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In electric power systems, the existence of constant power loads such as output-regulated power converters may bring instability problem to AC or DC distributed systems. Impedance based stability criteria has been proven a good tool for small-signal stability analysis. This works focuses on the developing of a comprehensive software tool which can extract DC or three phase AC impedances, and apply stability analysis. An algorithm is designed to select FFT window and adjust perturbation frequencies. This feature enables the software to accurately measure impedances even in existence of system line harmonics. Furthermore, multi-tone approach is developed to improve simulation time. The complete software tool is tested with simulation models and experiment results, to show the effectiveness. When multi-tone approach is applied on nonlinear loads, it gives incorrect results. The reason is that perturbation frequency will have overlapping with side-band harmonics. An algorithm is designed to avoid this problem. The algorithm is tested with 12-pulse diode rectifier simulation model, and 6-pulse diode rectifier simulation model and experimental test bed. Both simulation and experiment results verifies the concept. / Master of Science

Model fan blades designed to implement the wake management technique of trailing-edge blowing were tested in a linear cascade configuration. Measurements were made on two sets of blowing blades installed in the Virginia Tech low-speed linear cascade wind tunnel. The simple blowing blades were identical to the baseline GE Rotor B blades, aside from a slight difference in trailing-edge thickness, a set of internal flow passages, and a blowing slot just upstream of the trailing-edge on the suction side of the blade. The Kuethe vane blades were also slightly thicker at the trailing-edge, and had a set of nine evenly spaced vortex generators upstream of the blowing slot on the suction side. The cascade tunnel accommodates eight blades with adjustable tip-gap heights, although only the center four blades were replaced by blowing blades in this study. The tunnel has an inlet angle of 65.1â a, a stagger angle of 56.9â a and a flow turning angle of 11.8â a. The tip-gap was set to 0.004125c and the freestream velocity of 24.7m/s led to a Reynolds number based on the chord of 385,000. Blowing slot uniformity measurements made with a single hot-wire immediately behind the trailing-edge revealed that the blowing becomes more spanwise uniform as blowing rate is increased. The same occurs with the Kuethe vane blades, despite a spanwise serrated pattern that appears as a result of the upstream vortex generators. Cross-sections made perpendicular to the blade span gave preliminary evidence that the simple blowing wake deficit increases from the passive suction case at a blowing rate of 1.4% and becomes overblown by 2.6%. The Kuethe vane wake deficit does not increase at low blowing rates. Both sets of blowing blades indicated a slight angling of the wake towards the pressure side with blowing. Pitot-static full cross-sections of the simple blowing blades at x/ca = 0.839 and 1.877 verified the increase in wake depth and width at 1.4% as compared to the passive suction and non-blowing baseline cases, and the wake overblowing that occurs as blowing rate is increased to approximately 2.6%. The Kuethe vane blades only achieve partial wake cancellation at the maximum tested rate of 2.6% for these measurements. The results of the baseline study of Geiger (2005) are used for comparison with the mid-span velocity profiles made at four downstream locations. The velocity profiles clearly confirm the results of the normal-to-span and full cross-sections, while also revealing a decrease from the baseline of at least 25% in most of the maximum Reynolds normal stresses and turbulent kinetic energies at all rates between 1.4% and 2.7% for both sets of blowing blades. Spectral measurements of the simple blowing blades show clear reductions of the energy in the wake for all blowing rates over the majority of the range of normalized frequencies, while the Kuethe vane blades show reductions at all rates and all frequencies. By performing Fourier decompositions, the tone noise benefits over the non-blowing baseline blades are directly comparable in decibels. The optimum blowing rate for the simple blowing blades is clearly 2.5%, since this rate shows the most potential tone noise reduction. The Kuethe vane blades suggest decreases in tone noise over all of the tested blowing rates. / Master of Science

No / In recent years inverse tone mapping techniques have been proposed for enhancing low-dynamic range (LDR) content for a high-dynamic range (HDR) experience on HDR displays, and for image based lighting. In this paper, we present a psychophysical study to evaluate the performance of inverse (reverse) tone mapping algorithms. Some of these techniques are computationally expensive because they need to resolve quantization problems that can occur when expanding an LDR image. Even if they can be implemented efficiently on hardware, the computational cost can still be high. An alternative is to utilize less complex operators; although these may suffer in terms of accuracy. Our study investigates, firstly, if a high level of complexity is needed for inverse tone mapping and, secondly, if a correlation exists between image content and quality. Two main applications have been considered: visualization on an HDR monitor and image-based lighting.

Yes / Advanced drug delivery systems, such as ultrasound-mediated drug delivery, show great promise for increasing the therapeutic index. Improvements in delivery by altering the ultrasound parameters have been studied heavily in vitro but relatively little in vivo. Here, the same therapeutic microbubble and tumour type are used to determine whether altering ultrasound parameters can improve drug delivery. Liposomes were loaded with SN38 and attached via avidin: biotin linkages to microbubbles. The whole structure was targeted to the tumour vasculature by the addition of anti-vascular endothelial growth factor receptor 2 antibodies. Tumour drug delivery and metabolism were quantified in SW480 xenografts after application of an ultrasound trigger to the tumour region. Increasing the trigger duration from 5 s to 2 min or increasing the number of 5 s triggers did not improve drug delivery, nor did changing to a chirp trigger designed to stimulate a greater proportion of the microbubble population, although this did show that the short tone trigger resulted in greater release of free SN38. Examination of ultrasound triggers in vivo to improve drug delivery is justified as there are multiple mechanisms at play that may not allow direct translation from in vitro findings. In this setting, a short tone burst gives the best ultrasound parameters for tumoural drug delivery. / This research was funded by the EPSRC (EP/I000623/1, EP/L504993/1 and EP/P023266/1). S.D.E. is supported by the National Institute for Health Research infrastructure at Leeds. J.R.M. is supported by an EPSRC UKRI Innovation Fellowship (EP/S001069/1).

Ces dernières années, les contenus vidéos ont évolué très rapidement. En effet, les télévisions (TV) ont rapidement évolué vers l’Ultra Haute résolution (UHD), la Haute Fréquence d’images (HFR) ou la stéréoscopie (3D). La tendance actuelle est à l’imagerie à Haute Dynamique de luminance (HDR). Ces technologies permettent de reproduire des images beaucoup plus lumineuses que celles des écrans actuels. Chacune de ces améliorations représente une augmentation du coût de stockage et nécessite la création de nouveaux standards de compression vidéo, toujours plus performant. La majorité des consommateurs est actuellement équipé de TV ayant une Dynamique Standard (SDR) qui ne supportent pas les contenus HDR et ils vont lentement renouveler leurs écrans pour un HDR. Il est donc important de délivrer un signal HDR qui puisse être décodé par ces deux types d’écrans. Cette rétro compatibilité est rendue possible par un outil appelé TMO (Tone Mapping Operator) qui transforme un contenu HDR en une version SDR. Au travers de cette thèse, nous explorons de nouvelles méthodes pour améliorer la compression HDR rétro compatible. Premièrement, nous concevons un TMO qui optimise les performances d’un schéma de compression scalable où une couche de base et d’amélioration sont envoyées pour reconstruire les contenus HDR et SDR. Il est démontré que le TMO optimal dépend seulement de la couche SDR de base et que le problème de minimisation peut être séparé en deux étapes consécutives. Pour ces raisons, nous proposons ensuite un autre TMO conçu pour optimiser les performances d’un schéma de compression utilisant uniquement une couche de base mais avec un modèle amélioré et plus précis. Ces deux travaux optimisent des TMO pour images fixes. Par la suite, la thèse se concentre sur l’optimisation de TMO spécifiques à la vidéo. Cependant, on y démontre que l’utilisation d’une prédiction pondérée pour la compression SDR est aussi bon voir meilleur que d’utiliser un TMO optimisé temporellement. Pour ces raisons, un nouvel algorithme et de nouveaux modes de prédictions pondérées sont proposés pour gérer plus efficacement la large diversité des changements lumineux dans les séquences vidéos. / In recent years, video content evolved very quickly. Indeed, televisions (TV) quickly evolved to Ultra High Definition (UHD), High Frame Rate (HFR) or stereoscopy (3D). The recent trend is towards High Dynamic range (HDR). These new technologies allow the reproduction of much brighter images than for actual displays. Each of these improvements represents an increase in storage cost and therefore requires the creation of new video compression standards, always more efficient. The majority of consumers are currently equipped with Standard Dynamic Range (SDR) displays, that cannot handle HDR content. Consumers will slowly renew their display to an HDR one and it is therefore of great importance to deliver an HDR signal that can be decoded by both SDR and HDR displays. Such backward compatibility is provided by a tool called Tone Mapping Operator (TMO) which transforms an HDR content into an SDR version. In this thesis, we explore new methods to improve the backward compatible HDR compression. First, we design a Tone Mapping to optimize scalable compression scheme performances where a base and an enhancement layer are sent to reconstruct the SDR and HDR content. It is demonstrated that the optimum TMO only depends on the SDR base layer and that the minimization problem can be separated in two consecutive minimization steps. Based on these observations, we then propose another TMO designed to optimize the performances of compression schemes using only a base layer but with an enhanced and more precise model. Both of these works optimize TMO for still images. Thereafter, this thesis focuses on the optimization of video-specific TMO. However, we demonstrate that using a weighted prediction for the SDR compression is as good or even better than using a temporally optimized TMO. Therefore, we proposed a new weighted prediction algorithm and new weighted prediction modes to handle more efficiently the large diversity of brightness variations in video sequences.

by Mary Y.Y. Leung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (leaves 64-66). / Abstract --- p.i / Acknowledgments --- p.iii / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Video-On-Demand Environment --- p.1 / Chapter 1.2 --- Problem Definition --- p.3 / Chapter 2 --- Related Work --- p.7 / Chapter 2.1 --- Data Sharing Techniques --- p.7 / Chapter 2.1.1 --- Batching --- p.7 / Chapter 2.1.2 --- Buffering --- p.9 / Chapter 2.1.3 --- Static Partitioning --- p.10 / Chapter 2.1.4 --- Adaptive Piggybacking --- p.10 / Chapter 2.2 --- Providing VCR Functionalities --- p.12 / Chapter 3 --- System Model --- p.15 / Chapter 3.1 --- Operations involved in VCR Control --- p.15 / Chapter 3.2 --- Normal Playback Model --- p.17 / Chapter 3.3 --- VCR Model --- p.18 / Chapter 4 --- Resource Allocation for Normal Playback --- p.21 / Chapter 4.1 --- Mathematical Model --- p.22 / Chapter 4.1.1 --- Hits occurring within the same partition (hit w) --- p.24 / Chapter 4.1.2 --- Jump to other partitions (hito) --- p.27 / Chapter 4.1.3 --- Fast-forwarding to the end of a movie --- p.30 / Chapter 4.1.4 --- The expected hit probability P(hit) --- p.31 / Chapter 4.2 --- Model Verification --- p.32 / Chapter 5 --- Resource Allocation for VCR mode --- p.35 / Chapter 5.1 --- Scheme 1: No merging --- p.36 / Chapter 5.2 --- Scheme 2: Merging by adaptive piggybacking and buffering --- p.36 / Chapter 5.2.1 --- Resuming within the threshold (Δ ≤ k) --- p.38 / Chapter 5.2.2 --- Resuming beyond the threshold (Δ > k) --- p.39 / Chapter 5.3 --- Verification --- p.42 / Chapter 6 --- Applications to System sizing --- p.45 / Chapter 6.1 --- Cost of Resources for Normal Playback --- p.46 / Chapter 6.2 --- Cost of Resources for VCR functions --- p.48 / Chapter 6.3 --- Overall system cost --- p.49 / Chapter 6.4 --- Comparison --- p.50 / Chapter 6.4.1 --- Scheme 1 vs. Scheme 2 --- p.51 / Chapter 6.4.2 --- Scheme 2 vs. pure I/O & pure buffer --- p.54 / Chapter 6.4.3 --- Different values of k --- p.58 / Chapter 6.4.4 --- Different values of ψ --- p.60 / Chapter 7 --- Conclusions --- p.62 / Bibliography --- p.64 / Chapter A --- Appendix --- p.67 / Chapter A.l --- Rewind --- p.67 / Chapter A.1.1 --- Hits occurring within the same partition (hit w) --- p.67 / Chapter A.1.2 --- Jump to other partitions (hit0) --- p.68 / Chapter A.2 --- Pause --- p.70