, a proactive University Library Book Recommender System has been proposed in which hybrid filtering is used for enhanced and more accurate recommendations. The prototype designed was able to recommend the highest ten books for each user. We evaluated the accuracy of the results using Mean Absolute Error (MAE) and Root Mean Squared Error (RMSE). A measure value of 0.84904 MAE and 0.9579 RMSE found by our system shows that the combined use of both techniques gives an improved prediction accuracy for the University Library Book Recommender System.

Hand-intensive work is closely related to the prevalence of upper body and hand/wrist work-related musculoskeletal disorders (WMSDs) in office work, manufacturing, service industries, as well as the healthcare industry. Some risk factors include vibrations, forceful exertions, heavy manual handling, repetitive motions, and prolonged nonneutral wrist postures. To address the growing WMSD epidemic among various occupational groups, simple-to-use exposure measurements are required. However, common quantitative measurement methods for the hand/wrist, such as electrogoniometry and optical motion capture, are both costly and challenging to use. Small, portable inertial measurement units (IMUs) may therefore be considered as a potentially good, affordable wearable option for measuring hand/wrist posture. However, it is difficult to track the position and orientation of a rigid body due to, among other factors, the IMU sensors' sensitivity to ambient magnetic disturbances. As a result, despite advancements in hardware quality, there is still no widely accepted standard for IMU-based motion capture. This study attempted to address this issue by analysing various orientation algorithms to estimate wrist angle from two IMU sensors and compare them to the electrogoniometer-derived measures, i.e., the gold-standard method in field measurements. Five hand-intensive simulated work tasks, each lasting 4–10 minutes, were completed by six participants. These tasks were chosen to resemble some difficult real-world work conditions closely. The wrist posture of the participants was measured using an electrogoniometer and two IMU sensors that were mounted on top of the electrogoniometer's end blocks. The IMU signal of each sensor was processed using seven different orientation algorithms, and the flexion/extension and radial/ulnar deviation angles between them were extracted and compared to the corresponding electrogoniometer angles. For the best-performing orientation algorithm, which was a first-order complementary filter, the mean cross-correlation coefficient between the two measurements was between 0.41 and 0.90 for the flexion/extension and between 0.19 and 0.53 for the radial/ulnar deviation. The mean absolute error (standard deviation) of the best-performing algorithm for the 10th, 50th, and 90th percentile flexion/extension was 8.38 (8.5), 3.99 (3.4), and 11.93 (10) degrees and for the corresponding percentiles of radial/ulnar deviation it was 9.6 (6.5), 5.5 (4.8), and 10.21 (7.1) degrees.  This result can likely be further improved by applying a better orientation algorithm and reducing measurement artifacts such as sensor vibration. However, this experiment demonstrates the potential of IMU-based wrist angle estimation as a simple measurement tool for occupational risk assessment. / Manuellt fysiskt arbete kan orsaka arbetsrelaterade besvär i rörelseorganen i överkropp och hand/handled inom kontorsarbete, tillverkning, industri samt inom hälso- och sjukvårdssektorn. Vibrationer, kraftfulla ansträngningar, tung manuell hantering, upprepade rörelser och långvariga icke-neutrala handledsställningar är några av riskfaktorerna. För att komma till rätta med de arbetsrelaterade besvären bland olika yrkesgrupper, krävs lättanvända exponeringsmätmetoder, eftersom observationsmetoder har en låg tillförlitlighet och de sedvanliga objektiva kvantitativa mätmetoderna för hand/handled, såsom elektrogoniometri och optiska rörelsemätningar, är både dyra och svåra att använda. Små, bärbara s.k. inertial measurement units (IMUs) är därför ett utmärkt, prisvärt och praktiskt alternativ för att mäta hand-/handledsrörelse. Men att estimera positionen och orienteringen av en kroppsdel med hjälp av IMU-sensorer medför stora utmaningar inte minst på grund av sensorernas känslighet för omgivande magnetiska störningar. Trots framsteg i hårdvarukvalitet, finns det fortfarande ingen allmänt accepterad standardmetod för IMU-baserad rörelsemätning. Syftet med det här projektet var att öka kunskapen i det här området genom att analysera olika orienteringsalgoritmer för att uppskatta den absoluta handledsvinkeln från två IMU-sensorer och sedan jämföra den med motsvarande ifrån den etablerade standardmätmetoden med en elektrogoniometer. Fem simulerade handintensiva arbetsuppgifter, var och en mellan 4–10 minuter, genomfördes av sex deltagare. Dessa uppgifter valdes för att härma några arbetsförhållanden som har rapporterats ge risk för besvär. Deltagarnas handledsställning mättes med hjälp av en elektrogoniometer och två IMU-sensorer som monterades ovanpå elektrogoniometers ändblock. IMU-signalen från varje sensor analyserades med sju olika, tidigare framtagna, orienteringsalgoritmer, vinklarna för flexion/extension samt radial/ulnar deviation beräknades och jämfördes sedan med motsvarande elektrogoniometervinklar. För den bäst presterande algoritmen, en första ordningens komplementfilter, varierade den genomsnittliga korrelationskoefficienten mellan 0,41 och 0,90 för flexion/extension och mellan 0,19 och 0,53 för radial/ulnar deviation. Det genomsnittliga absoluta felet (standardavvikelse), för den bäst presterande algoritmen, för den 10:e, 50:e och 90:e percentilen flexion/extension var 8,38 (8,5), 3,99 (3,4) och 11,93 (10) grader. Motsvarande percentiler av radial/ulnar deviation var 9,6 (6,5), 5,5 (4,8) och 10,21 (7,1) grader. Detta resultat kan sannolikt förbättras ytterligare genom att tillämpa en bättre orienteringsalgoritm och minska mätartefakter från sensorvibrationer. Detta experiment visar dock potentialen för IMU-baserad handledsvinkeluppskattning som ett enkelt mätverktyg vid riskbedömningar inom manuella arbeten.

This dissertation aims to discover the hidden pattern and rationales behind China's South China Sea policies over the last one hundred years from the perspective of Chinese strategic culture. A historical-cultural approach is a powerful tool in uncovering deeper understandings of the Chinese way of policy making and strategy on issues such as the South China Sea. The key research questions include: first, is there any historical legitimacy in China's sovereignty claim over the South China Sea islands? Second, do Beijing's South China Sea policies in various periods have any regularity or pattern, and how did they serve China's grand strategies at the time? By utilizing extensive Chinese and English primary sources and other sources, this study conducts a comprehensive and in-depth analysis of the South China Sea issue from the framework of Chinese strategic culture.

CATD was not only adequate for analyzing the pursuit of erratically moving prey but also worked well when analyzing the pursuit of prey that remained stationary. It cannot be fully concluded that bats utilize the CATD strategy to successfully capture erratically flying prey. The angle remains relatively constant but does not exhibit a zero change in angle as by definition. The large forces experienced by the bat were seen when the bat began to rotate its body about its pitch axis or when the bat made a large turn. Moments were seen specifically when the bat began to bank into its last and final turn towards its target.; Digital recordings of three different species of bats were studied in this thesis to determine the forces and moments that were experienced throughout the bat's flight. The recordings were also studied to determine the pursuit strategies that were most effective for the bat to quickly capture its prey. A pursuit strategy is a strategic way to travel that will allow a pursuer to capture/approach their target the quickest. Therefore when a bat utilizes a particular pursuit strategy, it will adjust its position/ direction vector in a particular way that will allow it to approach its target very quickly. Data was collected directly from the video by manual collection utilizing Microsoft Visual Studio to extract frames, collect and record the data. This research was conducted to determine when throughout the flight the bat would experience significant forces and moments. The location and magnitude of the forces were reported along with an explanation of why the bat was experiencing a peak at each specific time. The forces and moments that the bat experienced thought-out the flight pursuit were calculated by relative velocity and acceleration calculations. In all four scenarios the bat experienced forces in relation to rotating its body about its center of mass. Forces were specifically seen when the bat periodically began to rotate its body before the final plunge to capture its prey. Prey avoidance and pursuit strategies were also studied and observed in this thesis which included the constant bearing and the constant absolute target direction. The intent was to determine which pursuit strategy bats use to quickly capture their prey. The constant bearing strategy is utilized to pursue prey moving along a smooth path, on the other hand the Constant Absolute Target Direction (CATD) pursuit strategy is utilized to capture erratically moving prey. For most of the bats analyzed, it was seen that the CATD strategy proved to be the preferred pursuit strategy.

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Aufkonvertierungs-Nanokristalle (UCNPs), wie NaYF4 Kristalle, welche mit Yb3+ and Er3+ Ionen dotiert sind, emittieren höher energetisches Licht im ultravioletten/sichtbaren und nahinfraroten Bereich, nachdem sie mit weniger energiereichem nahinfraroten Licht angeregt wurden. Damit besitzen sie einzigartige optische Eigenschaften, wie verschiedenfarbige Emissionsbanden, verringerte Hintergrundfluoreszenz, größere Eindringtiefen in organisches Probenmaterial und eine hohe Lichtstabilität. Diese Eigenschaften sind besonders in der optischen Bioanalyse, in medizinischen und technischen Anwendungen von Vorteil. In dieser Arbeit werden die photophysikalischen und spektralen Eigenschaften von UCNPs im Ensemble und an Einzelpartikeln untersucht. Ein dafür entwickeltes konfokales Mikroskop ermöglicht Einzelpartikelmessungen bis in den Sättigungsbereich der UCNPs bei hohen Laser Anregungsleistungsdichten (P). Die erste Studie dieser Arbeit umfasst Ensemble- und Einzelpartikelmessungen an Kern und Kern-Schale 𝛽-NaYF4 Kristallen, welche mit 20% Yb3+ und 1% bis 3% Er3+ Ionen dotiert sind, wobei die optischen Eigenschaften P-abhängig über sechs Größenordnungen untersucht wurden. Die zweite Studie diskutiert die Einflüsse bei starker Änderung der Yb3+/Er3+ Ionen Dotierung anhand von drei verschiedenen Probensystemen. Diese unterscheiden sich sowohl in der Partikelgröße als auch in der Synthesevorschrift. Bei der dritten Studie wurde die direkte Anregung von Yb3+ mit der von Nd3+ Ionen an Nd/Yb/Er dotierten NaYF4 Partikeln bezüglich des aufkonvertierten Lumineszenz Verhaltens in Wasser verglichen. In weiteren Messungen wurde sowohl der Lumineszenz Resonanz Energie Transfer (LRET) ausgehend von einem UCNP zu dem Farbstoff Sulforhodamine B, als auch plasmonische Wechselwirkungen von Au-Schale UCNPs bei Einzelpartikelmessungen untersucht. / Upconversion nanoparticles (UCNPs), such as, NaYF4 crystals co-doped with Yb3+ and Er3+ ions, emit higher energetic light in the UV/vis and NIR range under lower energetic NIR excitation. This generates unique optical properties, for example, multi-colour band emissions, reduced background fluorescence, deeper tissue penetration depths and high photostability rendering UCNPs attractive options for bioimaging, medicinal and engineering applications. In this thesis the influence of multi-factor parameters on the photo-physical and spectroscopic properties of UCNPs are investigated under ensemble and single particle (SP) condition. For this purpose, a confocal laser scanning microscope was constructed to enable the characterisation of individual UCNPs up to their saturation conditions at high laser power densities (P). At first, ensemble and SP studies of core- and core-shell 𝛽-NaYF4 crystals co-doped with 20% Yb3+ and 1% to 3% Er3+ are performed over a P-range of six orders of magnitude. The second part of this thesis discusses influences in a wide variation in Yb3+/Er3+ ion doping concentration. Thereby, three different sample sets of varying size have been studied, using different synthesis approaches. A comparison of the Nd- and Yb-excitation of Nd/Yb/Er triple-doped NaYF4 UCNPs regarding their upconversion luminescence performance in water is provided in the third section of the thesis. In further studies, the process of luminescence resonance energy transfer (LRET) from an UCNP to the sulforhodamine B dye and the plasmonic interaction of an Au-shelled UCNP have been examined at the SP level.

Abstract: The interest of major space agencies in the world for vision sensors in their mission designs has been increasing over the years. Indeed, cameras offer an efficient solution to address the ever-increasing requirements in performance. In addition, these sensors are multipurpose, lightweight, proven and a low-cost technology. Several researchers in vision sensing for space application currently focuse on the navigation system for autonomous pin-point planetary landing and for sample and return missions to small bodies. In fact, without a Global Positioning System (GPS) or radio beacon around celestial bodies, high-accuracy navigation around them is a complex task. Most of the navigation systems are based only on accurate initialization of the states and on the integration of the acceleration and the angular rate measurements from an Inertial Measurement Unit (IMU). This strategy can track very accurately sudden motions of short duration, but their estimate diverges in time and leads normally to high landing error. In order to improve navigation accuracy, many authors have proposed to fuse those IMU measurements with vision measurements using state estimators, such as Kalman filters. The first proposed vision-based navigation approach relies on feature tracking between sequences of images taken in real time during orbiting and/or landing operations. In that case, image features are image pixels that have a high probability of being recognized between images taken from different camera locations. By detecting and tracking these features through a sequence of images, the relative motion of the spacecraft can be determined. This technique, referred to as Terrain-Relative Relative Navigation (TRRN), relies on relatively simple, robust and well-developed image processing techniques. It allows the determination of the relative motion (velocity) of the spacecraft. Despite the fact that this technology has been demonstrated with space qualified hardware, its gain in accuracy remains limited since the spacecraft absolute position is not observable from the vision measurements. The vision-based navigation techniques currently studied consist in identifying features and in mapping them into an on-board cartographic database indexed by an absolute coordinate system, thereby providing absolute position determination. This technique, referred to as Terrain-Relative Absolute Navigation (TRAN), relies on very complex Image Processing Software (IPS) having an obvious lack of robustness. In fact, these software depend often on the spacecraft attitude and position, they are sensitive to illumination conditions (the elevation and azimuth of the Sun when the geo-referenced database is built must be similar to the ones present during mission), they are greatly influenced by the image noise and finally they hardly manage multiple varieties of terrain seen during the same mission (the spacecraft can fly over plain zone as well as mountainous regions, the images may contain old craters with noisy rims as well as young crater with clean rims and so on). At this moment, no real-time hardware-in-the-loop experiment has been conducted to demonstrate the applicability of this technology to space mission. The main objective of the current study is to develop autonomous vision-based navigation algorithms that provide absolute position and surface-relative velocity during the proximity operations of a planetary mission (orbiting phase and landing phase) using a combined approach of TRRN and TRAN technologies. The contributions of the study are: (1) reference mission definition, (2) advancements in the TRAN theory (image processing as well as state estimation) and (3) practical implementation of vision-based navigation. / Résumé: L’intérêt des principales agences spatiales envers les technologies basées sur la vision artificielle ne cesse de croître. En effet, les caméras offrent une solution efficace pour répondre aux exigences de performance, toujours plus élevées, des missions spatiales. De surcroît, ces capteurs sont multi-usages, légers, éprouvés et peu coûteux. Plusieurs chercheurs dans le domaine de la vision artificielle se concentrent actuellement sur les systèmes autonomes pour l’atterrissage de précision sur des planètes et sur les missions d’échantillonnage sur des astéroïdes. En effet, sans système de positionnement global « Global Positioning System (GPS) » ou de balises radio autour de ces corps célestes, la navigation de précision est une tâche très complexe. La plupart des systèmes de navigation sont basés seulement sur l’intégration des mesures provenant d’une centrale inertielle. Cette stratégie peut être utilisée pour suivre les mouvements du véhicule spatial seulement sur une courte durée, car les données estimées divergent rapidement. Dans le but d’améliorer la précision de la navigation, plusieurs auteurs ont proposé de fusionner les mesures provenant de la centrale inertielle avec des mesures d’images du terrain. Les premiers algorithmes de navigation utilisant l’imagerie du terrain qui ont été proposés reposent sur l’extraction et le suivi de traits caractéristiques dans une séquence d’images prises en temps réel pendant les phases d’orbite et/ou d’atterrissage de la mission. Dans ce cas, les traits caractéristiques de l’image correspondent à des pixels ayant une forte probabilité d’être reconnus entre des images prises avec différentes positions de caméra. En détectant et en suivant ces traits caractéristiques, le déplacement relatif du véhicule (la vitesse) peut être déterminé. Ces techniques, nommées navigation relative, utilisent des algorithmes de traitement d’images robustes, faciles à implémenter et bien développés. Bien que cette technologie a été éprouvée sur du matériel de qualité spatiale, le gain en précision demeure limité étant donné que la position absolue du véhicule n’est pas observable dans les mesures extraites de l’image. Les techniques de navigation basées sur la vision artificielle actuellement étudiées consistent à identifier des traits caractéristiques dans l’image pour les apparier avec ceux contenus dans une base de données géo-référencées de manière à fournir une mesure de position absolue au filtre de navigation. Cependant, cette technique, nommée navigation absolue, implique l’utilisation d’algorithmes de traitement d’images très complexes souffrant pour le moment des problèmes de robustesse. En effet, ces algorithmes dépendent souvent de la position et de l’attitude du véhicule. Ils sont très sensibles aux conditions d’illuminations (l’élévation et l’azimut du Soleil présents lorsque la base de données géo-référencée est construite doit être similaire à ceux observés pendant la mission). Ils sont grandement influencés par le bruit dans l’image et enfin ils supportent mal les multiples variétés de terrain rencontrées pendant la même mission (le véhicule peut survoler autant des zones de plaine que des régions montagneuses, les images peuvent contenir des vieux cratères avec des contours flous aussi bien que des cratères jeunes avec des contours bien définis, etc.). De plus, actuellement, aucune expérimentation en temps réel et sur du matériel de qualité spatiale n’a été réalisée pour démontrer l’applicabilité de cette technologie pour les missions spatiales. Par conséquent, l’objectif principal de ce projet de recherche est de développer un système de navigation autonome par imagerie du terrain qui fournit la position absolue et la vitesse relative au terrain d’un véhicule spatial pendant les opérations à basse altitude sur une planète. Les contributions de ce travail sont : (1) la définition d’une mission de référence, (2) l’avancement de la théorie de la navigation par imagerie du terrain (algorithmes de traitement d’images et estimation d’états) et (3) implémentation pratique de cette technologie.